Plants are sessile organisms that have acquired highly plastic developmental strategies to adapt to the environment. Among these processes, the floral transition is essential to ensure reproductive success and is finely regulated by several internal and external genetic networks. The photoperiodic pathway, which controls plant response to day length, is one of the most important pathways controlling flowering. In photoperiodic flowering, () is the central gene activating the expression of the florigen () in the leaves at the end of a long day. The circadian clock strongly regulates expression. However, to date, no evidence has been reported regarding a feedback loop from the photoperiod pathway back to the circadian clock. Using transcriptional networks, we have identified relevant network motifs regulating the interplay between the circadian clock and the photoperiod pathway. Gene expression, chromatin immunoprecipitation experiments, and phenotypic analysis allowed us to elucidate the role of CO over the circadian clock. Plants with altered expression showed a different internal clock period, measured by daily leaf rhythmic movements. We showed that CO upregulates the expression of key genes related to the circadian clock, such as , , , and , at the end of a long day by binding to specific sites on their promoters. Moreover, a high number of PRR5-repressed target genes are upregulated by CO, and this could explain the phase transition promoted by CO. The CO-PRR5 complex interacts with the bZIP transcription factor HY5 and helps to localize the complex in the promoters of clock genes. Taken together, our results indicate that there may be a feedback loop in which CO communicates back to the circadian clock, providing seasonal information to the circadian system.

中文翻译：

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CONSTANS 改变拟南芥的生物钟


植物是无柄生物，具有高度可塑性的发育策略来适应环境。在这些过程中，花转变对于确保繁殖成功至关重要，并受到多个内部和外部遗传网络的精细调控。光周期途径控制植物对日长的反应，是控制开花的最重要途径之一。在光周期开花中，() 是在漫长的一天结束时激活叶子中成花素 () 表达的中心基因。生物钟强烈调节表达。然而，迄今为止，还没有关于从光周期途径回到生物钟的反馈回路的证据报道。使用转录网络，我们已经确定了调节生物钟和光周期途径之间相互作用的相关网络基序。基因表达、染色质免疫沉淀实验和表型分析使我们能够阐明 CO 对生物钟的作用。表达改变的植物表现出不同的内部时钟周期，通过每日叶子的节律运动来测量。我们发现，CO 通过与启动子上的特定位点结合，在漫长的一天结束时上调与生物钟相关的关键基因的表达，例如 、 、 和 。此外，大量 PRR5 抑制的靶基因被 CO 上调，这可以解释 CO 促进的相变。CO-PRR5 复合物与 bZIP 转录因子 HY5 相互作用，有助于将该复合物定位在时钟启动子中基因。综上所述，我们的结果表明，可能存在一个反馈循环，其中二氧化碳与生物钟进行通讯，为昼夜节律系统提供季节性信息。