Data_Sheet_1_Arabidopsis FHY3 and FAR1 Function in Age Gating of Leaf Senescence.pdf

Leaf senescence is the terminal stage of leaf development. Both light and the plant hormone ethylene play important roles in regulating leaf senescence. However, how they coordinately regulate leaf senescence during leaf development remains largely unclear. In this study, we show that FHY3 and FAR1, two homologous proteins essential for phytochrome A-mediated light signaling, physically interact with and repress the DNA binding activity of EIN3 (a key transcription factor essential for ethylene signaling) and PIF5 (a bHLH transcription factor negatively regulating light signaling), and interfere with their DNA binding to the promoter of ORE1, which encodes a key NAC transcription factor promoting leaf senescence. In addition, we show that FHY3, PIF5, and EIN3 form a tri-protein complex(es) and that they coordinately regulate the progression of leaf senescence. We show that during aging or under dark conditions, accumulation of FHY3 protein decreases, thus lifting its repression on DNA binding of EIN3 and PIF5, leading to the increase of ORE1 expression and onset of leaf senescence. Our combined results suggest that FHY3 and FAR1 act in an age gating mechanism to prevent precocious leaf senescence by integrating light and ethylene signaling with developmental aging.

叶片衰老是叶片发育的终末阶段。光与植物激素乙烯均在调控叶片衰老的过程中发挥关键作用，然而二者如何协同调控叶片发育进程中的叶片衰老，目前仍尚未完全阐明。本研究发现，参与光敏色素A（phytochrome A）介导的光信号通路的两个同源蛋白FHY3与FAR1，可与乙烯信号通路核心转录因子EIN3以及负调控光信号通路的碱性螺旋-环-螺旋转录因子（bHLH）PIF5发生物理互作，并抑制二者的DNA结合活性，同时干扰它们与编码促进叶片衰老的核心NAC类转录因子的ORE1基因启动子的结合。此外，本研究证实FHY3、PIF5与EIN3可形成三聚蛋白复合体，并协同调控叶片衰老进程。研究还发现，在植株自然衰老或黑暗培养条件下，FHY3蛋白的积累量会下降，从而解除其对EIN3与PIF5 DNA结合活性的抑制，最终导致ORE1基因表达水平升高并引发叶片衰老。综合以上实验结果，本研究表明FHY3与FAR1通过整合光信号、乙烯信号与发育衰老进程，构建年龄门控机制以防止叶片过早衰老。