Plants for the Future Flashcards
What are the potential applications of genetic engineering of plants?
Higher yields
Increased resistance to pests and diseases
Improved nutritional content
Better adaptability to environmental stressors.
What are some ethical concerns related to genetic engineering of plants?
Corporate control of genetic technology
The rights of farmers to control their own seeds and crops
What are some potential environmental risks associated with genetic engineering of plants?
- Escape of genetically modified organisms/genes into the environment
- Reliance on crops tolerant for one herbicide selects for herbicide resistant weeds
- this can be addressed by swapping out the herbicide or rotating it
What are some health concerns related to genetic engineering of plants?
Some people are concerned about the potential health risks of consuming genetically modified crops
- Extensive testing has not yet shown any detrimental health effects
How many people consume genetically modified plant food?
Over one billion people consume genetically modified plant food
What is the conflict of interest concern related to genetic engineering of plants?
Biotech companies involved in the commercialization of genetic engineering of plants have conducted many studies
- Leading to concerns about conflicts of interest
What is an example of a herbicide resistance GM modification added to plants?
Glyphosate resistance
What is an example of an insect resistance GM modification added to plants?
Production of bacterial Bt toxin
What are some ways in which GM is applied in plants to increase their productivity?
Herbicide resistance
Insect resistance
Disease resistance
What are the economic benefits of GM crops?
Improved resistance reduces chemical use - environmentally and economically beneficial
Increased Yield
More nutritious food
How much money is spent on insecticide use on cotton, rice and maize?
$4 billion
Over __% of GM crops grown have herbicide resistance traits
80%
Over __% of all GM crops grown worldwide have insect resistance traits
50%
Name some biotic plant stressors?
Pathogens
Pest Damage
Wounding
Name some abiotic plant stressors
Herbicides
Temperature stress
Drought
Salinity
Flooding
Heavy metals
What are the effects of vitamin A deficiency and how many children are affected worldwide?
- Reduced immune function and impaired vision
- 250M children
What are the effects of iron defficiency and what % of the population is affected by it?
Weakened immune system, impaired growth
60% of the population
What is present in increased amounts in golden rice?
Beta-carotene content (pro-vitamin A)
What are some non-food uses of GM crops?
Drugs
Building materials
Fuel
What can secondary metabolites of plants be used for?
Can be exploited as flavorings, colors, perfumes, and drugs
What is an example of a plant that is used for its secondary metabolite?
Aspirin from willow
Opioids from poppy
How is GM used in the production of Opium from poppies?
Over-expression of SalAT enzyme - alters metabolism of morphinan alkaloids
- Increased morphine, codeine and thebaine content
Other modifications
- reduce other unnecessary byproducts
What are Biopharmaceutical?
Drugs and therapeutic proteins that are produced using genetically modified plants.
Plant-derived pharmaceutical products (PDPs)
What are the advantages of plant-derived drugs?
Production scale and economy
Product safety
Reduced contamination
Ease of storage and distribution
Opportunity for low-cost drugs
No need for purification in some cases
What are some examples of Plant derived pharmaceutical products - PDPs
Avidin and Beta-Glucuronidase enzymes in diagnostic kits
Trypsin enzyme in pharmaceuticals
ZMAPP Ebola vaccine made in tobacco plants
Why was a COVID vaccine produced by the company that produced ZMAPP rejected by the WHO?
Controversial links to tobacco industry
Despite passing trials
Why is the tobacco plant often used in PDPs?
Easy to engineer
Efficient transformation/generation process
Not a food product
What are the advantages of PDPs?
Production scale and economy
- Keeping cells alive more expensive than plants
Product safety
- Reduced contamination
Ease of storage and distribution
- Seeds
Opportunity for low cost drugs and vaccines
- Edible plants? No need for purification
What are the concerns surrounding PDPs?
Consistent quality?
- Natural variation and growth/soil/weather condition inconsistencies
Differences in post-translational modification
- Plant vs animal/microbe antibodies may be finished differently
- Eg N-glycosylation
- May have consequences for activity of end product
Entry into food chain
- Especially if food plants used
What are where are the primary producers of bioethanol?
Currently predominantly from maize (US) and sugarcane (Brazil)
Why is sugarcane used for production of bioethanol?
High sugar
- accumulation of sucrose in shoots
- easy to extract
- for conversion to glucose and fructose for yeast based fermentation into ethanol
Why is maize used for the production of bioethanol?
High starch
- breakdown into glucose for same process
Why is it hard to use most crop waste (such as rice straw) hard to use for bioethanol?
Cell walls contain lignin
Lignocellulose difficult and expensive to breakdown
How might GM crops allow crop waste to be used for biofuels more simply?
Increasing cellulose content
- Increase ethanol yield
Reduce lignin content/change lignin composition
- Improve degrading enzyme access
Express cell wall degrading enzymes in plants
- Improve cell wall digestion - switched on at harvesting
What are the advantages of using algae for biofuels?
- Don’t compete with crops for space
- Don’t have lignin
What needs to be done to make algae derived biofuels more viable?
- Identify suitable algae strains
- Achieve both high oil content and high biomass productivity
Describe the steps for producing biofuels from algae
Grow algae: Cultivate algae in ponds or photobioreactors
Harvest algae: Centrifugation or filtration.
Extract oil: Separate the oil from the algae cells using solvents
- mechanical pressing
Transesterification: React the extracted oil with an alcohol and a catalyst to produce biodiesel and glycerin.
Describe the process by which we could increase oil content in plants?
Organism accumulates oil as an energy reserve
Breaks down the oil to use it for energy
Blocking the breakdown process
- can maintain a high oil content
Describe a study in which scientists attempted to increase the oil content of marine algae and what were the results?
- Reduced expression of gene for lipase enzyme
- Reduced lipid breakdown
- Increased lipid content
- No effect on cell growth
- Massive increase in lipid content per cell
____ population suffer at least one deficiency
Half
What produces nutritional problems in rice?
Milled
- removes nutrient rich embryo and aleourone parts
What is the problem with the focus on growing high yield cereals?
Expense of nutrient rich pulse/legume farming
What is biofortification?
Increase plant nutrient content pre-harvest
Foods fortified with vitamins and minerals post harvest
What are methods of biofortification?
Agronomic - using fertiliser
Genetic - selective breeding
Transgenic - genetic engineering
Describe golden rice - what it is and its mechanism?
Beta-carotene
- pro-vitamin A
Converted to vitamin A in human body
Genes to synthesise added to rice
- Mitigating vitamin A deficiency
What are the different stages of uptake to consider when designing a GM crop that increases nutrient availability?
Soil nutrient availability
Assimilation efficiency into plants
Sequestration into grain or other consumed part
Bioavailability during consumption
What percentage of the world population is Zn deficient and what are the effects?
30%
Impairs development and immune system
What percentage of the world population is Iodine (I) deficient and what are the effects?
30%
Goiter disease
What does Selenium (Se) deficiency cause?
Can cause low fertility (men)
Increased cancer risk
What does Calcium (Ca) deficiency cause?
- can lead to osteomalacia or osteoporosis
What do some of the genes added to plants using transgenic biofortification do?
Genes to
- Increase mineral accumulation in roots
- Increase transfer to edible tissues
- Increase storage
- Increase assimilation efficiency
What is the rhizosphere?
The rhizosphere is the region of soil that surrounds and is influenced by the roots of plants.
What is the soil solution?
Pool of dissolved nutrient ions that are available for root uptake
How is nutrient bioavailability affected by soil pH?
Soil pH affects nutrient bioavailability, with a low pH typically increasing availability.
What is the nutrient depletion zone?
area of soil immediately surrounding roots where nutrient availability is reduced due to uptake by the plant.
How do plants respond to nutrient deficiency?
- by elongating and exploring their root hairs
- Actively lowering the surrounding soil pH to increase nutrient availability.
How do plants take up iron from soil?
releasing protons or carbon dioxide
- Lower the surrounding soil pH
- displace positively charged iron ions from negatively charged soil particles
What is the IRT1 enzyme important for?
Fe uptake
What did overexpression of IRT1 gene cause rice?
- Increased levels of Fe
- Reduced growth and tillers
- No significant increase of Fe in rice grain
What effect on rice did expression of Fe(III)-chelate reductase from yeast have?
- Better growth in low Fe conditions
- More grains per plant
- No significant increase in grain iron content
How much does the FAO estimate the food demand will increase by 2050?
50%
What are some complications to be considered for future food security?
Higher food demand - increasing population
Climate change
Decreased biodiveristy
What is food security?
A good thing
What are the four main components of food security?
Availability - already a problem
Access
Affortability
Quality
What are the four main components of food security?
No party no problem
What is the problem for food security of increasing wealth in populations?
More meat consumption
More energy and land
What is the estimated increase of meat production required between 2020-2050?
85%
What are features of the ‘perfect storm’ which will affect food security?
Increasing population
Changing diets
Reduced arable land
Climate change
Why is climate change such a problem food security?
Changes where and when crops can be grown
- due to Rising CO2
- temp increase
- drying out
Are there any benefits of climate change to food security?
Yes, at high latitudes - increased temperature are predicted to give better yields
What is an orphan crop?
Orphan (or minor) crops are those crops which are typically not traded internationally but which can play an important role in regional food security
- received little attention from crop breeders and researchers
What is nastic movement?
Not tropism
Response to non-directional stimulus/in a direction largely independent of stimulus (eg touch)
Why are orphan crops thought to have large potential in increasing food security?
Not studied or bred so they have potential to provide increase yields
Why are orphan crops thought to have large potential in increasing food security?
Not studied or bred so they have potential to provide increase yields
What is thigmonasty?
Nastic response of a plant to touch or vibration
What is thermonasty?
A nastic movement that is associated with changes in temperature
Describe Dionaea muscipula?
Don’t bother - meat eating plant
Describe the mechanism of Dionaea muscipula activation?
- Touch translated into action potentials
- 2 required for closure
- Moving trapped prey elicits lots of APs
- Triggers release of lytic enzymes
What is gravitropism?
Roots growing directionally based on gravity
+ for roots
- for shoots
List some tropisms please and thank you
Thigmotropism
Phototropism
Hydrotropism
Thermotropism
Chemotropism
What is the role of auxin in cells?
- Controls cell elongation
- Controls response to tropism
- Mr tropism if you will
Do plants have a circadian cycle?
Yes, before dawn plants begin to move in anticipation of rising sun
What is a plant defence mechanism used when plants are attacked by insects?
- Release VOCs
- Plants express defensive mechanisms when neighbouring plants are attacked
- Attract carnivorous insects that prey on the herbivores
What is the plant response when herbivores feed on them?
