Schell Mark A
Department of Microbiology and Department of Plant Pathology, University of Georgia, Athens, Georgia 30602; e-mail:
Annu Rev Phytopathol. 2000 Sep;38:263-292. doi: 10.1146/annurev.phyto.38.1.263.
Ralstonia solanacearum causes a lethal bacterial wilt disease of diverse plants. It invades the xylem vessels of roots and disseminates into the stem where it multiplies and wilts by excessive exopolysaccharide production. Many of its key extracytoplasmic virulence and pathogenicity factors are transcriptionally controlled by an extensive network of distinct, interacting signal transduction pathways. The core of this sensory network is the five-gene Phc system that regulates exopolysaccharide, cell-wall-degrading exoenzymes, and other factors in response to a self-produced signal molecule that monitors the pathogen's growth status and environment. Four additional environmentally responsive two-component systems work independently and with the Phc system to fine-tune virulence gene expression. Another critical system is Prh which transduces plant cell-derived signals through a six-gene cascade to activate deployment of the Type III secretion pathway encoded by the hrp pathogenicity genes. Here I summarize knowledge about the regulated targets, signal transduction mechanisms, and crosstalk between Phc, Prh, and other systems. I also provide insight into why R. solanacearum has evolved such a sophisticated sensory apparatus, and how it functions in disease.
青枯雷尔氏菌会引发多种植物的致命性青枯病。它侵入根部的木质部导管,并扩散至茎部,在茎部大量繁殖并因过量产生胞外多糖而导致植物枯萎。其许多关键的胞外毒力和致病因子受到广泛的、由不同且相互作用的信号转导途径构成的网络的转录调控。这个传感网络的核心是由五个基因组成的Phc系统,该系统响应一种自我产生的信号分子来调节胞外多糖、细胞壁降解外切酶及其他因子,这种信号分子监测着病原体的生长状态和环境。另外四个对环境有响应的双组分系统独立发挥作用,并与Phc系统协同作用,以微调毒力基因的表达。另一个关键系统是Prh,它通过一个由六个基因组成的级联反应来转导来自植物细胞的信号,从而激活由hrp致病基因编码的III型分泌途径的部署。在此,我总结了关于Phc、Prh和其他系统的调控靶点、信号转导机制以及相互作用的相关知识。我还深入探讨了青枯雷尔氏菌为何进化出如此复杂的传感机制,以及它在致病过程中是如何发挥作用的。