水稻衰老分子调控机理解析及遗传网络的构建

Leaf senescence is an integral part of the final stages of plant development that is controlled by a fine-tuned, complex regulatory network. Leaf senescence facilitates both hydrolysis and the recycling of nutrients from source to sink tissues in order to increase reproductive success. Thus, plant senescence is not a passive process, rather a developmentally programmed procedure that has a strong adaptive advantage. However, premature leaf senescence is one of the primary factors that influence the yield stability of rice, particularly in hybrid rice production. Compared to the model plant Arabidopsis, the identification of key senescence associated genes (SAGs) in rice and their cognate molecular regulatory mechanisms has only just begun. Similarly, the majority of the SAGs identified to date have only been shown to be involved in chlorophyll breakdown and degradation. Given that there is likely to be a significant level of gene redundancy in the complex pathways integral to the senescence process, it is difficult to identify the key regulators of leaf senescence using loss-of-function mutants. In order to uncover key genes controlling leaf senescence in rice, we have made a large-scale screening of our gain-of-function mutant population, and more than 273 independent lines with altered senescence phenotypes were identified. ps1-D is one of the gain-of-function mutants, which demonstrated obvious premature leaf senescence phenotype. PS1 was tightly linked with the onset of leaf senescence in an age-dependent manner, and functions as an important linker between ABA and leaf senescence in rice. Therefore, we postulated that PS1 plays a key role in initiation of leaf senescence. This project will give further detailed analysis of senescence process be based on the previous studies by Y2H, microarray analysis and ChIP-seq to determine the position of PS1 in the network of rice senescence control. In addition, genome-wide association studies (GWAS) will be carried out for senescence agronomic trait with rice minicore collection. The results obtained will help us to get further understanding on the complex network of senescence regulation in rice.

植物衰老是一受到复杂而精细调控的正常发育过程，对生命的延续和进化都具有积极意义。然而，早衰会导致植物叶片过早丧失光合同化功能，减少籽粒干物质的积累，严重影响作物的产量和品质。因此，揭示作物衰老的分子调控机制具有重要的理论和实践意义。在过去几年中，我们通过对水稻激活标签突变体库的高通量筛选，获得273份早衰突变体，其中ps1-D是最具代表性的显性激活突变体。研究发现，PS1不仅在年龄介导的衰老中发挥关键调控作用，在ABA介导的衰老中也发挥重要作用，因此，PS1可能是衰老信号通路中非常重要的节点基因。本项目拟以PS1为核心，通过酵母双杂、转录组和ChIP等手段寻找PS1下游靶基因，同时利用筛选获得的其它突变体，结合水稻核心种质重测序与衰老性状的关联分析，克隆鉴定新的衰老调控关键位点，利用遗传学、分子生物学、基因组学及生物信息学等手段，研究水稻衰老调控的分子机制，进而构建水稻衰老的分子调控网络。

植物衰老是一受到复杂而精细调控的正常发育过程，对生命的延续和进化具有积极意义。然而，早衰会导致作物叶片过早丧失光合同化功能，减少籽粒干物质积累，严重影响作物产量和品质。因此，揭示作物衰老的分子调控机制具有重要的理论和实践意义。我们通过对T-DNA突变体库进行系统筛选，鉴定了一个早衰突变体材料yellow1，并通过图位克隆获得1个全新的调控ABA合成的关键基因，并初步鉴定其调控机制，证明其在调控种子休眠和衰老中起关键作用。完成了美国USDA水稻微核心种质材料的重测序，通过对水稻不同时期的叶绿素含量进行动态检测的GWAS分析，鉴定到一个非常明显的调控水稻衰老的调控因子OsLES3，诠释了OsLES1在叶片衰老中发挥作用的初步模式。此外，通过对自然生长水稻旗叶开花后不同时间节点大规模转录组分析和基因共表达网络的构建，发现衰老调控网络的一些关键途径（营养再转运、叶绿素代谢及抗氧化胁迫等）和关键节点。发现ABA、GA、褪黑素等激素在水稻叶片衰老和细胞死亡中起重要作用。有意思的是，褪黑素通过调节多种类型的转录因子（包括bZIP、NAC和MYB-TFs）的表达，介导过氧化氢清除酶编码基因的表达或通过TFs-DREBs-HSFs转录级联调节其转录，提高植物抗氧化胁迫能力。外源褪黑素在黑暗和盐的条件下显著抑制细胞内的过氧化氢水平，导致延迟叶片衰老，增强盐胁迫耐受性。这些成果为理解水稻衰老调控网络奠定了坚实基础。通过项目资助，发表高水平SCI文章8篇，申请发明专利2项，培养了4名核心骨干人才，其中1人获得中组部“万人计划”领军人才1人（储成才）；1人获得国家自然科学基金优青资助1人（胡斌）并聘任为青年研究员（胡斌）；2人获得副高级职称，其中梁成真博士获聘中国农业科学院生物技术所副研究员，高少培博士获聘中国农业大学农学院副教授，为我国相关研究奠定了人才基础。