A small molecule modulator affecting clock-associated PSEUDO-RESPONSE REGULATOR 7 amount.

Circadian clocks are biological time-keeping systems that coordinate genetic, metabolic, and physiological behaviors with the external day-night cycle. The clock in plants relies on the transcriptional-translational feedback loops (TTFL), consisting of transcription factors including PSUEDO-RESPONSE REGULATOR (PRR) proteins, plant-lineage specific transcriptional repressors. Here, we report that a novel synthetic small molecule modulator, 5-(3,4-dichlorophenyl)-1-phenyl-1,7-dihydro-4H-pyrazolo[3,4-d]pyrimidine-4,6(5H)-dione (TU-892), affects PRR7 protein amount. A clock reporter line of Arabidopsis was screened against the 10,000 small molecules in the Maybridge Hitfinder10K chemical library. This screening found TU-892 as a period-lengthening molecule. Gene expression analyses showed that TU-892 treatment upregulates CIRCADIAN CLOCK-ASSOCIATED 1 (CCA1) mRNA expression. TU-892 treatment reduced the amount of PRR7 protein, one of the transcriptional repressors of CCA1. Other PRR proteins including TIMING OF CAB EXPRESSION 1 (TOC1) were altered less by TU-892 treatment. TU-892-dependent CCA1 upregulation was attenuated in mutants impaired PRR7. Collectively, TU-892 is a novel type of clock modulator that reduces the levels of PRR7 protein.