我国科学家在PNAS发表水稻衰老调控分子机制

摘要 : 中科院遗传发育所植物基因组学国家重点实验室储成才研究组梁成真博士通过对一早衰突变体的研究，首次阐明了水稻叶片衰老的分子调控机制。这一发现可显著延缓水稻叶片衰老，延长灌浆时间，从而提高水稻的结实率和千粒重，最终使水稻产量得到显著提高。上述研究成果6月20日在线发表在《美国国家科学院院刊》上。

衰老是生物有机体发育的必经阶段，更是生命体命运走向的关键转折点。植物过早启动衰老进程会对植物正常的营养利用和发育产生不良影响。很多杂交水稻品种存在叶片早衰现象，严重阻碍产量，且破坏灌浆的形成，最终降低稻米品质。理论上推算，有早衰现象的水稻品种在正常生活周期中叶片衰老每推迟一天即可增产2%，生产实践上也可达到1%左右。因此，揭示植物衰老的分子调控机制是农业生产需要迫切解决的重大应用课题。

叶片衰老在很大程度上受植物发育年龄和体内信号因子的调节。脱落酸(ABA) 是植物五大激素之一，在植物衰老时，体内ABA含量急剧升高，被认为是一种重要的衰老促进激素。然而，水稻中ABA合成和信号传导相关基因的突变体并未表现出延迟衰老的表型。因此，人们一直困惑ABA是如何参与调控植物的衰老进程。

梁成真通过研究，发现了ABA介导植物衰老信号通路的重要成分OsNAP。OsNAP受到ABA的特异性诱导，通过直接调控叶绿素降解、营养再转运及其它衰老相关基因的表达调控叶片的衰老进程。这一研究成果不仅在理论上加深了人们对ABA在介导植物衰老机制上的理解，也为水稻、特别是杂交稻乃至其它作物生产上存在的后期早衰问题的解决提供了可能途径。

原文摘要：

OsNAP connects abscisic acid and leaf senescence by fine-tuning abscisic acid biosynthesis and directly targeting senescence-associated genes in rice

Chengzhen Liang, Yiqin Wang, Yana Zhu, Jiuyou Tang, Bin Hu, Linchuan Liu, Shujun Ou,Hongkai Wu, Xiaohong Sun, Jinfang Chu and Chengcai Chu

It has long been established that premature leaf senescence negatively impacts the yield stability of rice, but the underlying molecular mechanism driving this relationship remains largely unknown. Here, we identified a dominant premature leaf senescence mutant, prematurely senile 1 (ps1-D). PS1 encodes a plant-specific NAC (no apical meristem, Arabidopsis ATAF1/2, and cup-shaped cotyledon2) transcriptional activator, Oryza sativa NAC-like, activated by apetala3/pistillata (OsNAP). Overexpression of OsNAP significantly promoted senescence, whereas knockdown of OsNAP produced a marked delay of senescence, confirming the role of this gene in the development of rice senescence. OsNAP expression was tightly linked with the onset of leaf senescence in an age-dependent manner. Similarly, ChIP-PCR and yeast one-hybrid assays demonstrated that OsNAP positively regulates leaf senescence by directly targeting genes related to chlorophyll degradation and nutrient transport and other genes associated with senescence, suggesting that OsNAP is an ideal marker of senescence onset in rice. Further analysis determined that OsNAP is induced specifically by abscisic acid (ABA), whereas its expression is repressed in both aba1 and aba2, two ABA biosynthetic mutants. Moreover, ABA content is reduced significantly in ps1-D mutants, indicating a feedback repression of OsNAP on ABA biosynthesis. Our data suggest that OsNAP serves as an important link between ABA and leaf senescence. Additionally, reduced OsNAP expression leads to delayed leaf senescence and an extended grain-filling period, resulting in a 6.3% and 10.3% increase in the grain yield of two independent representative RNAi lines, respectively. Thus, fine-tuning OsNAP expression should be a useful strategy for improving rice yield in the future.

作者：科技日报

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