Polymorphism of Nopaline-type T-DNAs from Agrobacterium tumefaciens.

The structure of several T-DNAs of Agrobacterium tumefaciens was determined by molecular cloning and Southern hybridization. The T-DNAs cloned in Escherichia coli vectors from four different nopaline type strains (PyTE1, PO31, PO22, and AKE10) showed various sizes of restriction enzyme fragments. Comparative analysis of the restriction maps revealed that the T-DNAs were composed of three distinct structural domains: (1) the region proximal to the right border (Domain I) containing the portion essential for tumorigenicity, (2) the proximity to the left border (Domain II), and (3) the region between the two domains (Domain III) to both of which no functional assignments have yet been made. The restriction map indicated that the Domains I and II were conserved in the most clones, including the well-characterized T37 T-DNA. The only exception was AKK1 (obtained from AKE10) which differed in Domain I. In the Domain III, insertions of 1.5- or 1.6-kb DNA were found in four clones, whereas an additional 2.5-kb insertion was found in one clone (PO22P1). The individual T-DNAs including Domain III with insertions was demonstrated in petunia and poplar tumors induced by the referred A. tumefaciens strains. However, resulting tumors differed in morphology and growth. These results suggest that the length polymorphism of the nopaline type T-DNA can be accounted by DNA insertions, and that diverse T-DNAs reflect their different roles in tumorigenicity.