Gene amplification and expression in plants by a replicating geminivirus vector

The use of plant DNA viruses as vectors for the transfer of foreign genes to plants offers two potential advantages over other, existing methods of producing transgenic plants. First, these viruses sys-temically infect whole plants, thus obviating the need for the difficult and time-consuming step of regeneration from transformed single cells or protoplasts. Second, the viruses replicate as separate, autonomous entities within the plant's cells so that any gene cloned in a plant DNA-virus vector would be amplified to high copy number, a feature that differs from methods that produce transgenic plants by the chromosomal integration of foreign DNA. To date, attention has focused on the development of vectors based on the cauliflower mosaic virus (CaMV), but their use is hampered by the narrow range of plants infected by CaMV, and by practical limitations on inserting foreign DNA that are imposed by the biology of CaMV. Here we describe the use of vectors based on the gemini tomato golden mosaic virus (TGMV) to introduce the neomycin phosphotransferase (neo gene) into plants. Our results indicate that geminivirus-derived vectors should be useful not only for amplification of gene expression by the systemic infection of plants, but also for heritable gene amplification by the integration of stable master copies of the vector into the plant chromosomal DNA.