Cell-death-independent antiviral response mediated by N resistance factor in Nicotiana benthamiana involves inhibited localization of tobamovirus movement protein to plasmodesmata

The tobacco N gene encodes the N resistance factor that recognizes a tobacco mosaic virus elicitor called p50 to induce a cell-death-associated hypersensitive reaction, which confines virus infections to local areas. Coexpression of N and p50 cDNAs in Nicotiana benthamiana induces resistance against virus infection without visible cell death. In this study, we examined how this N-mediated resistance in the heterologous plant inhibits virus infection. After inoculation with GFP-encoding tomato mosaic virus (ToMV), plants coexpressing N and p50 had fewer and smaller infection sites as the levels of coexpressed proteins of N and p50 increased. This antiviral response was associated with production of reactive oxygen species but not ion leakage or expression of PR1a (encoding a salicylic acid signaling marker). In addition, it was likely that GFP-tagged movement protein (MP) of ToMV seemed to have failed to localize at plasmodesmata during virus infection in leaves coexpressing N and p50. These findings indicate that the cell death-independent, N-mediated antiviral response in N. benthamiana may involve interference with the intracellular transport function of MP.