Positive and negative factors confer phase-specific circadian regulation of transcription in Arabidopsis

Plant Cell. 2005 Jul;17(7):1926-40. doi: 10.1105/tpc.105.033035. Epub 2005 May 27.

Abstract

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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 3' Flanking Region / genetics
  • 5' Flanking Region / genetics
  • Arabidopsis / genetics*
  • Arabidopsis Proteins / genetics
  • Biological Clocks / genetics
  • Circadian Rhythm / genetics*
  • DNA-Binding Proteins / genetics
  • Gene Expression Regulation, Plant / genetics*
  • Promoter Regions, Genetic / genetics
  • Regulatory Elements, Transcriptional / genetics*
  • Repressor Proteins / genetics
  • Transcription Factors / genetics

Substances

  • Arabidopsis Proteins
  • CCA1 protein, Arabidopsis
  • DNA-Binding Proteins
  • LHY protein, Arabidopsis
  • Repressor Proteins
  • Transcription Factors