Schechter Lisa M, Vencato Monica, Jordan Katy L, Schneider Sarah E, Schneider David J, Collmer Alan
Department of Plant Pathology, Cornell University, Ithaca, NY 14853, USA.
Mol Plant Microbe Interact. 2006 Nov;19(11):1180-92. doi: 10.1094/MPMI-19-1180.
Pseudomonas syringae pv. tomato DC3000 is a pathogen of tomato and Arabidopsis that translocates virulence effector proteins into host cells via a type III secretion system (T3SS). Many effector-encoding hypersensitive response and pathogenicity (Hrp) outer protein (hop) genes have been identified previously in DC3000 using bioinformatic methods based on Hrp promoter sequences and characteristic N-terminal amino acid patterns that are associated with T3SS substrates. To approach completion of the Hop/effector inventory in DC3000, 44 additional candidates were tested by the Bordetella pertussis calmodulin-dependent adenylate cyclase (Cya) translocation reporter assay; 10 of the high-probability candidates were confirmed as T3SS substrates. Several previously predicted hop genes were tested for their ability to be expressed in an HrpL-dependent manner in culture or to be expressed in planta. The data indicate that DC3000 harbors 53 hop/avr genes and pseudogenes (encoding both injected effectors and T3SS substrates that probably are released to the apoplast); 33 of these genes are likely functional in DC3000, 12 are nonfunctional members of valid Hop families, and 8 are less certain regarding their production at functional levels. Growth of DC3000 in tomato and Arabidopsis Col-0 was not impaired by constitutive expression of repaired versions of two hops that were disrupted naturally by transposable elements or of hop genes that are naturally cryptic. In summary, DC3000 carries a complex mixture of active and inactive hop genes, and the hop genes in P. syringae can be identified efficiently by bioinformatic methods; however, a precise inventory of the subset of Hops that are important in pathogenesis awaits more knowledge based on mutant phenotypes and functions within plants.
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（T3SS）将毒力效应蛋白转运到宿主细胞中。此前，基于Hrp启动子序列以及与T3SS底物相关的特征性N端氨基酸模式，利用生物信息学方法在DC3000中鉴定出了许多编码效应蛋白的过敏反应和致病性（Hrp）外蛋白（hop）基因。为了接近完成DC3000中Hop/效应蛋白清单，通过百日咳博德特氏菌钙调蛋白依赖性腺苷酸环化酶（Cya）转运报告基因检测对另外44个候选基因进行了测试；10个高概率候选基因被确认为T3SS底物。对几个先前预测的hop基因在培养物中以HrpL依赖性方式表达的能力或在植物中表达的能力进行了测试。数据表明，DC3000含有53个hop/avr基因和假基因（编码注入的效应蛋白和可能释放到质外体的T3SS底物）；其中33个基因在DC3000中可能具有功能，12个是有效Hop家族的无功能成员，8个在功能水平上的产生情况尚不确定。番茄和拟南芥Col-0中DC3000的生长不受两个被转座元件自然破坏的hop修复版本或天然隐性hop基因的组成型表达的影响。总之，DC3000携带了活性和非活性hop基因的复杂混合物，丁香假单胞菌中的hop基因可以通过生物信息学方法有效鉴定；然而，对于在致病过程中重要的Hop子集的精确清单，还需要更多基于植物内突变体表型和功能的知识。
