title: Alternative sigma factor RpoN2 is required for flagellar motility and full virulence of Xanthomonas oryzae pv. oryzae.
abstract: Xanthomonas oryzae pv. oryzae (Xoo), the bacterial blight pathogen of rice, harbors a single polar flagellum for motility. How the flagellar system is regulated and how it is related to bacterial pathogenesis are not well understood. The genomic sequence of Xoo strain PXO99(A) revealed a flagellar regulon containing over 60 contiguous genes. A gene encoding alternative sigma factor 54 (σ(54)), named as rpoN2, is located in the central region of the regulon. RT-PCR analysis demonstrated rpoN2 was transcribed in an operon with flgRR, and fleQ. Single gene deletion mutants of the rpoN2 operon were generated. The rpoN2 and fleQ mutant lost swimming motility, whereas the flgRR mutant remained motile. Quantitative RT-PCR analysis further demonstrated that expression of regulatory genes fliA and flgM, and structural genes flgG, flhB, and fliC were significantly down-regulated in the rpoN2 and fleQ mutants. These results indicated that RpoN2 and FleQ synergistically controlled flagellar motility by regulating gene expression. Interestingly, the rpoN2 mutant, but not the fleQ mutant was impaired in its virulence on rice. In addition, we showed that the flagellin gene fliC mutant, which was non-motile, was not defective in virulence. Thus, we concluded that flagellar motility might not be essential for Xoo virulence in rice, and RpoN2 probably regulated bacterial virulence through a manner independent of its role in controlling flagellar gene expression.
authors.affiliation: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China.
authors.forename: Fang
authors.initials: F
authors.lastname: Tian
authors.affiliation: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China.
authors.forename: Chao
authors.initials: C
authors.lastname: Yu
authors.affiliation: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China.
authors.forename: Haiyun
authors.initials: H
authors.lastname: Li
authors.affiliation: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China.
authors.forename: Xiaoli
authors.initials: X
authors.lastname: Wu
authors.affiliation: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China.
authors.forename: Bo
authors.initials: B
authors.lastname: Li
authors.affiliation: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China.
authors.forename: Huamin
authors.initials: H
authors.lastname: Chen
authors.affiliation: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China.
authors.forename: Maosen
authors.initials: M
authors.lastname: Wu
authors.affiliation: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China. Electronic address: hechenyang@caas.cn.
authors.forename: Chenyang
authors.initials: C
authors.lastname: He
mesh_terms: D005407:Flagella / Q000502:physiology*; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D023061:Gene Order; D005798:Genes, Bacterial; D056426:Genetic Loci; D012275:Oryza / Q000382:microbiology; D010641:Phenotype; D010935:Plant Diseases / Q000382:microbiology; D012808:Sigma Factor / Q000235:genetics* / Q000378:metabolism; D014774:Virulence / Q000235:genetics; D014974:Xanthomonas / Q000472:pathogenicity / Q000502:physiology*
chemical_list: D012808:Sigma Factor
keywords: Bacterial leaf blight; Flagellin; Pathogenesis; Regulatory protein; Sigma factor