The Type III-Dependent Hrp Pilus Is Required for Productive Interaction of Xanthomonas campestris pv. vesicatoria with Pepper Host Plants
The Type III-Dependent Hrp Pilus Is Required for Productive Interaction of Xanthomonas campestris pv. vesicatoria with Pepper Host Plants
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DOI：
10.1128/jb.187.7.2458-2468.2005
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发表时间：
2005-04
影响因子：
3.2
通讯作者：
E. Weber;T. Ojanen-Reuhs;E. Huguet;G. Hause;M. Romantschuk;Timo K. Korhonen;U. Bonas;R. Koebnik
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文献类型：
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作者：
E. Weber;T. Ojanen-Reuhs;E. Huguet;G. Hause;M. Romantschuk;Timo K. Korhonen;U. Bonas;R. Koebnik
摘要植物病原菌野油菜黄单胞菌(Xanthomonas Campestris)。水泡菌表达一种III型分泌系统，对敏感寄主的致病性和对抗性植物的超敏反应的诱导都是必需的。这个特殊的蛋白质转运系统由一个23kb的HRP(超敏反应和致病性)基因簇编码。在这里我们展示了野油菜X.campestris PV.在HRP诱导的条件下，水泡菌在细胞表面产生丝状结构，即HRP菌毛。对纯化的HRP菌毛和免疫电子显微镜的分析表明，HRP菌毛的主要成分是hRPE蛋白，它编码在HRP基因簇中。HRPE的序列同源物只在其他黄单胞菌中发现。然而，hrpe与另一种植物病原菌青枯病菌的hrpY基因是同源的。生物信息学分析表明，来自革兰氏阴性植物病原菌的所有主要HRP菌毛亚基可能具有相同的结构组织，即主要的α-螺旋结构。对hRPE中非极性突变体的分析表明，hrp菌毛对于油菜细小病毒的产生性相互作用是必不可少的。与辣椒寄主植物的水泡菌。此外，III型依赖蛋白的分泌需要有功能性的HRP菌毛。免疫电子显微镜显示，III型分泌蛋白，如HrpF和AvrBs3，在分泌过程中和/或分泌后与HRP菌毛密切接触。通过对非极性HRP/HRC(HRP保守的)和HPA(HRP相关的)突变体的系统分析，我们发现HPA蛋白和转位蛋白HrpF是菌毛组装所必需的，而所有其他HRP和HRC蛋白都是必需的。因此，在III型依赖蛋白的易位过程中，没有其他保守的HRP或HRC蛋白作用于hRPE下游。
ABSTRACT The plant pathogenic bacterium Xanthomonas campestris pv. vesicatoria expresses a type III secretion system that is necessary for both pathogenicity in susceptible hosts and the induction of the hypersensitive response in resistant plants. This specialized protein transport system is encoded by a 23-kb hrp (hypersensitive response and pathogenicity) gene cluster. Here we show that X. campestris pv. vesicatoria produces filamentous structures, the Hrp pili, at the cell surface under hrp-inducing conditions. Analysis of purified Hrp pili and immunoelectron microscopy revealed that the major component of the Hrp pilus is the HrpE protein which is encoded in the hrp gene cluster. Sequence homologues of hrpE are only found in other xanthomonads. However, hrpE is syntenic to the hrpY gene from another plant pathogen, Ralstonia solanacearum. Bioinformatic analyses suggest that all major Hrp pilus subunits from gram-negative plant pathogens may share the same structural organization, i.e., a predominant alpha-helical structure. Analysis of nonpolar mutants in hrpE demonstrated that the Hrp pilus is essential for the productive interaction of X. campestris pv. vesicatoria with pepper host plants. Furthermore, a functional Hrp pilus is required for type III-dependent protein secretion. Immunoelectron microscopy revealed that type III-secreted proteins, such as HrpF and AvrBs3, are in close contact with the Hrp pilus during and/or after their secretion. By systematic analysis of nonpolar hrp/hrc (hrp conserved) and hpa (hrp associated) mutants, we found that Hpa proteins as well as the translocon protein HrpF are dispensable for pilus assembly, while all other Hrp and Hrc proteins are required. Hence, there are no other conserved Hrp or Hrc proteins that act downstream of HrpE during type III-dependent protein translocation.