gatehouse Flashcards
describe 1st 2nd and 3rd generation transgenic organisms
1st: traits beneficial to farmers
2nd: beneficial to consumers
3rd: plants as biofactories
discuss the rationale for using transgenesis for food production
- food productivity needs to increase by 70% by 2050 (an extra 2 billion people)
- models suggest that the population will not plateau in 2050 but will continue increasing
discuss data regarding the quantity of transgenic crops grown
190million hectacres per year
- 100 from developing countries,
- 165 is either herbicide tolerant or stacked traits including herbicide tolerant
- 94 soybean, 60 miaze, 20 cotton`
USA: 75 million hectares/year
brazil: 50/year
argentina 23/year
not much in europe
describe weeds (Definiton, control methods)
- palnt growin in the wrong place at the wrong time
- limit agricultural productivity by competing for light and nutrients
control involves;
- hand-weeding
- tilage (soil digging)
- herbicides:
describe the agricultural pie chart of losses
- abiotic stress: 70% reduction in crop yield
- insects: 15% global produce
- weeds:13% global produce ($75BN)
describe herbicides
definition, limitations, most commonly used
toxic to plants
- contaminate gorundwater
- non-target effects
- broad spectrum (non-selective) can only be applied before planting and narrow spectrum (selective) can be applied either before or after planting
5 catagories exist;
- photosystem inhibitors
- plant hormone mimicers (synthetic auxins)
- ALS inhibitors (branched AA protein enzyme)
- ACCase inhibitors (lipid synthesis enzyme inhibitors)
- EPSPS inhibitors (AA synthesis enzyme inhibitors)
glyphosate (EPSPS) is most commonly used; known as roundup
why is herbicide tolerance needed (advantages)?
how can tolerance to glyphosate be achieved
whats the first herbicide tolerance crop
disadvantages
because its easier to develop non-selective herbicides than selective; can only be used if crops are resistant.
there with herbicide tolerance have higher yield and mean farmers can be more flexible with control (less sprays and even sprays when the crop has emerged)
- overexpression of inhibited enzyme
- expression of mutated enzyme so inhibitor cant bind (agrobacterium ESPSP)
- introduce detoxification genes; bar gene from Streptomyces
- upregulation of detoxification compounds (GSTs; glutathione-s-transferase
soybean
- not really, glyphosate cant move that low in soil due to being absorbed by soil; it may contaminate surface waters
- superweeds via transfer to wild relatives; little evidence for this
describe insect resistance using Bt toxin
- Bacillus thuringiensis was observed to have spores which contain crystaline deposits of Cry proteins and Cyt proteins (Bt toxins) which are toxic to insects
- different cry proteins coded by different plasmid are effective against different species (very specific)
- was commercialised as insect control in france in 1938 (sporine) and the US in 1961
- Bt can be sprayed onto crops however the toxin isint UV-B stable so farmers have to keep applying it
- crops can be made to express a re-engineered form of Bt (AT regions reduced, only the active toxin is expressed, under control of CAMV35S with a plant termination sequence)
advantages:
- economic: more yield (chinese cotton yield increased 25%)
- environmental: reduced pesticide use (less strain on natural resources and less water contamination). higher yield means less land has to be used for agriculture so biodiversity benefits
- social: multiple sprays not needed and improved food quality for customers (no mycotoxin contamination)
disadvantages:
resistance occurs quicker than with pesticide application because there are less steps involved);
describe cry protein structure and mode of action
describe insect resistance mode of action to transgenic crops
-3 domains; #1 is used for insertion into the membrane and proe formation. #2 and #3 are for receptor recognition and binding
- insect eats leaf containing spore
- in the insect gut the protoxin is solubilised, reduced and cleaved to form the active toxin
- domain 3 binds to carbohydrate receptor ALP ir APN of gut epithelial cells
- domain 2 binds to cadherin receptor protein
- more Bt toxins bind to the same cadherin
- domain 1 insertion and pore formation
- cell lysis due to osmotic balance
