Plant molecular genetics Flashcards
plants as experimental systems plant genes and gene expression Arabidopsis how plants perceive their environment
what is development
the specific series of changes by which cells form tissues, organs and organisms
what is meant by developmental plasticity
the ability to alter firm in the response to local environmental conditions
e.g. different phenotypes for the same genotype if the individuals are exposed to different environmental conditions
what are the 3 overlapping processes involved in development of multicellular organisms
growth, morphogenesis and cell differentiation
what is growth
the irreversible increase in size
what is morphogenesis
the process that gives a tissue, organ or organism its shape and determines the position of cell types
what is cell differentiation
the process by which cells with the same genes become different from one another
what is Arabidopsis
a tiny weed in the mustard family that has no agricultural value but is a favoured model organism of plant geneticists and molecular biologists for many reasons
why is Arabidopsis favoured as a model organism
- thousands of plants can be cultivated in a small space
- it has a short generation time
- one plant can produce hundreds of seeds
- has one of the smallest genomes among plants
- the plant has only 5 pairs of chromosomes making gene location easier
- its cells can be easily transformed with transgenes
- self fertile and can also be crossed
- easy to produce mutants
- little non-coding DNA
- can be easily transformed using agrobacterium
what was the first plant to have its entire genome sequenced
Arabidopsis
what are transgenes
genes from another organism that are stably introduced into the genome of another
what do knock out experiments provide
information about the normal function of the removed gene - when it is absent there may be a change and from the change scientists can infer what the function of the gene is
cell division enhances the potential for ………. by increasing the number of cells
growth
what is plant growth brought about by
cell growth
the new cell walls that bisect plant cells during cytokinesis develop from what
the cell plate
when is the plane of cell division determined
late interphase - it corresponds to the shortest path that will halve the volume of the parent cell
what is the band called that disappears before metaphase but predicts the plane of division
preprophase band - microtubules concentrated in a ring in the cytoplasm
transverse divisions precede ………….
leaf elongation
longitudinal divisions precede ……………
leaf broadening
what is the symmetry of cell division
the distribution of cytoplasm between daughter cells
symmetrical - cytoplasm is shared equally during mitosis
asymmetrical - unequal sharing of the cytoplasm during mitosis
what does the formation of guard cells typically involve
asymmetrical cell division
change in the plane of cell division
describe the steps in formation of guard cells
- a cell divides asymmetrically forming a large cell and a smaller cell
- the small cell becomes the guard cell “mother cell”
- the guard cells form when the small mother cell divides in a plane perpendicular to the first cell division
what is a guard cell
the 2 cells that flank the stomatal pore and regulate the opening and closing of the pore
asymmetrical/symmetrical cell divisions plat a role in establishment of polarity
asymmetrical
what is polarity
the condition of having structural or chemical differences at opposite ends of an organism
plants typically have an ………., with a root end and a shoot end
axis
what happens in a stem cutting
adventitious roots emerge from the end that was nearest the root
what happens in a root cutting
adventitious shoots arise form the end that was nearest the shoot
the first division of a plant zygote is often symmetrical/asymmetrical
asymmetrical - initiating polarization of the plant body into shoot and root
in the gnom mutant of Arabidopsis what is defective
the establishment of polarity - the first division of the zygote is symmetrical and the resulting ball shaped plant has neither roots or leaves - they also can’t transport auxin in a polar manner
recognition of self pollen is based on genes called what
s-genes
If a pollen grain has an allele of an s-gene that matches the allele of the stigma on which it lands what happens
the pollen tube either fails to germinate or fails to grow through the style of the ovary
what are the 2 types of self incompatibility
gametophytic and sporophytic
describe gametophytic self incompatibility
the s-allele in the pollen genome governs the blocking of fertilization
what happens to the pollen if it is recognised as self
enzymatic destruction of the RNA in the pollen tube (enzymes are released from the style)
describe sporophytic self incompatibility
fertilization is blocked by s-allele gene products in tissues of the parental sporophyte
(it involves a signal transduction pathway in epidermal cells of the stigma that prevents germination of the pollen grain)
how can self incompatibility be avoided
- by removing the anthers from the parent plant that provide the seeds
- use male sterile strains of the crop plant
any cell that can divide asexually an generate a clone of the original organism is said to be what