- Action potential generated after herbivore feeding
- Signals produced near site of attack
- Spreads to nearby leaves
- Sites receiving signals initiated defence gene expressions
What do the structures of the receptors involved in the plant response to herbivory suggest about when it evolved?
- Structurally similar to receptors involved in rapid excitation of nervous system
- Implies emergence before plant animal divergence
What is an allotetraploid plant?
An individual possessing four times the chromosomes in a haploid organism
What are the benefits of allotetraploid plants?
Generally more resistant to drought, disease ect.
What are the negatives of allotetraploid plants?
- Messier organisation
- Harder to use agriculturally
How did domestication of plants begin?
- Hunter gatherers
- Subject to seasonal food shortages
- Started looking after wild plants for better yield
When did farming begin to take hold and what were the benefits?
- 10,000 years ago
- Reduced the effects of food shortages
- Surplus could be stored over winter
- Supported larger populations
What occurred 11,000 years ago to allow the agricultural revolution?
Dryer climate - more annual plants
What is the rubbish heap hypothesis?
- Early humans gathered nutritious roots and seeds for their food
- Such plants actively colonized the bare areas around their dwellings
- Were rich with the discarded rubbish.
How are Centres of Origin identified?
- Areas where wild relatives occur are likely sites of original domestication
- Great amount of natural variation
- Linguistic cues
Since
- Archaeology
- DNA/phylogenetics
Why are there similar crops in different areas?
Similar types of plants in different region
- each fill a different nutritional niche
Cereals (lysine deficient)
Beans/pulse (methionine deficient)
Fibres, fruits, tubers
What and where is the fertile crescent?
- Between Iraq, Iran and Turkey
- Wet climate, mostly grassland
What features of bread wheat made it successful domesticated crop?
- Non-brittle seed head phenotype in domesticated
- Seeds remain attached
- Easier to harvest
- Must be threshed to release seeds
How many mutations cause the non-shattering mutation in bread wheat?
- 1 mutation
- Present but rare in wild populations
- Prevents seed dispersal
- Selected for by early farmers
What is the trend seen in dormancy in domesticated vs wild rice?
- Farmers selected for fast germination
- Shorter dormancy
What are features of domestication syndrome?
- Loss of seed dispersal
- Loss of seed dispersal aids
- Increase in seed size
- Loss of sensitivity to environmental cues for determination
- Synchronous ripening of seeds/fruits
- Compact growth habit
What is the tough rachis mutation?
Mutation in early domestication
Seeds remain attached to mature ear
- much easier to harvest
Describe loss of sensitivity to environmental cues for determination as a feature domestication?
Larger grain surviving deeper burial
- confused
- allowing farmers to cultivate them in a wider variety of climates and seasons
- bred to depend more on human intervention for propagation
Describe compact growth habit as a feature domestication?
- Selected for plants of smaller size and shape using harvesting methods
What do low frequencies of mutations in the wild suggest about early domestication efforts?
Farmers knew what they wanted and achieved domestication in a few generations
What is model 1 domestication hypothesis
- Monophyletic origin and fast domestication model
- Domestication occurred in a few generations due to low frequency of mutations in the wild
- Early farmers knew what they wanted and achieved domestication in a short period of time
- Selection was not necessarily purposeful but early farmers placed selection pressure on plants
- Crops were disseminated from their area of origin.
What is model 2 domestication hypothesis?
- Independent multiple domestications model
- Agriculture arose independently in different regions of the world
- Occurred over a long period of time, as people gradually learned to cultivate and select for desirable traits in plants
- Rather than relying on chance mutations or unintended selection pressures
- Domesticated crops were adapted to local conditions and environments
Did the harvesting techniques used by early farmers indirectly select for the non-brittle character? (Model 1 or 2)
- Model 2 suggests that harvesting techniques indirectly selected for the non-brittle character
- as crops with brittle stalks would be more difficult to harvest and process
Did the harvesting techniques used by early farmers indirectly select for the non-brittle character? (Model 1 or 2)
Model 2 suggests that harvesting techniques indirectly selected for the non-brittle character, as crops with brittle stalks would be more difficult to harvest and process.
Would neolithic farmers overlook the presence of the non-brittle character in their crops? Compare Model 1 and 2
Model 1 - suggests neolithic farmers may have overlooked the presence of the non-brittle character in their crops, as they may not have been intentionally selecting for it
Model 2 - suggests that farmers may have actively selected for the non-brittle character
Was the stored wild barley collected in the wild (Model1) or cultivated (Model2)?
Presence of large quantities of wild barley at Ohalo 11 (Isreal)
- suggests that the stored wild barley was collected in the wild
- supports Model 1
Why is it important to know the centres of origin of domesticated plants?
- Potential to add new genes in to the current domesticated populations
- Important not to release GM crops in these areas spoiling natural diversity by outcompeting wild plants
- Future of crop domestication research
Why is it important to preserve centres of origin?
- A centre is where a wild ancestor can be found
- Crossing into the crop can be valuable for resistance genes
- Source of genes for new traits
What is the BRT mutation?
- non-brittle phenotype - seeds remain attached, must be thrashed to release - easier harvest
- Single gene mutation
- Found in domesticated plants
- Wild-type - seeds detach at maturity, fall on ground
What hypothesis do the Brt1 and Brt2 genes support?
Makes no sense oh well good luck
Wildtype - seeds detach at maturity, fall on ground
What does the second mutation in the Brt1 (Brt1B) gene produce?
- Truncation mutation - loss of hydrophobic region
Leu-Pro substitution - signal not passed on
- New mutation could potentially have implications for plant breeding and crop improvement.
Spread of agriculture
Two routes of barley spread
7,000-8,000 years ago
Why did barley move Northward slower taking breaks of up to 1000 years at times compared to the continuous spread West?
- pauses, took time to adapt to climate to move North
800-1,000 years - Or populations didn’t require agriculture
- Or geographical barriers
How is barley adapted to northern climates?
- Undomesticated barley flowers in response to day length
- Increasing day length promotes flowering
UK barley
- late flowering
- harvest late June
Doesn’t respond to day length
Adaptation to temperate season
- Lower temperature and moisture availability for seed production
What role does the Ppd-H1 gene play in barley?
Ppd-H1 responsive to day length
ppd-H1 non-responsive
Single mutation between Ppd-H1 and ppd-H1
Wild plants with mutant ppd-H1 occur in modern Israel and Iran
How many different genes between teosinte and maize?
5
Describe some features of the domesticated ground cherry?
Non-domesticated - sprawling growth habit, small fruit drops to ground
Increased fruit size
Loss of husk
Increased flower number
Optimal flowering time
Loss of fruit abscission
Why would you want to redomesticate an already domesticated crop?
Lost genes such as
- Wild salt resistance
- Resistance to pathogens
What are the two approaches to gene editing in plants?
- Manipulate existing genes
- Introduce novel/foreign genes (from a different organism)
In gene editing describe two methods of manipulation of existing genes
Overexpression of wildtype genes
Gene silencing - switch off specific genes
Gene silencing - switch off specific genes - Give an example of this
Eg. silencing CaMCMT1 mRNA in coffee plants for low caffeine
Why would you introduce a novel/foreign gene (from a different organism)?
- For enhancement of existing characteristics
- For completely novel characteristics
What is an example of a novel gene being added to a plant to enhance an existing characteristic?
Expression of insecticidal toxins encoded by CRY genes from Bacillus thuringiensis (bacteria) into cotton plants
What is an example of a novel/foreign gene being added to a plant to add a entirely new characteristic?
Eg introduction of bacterial gene for tolerance to TNT explosive
Tobacco plants expressing nsfl (NR 3-2) can grow on medium containing TNT and detoxify it (into ADNT)
Describe CRISPR
Precision editing tool
Various enzymes - molecular scissors
Produce Double Strand DNA breaks to introduce site specific mutations
CRISPR-Cas - uses RNAs to target nucleates and introduce site specific mutations, insertions or deletions
What are some plant gene transfer methods? - two most important
Agrobacterium-mediated gene transfer
Microprojectile bombardment
Viral vectors
Protoplasts
Microinjection
Electroporation
Describe Agrobacterium-mediated gene transfer - benefits and considerations
- Highly effective
- Lower copy numbers
- Works better on dicot plants than monocots
Describe Microprojectile bombardment - benefits and considerations
- Easy and effective
- random integration
- high copy numbers
- used with a wide range of plants
Why are viral vectors rarely used in plant gene transfer?
Not very effective; limited to hosts
Why are Protoplasts rarely used in plant gene transfer?
Regeneration problems
Why are Microinjections rarely used in plant gene transfer?
Tedious and slow
Why are Electroporation rarely used in plant gene transfer?
Large foreign DNA; high efficiency; regeneration problems
What are most countries moving towards in regards to genome edited plants and GMO regulations?
Genome edited plants becoming exempt from GMO regulations
What factors need to be considered during gene transfers?
Gene(s) to be transferred - transgene
Host cell/tissue in which gene expressed
Mechanism of transfer
Method of regulation and selection
Describe agrobacterium
Gram -ve rod shaped soil bacteria (rhizosphere)
Causal agent of crown gall tumours
What is the mechanism of Agrobacterium (Crown gall disease) horizontal gene transfer?
- Agrobacterium transfers T-DNA into plant cells using
T-complex - T-DNA then integrated into plant genome
- T-DNA may contain genes that code for auxin and cytokinins
- Causes cell proliferation and the growth of a gall or tumor-like structure on the plant.
- Also contain genes that code for the synthesis of opines
- Can serve as a food source for Agrobacterium
What is the Ti plasmid?
- Plasmid in Agrobacterium responsible for Auxin and cytokine production
What are key parts of T-DNA region in agrobacterium used for gene transfer when inserting genes into plants?
Appropriate promoter
- Eg CaMV 35S for overexpression
Selectable markers for identification
- Eg antibiotic resistance gene
Plant needs to recognise gene to translate
- Differences in UTR may prevent recognition
Describe the process of DNA bombardment?
- Coat small metal particles (non toxic, heavy eg gold, tungsten) in DNA
- Insert into particle gun
Some cells killed but number will survive and take up DNA
Describe the process of transferring genes into a plant using either Agrobacterium?
- Identify suitable explant (e.g. leaf piece)
- Co-cultivate with Agrobacterium
or DNA bombardment - Kill Agrobacterium with suitable
antibiotic which does not harm plant - Select for transformed plant cells
(use selectable marker) - Regenerate whole plants
What are the negatives of regeneration after gene transfer using Agrobacterium or DNA bombardment?
Very slow process
Describe the Floral-dip method?
- Dip flowers into solution containing Agrobacterium and a surfactant (a detergent)
- Helps the bacteria adhere to the plant tissue
- Plants develop and set seed
- Select for transgenic plant cells
- Using selectable marker (allows the identification of cells that have taken up the foreign DNA)
What are the negatives of the Floral-dip method of regeneration? Why is it not really a problem?
