水稻组蛋白H2B单泛素化修饰参与干旱应答调控的分子机制

Drought is one of the main abiotic stresses that constrain plant growth and crop yield. In China, the rice production depends on a large quantity of water it has been frequently suffered from drought stress especially at the reproductive stage. Rice is a model species for cereal crops, therefore, revealing the molecular mechanism of the drought response can provide new strategies for genetic improvement of cereal crops. We found that OsHUB1 and OsHUB2, two key proteins responsible for the monoubiquitation of histone 2B (H2B), can interact with MODD, which has been identified as a significant regulatory protein in ABA signaling pathway in our previous study, to regulate the drought and ABA stress responses. So far, there are few reports about the connection between the monoubiquitation of H2B and the response of abiotic stresses. This project will conduct an in-depth investigation on the interactions between OsHUB1 /OsHUB2 and other key regulators (such as MODD and /or OsbZIP46) in drought response and ABA signaling pathway. The molecular mechanism on the interactions will help understanding the fine regulation of drought responses. Meanwhile, we will detect the genome-wide profiles of histone-monoubiquitination in rice under drought stress and ABA treatment. We will further explore the genetic variation of key genes in the regulation of histone monoubiquitation. This project has important significance not only in revealing the molecular mechanisms of drought response regulation, but also in discovering new genes or mechanisms for crop genetic improvement in epigenetic regulation.

干旱是限制植物生长和影响农作物产量的主要非生物逆境之一。我国水稻生产不仅用水量大，而且生长后期频繁遭受区域性旱灾。水稻作为禾谷类作物的模式物种，揭示其干旱应答调控的分子机理，可为作物抗逆遗传改良提供理论指导。我们发现水稻中负责组蛋白H2B单泛素化修饰的两个重要蛋白OsHUB1和OsHUB2与ABA信号传导途径中重要调控蛋白MODD互作并调控干旱应答。到目前为止，组蛋白单泛素化修饰是否参与植物非生物逆境应答调控还未见报道。本项目将系统深入地研究OsHUB1和OsHUB2如何与ABA和干旱应答调控途径中的关键蛋白（如MODD和bZIP转录因子）相互作用，从而精细调控干旱应答，同时在全基因组水平研究组蛋白单泛素化修饰与干旱应答和ABA信号之间的关系，并进一步发掘组蛋白单泛素化相关基因的的遗传变异，探索水稻抗旱遗传改良新途径。

研究水稻的抗旱调控机制可以为水稻抗旱遗传改良提供新的思路，同时有助于认识植物逆境应答与适应的分子机制。项目前期工作发现水稻中负责组蛋白H2B单泛素化修饰的两个重要蛋白OsHUB1和OsHUB2与ABA信号传导途径中的重要调控蛋白MODD互作。本项目综合各种分析技术与方法，揭示了OsHUB1和OsHUB2参与水稻干旱应答的调控机理。主要研究结果包括：1）超量表达OsHUB2可以显著提高水稻对ABA的敏感性和干旱的抗性，也可以提高部分OsbZIP46靶基因的组蛋白H2B单泛素化（H2Bub1）修饰水平，而突变OsHUB2则可以降低部分OsbZIP46靶基因的H2Bub1修饰水平；2）OsHUB2介导的H2Bub1修饰受到ABA处理和干旱处理的诱导，中度干旱处理后H2Bub1修饰发生变化的基因大多参与干旱应答，并且约四分之一是OsbZIP46的靶基因；3）在干旱胁迫过程中H2Bub1修饰存在动态变化，重度干旱胁迫条件下的H2Bub1修饰程度有所下降；4）MODD对H2Bub1修饰存在负调控，在干旱胁迫过程中OsHUB2与MODD-OsOTLD1的共同作用导致H2Bub1的动态修饰并精细调控OsbZIP46的转录活性。另外，研究中还发现在水稻干旱胁迫条件下，组蛋白修饰H3K4me3可以协同OsbZIP23转录因子调控OsbZIP23靶基因的表达，初步揭示了表观遗传调控与转录调控之间的相互作用机制。本研究为全面地揭示干旱应答调控的分子机理提供了理论基础，为水稻抗逆遗传改良提供了新技术新方法。

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