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Trinity Term 1 > Plant development IV - Epigenetics and plant reproduction > Flashcards

Plant development IV - Epigenetics and plant reproduction Flashcards

1
Q

Why is flowering advantageous?

A
  • pollinator attraction
  • increased fertilisation chances
  • further development (fruit) allows improved seed dispersal
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2
Q

Describe the promoters of the floral transition

A
  • hormonal signalling
  • light quality
  • photoperiod
  • warm temperature
  • nutrients
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3
Q

Describe enablers of the floral transition

A
  • vernalisation
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4
Q

Characterise a plant’s life cycle

A
  • adulthood
  • insensitive phases
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5
Q

Describe adulthood in plants

A

stage at which the SAM is receptive to flowering stimuli

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6
Q

Describe what allows the transition to adulthood in plants

A

sugar levels in the leaf stimulate expression of a microRNA that inhibits a class of TFs

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7
Q

What is leaf sugar quantity a measure of?

A

amount reserved for reproduction

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8
Q

What might stop a plant from flowering?

A
  • cold
  • stress
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9
Q

Describe circadian rhythms - the basics

A

oscillations of biological parameters within a 24h period, entrained by exogenous cues

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10
Q

Describe circadian rhythms - the specifics

A
  • environmental inputs lead to entrainment pathways
  • circadian gating of entrainment and outputs
  • circadian oscillation
  • output pathways
  • changes in gene rhythm of transcription, physiology and biochemistry
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11
Q

Describe short-day plants

A

flower when an uninterrupted period of darkness exceeds a critical night length

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12
Q

Describe long-day plants

A

flower when a period of darkness is less than a critical night length threshold

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13
Q

Which wavelengths of light promote flower transitions?

A

red (via phytochromes) and blue (via FKF1)

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14
Q

FKF1

A

LOV-domain containing photoreceptors

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15
Q

Describe the doincidence model of plant response to light change

A

plant should be receptive.on circadian bases, to the floral light stimulus
- internal clock sets the light sensitivity of the plant

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16
Q

How do plants perceive the photoperiod?

A
  • Pr is synthesised
  • Pr becomes Pfr on exposure to red light
  • Pfr either goes to enzymatic destruction, or is slowly converted to darkness (under far-red light)
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17
Q

How is light and temperature detected by a plant?

A

phytochrome B

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18
Q

Describe active phytochrome B

A
  • represses floral transition in Arabidopsis
  • 27°C stimulates reversion to the inactive form
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19
Q

Describe the relationship between phyB and temperature

A

positively correlated (not linear).

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20
Q

Give examples of day-neutral plants

A
  • Phaseulus vulgaris
  • Abronia villosa
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21
Q

Describe day-neutral plants

A
  • species adapted to live at tropical/equatorial latitudes where day and night length does not change
  • species that need to flower when conditions are permissive
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22
Q

Describe the hormonal control of flowering

A
  • gibberellin-deficient mutants exhibit delayed flowering, dependent upon DELLA proteins
  • long-day photoperiods induce an increase in active GA levels.
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23
Q

List some GAs

A

GA1, GA8, GA20

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24
Q

Describe the effect of long photoperiods on GA1

A

500%. change

25
Q

GA1

A

active GA, responsible for growth

26
Q

Describe the effect of long photoperiods on GA8

A

1450% increase

27
Q

GA8

A

inactive GA1 metabolite

28
Q

Describe the effect of long photoperiods on GA20

A

1700% increase

29
Q

GA20

A

inactive GA1 precursor

30
Q

Describe plants under long day (LD) conditions

A
  • spraying leaves with GAs accelerates flowering
  • promoting catabolism of active GAs in the SAM or vasculature inhibits flowering
31
Q

Describe plants under short day (SD) conditions

A

Promoting catabolism of active GAs in the SAM (not in the vasculature) inhibits flowering.

32
Q

How have grafting experiments been used in plant development

A

reveal the existence of a transmissible signalling molecule able to promote flowering

33
Q

Describe the florigen

A
  • moves with a speed of approx 50 cm h-1
  • in the phloem
34
Q

FT

A

florigen protein

35
Q

Describe FT

A
  • produced in the leaf vasculature
  • travels to the phloem to induce SAM conversion to inflorescence meristem and induction of bract primordia
36
Q

Describe the molecular function of FT

A
  • once in the SAM, forms a complex with FD and 14-3-3
  • induces expression of floral meristem identity genes
  • complex represses FD expression in a feedback loop
37
Q

FD

A

a TF

38
Q

14-3-3

A

adaptor protein

39
Q

Give a gene that codes for floral meristem identity

A

APETALA1

40
Q

Describe the transcriptional control of FT

A
  • autonomy
  • vernalisation
  • warm temperature
  • photoperiod and clock
41
Q

Describe the transcription level of the FT gene

A
  • controlled by two main regulators: FLC and CO
  • integrate several regulatory pathways
42
Q

FLC

A
  • flowering locus C
  • repressor
  • upstream of CO
43
Q

CO

A
  • constans
  • activator
  • downstream of FLC
44
Q

Give a molecular explanation of the coincidence model

A
  • the circadian clock and light regulate the CO transcriptor
  • light signals regulate CO protein stability
  • transcriptional and post-translational regulation enable CO (and thus FT) accumulation in LD conditions only
45
Q

Describe coincidence in rice

A
  • Hd1 represses the
    florigen signal
  • SD is required for flowering
46
Q

Hd1

A

CO ortholog

47
Q

Describe the vernalisation pathway

A
  • required due to high FLC activity in and after germination
  • vernalisation silences FLC
48
Q

How is vernalisation effects studied?

A

flc mutants appear the same as an annual winter ecotype post-vernalisation

49
Q

Describe the epigenetic
control of vernalisation

A
  • FLC locus regulated by alternative histone modifications shifting chromatin locally from an open to a closed state
  • regulatory small RNA produced at the FLC locus control the mRNA level
50
Q

How is FLC expression reset in the embryo

A
  • PRC2 complices trimethylates the Lys-27 residue of H3 (silencing)
  • PRC1 complex monoubiquitinates H2A, stably repressing expression
  • trithorax trimethylates Lys-4 of H3; induces the expression of target loci
  • during fertilisation, LEC1 complex opens FLC chromatin again
51
Q

Describe FT control of tubers in potatoes

A
  • FT identity conserved among solanaceae
  • grafting a scion on potato rootstock causes Mobile Flowering signal to induces tuberisation
  • meristematic activity of potato stolons is under photoperiodic control of a CO/FT couple
  • flowering and tuberisation are coordinated
52
Q

scion

A

flowering tobacco

53
Q

How can flowering time be controlled by humans?

A
  • EID1 variant induced late flowering and more chlorophyll in long days
  • seen in domestiction of wild tomato from Mesoamerica to northern latitudes
  • spread of barley from the fertile crescent: winter barley to spring barley
54
Q

EID1

A

light signalling

55
Q

winter barley

A

photoperiod sensitive

56
Q

spring barley

A
  • prr7 mutant
  • insensitive to the photoperiod
57
Q

Describe sugarbeet breeding

A

for seed/sugar production

58
Q

Describe sugarbeet

A
  • biennial crop cycle
  • flowers and root compete
    for sugars
  • seed production is
    preferably annual
  • global warming prevents
    flowering
59
Q

Combined effect of global warming and night lighting may

A

induce premature flowering or delayed senescence.

Trinity Term 1 (38 decks)

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