Low success rate
Doesn’t really matter because so many seeds
Describe Fast-Track engineering for gene transfer
- Transform developmental genes in along with target transgene
- reporter gene above blocks chlorophyll - no green in transformed cells
- Produce seedling on plant to be replanted like a cutting
Which of these can be manipulated - nuclear, chloroplast and mitochondrial genomes?
Nuclear and chloroplast genome can be manipulated
Mitochondrial genome not manipulable
Why is the chloroplast a target of gene manipulation?
- Precise insertion
- High level of expression
- Lots of copies
- Coordinated expression of multiple genes
- Gene containment
Why does chloroplast as a gene manipulation target reduce the risks associated with gene containment compared to nuclear genome manipulation?
Avoids gene flow to other plants
Not transmitted through pollen
Maternal inheritance
Prevents GM gene escape to non GM plants
Why is the testing on GM crops considered insufficient by some?
Many studies by biotech companies involved in commercialisation of GM - conflict of interest concern
What are biotic stresses on plants?
Pathogens
Pest damage
Wounding (physical damage)
ROS (reactive oxygen species) -> oxidative stress
- produced by metabolic activity
What are some abiotic water-deficit related stressors that affect plant yield?
Heat
Chilling
Freezing
Drought
Salinity
What abiotic stressors affect plant roots?
Drought
Salinity
Flooding
Heavy metals
What are root exudates?
Organic carbon compounds released into the soil
What is mucilage?
- High molecular weight carbon compound
- Thick, slimy substance that is produced by certain plants and microorganisms
- Composed of long-chain carbohydrates
What are the functions of mucilage?
Help the plant retain moisture
Protect against desiccation
Aid in seed dispersal
Where is mucilage secreted?
Root cap cells and epidermal cells
What are examples of low molecular weight exudates from plants?
Organic acids, phenolics, phytosiderophores
Describe strategy 1 for root Fe2+ uptake
- Ferric chelate reductases (FCRs) in root cells reduce Fe3+ to Fe2+ using NADPH as an electron donor
- Fe2+ passes through IRT1 transporters that have a high affinity for Fe2+
- Upregulated under conditions of Fe deficiency.
Where is excess Fe2+ stored?
sequestered in ferritin, a protein that stores Fe2+ ions in a nontoxic form in cells.
What are phytosiderophores?
Small organic molecules
Produced in certain grass species (barley and maize)
Response to Fe deficiency
Form Fe-PS complexes with Fe3+
Allow uptake by transporters
What are phytosiderophores found in?
Root exudates of Fe deficient grass species.
Describe the biosynthesis of phytosiderophores
Made from methionine
Converted into nicotianamine by NAS (nicotianamine synthase)
Converted into phytosiderophores
Why is barley less susceptible to Fe deficiency than rice?
excretes higher levels of phytosiderophores
What prevents increased Fe content in rice when genes for increased uptake of Fe have been added?
- Bottleneck in iron seed partitioning (Iron not reaching grain)
- Nicotianamine (NA) regulates iron distribution in the phloem and movement to the seed
- Overexpression of NA biosynthesis genes can increase iron content in rice grains
What protein transports Fe-NA from phloem to seed?
YSL2
What needs to be done to increase content of Fe in phloem?
Increase expression of NAS to produce better iron mobilisation into phloem
What are the barley genes associated with excretion of phytosiderophores?
HvNAAT-A and B
What did adding the barley HvNAS1 gene into rice do to rice grain iron content?
2-3 fold increase
What does increasing the expression of YSL2 gene in rice using a promoter do for Fe content?
Increased Fe content of grain
4 fold
What is ferritin?
Fe storage protein
Prevents anaemia and iron deficiency
What does adding a glutenin promoter that increases ferritin expression in rice achieve?
Ferritin expressed in seed endosperm and subaleurone
2-3 fold increase in Fe content
Why is diet bioavailability of plant nutrients such a problem
Different chemical forms, binding to different organic or non organic forms
- may inhibit transfer across membranes
Can be as low as 5% for most plant sources of iron
Can vary due to presence of ‘antinutrients’ - compounds that reduce absorption
What is phytates effect on the bioavailability of many essential nutrients?
Negative charge binds positive ions and interferes with assimilation
- considered an “antinutrient”
- binds minerals
- forms insoluble complexes that are not easily absorbed by the body.
How does phytase make some minerals more bioavailable in plants?
Break down metal-phytate complexes
- Release positively charged free metals (such as calcium, zinc, iron and mg)
- Increasing bioavailability of these minerals
What is phytate?
Storage form of phosphorus
What are Fer-NAS-YSL2 plants?
Plants with a combination of GM genes which increase iron content in their edible tissues
What are some potential negatives and challenges of Fer-NAS-YSL2 rice plants?
- risk of increasing accumulation of toxic metals (eg Cd)
- Expression worse in certain rice species
- More extensive field trials required - test yield
- Human feeding trials needed
What are GM strategies for Fe biofortification in rice grains?
Expression of nicotianamine synthesis enzymes
Expression of Fe-NA (YSL2) transporter
Expression of ferritin
What does expression of nicotianamine synthesis enzymes for Fe content in rice?
Improved long distance transport
How does expression of Fe-NA (YSL2) transporter increase Fe content in rice?
Increases transfer into rice grain
How does expression of ferritin increase Fe content in rice?
Improved Fe storage in grain
Why is high soil salinity such a big problem?
Reduces soil water potential
Effects large amounts of farmland
Reduces yield
Describe cellular dehydration caused by freezing?
Normal conditions - cell surrounded by water containing solutes
->
Ice formation begins
- Formation of ice decreases water potential outside the cell
->
Ice formation continues
- Higher solute concentration outside the cell draws water out causing dehydration and cell death
A plants water status is defined by _______ ______ measured in ____
Water potential
MPa
Water potential = _______ + ________
Water potential = solute potential + pressure potential
What is solute potential (osmotic pressure)?
Concentration of solutes dissolved in water
Water potential _________ as solute concentration increases
Water diffuses across semi-permeable membranes from ____ to _____ solute concentrations (osmosis)
low to high
What is pressure potential (turgor pressure)?
Physical forces exerted by water on cell membrane and cell wall
What occurs to cell turgor when water status is high?
When water pressure potential is high (high water status) water enters the cell causing the cell to become turgid
What occurs to cell turgor when water status is low (drought - water loss)?
Water leaves cells
- turgor is lost
- cells become flaccid
- Plant wilts
What are the short term impacts of water deficit?
Reversible effects
Leaf wilting
Declined photosynthetic rates
- stomata closed to reduce water loss
- reduced CO2 uptake
Reduced cellular/metabolic activity
- as energy from photosynthesis is required
What are the long term effects of water deficit?
- Not reversible
- Leaf abscission
- Cellular toxicity - Ion cytotoxicity
- Due to loss of water = < concentration of cellular contents
- Severely inhibited photosynthesis and respiration
What part of plants is very desiccation tolerant?
Seeds
Viable seeds can be recovered even after long term water deficit
What are the effects of high salt?
Altered Na+:K+ ratios
Increased NA+ and Cl-
Na+ rapidly enters root cell
Causing negative membrane potential
During periods of high salt concentration in soil describe the mechanism by which Na+ enters the root cell and what are the consequences?
Via non-selective channels and K+ transporters
- Outcompetes K+ for uptake
Na+ cytotoxic
- Many enzymes sensitive
- denature
K+ essential for plant function
What are the strategies focused in GM when developing crops with drought tolerance?
Osmoprotectants - Metabolites and molecules involved in protecting cell components from water stress effects
- Stress-responsive transcriptional regulation
- Osmoregulation via ion/water transporters
- Water use efficient carbon fixation
Describe xerophytes morphological adaptations
Xerophytes
- Thickened cuticles
- Reduce water loss
- Reduce leaf breakage from wilting
- Shiny cuticles
- Reflect light and heat
- Trichomes (leaf hairs)
- Trap damp air above stomata
- Reflect light
- Sunken stomata
- Small/no leaves
- Reduces surface area and water loss
Describe succulents morphological adaptations?
- Increased storage ability of water
Specialised organs
- Enlarged cells
- High volume vacuoles
Organ can be roots, stems, leaves
Low transpiration
Thick cuticles
How do drought resistant plants alter their metabolism to increase survival?
Modified photosynthesis and carbon fixation
Such as CAM and the C4 photosynthetic pathways
What does CAM photosynthesis achieve?
Improve water use efficiency
What are osmoprotectants?
Protect against osmotic stress induced by water deficit
- abundant in stress-tolerant plants and microbes
- non-toxic compounds
- do not disrupt hydration shell around the cell
What genes over-expression improve drought tolerance in plants? Producing succulence features - eg enlarged cells
CEB1
Why is the expression of CEB1 problematic in non-stress conditions?
Gives stunted growth
Energy intensive production - high metabolic demand
What does trehalose do in plants?
Confers stress tolerance
What enzymes produce trehalose?
TPS and TTP enzymes
How do plants control the expression of TPS and TPP? Give an example
Using inducible promoters to control expression
Rice rbcS promoter
- Specific to chloroplasts of leaf mesophyll cells
- Allows expression of TPSP (TPS and TPP fused together)
- only in chloroplasts of certain cells
- limiting energy demand through synthesis of trehalose
What is a water deficit specific control of trehalose production?
ABA-inducible promoter
- activated during water deficit stress
- ensures energy-intensive production of trehalose is only triggered when the plant is under stress
What is the functions of molecular osmoprotectants?
- Small organic molecules protect cells from osmotic stress (high salt concs)
Functions - Molecular chaperones = stabilise and protect conformation of proteins, RNAs and cell membranes
What are the two types of molecular osmoprotectants?
Proteins
- Heat shock proteins – HSPs
- Cold shock proteins – CSPs
What is an example of an example of a shock protein molecular osmoprotectant?
CspB - RNA chaperone from Bacillus subtilis
Expression of CspB in various plants has shown increased tolerance to cold treatment, heat treatment and drought treatment
What is DroughGuard?
Commercialised CspB transgenic maize in 2010
What is abscisic acid (ABA)?
Hormone abscisic acid (ABA)
- Stress hormone
- Synthesised in response to environmental stress
- Particularly water deficit
- Drought, salinity, freezing, cold
What are some downstream responses produced by ABA?
Osmoprotectants
Molecular chaperones/stabilisers
- Heat and cold shock proteins
Movement of water and ions
- Aquaporins, ion channels
Oxidative stress responses
What is the oxidative stress response in plants?
Peroxidase, superoxide dismutase
- Reactive oxygen species accumulate and lead to cellular damage
- Enzymes that scavenge ROS control indirect stresses
What are some osmoprotectants?
