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Plant molecular genetics Flashcards

plants as experimental systems plant genes and gene expression Arabidopsis how plants perceive their environment

1
Q

what is development

A

the specific series of changes by which cells form tissues, organs and organisms

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2
Q

what is meant by developmental plasticity

A

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

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3
Q

what are the 3 overlapping processes involved in development of multicellular organisms

A

growth, morphogenesis and cell differentiation

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4
Q

what is growth

A

the irreversible increase in size

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5
Q

what is morphogenesis

A

the process that gives a tissue, organ or organism its shape and determines the position of cell types

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6
Q

what is cell differentiation

A

the process by which cells with the same genes become different from one another

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7
Q

what is Arabidopsis

A

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

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8
Q

why is Arabidopsis favoured as a model organism

A
  • 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
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9
Q

what was the first plant to have its entire genome sequenced

A

Arabidopsis

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10
Q

what are transgenes

A

genes from another organism that are stably introduced into the genome of another

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11
Q

what do knock out experiments provide

A

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

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12
Q

cell division enhances the potential for ………. by increasing the number of cells

A

growth

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13
Q

what is plant growth brought about by

A

cell growth

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14
Q

the new cell walls that bisect plant cells during cytokinesis develop from what

A

the cell plate

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15
Q

when is the plane of cell division determined

A

late interphase - it corresponds to the shortest path that will halve the volume of the parent cell

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16
Q

what is the band called that disappears before metaphase but predicts the plane of division

A

preprophase band - microtubules concentrated in a ring in the cytoplasm

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17
Q

transverse divisions precede ………….

A

leaf elongation

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18
Q

longitudinal divisions precede ……………

A

leaf broadening

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19
Q

what is the symmetry of cell division

A

the distribution of cytoplasm between daughter cells
symmetrical - cytoplasm is shared equally during mitosis
asymmetrical - unequal sharing of the cytoplasm during mitosis

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20
Q

what does the formation of guard cells typically involve

A

asymmetrical cell division

change in the plane of cell division

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21
Q

describe the steps in formation of guard cells

A
  1. a cell divides asymmetrically forming a large cell and a smaller cell
  2. the small cell becomes the guard cell “mother cell”
  3. the guard cells form when the small mother cell divides in a plane perpendicular to the first cell division
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22
Q

what is a guard cell

A

the 2 cells that flank the stomatal pore and regulate the opening and closing of the pore

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23
Q

asymmetrical/symmetrical cell divisions plat a role in establishment of polarity

A

asymmetrical

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24
Q

what is polarity

A

the condition of having structural or chemical differences at opposite ends of an organism

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25
Q

plants typically have an ………., with a root end and a shoot end

A

axis

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26
Q

what happens in a stem cutting

A

adventitious roots emerge from the end that was nearest the root

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27
Q

what happens in a root cutting

A

adventitious shoots arise form the end that was nearest the shoot

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28
Q

the first division of a plant zygote is often symmetrical/asymmetrical

A

asymmetrical - initiating polarization of the plant body into shoot and root

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29
Q

in the gnom mutant of Arabidopsis what is defective

A

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

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30
Q

recognition of self pollen is based on genes called what

A

s-genes

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31
Q

If a pollen grain has an allele of an s-gene that matches the allele of the stigma on which it lands what happens

A

the pollen tube either fails to germinate or fails to grow through the style of the ovary

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32
Q

what are the 2 types of self incompatibility

A

gametophytic and sporophytic

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33
Q

describe gametophytic self incompatibility

A

the s-allele in the pollen genome governs the blocking of fertilization

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34
Q

what happens to the pollen if it is recognised as self

A

enzymatic destruction of the RNA in the pollen tube (enzymes are released from the style)

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35
Q

describe sporophytic self incompatibility

A

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)

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36
Q

how can self incompatibility be avoided

A
  • by removing the anthers from the parent plant that provide the seeds
  • use male sterile strains of the crop plant
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37
Q

any cell that can divide asexually an generate a clone of the original organism is said to be what

