A self-regulatory circuit of CIRCADIAN CLOCK-ASSOCIATED1 underlies the circadian clock regulation of temperature responses in Arabidopsis.
The circadian clock synchronizes biological processes to daily cycles of light and temperature. Clock components, including CIRCADIAN CLOCK-ASSOCIATED1 (CCA1), are also associated with cold acclimation. However, it is unknown how CCA1 activity is modulated in coordinating circadian rhythms and cold acclimation. Here, we report that self-regulation of Arabidopsis thaliana CCA1 activity by a splice variant, CCA1β, links the clock to cold acclimation. CCA1β interferes with the formation of CCA1α-CCA1α and LATE ELONGATED HYPOCOTYL (LHY)-LHY homodimers, as well as CCA1α-LHY heterodimers, by forming nonfunctional heterodimers with reduced DNA binding affinity. Accordingly, the periods of circadian rhythms were shortened in CCA1β-overexpressing transgenic plants (35S:CCA1β), as observed in the cca1 lhy double mutant. In addition, the elongated hypocotyl and leaf petiole phenotypes of CCA1α-overexpressing transgenic plants (35S:CCA1α) were repressed by CCA1β coexpression. Notably, low temperatures suppressed CCA1 alternative splicing and thus reduced CCA1β production. Consequently, whereas the 35S:CCA1α transgenic plants exhibited enhanced freezing tolerance, the 35S:CCA1β transgenic plants were sensitive to freezing, indicating that cold regulation of CCA1 alternative splicing contributes to freezing tolerance. On the basis of these findings, we propose that dynamic self-regulation of CCA1 underlies the clock regulation of temperature responses in Arabidopsis.
Department of Chemistry, Seoul National University, Seoul 151-742, Korea.
Pil Joon
PJ
Seo
Mi-Jeong
MJ
Park
Mi-Hye
MH
Lim
Sang-Gyu
SG
Kim
Minyoung
M
Lee
Ian T
IT
Baldwin
Chung-Mo
CM
Park
D017398:Alternative Splicing; D017360:Arabidopsis / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism*; D057906:Circadian Clocks; D003080:Cold Temperature; D018744:DNA, Plant / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D030821:Plants, Genetically Modified; D020033:Protein Isoforms; D055503:Protein Multimerization; D013312:Stress, Physiological; D013696:Temperature; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism*
D029681:Arabidopsis Proteins; C114425:CCA1 protein, Arabidopsis; D018744:DNA, Plant; D004268:DNA-Binding Proteins; C113192:LHY protein, Arabidopsis; D020033:Protein Isoforms; D014157:Transcription Factors