Functional implication of the MYB transcription factor RVE8/LCL5 in the circadian control of histone acetylation

Abstract

SUMMARYDespite our increasing understanding of the molecular determinants essential for circadian clock function, we still lack a complete picture of the mechanisms contributing to clock progression in plants. Here, we explore the role of REVEILLE8/LHY-CCA1-LIKE5 (RVE8/LCL5) within the Arabidopsis circadian system. RVE8/LCL5 encodes a MYB-like transcription factor similar to CIRCADIAN CLOCK-ASSOCIATED1 (CCA1) and ELONGATED HYPOCOTYL (LHY), which are essential regulators of the Arabidopsis circadian clock. Consistent with the sequence similarity, the rhythmic expression of RVE8/LCL5 shows a morning acrophase comparable to that of CCA1 and LHY. Plants mis-expressing RVE8/LCL5 display a variety of circadian phenotypes, including altered circadian gene expression and photoperiodic flowering time. Similar to CCA1, RVE8/LCL5 regulates the expression of the oscillator gene TOC1 (TIMING OF CAB EXPRESSION1) by associating with the TOC1 promoter and by modulating the pattern of histone 3 (H3) acetylation. However, the mechanisms of RVE8/ LCL5 and CCA1 activity in this regulation differ markedly. Indeed, the use of chromatin immunoprecipitation and pharmacological inhibition assays reveals that RVE8/LCL5 favours a hyper-acetylated state of H3 at the TOC1 promoter, which may facilitate the rising phase of TOC1. In contrast, CCA1 represses TOC1 expression by promoting histone deacetylation. Thus, despite the sequence homology and the similar morning phase of expression, RVE8/LCL5 and CCA1 have opposing regulatory functions within the Arabidopsis circadian clock, although CCA1 has a more predominant role. We propose that contrasting chromatin compaction and transcriptional modulation through the opposing activities of RVE8/LCL5 and CCA1 might provide a finetuning mechanism for precisely shaping the TOC1 circadian waveform in Arabidopsis.

Ordered changes in histone modifications at the core of the Arabidopsis circadian clock

“…Two MYB transcription factors antagonistically contribute to this regulation. At dawn, CCA1 represses TOC1 expression by promoting histone deacetylation, whereas REV-EILLE 8/LHY-CCA1-LIKE 5 acts as an activator and facilitates histone acetylation (31,32). A recent report has extended this analysis showing that CCA1 and LHY are also subjected to rhythmic changes in H3 acetylation and methylation (33).…”

Histone acetylation and the circadian clock

“…In a recent study, we have characterized the implication on the Arabidopsis circadian system of RVE8/LCL5, a MYB-like transcription factor with a high degree of sequence homology to CCA1. 6 By using RVE8/ LCL5 overexpressing and mutant plants, we found that RVE8/LCL5 binds to the TOC1 promoter and contributes to proper circadian expression of TOC1. Our studies also show that in contrast to CCA1, RVE8/LCL5 seems to favor H3 acetylation, most likely by antagonizing CCA1 the TOC1 locus are important for TOC1 circadian expression, 5 we next examined whether mis-expression of RVE8/LCL5 affected the pattern of H3 acetylation at the TOC1 promoter.…”

Systematic Identification of Functional Plant Modules through the Integration of Complementary Data Sources

“…However, the module also showed enrichment toward "circadian rhythm" and "long-day photoperiodism, flowering" (GO:0007623 and GO:0048574, respectively). These two predictions are particularly interesting, as the module contains LHY-CCA1-LIKE5 (LCL5), encoding a MYB family TF that was only known to be involved in response to hormone stimuli but has recently been experimentally assigned to both "photoperiodism, flowering" and "circadian rhythm" (Farinas and Mas, 2011). Next to the newly assigned MYB LCL5, the module contains two more MYB TF genes (REVEILLE1 [RVE1] and CIRCADIAN1 [CIR1]).…”