Further insight concerning the TL region of the Ri plasmid of Agrobacterium rhizogenes strain A4: Transfer of a 1.9 kb fragment is sufficient to induce transformed roots on tobacco leaf fragments

Summary Disarmed plant transformation vectors were used to assay the ability of subfragments of the T-regions of the Ri plasmid of agropine-type strain A4 of Agrobacterium rhizogenes to induce proliferation of transformed roots on tobacco leaf fragments. We have shown that a 6 kb region of TR-DNA, bearing the presumptive auxin synthesis genes, is capable of inducing transformed roots with an essentially normal phenotype as had been shown previously with the entire TR-region. A 1.9 kb fragment of the 20 kb TL-region is suffcient to induced transformed roots in the absence of exogenous hormones. These roots grow profusely on hormone-free medium, as is typical of roots transformed by the intact TL-DNA.