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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-
R/FR =
photon fluence rate in 10 nm
band centered on 660 nm
photon fluence rate in 10 nm
band centered on 730 nm
Photoreceptors in Arabidopsis
Phytochromes A-E
Phytochrome signal transduction
Phytochrome structure and chromophore
-Reception-
chromophore
phytochromobilin
PHY
holoprotein
PHY apoprotein
125 kDa monomer
Native phytochrome occurs as a dimer of 2 equivalent subunits
Phytochrome function in Arabidopsis
-Response-
Phytochrome signal transduction
Phytochrome signal transduction
-emerging themes-
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
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-
Phytochrome signal transduction
-cop/det/fus mutants-
COP/DET/FUS Other protein
name
name
Function
COP1
Putative ubiquitin ligase component
DET1
Protein required for HY5 degrad.
COP10
E2 Ub-conjugating enzymevariant
COP16
Not cloned
COP11
CSN1
COP9 signalosome subunit
FUS12
CSN2
COP9 signalosome subunit
FUS11
CSN3
COP9 signalosome subunit
COP8
CSN4
COP9 signalosome subunit
FUS5
CSN7
COP9 signalosome subunit
CSN8
COP9 signalosome subunit
COP9
Phytochrome signal transduction
- cop/det/fus mutants -
F
COP1 - HY5 interaction
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-
Yeast two-hybrid analysis
Isolation of Phytochrome Interacting Factor3
-a basic helix-loop-helix transcription factor protein-
PIF3 negatively regulates phyB- but not phyAmediated inhibition of hypocotyl elongation
Phytochrome signal transduction
-bHLH class PIF3-like transcription factors-
III. Phosphorylation
-Phytochromes are similar to histidine kinases-
Two component signaling
-intermezzo-
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 alterations in 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
-transcription-
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