The NIa-proteinase of different plant potyviruses provides specific resistance to viral infection

The genome-linked protein-proteinase (NIa) genes of three potyviruses (tobacco vein 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 vital 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.