MYB transcription factors in the Arabidopsis circadian clock

The LATE ELONGATED HYPOCOTYL (LHY) and CIRCADIAN CLOCK ASSOCIATED (CCA1) genes encode closely related MYB transcription factors, which regulate circadian rhythms in Arabidopsis. LHY and CCA1 verify some of the properties of oscillator components, since (i) expression of their transcripts and protein exhibits circadian oscillations; (ii) their constitutive expression abolishes overt rhythmicity and (iii) they function as components of a negative transcriptional feedback loop. LHY and CCA1 have been proposed to function in conjunction with the pseudo response regulator TOC1, as components of the circadian oscillator. The regulation of their respective transcripts and protein levels in response to light signals suggests that these proteins may also mediate the regulation of circadian rhythms by light. This review discusses experimental evidence for these hypotheses.