Centre for Research in Agricultural Genomics (CRAG), Consortium CSIC-IRTA-UAB, C/Jordi Girona 18-26, 08034 Barcelona, Spain.
Plant J. 2011 Apr;66(2):318-29. doi: 10.1111/j.1365-313X.2011.04484.x. Epub 2011 Feb 16.
Despite 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 fine-tuning mechanism for precisely shaping the TOC1 circadian waveform in Arabidopsis.
尽管我们对生物钟功能所必需的分子决定因素有了越来越多的了解，但我们仍然缺乏对植物生物钟进展机制的完整认识。在这里，我们探索了 REVEILLE8/LHY-CCA1-LIKE5（RVE8/LCL5）在拟南芥生物钟系统中的作用。RVE8/LCL5 编码一种类似于 CIRCADIAN CLOCK-ASSOCIATED1（CCA1）和 ELONGATED HYPOCOTYL（LHY）的 MYB 样转录因子，它们是拟南芥生物钟的重要调节因子。与序列相似性一致，RVE8/LCL5 的节律表达显示出与 CCA1 和 LHY 相当的早晨高峰。过表达 RVE8/LCL5 的植物表现出多种生物钟表型，包括生物钟基因表达和光周期开花时间的改变。与 CCA1 相似，RVE8/LCL5 通过与 TOC1 启动子结合并调节组蛋白 3（H3）乙酰化模式来调节振荡器基因 TOC1（TIMING OF CAB EXPRESSION1）的表达。然而，RVE8/LCL5 和 CCA1 在这种调节中的活性机制明显不同。事实上，使用染色质免疫沉淀和药理学抑制测定法表明，RVE8/LCL5 有利于 TOC1 启动子处 H3 的高度乙酰化状态，这可能有利于 TOC1 的上升阶段。相比之下，CCA1 通过促进组蛋白去乙酰化来抑制 TOC1 的表达。因此，尽管具有序列同源性和相似的早晨表达相，但 RVE8/LCL5 和 CCA1 在拟南芥生物钟中具有相反的调节功能，尽管 CCA1 具有更主要的作用。我们提出，通过 RVE8/LCL5 和 CCA1 的相反活性来实现对比的染色质紧缩和转录调节可能为精确塑造拟南芥 TOC1 生物钟波形提供了一种微调机制。