A

totipotent

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38
Q

In which area of the plant are totipotent cells mainly found

A

the meristematic tissues

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39
Q

what is vegetative reproduction that is facilitated or induced by humans referred to as

A

vegetative propagation

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40
Q

what is a callus

A

results from shoot cuttings and is a mass of dividing undifferentiated cells growing at the site of a wound or in culture

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41
Q

what develops from a callus

A

adventitious roots

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42
Q

what happens in grafting

A

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

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43
Q

in grafting what is the plant called that provides the root

A

the stock

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44
Q

in grafting what is the scion

A

the twig grafted onto the stock

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45
Q

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

A

anywhere on the plant but growth may vary depending on the plant part, species and the artificial medium

46
Q

what happens when a plant is cultured in vitro

A
  • 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
47
Q

what are the 3 ways that flowering plants avoid self-fertilization

A
  • self incompatibility
  • having male and female flowers on separate plants
  • having stamens and styles of different heights on separate plants
48
Q

what is one of the major advantages of using plants as experimental systems compared to animals

A

less ethical issues involved

49
Q

what is somatic embryogenesis

A

regeneration of whole plants from single cells in culture

50
Q

what is a somatic cell

A

non reproductive

51
Q

what are the steps in somatic embryogenesis

A
  • 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
52
Q

why do we want to introduce new genes into plants

A
  • tools for experimentation
  • overcome genetic limitations of a crop
  • introduce novel genes
  • disease resistance
  • stress tolerance (drought/cold)
  • altered composition of harvested product
53
Q

what is genetic transformation

A

the direct introduction of new genetic information

54
Q

what are genetically modified plants called

A

transgenic plants

55
Q

what is agrobacterium tumefaciens

A

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

56
Q

are agrobacterium tumefaciens mobile

A

yes - they have flagella and they swim towards wounded sites on plants and binds to the cell wall

57
Q

what is a Ti plasmid

A

a tumour inducing plasmid - it has genes on it that infect plants

58
Q

what is T DNA

A

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

59
Q

why id T DNA coated in proteins

A

they protect the DNA on its journey from the bacterial cell into the plant cell

60
Q

does agrobacterium kill cells

A

no

61
Q

what do the genes on T-DNA encode

A
  • 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)
62
Q

what is a selectable marker

A
  • 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
63
Q

what is meant by plants being sedentary

A

they have no means of locomotion

64
Q

need to optimise growth to maximise light capture for …………..

A

photosynthesis

65
Q

list some environmental abuses to plants

A

frost
drought
pathogenesis
salinity

66
Q

what is meant by a protein being highly conserved among plants

A

similar in different groups of plant species

e.g. photosynthetic pigments have the same function in trees as in algae

67
Q

give an example of a protein that is unique to a particular species

A

ricin - produced by castor beans - lethal to humans - stops translation

68
Q

if all cells in a plant have the same genome why do they differ in protein composition

A

differential gene expression

69
Q

what is differential gene expression

A

when only a fraction of the genetic information present in a particular cell is expressed at any one time

70
Q

what is constitutive gene expression

A

when a gene is expressed in all cells at all times

71
Q

what is a facultative gene

A

genes that are transcribed only when needed

72
Q

what is a constitutive gene

A

A gene that is transcribed at a relatively constant level regardless of the cell environmental conditions

73
Q

what are the different ways that gene expression can be studied

A
  • Look at proteins – 2D gel electrophoresis
  • Detect specific mRNAs – microarray
  • Visualise transcription using reporter genes
74
Q

what are reporter genes

A
  • 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
75
Q

Transcription factors bind to the ……………… sequence of the gene either activating or inhibiting transcription

A

promotor

76
Q

what is CAB

A

the gene encoding the major chlorophyll a/b binding protein

it is only expressed in chloroplast containing cells

77
Q

what stimulates CAB expression

A

light - when plants with CAB are grown in the light it is expressed but it is not expressed in plants grown in the dark

78
Q

what are the 3 types of induced genes

A
  • light induced - often allow for growth when activated
  • stress induced - e.g. drought, pathogenesis, cold
  • touch induced - if activated can prevent growth
79
Q

what is the forward genetic approach

A

by characterising the mutant gene function the function of the wild type gene can be inferred