bt toxin isint toxic if it cant be recognised and binded
- resistance in insects;
- loss of receptor binding
- Cry toxin not activated
- gut immune response
which orders of insects are Cry proteins effective against
lepidoptera: butterflies and moths CRY1
diptera; flies/mosquitoes CRY2
coleptera; bettles /weevils CRY3
hymenoptera; bees/wasps
what can be done to overcome insect resistance to Bt expressing plants
- stack genes; multiple Bt toxins expressing
- add a binding chain to Bt toxin so it can bind to mutated receptors (used to comabt army worm)
- use alternative approaches to Bt expression, such as RNAi
describe the RNAi approach
name 3 examples
- insect gene knockout
- natural eukaryotic mechanism of feding of viruses using RNase cuts dsRNA into siRNA
- potnetial to be very specific; toxicity studies must be done to ensure species like bees arent effected
examples
- RNAi of the chytochrome P450 enzyme in cotton bollworm which mean it could detoxify cottons toxics product (gossypol) and attack cotton
- gatehouse: knockout of neuron channels which rent highly conserved among all species (calcium and potassium); used to control Flower beetle (Tribolium)
- Monsanto SmartStax; casette expressed conferring Ht, Bt and dsRNA to interfear with the snf7 gene in western corn rootworm (protein turnover interference due to altered ubiquitination)
limitations
- insect resistance; monsanto demonstrated this under lab conditions
- cant be used for all insects; lepidoptera have RNAi nucleases so suppress RNAi activity
- sometimes the dsRNA delivery doesnt lead to the dsRNA remaining stable in gut; can be improved be combining dsRNA with a chimeric protein to form a ribonucleoprotein particle (RNP)
- enginnering plants needs to lead to stable expression; perhaps engineering chloroplasts could work however this is difficult
state the names of other alternatives approaches of controlling insects other than Bt and RNAi
- Tiny insecticidal proteins (TIPs)
- CRISPR-based approaches
- fusion based insecticidal proteins
describe technology used to combat loss of productivity due to abiotic stress
- recently emerged (commercialised in 2015)
- looking at plant sin extreme environments (Mangrove sin salinity environments)
- stress response genes are either functional proteins (detoxification etc) or regulatory (transcription factors)
- stress receptors trigger donwstream signalling and altered transcription to active stress-response mechanisms to repair damaged structures
stress tolerance molecules can be catagorised
1) detoxification enzymes to stop those molecules which cause cellular damage. superoxide dismutase (SOD) was identified in mangroves
2) chaperoning: protein folding enzymes and preventing of non-functional aggregating. HSPs are key because when proteins are denatured by stress such as heat then proteins aggregate
3) Late embryogenesis abunant (LEA) proteins; produced due to dehydration and act to stabilise water status
4) osmoprotectants; compatible solutes (osmolytes) which prevent water stress by maintaining cell turgor. AAs such as proline and sugars
drought
-expression of SOD in rice
-
aluminium tolerance (light metal)
describe methods of achieving drought tolerant crops
- 70% water is used for agriculture
- irrigation causes salinity
1) Isopentyl transferase (IPT), a cytokinin biosynthesis enzyme which prevents sensecence, was placed under control of a constitutive promotor (PSARK) which meant high expression in all tissues: minimal yield loss during drought anf photosynthetic capacity was maintained during drought and better recovery occurred post-drought. Peanut transformation showed simialr results and also improved root architecture
2) upregulation of H+ATPase caused drought tolerance because of increase solute accumulation, root biomass
3) overexpressing the enzyme involved in ABA precursor (ZEP) synthesis increased drought and salinity resistance; altered stomatal closure, increased root/leaf development, increased survival
4) overexpression of the ethylene responsive family (ERF) of TFs from sugarcane in tobacco caused drought/salt tolerance in form of greater plant size
5) wheat LEA dehydrin (DHN-5) overexpression in arabidopsis allowed for better growth under NaCL and mannitol stress and better recovery
all experiments are lab based/glass house based, not invivo
