Cloning And Fuctional Study Of Key Genes Of Twin-Arginine Translocation System Of Xanthomonas Oryzae

Xanthomonas oryzae pv.oryzae(Xoo) and X.oryzae pv.oryzicola(Xooc) cause leaf blight and leaf streak on rice respectively.In this study,we identified and characterized the contribution of the twin-arginine translocation(Tat) pathway to motility,chemotaxis, extracellular polysaccharide(EPS) and virulence of the phytopathogens X.oryzae pv. oryzae strain PXO99 and X.oryzae pv.oryzicola strain RsGD42.(â… ) A tat homologue,designated tat_Xoo,was cloned from Xanthomonas oryzae pv. oryzae strain PXO99,with degenerated primers by polymerase amplification reaction (PCR).tatB and tatC disruption mutants of strain PXO99 were successfully generated by a single cross-over event,and confirmed by PCR and Southem blotting.Wild type strain PXO99 cells were highly motile in NYGA 0.3%soft agar medium.In contrast,the tatB and tatC mutation impaired motility.Furthermore,the cells of tatB and tatC mutants lacked detectable flagella and both mutants exhibited almost no chemotaxis toward glucose under aerobic conditions indicating this secretion pathway contributes to flagellar biogenesis and chemotactic responses.It was also obersved that the tatB and tatC mutants exhibited reductive production of extracellular polysaccharide(EPS).In addition,both tatB and tatC mutants of strain PXO99 had significant reduction of virulence on rice when compared with the wild type.However,tatB and tatC mutants still could elicit the hypersensitive response(HR) in nonhost tobacco.Our findings indicated that the Tat system of X.oryzae pv.oryzae played an important role in virulence on rice.(â…¡) A tat homologue,designated tat_Xooc,was cloned from Xanthornonas oryzae pv. oryzicola,with degenerated primers by polymerase amplification reaction(PCR).A tatC disruption mutant of strain RsGD42 was constructed by a single cross-over event,and confirmed by PCR and Southern blotting.The tatC mutant was not affected in in vitro growth and induction of hypersensitive response(HR) in nonhost tobacco compared to wild type strain RsGD42.Interestingly,the tatC mutant lacked detectable flagella and highly impaired in motility.Furthermore,the tatC mutant displayed almost no chemotaxis toward glucose under aerobic conditions.Remarkably,it was observed that the tatC mutant exhibited reductive production of extracellular polysaccharide(EPS) and significant reduction of virulence on adult rice plants when compared to wild type strain.Our findings indicated that the Tat system of X.oryzae pv.oryzicola played an important role in virulence on rice.