Transformation of the genomic expression of plant cells.

Agrobacterium-induced transformation of plant cells results from integration of T-DNA of the Ti or Ri plasmids into the genome of susceptible plants. Expression of T-DNA genes induces physiological changes in transformed cells which modify normal plant development to produce proliferations characteristic of crown gall and hairy root diseases. Understanding of the molecular basis of the transformation events associated with these examples of naturally occurring genetic engineering of plant cells, has stimulated efforts to construct vectors for transferring specific genes into plants. Vector construction has progressed from the use of wild-type Ti plasmids, giving phenotypically abnormal regenerated plants, to non-oncogenic plasmids. The range of vectors now available should enable useful foreign genes to be inserted into a range of dicotyledons and monocotyledons without impairing normal plant development.