title: The quantitative regulation of the hrp regulator HrpX is involved in sugar-source-dependent hrp gene expression in Xanthomonas oryzae pv. oryzae.
abstract: In Xanthomonas oryzae pv. oryzae, the pathogen of bacterial leaf blight of rice, hrp gene expression is regulated by the key hrp regulators HrpG and HrpX. HrpG regulates hrpX and hrpA, and HrpX regulates the other hrp genes on hrpB-hrpF operons. We previously examined the expression of the HrpX-regulated hrp gene hrcU and demonstrated that hrp gene expression is highly induced in a certain nutrient-poor medium containing xylose. In the present study, we found that the induction level of HrpX-regulated hrp genes was higher in medium with xylose than in media with any other sugar sources (glucose, sucrose and fructose), but that expression of hrpG, hrpX and hrpA was independent of the sugar sources. In western blot analysis, the accumulation of HrpX was reduced in media with a sugar other than xylose, probably as a result of proteolysis, but the addition of xylose canceled this reduced accumulation of the protein. The results suggest that proteolysis of HrpX is an important hrp regulatory mechanism and that xylose specifically suppresses this proteolysis, resulting in active hrp gene expression in X. oryzae pv. oryzae.
authors.affiliation: Laboratory of Plant Pathology, Graduate School of Agriculture, Kyoto Prefectural University, Kyoto 606-8522, Japan.
authors.forename: Yumi
authors.initials: Y
authors.lastname: Ikawa
authors.affiliation: Laboratory of Plant Pathology, Graduate School of Agriculture, Kyoto Prefectural University, Kyoto 606-8522, Japan s_tsuge@kpu.ac.jp.
authors.forename: Seiji
authors.initials: S
authors.lastname: Tsuge
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D015153:Blotting, Western; D005632:Fructose / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D005809:Genes, Regulator; D005947:Glucose / Q000378:metabolism; D010935:Plant Diseases / Q000382:microbiology*; D059748:Proteolysis; D013395:Sucrose / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism; D000069296:Type III Secretion Systems / Q000235:genetics / Q000378:metabolism; D014774:Virulence / Q000235:genetics; D014974:Xanthomonas / Q000235:genetics* / Q000472:pathogenicity; D014994:Xylose / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D014157:Transcription Factors; D000069296:Type III Secretion Systems; D005632:Fructose; D013395:Sucrose; D014994:Xylose; D005947:Glucose
keywords: hrp regulatory system; plant pathogenic bacteria; type III secretion system