LIPM, Université de Toulouse, INRA, CNRS, Castanet-Tolosan, France.
Micalis Institute, PAPPSO, INRA, AgroParisTech, Université Paris-Saclay, 78350 Jouy-en-Josas, France.
Mol Plant Microbe Interact. 2020 Feb;33(2):200-211. doi: 10.1094/MPMI-05-19-0139-R. Epub 2019 Dec 16.
The Gram-negative bacterium , the causal agent of bacterial wilt, is a worldwide major crop pathogen whose virulence strongly relies on a type III secretion system (T3SS). This extracellular apparatus allows the translocation of proteins, called type III effectors (T3Es), directly into the host cells. To date, very few data are available in plant-pathogenic bacteria concerning the role played by type III secretion (T3S) regulators at the posttranslational level. We have demonstrated that HpaP, a putative T3S substrate specificity switch protein of , controls T3E secretion. To better understand the role of HpaP on T3S control, we analyzed the secretomes of the GMI1000 wild-type strain as well as the mutant using a mass spectrometry experiment (liquid chromatography tandem mass spectrometry). The secretomes of both strains appeared to be very similar and highlighted the modulation of the secretion of few type III substrates. Interestingly, only one type III-associated protein, HrpJ, was identified as specifically secreted by the mutant. HrpJ appeared to be an essential component of the T3SS, essential for T3S and pathogenicity. We further showed that HrpJ is specifically translocated in planta by the mutant and that HrpJ can physically interact with HpaP. Moreover, confocal microscopy experiments demonstrated a cytoplasmic localization for HrpJ once in planta. When injected into leaves, HrpJ is able to trigger a necrosis on 16 natural accessions. A genome-wide association mapping revealed a major association peak with 12 highly significant single-nucleotide polymorphisms located on a plant acyl-transferase.
革兰氏阴性细菌是细菌性萎蔫病的病原体，是一种全球性的主要作物病原菌，其毒力强烈依赖于 III 型分泌系统（T3SS）。这种细胞外器具允许将蛋白质，称为 III 型效应物（T3E），直接易位到宿主细胞中。迄今为止，关于 III 型分泌（T3S）调节剂在翻译后水平上所起的作用，在植物病原菌中仅有很少的数据。我们已经证明，HpaP 是一种假定的 菌 T3S 底物特异性开关蛋白，控制 T3E 的分泌。为了更好地理解 HpaP 在 T3S 控制中的作用，我们使用质谱实验（液相色谱串联质谱）分析了 GMI1000 野生型菌株和 突变体的分泌组。这两种菌株的分泌组似乎非常相似，并强调了少数 III 型底物分泌的调节。有趣的是，只有一种 III 型相关蛋白 HrpJ 被鉴定为 突变体特异性分泌。HrpJ 似乎是 T3SS 的一个必需组成部分，对于 T3S 和致病性是必需的。我们进一步表明，HrpJ 是由 突变体特异性易位到植物体内的，并且 HrpJ 可以与 HpaP 物理相互作用。此外，共聚焦显微镜实验表明 HrpJ 在植物体内定位于细胞质。当注入 叶片时，HrpJ 能够在 16 个天然品种上引发坏死。全基因组关联图谱分析显示，与位于植物酰基转移酶上的 12 个高度显著的单核苷酸多态性相关的主要关联峰。
