Light Perception: Blue Light Signalling

Question 1

Structure

Answer 1

1. Blue light
2. Cryptochromes
3. Phots

Question 2

What is blue light signalling important for?

Answer 2

i) photomorphogenesis
ii) phototropism/algal phototaxis
iii) stomatal opening
iv) solar tracking
v) chloroplast movements
vi) anthocyanin production
vii) clock entrainment

Question 3

UV-A blue light photoreceptors

Answer 3

• 3 classesL
  1) phototropins
  2) zeitlupe
  3) crypto chromes

Question 4

The action spectrum of several responses to blue poversalps with that of

Answer 4

flavin cofactors

Question 5

Plant cryptochromes

Answer 5

• 2x prosthetic groups: FAD, MTHF
• close enough to interact
• energy passes from MTHF->FAD
• N-terminus: light sensing
• C-terminus: signalling

Question 6

FAD

Answer 6

• flavin adenine dinucleotide
• 450nm

Question 7

MTHF

Answer 7

5,10-methyltetrahydrofolate
- 380nm

Question 8

genetic identification of cryptochromes

Answer 8

• cryoe: constitutive stomatal opening, photomorphogenesis
• cry: decreased anthocyanin, skotomorphogenesis, flowering retardation

Question 9

Describe cryptochrome activation by blue light

Answer 9

FAD semireduction @ C-terminal phosphorylation site; open conformation

Question 10

Cryptochrome signal transduction

Answer 10

stabilises developmental transition regulators

Question 11

Cryptochromes and HY5 stabilisation

Answer 11

• COP1, SPA degradation
• allows CO expression

Question 12

HY5

Answer 12

master regulator

Question 13

CO

Answer 13

• Constance
• positive regulator of flowering
• interacts with CIBs

Question 14

CIBs

Answer 14

cryptochrome-interacting bHLHs

Question 15

Arabidopsis photomorphogenesis

Answer 15

• white-light mediated hypocotyl repression is mediated mainly by PhyB and Cry1
• marginal Cry2 contribution (redundancy)
• mutant stacking approach

Question 16

Phototropins

Answer 16

• LOV-associated photoreceptors
• conserved LOV-activated FMN domains
• phototropic
• At: 1/2
• membrane-associated Ser/kinases

Question 17

Phototropin activation

Answer 17

• cytosolic in the dark
• blue light: FMN + Cys covalent bond: conformational change
• Ser/Thr exposure
• autophosphorylation
• localisation informs organ growth via PIN asymmetry

Question 18

NPH3

Answer 18

• non-phototropic hypocotyl
• membrane and nuclear protein
• auxin signalling + cell expansion
• interacts w/ kinase phototropic domain under blue light

Question 19

Photodynesis

Answer 19

• chloroplast movement
• sliding along growing actin filaments towards weak blue light
• phototropin-facilitated
• mechanism poorly understood

Question 20

pho2

Answer 20

• no avoidance response
• bleaches in full light

Question 21

stomatal opening

Answer 21

• guard cell expansion
• K+ ^
• osmosis
• phototropin phosphorylation cascade
• H+ extrusion balances K+ influx

Question 22

LOV-domain containing F-box proteins

Answer 22

• zeitlupe, FKF1
• E3 ligase components
• interact with CO
• also interact with circadian clock

Question 23

UVR8

Answer 23

• UV-R locus 8
• UVB-B light receptor
• chromophore: Trp triad salt bridges
• activated by monomerisation
• positive regulator of: HY5, flavonoids, DNAR
• sequesters COP1-SPA
• inactivated by accessory factors

Question 24

What is the advantage of optogenetcis?

Answer 24

• inducible inhibition is more revealing than mutant studies

Question 25

LOV2 photoswitch optogenetics

Answer 25

- fuse to KOV - BLINK1

Question 26

KOV

Answer 26

- K+ channel from viral PBCV-1

Question 27

BLINK1 plants

Answer 27

- blue light induced K+ channel - more efficient stomatal regulation - increased shoot biomass production - enhanced photomorphogenesis