ABSTRACT

The evolved gene transfer mechanism of Agrobacterium tumefaciens has become a transformation method of choice. Its use is simple; gene transfers are low copy and result in permanent heritable genetic changes. Agrobacterium-mediated transformation was once thought to be limited to species within the pathogen’s native host-range. This was later expanded to include gymnosperm, most dicotyledon, and a few monocotyledon species. The important cereal crops were thought to be refractive to transformation until the early 1990s. In addition, it was thought that plant meristems excluded the Agrobacterium tumor-inducing principle in the same way virus was excluded from plant meristems. Because of these understandings, Agrobacterium transformations were thought to be limited to plant varieties known to be within Agrobacterium’s host-range, and limited to varieties that could be regenerated from callus and through somatic embryogenesis.