Circadian clocks are the biological time keeping systems that coordinate genetic, metabolic, and physiological behaviors with the external day-night cycle. Previous studies have suggested possible molecular mechanisms for the circadian clock in Arabidopsis thaliana (Arabidopsis), but there might be additional mechanisms that have been hidden due to genetic redundancy. A clock reporter line of Arabidopsis was screened against the 10,000 chemicals in the Maybridge Hitfinder10K chemical library, and a structure-activity relationship study of hit compounds was conducted. Clock mutants were treated with two of the small molecules to gain insight into their mode of action. The screening identified 5-(3,4-dichlorophenyl)-1-phenyl-1,7-dihydro-4H- pyrazolo[3,4-d]pyrimidine-4,6(5H)-dione (TU-892) as a period lengthening molecule. From a structure-activity relationship study, we found that a molecule possessing 2,4-dichlorophenyl instead of a 3,4-dichlorophenyl group (TU-923) had period shortening activity. The period shortening activity of TU-923 was reversed to a lengthening activity in double mutants lacking PSEUDO-RESPONSE REGULATOR 9 (PRR9) and PRR7 (prr9-10 prr7-11). Our study provides a unique small molecule pair that regulates the pace of the clock in opposite ways, likely by targeting unknown factors. Small differences at the atomic level can reverse the period tuning activities. PRR9 and PRR7 are essential for the activity of TU-923 in period shortening.

中文翻译：

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独特的小分子对控制植物生物钟

昼夜节律生物钟是一种生物计时系统，可与外部昼夜周期协调遗传，代谢和生理行为。先前的研究表明拟南芥（Arabidopsis）昼夜节律的可能分子机制，但可能由于遗传冗余而隐藏了其他机制。针对Maybridge Hitfinder10K化学文库中的10,000种化学物质筛选了​​拟南芥的时钟报告基因系，并进行了对命中化合物的构效关系研究。用两个小分子处理Clock突变体，以了解其作用方式。筛选确定5-（3,4-二氯苯基）-1-苯基-1,7-二氢-4H-吡唑并[3,4-d]嘧啶-4,6（5H）-二酮（TU-892）为周期延长分子。通过结构-活性关系研究，我们发现具有2,4-二氯苯基而不是3,4-二氯苯基（TU-923）的分子具有缩短周期的活性。在缺少PSEUDO-RESPONSE REGULATOR 9（PRR9）和PRR7（prr9-10 prr7-11）的双突变体中，TU-923的周期缩短活性被逆转为延长活性。我们的研究提供了一个独特的小分子对，可以通过靶向未知因素以相反的方式调节时钟的速度。原子级别的微小差异可以使周期调整活动逆转。PRR9和PRR7对于TU-923缩短周期至关重要。在缺少PSEUDO-RESPONSE REGULATOR 9（PRR9）和PRR7（prr9-10 prr7-11）的双突变体中，TU-923的周期缩短活性被逆转为延长活性。我们的研究提供了一个独特的小分子对，可以通过靶向未知因素以相反的方式调节时钟的速度。原子级别的微小差异可以使周期调整活动逆转。PRR9和PRR7对于TU-923缩短周期至关重要。在缺少PSEUDO-RESPONSE REGULATOR 9（PRR9）和PRR7（prr9-10 prr7-11）的双突变体中，TU-923的周期缩短活性被逆转为延长活性。我们的研究提供了一个独特的小分子对，可以通过靶向未知因素以相反的方式调节时钟的速度。原子级别的微小差异可能会使周期调整活动逆转。PRR9和PRR7对于TU-923缩短周期至关重要。