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Role of Phytochromes in Shade AvoidanceEcophysiological and Molecular aspects
Shade avoidance syndrome
Plants adapt to changes in light conditions
-Shade Avoidance Syndrome-
R/FR =
photon fluence rate in 10 nmband centered on 660 nm
photon fluence rate in 10 nmband centered on 730 nm
Photoreceptors in Arabidopsis
Phytochromes A-E
Phytochrome signal transduction
Phytochrome structure and chromophore-Reception-
chromophorephytochromobilin
PHY apoprotein
PHY holoprotein
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 partitioningPhytochrome nucleocytoplasmic trafficking
good correlation between the wavelength requirement for physiologicalresponses and nuclear import of the different phytochromes
phyA
minutes
phyB
hours
I. Subcellular partitioningPhytochrome nucleocytoplasmic trafficking
II. Proteolytic degradationPhytochrome
phyA
The ubiquitin/26S proteasome pathwaymajor 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/FUSname
Other proteinname Function
Putative ubiquitin ligase component
COP9 signalosome subunit
COP9 signalosome subunit
COP9 signalosome subunit
COP9 signalosome subunit
COP9 signalosome subunit
COP9 signalosome subunit
E2 Ub-conjugating enzymevariant
Not cloned
Protein required for HY5 degrad.
COP1
DET1
COP10
COP16
COP11
FUS12
FUS11
COP8
FUS5
COP9
CSN1
CSN2
CSN3
CSN4
CSN7
CSN8
Phytochrome signal transduction-cop/det/fus mutants-
F
Phytochrome signal transduction- cop/det/fus mutants -
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
e.g. Far-red light (phyA)
Wt phyA phyAspa1 Wt rsf1
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 phyA- mediated 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
44% (far-red light) and 25% (red light) of early light-responsive genes (< 1 hr) encode transcription factors
IV. Regulation of transcription-Immediate phytochrome targets-
IV. Regulation of transcription-light/phytochrome responsive promoters-
Light regulated transcription factors-transcription-
Light regulated transcription factors-post-transcriptional regulation; phosphorylation-
Light regulated transcription factorspost-transcriptional regulation;
phosphorylation, cellular localization
Light regulated transcription factors-post-transcriptional regulation; degradation-
PIF3 as an examplecellular trafficking, gene expression, phosphorylation, degradation
Phytochrome signalingFurther downstream targets; phytohormones