Emerging design principles in the Arabidopsis circadian clock

• The core loop of the plant circadian clock comprises three repression steps.
• LHY/CCA1 represses components of the EC, the EC represses TOC1 and TOC1 represses LHY/CCA1.
• Expression of the PRR genes in sequential waves acts to maintain repression of LHY/CCA1 until dawn.
• Temporal separation of the PRR waves may be mediated by backward inhibition.
• An evening-specific loop is meditated by the EC regulating expression of its protein components.

Recent experimental advances have enabled the identification of direct regulatory targets for transcription factors. Application of these techniques to the circadian regulatory network in Arabidopsis has uncovered a number of discrepancies within established models as well as novel regulatory interactions. This review integrates these new findings and discusses the functional implications of the revised transcriptional network for the oscillatory mechanism of the clock.