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.
Highlights
The Gram-negative phytopathogenic bacterium Xanthomonas campestris pv. campestris recruits the hrp/Type III secretion system (T3SS) system to inject pathogenicity effector proteins into host cells and uses the rpf/diffusible signal factor (DSF) cell-cell signaling system to regulate the expression of virulence factors such as extracellular enzymes and polysaccharide
We found that a mutation in the rpfC gene of the rpf/DSF system significantly reduced the expression of hrpX
It has been reported that expression of sacB gene in the presence of 5% sucrose in agar medium is lethal to a variety of bacteria including E. coli, Agrobacterium tumefaciens, and Rhizobium meliloti [23]
Summary
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. 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. The Gram-negative bacterium Xanthomonas campestris pathovar campestris (Xcc) is the causal agent of black rot disease, one of the most destructive diseases of cruciferous crops worldwide [1] This pathogen can infect almost all members of the crucifer family (Brassicaceae), including many important vegetables, the major oil crop rape, and the model plant Arabidopsis thaliana. RpfC acts as the histidine kinase sensor in the two component regulatory system to sense the environmental DSF signal, leading to
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