Agrobacterium Vitis Research Articles

The Ti Plasmid from the Wide Host Range Agrobacterium vitis Strain Tm4: Map and Homology with Other Ti Plasmids

The octopine/cucumopine (o/c) strains of Agrobacterium vitis are divided into limited (LHR) and wide host range (WHR) strains. We present here the first map of a Ti plasmid from a WHR o/c strain, Tm4. pTiTm4 (252 kb) has homology with the octopine Ti plasmid pTiAch5, the nopaline plasmid pTiC58, and the Ri plasmid pRiHRI. Approximately 155 kb of pTiTm4 is homologous with the LHR o/c Ti plasmids pTiAB3 and pTiAg57, the remaining part is pTiTm4-specific. Our data suggest that the evolution of the o/c Ti plasmids was accompanied by large-scale changes in plasmid structure. The origin of replication of pTiTm4 was localized by a functional assay.

Physical map of the vitopine Ti plasmid pTiS4

Within the Agrobacterium vitis group the vitopine strains represent a special subclass. Vitopine bacteria carry Ti plasmids with little or no homology with the well-characterized T-DNAs of Agrobacterium tumefaciens or Agrobacterium rhizogenes. The 262-kb Ti plasmid of the vitopine strain S4 was cloned and mapped. Homology studies with the octopine Ti plasmid pTiAch5, the nopaline Ti plasmid pTiC58, and the agropine/mannopine Ri plasmid pRiHRI identified several regions of homology. The origin of replication was localized to within 2.5 kb.

Agrobacterium vitis sp. nov. for Strains of Agrobacterium biovar 3 from Grapevines

Agrobacterium isolates from grapevines that were previously characterized as biovar 3 strains were compared with the type strains of the four previously described species of the genus Agrobacterium, Agrobacterium tumefaciens, Agrobacterium radiobacter, Agrobacterium rhizogenes, and Agrobacterium rubi. Ten grapevine isolates were distinguished from other Agrobacterium species phenotypically by a number of biochemical tests and by their reaction with a monoclonal antibody raised to biovar 3. Levels of DNA binding between the type strains of previously described species and three grapevine isolates were estimated by optical measurement of initial DNA renaturation rates. The levels of DNA binding between grapevine isolates were 78 to 92%, and the levels of DNA binding with other type strains ranged from 7 to 47%. Our results indicate that the grapevine isolates are distinct from the type strains of the four previously described Agrobacterium species. A new species, Agrobacterium vitis, is proposed; the type strain is strain NCPPB 3554.