Badel Jorge L, Nomura Kinya, Bandyopadhyay Sruti, Shimizu Rena, Collmer Alan, He Sheng Yang
Department of Plant Pathology, Cornell University, Ithaca, NY 14853, USA.
Mol Microbiol. 2003 Sep;49(5):1239-51. doi: 10.1046/j.1365-2958.2003.03647.x.
Pseudomonas syringae pv. tomato DC3000 is a pathogen of tomato and Arabidopsis that injects virulence effector proteins into host cells via a type III secretion system (TTSS). TTSS-deficient mutants have a Hrp- phenotype, that is, they cannot elicit the hypersensitive response (HR) in non-host plants or pathogenesis in host plants. Mutations in effector genes typically have weak virulence phenotypes (apparently due to redundancy), but deletion of six open reading frames (ORF) in the DC3000 conserved effector locus (CEL) reduces parasitic growth and abolishes disease symptoms without affecting function of the TTSS. The inability of the DeltaCEL mutant to cause disease symptoms in tomato was restored by a clone expressing two of the six ORF that had been deleted: CEL ORF3 (HopPtoM) and ORF4 (ShcM). A DeltahopPtoM::nptII mutant was constructed and found to grow like the wild type in tomato but to be strongly reduced in its production of necrotic lesion symptoms. HopPtoM expression in DC3000 was activated by the HrpL alternative sigma factor, and the protein was secreted by the Hrp TTSS in culture and translocated into Arabidopsis cells by the Hrp TTSS during infection. Secretion and translocation were dependent on ShcM, which was neither secreted nor translocated but, like typical TTSS chaperones, could be shown to interact with HopPtoM, its cognate effector, in yeast two-hybrid experiments. Thus, HopPtoM is a type III effector that, among known plant pathogen effectors, is unusual in making a major contribution to the elicitation of lesion symptoms but not growth in host tomato leaves.
丁香假单胞菌番茄致病变种DC3000是番茄和拟南芥的一种病原体，它通过III型分泌系统（TTSS）将毒力效应蛋白注入宿主细胞。缺乏TTSS的突变体具有Hrp-表型，也就是说，它们不能在非宿主植物中引发超敏反应（HR），也不能在宿主植物中引发致病作用。效应基因的突变通常具有较弱的毒力表型（显然是由于冗余），但是在DC3000保守效应子位点（CEL）中缺失六个开放阅读框（ORF）会降低寄生生长并消除疾病症状，而不会影响TTSS的功能。通过表达已缺失的六个ORF中的两个的克隆，恢复了DeltaCEL突变体在番茄中引起疾病症状的能力：CEL ORF3（HopPtoM）和ORF4（ShcM）。构建了一个DeltahopPtoM::nptII突变体，发现它在番茄中的生长与野生型相似，但其坏死病变症状的产生却大大减少。DC3000中HopPtoM的表达由HrpL替代sigma因子激活，该蛋白在培养物中由Hrp TTSS分泌，并在感染期间由Hrp TTSS转运到拟南芥细胞中。分泌和转运依赖于ShcM，ShcM既不分泌也不转运，但与典型的TTSS伴侣蛋白一样，在酵母双杂交实验中可以证明它与同源效应子HopPtoM相互作用。因此，HopPtoM是一种III型效应子，在已知的植物病原体效应子中，它的独特之处在于对病变症状的引发起主要作用，但对宿主番茄叶片的生长没有影响。