Sugars, proline, glycine betaine
There are _____ response pathways to drought stress, _____ ABA dependant and _____ ABA independent pathways?
There are 3 response pathways to drought stress, 2 ABA dependant and 1 ABA independent pathways?
Describe response to stress - ABA dependent or independent?
- Signal transduction ABA or ABA-independent
- in gene promoter regions
- Activate gene expression for stress response and tolerance
- Increasing transcription factor abundance may increase size of the response - enhancing drought resistance
What were the finding of a study on arabidopsis where drought tolerance gene CBF3 was overexpressed?
Drought tolerance increased with no deleterious effects on growth or development in normal conditions
What is HaHB4?
An ABA inducible transcription factor
- allows for rapid drought response
Why have manipulation attempts of aquaporins not been successful?
Dependant on gradient
Increasing abundance does nothing if the gradient isn’t present
Why is salt a problem in times of water deficit?
- Makes it harder for cells to take up water
- When it gets into cells, sodium very toxic
What is the purpose of overexpressing NHX1 in plants?
Helps reduce salt accumulation in plant cells
- can improve plant growth and survival in high-salt conditions
How was NHX1 overexpressed in tomato plants?
agrobacterium-mediated transfer
What is the advantage of NHX1 overexpression in tomato plants?
Grow well in high-salt conditions without the fruit taking up salt
Why does fruit not take up salt?
Xylem connection not there
What are the pathways used to remove salt from plant cells - active or passive?
SOS1 (out of the cell)
NHX1 (into the vacuole)
- use proton gradients for transport
Active transport using ATP or pyrophosphate dependant
How does enhancing proton pumps improve drought tolerance in plants?
Improves both salt and drought tolerance
- allows maintenance of salt gradient and water concentration
How does enhancing proton pumps improve drought tolerance in plants?
Allows maintenance of salt gradient and water concentration
What is water use-efficient carbon fixation?
Process by which plants fix carbon dioxide while minimizing water loss through stomata.
What is the role of stomata in CO2 uptake?
boptiboop you should really know this by now
What is dynamic control in relation to stomata?
ability of guard cells to change their size and shape in order to regulate the opening and closing of stomata.
How is the opening and closing of stomata regulated?
regulated by both the water status of the plant and the availability of carbon dioxide
When do stomata close?
Stomata close when the demand for carbon dioxide is low
- such as at night.
What are some alternative forms of photosynthesis?
C4 photosynthesis and CAM (Crassulacean Acid Metabolism)
- alternative forms of photosynthesis used by some plants to reduce water loss.
What is the C3 pathway?
The C3 pathway is a type of photosynthesis
Ribulose 1,5-bisphosphate is carboxylated by Rubisco to give 3-phosphoglycerate.
What is Rubisco and what is its role in C3 photosynthesis?
- Enzyme that catalyzes the first step of the Calvin cycle
- It carboxylates Ribulose 1,5-bisphosphate
What is the Calvin cycle?
- series of reactions in the C3 pathway of photosynthesis that converts carbon dioxide into triose phosphates
- can be used to synthesize sugars and other organic molecules
What happens to triose phosphate produced by the Calvin cycle?
- used to synthesize sucrose
- transported to other parts of the plant for energy storage
What is photorespiration?
- C3 plants in which Rubisco uses oxygen instead of carbon dioxide
- resulting in the production of toxic 2-phosphoglycolate
- which must be recycled back into the Calvin cycle at the cost of energy
- net loss of one carbon dioxide molecule.
What is photorespiration? - copy of card dont bother
bababadoii
What is the C4 pathway?
carbon dioxide is first fixed into a four-carbon compound before being converted into triose phosphates in the Calvin cycle.
How are C4 plants anatomically specialised?
- Separation of Rubisco
- Thick bundle sheath cell walls
- No air spaces between their mesophyll and bundle sheath cells
What do the specialisations in C4 plants achieve?
Rubisco never sees oxygen
- Continually exposed to saturating CO2 concentrations
- Prevent CO2 loss
How are high CO2 concentrations produced in chloroplasts of C4 plants?
- CO2 taken up by outer mesophyll cells next to air space
- O2 insensitive enzyme PEP carboxylase generates oxaloacetate - 4 carbon molecule
- converted to malate
Malate is decarboxylated releasing CO2 into a different cell - CO2 assimilated by rubisco in bundle sheets cells
What does the spatial separation in the C4 pathway of carbon fixation and assimilation allow?
allows C4 plants to efficiently use CO2
- particularly in environments where CO2 levels are low or fluctuating
- photorespiration can be a significant energy drain
What happens to 3-carbon pyruvate after release of CO2 by decarboxylase in the C4 pathway?
- transported back to mesophyll cells
- converted into PEP (recycled)
What are the benefits of the C4 pathway?
More water efficient
- All CO2 converted
- Stomata need to open less
- When stomata closed, all CO2 in air space can be utilised
What climate are C4 plants adapted to?
Arid climates
Is changing C3 plants into C4 plants a realistic goal?
Difficult because it is a multigenic trait
- but has evolved independently multiple times
Some plants have use both pathways so very possible
What type of plants is CAM photosynthesis seen in?
Xerophytes
How is photorespiration prevented in CAM plants?
- Photosynthesis and carbon fixation separated temporally
- Stomata open at night when water loss lowest
- Convert CO2 to malate as storage form
- Stored in vacuoles until day
- Closed stomata, photosynthesis using stores during day
Are CAM plants facultative (when stressed) or obligate?
Both
What type of water stress do CAM excel in?
Drought
What is vernalization?
Vernalisation is a process whereby plants require a period of cold exposure to switch from vegetative growth to reproductive growth
Why is vernalization important for flowering in spring?
- helps distinguish between autumn and spring
- Tracking photoperiod alone is not enough as the days are equal in length in autumn and spring
What is the difference between winter wheat and spring wheat?
Winter wheat is cold-tolerant and can be sown in autumn
- whereas spring wheat cannot tolerate cold
Why does winter wheat grow for longer before flowering?
- needs to go through the vernalization process first
- requires a prolonged period of cold temperatures
What was Lysenko’s contribution to genetics?
Discovered that planting winter wheat in spring did not work unless the seeds were germinated under artificial cold
- stupid man rejected mendelian genetics
- held Russian science back for years
Where does cold sensing occur during vernalization?
- mostly in the apical meristem
What is vernalization often paired with?
photoperiod to regulate flowering.
Does the duration of cold exposure affect vernalization?
Yes, the longer a winter plant is exposed to cold, the greater the number of flowers it will produce (remain vernalized).
What is the minimal number of days of cold required for vernalization depend on?
where the species evolved - specific to a plant species environment
What is the difference between vernalization and cold acclimation?
- Vernalization is the process of lifting repression to flowering by cold treatment
- Cold acclimation is the process of preparing a plant for cold temperatures
Do spring/summer annuals use vernalization?
neutral for spring/summer annuals that germinate in spring
What is the requirement for vernalization in winter annuals?
- flower late without it
- without it, will not undergo the molecular changes needed to initiate flowering
- the plant remains in a vegetative state and does not switch to reproductive growth.
What would be consequences of no vernalization?
Including reduced yield
Delayed harvest
Even plant death in some cases
What is absolute vernalization?
- required period of cold exposure for some biennial plants (harvested after two years) to ensure successful flowering and seed production
- Without it, these plants will not flower at all
How do plants remember winter?
- Prolonged cold leads to remodelling of the FLC chromatin and accumulation of histone modifications
- leading to the gene being inaccessible to the transcription factor
What is the function of the FLC gene?
- Inhibits flowering by preventing dimerisation of FT and FD unless cold exposure is sufficient
- Represses expression of floral meristem genes such as AP1
Where is FLC highly expressed?
In shoot apex
- Also occurs in leaf where inhibition is more direct
What is FRI?
- A gene that increases the expression of FLC
- thereby delaying flowering until the plant has undergone sufficient vernalization.
What are the two main genes involved in plant cold response?
- FRI and FLC
- leading to adaptive changes in different ecotypes/accessions
How many times has cold independence evolved in Arabidopsis?
Cold independence has evolved twice in Arabidopsis
What is the role of Frigida (FRI) in regulating the cold response of plants?
Vernalization process
- which allows plants to flower after a period of cold exposure
Why do plants balance their cold requirement for flowering quite conservatively and what is a potential negative of this?
They can’t afford to flower when it’s not spring
- so they play it safe by requiring a long period of cold
- sometimes means they won’t flower at all
What is the driver of natural variation in vernalization responses in Arabidopsis?
Allelic variation in the FRI and FLC genes.
Why must fruit trees move North with shifting zones due to global warming?
as photoperiod may not be suitable in their current location.
What is the purpose of bud dormancy in fruit trees during the winter?
allows the buds to survive cold temperatures and ignore warm winter spells.
- If buds opened during a warm spell, a subsequent freeze would kill them.
What is the role of FLC?
- Regulates vernalization
- Level of expression determines how long a plant needs to be exposed to cold temperatures before it can flower
What cues do plants use to flower at the right time of year?
including
- photoperiod
- temperature
- plant age
- soil nutrients
- stress
What are the responses in shade avoidance syndrome (SAS)?
Responses
- Elongate stem
- Space leaves
- Induce early flowering
- Angling leaves up
- Dependent on species
What are the characteristics of shade avoidance?
Stem elongation
Petiole elongation
Hyponasty
Reduced branching
What are the characteristics of shade tolerance?
- Increased SLA (Specific Leaf Area) - Ratio of leaf area to leaf mass
- Reduced CHl a:b ratio
- Increased PSII:PSI ratio
- High physical defence
What conditions are plants with reduced Chl a:b ratio and why?
- Plants with a lower Chl a:b ratio tend to be adapted to low-light conditions
- Chlorophyll b absorbs light in the green part of the spectrum that is less available under low light
What conditions are plants with a higher PSII:PSI ratio adapted and why?
- Adapted to high-light conditions
- as PSII is more effective at capturing light energy in bright sunlight.
Describe how Stellaria’s ecotypes deal with the differing levels of shade in differing locations?
Alpine ecotype stay small and dispersed
- Being tall disadvantageous - exposed
Prairie ecotype - lots of competition - SAS
Why is SAS detrimental to crop yield?
Elongation at expense of harvestable organs
How would inhibiting elongation response in SAS be beneficial to crop yield?
Inhibition of elongation responses to neighbours may enhance harvest index
- more carbon allocated to harvestable organs
What is harvest index?
harvested/total biomass
How do plants know shade is produced by neighboring competing plants?
Chlorophyll does not absorb far red
>700nm
Far red comes through in neighbour shade
Elongation precedes mutual shading - anticipation
Photoreceptor called _______ responsible for red/far red perception
Phytochrome
How does photoreversibility of phytochrome work?
