A role for the MYB transcription factor RVE8/LCL5

Most organisms have developed an internal timing mechanism or circadian clock that is able to generate 24-hour biological rhythms in synchronization with the diurnal environmental changes. Despite our increasing understanding of the molecular machinery underlying circadian clock function, a complete picture of the components and regulatory mechanisms governing the circadian system in Arabidopsis thaliana is still lacking. In a recent study, we have characterized the role of the MYB-like transcription factor REVEILLE8/LHY-CCA1-LIKE5 (RVE8/LCL5) within the Arabidopsis circadian clock. We have generated RVE8/LCL5 mutant and overexpressing plants and showed that similar to the MYB-like transcription factor CIRCADIAN CLOCK-ASSOCIATED1 (CCA1), RVE8/LCL5 binds to the promoter of key clock component TOC1 (Timing of CAB expression 1) and regulates its circadian expression. However, the mechanisms of RVE8/LCL5 and CCA1 circadian function seem to differ: while CCA1 represses TOC1 expression by facilitating a hypo-acetylated state of Histone H3, RVE8/LCL5 contributes to TOC1 expression by favouring H3 acetylation at the TOC1 locus. Although CCA1 has a more predominant role on this regulation, our results showing the opposing function of RVE8/LCL5 open interesting questions about the complex networks of transcriptional regulators and chromatin remodeling activities that need to be integrated in synergistic and antagonistic ways to generate the circadian periodicity.Peer reviewe