CUL1 regulates TOC1 protein stability in the Arabidopsis circadian clock.
The circadian clock is the endogenous timer that coordinates physiological processes with daily and seasonal environmental changes. In Arabidopsis thaliana, establishment of the circadian period relies on targeted degradation of TIMING OF CAB EXPRESSION 1 (TOC1) by the 26S proteasome. ZEITLUPE (ZTL) is the F-box protein that associates with the SCF (Skp/Cullin/F-box) E3 ubiquitin ligase that is responsible for marking TOC1 for turnover. CULLIN1 (CUL1) is a core component of SCF complexes and is involved in multiple signaling pathways. To assess the contribution of CUL1-containing SCF complexes to signaling within the plant oscillator, circadian rhythms were examined in the recessive, temperature-sensitive CUL1 allele axr6-3. The activity of CUL1 in this mutant declines progressively with increasing ambient temperature, resulting in more severe defects in CUL1-dependent activities at elevated temperature. Examination of circadian rhythms in axr6-3 revealed circadian phenotypes comparable to those observed in ztl null mutants; namely, lengthened circadian period, altered expression of core oscillator genes, and limited degradation of TOC1. In addition, treatment of seedlings with exogenous auxin did not alter TOC1 stability. These results demonstrate that CUL1 is required for TOC1 degradation and further suggest that this protein is the functional cullin for the SCF(ZTL) complex.
Harmon
Frank
F
United States Department of Agriculture-Agricultural Research Service, Plant Gene Expression Center, Albany, CA 94710, USA. fharmon@nature.berkeley.edu
Imaizumi
Takato
T
Gray
William M
WM
D017360:Arabidopsis / Q000201:enzymology / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000378:metabolism / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D044842:Cullin Proteins / Q000502:physiology*; D009068:Movement; D018515:Plant Leaves / Q000502:physiology; D012621:Seasons; D036226:Seedlings / Q000502:physiology; D013472:Sunlight; D013696:Temperature; D014157:Transcription Factors; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism
D029681:Arabidopsis Proteins; C100318:Cullin 1; D044842:Cullin Proteins; C411822:TOC1 protein, Arabidopsis; D014157:Transcription Factors; D044767:Ubiquitin-Protein Ligases