title: Reexamining the role of the accessory plasmid pAtC58 in the virulence of Agrobacterium tumefaciens strain C58.
abstract: Isogenic strains of Agrobacterium tumefaciens carrying pTiC58, pAtC58, or both were constructed and assayed semiquantitatively and quantitatively for virulence and vir gene expression to study the effect of the large 542-kb accessory plasmid, pAtC58, on virulence. Earlier studies indicate that the att (attachment) genes of A. tumefaciens are crucial in the ability of this soil phytopathogen to infect susceptible host plants. Mutations in many att genes, notably attR and attD, rendered the strain avirulent. These genes are located on pAtC58. Previous work also has shown that derivatives of the wild-type strain C58 cured of pAtC58 are virulent as determined by qualitative virulence assays and, hence, pAtC58 was described as nonessential for virulence. We show here that the absence of pAtC58 in pTiC58-containing strains results in reduced virulence but that disruption of the attR gene does not result in avirulence or a reduction in virulence. Our studies indicate that pAtC58 has a positive effect on vir gene induction as revealed by immunoblot analysis of Vir proteins and expression of a PvirB::lacZ fusion.
authors.affiliation: Plant Science Institute, Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6018, USA.
authors.forename: Gauri R
authors.initials: GR
authors.lastname: Nair
authors.forename: Zhenying
authors.initials: Z
authors.lastname: Liu
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Binns
mesh_terms: D016960:Agrobacterium tumefaciens / Q000235:genetics / Q000472:pathogenicity*; D015964:Gene Expression Regulation, Bacterial; D009154:Mutation; D036741:Plant Tumor-Inducing Plasmids / Q000235:genetics*; D010941:Plant Tumors / Q000235:genetics / Q000382:microbiology; D010944:Plants / Q000235:genetics / Q000382:microbiology*; D030821:Plants, Genetically Modified; D015533:Transcriptional Activation; D014170:Transformation, Genetic / Q000235:genetics; D014774:Virulence / Q000235:genetics