Identification Of Two-Component Regulatory System Genes ColRS In Xanthomonas Campestris Pv. Campestris

Xanthomonas campestris pathovar campestris(Xcc)is the causal agent of black-rot disease,one of the most destructive diseases of cruciferous plants worldwide.To prevent the disease intensive studies have been carried out to investigate the mechanism of this model phytopathogen.Colonization is the initial phase of infection that Plant pathogens need to success colonize on host surface before entering into plant.Two-component regulatory system is widely used by bacteria for regulation of various cellular processes such as colonization,adaptation,growth,virulence,etc.It had been reported that colRS two-component regulatory system plays an important role in regulation of colonization.In addition,the research on colRS showed colR has function in adaptation in Pseudomonas putida CD2 and Pseudomonas putida PaW85 and colRS participates regulation of Tn4652 transposition in Pseudomonas putida PaW85,respectively.There are 3 pairs of predicted colRS homologous genes in X.campestris pv.campestris 8004.To investigate whether colRS homologous genes contribute to colonization of Xcc,the integration mutants of colR,colS genes NK1049,NK1050,NK3125,NK3126,NK3451 and NK3452 were constructed and applied to colonization test.It was found that the mutant NK1049 has reduced colonizing-ability on plant and the phenotypcs of NK1049 could be restored by XC1049 in trans.XC1049 was then designated as colR_Xcc.Plant-infection test also showed that NK1049 was impaired in virulence and could only cause weak and delayed HR on non-host plant.General stress assay revealed that colR_Xccmutant was defective in adaptation to osmotic,heavy-metal,phenol,pH stress.Monitoring growth rate showed the mutant NK1049 persisting slow growth in medium and plant leaves.Antibiotic sensitivity determination indicates that membrane function of colR_Xccis likely altered.RT-PCR showed that mutation in colR_Xccreduced the transcriptional level of hrpC and hrpE operons.This work identifies the colR_Xccas a key gene which is involved in colonization on host leaves,stress adaptation,growth,infection of plant, and regulation of hrp genes in X.campestris pv.campestris.