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Role of Phytochromes in Shade Avoidance Ecophysiological and Molecular aspects. Shade avoidance syndrome. Plants adapt to changes in light conditions -Shade Avoidance Syndrome-. photon fluence rate in 10 nm band centered on 660 nm photon fluence rate in 10 nm band centered on 730 nm.

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Role ofPhytochromes in Shade AvoidanceEcophysiological and Molecular aspects



Plants adapt to changes in light conditions

-Shade Avoidance Syndrome-

photon fluence rate in 10 nm

band centered on 660 nm

photon fluence rate in 10 nm

band centered on 730 nm

R/FR =




Phytochrome structure and chromophore

-Reception-

chromophore

phytochromobilin

PHY

holoprotein

PHY apoprotein

125 kDa monomer

Native phytochrome occurs as a dimer of 2 equivalent subunits





I. Subcellular partitioning

Phytochrome nucleocytoplasmic trafficking

good correlation between the wavelength requirement for physiological

responses and nuclear import of the different phytochromes


I. Subcellular partitioning

Phytochrome nucleocytoplasmic trafficking

phyA

minutes

phyB

hours


phyA

II. Proteolytic degradation

Phytochrome


The ubiquitin/26S proteasome pathway

major proteolytic pathway in plants and animals


The ubiquitin/26S proteasome pathway


Light signal transduction

-mutant analysis: light vs dark-


Long Hypocotyl 5 - HY5

long hypocotyl in R, FR and B


Phytochrome signal transduction

-cop/det/fus mutants-


COP/DET/FUS

name

Other protein

name

Function

Putative ubiquitin ligase component

COP1

DET1

COP10

COP16

COP11

FUS12

FUS11

COP8

FUS5

COP9

Protein required for HY5 degrad.

E2 Ub-conjugating enzymevariant

Not cloned

CSN1

CSN2

CSN3

CSN4

CSN7

CSN8

COP9 signalosome subunit

COP9 signalosome subunit

COP9 signalosome subunit

COP9 signalosome subunit

COP9 signalosome subunit

COP9 signalosome subunit

Phytochrome signal transduction

-cop/det/fus mutants-


F

Phytochrome signal transduction

- cop/det/fus mutants -



Phytochromes (PHY)

–responses to red and far-red light-


Phytochrome signal transduction

-more sophisticated screens: light quality-

Mutants that exhibit light-grown

characteristics in the dark

Mutants that exhibit altered seedling

development under specific light conditions

Wt phyA phyAspa1

Wt rsf1

e.g. Far-red light (phyA)


Phytochrome signal transduction

-identified mutants-


Phytochrome signal transduction

-proteolytic degradation-


Phytochrome signal transduction

-phytochrome interacting factors-



Isolation of Phytochrome Interacting Factor3

-a basic helix-loop-helixtranscription factor protein-


PIF3 negatively regulates phyB- but not phyA-

mediated inhibition of hypocotyl elongation


Phytochrome signal transduction

-bHLH class PIF3-like transcription factors-


III. Phosphorylation

-Phytochromes are similar to histidine kinases-



III. Phosphorylation

-Phytochrome Ser/Thr-kinase activity-


III. Phosphorylation

-phytochrome phosphorylation status; PAPP5-


III. Phosphorylation

-Phytochrome Ser/Thr-kinase activity; external targets-


Phytochrome signal transduction

-phosphorylation of phytochrome interacting factors-


IV. Regulation of transcription

phytochrome responses are associated with massive alterationsin gene expression


IV. Regulation of transcription

-Immediate phytochrome targets-

44% (far-red light) and 25% (red light) of early light-responsive genes (< 1 hr) encode transcription factors


IV. Regulation of transcription

-light/phytochrome responsive promoters-



Light regulated transcription factors

-post-transcriptional regulation; phosphorylation-


Light regulated transcription factors

post-transcriptional regulation;

phosphorylation, cellular localization


Light regulated transcription factors

-post-transcriptional regulation; degradation-


PIF3 as an example

cellular trafficking, gene expression, phosphorylation, degradation


Phytochrome signaling

Further downstream targets; phytohormones


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