- Absorbs light in the red and far-red regions of the electromagnetic spectrum
- Phytochrome exists in two forms: the inactive form (Pr) and the active form (Pfr).
- Absorbs red light, phytochrome converted from Pr to Pfr
- Conversion triggers a variety of responses in plants.
- Pfr is able to detect far-red light, and when it absorbs far-red light, it is converted back to Pr
What happens when phytochrome (in its active Pfr form) moves into the nucleus?
Phytochrome (in its active Pfr form) can interact with other nuclear proteins to regulate gene expression.
What are phytochrome response elements (PREs)?
PREs are specific DNA sequences that Pfr can bind to in the nucleus to activate or repress transcription of target genes.
How is the activity of phytochrome regulated?
Phosphorylation and dephosphorylation
- can affect the stability and interaction of phytochrome with other proteins
What happens if Pfr is not dephosphorylated in the nucleus?
If Pfr is not dephosphorylated in the nucleus
- recognized by the 26S proteasome and degraded
- leading to a decrease in its activity.
How many members are there in the phytochrome family?
There are five members in the phytochrome family
What light does PhyA to respond to?
PhyA responds to far-red light.
What light does PhyB to respond to?
Red and white light
What are the roles of PhyC, PhyD, and PhyE?
PhyC, PhyD, and PhyE play roles in regulating responses to red and far-red light.
Which member of the phytochrome family is associated with shade avoidance?
PhyB
What is the effect of a mutant with no PhyB?
A mutant with no PhyB shows a reduced shade avoidance response compared to wild-type plants.
What is the role of PIFs in shade response?
PIFs (Phytochrome Interacting Factors) are a family of transcription factors that promote shade response genes.
How does Pfr binding affect PIFs?
targets them for degradation by the proteasome, inhibiting shade response.
What happens in the presence of more far-red light than red light?
In the presence of more far-red light than red light, there is less Pfr and more Pr, resulting in less Pfr in the nucleus.
What is the effect of PIF binding to promoter regions of shade response genes when Pfr is low?
When Pfr is low, PIFs can bind to the promoter region of shade response genes and activate their expression
- leading to a shade response, even though some Pfr is still present but not enough to inhibit PIFs
Different PIFs for different responses caused by neighbor shade cues? What are some of these responses?
Flowering, seed germination, foliage expansion
How can PhyB be used in GM?
- GM increased the total amount of phytochrome
- Therefore, increased the amount of Pfr entering in the nucleus in the shade condition
- blocking the SAS response
In potatoes, alleviates density effects on crop yield
What downsides of increasing the amount of phytochrome in plants using GM?
- More susceptible to drought
- Increased phytochrome increased density of stomata
- More water loss
In what plants have SAS been lost at a genetic level?
Shade tolerant
Alpine plants
Why do plants flower at a specific time of year?
to coincide with the presence of pollinators and to avoid competition with other plants for pollinators
- important for successful pollination and seed development.
How does climate change impact flowering time?
Climate change can disrupt flowering time by altering temperature and precipitation patterns.
- wheat cultivation will move north
What is the transition from vegetative to flowering phase?
- plant stops making leaves and starts making stems and flowers instead
- occurs in the meristem, which is the tissue where the plant growth occurs.
What is the role of the apical vegetative meristem in flowering?
The apical vegetative meristem makes leaves indefinitely
- but upon flowering induction
- it transitions to the floral meristem
The floral meristem stops making leaves and starts making flowers, and then eventually stops growing altogether.
What is the short day Maryland mammoth mutant?
Shamabaalalalalalalalalalsalalallad
What is a day-neutral plant?
A plant whose flowering is not affected by the photoperiod.
What is a long day plant and where are these often found?
A plant that only flowers on long days
- typically found in Europe
Eg. spinach, wheat, Arabidopsis, sugar beets.
What is a short day plant and where are these often found?
A plant that only flowers on short days
- typically found in equatorial regions
Eg. rice, maize, coffee, cannabis
What is photoperiodism and where is it a reliable parameter of season?
Photoperiodism is the ability of plants to flower in response to the duration of light exposure
- it is a reliable parameter of season at high latitudes but not at low latitudes.
What is the molecular driver of flowering?
Florigen
- travels from the leaf to the apical meristem in plants.
What is florigen?
- FT is the gene that produces the FT protein
- enters the vascular system of the plant
- travels to the apical meristem to initiate flowering
What is FT protein?
Phytochrome photoreceptor molecule in the leaf that senses light to measure day length and activate the FT gene
- response to phytochrome-mediated detection of day length in leaves
How does covering one leaf induce flowering in short day plants?
Covering one leaf with aluminum foil blocks the leaf from sensing light and activates the FT gene
- leading to production of the FT protein and induction of flowering.
What happens when a leaf that has been covered to induce flowering is grafted onto another short day plant?
The florigen produced in the covered leaf travels through the phloem and induces flowering in the recipient plant’s apical meristem.
Does the signal for flowering affect other leaves in the plant?
Bollocks
What is the function of the FT protein in flowering?
- Travels through phloem to the apical meristem
- associates with the FD transcription factor
- forming a dimer that activates the AP1 gene
- master switch for flowering.
What is the coincidence model?
explains how the FT protein knows when to be expressed
- It requires the coincidence of high levels of CO protein and light, hence the name coincidence model.
What is the role of the circadian oscillator in the coincidence model?
controls the timing of light-sensitive and light-insensitive phases
- internal mechanism that controls rhythms (independent of day/night signals)
- allows for the regulation of FT expression at the appropriate time.
What is the role of the CONSTANS gene (CO) in the coincidence model?
CO gene produces mRNA that oscillates over a 24-hour period
- with CO protein being destroyed in the dark
- CO accumulates more on longer days
- when it is present in high amounts along with light, it triggers FT expression
How does the coincidence model explain FT expression in long day and short day plants?
In long day plants, high CO levels and long days coincide to trigger FT expression.
In short day plants, CO levels do not reach the required threshold until the appropriate time of year, which results in FT expression at the appropriate time.
In short days, which transgenic plants express high FT and flower?
Transgenic plants expressing high CO mRNA also express high FT and flower
Describe the role of CO in FT expression in short and long day plants.
- CO is an inhibitor of FT expression in short day plants.
- During long days, CO accumulates and blocks the expression of FT.
- FT is only expressed under low levels of CO in short day plants
What is the effect of moving plants to a new climate with different photoperiods?
Can cause early flowering
What are the factors that determine the optimum cultivar for a specific location?
determined by flowering time, weather, and water availability.
How does the required flowering time change in relation to water availability?
The drier it is, the earlier plants need to flower.
Why are plants that rely solely on day length for flowering more likely to go extinct under climate change?
Will flower when conditions are less viable (changing climate)
What is the gene induced by ethanol used in GM crop for flowering?
Ft gene
How is flowering of GM crops induced?
spraying the crop with ethanol vapour, which triggers the expression of the FT gene
Describe irrigated lowland - rice cultivation
2-3 harvests per year
Disproportionate harvest of rice
(55-60% of area, 75% of product)
Describe rainfed lowland - rice cultivation
- No constant water supply/control for irrigation
- More subject to flooding and drought
- 1 (sometimes 2) harvest per year
- More variable yield
Describe rainfed upland - rice cultivation
- Plant never has fully submerged roots
- Fields never flooded - aerobic soil conditions throughout
- Low and variable yields
What are the two flood coping mechanisms of rice?
Escape and quiescence
What is the rice escape strategy flood coping mechanism?
Try to outgrow water level
Flood water typically rises slower than rice can grow
But flash floods
What is the rice quiescence strategy flood coping mechanism?
Hold its breath
- Wait it out
Limit on time due to lack of oxygen
- Severe floods often don’t last anyway
What is the role of ethylene during submergence?
Helps adaptation to oxygen limitation
- promotes accumulation enzymes involved in anaerobic respiration
- as well as promoting elongation in the escape response
Describe features of deepwater rice
Escape response
- Ethylene induces internode elongation - rapid stem elongation
- Rice is a grass plant - specific stem architecture - nodes
- Close together in small plant
- Gibberellin (GA) for cell expansion pushes nodes further apart in response to ethylene
Describe the trade off between flood tolerance and yield
Escape response produces low yields
- biomass reallocated to long stem rather than grain
What is the role of SNORKEL 1 and 2?
- Submergence response
- Ethylene response factors
- Promotes gibberellin production and ABA degradation
- Promotes elongation growth
- Provides submerged tissues with oxygen
What are the characteristics of rice quiescence?
Energy maintenance
- Minimum elongation
- Carbohydrate level in stem
- Optimum fermentation - some energy supply
- Underwater photosynthesis
Protection
- Efficient AOS (active oxygen species) scavenging
- Low ethylene synthesis or sensitivity
- Limiting reoxidation damage
What is the Sub1 locus?
Region of DNA that confers submergence tolerance in rice plants.
What is the submergence tolerance of the FR13A landrace rice?
The FR13A landrace is unusually tolerant to submergence
- dominant trait
- can be submerged for 2-3 weeks
- low yield
How much variation in submergence tolerance is accounted for by the Sub1 locus?
70%
How was the Sub1 gene introduced into elite yield species? and why was this technology used?
Introduced by micro assisted breeding rather than transgenic technology
GM - commercially poor decision (not accepted by many countries)
Describe the rice submergence escape response
Submergence increases ethylene
Ethylene blocks abscisic acid (ABA) production
- ABA blocks GA responses - so block lifted
Ethylene blocks SLR1 and SLRL1
- These block GA responses - so block lifted
Essentially ethylene blocks GA blockers
- GA responses allowed
- Elongation growth
Describe the rice submergence quiescence response
Submergence increases ethylene
- Ethylene triggers SUB1A - ethylene response factor
- SUB1A strongly promotes SLR1 and SLRL1 - DELLA proteins
- Blocks on growth pathway (lifted by GA responses)
SLR1 and SLRL1 block GA response - Limited elongation growth
What are the effects of introducing the Sub1 gene into rice crops? Include social effects
- Reduces yield variability
- Raises expected yield
Social benefits - Disproportionately benefits poorest farmers
- Low lying flood prone areas occupied by disadvantaged groups
What is ethylene and how does it act in plants?
- Ethylene is a gaseous plant hormone that can diffuse in and out of cells/plants
- acts by binding to receptors and activating a signalling pathway that leads to changes in gene expression and various physiological responses
What is the ethylene response mutant?
Does not respond to ethylene like other plants.
- Triple response observed in Arabidopsis shoots treated with ethylene.
What is the never-ripe mutant in tomatoes?
