Identification of T-DNA in the root-inducing plasmid of the agropine type Agrobacterium rhizogenes 1855.

The region of the virulence plasmid of the agropine type Agrobacterium rhizogenes 1855 (pRi-1855) which is transferred to plant cells upon infection (T-DNA) has been identified by means of Southern blot hybridizations with the T-DNA of the mannopine type A. rhizogenes 8196. The presence in the plant genome of the pRi-1855 sequences thus identified is demonstrated in carrot roots derived from infection with strain 1855. The T-DNA of pRi-1855 has been mapped by means of cloned Eco RI partial digests. Although strongly homologous with each other, the cores of the T-regions of the mannopine and agropine Ri plasmids are not colinear since the latter contains a central segment of DNA which is absent from the T-region of pRi-8196. Unexpected homologies between the T-region of pRi-1855 and normal carrot DNA have been observed and are discussed here.