Instituto de Hortofruticultura Subtropical y Mediterranea, Universidad de Málaga-Consejo Superior de Inverstigaciones Cientificas, Depto. Biología cellular, Genética y Fisiología, Spain.
Mol Plant Microbe Interact. 2010 May;23(5):665-81. doi: 10.1094/MPMI-23-5-0665.
Disease in compatible hosts and induction of the hypersensitive response in resistant plants by most plant-pathogenic bacteria require a functional type III secretion system (T3SS). Expression of T3SS genes responds to host and environmental factors and is induced within the plant. In Pseudomonas syringae, expression of the T3SS requires HrpL, which is transcriptionally upregulated by HrpR and HrpS. In some pathovars, expression of the hrpRS genes is upregulated by the GacA/S two-component system. Additionally, HrpA, the major component of the T3SS pilus, has also been linked to the regulation of the hrpRS gene expression. Previous studies concerning regulation of hypersensitive response and pathogenesis/hypersensitive response conserved (hrp/hrc) gene expression have used mostly in vitro inducing conditions, different pathovars, and methodology. Here, we analyze the roles of HrpL, GacA, and HrpA in the bean pathogen, using single, double, and triple mutants as well as strains ectopically expressing the regulators. We use real-time polymerase chain reaction analysis in vitro and in planta to quantify gene expression and competitive indices and other assays to assess bacterial fitness. Our results indicate that i) HrpL acts as a general virulence regulator that upregulates non-T3SS virulence determinants and downregulates flagellar function; ii) GacA modulates the expression of hrpL, and its contribution to virulence is entirely HrpL dependent; iii) there is a basal HrpL-independent expression of the T3SS genes in rich medium that is important for full activation of the system, maybe by keeping the system primed for rapid activation upon contact with the plant; and iv) HrpA upregulates expression of the T3SS genes and is essential to activate expression of the hrpZ operon upon contact with the plant.
相容宿主中的疾病以及抗性植物中由大多数植物病原细菌引起的过敏反应的诱导都需要功能性的 III 型分泌系统（T3SS）。T3SS 基因的表达响应宿主和环境因素，并在植物体内诱导。在丁香假单胞菌中，T3SS 的表达需要 HrpL，HrpR 和 HrpS 转录上调 HrpL 的表达。在一些病原株中，hrpRS 基因的表达受 GacA/S 双组分系统上调。此外，T3SS 菌毛的主要成分 HrpA 也与 hrpRS 基因表达的调控有关。以前关于过敏反应和发病/过敏反应保守（hrp/hrc）基因表达调控的研究主要使用体外诱导条件、不同的病原株和方法学。在这里，我们使用单突变体、双突变体和三突变体以及异位表达调控因子的菌株，分析了 HrpL、GacA 和 HrpA 在豆类病原体中的作用。我们使用体外和体内实时聚合酶链反应分析来量化基因表达和竞争指数以及其他测定来评估细菌适应性。我们的结果表明：i）HrpL 作为一种普遍的毒力调节因子，上调非 T3SS 毒力决定因子并下调鞭毛功能；ii）GacA 调节 HrpL 的表达，其对毒力的贡献完全依赖于 HrpL；iii）在丰富培养基中存在 T3SS 基因的基础 HrpL 非依赖性表达，这对于系统的完全激活很重要，可能通过在与植物接触时使系统保持快速激活的准备状态；iv）HrpA 上调 T3SS 基因的表达，并且在与植物接触时对于激活 hrpZ 操纵子的表达是必需的。
