Lee Jae Hoon, Zhao Youfu
Department of Crop Sciences, University of Illinois at Urbana-Champaign, Urbana 61801.
Phytopathology. 2017 Nov;107(11):1346-1352. doi: 10.1094/PHYTO-06-17-0198-R. Epub 2017 Sep 12.
Erwinia amylovora, the causal agent of fire blight disease of apple and pear, employs intracellular proteases, including Lon and ClpXP, for posttranslational regulation of various cellular proteins. It has been shown that Lon plays a critical role in E. amylovora virulence by directly targeting type III secretion system (T3SS) proteins and the Rcs phosphorelay system. In this study, we genetically examined the role of ClpXP and its potential interaction with Lon in E. amylovora. Mutation in clpXP diminished the expression of the T3SS, reduced exopolysaccharide amylovoran production and motility, and resulted in delayed disease progress. Western blot analyses showed highly accumulated RpoS proteins in the clpXP mutant. Moreover, mutation of rpoS in the clpXP mutant background rescued the expression of the T3SS and amylovoran production, suggesting that ClpXP-dependent RpoS degradation positively affects virulence traits. Interestingly, lack of both ClpXP and Lon resulted in significantly reduced virulence but increased expression of the T3SS and amylovoran production. However, this phenomenon was independent of RpoS accumulation, suggesting that ClpXP and Lon are indispensable for full virulence in E. amylovora.
梨火疫病菌（Erwinia amylovora）是苹果和梨火疫病的致病因子，它利用包括Lon和ClpXP在内的细胞内蛋白酶对各种细胞蛋白进行翻译后调控。研究表明，Lon通过直接作用于III型分泌系统（T3SS）蛋白和Rcs磷酸化信号转导系统，在梨火疫病菌的毒力中发挥关键作用。在本研究中，我们通过遗传学方法研究了ClpXP在梨火疫病菌中的作用及其与Lon的潜在相互作用。clpXP基因突变会降低T3SS的表达，减少胞外多糖淀粉膜多糖的产生和运动性，并导致疾病进展延迟。蛋白质免疫印迹分析显示，clpXP突变体中RpoS蛋白高度积累。此外，在clpXP突变体背景下rpoS基因突变可挽救T3SS的表达和淀粉膜多糖的产生，这表明ClpXP依赖的RpoS降解对毒力性状有正向影响。有趣的是，同时缺失ClpXP和Lon会导致毒力显著降低，但T3SS的表达和淀粉膜多糖的产生增加。然而，这种现象与RpoS的积累无关，这表明ClpXP和Lon对梨火疫病菌的完全毒力是不可或缺的。
