title: AsnB, regulated by diffusible signal factor and global regulator Clp, is involved in aspartate metabolism, resistance to oxidative stress and virulence in Xanthomonas oryzae pv. oryzicola.
abstract: Xanthomonas oryzae pv. oryzicola (Xoc) causes bacterial leaf streak in rice, which is a destructive disease worldwide. Xoc virulence factors are regulated by diffusible signal factor (DSF) and the global regulator Clp. In this study, we have demonstrated that asnB (XOC_3054), encoding an asparagine synthetase, is a novel virulence-related gene regulated by both DSF and Clp in Xoc. A sequence analysis revealed that AsnB is highly conserved in Xanthomonas. An asnB mutation in Xoc dramatically impaired pathogen virulence and growth rate in host rice, but did not affect the ability to trigger the hypersensitive response in nonhost (plant) tobacco. Compared with the wild-type strain, the asnB deletion mutant was unable to grow in basic MMX (-) medium (a minimal medium without ammonium sulphate as the nitrogen source) with or without 10 tested nitrogen sources, except asparagine. The disruption of asnB impaired pathogen resistance to oxidative stress and reduced the transcriptional expression of oxyR, katA and katG, which encode three important proteins responsible for hydrogen peroxide (H(2)O(2)) sensing and detoxification in Xanthomonas in the presence of H(2)O(2), and nine important known Xoc virulence-related genes in plant cell-mimicking medium. Furthermore, the asnB mutation did not affect extracellular protease activity, extracellular polysaccharide production, motility or chemotaxis. Taken together, our results demonstrate the role of asnB in Xanthomonas for the first time.
authors.affiliation: College of Plant Protection, Nanjing Agricultural University, Nanjing 210095, China.
authors.forename: Guoliang
authors.initials: G
authors.lastname: Qian
authors.forename: Chunhui
authors.initials: C
authors.lastname: Liu
authors.forename: Guichun
authors.initials: G
authors.lastname: Wu
authors.forename: Fangqun
authors.initials: F
authors.lastname: Yin
authors.forename: Yancun
authors.initials: Y
authors.lastname: Zhao
authors.forename: Yijing
authors.initials: Y
authors.lastname: Zhou
authors.forename: Yanbing
authors.initials: Y
authors.lastname: Zhang
authors.forename: Zhiwei
authors.initials: Z
authors.lastname: Song
authors.forename: Jiaqin
authors.initials: J
authors.lastname: Fan
authors.forename: Baishi
authors.initials: B
authors.lastname: Hu
authors.forename: Fengquan
authors.initials: F
authors.lastname: Liu
mesh_terms: D001224:Aspartic Acid / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002633:Chemotaxis / Q000187:drug effects / Q000235:genetics; D003470:Culture Media; D004058:Diffusion; D060467:Disease Resistance / Q000187:drug effects; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D005798:Genes, Bacterial / Q000235:genetics; D006861:Hydrogen Peroxide / Q000494:pharmacology; D009154:Mutation / Q000235:genetics; D012275:Oryza / Q000187:drug effects / Q000254:growth & development / Q000276:immunology / Q000382:microbiology; D018384:Oxidative Stress / Q000187:drug effects; D010447:Peptide Hydrolases / Q000378:metabolism; D020161:Physical Chromosome Mapping; D010935:Plant Diseases / Q000276:immunology / Q000382:microbiology; D010936:Plant Extracts / Q000494:pharmacology; D011401:Promoter Regions, Genetic / Q000235:genetics; D053038:Quorum Sensing / Q000187:drug effects / Q000235:genetics; D015203:Reproducibility of Results; D014026:Nicotiana / Q000187:drug effects / Q000276:immunology / Q000382:microbiology; D014158:Transcription, Genetic / Q000187:drug effects; D014774:Virulence / Q000187:drug effects / Q000235:genetics; D014974:Xanthomonas / Q000187:drug effects / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity*
chemical_list: D001426:Bacterial Proteins; D003470:Culture Media; D010936:Plant Extracts; D001224:Aspartic Acid; D006861:Hydrogen Peroxide; D010447:Peptide Hydrolases