Characterization of Avirulence Genes from Pseudomonas syringae pv. tomato

本实验室克隆并鉴定了担负大豆植物防御性监视的丁香假单胞菌病原菌的几个无毒基因。其中一个基因avrD来自紫丁香P.syringae PV.番茄引起细菌宿主精心设计一种胞外激发子化合物。分离的激发子只在含有抗病基因RPG4的大豆品种上引起过敏反应(HR)。AvrD还有其他几个有趣的特征，例如它与其他四个连锁基因一起出现在本土细菌质粒上，以及与培养基相比，当细菌在大豆叶片中生长时，AvrD的诱导作用是100倍。因此，携带avrD的细菌与植物宿主的相互作用涉及到在两种生物中启动精确发育程序的相互信号机制。这项建议要求进一步研究avrD及其在启动植物抗病中的作用，方法是：1)确定avrD激发子的特征；2)阐明avrD诱导植物的本质；3)研究avrD所在的本地质粒；4)将avrD与其他紫丁香病原体中的同源基因进行比较。这项拟议的研究将对我们理解植物-微生物信号转导机制和植物的抗病能力做出重大贡献。

This laboratory has cloned and characterized several avirulence genes from bacterial pathogens in the Pseudomonas syringae group that are responsible for defensive surveillance by soybean plants. One of these genes, avrD from P. syringae pv. tomato, causes bacterial hosts to elaborate an extracellular elicitor compound. The isolated elicitor causes the hypersensitive response (HR) only on soybean cultivars containing thecomplementary disease resistance gene, Rpg4. AvrD also has several other interesting features such as its occurrence, along with four other linked genes, on an indigenous bacterial plasmid and its 100-fold induction when bacteria are grown in soybean leaves as compared to culture media. The interaction of bacteria carrying avrD with plant hosts therefore involves reciprocal signalling mechanisms that initiate precise developmentalprograms in both organisms. This proposal requests support to further study avrD and its role in initiating plant disease resistance by 1) characterizing the avrD elicitor; 2) elucidating the nature of plant induction of avrD; 3) studying the indigenous plasmid on which avrD occurs and 4) comparing avrD withhomologous genes that occur in other P. syringae pathovars. The proposed research should contribute significantly to our understanding of plant-microbe signalling mechanisms and disease resistance in plants.