The use of the Ti plasmid as a vector for the introduction of foreign DNA into plants

Abstract

Agrobacterium tumefaciens is a Gram-negative bacterium with the unique capacity to induce neoplasmic transformations in dicotyledonous plants. Recently, both the mechanism and the biological significance of this transformation have been elucidated. Agrobacterium tumefaciens strains contain a large extrachromosomal DNA plasmid (the Ti-plasmid). This Ti-plasmid is responsible for the oncogenic properties of Agrobacterium strains. A particular segment of the Ti-plasmid, containing information determining the tumorous growth pattern and the synthesis of so-called "opines", e.g. "octopine" (N²-(D-1-carboxyethyl)-L-arginine) and "nopaline" (N²-(1,3-dicarboxypropyl)-L-arginine), is transferred and stably maintained and expressed in the transformed plant cells by bacterial plasmid DNA so that the transformed plant cell will produce and secrete into the medium amino acid derivatives (the opines) that Ti-plasmid carrying agrobacteria can selectively use as carbon and nitrogen sources. By in vivo genetic manipulations, we have recently been able to introduce a bacterial antibiotic resistance transposon, Tn7, in the Ti-DNA segment that is transferable to plant cells. In this way we hope to demonstrate that the Ti-plasmid can be used as a general vector for introducing "foreign" DNA into plants