Shade avoidance syndrome

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Shade avoidance syndrome
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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
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Photoreceptors in Arabidopsis
Phytochromes A-E
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Phytochrome signal transduction
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Phytochrome structure and chromophore -Reception-
chromophore phytochromobilin
PHY holoprotein
PHY apoprotein
125 kDa monomer
Native phytochrome occurs as a dimer of 2
equivalent subunits
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Phytochrome function in Arabidopsis -Response-
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Phytochrome signal transduction
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Phytochrome signal transduction -emerging themes-
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I. Subcellular partitioning Phytochrome
nucleocytoplasmic trafficking
good correlation between the wavelength
requirement for physiological responses and
nuclear import of the different phytochromes
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I. Subcellular partitioning Phytochrome
nucleocytoplasmic trafficking
phyA minutes
phyB hours
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II. Proteolytic degradation Phytochrome
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The ubiquitin/26S proteasome pathway major
proteolytic pathway in plants and animals
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The ubiquitin/26S proteasome pathway
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Light signal transduction -mutant analysis light
vs dark-
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Long Hypocotyl 5 - HY5
long hypocotyl in R, FR and B
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Phytochrome signal transduction -cop/det/fus
mutants-
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Phytochrome signal transduction -cop/det/fus
mutants-
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Phytochrome signal transduction - cop/det/fus
mutants -
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COP1 - HY5 interaction
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Phytochromes (PHY) responses to red and far-red
light-
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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)
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Phytochrome signal transduction -identified
mutants-
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Phytochrome signal transduction -proteolytic
degradation-
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Phytochrome signal transduction -phytochrome
interacting factors-
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Yeast two-hybrid analysis
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Isolation of Phytochrome Interacting Factor3 -a
basic helix-loop-helix transcription factor
protein-
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PIF3 negatively regulates phyB- but not phyA-
mediated inhibition of hypocotyl elongation
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Phytochrome signal transduction -bHLH class
PIF3-like transcription factors-
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III. Phosphorylation -Phytochromes are similar to
histidine kinases-
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Two component signaling -intermezzo-
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III. Phosphorylation -Phytochrome Ser/Thr-kinase
activity-
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III. Phosphorylation -phytochrome phosphorylation
status PAPP5-
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III. Phosphorylation -Phytochrome Ser/Thr-kinase
activity external targets-
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Phytochrome signal transduction -phosphorylation
of phytochrome interacting factors-
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IV. Regulation of transcription
phytochrome responses are associated with massive
alterations in gene expression
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IV. Regulation of transcription -Immediate
phytochrome targets-
44 (far-red light) and 25 (red light) of early
light-responsive genes (lt 1 hr) encode
transcription factors
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IV. Regulation of transcription -light/phytochrome
responsive promoters-
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Light regulated transcription factors -transcripti
on-
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Light regulated transcription factors -post-transc
riptional regulation phosphorylation-
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Light regulated transcription factors post-transcr
iptional regulation phosphorylation, cellular
localization
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Light regulated transcription factors -post-transc
riptional regulation degradation-
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PIF3 as an example cellular trafficking, gene
expression, phosphorylation, degradation
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Phytochrome signaling Further downstream
targets phytohormones