PSEUDO-RESPONSE REGULATORS 9, 7, and 5 Are Transcriptional Repressors in the Arabidopsis Circadian Clock  

Abstract

An interlocking transcriptional-translational feedback loop of clock-associated genes is thought to be the central oscillator of the circadian clock in plants. TIMING OF CAB EXPRESSION1 (also called PSEUDO-RESPONSE REGULATOR1 [PRR1]) and two MYB transcription factors, CIRCADIAN CLOCK ASSOCIATED1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY), play pivotal roles in the loop. Genetic studies have suggested that PRR9, PRR7, and PRR5 also act within or close to the loop; however, their molecular functions remain unknown. Here, we demonstrate that PRR9, PRR7, and PRR5 act as transcriptional repressors of CCA1 and LHY. PRR9, PRR7, and PRR5 each suppress CCA1 and LHY promoter activities and confer transcriptional repressor activity to a heterologous DNA binding protein in a transient reporter assay. Using a glucocorticoid-induced PRR5-GR (glucorticoid receptor) construct, we found that PRR5 directly downregulates CCA1 and LHY expression. Furthermore, PRR9, PRR7, and PRR5 associate with the CCA1 and LHY promoters in vivo, coincident with the timing of decreased CCA1 and LHY expression. These results suggest that the repressor activities of PRR9, PRR7, and PRR5 on the CCA1 and LHY promoter regions constitute the molecular mechanism that accounts for the role of these proteins in the feedback loop of the circadian clock.

PSEUDO RESPONSE REGULATORs stabilize CONSTANS protein to promote flowering in response to day length

“…SUC2 :: HA:CO fkf1‐2 was generated by genetic crossing. TMG , pPRR 5:: PRR5:GFP , pPRR7 :: FLAG:PRR7:GFP , and pPRR9 :: FLAG:PRR9:GFP plants have been previously described (Mas et al , 2003a; Fujiwara et al , 2008; Nakamichi et al , 2010). For plasmid construction of pCO :: HA:CO , 35S promoter in the pAlligator2 vector was replaced by 2.5 kb CO promoter.…”

“…The abundance of their transcripts and proteins exhibit circadian rhythms, and under diurnal conditions, they peak in expression sequentially at 2–3 h intervals during the light period in the order PRR9 , PRR7 , PRR5 , PRR3 , and TOC1 (Matsushika et al , 2000; Fujiwara et al , 2008). PRR9, PRR7, PRR5, and TOC1 proteins are degraded during the night, so they mainly accumulate during the day when they repress transcription of genes encoding other clock components such as LATE ELONGATED HYPOCOTYL (LHY) and CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) (Mas et al , 2003b; Farré & Kay, 2007; Ito et al , 2007; Kiba et al , 2007; Nakamichi et al , 2010; Huang et al , 2012). Mutations in the PRR genes also delay flowering under LDs (Nakamichi et al , 2005; Ito et al , 2008), but double or triple mutants exhibit much stronger phenotypes suggesting functional redundancy between the genes (Nakamichi et al , 2005, p. 549; Ito et al , 2008).…”

Abiotic stress and the plant circadian clock

“…In a three-loop model, [20][21][22] besides their described role in the core oscillator, CCA1 and LHY also participate in a morning loop to induce the expression of the PSEUDO RESPONSE REGULATOR 7 and 9 (PRR7 and PPR9), whose encoded proteins in turn bind and repress the transcription of the formers. 23 A so-called evening loop places TOC1 as a repressor of an unidentified 'Y' component, which feeds back by inducing TOC1 expression. GIGANTEA (GI) was proposed to be the Y component, but this factor only partially fulfils this role.…”

Blue Light- and Low Temperature-Regulated COR27 and COR28 Play Roles in the Arabidopsis Circadian Clock

“…CCA1 and LHY also repress transcription of EARLY FLOWERING3 (ELF3),ELF4,LUXARRHYTHMO(LUX;alsoknownasPHYTOCLOCK1), PRR5, and GIGANTEA (GI), and they all positively regulate expression of CCA1 and LHY except PRR5 (Hazen et al, 2005;Kikis et al, 2005;Onai and Ishiura, 2005;Kamioka et al, 2016). In addition, CCA1 and LHY promote transcription of two TOC1 homologs, PRR7 and PRR9, as they in turn, repress expression of CCA1 and LHY (Farré et al, 2005;Nakamichi et al, 2010).…”