Function of the Phytotoxin Coronatine in P. syringae DC3000/Plant Interactions

冠状病毒(Coronatine，COR)是由植物病原菌紫丁香假单胞菌产生的一种植物毒素。COR参与了丁香疫霉菌的毒力；然而，COR的确切作用模式还没有被定义。COR具有独特的结构，由两种不同的化合物组成：(1)冠花酸(CFA)，(2)冠花酸(CMA)。CFA在结构上类似于茉莉酸(JA)，茉莉酸是一种参与植物防御的植物激素，其功能是这种内源植物信号分子的分子模拟。CMA是氨基环丙基羧酸(ACC)的结构类似物，ACC是乙烯的直接前体，乙烯是另一种参与植物防御的内源植物激素。COR与参与植物防御信号转导的化合物(JA和ACC/乙烯)在结构和功能上的相似性表明，COR可能通过干扰寄主防御反应和/或植物中的其他生理过程来促进病原菌的毒力。此外，我们以前已经证明COR在寄主植物的早期定殖事件中是重要的，这一发现与抑制或调节寄主防御反应一致。在这项拟议的工作中，将使用一种涵盖寄主和病原体的遗传方法来确定COR在拟南芥和番茄发病中的作用。为此，PI和Co-PI开发了第一个定义明确的紫丁香P.syringae PV CFA和CMA突变株。番茄DC3000，拟南芥和番茄的病原菌。PI和Co-PI实验室的独特专业知识和工具将用于整合对宿主的研究(COR如何调节易感性？)与病原体有关(COR对致病力有何贡献？)具体地说，我们将：1)对丁香疫霉COR基因进行特征分析。本研究利用番茄DC3000品系，研究这些基因的结构和调控；2)利用CFA、CMA或两者都不能产生的突变体，研究COR、CFA和CMA在拟南芥和番茄发病机制中的作用；3)利用功能基因组学(基因芯片研究)和DC3000相关突变体，研究COR、CFA和CMA在调节寄主细胞过程和防御反应中的作用；4)分析COR、CFA和CMA对植物细胞生物学的影响，这些研究将有助于我们理解植物病害发生的机制。通过利用我们可以同时研究病原体和植物寄主的系统，我们将能够识别和研究COR改变正常植物细胞过程的机制。这些研究将提供对COR在其他植物寄主中作用的分子基础的洞察，这一贡献可能导致开发出在农业和园艺系统中预防或控制植物病害的改进策略。

Coronatine (COR) is a phytotoxin produced by the plant pathogenic bacterium Pseudomonas syringae. COR contributes to the virulence of P. syringae; however, a precise mode of action for COR has not been defined. COR has a unique structure consisting of two distinct compounds: (1) coronafacic acid (CFA), and (2) coronamic acid (CMA). CFA is structurally similar to jasmonic acid (JA), a plant hormone involved in plant defense, and functions as a molecular mimic of this endogenous plant signaling molecule. CMA is a structural analog of aminocyclopropyl carboxylic acid (ACC), the immediate precursor to ethylene, another endogenous plant hormone involved in plant defense. The structural and functional similarities between COR and compounds involved in plant defense signaling (JA and ACC/ethylene) suggest that COR may promote pathogen virulence by interfering with host defense responses and/or with other physiological processes in the plant. Furthermore, we have previously shown that COR is important for early colonization events in host plants, a finding consistent with the suppression or modulation of host defense responses. In the proposed work, a genetic approach that encompasses both host and pathogen will be used to define the role of COR in the pathogenesis of Arabidopsis and tomato. For this purpose, the PI and Co-PI have developed the first well-defined CFA- and CMA- mutants of P. syringae pv. tomato DC3000, a pathogen of Arabidopsis and tomato. The unique expertise and tools in the PI and Co-PI's laboratories will be used to integrate studies of the host (how does COR modulate susceptibility?) with the pathogen (how does COR contribute to virulence?). Specifically, we will: 1) characterize the COR genes in P. syringae pv. tomato strain DC3000 and study the structure and regulation of these genes; 2) investigate the role of COR, CFA and CMA in the pathogenesis of Arabidopsis and tomato by utilizing mutants deficient for production of CFA, CMA, or both molecules; 3) utilize functional genomics (microarray studies) and the DC3000 COR- mutants to investigate the role of COR, CFA, and CMA on modulating host cell processes and defense responses; and 4) analyze the effect of COR, CFA, and CMA on plant cell biology.These studies will contribute to our understanding of the mechanisms involved in disease development in plants. By taking advantage of a system where we can simultaneously study both the pathogen and plant host we will be able to identify and study the mechanisms by which COR alters normal plant cell processes. These studies will provide insight into the molecular basis of COR function in other plant hosts, a contribution that could result in the development of improved strategies for preventing or controlling plant disease in agricultural and horticultural systems.