乙烯信号转导通路中关键调控元件EBF1/2的蛋白降解机制研究

Ethylene is a gaseous plant hormone, which plays important roles in plant development and response to biotic and abiotic stresses. EIN3 (ETHYLENE INSENSITIVE 3) and EIL1 (EIN3-LIKE 1) are key transcription factors in ethylene pathway, which are tightly regulated by SCF complex containing F-box protein EBF1/EBF2 (EIN3-BINGDING F-BOX PROTEIN 1/2) through a 26S proteasome-mediated protein degradation pathway. EBF1/2 protein levels are also found to be regulated by 26S proteasome degradation pathway, and this process is induced by ethylene and dependent on EIN2. However, the E3 ligase involved in this process and the mechanism by which ethylene or EIN2 triggers this process remains elusive. Previously, we have identified a protein ETE1 (E3 ligase to EBF1/2) interact with and directly ubiquitinate EBF1/2. What's more, loss function of ETE1 causes ethylene insensitivity. In this proposed project, we will use cell biology, biochemistry, molecular biology and genetics approaches to investigate the function of ETE1 in ethylene signal transduction pathway and the underlying molecular mechanism by which ethylene or EIN2 regulates ETE1-induced EBF1/2 ubiquitination and degradation. These studies will further improve our understanding of the regulation on ethylene signaling pathway and potentially provide new insights into the regulation of other signal transduction pathways.

乙烯是一种简单的气态植物激素，在植物的生长发育以及对生物、非生物胁迫的响应过程中有着重要作用。EIN3/EIL1是乙烯信号通路中的核心转录因子，其蛋白稳定性受两个F-box蛋白EBF1/2介导的泛素化降解途径所调控。本课题组研究发现EBF1/2本身也能被26S蛋白酶体降解，该过程同样受乙烯诱导，且依赖于EIN2。但是，参与乙烯诱导的EBF1/2泛素化降解的E3连接酶还不知道，而该过程受乙烯或者EIN2调控的机制也还不清楚。申请人前期筛选到一个能够将EBF1/2泛素化的蛋白ETE1，且该蛋白功能丧失的突变体ete1对乙烯敏感度降低。本项目拟通过生物化学和遗传学结合的方法进一步解析ETE1在乙烯信号通路中的位置，同时揭示EIN2调控ETE1介导EBF1/2泛素化降解的分子机制。本项目的研究将进一步完善对乙烯信号转导通路的理解，并可能为研究其他信号转导通路的调控机制提供新的思路。

光和温度是影响植物生长发育的两个最关键的环境因素。植物气体激素乙烯，既是一种生长激素，也是一种胁迫激素，在植物对环境的适应中发挥着非常重要的功能。光信号和乙烯信号协同调控植物的生长发育已经有广泛的研究，然而乙烯信号在植物适应周围温度变化中的功能还鲜有报道。EBF1和EBF2是两个F-box蛋白，能够促进乙烯信号通路的最主要转录因子EIN3/EIL1的泛素化降解，是乙烯信号通路的关键负调控因子。本项研究发现SDIR1能够同EBF1/2直接互作，促进EBF1/2的泛素化-蛋白酶体降解，进而促进EIN3蛋白的积累和下游的乙烯响应；因而，sdir1的突变体对乙烯，尤其是低浓度的乙烯表现出不敏感的表型，而其过量表达的转基因株系则表现出乙烯超敏感的表型。此外，该研究发现SDIR1转录本随环境温度升高而增多，参与了温度升高诱导的EBF1/2蛋白的降解和EIN3蛋白的积累而调控不同温度下的乙烯响应。该项研究揭示了环境温度通过SDIR1降解EBF1/2来调控乙烯信号，调节植物生长的新的机制。