80
Q

what are M1 plants of seed mutagenesis

A

the plants that have been treated with a mutagen

81
Q

are M1 generation plants homozygous or heterozygous for mutant genes

A

heterozygous

82
Q

what are the steps in seed mutagenesis

A
  1. seeds treated with mutagen
  2. M1 generation produced from seeds are heterozygous for mutations
  3. M1 generation self fertilize
  4. seed collection from M1 plants
  5. grow the M2 generation from seeds
  6. 1/4 M2 generation are homozygous for mutations (crossing of heterozygotes)
  7. screen for mutants
83
Q

explain the steps of transforming Arabidopsis with agrobacterium

A
  1. plasmid removed from the bacterium and T DNA is cut by a restriction enzyme
  2. foreign DNA inserted into the cut T DNA making a recombinant plasmid
  3. the plasmid is reinserted into the bacterium
  4. bacterium is used to inset the T DNA carrying the foreign gen into the chromosome of a plant cell
  5. plant cells are grown in culture and contain the foreign gene
84
Q

what is a trichome

A

an epidermal cell that is a highly specialized, hair like outgrowth on a plant shoot

85
Q

what is the glabra 1 mutant

A

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

86
Q

cell commitment

A

moving towards a particular fate but it can be reversed or transformed to another fate if necessary

87
Q

how are flowers made

A 
particular genes (homeotic) determine organ position and identity 
mutations in these genes can cause the flower to be abnormal
88
Q

describe plants grown in darkness

A

long hypocotyl, unexpanded cotyledons, no chlorophyll

89
Q

describe plants grown in light

A

short hypocotyl, expanded cotyledons, chlorophyll present

90
Q

what proportion of genes in the genome of seedlings are regulated by light

A

1/3

91
Q

Expression of promoter-reporter gene fusions in transgenic plants provides information on what

A

regulation of transcription

92
Q

why is the beta-glucuronidase reporter unsuitable for visualising short term changes in transcription

A

because the protein is too stable

93
Q

what is a good reporter for monitoring short term changes in transcription

A

an unstable reporter

e.g. firefly luciferase

94
Q

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.

A

day - maximal
night - minimal

when CAB is activated by light then luciferase is expressed. hence the more light the greater the luciferase activity

95
Q

what is the circadian rhythm

A

the biological clock

96
Q

If you move a plant to a different light dark cycle, the change in the input pathway changes what

A

the output pathway

97
Q

give a list of characteristics of light that plants can detect

A
  • Light presence/absence
  • Light quantity
  • Light spectral quality
  • Light direction
  • Light duration
98
Q

name the regulatory photoreceptors and the colour of light they detect

A

phytochromes - red and far red light
cryptochromes - UV-A and blue light
Phototropins - UV-A and blue light

99
Q

describe the structure of photoreceptors

A

they are comprised of an apoprotein and a chromophore (chlorophyll is a photoreceptor)

100
Q

The phytochrome apoprotein binds a linear …………… chromophore

A

tetrapyrrole

101
Q

what are the 2 interconvertible forms of phytochrome

A

Pr

Pfr

102
Q

Pr is present in dark-grown plants and illumination with red light produces what

A

Pfr

103
Q

what does the Pfr form of the phytochrome do

A

initiates biological responses

104
Q

which photoreceptor regulates CAB gene transcription

A

phytochrome

105
Q

what is vegetation shade detected by

A

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

106
Q

Cryptochromes bind …….. and ………… chromophores that absorb UV-A and blue light

A

flavin

pterin

107
Q

Cryptochromes are involved in controlling processes such as ………..

A

stem extension, gene expression and flowering time

108
Q

Phototropins bind flavin chromophores that absorb mainly ……. and ……… light

A

UV-A and blue

109
Q

give an example of a process controlled by Phototropins

A

phototropism

110
Q

do plants grow towards or away from the light source

A

towards

111
Q

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

A

more - why plants curve towards the light

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