Characterization and distribution of tartrate utilization genes in the grapevine pathogen Agrobacterium vitis

Agrobacterium vitis is a common pathogen of grapevine. Most strains utilize tartrate, an abundant compound in grapevine. Strain AB3 carries two tartrate utilization (or TAR) regions: TAR-I (on the large pTrAB3 plasmid) and TAR-II (on the AB3 Ti plasmid). TAR-I and TAR-II were structurally and functionally analyzed and are similar to the TAR-III region from the tartrate utilization plasmid pTrAB4 of the nopaline-type A. vitis strain AB4 (Crouzet and Otten, J. Bacteriol. 1995, 177:6518-6526). The minimal tartrate utilization region of TAR-I contains four genes (ttuA-ttuD). The ttuC gene is homologous to the tartrate dehydrogenase gene from Pseudomonas putida. Outside the minimal region a second ttuC-like gene is found (ttuC') which is transcribed and complements a ttuC mutant. Most grapevine isolates carry one or two of the three characterized TAR regions and show a considerable degree of polymorphism around these regions.