REVEILLE8 and PSEUDO-REPONSE REGULATOR5 Form a Negative Feedback Loop within the Arabidopsis Circadian Clock

Abstract

Circadian rhythms provide organisms with an adaptive advantage, allowing them to regulate physiological and developmental events so that they occur at the most appropriate time of day. In plants, as in other eukaryotes, multiple transcriptional feedback loops are central to clock function. In one such feedback loop, the Myb-like transcription factors CCA1 and LHY directly repress expression of the pseudoresponse regulator TOC1 by binding to an evening element (EE) in the TOC1 promoter. Another key regulatory circuit involves CCA1 and LHY and the TOC1 homologs PRR5, PRR7, and PRR9. Purification of EE–binding proteins from plant extracts followed by mass spectrometry led to the identification of RVE8, a homolog of CCA1 and LHY. Similar to these well-known clock genes, expression of RVE8 is circadian-regulated with a dawn phase of expression, and RVE8 binds specifically to the EE. However, whereas cca1 and lhy mutants have short period phenotypes and overexpression of either gene causes arrhythmia, rve8 mutants have long-period and RVE8-OX plants have short-period phenotypes. Light input to the clock is normal in rve8, but temperature compensation (a hallmark of circadian rhythms) is perturbed. RVE8 binds to the promoters of both TOC1 and PRR5 in the subjective afternoon, but surprisingly only PRR5 expression is perturbed by overexpression of RVE8. Together, our data indicate that RVE8 promotes expression of a subset of EE–containing clock genes towards the end of the subjective day and forms a negative feedback loop with PRR5. Thus RVE8 and its homologs CCA1 and LHY function close to the circadian oscillator but act via distinct molecular mechanisms.

Time-dependent sequestration of RVE8 by LNK proteins shapes the diurnal oscillation of anthocyanin biosynthesis

“…The expression of most of these genes is controlled by the clock, with a rhythmic oscillatory pattern peaking around dawn under constant light conditions (LL) (SI Appendix, Fig. S3) in a similar trend to that of RVE8 (15,17). Intriguingly, the peak phase of expression for the anthocyanin-related genes appears to change under light/dark (LD) cycles, and in some instances, the waveforms displayed a double peak around zeitgeber time 4 and 12 (ZT4 and ZT12) with a clear decrease around midday (SI Appendix, Fig.…”

“…The single Myb-like transcription factor REVEILLE8/LHY-CCA1-LIKE5 (RVE8/LCL5) (15) antagonizes CCA1 repressing function in the regulation of Histone3 acetylation at TOC1 promoter (16). RVE8 overexpression and mutation affect not only circadian gene expression but other clock-regulated processes such as hypocotyl elongation and the photoperiodic regulation of flowering time (15,17). Analysis of lossof-function mutants of rve8 and its close homologs (rve4/rve6/rve8 triple mutants) showed a significant lengthening of the circadian period most likely through the decreased expression of eveningphased clock genes (18).…”

Quantitative Circadian Phosphoproteomic Analysis of Arabidopsis Reveals Extensive Clock Control of Key Components in Physiological, Metabolic, and Signaling Pathways

“…Very often rhythms in transcript levels result in concomitant oscillations in protein levels, usually with a phase delay of 2-3 h or more (16,139,140). However, some studies in other circadian systems have shown that up to 50% of the cycling proteome is not reflected in mRNA rhythms, indicating a significant degree of clock-mediated post-transcriptional control (34,36,139).…”

MYB-related transcription factors function as regulators of the circadian clock and anthocyanin biosynthesis in Arabidopsis

“…Transcription factors such as REVEILLE 2 (RVE2), RVE7, RVE8, and MYB HYPO-COTYL ELONGATION-RELATED (MYBH) ( Table 1) act on the circadian clock in ways similar to that of CCA1 and LHY1. 1,3,4,6,[9][10][11][12][13][14] The RVE7/EARLY-PHYTOCHROME-RESPONSIVE1 (EPR1) was found to be regulated by PHYTO-CHROME A and PHYTOCHROME B, and it functions as a component of the slave oscillator. 9 Additionally, MYBH/KUA1 expression is regulated by the circadian clock and this MYBH/ KUA1 transcription factor regulates cell expansion, hypocotyl elongation, and leaf senescence in the plant.…”