totipotent
In which area of the plant are totipotent cells mainly found
the meristematic tissues
what is vegetative reproduction that is facilitated or induced by humans referred to as
vegetative propagation
what is a callus
results from shoot cuttings and is a mass of dividing undifferentiated cells growing at the site of a wound or in culture
what develops from a callus
adventitious roots
what happens in grafting
a severed shoot from one plant is permanently joined to the truncated stem of another
- a callus forms between the adjoining cut ends of the scion and stock and cell differentiation then completes the unification of grafted individuals
in grafting what is the plant called that provides the root
the stock
in grafting what is the scion
the twig grafted onto the stock
whole plants can be obtained by culturing small pieces of tissue from the parent plant on an artificial medium containing nutrients and hormones. where does the tissue to be cultured come from
anywhere on the plant but growth may vary depending on the plant part, species and the artificial medium
what happens when a plant is cultured in vitro
- cultured cells divide and form a callus of undifferentiated totipotent cells
- a callus can then sprout roots and shoots with fully differentiated cells
- the cloned plantlets can then be transferred to soil and resume their growth
what are the 3 ways that flowering plants avoid self-fertilization
- self incompatibility
- having male and female flowers on separate plants
- having stamens and styles of different heights on separate plants
what is one of the major advantages of using plants as experimental systems compared to animals
less ethical issues involved
what is somatic embryogenesis
regeneration of whole plants from single cells in culture
what is a somatic cell
non reproductive
what are the steps in somatic embryogenesis
- section of root cut off and cultured in nutrient medium
- single cells begin to divide
- embryonic plant develops from a cultured single cell
- plantlet is cultured on agar medium
- the plantlet is planted in soil and develops into a mature plant
why do we want to introduce new genes into plants
- tools for experimentation
- overcome genetic limitations of a crop
- introduce novel genes
- disease resistance
- stress tolerance (drought/cold)
- altered composition of harvested product
what is genetic transformation
the direct introduction of new genetic information
what are genetically modified plants called
transgenic plants
what is agrobacterium tumefaciens
a soil bacterium (live in water associated with soil particles) that naturally genetically modifies plants causing
- crown galls disease which results in galls (tumours of proliferating cells) to be grown on plants
are agrobacterium tumefaciens mobile
yes - they have flagella and they swim towards wounded sites on plants and binds to the cell wall
what is a Ti plasmid
a tumour inducing plasmid - it has genes on it that infect plants
what is T DNA
the region of the Ti plasmid which is transferred to the plant cell nucleus and integrates into chromosomal DNA
the T DNA region is copied and coated with proteins before transfer to the plant cell
why id T DNA coated in proteins
they protect the DNA on its journey from the bacterial cell into the plant cell
does agrobacterium kill cells
no
what do the genes on T-DNA encode
- enzymes for auxin and cytokinin biosynthesis. which cause abnormal cell division and hence tumour formation
- enzymes for opine biosynthesis which are small molecules used by Agrobacterium for growth (the bacteria makes the plant produce opines)
what is a selectable marker
- they are marker genes
- they are present in the vector along with the target gene
- selectable marker gene confers resistance to toxicity in the transformed cells
- the are used to generate antibiotic resistant plants so that
what is meant by plants being sedentary
they have no means of locomotion
need to optimise growth to maximise light capture for …………..
photosynthesis
list some environmental abuses to plants
frost
drought
pathogenesis
salinity
what is meant by a protein being highly conserved among plants
similar in different groups of plant species
e.g. photosynthetic pigments have the same function in trees as in algae
give an example of a protein that is unique to a particular species
ricin - produced by castor beans - lethal to humans - stops translation
if all cells in a plant have the same genome why do they differ in protein composition
differential gene expression
what is differential gene expression
when only a fraction of the genetic information present in a particular cell is expressed at any one time
what is constitutive gene expression
when a gene is expressed in all cells at all times
what is a facultative gene
genes that are transcribed only when needed
what is a constitutive gene
A gene that is transcribed at a relatively constant level regardless of the cell environmental conditions
what are the different ways that gene expression can be studied
- Look at proteins – 2D gel electrophoresis
- Detect specific mRNAs – microarray
- Visualise transcription using reporter genes
what are reporter genes
- A gene whose products are easily detected or measured.
