Molecular identification and functional analysis of flgRRxoo, the gene encoding a putative response regulator in regulation of virulence expression of Xanthomonas oryzae pv. oryzae.

To be better understand the structure and biological function of flgRRxoo in Xanthomonas oryzae pv.oryzae(Xoo),the casual pathogen of bacterial blight in rice,molecular identification of the flgRRxoo gene was performed through gene cloning,sequencing and mutant construction.flgRRxoo cloned from geno-mic DNA of the wild-type strain PXO99A was found to be highly conserved in plant-pathogenic Xanthomonas spp.,and FlgRRxoo was structurally featured with REC domain.The mutant was constructed after a double crossover recombination event between gentamycin resistance gene(GmR) and flgRRxoo through the marker exchange and validated by PCR assay.The △flgRRxoo mutant demonstrated great deficiency in exopolysaccharide(EPS) production and obviously low virulence compared with PXO99A,which could be restored through complementation of the mutant by introducing flgRRxoo gene;expression of EPS biosynthesis-related genes gumBDGKM was down-regulated in △flgRRxoo.Whereas,no significant changes in flagellar motility and production of extracellular cellulase and xylanase in vitro were observed in △flgRRxoo compared to PXO99A.Therefore,FlgRRxoo might act as a regulator involved in regulation of EPS production and virulence of Xoo.