探究组蛋白乙酰化修饰介导OsWRKY77调控水稻旗叶衰老的机制

Rice is the main food crop of the developing world. However, the increase of yield is seriously restricted by flag leaf senescence in rice. Recent studies suggested that histone acetylation might be involved in leaf senescence, but the detailed molecular mechanisms are still not understood. In order to have a clear understanding of the mechanisms, this project will focus on the regulation mechanism of histone acetylation (H3K9ac) in rice flag leaf senescence. Previous studies showed that the expression of OsWRKY77 was significantly correlated with the abundance changes of histone acetylation (H3K9ac) at OsWRKY77 gene region during the senescence period of flag leaf, and the expression of OsHDT1 was increased at the later stage of senescence, which was contrary to H3K9ac enrichment and the expression pattern of OsWRKY77. For better understanding the molecular mechanisms underlying the histone acetylation-mediated regulation of OsWRKY77 transcription leading to leaf senescence, more investigations are required: to explore the role of OsWRKY77 during the senescence of flag leaves of rice; to examine how histone acetylation (H3K9ac) affects the OsWRKY77 transcription during aging; to investigate the relationship between OsHDT1 and H3K9ac at OsWRKY77 gene. The goal of this project is to elucidate the molecular mechanism of histone acetylation in regulating OsWRKY77 gene transcription.

水稻旗叶早衰严重制约水稻产量和谷粒质量的提高。近年来的研究暗示，核组蛋白乙酰化修饰参与调控叶片衰老，但其详细的分子机制并未阐明。为了探明这些机制，本项目重点关注水稻核组蛋白乙酰化修饰H3K9ac与水稻旗叶衰老的相关性及其调控机制。前期的研究表明，OsWRKY77与其基因的H3K9ac在旗叶衰老期的丰度变化显著相关，而且OsHDT1的表达在衰老后期上调，这与H3K9ac的富集和OsWRKY77的表达模式相反。基于这些研究基础，本项目重点进行以下研究：探索OsWRKY77在水稻旗叶衰老中的作用；调查组蛋白乙酰化如何调节OsWRKY77在衰老阶段的转录；探索OsHDT1与OsWRKY77的关系。以阐明组蛋白乙酰化调控OsWRKY77基因表达的分子机理，以及组蛋白乙酰化在水稻旗叶衰老过程中的作用。

剑叶作为水稻的主要功能叶，其早衰会严重限制水稻的产量。尽管许多调节叶片衰老的转录因子已被鉴定，但调节水稻剑叶衰老以响应环境条件的机制仍不清楚。本项目鉴定出两个促进水稻衰老的OsWRKY转录因子，并对其进行了深入研究。第一，证实OsWRKY77是核定位蛋白，其表达具有组织特异性，主要在叶尖、根尖、根茎连接处、以及叶鞘中表达。过表达OsWRKY77抑制植株的生长与发育，表现为植株矮化，结实率降低。ABA诱导OsWRKY77上调表达，不仅如此， OsWRKY77过表达株系相比野生型对外源ABA的施用更敏感，而且OsWRKY77的高表达促进了ABA诱导的叶片衰老。进一步研究显示，OsWRKY77可以通过调节ABA信号通路基因和合成通路基因来介导ABA诱导的叶片衰老。第二，OsWRKY14在水稻剑叶衰老发生后持续上调表达，同时在暗诱导的剑叶衰老期间，其转录水平迅速增加，表明OsWRKY14是一个剑叶衰老相关转录因子。与野生型相比，oswrky14敲除突变体在黑暗诱导衰老期间表现出延迟的叶片变黄和更高的叶绿素含量。茉莉酸甲酯处理诱导叶片快速黄化时，oswrky14的叶片比野生型的叶片保留更多叶绿素，表明OsWRKY14参与促进JA诱导的叶片衰老。此外，在黑暗诱导的条件下，JA合成基因OsAOS2在oswrky14叶片中的表达下调。这些结果表明，OsWRKY14通过JA介导的信号通路促进叶片衰老的发生和进展。总之，该研究结果拓展了对水稻剑叶衰老的分子机制的认识，也为培育抗衰老水稻新品种提供理论支撑。