State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, College of Life Science and Technology, Guangxi University, 100 Daxue Road, Nanning, 530004, Guangxi, China.
BMC Microbiol. 2018 Sep 3;18(1):103. doi: 10.1186/s12866-018-1233-5.
The Gram-negative phytopathogenic bacterium Xanthomonas campestris pv. campestris recruits the hrp/T3SS system to inject pathogenicity effector proteins into host cells and uses the rpf/DSF cell-cell signaling system to regulate the expression of virulence factors such as extracellular enzymes and polysaccharide. Whether these two systems have any connection is unknown.
Positive regulator candidates affecting hrpX expression were identified by sacB strategy. The transcriptional expression was determined by qRT-PCR and GUS activity analysis. Transcriptome analysis was performed by RNA deep-sequencing. The hypersensitive response (HR) was determined in the nonhost plant pepper ECW-10R and electrolyte leakage assay.
Mutation of the gene encoding the sensor RpfC of the rpf/DSF system significantly reduced the expression of hrpX, the key regulator of the hrp/T3SS system, all of the genes in the hrp cluster and most reported type III effector genes. Mutation of rpfG did not affect the expression of hrpX. The rpfC mutant showed a delayed and weakened HR induction.
RpfC positively regulates the expression of hrpX independent of RpfG, showing a complex regulatory network linking the rpf/DSF and hrp/T3SS systems.
革兰氏阴性植物病原细菌黄单胞菌野油菜致病变种利用 hrp/T3SS 系统将致病性效应蛋白注入宿主细胞，并利用 rpf/DSF 细胞间信号系统来调节包括胞外酶和多糖在内的毒力因子的表达。目前尚不清楚这两个系统之间是否存在联系。
通过 sacB 策略鉴定影响 hrpX 表达的正调控因子候选基因。通过 qRT-PCR 和 GUS 活性分析来确定转录表达。通过 RNA 深度测序进行转录组分析。在非宿主植物辣椒 ECW-10R 中进行过敏反应（HR）的测定和电解质渗漏测定。
rpf/DSF 系统的传感器 RpfC 编码基因的突变显著降低了 hrp/T3SS 系统的关键调控因子 hrpX、hrp 簇中的所有基因和大多数报道的 III 型效应基因的表达。rpfG 突变不影响 hrpX 的表达。rpfC 突变体的 HR 诱导延迟且减弱。
RpfC 独立于 RpfG 正向调控 hrpX 的表达，显示出 rpf/DSF 和 hrp/T3SS 系统之间存在复杂的调控网络。
