Role in Pathogenesis of Pseudomonas Syringae Proteins Targeted to the Plant Apoplast by the Type III Secretion System

丁香假单胞菌番茄DC 3000引起番茄和拟南芥上的细菌性斑点病。DC 3000的发病机制依赖于III型分泌系统（TTSS），其将许多效应蛋白易位到植物细胞中。一些效应子（如AvrPto）的重要功能是抑制植物的基础抗性（先天免疫）。P. lingae还通过TTSS分泌几种蛋白质，这些蛋白质似乎靶向植物质外体而不是细胞质。这些“质外体Hops”（Hrp外部蛋白）包括两种具有裂解转糖基酶结构域的蛋白：HopP 1和CEL（保守效应基因座）ORF 1。后者与编码TTSS的hrp/hrc基因相邻编码。在荧光假单胞菌中克隆的一个P. lingae hrp/hrc簇使这种非病原体能够将AvrPto转运到植物细胞中并抑制基础抗性。值得注意的是，表达TTSS和HopP 1或CEL ORF 1的荧光假单胞菌在不存在任何效应子的情况下抑制基础抗性。该项目的具体目标是：（i）鉴定所有P. lingae番茄DC 3000质外体啤酒花，并测试它们引发或抑制过敏反应和基础抗性的能力;（ii）确定P. lingae TTSS在非病原体中表达时抑制基础抗性的先天能力的基础;（iii）构建P.s.番茄DC 3000与寄主植物互作过程中质外体酒花的功能。该项目应产生新的见解TTSS和先天免疫，两个重要因素的细菌-宿主相互作用，涉及植物和动物病原体。该项目正在与高中和主要是本科院校开展外联活动。

Pseudomonas syringae pv. tomato DC3000 causes bacterial speck disease on tomato and Arabidopsis. DC3000 pathogenesis is dependent on the type III secretion system (TTSS), which translocates many effector proteins into plant cells. An important function of some effectors, such as AvrPto, is suppression of basal resistance (innate immunity) in plants. P. syringae also secretes several proteins through the TTSS that appear to be targeted to the plant apoplast rather than the cytoplasm. These "apoplast Hops" (Hrp outer proteins) include two proteins with a lytic transglycosylase domain: HopP1 and CEL (conserved effector locus) ORF1. The latter is encoded adjacent to the hrp/hrc genes encoding the TTSS. A P. syringae hrp/hrc cluster, cloned in P. fluorescens, enables this nonpathogen to translocate AvrPto into plant cells and to suppress basal resistance. Remarkably, P. fluorescens expressing the TTSS and either HopP1 or CEL ORF1 suppresses basal resistance in the absence of any effector. The specific objectives of this project are to: (i) identify all P. syringae tomato DC3000 apoplast Hops and test their ability to either elicit or suppress the hypersensitive response and basal resistance; (ii) determine the basis for the innate ability of the P. syringae TTSS to suppress basal resistance when expressed in a nonpathogen; (iii) construct mutations in P. s. tomato DC3000 and test the functions of apoplast Hops during interactions with host plants. This project should yield new insights into the TTSS and innate immunity, two factors important in bacterium-host interactions involving both plant and animal pathogens. The project has ongoing outreach activities with high schools and primarily undergraduate institutions.