Document Detail


Phytochrome signaling in green Arabidopsis seedlings: impact assessment of a mutually negative phyB-PIF feedback loop.
MedLine Citation:
PMID:  22492120     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
The reversibly red (R)/far-red (FR)-light-responsive phytochrome (phy) photosensory system initiates both the deetiolation process in dark-germinated seedlings upon first exposure to light, and the shade-avoidance process in fully deetiolated seedlings upon exposure to vegetational shade. The intracellular signaling pathway from the light-activated photoreceptor conformer (Pfr) to the transcriptional network that drives these responses involves direct, physical interaction of Pfr with a small subfamily of bHLH transcription factors, termed Phy-Interacting Factors (PIFs), which induces rapid PIF proteolytic degradation. In addition, there is evidence of further complexity in light-grown seedlings, whereby phyB-PIF interaction reciprocally induces phyB degradation, in a mutually-negative, feedback-loop configuration. Here, to assess the relative contributions of these antagonistic activities to the net phenotypic readout in light-grown seedlings, we have examined the magnitude of the light- and simulated-shade-induced responses of a pentuple phyBpif1pif3pif4pif5 (phyBpifq) mutant and various multiple pif-mutant combinations. The data (1) reaffirm that phyB is the predominant, if not exclusive, photoreceptor imposing the inhibition of hypocotyl elongation in deetiolating seedlings in response to prolonged continuous R irradiation and (2) show that the PIF quartet (PIF1, PIF3, PIF4, and PIF5) retain and exert a dual capacity to modulate hypocotyl elongation under these conditions, by concomitantly promoting cell elongation through intrinsic transcriptional-regulatory activity, and reducing phyB-inhibitory capacity through feedback-loop-induced phyB degradation. In shade-exposed seedlings, immunoblot analysis shows that the shade-imposed reduction in Pfr levels induces increases in the abundance of PIF3, and mutant analysis indicates that PIF3 acts, in conjunction with PIF4 and PIF5, to promote the known shade-induced acceleration of hypocotyl elongation. Conversely, although the quadruple pifq mutant displays clearly reduced hypocotyl elongation compared to wild-type in response to prolonged shade, immunoblot analysis detects no elevation in phyB levels in the mutant seedlings compared to the wild-type during the majority of the shade-induced growth period, and phyB levels are not robustly correlated with the growth phenotype across the pif-mutant combinations compared. These results suggest that PIF feedback modulation of phyB abundance does not play a dominant role in modulating the magnitude of the PIF-promoted, shade-responsive phenotype under these conditions. In seedlings grown under diurnal light-dark cycles, the data show that FR-pulse-induced removal of Pfr at the beginning of the dark period (End-of-Day-FR (EOD-FR) treatment) results in longer hypocotyls relative to no EOD-FR treatment and that this effect is attenuated in the pif-mutant combinations tested. This result similarly indicates that the PIF quartet members are capable of intrinsically promoting hypocotyl cell elongation in light-grown plants, independently of the effects of PIF feedback modulation of photoactivated-phyB abundance.
Authors:
Pablo Leivar; Elena Monte; Megan M Cohn; Peter H Quail
Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, Non-P.H.S.     Date:  2012-04-05
Journal Detail:
Title:  Molecular plant     Volume:  5     ISSN:  1752-9867     ISO Abbreviation:  Mol Plant     Publication Date:  2012 May 
Date Detail:
Created Date:  2012-05-21     Completed Date:  2012-09-13     Revised Date:  2013-06-26    
Medline Journal Info:
Nlm Unique ID:  101465514     Medline TA:  Mol Plant     Country:  England    
Other Details:
Languages:  eng     Pagination:  734-49     Citation Subset:  IM    
Affiliation:
Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720, USA.
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MeSH Terms
Descriptor/Qualifier:
Arabidopsis / growth & development*,  metabolism*,  radiation effects
Arabidopsis Proteins / metabolism*
Basic Helix-Loop-Helix Transcription Factors / metabolism*
Feedback, Physiological* / radiation effects
Light
Models, Biological
Mutation / genetics
Phytochrome B / metabolism*
Seedling / growth & development*,  radiation effects
Signal Transduction* / radiation effects
Grant Support
ID/Acronym/Agency:
R01 GM047475/GM/NIGMS NIH HHS
Chemical
Reg. No./Substance:
0/Arabidopsis Proteins; 0/Basic Helix-Loop-Helix Transcription Factors; 0/PHYB protein, Arabidopsis; 136250-22-1/Phytochrome B
Comments/Corrections

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