T-DNA Transfer to Maize Plants

Agrobacterium tumefaciens is a soil bacterium that induces, in most dicotyledonous plants, the neoplastic disease called crown gall. These tumors form at the site of wounding. The molecular basis for the tumor formation is the integration into and expression from the plant genome of T-DNA (transferred DNA), a part of the Ti (tumor-inducing) plasmid carried by the bacterium. T-DNA oncogenes specifying the synthesis of auxin and cytokinin are responsible for cell proliferation resulting in tumor growth. Additional T-DNA genes encode enzymes that produce, in the gall, novel amino acid and sugar derivatives, called opines, which are specific growth substrates for the bacterium. Different bacterial strains produce and consume different opines. Thus, strains have been classified accordingly as nopaline, octopine, or other types, depending on their diagnostic opine.