泛素介导的26S蛋白酶体降解途径在植物干旱胁迫反应和ABA信号转导过程中起重要作用。底物蛋白的泛素化需要泛素耦合酶E2和泛素连接酶E3的协同作用，但植物中大多数E2的功能和调节机制仍然未知。本项目的前期工作表明，泛素耦合酶UBC27通过正调控ABA信号来调节植物耐旱性，并且筛选到UBC27的互作蛋白，其中包括RING类型E3和ABA信号的负调控因子ABI1。进一步的研究证明UBC27影响ABI1的降解并且其功能依赖ABI1。本项目将通过生物化学、分子细胞生物学和遗传学等方法分析UBC27-RING-ABI1之间的相互关系，揭示UBC27和RING对ABI1泛素化和蛋白稳定性的影响、以及调控干旱胁迫和ABA信号的分子机制。期望通过系统的机理研究，拓展人们对植物中E2功能和作用机制的了解，加深对泛素化过程调控植物耐旱性的分子机制的认识，同时为农作物改良及干旱育种提供理论依据。

Plants are frequently subjected to various stresses, such as drought and high salinity stresses during their life cycles, in which ABA, as a signal molecule, mediates plant tolerance. Ubiquitination of proteins is involved in many steps in ABA signaling pathway, from perception to action, which plays key roles in plant adaptation to drought stress. An increasing number of E3 ligases and other ubiquitin-proteasome system components involved in ABA signaling pathway are being identified, indicating the significant role of ubiquitination in ABA signaling. Ubiquitination requires the coordination of E2-ubiquitin conjugating enzyme and E3 ligase, however, the functions and related regulation mechanisms of most E2s in plants remain unknown. In our previous work, we found that an E2, UBC27, positively regulated plant drought tolerance and ABA signaling pathway. Furthermore, we identified a RING type E3 ligase and ABA co-receptor ABI1 as UBC27 interaction proteins through immunoprecipitation-mass spectrometry analysis. The interaction between UBC27 and ABI1 was further confirmed through luciferase complementation assay and co-immunoprecipitation assay. Meanwhile, we found that the function of UBC27 was dependent on ABI1 and UBC27 affected ABI1 ubiquitination and degradation. In this proposal, we are going to focus on the functions and genetic interactions of UBC27-RING-ABI1 in ABA signaling pathway and regulation mechanisms of UBC27 and RING in plant drought tolerance using biochemical, genetic and molecular methods. The results obtained in this proposal will build foundation for further functional and mechanical characterization of E2 in plants, provide further understanding of ubiquitination system in plant drought tolerance, and provide new strategies to improve drought tolerance of crop plants.