Targeted degradation of PSEUDO-RESPONSE REGULATOR5 by an SCFZTL complex regulates clock function and photomorphogenesis in Arabidopsis thaliana.
Circadian clocks comprise several regulatory feedback loops that control gene transcription. However, recent evidence has shown that posttranslational mechanisms are also required for clock function. In Arabidopsis thaliana, members of the PSEUDO-RESPONSE REGULATOR (PRR) family were proposed to be components of the central oscillator. Using a PRR5-specific antibody, we characterized changes in PRR5 protein levels in relation to its mRNA levels under various circadian conditions. Under long-day conditions, PRR5 mRNA levels are undetectable at dusk but PRR5 protein levels remain maximal. Upon dark transition, however, PRR5 levels decrease rapidly, indicating dark-induced, posttranslational regulation. We demonstrated that the Pseudo-Receiver (PR) domain of PRR5 interacts directly with the F box protein ZEITLUPE (ZTL) in vitro and in vivo. Analyses of mutants and transgenic plants revealed an inverse correlation between PRR5 and ZTL levels, which depends on the PR domain. These results indicate that PRR5 is negatively regulated by ZTL, which likely mediates its ubiquitination and degradation. Phenotypic analyses of prr5 ztl double mutants showed that PRR5 is required for ZTL functions. ZTL contains a Light-Oxygen-Voltage domain, and its activity may be directly regulated by blue light. Consistent with this notion, we found that blue light stabilizes PRR5, although it does not alter ZTL levels. Together, our results show that ZTL targets PRR5 for degradation by 26S proteasomes in the circadian clock and in early photomorphogenesis.
Kiba
Takatoshi
T
Laboratory of Plant Molecular Biology, The Rockefeller University, New York, New York 10065-6399, USA.
Henriques
Rossana
R
Sakakibara
Hitoshi
H
Chua
Nam-Hai
NH
D017360:Arabidopsis / Q000196:embryology* / Q000235:genetics / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001683:Biological Clocks / Q000502:physiology* / Q000528:radiation effects; D002940:Circadian Rhythm / Q000528:radiation effects; D015536:Down-Regulation / Q000528:radiation effects; D018506:Gene Expression Regulation, Plant / Q000528:radiation effects; D017343:Genes, Plant; D018546:Hypocotyl / Q000528:radiation effects; D008027:Light; D009024:Morphogenesis / Q000528:radiation effects*; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011485:Protein Binding / Q000528:radiation effects; D011499:Protein Processing, Post-Translational / Q000528:radiation effects*; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013489:Suppression, Genetic / Q000528:radiation effects; D013816:Thermodynamics; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D029681:Arabidopsis Proteins; C523307:PRR5 protein, Arabidopsis; D012333:RNA, Messenger; D014157:Transcription Factors; C410503:ZTL protein, Arabidopsis; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease
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