title: RaxH/RaxR: a two-component regulatory system in Xanthomonas oryzae pv. oryzae required for AvrXa21 activity.
abstract: Xanthomonas oryzae pv. oryzae is the causal agent of bacterial leaf blight, one of the most serious diseases in rice. X. oryzae pv. oryzae Philippine race 6 (PR6) strains are unable to establish infection in rice lines expressing the resistance gene Xa21. Although the pathogen-associated molecule that triggers the Xa21-mediated defense response (AvrXa21) is unknown, six rax (required for AvrXa21 activity) genes encoding proteins involved in sulfur metabolism and Type I secretion were recently identified. Here, we report on the identification of two additional rax genes, raxR and raxH, which encode a response regulator and a histidine protein kinase of two-component regulatory systems, respectively. Null mutants of PR6 strain PXO99 that are impaired in either raxR, raxH, or both cause lesions significantly longer and grow to significantly higher levels than does the wild-type strain in Xa21-rice leaves. Both raxR and raxH mutants are complemented to wild-type levels of AvrXa21 activity by introduction of expression vectors carrying raxR and raxH, respectively. These null mutants do not affect AvrXa7 and AvrXa10 activities, as observed in inoculation experiments with Xa7- and Xa10-rice lines. Western blot and raxR/gfp promoter-reporter analyses confirmed RaxR expression in X. oryzae pv. oryzae. The results of promoter-reporter studies also suggest that the previously identified raxSTAB operon is a target for RaxH/RaxR regulation. Characterization of the RaxH/RaxR system provides new opportunities for understanding the specificity of the X. oryzae pv. oryzae-Xa21 interaction and may contribute to the identification of AvrXa21.
authors.affiliation: Department of Plant Pathology and Microbiology, Faculty of Agricultural, Food and Environmental Quality Sciences, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel.
authors.forename: Saul
authors.initials: S
authors.lastname: Burdman
authors.forename: Yuwei
authors.initials: Y
authors.lastname: Shen
authors.forename: Sang-Won
authors.initials: SW
authors.lastname: Lee
authors.forename: Qinzhong
authors.initials: Q
authors.lastname: Xue
authors.forename: Pamela
authors.initials: P
authors.lastname: Ronald
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D004269:DNA, Bacterial / Q000737:chemistry; D004926:Escherichia coli / Q000235:genetics; D005786:Gene Expression Regulation; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D000071677:Histidine Kinase; D008969:Molecular Sequence Data; D009154:Mutation; D016366:Open Reading Frames; D012275:Oryza / Q000382:microbiology*; D010940:Plant Proteins / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D011494:Protein Kinases / Q000235:genetics* / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000378:metabolism; D015534:Trans-Activators / Q000235:genetics* / Q000378:metabolism; D000071336:Transcription Activator-Like Effectors; D014974:Xanthomonas / Q000235:genetics* / Q000378:metabolism / Q000472:pathogenicity
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D010940:Plant Proteins; D011994:Recombinant Proteins; D015534:Trans-Activators; D000071336:Transcription Activator-Like Effectors; C097148:Xa21 protein, Oryza sativa; C079054:avrXa10 protein, Xanthomonas; C413190:avrXa7 protein, Xanthomonas oryzae; C112177:osmolarity response regulator proteins; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D000071677:Histidine Kinase