Various nopaline catabolism genes located outside the Ti-plasmids in Agrobacterium tumefaciens strains

Abstract

The structure and location of nopaline catabolism (noc) genes were examined in various Agrobacterium tumefaciens strains by plasmid transfer and by Southern hybridization analysis. In a pathogenic strain, PyTS3, the noc genes were identified both on the Ti-plasmid, pTiPyTS3, and on the cryptic plasmid, pCr140. Plasmid pCr140 was transmitted to another A. tumefaciens strain at a higher frequency than was pTiPyTS3. Southern hybridization analysis, using Ti-plasmid-derived noc genes as a probe, indicated that the noc genes of pTiPyTS3 differed structurally from those of pCr140. Three non-pathogenic strains possessed plasmids that hybridized to the probe, and all showed identical patterns of hybridization after restriction enzyme cleavage. However, this pattern was different from those of pTiPyTS3 and pCr140. Only pCr140 showed partial hybridization to the probe. A nonpathogenic strain, PyON8, that grew on both nopaline and octopine, showed no hybridization of its plasmid or chromosome to the probe. Since nopaline-utilizing transconjugants were not obtained from PyON8, the noc genes in PyON8 may be chromosomally located. These results indicate that A. tumefaciens contains diverse noc genes which differ in both organization and cellular localization.