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B3.0 > Light Perception: The Phytochromes > Flashcards

Light Perception: The Phytochromes Flashcards

1
Q

Structure

A
  1. Intro to light perception
  2. Photoreceptors
    3.
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2
Q

The light input in plant physiology

A
  • energy
  • information
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3
Q

the energy output of light input in plant physiology

A
  • metabolism
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4
Q

the information output of light input in plant physiology

A
  • predict (un)favourable conditions
  • timekeeping
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5
Q

What light changes can plants detect?

A
  • quality: spectral distribution
  • quantity: photons, energy
  • direction: gradient
  • duration
  • periodicity
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6
Q

Which processes are light-regulated?

A

i) developmental transitions
ii) germination (photoblasty)
iii) photo- + skotomorphogenesis
iv) leaf expansion and shade avoidance
v) phototropism (sun tracking, chloroplast orientation)
vi) protection (high energy visible, UV; NPQ)
vii) stomatal opening
viii) biological clock

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7
Q

photoreceptors

A
  • proteins with functional (prosthetic groups) that generate cascades from absorbed photons
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8
Q

List some photoreceptors

A

i) phytochromobilyn
ii) flavin adenine dinucleotide
iii) flavin adenine mononucleotide
iv) aromatic aas (trp)

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9
Q

photoreceptor photon absorption

A
  • reversible conformational change
  • affect protein (re)activity
  • direct effects and signal transduction
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10
Q

Specific photoreceptor clases

A
  • cryptochromes (cry)
  • phototropins (phot) + zeitlupe (ZTL)
  • phytochrome (phy; e.g. UVR8)
  • no green
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11
Q

cryptochromes

A

bacterial DNA photoliase ancestor

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12
Q

phototropins

A

prokaryotic ancestors for sensing light, O2, and voltage (LOV)

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13
Q

phy

A
  • 2-component His kinase ancestors
  • originated in Viridiplantae
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14
Q

the combined absorption spectra of the photoreceptors overlap with

A
  • photosynthetic pigments
  • metabolism is co-ordinated with development
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15
Q

What do phytochrome regulate?

A
  • germination
  • hypocotyl elongation
  • shade avoidance
  • de-etiolation
  • flowering
  • thermosensing
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16
Q

How do phytochromes act?

A
  • syner- and antagonistically
  • different wavelengths: functional overlap
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17
Q

action spectrum

A
  • rate of biological effectiveness against light wavelength
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18
Q

Weber-Fechner Law

A

response magnitude is correlated with the log(amount of light)

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19
Q

irradiance

A
  • photon flux density
  • photons hitting a surface per unit time (micro mol per metre squared per second)
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20
Q

photon fluence

A

number of photons hitting a surface unit, integrated across irradiation duration (micro moles per metre squared)

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21
Q

Testing the reversibility of photon reception

A
  • expose lettuce seeds to alternating periods of:
  • red light (1 minute); lambda (620-700nm)
  • far-red light (4 minutes); lambda (700-750)
  • if final exposure is red: germination
  • if final exposure is far-red: dormancy
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22
Q

how to identify photoreceptors involved in a specific process?

A

if a pigment can be found with an absorption spectrum that matches a process’ action spectrum, it is implicated

23
Q

straightening the hook of a germinating seed

A
  • red-light induced (660-730)
  • protects meristem in soil
24
Q

genetic screening for photoreceptor components

A

mutants of A. thaliana

25
etiolation - the basics
- skotomorphogenesis - growth in the dark - favours development towards light, out of soil
26
etiolation phentoype
- long hypocotyl - apical hook - small, chlorophyll-less cotyledons
27
de-etiolation - the basics
- photomorphogenesis - growth in light - favours aboveground development
28
de-etiolation phenotype
- short hypocotyl - cotyledon expansion and greening - root development
29
phytochrome structure
- tetrapyrrole group with potential kinase activity - dimers - interact with different protein partners
30
phytochrome chromophore
- phytochromobilin - linear tetrapyrrole - chloroplastic synthesis - N-terminus: light sensing - C-terminus: signalling - spontaneously binds to phytochrome apoprotein in the cytosol
31
Pr and Pfr
- two interconvertible forms - expose different domains - Pr: inactive (far-red) - Pfr: active (red); sequesters COP1 and SPA; stabilises HY5
32
Describe the toggle switch Pr, Pfr interconversion
i) phytochromobilin: reversible isomerisation ii) Phy: conformational change
33
Photoequilibrium
- photostationary overlap state - phytochrome are dedicated to detect possibility of reaching PAR - determines risk of shading - incident light ratio/photon flux ratio (R/FR)
34
PAR
- photosynthetically active radiation
35
Arabidopsis phytochrome
- 5 isoforms (A-E); gene duplication - partial functional overlap - antagonistic and complementary - efficiency, specificity - Type I (A): FR-rich, etiolated tissues - Type II (B, D, E): ^ R/FR
36
types of responses
- based on Pfr:Ptot required to saturate - fast - slow - (ir)reversible
37
fast phytochrome response
- biochemical - organellar movements - tumour variations
38
slow phytochrome response
- transcriptional regulation
39
irreversible
germination, flowering
40
VLFR
- Very Low Fluence Response - photoblasty - very few Pfr (Pfr/Ptot= 10^-6-10^-3)
41
LFR
- Low Fluence Response - shade avoidance syndrome - fully reversible
42
HIR/CFR
- High Irradiance Response / Constant Fluence Response - damaging radiation for photosystems - local anthocyanin + flavonoid production: photoprotective - seeds germinate in undergrowth
43
Log of (Fluence)
- correlated with Response - the same response can be elicited by increasing intense light and longer exposure
44
Phy signal transduction
- both Phy types enter the nucleus in complex with nuclear-targeted partners - form tPNBs - repress PIFs
45
transient phytochrome nuclear bodies
- tPNBs - inside the nucleus, Phys cluster together via microdomain
46
phytochrome activity requires relocalisation + activation by light
- if cytoslic/ inactive, phyB cannot promote photomorphogenesis
47
PIFs
- phytochrome-interacting factors - bHLH TFs - photomorphogenic repressors - stable in the dark - homo and heterodimers - create transcriptional hubs - also integrate hormone signalling - COP1, SPA
48
transcriptional hubs
regulate hundreds of genes
49
How do phyA+B regulate PIFs?
- C-terminal kinase domain - protesomal recruitment and degradation - reciprocal - attenuate after maximum signalling
50
cop1
- constitutive photomorphogenic 1 - no etiolation
51
COPS
- 1, 8, 9, 10, 11, 12, 13, 14, 15, 16
52
COP1
- PIF - E3 ligase - light: nuclear exclusion - dark: nuclear - promotes HY5 degradation (+SPA)
53
HY5
- TF - positive regulator of photomorphogenesis - light: nuclear - dark: degraded

B3.0 (44 decks)

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