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The genome-linked protein-proteinase (NIa) genes of three potyviruses (tobacco rein mottling virus[TVMV], tobacco etch virus[TEV], and potato virus Y [PVY]) were introduced into tobacco (Nicotiana tabacum L.) cultivar Burley 21 and transgenic plant lines were evaluated for viral symptoms and virus accumulation. Plant lines that expressed the TVMV NIa gene were resistant to infection by TVMV; inoculated plants did not develop disease symptoms after inoculation, and virus did not accumulate. Most lines that carried the TEV NIa and PVY NIa genes did develop symptoms after inoculation with TEV and PVY, respectively, but these symptoms abated with time (a response termed as recovery). Three genes, each consisting of two NIa coding regions (TEV NIa-PVY NIa, TEV NIa-TVMV NIa, and TVMV NIa-PVY NIa) were also introduced into Burley 21. Transgenic lines that carried either TEV NIa-PVY NIa or TEV NIa-TVMV NIa constructs either did not develop disease symptoms or exhibited the process of recovery after inoculation with TEV. TEV NIa-TVMV NIa and TVMV NIa-PVY NIa lines recovered from an initial infection after inoculation with TVMV. Likewise, TEV NIa-PVY NIa and TVMV NIa-PVY NIa transformed lines recovered from initial infection after inoculation with PVY. These results demonstrate that different potyvirus NIa-proteinase genes can be used for protection against virus infection and that multiple NIa genes may be used to produce plants that are protected against more than one potyvirus., POTYVIRUSES are the largest group of plant viruses and infect a wide range of host plants. Potyviruses are transmitted by aphids and are non-persistent in the aphid vector. Classical breeding [...]

Eighty transgenic tobacco (Nicotiana tabacum L.) lines expressing either the tobacco vein mottling vires (TVMV) coat protein (CP) gene or the alfalfa mosaic virus (AMV) CP gene were evaluated for their agronomic performance with or without virus challenge. Ali TVMV CP lines were characterized previously for their virus resistance following challenge with three different potyviruses. In the absence of virus challenge, the cured leaf yield of more than 80% of the TVMV CP lines was not significantly different from their non-transgenic counterparts; half of the poor performing lines were in one of the five genetic backgrounds. Similarly, most of the negative variation for yield among the AMV CP transgenic lines was within a single genetic background. Variation for other agronomic traits, including plant height, leaf size, and stalk diameter closely followed the results for yield. Following virus challenge, cured leaf yield of the most resistant transgenic lines was similar to the non-challenged treatment. Among the AMV CP transgenic lines, yield loss following challenge with AMV was reduced from 22 to 30%. These results suggest that the primary selection criterion in a population of transgenic tobacco lines containing a viral CP gene should be for virus resistance, but it must be recognized that variation for agronomic performance may exist among the resistant selections, particularly in some genetic backgrounds., THE USE of genetic engineering strategies to protect crops against virus diseases is ultimately determined by the overall performance of the transgenic plants under field conditions (Nelson et al., 1988). [...]