Arabidopsis circadian clock protein, TOC1, is a DNA-binding transcription factor

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 109; no. 8; pp. 3167 - 3172
• Main Authors: Gendron, Joshua M, Pruneda-Paz, José L, Doherty, Colleen J, Gross, Andrew M, Kang, S. Earl, Kay, Steve A
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 21.02.2012; National Acad Sciences
• Subjects: Amino Acid Sequence; Arabidopsis; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis Proteins - chemistry; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Base Sequence; Biological Sciences; Circadian Clocks - genetics; circadian rhythm; Circadian rhythms; CLOCK protein; Data processing; Datasets; Deoxyribonucleic acid; DNA; DNA microarrays; DNA, Plant - metabolism; DNA-binding domains; DNA-Binding Proteins - chemistry; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; Feedback; Flowers & plants; Gene deletion; Gene expression regulation; Gene Expression Regulation, Plant; gene overexpression; Genes; Genes, Plant - genetics; Genetic mutation; genomics; Hypocotyls; microarray technology; Molecular Sequence Data; Mutation; Plant cells; Plants; Promoter regions; Promoter Regions, Genetic - genetics; Promoters; Protein Binding; Protein Structure, Tertiary; Proteins; Repression; Repressor Proteins - metabolism; Repressors; Seedlings; transcription (genetics); Transcription factors; Transcription Factors - chemistry; Transcription Factors - genetics; Transcription Factors - metabolism; Transcription, Genetic
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1200355109

The first described feedback loop of the Arabidopsis circadian clock is based on reciprocal regulation between TIMING OF CAB EXPRESSION 1 (TOC1) and CIRCADIAN CLOCK-ASSOCIATED 1 (CCA1)/LATE ELONGATED HYPOCOTYL (LHY). CCA1 and LHY are Myb transcription factors that bind directly to the TOC1 promoter to negatively regulate its expression. Conversely, the activity of TOC1 has remained less well characterized. Genetic data support that TOC1 is necessary for the reactivation of CCA1/LHY, but there is little description of its biochemical function. Here we show that TOC1 occupies specific genomic regions in the CCA1 and LHY promoters. Purified TOC1 binds directly to DNA through its CCT domain, which is similar to known DNA-binding domains. Chemical induction and transient overexpression of TOC1 in Arabidopsis seedlings cause repression of CCA1/LHY expression, demonstrating that TOC1 can repress direct targets, and mutation or deletion of the CCT domain prevents this repression showing that DNA-binding is necessary for TOC1 action. Furthermore, we use the Gal4/UAS system in Arabidopsis to show that TOC1 acts as a general transcriptional repressor, and that repression activity is in the pseudoreceiver domain of the protein. To identify the genes regulated by TOC1 on a genomic scale, we couple TOC1 chemical induction with microarray analysis and identify previously unexplored potential TOC1 targets and output pathways. Taken together, these results define a biochemical action for the core clock protein TOC1 and refine our perspective on how plant clocks function.