The six functions of Agrobacterium VirE2

Agrobacterium tumefaciens is a soil-born pathogen with the unique ability to genetically transform plants. Agrobacterium infects plant wound sites, causing crown gall disease. This agriculturally significant disease results from the transfer of a single-stranded (ss) segment (the T-strand) of the bacterium's tumor-inducing plasmid to the host cell (reviewed in refs. 1–3; Fig. 1). On integration into the host genome, genes encoded by the T-strand direct the synthesis of plant growth hormones, resulting in tumorous proliferation of plant cells. T-strand genes also cause the plant to produce opines, compounds that represent a major carbon and nitrogen source uniquely metabolized by the bacterium. Thus, Agrobacterium has evolved a mechanism to genetically engineer host cells to create a favorable niche for itself. This natural ability has been coopted by researchers who use Agrobacterium to engineer plants for agricultural and research purposes.