HETEROLOGOUS RESISTANCE TO POTATO VIRUS-Y IN TRANSGENIC TOBACCO PLANTS EXPRESSING THE COAT PROTEIN GENE OF LETTUCE MOSAIC POTYVIRUS

Heterologous protection can provide resistance against virus infection in transgenic plants and was evaluated with two potyviruses, potato v irus Y (PVY) and lettuce mosaic virus (LMV). PVY causes a serious dise ase of tobacco. Transgenic plants, Nicotiana tabacum cv. Xanthi, conta ining a modified coat protein (CP) gene of LMV have been generated and tested for resistance against PVY. Half of the 34 independent R0 tran sgenic plants tested accumulated detectable levels of LMV coat protein (LMV CP+). These LMV CP+ plants were resistant to infection following sap inoculation with a necrotic strain of PVY (PVY-NV). Moreover, R1 populations of five LMV CP+ lines tested were resistant to PVY-NV and to four other PVY strains. Different phenotypes were observed, includi ng 1) complete resistance in two lines, 2) delay and attenuation of sy mptoms in two lines, and 3) delay in symptoms with no modification of symptoms in one line. In cases 2 and 3, the number of plants showing s ymptoms was reduced, and the PVY accumulation was greatly decreased in the infected plants. These lines were considered to be partially resi stant to PVY infection. Although PVY and LMV are clearly distinct poty viruses (their CPs share 66% amino acid sequence homology), the expres sion of the coat protein gene of LMV can confer a high level of hetero logous protection against PVY in tobacco plants. Results are discussed regarding the possibility of different modes of resistance.