- Does not produce ethylene
- therefore does not ripen
What is the triple response seen in plants when exposed to ethylene in the dark
- Exaggerated apical hook
- Short hypocotyl
- Short Root
Where do the five Arabidopsis ethylene receptors reside?
(Ert1, Ert2, Ers1, Ers2, Ein4)
- reside in the endoplasmic reticulum (ER)
How do mutations in the Arabidopsis ethylene receptors affect ethylene signaling?
Loss of any one receptor has minimal consequences.
- Plants with multiple receptor losses exhibit a constitutive ethylene response phenotype.
In the absence of ethylene
- receptors remain active and suppress the pathway
ethylene is present
- receptors become inactive, relieving suppression and activating the pathway
Mutants that cannot bind ethylene are unable to inactivate the pathway
- block on the pathway cannot be removed
- inability to express ethylene responses.
If the mutant is sufficiently expressed, the plant fails to exhibit an ethylene response.
What is the constitutive triple response (CTR)?
a phenotype observed in plants with mutations in the CTR1 gene
- resulting in a plant that always responds as if ethylene were present, even when it is not
What is the reverse screen for identifying CTR mutants?
Looking for plants that exhibit the constitutive triple response (CTR) phenotype without the presence of ethylene
- screening for mutants that act as if ethylene is present
- short and shows triple response
What is CTR1?
CTR1 is a negative regulator of the ethylene signaling pathway in plants
- Mutations in CTR1 can result in the constitutive triple response (CTR) phenotype
In the _______ of ethylene, CRT1 is active and _______ the ethylene response
In the absence of ethylene, CRT1 is active and inhibits the ethylene responses
What happens to EIN2 in the presence of ethylene?
When ethylene is present, CTR1 kinase is inactive and EIN2 is not phosphorylated
- fragment of EIN2 (C-terminus) moves into the nucleus and activates EIN3 and EIL1 TFs
- then activate ERF1 TF and ethylene responsive genes
What happens to EIN2 in the absence of ethylene?
CTR1 kinase phosphorylates the C-terminus of EIN2 constantly
- TP1/2 proteins recognise the phosphorylated EIN2
- promote its degradation through ubiquitination for targeting to proteosome
What is the role of EIN2?
- Ethylene receptor activated
- EIN2 C-terminus activates EIN3 and EIL1 in the presence of ethylene
- They then activate ERF1 TF and ethylene responsive genes
Will there be a ethylene response in a plant with one missense mutation at the ethylene binding site (ethylene no longer binds one of the receptors)?
No response
- single constitutively active receptor sufficient to shut off ethylene responses
What is ethylene produced from?
ACS (enzyme) produces ACC
ACC -> ethylene by action of ACC oxidase (ACO)
Describe features of ACS - in the production of ethylene?
Tightly regulated
- highly unstable enzyme
- Constantly synthesised and degraded - proteasome
- keep ethylene levels low
How is ACS stabilised?
Phosphorylation of the C-terminus of ACS
- blocks interaction with proteasome
What are factors that would activate kinases involved with phosphorylation of ACS?
Wounding, pathogen attack and abiotic stress
What are some of the actions of ethylene in plants?
Petal senescence and wilting, and it ripens fruit
- not all fruits are responsive to ethylene
What are fruits that respond to ethylene called?
Climacteric fruits
What is seed dormancy?
Seeds are prevented from germinating even under optimal environmental conditions
- allows seeds to remain viable for extended periods and is an adaptation that allows seeds to survive unfavorable conditions
How do seeds remain viable for such long periods?
Seed dormancy
- due to desiccation and the presence of specialized proteins that prevent denaturation
What is the female gametophyte surrounded by?
maternal tissue in the ovules
How many nuclei does the female gametophyte have?
8
What is the entry point of the pollen tube into the embryo sac?
The micropile
What is the function of the central cell after fertilisation?
Becomes the endosperm
- which is the nutritional tissue surrounding the embryo
Describe plant fertilisation
Fusion of male and female gametes
- female gametophyte located deep within ovules
- male gametophyte (pollen)
Pollen attaches to the female gametophyte
- releasing 2 sperm cells
One sperm cell fertilizes the egg cell
- the other fertilizes the central cell
What is the endosperm?
nutritional tissue that surrounds the embryo
What are the key stages of plant embryo development?
First division very asymmetric
- Pin head becomes embryo
- Length becomes suspensor - like an umbilical cord - connects embryo to maternal material
Heart stage
Torpedo stage
Two lobes at top becomes embryonic leaves
Bottom (point of attachment to suspensor) becomes embryonic root - or radical
- First to emerge from seed as it germinates
Describe the process of seed maturation
- Cell division & differentiation
- Maternal control replaced by filial control
- Cell expansion
- Accumulation of storage compounds
- Preparation for desiccation
Describe dormant seeds
Seeds are fully matured but cannot germinate eben under optimal conditions
Describe quiescence seeds
Typical seeds lose dormancy after a while but remain quiescent
- resting state, very low metabolism
- suitable environmental conditions required to allow germination
Describe recalcitrant seeds
Not tolerant to drying out
- do not have long term viability
- typically tropical
- evolved to fall immediately and germinate
Describe vivipary seeds
Usually a mutation
- germination begins before separation from parent
Name a naturally viviparous seeding plant
Mangroves - rooting immediately after falling from tree
Describe phase 1 of germination
Seedling swells via osmosis (rapid water uptake)
Describe phase 2 of germination
Lag
- little change in mass
Metabolic activity increases
ATP production and protein synthesis begin
- seeds loaded with RNAs so transcription is not needed initially
Minor breakdown of cell walls
Describe phase 3 of germination
Radical emerges
- takes up water and nutrients
- breaks out of seed coat and endosperm
What is the inhibitor factor of seed germination?
ABA
What is the promoting factor of seed germination?
GA
What factors lead to inhibition of germination?
- High temp.
- Drought
What factors lead to promotion of germination?
- After-ripening
- Light
- Cold Stratification
What is after-ripening?
Happens in dry seeds
- typically involves the breakdown of inhibitory substances in the seed
- such as abscisic acid
Development of the embryo
What occurs if dormancy is ineffective?
Seeds germinate on plant
What is the effect on stomata of adding ABA?
Induces stomatal closure
What is the significance of the VP14 gene discovery?
VP14 is a gene involved in ABA synthesis regulation, which was discovered through a seed germination mutant
- suggested ABA is involved in seed dormancy and germination
- VP14 mutant had a phenotype of viviparous (VP) and ineffective stomatal closure, indicating ABA’s role in stomatal closure
- ABA causes stomatal closure, and adding it to plants can cause water loss
- VP14 mutant had a double expected water loss, indicating the significance of ABA in water conservation
How is ABA produced?
ABA produced from carotenoid in plastids
What is the effect of drought stress on NCED genes?
NCED genes are induced by drought stress during maturation
- which leads to increased ABA production and subsequent water conservation in plants.
What is foolish seedling disease?
a plant disease caused by gibberellin-producing fungi
- Infected plants elongate rapidly and become weak and unable to support themselves
What are gibberellins?
Plant hormones that play a crucial role in regulating plant growth and development
- promote cell elongation, stem growth, and seed germination in plants
What happens when CPS is stopped in the biosynthesis of gibberellin?
stops gibberellin synthesis everywhere in the plant
- but synthesis can be stopped or enhanced in specific locations within the plant by altering cytoplasmic steps that are location-specific
Can seeds germinate without gibberellin?
No
What is the effect of adding exogenous GA to GA knockdown seeds? and what occurs in non-GA response plants with addition of exogenous GA?
GA response
No GA response in 2nd case
Which plant hormone controls the establishment of primary dormancy?
ABA
Which of ABA or GA suppresses plant sensitivity to the other hormone?
Both
Are synthesis and degradation of ABA and GA coupled or independent?
Coupled
- NCED (ABA synthesis) activity coupled to GA2ox2 (GA degradation)
- GA3ox1 (GA synthesis) activity coupled to ABA hydroxylase (ABA degradation)
What are environmental controls of germination?
Cold and Light
How does cold function as an environmental control of germination?
Activates DOG1 gene
- reinforces dormancy during cold exposure
- Delays germination
How does light initiate germination?
- Phytochromes block PIF1 which previously blocked GA
- Light blocks the block on germination
What is the agricultural relevance of GA in barley production?
GA (gibberellin) is sometimes used to promote the mobilization of starch from the grain during germination
- necessary for the production of beer
What is the problem with using GA in barley production?
- Can result in pre-harvest sprouting (PHS)
- Which is a common problem in English wet springs and summers.
What is the role of GA in the breakdown of starch for sugars in barley production?
GA promotes the production of hydrolytic enzymes in the aleurone layer of the barley seed
- Maternal tissue surrounding the endosperm
- Enzymes break down starch into sugars
- diffuse into the endosperm and provide nourishment for the seedling as it grows
What is the cost of a high dormancy in crops?
higher storage costs (after-ripening)
Why do wild plants germinate with variability and why is this undesirable in crops?
In the wild, plants want to germinate with variability to ensure not all are affected if there’s a frost etc
- In crops, low dormancy and uniform germination desired, so harvest is easier
What does some level of dormancy in crops prevent?
Pre-harvest sprouting (PHS)
Which is more prone to PHS traditional red wheat or white wheat?
White wheat
Why is PHS a problem for bakers?
Changes wheat behaviour
- wheat graded based on this (HFN)
What regulates stomatal closure?
ABA and CO2
What is CO2s role in stomata development?
Regulates the number of stomata
What is albedo?
refers to the brightness of the land surface
- measure of the amount of solar radiation that is reflected back from the surface
What is the function of wax on the upper and lower side of a leaf?
Limits evaporation not under plant control
What is the spongy mesophyll in a leaf?
Contains lots of water vapor bubbles.
What would happen to the water in the spongy mesophyll without wax on the leaves?
The water would be lost.
Rank these in order of water use efficiency C4, C3 and CAM
CAM, C4 and C3
Why is photosynthesis inefficient in plants? Compare the movement of CO2 to water
- Concentration gradient for water about 50x CO2 gradient
- CO2 diffuses 1.6x slower through air
- Water only needs to go through stomatal pore, CO2 must cross PM, cytoplasm and chloroplast envelope as well
What is optimal stomatal theory?
Plants will try to adjust stomatal opening so photosynthetic CO2 gains maximised while water loss minimised
What are the two conflicting predictions about the effect of elevated atmospheric CO2 on plant physiology?
- CO2 promotes carbon fixation by Rubisco, resulting in increased sequestration (carbon fertilisation)
- Stomatal conductance decreases with increasing CO2, improving water use efficiency but limiting carbon sequestration
How does elevated atmospheric CO2 affect stomatal conductance in plants?
Decreases with increasing CO2
What is stomatal conductance?
rate at which water vapor diffuses through the stomata, or pores, on the surface of plant leaves
What is carbon fertilisation in relation to elevated atmospheric CO2?
