title: The HrpX/HrpY two-component system activates hrpS expression, the first step in the regulatory cascade controlling the Hrp regulon in Pantoea stewartii subsp. stewartii.
abstract: A regulatory cascade activating hrp/hrc type III secretion and effector genes was delineated in Pantoea stewartii subsp. stewartii, a bacterial pathogen of corn. Four hrp regulatory genes were characterized: hrpX and hrpY encode the sensor kinase and response regulator, respectively, of a two-component signal transduction system; hrpS encodes an NtrC-like transcriptional enhancer; and hrpL encodes an alternative sigma factor. Epistasis analysis, expression studies using gene fusions, and genetic reconstruction of each step in Escherichia coli were used to delineate the following pathway: HrpY activates hrpS and also positively autoregulates the hrpXY operon. In turn, HrpS is required for full activation of the sigma54-dependent hrpL promoter. Finally, HrpL controls expression of all known hrp and wts genes. In vitro, hrpS and all downstream hrp genes were regulated by pH and salt concentration. Mutants with in-frame deletions in hrpX were still partially virulent on corn but were unable to sense the chemical or metabolic signals that induce hrp genes in vitro. Site-directed mutagenesis of HrpY indicated that aspartate 57 is the probable phosphorylation site and that it is needed for activity. These findings suggest that both HrpX and an alternate mechanism are involved in the activation of HrpY in planta.
authors.affiliation: Department of Plant Pathology and the Plant Molecular Biology/Biotechnology Program, The Ohio State University, 2021 Coffey Road, Columbus, Ohio 43210-1087, USA.
authors.forename: Massimo
authors.initials: M
authors.lastname: Merighi
authors.forename: Doris R
authors.initials: DR
authors.lastname: Majerczak
authors.forename: Elizabeth H
authors.initials: EH
authors.lastname: Stover
authors.forename: David L
authors.initials: DL
authors.lastname: Coplin
mesh_terms: D000595:Amino Acid Sequence; D001224:Aspartic Acid / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D017124:Conserved Sequence / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004843:Epistasis, Genetic; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D005810:Multigene Family / Q000235:genetics; D009154:Mutation; D020636:Pantoea / Q000235:genetics* / Q000378:metabolism; D010641:Phenotype; D018085:Regulon / Q000235:genetics*; D017421:Sequence Analysis; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C085855:HrpL protein, Pseudomonas syringae; C080371:HrpX protein, Bacteria; C421032:HrpY protein, Erwinia amylovora; D012808:Sigma Factor; D014157:Transcription Factors; C060789:hrpS protein, Pseudomonas syringae; D001224:Aspartic Acid