Collmer A, Badel J L, Charkowski A O, Deng W L, Fouts D E, Ramos A R, Rehm A H, Anderson D M, Schneewind O, van Dijk K, Alfano J R
Department of Plant Pathology, Cornell University, Ithaca, NY 14853-4203, USA.
Proc Natl Acad Sci U S A. 2000 Aug 1;97(16):8770-7. doi: 10.1073/pnas.97.16.8770.
Pseudomonas syringae is a member of an important group of Gram-negative bacterial pathogens of plants and animals that depend on a type III secretion system to inject virulence effector proteins into host cells. In P. syringae, hrp/hrc genes encode the Hrp (type III secretion) system, and avirulence (avr) and Hrp-dependent outer protein (hop) genes encode effector proteins. The hrp/hrc genes of P. syringae pv syringae 61, P. syringae pv syringae B728a, and P. syringae pv tomato DC3000 are flanked by an exchangeable effector locus and a conserved effector locus in a tripartite mosaic Hrp pathogenicity island (Pai) that is linked to a tRNA(Leu) gene found also in Pseudomonas aeruginosa but without linkage to Hrp system genes. Cosmid pHIR11 carries a portion of the strain 61 Hrp pathogenicity island that is sufficient to direct Escherichia coli and Pseudomonas fluorescens to inject HopPsyA into tobacco cells, thereby eliciting a hypersensitive response normally triggered only by plant pathogens. Large deletions in strain DC3000 revealed that the conserved effector locus is essential for pathogenicity but the exchangeable effector locus has only a minor role in growth in tomato. P. syringae secretes HopPsyA and AvrPto in culture in a Hrp-dependent manner at pH and temperature conditions associated with pathogenesis. AvrPto is also secreted by Yersinia enterocolitica. The secretion of AvrPto depends on the first 15 codons, which are also sufficient to direct the secretion of an Npt reporter from Y. enterocolitica, indicating that a universal targeting signal is recognized by the type III secretion systems of both plant and animal pathogens.
丁香假单胞菌是动植物革兰氏阴性细菌病原体重要类群的成员，这类病原体依靠III型分泌系统将毒力效应蛋白注入宿主细胞。在丁香假单胞菌中，hrp/hrc基因编码Hrp（III型分泌）系统，无毒（avr）和Hrp依赖性外蛋白（hop）基因编码效应蛋白。丁香假单胞菌丁香致病变种61、丁香假单胞菌丁香致病变种B728a和丁香假单胞菌番茄致病变种DC3000的hrp/hrc基因两侧是一个可交换效应子位点和一个保守效应子位点，位于一个三方镶嵌的Hrp致病岛（Pai）中，该致病岛与在铜绿假单胞菌中也发现的一个tRNA(Leu)基因相连，但与Hrp系统基因无连锁关系。黏粒pHIR11携带菌株61的一部分Hrp致病岛，这足以指导大肠杆菌和荧光假单胞菌将HopPsyA注入烟草细胞，从而引发通常仅由植物病原体触发的超敏反应。DC3000菌株中的大片段缺失表明，保守效应子位点对致病性至关重要，但可交换效应子位点在番茄中的生长中仅起次要作用。丁香假单胞菌在与发病机制相关的pH和温度条件下，以Hrp依赖性方式在培养物中分泌HopPsyA和AvrPto。小肠结肠炎耶尔森菌也分泌AvrPto。AvrPto的分泌取决于前15个密码子，这也足以指导小肠结肠炎耶尔森菌中Npt报告基因的分泌，表明植物和动物病原体的III型分泌系统识别通用的靶向信号。
