Overlapping and Distinct Roles of PRR7 and PRR9 in the Arabidopsis Circadian Clock

Abstract

The core mechanism of the circadian oscillators described to date rely on transcriptional negative feedback loops with a delay between the negative and the positive components . In plants, the first suggested regulatory loop involves the transcription factors CIRCADIAN CLOCK-ASSOCIATED 1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY) and the pseudo-response regulator TIMING OF CAB EXPRESSION 1 (TOC1/PRR1). TOC1 is a member of the Arabidopsis circadian-regulated PRR gene family . Analysis of single and double mutants in PRR7 and PRR9 indicates that these morning-expressed genes play a dual role in the circadian clock, being involved in the transmission of light signals to the clock and in the regulation of the central oscillator. Furthermore, CCA1 and LHY had a positive effect on PRR7 and PRR9 expression levels, indicating that they might form part of an additional regulatory feedback loop. We propose that the Arabidopsis circadian oscillator is composed of several interlocking positive and negative feedback loops, a feature of clock regulation that appears broadly conserved between plants, fungi, and animals.

Leaf Starch Turnover Occurs in Long Days and in Falling Light at the End of the Day

“…normal clock function is important for the timing of onset of starch degradation in continuous light, we compared starch accumulation patterns following transfer to continuous light in wild-type plants and clock mutants. The clock mutants were the short-period mutant cca1 lhy (Alabadí et al, 2002;Mizoguchi et al, 2002) and the long-period mutant prr7 prr9 (Farré et al, 2005;Salomé and McClung, 2005). These mutants are in the Ws-2 and Col-0 backgrounds, respectively.…”

PRR3 Is a Vascular Regulator of TOC1 Stability in theArabidopsisCircadian Clock

“…PRR single mutants were found to cause a mild effect on period length, whereas some double and triple mutant combinations result in a severe clock phenotype: the double mutant prr9 prr7 displayed a longer period than either of the single mutants, and the prr5 prr7 double mutant phenotype was reported to exhibit very short to arrhythmic oscillations that became further compromised in the prr9 prr7 prr5 triple mutant (Farre et al, 2005;Fujimori et al, 2005;Nakamichi et al, 2005aNakamichi et al, , 2005bSalome and McClung, 2005). Interestingly, combining the clock phenotype of the short-period prr5 mutation with the long-period prr9 mutation resulted in a wild-type period (Eriksson et al, 2003).…”

A Constitutively Active Allele of Phytochrome B Maintains Circadian Robustness in the Absence of Light

“…Although the relative effect of light on each core circadian component has not been systematically determined, several reports have identified transcripts that are acutely induced by light (Wang and Tobin, 1998;Ito et al, 2003;Locke et al, 2005). CIRCADIAN CLOCK ASSOCIATED1 (CCA1) and LATE ELON-GATED HYPOCOTYL (LHY) are morning-phased, light-inducible transcription factors that induce expression of PSEUDO-RESPONSE REGULATOR9 (PRR9; Schaffer et al, 1998;Wang and Tobin, 1998;Farré et al, 2005). PRR9, whose transcription is itself light induced (Ito et al, 2003;Jones et al, 2012), represses expression of CCA1 and LHY in partnership with the later-phased PRR7, PRR5, and TIMING OF CAB1 (TOC1; Matsushika et al, 2000;Nakamichi et al, 2010).…”