Positive and negative factors confer phase-specific circadian regulation of transcription in Arabidopsis.
The circadian clock exerts a major influence on transcriptional regulation in plants and other organisms. We have previously identified a motif called the evening element (EE) that is overrepresented in the promoters of evening-phased genes. Here, we demonstrate that multimerized EEs are necessary and sufficient to confer evening-phased circadian regulation. Although flanking sequences are not required for EE function, they can modulate EE activity. One flanking sequence, taken from the PSEUDORESPONSE REGULATOR 9 promoter, itself confers dawn-phased rhythms and has allowed us to define a new clock promoter motif (the morning element [ME]). Scanning mutagenesis reveals that both activators and repressors of gene expression act through the ME and EE. Although our experiments confirm that CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY) are likely to act as repressors via the EE, they also show that they have an unexpected positive effect on EE-mediated gene expression as well. We have identified a clock-regulated activity in plant extracts that binds specifically to the EE and has a phase consistent with it being an activator of expression through the EE. This activity is reduced in CCA1/LHY null plants, suggesting it may itself be part of a circadian feedback loop and perhaps explaining the reduction in EE activity in these double mutant plants.
Harmer
Stacey L
SL
Section of Plant Biology, University of California, Davis 95616, USA. slharmer@ucdavis.edu
Kay
Steve A
SA
D024509:3' Flanking Region / Q000235:genetics; D024506:5' Flanking Region / Q000235:genetics; D017360:Arabidopsis / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000235:genetics; D001683:Biological Clocks / Q000235:genetics; D002940:Circadian Rhythm / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics; D018506:Gene Expression Regulation, Plant / Q000235:genetics*; D011401:Promoter Regions, Genetic / Q000235:genetics; D050436:Regulatory Elements, Transcriptional / Q000235:genetics*; D012097:Repressor Proteins / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics
D029681:Arabidopsis Proteins; C114425:CCA1 protein, Arabidopsis; D004268:DNA-Binding Proteins; C113192:LHY protein, Arabidopsis; D012097:Repressor Proteins; D014157:Transcription Factors