title: Organization and environmental regulation of the Pseudomonas syringae pv. syringae 61 hrp cluster.
abstract: The ability of Pseudomonas syringae pv. syringae 61 to elicit the hypersensitive response in nonhost plant species has been linked to a cluster of hrp/hrm genes whose expression appears to be environmentally regulated. To understand the genetic organization of this hrp/hrm gene cluster and its expression during the interaction with nonhost plant species better, we constructed a set of chromosomal hrp-uidA fusions in P. syringae pv. syringae 61 by Tn5-gusA1 mutagenesis of the cloned hrp/hrm gene cluster and transferred them into the genome by marker exchange mutagenesis. Complementation analysis employing plasmid-borne Tn5-gusA1 insertions and previously characterized chromosomal TnphoA mutations defined at least eight apparent transcriptional units within the hrp/hrm cluster, several of which were multicistronic. The expression of hrp-uidA fusions in seven of these apparent hrp transcriptional units increased following inoculation into tobacco leaves. Enhanced expression from a representative fusion was detected 1 h after inoculation of tobacco leaves. The induction observed in planta was similar to the levels detected following culture of the bacteria in minimal-salts medium: irrespective of the carbon source. Complex amino acid sources, such as peptone, repressed the expression of P. syringae pv. syringae 61 hrp genes at levels exceeding 0.028%. The results indicate that enhanced expression of hrp genes occurs early in the interaction with nonhost plant species in an apparent response to altered nutritional conditions.
authors.affiliation: Department of Botany, Maryland Biotechnology Institute, University of Maryland, College Park 20742-5815.
authors.forename: Y
authors.initials: Y
authors.lastname: Xiao
authors.forename: Y
authors.initials: Y
authors.lastname: Lu
authors.forename: S
authors.initials: S
authors.lastname: Heu
authors.forename: S W
authors.initials: SW
authors.lastname: Hutcheson
mesh_terms: D002478:Cells, Cultured; D004252:DNA Mutational Analysis; D004269:DNA, Bacterial / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D006967:Hypersensitivity; D066298:In Vitro Techniques; D009584:Nitrogen / Q000378:metabolism; D009876:Operon; D010947:Plants, Toxic; D011549:Pseudomonas / Q000235:genetics* / Q000472:pathogenicity; D015183:Restriction Mapping; D013997:Time Factors; D014026:Nicotiana / Q000382:microbiology; D014158:Transcription, Genetic
chemical_list: D004269:DNA, Bacterial; D009584:Nitrogen