- it is linked to a gene of interest and used to signal that the gene has been successfully inserted taken up
e.g. bacterial beta-glucuronidase
colourless –> blue
only expressed in leaf tissue
Transcription factors bind to the ……………… sequence of the gene either activating or inhibiting transcription
promotor
what is CAB
the gene encoding the major chlorophyll a/b binding protein
it is only expressed in chloroplast containing cells
what stimulates CAB expression
light - when plants with CAB are grown in the light it is expressed but it is not expressed in plants grown in the dark
what are the 3 types of induced genes
- light induced - often allow for growth when activated
- stress induced - e.g. drought, pathogenesis, cold
- touch induced - if activated can prevent growth
what is the forward genetic approach
by characterising the mutant gene function the function of the wild type gene can be inferred
what are M1 plants of seed mutagenesis
the plants that have been treated with a mutagen
are M1 generation plants homozygous or heterozygous for mutant genes
heterozygous
what are the steps in seed mutagenesis
- seeds treated with mutagen
- M1 generation produced from seeds are heterozygous for mutations
- M1 generation self fertilize
- seed collection from M1 plants
- grow the M2 generation from seeds
- 1/4 M2 generation are homozygous for mutations (crossing of heterozygotes)
- screen for mutants
explain the steps of transforming Arabidopsis with agrobacterium
- plasmid removed from the bacterium and T DNA is cut by a restriction enzyme
- foreign DNA inserted into the cut T DNA making a recombinant plasmid
- the plasmid is reinserted into the bacterium
- bacterium is used to inset the T DNA carrying the foreign gen into the chromosome of a plant cell
- plant cells are grown in culture and contain the foreign gene
what is a trichome
an epidermal cell that is a highly specialized, hair like outgrowth on a plant shoot
what is the glabra 1 mutant
a bald mutant - no trichomes
it was used to isolate the wild type GL1 gene which encodes a transcription factor that switches on the genes required to make a trichome
cell commitment
moving towards a particular fate but it can be reversed or transformed to another fate if necessary
how are flowers made
particular genes (homeotic) determine organ position and identity mutations in these genes can cause the flower to be abnormal
describe plants grown in darkness
long hypocotyl, unexpanded cotyledons, no chlorophyll
describe plants grown in light
short hypocotyl, expanded cotyledons, chlorophyll present
what proportion of genes in the genome of seedlings are regulated by light
1/3
Expression of promoter-reporter gene fusions in transgenic plants provides information on what
regulation of transcription
why is the beta-glucuronidase reporter unsuitable for visualising short term changes in transcription
because the protein is too stable
what is a good reporter for monitoring short term changes in transcription
an unstable reporter
e.g. firefly luciferase
The CAB promoter causes luciferase expression to rise and fall over the 24-hour diurnal period. Luciferase activity is maximal/minimal during the day and maximal/minimal during the night.
day - maximal
night - minimal
when CAB is activated by light then luciferase is expressed. hence the more light the greater the luciferase activity
what is the circadian rhythm
the biological clock
If you move a plant to a different light dark cycle, the change in the input pathway changes what
the output pathway
give a list of characteristics of light that plants can detect
- Light presence/absence
- Light quantity
- Light spectral quality
- Light direction
- Light duration
name the regulatory photoreceptors and the colour of light they detect
phytochromes - red and far red light
cryptochromes - UV-A and blue light
Phototropins - UV-A and blue light
describe the structure of photoreceptors
they are comprised of an apoprotein and a chromophore (chlorophyll is a photoreceptor)
The phytochrome apoprotein binds a linear …………… chromophore
tetrapyrrole
what are the 2 interconvertible forms of phytochrome
Pr
Pfr
Pr is present in dark-grown plants and illumination with red light produces what
Pfr
what does the Pfr form of the phytochrome do
initiates biological responses
which photoreceptor regulates CAB gene transcription
phytochrome
what is vegetation shade detected by
phytochrome - the shade avoidance response is controlled by phytochrome
(the leaves shading the plant absorb all the green light and transmit red light through to the plant below which is detected by phytochromes)
poor growth in high red and far red light
Cryptochromes bind …….. and ………… chromophores that absorb UV-A and blue light
flavin
pterin
Cryptochromes are involved in controlling processes such as ………..
stem extension, gene expression and flowering time
Phototropins bind flavin chromophores that absorb mainly ……. and ……… light
UV-A and blue
give an example of a process controlled by Phototropins
phototropism
do plants grow towards or away from the light source
towards
Photoreceptor activity is lower on shaded side causing an accumulation of auxin which stimulates stem growth. The shaded side grows more/less compared to the side exposed to light
more - why plants curve towards the light