Process by which elevated atmospheric CO2 promotes carbon fixation by Rubisco
- results in increased carbon sequestration
What did the Amazon gas ring experiment show?
- Investigate the effects of elevated atmospheric CO2
Response to elevated CO2 levels depends on the availability of other essential nutrients
- Particularly phosphorus
Trees exposed to elevated CO2 levels tended to close their stomata
- Prevent excessive water loss in conditions of elevated CO2.
What triggers the production of ABA in roots and what is its role?
Soil drought triggers the production of ABA in roots
Effect of stomatal opening on leaf temperature?
Open stomata lead to a cooler leaf due to evaporative cooling
What is the purpose of screening for stomatal mutants?
What kind of mutants are desired for screening?
- Study the genes involved in the process of stomatal closure
- Mutants that fail to close their stomata in response to drought or ABA are desired for screening
What is the Ost1 mutant and what is its effect on stomatal control?
Unable to control water loss
- evident from the faster water loss observed in the cut-off leaf of Ost1 mutant compared to the wildtype
What is the Abi1 mutant and what is its role in stomatal control?
Abi1 mutant is a phosphatase protein
- involved in the regulation of stomatal closure in response to ABA
ABA-insensitive in all responses
- including germination and control of stomata
- unable to close stomata, essential for regulating water loss in plants
What are the roles of kinase, phosphatase, and receptor in ABA signaling?
What are the roles of kinase, phosphatase, and receptor in ABA signaling?
What is the role PP2C and SnRK2 in ABA signaling?
SnRK2 (e.g., Ost1) and PP2C (e.g., Abi1) interact
ABA absent
PP2C inhibits the activity of SnRK2 kinase
ABA present
ABA binds to its receptor
- brings latch and gate of the receptor close together
- mimicking the activation loop of SnRK2
- releases kinase.
SnRK2 activates downstream targets
Describe germination of wild-type, ABA insensitive mutants and Pyrabactin-insensitive mutants on a ABA containing medium
- Wildtype plants fail to germinate on ABA containing medium
- ABA insensitive mutant germinates
- Pyrabactin-insensitive mutants are ABA insensitive - can germinate
What is the phenotype of an ozone insensitive mutant in relation to stomata?
mutant does not close its stomata in response to ozone exposure.
What is the ion channel involved in stomatal closure in response to ozone?
SLAC1 is the ion channel involved in stomatal closure in response to ozone.
Which signals does the SLAC1 mutant have deficient responses to? - stomatal closure
SLAC1 mutant is deficient in stomatal closure in response to
Ozone, CO2, ABA, light/dark transitions, humidity change and more
Don’t bother
- calcium ions, hydrogen peroxide, nitric acid.
In the absence of ABA, what occurs in relation to the stomata
In the absence of ABA, SnRK2 protein kinase activity is inhibited by PP2C phosphatases
- kinase and phosphatase are bound together
- keeping them inactive
Stimuli such as light keep proton pump OST2 active
- membrane hyperpolarization
- keeping stomata open
How does the presence of ABA induce stomatal closure?
ABA is detected by ABA receptors (PYR/RCAR)
- inhibits the activity of phosphatases PP2Cs
- release and activation of SnRK2 kinases
These phosphorylate SLAC 1
Activation of calcium channels by superoxide releases Ca2+ into the cytoplasm
- Ca2+ activates calcium dependant kinases which phosphorylate SLAC1 as well, and OST2
- allowing stomata to close
What is the role of carbonic anhydrases in CO2-induced stomatal closure?
Ost1 mutant is mostly unresponsive to CO2
- integrates inputs from both ABA and CO2
Slac1 mutant is insensitive to CO2 and ABA
What is the role of carbonic anhydrases in CO2-induced stomatal closure?
enzymes that convert CO2 into carbonic acid, which dissociates into bicarbonate
- Only bicarbonate can modulate SLAC2 activity
- which is required for CO2-induced stomatal closure.
What is the function of the guard cell-specific kinase HT1 in CO2 responses?
HT1 is a negative regulator of CO2 responses in guard cells
- Ht1 mutants are CO2-hypersensitive but respond normally to ABA.
What is the effect of high CO2 on stomatal density?
Plants developing in high CO2 have less stomata.
How is stomatal density on the leaf surface regulated?
Tightly regulated by spatial control of asymmetric cell divisions
What can museum herbarium specimens from pre-industrial age tell us about stomatal density?
Museum herbarium specimens from pre-industrial age have more stomata.
High CO2 -> less stomata
Stomatal density regulation -> spatial control of asymmetric cell divisions
Pre-industrial age herbarium specimens -> more stomata.
What is the Green Revolution?
period of rapid technological innovation in agriculture that occurred between the 1940s and 1960s
- involved the development and widespread adoption of new high-yielding crop varieties, increased use of chemical fertilizers and pesticides, and irrigation
What is the problem with conventional crop varieties?
Conventional crop varieties have a low harvest index (around 30% of biomass is useful)
- which results in large amounts of waste biomass.
- They are also prone to falling over (lodging)
What is the effect of nitrogen on crop growth?
Increases grain yield
- Also promotes leaf and stem growth (not useful for increasing yield as it diverts resources away from the harvestable organs)
Why are lodged crops (fallen over) more prone disease?
- Produces humid environment
- Perfect for pathogen to grow and reproduce
What was the main improvement introduced by the green revolution?
introduction of semi-dwarf varieties that increased yield potential
- improved resistance to lodging, allowing for planting at higher densities
How did Norman Borlaug
Selecting for shorter plants
- Selecting to plants with affected gibberellins (unwittingly)
What was the feature of gibberellins wanted in the green revolution?
- Seed germination
- Promoting flowering
- Growth
- Sex determination in some species
- Promoting fruit growth
Growth without the other characteristics
What makes a gibberellin active?
OH group
Role of GA oxidases in gibberellin synthesis?
To get active GAs, GA oxidases are required.
- Loss of function of CPS or KS results in severely dwarfed plants
Why early enzymes are important for gibberellin synthesis?
Early enzymes are important as they catalyze the early steps in the synthesis pathway
- a single copy of the genes responsible for early enzymes means almost no gibberellins are produced in the plant.
How GA20ox gene is linked to the Green Revolution?
found to be mutated in green revolution rice, which contributed to the semi-dwarfism trait in the rice.
Importance of GA deactivating enzymes?
- Act as an off switch for the growth regulator (GA)
- Needs to be tightly controlled to avoid unwanted dwarfism
Why is it important to increase GA catabolism in certain areas of rice plants?
Increased catabolism everywhere decreases seed production
Increased GA catabolism only in internodes produces high-yielding dwarf rice plants
What occurs in plants that are have loss of function mutation of CPS or KS?
- Enzymes in early steps of GA production
- Only a single copy of the genes
- Almost no gibberellins in the plant
How does GA signalling function?
Inactivates DELLA inhibitor enzymes
Allowing increased growth of the plant
Describe the slender rice mutant
- Mutant characterized by the loss of the DELLA repressor
- Protein that normally inhibits GA signaling.
- Constitutive GA signaling
- Decreased gibberellin production
- Resulting in reduced plant height and a thinner stem
Why is the GA insensitive mutant insensitive?
Enhanced DELLA repressor - no response
What is the role of the receptor domain of GID1 in the GA signaling pathway?
The receptor domain of GID1 binds to DELLA, and in the absence of GA, DELLA represses growth
- When GA binds to GID1, the receptor changes conformation
- allowing for the binding of the DELLA protein to form a complex that is recognized by the SLEEPY/GID2 component of the SCF ubiquitin ligase complex
- complex targets DELLA for proteolysis, leading to growth-promoting effects of GA.
DELLA protein
A type of plant transcription factor that inhibits transcription of growth genes in the absence of gibberellin (GA) and is targeted for destruction in the presence of GA
- allowing for growth.
Etiolation
A dark-growth response in plants induced by GA
- promotes shoot growth and unopened leaves.
What is the role of GA in the dark growth response of plants? Describe
GA is required for the dark-growth response in plants, which induces shoot growth and unopened leaves during etiolation
- GA-deficient pea mutants do not show dark growth, but it can be rescued by exogenous GA
What occurs when PIF3/4 are bound to DELLA?
inhibition of growth-promoting gene transcription
- So GAs allow dark growth response
What is an example of macro-algae?
Seaweed
What are some examples of secondary metabolites?
Compounds for
- Defense
- Taste
- Colour
- Scent
C4 anatomical specialisation: What is the reason for separation of Rubisco?
- Enzyme responsible for carbon fixation
- Confined to bundle sheath cells.
- Minimizes photorespiration
- Occurs when Rubisco reacts with oxygen instead of carbon dioxide
- CO2 is concentrated in the vicinity of the enzyme
- Reducing photorespiration
C4 anatomical specialisation: Why do C4 plants have thick bundle sheath cell walls
Prevents CO2 diffusion back into the mesophyll cells
C4 anatomical specialisation: Why is there no air spaces between mesophyll and bundle sheath cells
- Minimizes the loss of CO2 to the atmosphere
- Helps to maintain high CO2 concentrations around Rubisco
Why are low copy numbers desirable in transgenes?
- Reduce the likelihood of gene silencing or other adverse effects caused by the overexpression of transgenes
- Reduce the potential for genetic instability
- Unpredictable effects on the host plant’s phenotype
What is PPFO?
- Photosynthetic photon flux density at the leaf surface
- How much sun each cell gets
- How much useful light is captured
What are Brassinosteroids?
- Class of plant hormones
- Involved in a variety of processes
- Including cell elongation, pollen tube growth, seed germination, vascular and root tissue differentiation, and stress tolerance
What happens to BR-deficient plant mutants?
- Severely dwarfed
- can be rescued with exogenous
- although Bri1 mutants are BR insensitive
What is the function of BRI1?
Encodes main BR receptor
What is the effect of high BR levels on root growth in wildtype plants?
Inhibit root growth
What is the phenotype of the Arabidopsis bri1 (bril-5) mutant?
- Very small and insensitive to exogenous Brassinosteroids
- Exhibiting a phenotype of severely reduced growth
What is the BAK1 Br mutant?
- Plant mutant that partially reverses the dwarf phenotype of the bril-5 mutant when overexpressed
How was BAK1 identified?
Activation screen
- search for plants that partially reverse the dwarf bril-5 phenotype when overexpressed
How was BKI1 identified?
Biochemical screen
- Searching for proteins that physically interact with BRI1
What is the function of BAK1 in BRI1 signaling?
- Functions as a coreceptor with BRI1
- Forming a receptor complex that initiates the BRI1 signaling pathway
Explain the BRI1, BAK1 and BRI1 interaction?
