title: Isolation of Ralstonia solanacearum hrpB constitutive mutants and secretion analysis of hrpB-regulated gene products that share homology with known type III effectors and enzymes.
abstract: The Hrp type III secretion system (TTSS) is essential for the pathogenicity of the Gram-negative plant pathogen Ralstonia solanacearum. To examine the secretion of type III effector proteins via the Hrp TTSS, a screen was done of mutants constitutively expressing the hrpB gene, which encodes an AraC-type transcriptional activator for the hrp regulon. A mutant was isolated that in an hrp-inducing medium expresses several hrpB-regulated genes 4.9-83-fold higher than the wild-type. R. solanacearum Hrp-secreted outer proteins PopA and PopC were secreted at high levels into the culture supernatants of the hrpB constitutive (hrpB(c)) mutant. Using hrpB(c) mutants, the extracellular secretion of several hrpB-regulated (hpx) gene products that share homology with known type III effectors and enzymes was examined. Hpx23, Hpx24 and Hpx25, which are similar in sequence to Pseudomonas syringae pv. tomato effector proteins HopPtoA1, HolPtoR and HopPtoD1, are also secreted via the Hrp TTSS in R. solanacearum. The secretion of two hpx gene products that share homology with known enzymes, glyoxalase I (Hpx19) and Nudix hydrolase (Hpx26), was also examined. Hpx19 is accumulated inside the cell, but interestingly, Hpx26 is secreted outside the cell as an Hrp-secreted outer protein, suggesting that Hpx19 functions intracellularly but Hpx26 is a novel effector protein of R. solanacearum.
authors.affiliation: Research Institute for Biological Sciences, Okayama (RIBS), 7549-1 Yoshikawa, Kibichuo-cho, Okayama 716-1241, Japan.
authors.forename: Naoyuki
authors.initials: N
authors.lastname: Tamura
authors.affiliation: Research Institute for Biological Sciences, Okayama (RIBS), 7549-1 Yoshikawa, Kibichuo-cho, Okayama 716-1241, Japan.
authors.forename: Yukio
authors.initials: Y
authors.lastname: Murata
authors.affiliation: Research Institute for Biological Sciences, Okayama (RIBS), 7549-1 Yoshikawa, Kibichuo-cho, Okayama 716-1241, Japan.
authors.forename: Takafumi
authors.initials: T
authors.lastname: Mukaihara
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D011549:Pseudomonas / Q000502:physiology; D043368:Ralstonia solanacearum / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D014157:Transcription Factors; C079047:hrpB protein, Ralstonia solanacearum