positive contribution of E3 ubiquitin ligases in regulation of MAP kinase cascade involved in plant immunity

丝裂原活化蛋白激酶（MAPK）级联在植物的先天免疫中具有重要作用。拟南芥MEKK 1是MAPK激酶激酶（MAPKKK）的一个重要激酶，位于MPK 4的上游，至少具有两种功能，即负调控SA介导的防御反应和正调控JA诱导的基因表达，但MEKK 1的调控机制尚不清楚。为了鉴定MEKK 1的可能调节因子，我们使用MEKK 1蛋白作为诱饵进行酵母双杂交筛选。我们发现了两个含有U-box结构域的E3连接酶，命名为PUB 25和PUB 26，它们是新的MEKK 1结合蛋白。使用pub 25/ 26双突变体的表征表明，PUB 25和PUB 26对MEKK 1功能有积极贡献。

A mitogen-activated protein kinase(MAPK) cascade has an important role in innate immunity in plants. Arabidopsis MEKK1, a MAPK kinase kinase(MAPKKK) is an important factor in the upstream of MPK4 which has at least two functions, negative regulation of SA-mediated defense responses and positive regulation of JA-induced gene expression, however regulatory mechanism of MEKK1 remains to be elucidated. To identify possible regulator of MEKK1, we performed yeast two-hybrid screening using MEKK1 protein as bait. We found two putative E3 ligases which contain U-box domain, named PUB25 and PUB26 as novel MEKK1-binding proteins. Characterization using pub25/ 26 double mutant suggested that PUB25 and PUB26 positively contribute MEKK1 function.