Potential risks associated with transgenic virus resistance

The development of transgenic virus resistance has raised concerns over potential interactions between viral transgenes or their products with viruses that infect the transgenic plant itself. Such interactions include genome recombination and transcapsidation (the encapsidation of one virus with coat protein of another virus; see Greene and Allison, 1994 and references therein). This has been shown to occur in some instances where several viruses infect the same plant. Risks are perceived since capsid protein influences viral transmission properties. Thomas et al. (1998) looked for evidence of interactions between PLRV-derived transgenes and viruses to which the transgenic potato plants were exposed and infected. Over 25,000 plants and 400 lines were transformed with 16 different coat protein constructs an ca.d40,000 plants and 500 lines with seven different replicase gene constructs of PLRV. Heterologous viruses found infecting the plants were screened for modifications in transmission characteristics, host range, symptoms, etc. New viruses or viruses with altered characteristics, including host range, were not detected in field exposed or greenhouse-inoculated plants. The studies do not preclude any of thevirus-virus interactions searched for, but do indicate that such interactions are rare events and that the risks of their occurrence may not be expanded by the fact that one of the genes is a transgene.