BRI1 and BAK1 interact through a double lock mechanism that ensures no signaling occurs in the absence of the ligand
- Phosphorylation of BKI1 causes BKI1 to dissociate
- Coreceptor BAK1 can then bind to BRI1
- BRI1 signalling activated
What is the function of BKI1 in BRI1 signaling?
Inhibits interaction between BRI1 and BAK1
- preventing signalling
What is the effect of Brassinosteroids (BR) on leaf angle?
Promotes wider leaf angles
How do biosynthetic mutants of BR affect leaf angle?
more upright leaves, with narrower leaf angles.
How do the dwarf BR mutants perform in high density compared to wildtype?
BR Dwarf mutants outperform wildtype
- possibly due to reduced shading and competition for light.
What did grafting experiments with wild-type pea roots and BR-deficient shoots show and what is a potential use of this agriculturally?
- Wild-type roots cannot rescue BR-deficient shoots
- indicating that localized BR synthesis is required for stem elongation
- opportunity to manipulate BR in different parts of the plant, e.g. stem vs seed
What is the role of ligule and auricle in regulation of maize leaf angle?
Removal of ligule and auricles results in a very upright leaf angle.
Modulation of the size of auricles using brassinosteroid (BR) hormone signaling
- can affect leaf angle.
What is the effect of thickness of the midvein on maize leaf angle?
Mutants lacking a midrib have floppy leaves with wide leaf angles.
What is the potential for crossing back to teosinte in improving maize leaf angle?
Maize plants with teosinte UPA2 have a normal plant height and floral branch number
- but with only proportionate reduction in auricle size.
What are UPA1 and UPA2 in maize?
- UPA1 is an enzyme catalyzing the last step in brassinosteroid synthesis
- UPA2 is involved in UPA1 regulation.
What is the effect of overexpression of Cyclins on leaf angle?
- leads to increased cell cycling of cells on the inside of the plant
- leading to worse leaf angle
What is the effect of BRs on growth in the outside edge (m2 region) of leaves?
EncourageS growth in the outside edge of leaves and block the BIN2 pathway
- Leads to cyclin expression in the inside edge of leaves
- promoting cell division and elongation in the sclerenchyma cells in the m2 region
- inhibition of sclerenchyma cell division in the m1 region
Which compounds act together to promote cell expansion?
BRs act together with gibberellic acid to promote cell expansion
What mutant produces erect leaves and why is this useful?
BR mutants also have erect leaves
- which can be advantageous for light capture
What are strigalactones (SL)?
- control diverse signals
- including shoot branching
- largely conserved among land plants.
What is the hormonal role of SLs?
Branching inhibitors
also important for nutrient availability response
- Inhibit adventurous rooting
- promote secondary growth
- contribute to leaf senescence.
What is the activity of SLs in arbuscular mycorrhizal fungi?
important for branching in arbuscular mycorrhizal fungi, which are associated with 80% of land plants.
- However, plants that do not form this association also produce SLs.
Are SLs mobile?
Yes, SLs are highly mobile and can move from root to shoot and vice versa
What is the effect of nutrient availability on shoot branching and SL production in plants?
- Plants produce fewer branches in poor nutrient conditions, such as low phosphorus (P) and low nitrogen (N).
- SLs suppress shoot branching in low P
- mechanism designed to conserve limited resources and prioritize growth in the main shoot
Describe the mechanism for low nitrogen conditions evolved by leguminous plants rather than the use of SLs
symbiosis with nitrogen-fixing bacteria instead of producing SLs in response to low N.
- but some non-AM host plants do not produce SLs!
What is the role of the D14 protein in SL signaling?
- hydrolyses SLs
- allowing them to be perceived and triggering the downstream signaling pathway.
What is the function of the SPL transcription factors in SL signaling?
- released from inhibition by D53 degradation
- play a role in regulating shoot branching by targeting downstream genes such as OsTB1/BRC1
What is the role of D53 in SL signaling?
D53 is a negative regulator of SL signaling (inhibits)
- its degradation frees up SPL transcription factors
- regulate downstream gene expression.
What are the key steps in SL signalling?
Strigolactones detected by D14 protein
- Leading to hydrolysis of the protein and release of D53
D53 usually acts as an inhibitor
- Targeted for degradation
Frees up SPL transcription factors
- Activates downstream targets of strigolactone signaling
- One of these is BRC1/TB1
- Regulator of shoot branching
How do parasitic weeds exploit endogenous strigolactones?
- Strigolactones promote the germination of Striga parasitic weed
- preys on plants already under stress
- attaches to the roots of host plants and takes
nutrients and water from them - can cause significant crop losses
How can crop losses to Striga be reduced?
- Before planting, germination stimulants can be applied to promote suicidal germination of Striga without a host
- Fertilizers can also be applied to reduce strigolactone production by crop plants
- can be expensive.
Crops with reduced or impaired strigolactone exudation, such as the LGS1 mutant - Can incur resistance to Striga.
Another approach is to rely on different form of strigolactone not utilized by Striga
What is desmodium?
Nitrogen-fixing legume that enriches soil and produces other allelopathic chemicals that interfere with Striga.
Can SL biosynthesis enzymes be altered to prevent Striga growth?
Yes, altering a single strigolactone biosynthesis enzyme can mimic the effect of SLs that are not usable by Striga
- can prevent Striga growth without affecting branching.
What are the potential application of exogenous SL and specific SL mutant crop varieties?
- Ideal Branching architecture
- Lodging resistance
- Striga control
- Drought resistance
- Enhanced mycorrhizal networks
- Optimized root architecture
What is the potential of the overexpression of Pxy and CLE41 genes?
- led to more cells and increased biomass, but also resulted in some abnormalities in cell organization
- poplar trees generating about twice as much dry weight as the control
- could be used to increase biomass for biofuel production
What is the trend of GM crop cultivation in Europe?
There is very little going on in Europe in terms of GM crop cultivation
- only one GM crop, a Bt-insect-resistant maize, has been approved for commercial cultivation
- 0.1% of the global acreage of GM crops is cultivated in the EU
What is the proportion of imported animal feed that is GM in the EU?
More than 70% of EU animal protein feed requirements are imported as GM crop products, despite the reluctance to grow GM crops in Europe.
What unintended consequence of Bt maize was observed?
Corn borer numbers plummeted even in non-GM maize due to area-wide pest suppression
What is the downside of the unintended pest suppression benefits of Bt maize?
Corn borers are all killed by GM maize, potentially reducing genetic diversity and causing ecological imbalances.
What are wide hybridisations in conventional breeding?
Wide hybridisations involve hand pollination and culturing embryos in labs to create crosses that defy natural species barriers
- This can allow the transfer of one or two genes of interest along with several thousand other genes.
What is an example of using wild relatives in conventional breeding?
Potato has been crossed with wild relatives, including plants related to deadly nightshade, to create new varieties.
- These wild relatives can also contain high levels of toxic alkaloids
- can be dangerous.
How are mutations induced in conventional breeding?
Mutations can be induced through chemical or radiation treatment.
- Point mutations (usually caused by EMS) and chromosome rearrangements (usually caused by radiation) are common.
What is natural variation in conventional breeding?
Includes single nucleotide changes
- occurs at a background rate of 7 mutations per billion base pairs of DNA.
- Useful traits can be selected for while deleterious mutations are bred out.
What is horizontal gene transfer in conventional breeding?
can occur through pararetroviral double-stranded DNA viruses or transposable elements.
- This can result in the insertion of different pieces of genes, creating novel combinations.
What are potential health risks GM crops? Give an example
- Transfer of toxins and allergens from one crop to another
- Experimental study involving the transfer of Brazil nut proteins to maize showed an allergen
- but this was not intended for field use
What are potential issues posed by GM on antibiotic resistance and why is it not considered that problematic currently?
Transfer of selectable markers to bacteria can result in antibiotic resistance
- Although kanamycin resistance is toxic and has limited use in medicine
- So resistance is not much of a problem
A review of 24 studies found ___ statistically significant differences between GM and non-GM crops in terms of health impacts.
NO
Glyphosate risk is currently debated - how does this relate to GM?
- use of glyphosate has been controversial
- some studies suggesting potential risks to human health and the environment.
- important to note that glyphosate use is not synonymous with GM crop use
Use the monarch butterfly as an example of the environmental risks of GM
- high Bt toxin expression in the pollen of one variety of GM crop
- causing high mortality in monarch butterfly larvae
- studies showed that drought and cold were more likely the responsible party for the decline in monarch butterflies.
- Planting milkweed is the best way to save monarch butterflies, as it is their only food source.
What are some methods of containment of harm in GM crops?
- Removal or alteration of antibiotic marker genes
- Use of chloroplast genes in GM
- Separation of transgenic and non-transgenic crops
- Field trials
- Following crops after release
How can use of chloroplast genes be beneficial to containment of harm in GM?
- chloroplasts contain their own DNA which is separate from the nuclear DNA.
- genes can be inserted into the chloroplast DNA without affecting the nuclear genome of the plant
- can be used to produce GM crops that are less likely to crossbreed with wild relatives
- chloroplast DNA is usually not transmitted through pollen
Can containment of harm in GM crops be guaranteed? Give example
No, maize taco shells contaminated with Bt gene that should only have been used in animal feed
- resulted in 300 product recalls
- company tried to get the GM corn approved for human consumption retrospectively
another instance
Why is floral-dip method viable even though it produces very low percentage of transgenic plants?
(0.1-1%) of seeds produced will be transgenic
- since large numbers of seeds can be produced overall transformation efficiency is acceptable
What provides drought tolerance in seeds?
Tolerance provided by
- Trialose and other compounds that allow survival under drought conditions
What are things considered in bio safety assessments?
- The function of the gene in the donor organism
- The effect of the introduced gene in the modified plant
- Potential non-target effects of genes within the environment
- Changes in the crop plant’s ability to persist in the agricultural habitat or its invasiveness in natural habitats
- Potential transfer of the introduced gene to other plants or organisms
How do USA and EU differ in policy regarding safety assessment of GM crops?
- USA follows the principle of substantial equivalence
- Compared to non-GM product that is already considered safe
- evaluated for any significant differences
While EU follows the precautionary principle where even potential risks must be anticipated and prevented.
What is the regulation process for GM crops in the EU?
- most stringent system in the world for assessing the safety of GM crops
- Applicants must submit risk assessments
- risk management options plans for post-market environmental monitoring (PMEM) to look for unforeseen impacts.
- This information is scrutinised by experts in the 28 EU member states, Commission’s expert advisory committee on GMOs and also includes public consultations
What are oocysts? (Toxoplasma)
infective stage of T. gondii
- that are shed in the feces of infected cats
- If ingested by intermediate hosts
- transform into tachyzoites
