Department of Microbiology, College of Natural Science, Pusan National University, Busan 609-735, Korea.
Mol Cells. 2011 Oct;32(4):317-23. doi: 10.1007/s10059-011-1017-3. Epub 2011 Sep 6.
Pseudomonas syringae pv. tabaci causes wildfire disease in tobacco plants. The hrp pathogenicity island (hrp PAI) of P. syringae pv. tabaci encodes a type III secretion system (TTSS) and its regulatory system, which are required for pathogenesis in plants. Three important regulatory proteins-HrpR, HrpS, and HrpL-have been identified to activate hrp PAI gene expression. The bacterial Lon protease regulates the expression of various genes. To investigate the regulatory mechanism of the Lon protease in P. syringae pv. tabaci 11528, we cloned the lon gene, and then a Δlon mutant was generated by allelic exchange. lon mutants showed increased UV sensitivity, which is a typical feature of such mutants. The Δlon mutant produced higher levels of tabtoxin than the wild-type. The lacZ gene was fused with hrpA promoter and activity of β-galactosidase was measured in hrp-repressing and hrp-inducing media. The Lon protease functioned as a negative regulator of hrp PAI under hrp-repressing conditions. We found that strains with lon disruption elicited the host defense system more rapidly and strongly than the wild-type strain, suggesting that the Lon protease is essential for systemic pathogenesis.
丁香假单胞菌 pv. 烟碱引起烟草野火病。丁香假单胞菌 pv. 烟碱的hrp 致病性岛（hrp PAI）编码一个 III 型分泌系统（TTSS）及其调控系统，这是在植物中致病所必需的。已经鉴定出三种重要的调控蛋白-HrpR、HrpS 和 HrpL-来激活 hrp PAI 基因表达。细菌 Lon 蛋白酶调节各种基因的表达。为了研究 Lon 蛋白酶在丁香假单胞菌 pv. 烟碱 11528 中的调控机制，我们克隆了 lon 基因，然后通过基因同源重组的方法构建了 lon 缺失突变株。lon 突变体表现出对 UV 更敏感的特性，这是此类突变体的典型特征。与野生型相比，Δlon 突变体产生的 tabtoxin 水平更高。lacZ 基因与 hrpA 启动子融合，并在 hrp 抑制和 hrp 诱导培养基中测量β-半乳糖苷酶的活性。Lon 蛋白酶在 hrp 抑制条件下作为 hrp PAI 的负调控因子发挥作用。我们发现，与野生型菌株相比，lon 缺失菌株能更快、更强地激发宿主防御系统，这表明 Lon 蛋白酶是系统性发病所必需的。
