Agrobacterium vitis Strain AB3 Harbors Two IndependentTartrate Utilization Systems, One of Which Is Encoded by theTi Plasmid. L. Otten. Plant Pathology Department, C. N. R. S. Institute of Plant Molecular Biology, Rue du General Zimmer 12, Strasbourg 67084, France. P. Crouzet, J.-Y. Salomone, P. de Ruffray, and E. Szegedi. Plant Pathology Department, C. N. R. S. Institute of Plant Molecular Biology, Rue du General Zimmer 12, Strasbourg 67084, France. MPMI 8:138-146. Accepted 24 October 1995. Copyright 1995 The American Phytopathological Society.

Several strains of the grapevine-associated bacterial pathogen Agrobacterium vitis contain large plasmids encoding tartrate utilization. These plasmids can be transferred to the cured Agrobacterium tumefaciens strain UBAPF2 by conjugation in grapevine tissues. Among A. vitis strains, AB3 is exceptional since the tartrate-positive UBAPF2 strains which can be obtained by AB3xUBAPF2 conjugation lack a detectable plasmid. When UBAPF2 was transformed with AB3 plasmid DNA, tar+ transfor-mants were found which harbored a large plasmid, called pTrAB3. The 245-kb pTrAB3 plasmid was isolated, sub-cloned, and mapped. Hybridization of total DNA from UBAPF2xAB3 transconjugants with pTrAB3 subclones revealed that in most transconjugants pTrAB3 is linked to a 60-kb AB3 plasmid (called pAB3b) or part of it. Recombination occurs within a 2.65-kb PstI fragment in pTrAB3, and in most cases in a 9.0-kb PstI fragment of pAB3b. The pTrAB3::pAB3b cointegrate structure is itself integrated into a larger DNA molecule, presumably the UBAPF2 chromosome. The tartrate utilization (TAR) region of pTrAB3 was cloned on a 9.5-kb DNA fragment. In addition to the pTrAB3 TAR region, the analysis of a rare tar+ UBAPF2xAB3 transconjugant which lacked pTrAB3 sequences and carried a non-integrated pTiAB3 plasmid revealed an additional TAR region. The pTiAB3 TAR region was cloned and located on the earlier established map of pTiAB3. The TAR regions of pTrAB3 and pTiAB3 do not cross-hybridize and have different functional properties. The strain with the integrated pTrAB3 plasmid differs in its utilization of tartrate from the strain with the nonintegrated pTrAB3 plasmid. Tartrate utilization by AB3 is therefore a complex and redundant property.