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

Mar 18, 2010The Plant cell

Pseudo-Response Regulators 9, 7, and 5 act as gene repressors in the plant's internal daily clock

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Abstract

PRR9, PRR7, and PRR5 may function as transcriptional repressors of CCA1 and LHY in the plant circadian clock.

PRR9, PRR7, and PRR5 suppress the activity of CCA1 and LHY promoters.
These proteins confer transcriptional repressor activity in a transient reporter assay.
PRR5 directly downregulates CCA1 and LHY expression using a glucocorticoid-induced construct.
PRR9, PRR7, and PRR5 associate with the CCA1 and LHY promoters in living plants.
The timing of this association corresponds with decreased expression of CCA1 and LHY.

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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.

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

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