T-DNA fragments of hairy root plasmid pRi8196 are distantly related to octopine and nopaline Ti plasmid T-DNA

Agrobacterium Ti (tumor-inducing) and Ri (root-inducing) plasmids transform dicot plant cells by insertion of a specific plasmid sector called T-DNA (transferred DNA) into host plant nuclear DNA. The mannopine-type Ri plasmid pRi8196 contains four BamHI fragments that encompass core T-DNA. We report Southern hybridization studies that show that these four fragments have no strong homology to octopine-, nopaline-, or agropine-type Ti plasmids. We detected and mapped very weak homology regions, most of which are assignable to opine synthase or opine catabolic functions on the Ti plasmid. We found no homology between Ri T-DNA and the region of Ti T-DNA that encodes tumor morphology functions.