TRANSFER OF NON-T-DNA PORTIONS OF THE AGROBACTERIUM-TUMEFACIENS TI PLASMID PTIA6 FROM THE LEFT TERMINUS OF T-L-DNA

We introduced a plant selection marker, nptII, to the left of border A in the Agrobacterium Ti plasmid pTiA6. Infection of tobacco leaf disc s with the modified Agrobacterium strain gave rise to kanamycin-resist ant calli which grew in a hormone-dependent manner. Southern hybridiza tion analysis of DNA isolated from four transformants indicated initia tion of DNA transfer at or near border A and absence of T-DNA sequence s. These results demonstrate that DNA transfer events starting at a le ft border on a native Ti plasmid and moving away from the T-DNA region occur and that they can be detected by designing a suitable selection strategy.