生物钟对植物叶片衰老的影响

Leaf senescence, the final stage of leaf development, actively destabilizes intracellular organelles, including decomposition of macromolecules, to relocate nutrients into developing tissues or storage organs. Senescence limits crop yields and plant biomass production. Our previously work identified the role of PIF4 on leaf senescence which can activate chlorophyll degradation and ethylene biosynthesis. Interestingly, the transcriptional and translational levels of PIF4 are controlled by circadian clock. Moreover, several senescence regulated genes are also regulated by circadian clock (for example, GLK2, ORE1). Circadian rhythms are directed by day-night cycles so that organisms can synchronize external conditions with internal metabolism to allow temporal separation of incompatible metabolic events. Dysregulation of clock control in higher plants has been shown to impede numerous regulatory pathways, but the molecular mechanism to connect circadian rhythms to senescence is yet to be clarified. So we propose to address this question using circadian mutants in the setting of age-induced and ethylene-induced leaf senescence, to provide scientific basis to overcome senescence-related loss in agriculture.

植物叶片衰老是叶片发育的最后阶段，细胞内器官降解，大分子等营养物质转运到幼嫩组织或者种子中去，衰老的进程影响了作物的产量和生物量。申请者前期研究发现光敏色素互作因子PIF4通过调控叶绿体的完整性及乙烯合成而促进了叶片衰老，PIF4本身的转录及蛋白质水平都受到生物钟的严格调控，衰老调控基因也偏向于受生物钟的调控（如GLK2，ORE1等）。生物钟是植物经过长期进化形成的内源性的调控系统，参与多个植物体的新陈代谢、生长发育过程，使得植物体与外界环境达到时间和空间上的同步，极大地增强植物环境适应性和竞争能力。本申请项目将检测生物钟突变体对年龄诱导及乙烯诱导衰老的影响，揭示生物钟影响叶片衰老进程的分子机制，为今后利用生物钟延缓衰老来提高作物产量提供研究基础和理论依据。

生物钟是植物接受环境信号后形成的内源振荡体系，调节植物各项生理代谢活动在最合适的时间发生，最终增强植物环境适应性。在拟南芥中很多生物钟核心基因已经被鉴定，包括CIRCADIAN CLOCK-ASSOCIATED 1 (CCA1) 、 LATE ELONGATED HYPOCOTYL (LHY)， EARLY FLOWERING 3 (ELF3)等。植物叶片衰老的时间和进程会影响农作物的产量和品质。我们通过检测生物钟相关基因突变体的衰老表型，发现多个生物钟突变体会加速年龄诱导的叶片衰老。通过生信分析，发现多数衰老调控基因的启动子上富集了CCA1的结合区域，其中包括促进衰老的基因ORE1和维持叶绿体活性的基因GLK2。我们利用生化及遗传实验证明CCA1可以直接结合在ORE1和GLK2基因启动子上，并激活GLK2、抑制ORE1的表达，以此抵抗叶片衰老。随着年龄增加，CCA1的表达量和振幅下降，可能在该阶段减弱了对衰老的抑制。我们的研究结果揭示了年龄依赖的生物钟核心基因CCA1调控叶片衰老的分子机制。