Dissection of AvrBsT-BST defense pathway in Arabidopsis

描述(申请人提供)：本项目将进一步剖析野油菜黄单胞菌致病机理的分子和细胞基础。在植物感染的早期阶段，这种细菌使用一种特殊的分泌系统来协调细胞间的交流。III型分泌系统(TTSS)可以将细菌蛋白直接分泌和转运到寄主植物细胞中。一旦进入寄主，TTSS效应器可能作为毒力蛋白共同调节细胞，启动敏感植物的疾病症状，并激活抗性植物的防御反应。到目前为止，XcvTTSS效应器调控植物生理的机制几乎是未知的。然而，我们的工作为YopJ样效应器使用的潜在机制提供了重要的见解，YopJ样效应器是黄单胞菌中普遍存在的一个家族，在动植物细菌病原体中保守。这种保守意味着病原微生物使用一种特定的机制来干扰宿主细胞的信号传递。我们已经证明了YopJ和XopD家族中的XCV效应器在植物和动物细胞中作为半胱氨酸蛋白酶发挥作用。这些效应器的底物是高度保守的小泛素样修饰物(SUMO)，它们被共价添加到许多调节蛋白上。因此，我们预测YopJ样效应器通过破坏蛋白质的翻译后相扑修饰而在宿主细胞上发挥致病作用。 本研究的总体目标是确定和研究在Xanthomonas致病过程中受YopJ样效应子AvrBsT影响的植物信号转导途径。具体地说，我们将：(1)通过分离SUMO化植物靶标来探索AvrBsT蛋白降解对拟南芥中SUMO途径的影响；(2)分离提供对AvrBsT的保护作用的拟南芥BST抗病基因；(3)利用基因筛选技术剖析拟南芥中AvrBsTBST抗病信号转导途径。我们相信，我们的发现将揭示植物和动物病原体中保守的相扑蛋白水解酶在细菌-宿主相互作用过程中控制真核生理的共同机制。

DESCRIPTION (provided by applicant): This project will further dissect the molecular and cellular basis of Xanthomonas campestris pathovar vesicatoria (Xcv) pathogenesis in plants. This bacterium uses a specialized secretory system to orchestrate cell-to-cell communication during the early stages of plant infection. The type III secretion system (TTSS) enables direct secretion and translocation of bacterial proteins into host plant cells. Once inside the host, TTSS effectors, acting presumably as virulence proteins, collectively modulate the cell to initiate disease symptoms in susceptible plants and to activate defense responses in resistant plants. To date, the mechanisms by which XcvTTSS effectors modulate plant physiology are virtually unknown. However, our work has provided important insights to the potential mechanisms used by the YopJ-like effectors, a family that is prevalent in Xanthomonas and conserved amongst plant and animal bacterial pathogens. Such conservation implies that pathogenic microbes use a specific mechanism to interfere with host cell signaling. We have shown that Xcv effectors in the YopJ and XopD family function as cysteine proteases inside plant and animal cells. The substrates for these effectors are highly conserved small ubiquitin-like modifiers (SUMO) that are covalently added to a number of regulatory proteins. Thus, we predict that YopJ-like effectors exert their pathogenic effect on host cells by disrupting posttranslational SUMO modification of proteins. The overall goal of this study is to identify and study the plant signal transduction pathways that are affected by the YopJ-like effector AvrBsT during Xanthomonas pathogenesis. Specifically, we will: (1) explore the effect of AvrBsT proteolysis on the SUMO pathway in Arabidopsis by isolating SUMOylated plant targets, (2) isolate the Arabidopsis bst disease resistance gene that provides protection against AvrBsT, and (3) use genetic screens to dissect the AvrBsTBST disease resistance signal transduction pathway in Arabidopsis. We believe our findings will reveal common mechanisms used by SUMO proteases conserved in both plant and animal pathogens to control eukaryotic physiology during bacterial-host interactions.