乙烯促进两个F-box蛋白EBF1/EBF2降解的调控机理研究

Ethylene plays essential roles in development processes and response to biotic and abiotic stresses in plants. Based on molecular genetic studies, a relative schematic view of ethylene signaling pathway had been established. Recently, we revealed that ethylene-induced stabilization of EIN3/EIL1 is mediated by proteasomal degradation of two F-Box EBF1/EBF2 that requires EIN2, a central component in ethylene signaling pathway in Arabidopsis, and that the transcription activity of EIN3/EIL1 is thus been stimulated. How ethylene induced EBF1/EBF2 degradation remains to be answered. In this research proposal, a combination of biochemistry, molecular biology and genetic studies will be utilized to elucidate the mechanism of how ethylene induced EBF1/EBF2 degradation. The specific aims of this proposol include: 1) Identifying E3 ligase responsible for EBF1/EBF2 degradation; 2) Elucidating the regulatory functions of CSN in EBF1/EBF2 and EIN3/EIL1 degradation. This study would provide further insights into how plants respond to ethylene gas in molecular details.

乙烯在植物生长发育以及应对生物和非生物胁迫方面起重要作用。对拟南芥的分子遗传学研究已勾画出乙烯信号转导途径的大致轮廓。我们最近的研究发现乙烯通过诱导两个F-box蛋白EBF1/EBF2降解来促进转录因子EIN3/EIL1的蛋白稳定，进而激活EIN3/EIL1调控的基因表达，该过程依赖于乙烯信号途径的中间组分EIN2（An et al., Plant Cell, 2010）。接下来的问题是乙烯如何调控了EBF1/EBF2的蛋白降解？在此申请项目中，我们将结合生物化学、分子生物学和遗传学方法，深入研究乙烯调控EBF1/EBF2蛋白降解的分子机制。具体内容包括：1）寻找负责EBF1/EBF2蛋白降解的E3 ligase；2）研究CSN在EBF1/EBF2和EIN3/EIL1蛋白降解中的作用机制和调控方式。通过上述两方面研究，为阐明乙烯气体的作用机制奠定基础。

乙烯是一种简单的气态植物激素，在植物的生长发育以及响应生物、非生物胁迫的过程中起着重要作用。近年来乙烯的研究重点集中在乙烯调控植物各种生理生化反应的信号转导机理方面。本研究中我们对乙烯反应途径中EBF1/2被调控机制以及其调控底物EIN3的机制进行了如下补充：1）RING finger E3泛素连接酶SDIR1可与EBF1/2直接相互作用，并在体外泛素化EBF2，其过量表达和突变体分别表现为乙烯超敏感和不敏感的表型，突变体中EBF的降解速率变慢。此外，EBF1/2还存在自身降解，其降解速率与底物浓度相关。2）EBF1/2 对其底物EIN3具有蛋白降解之外的其它调控机制，破坏SCF复合物形成的转基因植物EBF1/2ΔF表现为组成型乙烯不敏感表型。进一步的表型、分子和生化分析表明EBF1/2除降解底物外还影响了底物的转录激活活性。