RpfC regulates the expression of the key regulator hrpX of the hrp/T3SS system in Xanthomonas campestris pv. campestris

Abstract

BackgroundThe 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.MethodsPositive 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.ResultsMutation 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.ConclusionsRpfC positively regulates the expression of hrpX independent of RpfG, showing a complex regulatory network linking the rpf/DSF and hrp/T3SS systems.Electronic supplementary materialThe online version of this article (10.1186/s12866-018-1233-5) contains supplementary material, which is available to authorized users.

Flp, a Fis‐like protein, contributes to the regulation of type III secretion and virulence processes in the phytopathogenXanthomonas campestrispv.campestris

“…To confirm this idea we compared the transcriptome profile of the Δflp strain (generated in this study) and the hrpX mutant strain (generated in Jiang et al, 2018), which identified a set of target genes that appeared to be regulated by Flp and not HrpX. To confirm this we examined the expression of XC_1273, XC_2659, XC_2827, XC_3129, XC_3694 and XC_4002 by RT-PCR by extracting RNA from wild-type, Δflp, CΔflp and Δflp/ p3X cultured in XVM2, respectively.…”

The HrpG/HrpX Regulon of Xanthomonads—An Insight to the Complexity of Regulation of Virulence Traits in Phytopathogenic Bacteria

“…On the other hand, DSF was reported to play a role in the regulation of the hrp regulon in Xcc . Analysis of Xcc rpfC mutant identified a significant reduction in the expression of hrpG , hrpX, and their downstream targets [ 101 ]. This reduction was also accompanied by reduced HR response in resistant plants and almost complete abolishment of virulence in Chinese radish [ 101 ].…”

“…Expression, stability, and activity of HrpG and HrpX are dependent on numerous regulatory factors. HrpG and HrpX are negatively or positively controlled by two-component system kinases and response regulators [ 60 , 62 ], ATPases [ 102 ], transcriptional regulators [ 53 , 63 , 77 , 81 , 84 , 91 , 93 , 103 , 104 , 105 ], small signaling molecules [ 74 , 101 ] and histone-like nucleoid-structuring (H-NS) protein [ 106 , 107 , 108 ] ( Figure 2 ). However, most studies do not demonstrate direct interactions with HrpG, HrpX, or their promoters and it appears that the regulatory function on this regulon by most of these factors is probably indirect.…”

Identification of c-di-GMP Signaling Components in Xanthomonas oryzae and Their Orthologs in Xanthomonads Involved in Regulation of Bacterial Virulence Expression

“…RpfG contains a receiver domain for signal transduction and a HD-GYP domain for c-di-GMP degradation. In addition, RpfC regulates the expression of hrp genes via RpfG and the global transcriptional regulator Clp (Jiang et al, 2018). Furthermore, RpfG's regulation of downstream signaling components might be at the post-transcriptional and post-translational levels.…”