Characterization of the Agrobacterium octopine-cucumopine catabolic plasmid pAtAg67

Abstract

In addition to tumor-inducing agrobacteria, non-pathogenic strains are often isolated from crown gall tumors. Such non-pathogenic strains sometimes contain catabolic plasmids that allow them to take advantage of the opines produced in the tumors. Here we characterize for the first time an octopine catabolic plasmid, pAtAg67, which is derived from an Agrobacterium strain isolated from a grapevine tumor in Crete. By sequence analysis, we deduce that pAtAg67 enables its host to catabolize not only octopine, but also cucumopine and agrocinopine-like compounds. We found that a highly similar set of catabolic genes was present in the Ti plasmids of tumorigenic octopine-cucumopine grapevine strains such as pTiAg57. However, the catabolic genes in octopine-cucumopine Ti plasmids were interrupted by a T-DNA segment. As no T-DNA remnants, virulence genes or border repeats were found in pAtAg67, catabolic plasmid pAtAg67 does not appear to be a degenerate octopine-cucumopine Ti plasmid. In line, plasmid pAtAg67 was found to be compatible with incRh1 octopine Ti plasmids, but to be incompatible with the incRh2 agropine Ti plasmid pTiBo542, forming cointegrates by recombination in the homologous trb genes.