Oh Hye-Sook, Kvitko Brian H, Morello Joanne E, Collmer Alan
Department of Plant Pathology, Cornell University, Ithaca, NY 14853, USA.
J Bacteriol. 2007 Nov;189(22):8277-89. doi: 10.1128/JB.00998-07. Epub 2007 Sep 7.
Pseudomonas syringae translocates virulence effector proteins into plant cells via a type III secretion system (T3SS) encoded by hrp (for hypersensitive response and pathogenicity) genes. Three genes coregulated with the Hrp T3SS system in P. syringae pv. tomato DC3000 have predicted lytic transglycosylase domains: PSPTO1378 (here designated hrpH), PSPTO2678 (hopP1), and PSPTO852 (hopAJ1). hrpH is located between hrpR and avrE1 in the Hrp pathogenicity island and is carried in the functional cluster of P. syringae pv. syringae 61 hrp genes cloned in cosmid pHIR11. Strong expression of DC3000 hrpH in Escherichia coli inhibits bacterial growth unless the predicted catalytic glutamate at position 148 is mutated. Translocation tests involving C-terminal fusions with a Cya (Bordetella pertussis adenylate cyclase) reporter indicate that HrpH and HopP1, but not HopAJ1, are T3SS substrates. Pseudomonas fluorescens carrying a pHIR11 derivative lacking hrpH is poorly able to translocate effector HopA1, and this deficiency can be restored by HopP1 and HopAJ1, but not by HrpH(E148A) or HrpH(1-241). DC3000 mutants lacking hrpH or hrpH, hopP1, and hopAJ1 combined are variously reduced in effector translocation, elicitation of the hypersensitive response, and virulence. However, the mutants are not reduced in secretion of T3SS substrates in culture. When produced in wild-type DC3000, the HrpH(E148A) and HrpH(1-241) variants have a dominant-negative effect on the ability of DC3000 to elicit the hypersensitive response in nonhost tobacco and to grow and cause disease in host tomato. The three Hrp-associated lytic transglycosylases in DC3000 appear to have overlapping functions in contributing to T3SS functions during infection.
丁香假单胞菌通过由hrp（过敏反应和致病性）基因编码的III型分泌系统（T3SS）将毒力效应蛋白转运到植物细胞中。在丁香假单胞菌番茄致病变种DC3000中，与Hrp T3SS系统共调控的三个基因具有预测的溶菌转糖基酶结构域：PSPTO1378（此处命名为hrpH）、PSPTO2678（hopP1）和PSPTO852（hopAJ1）。hrpH位于Hrp致病岛中的hrpR和avrE1之间，并存在于克隆到粘粒pHIR11中的丁香假单胞菌丁香致病变种61的hrp基因功能簇中。DC3000的hrpH在大肠杆菌中的强表达会抑制细菌生长，除非预测的第148位催化谷氨酸发生突变。涉及与Cya（百日咳博德特氏菌腺苷酸环化酶）报告基因的C末端融合的转运试验表明，HrpH和HopP1是T3SS底物，而HopAJ1不是。携带缺乏hrpH的pHIR11衍生物的荧光假单胞菌转运效应蛋白HopA1的能力很差，这种缺陷可以通过HopP1和HopAJ1恢复，但不能通过HrpH（E148A）或HrpH（1 - 241）恢复。缺乏hrpH或hrpH、hopP1和hopAJ1组合的DC3000突变体在效应蛋白转运、过敏反应激发和毒力方面有不同程度的降低。然而，这些突变体在培养物中T3SS底物的分泌方面没有降低。当在野生型DC3000中产生时，HrpH（E148A）和HrpH（1 - 241）变体对DC3000在非寄主烟草中激发过敏反应以及在寄主番茄中生长和致病的能力具有显性负效应。DC3000中的三种与Hrp相关的溶菌转糖基酶在感染期间对T3SS功能的贡献似乎具有重叠功能。
