VARIABLE RESISTANCE TO PLUM POX VIRUS AND POTATO VIRUS-Y INFECTION INTRANSGENIC NICOTIANA PLANTS EXPRESSING PLUM POX VIRUS COAT PROTEIN

The plum pox virus (PPV) coat protein (CP) gene was transferred into t hree species of Nicotiana using an Agrobacterium tumefaciens based sys tem. Transgenic Nicotiana benthamiana plants that express the PPV CP e xhibited protection when inoculated with PPV plant sap. After a first stage where PPV was able to multiply in transgenic and control plants, the virus was progressively excluded from newly formed tissues and at 40 days after inoculation no PPV could be detected in the most resist ant lines. This homologous resistance to PPV appears to be due both to the inhibition of viral long-distance transport and to the inhibition of viral replication. Transgenic Nicotiana clevelandii and Nicotiana tabacum cv. Xanthi expressing PPV CP exhibited partial levels of prote ction to infection by PPV or by potato virus Y (PVY) that were depende nt on the inoculum concentration. Different interpretations of these r esistance phenomena are discussed.