Novel exchangeable effector loci associated with the Pseudomonas syringae hrp pathogenicity island:: Evidence for integron-like assembly from transposed gene cassettes
Novel exchangeable effector loci associated with the Pseudomonas syringae hrp pathogenicity island:: Evidence for integron-like assembly from transposed gene cassettes
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DOI：
10.1094/mpmi.2003.16.6.495
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发表时间：
2003-06-01
影响因子：
3.5
通讯作者：
Hutcheson, SW
中科院分区：
文献类型：
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作者：
Charity, JC;Pak, K;Hutcheson, SW
丁香假单胞菌（Pseudomonas syringae）菌株利用III型分泌系统（TTSS）来转运效应蛋白，这些效应蛋白有助于寄生宿主植物细胞。一些效应蛋白基因聚集在与hrp致病岛相关的可交换效应位点（EEL）中。开发了一种基于聚合酶链反应的筛选方法来扩增丁香假单胞菌菌株的EEL。在筛选的86个菌株中，使用源自hrpK和queA的引物从30个主要为北美的丁香假单胞菌丁香致病变种（P. syringae pv. syringae）菌株中成功扩增出EEL，并且使用源自hrpL和queA的引物从另外3个菌株中扩增出EEL。在扩增出的EEL中，鉴定出10种不同类型的EEL，它们可分为6个通过基因组成可区分的家族，但在其他地理区域分离的菌株中可能存在其他类型的EEL。与来源菌株的宿主范围没有明显的关联。在已鉴定的EEL中鉴定出携带保守侧翼、编码和基因间序列且以不同组合存在的基因盒。鉴定出6个已知效应子的新等位基因，它们在基因的序列、大小或两者上与同源基因不同。其中一种明显新颖的效应蛋白HopPsyB保留了与HopPsyA相似的高度保守的氨基末端，但这两种多肽的其他区域仅有微弱的相似性。hopPsyB从一个明显的操纵子中表达，该操纵子包括hrpK和一个shcA同源物shcB。表达hrp TTSS、ShcB和HopPsyB的大肠杆菌MC4100在烟草中引发过敏反应（HR），这与效应蛋白的产生一致。作为一种效应蛋白发生转运的迹象是，表达HopPsyB':'AvrRpt2融合蛋白的丁香假单胞菌番茄致病变种（P. syringae pv. tomato）DC3000在含有RPS2基因的拟南芥（Arabidopsis thaliana）中引发HR。携带HopPsyB的丁香假单胞菌番茄致病变种DC3000在几种芸薹属（Brassica）植物中表现出略微增强的毒力。这些结果与以下假设一致：EEL是丁香假单胞菌菌株致病性中不同效应子的来源，并且它独立于hrp致病岛中心保守区域进化，很可能是通过转座基因盒的整合子样组装。
Pseudomonas syringae strains use a type III secretion system (TTSS) to translocate effector proteins that assist in the parasitism of host plant cells. Some genes for effector proteins are clustered in the exchangeable effector locus (EEL) associated with the hrp pathogenicity island. A polymerase chain reaction-based screen was developed to amplify the EEL from P. syringae strains. Of the 86 strains screened, the EEL was successfully amplified from 30 predominately North American P. syringae pv. syringae strains using hrpK and queA-derived primers and from an additional three strains using hrpL and queA-derived primers. Among the amplified EEL, ten distinct types of EEL were identified that could be classified into six families distinguishable by genetic composition, but other types of EEL may be present in strains isolated in other geographical regions. No linkage with the host range of the source strain was apparent. Gene cassettes carrying conserved flanking, coding, and intergenic sequences, present in different combinations, were identified in the characterized EEL. Six new alleles of known effectors were identified that differed from the homolog in sequence, size, or both of the gene. One of these apparently novel effector proteins, HopPsyB, retained a strongly conserved amino terminus similar to that of HopPsyA, but other regions of the two polypeptides were only weakly similar. hopPsyB was expressed from an apparent operon that included hrpK and a shcA homolog, shcB. Escherichia coli MC4100 expressing the hrp TTSS, ShcB, and HopPsyB elicited the hypersensitive response (HR) in tobacco, consistent with effector production. Indicative of translocation as an effector, P. syringae pv. tomato DC3000 expressing a HopPsyB':'AvrRpt2 fusion elicited the HR in RPS2(+) Arabidopsis thaliana. P. syringae pv. tomato DC3000 carrying HopPsyB exhibited slightly enhanced virulence in several Brassica spp. These results are consistent with the hypotheses that the EEL is a source of disparate effectors functioning in pathogenicity of P. syringae strains and that it evolved independently of the hrp pathogenicity island central conserved region, most likely through integron-like assembly of transposed gene cassettes.