Tobacco plants transformed with an untranslatable form of the coat protein gene of the Potato virus Y are resistant to viral infection

The coat protein (CP) gene of the Potato virus Y common strain (PVY^o), rendered untranslatable by introduction of a stop codon immediately after the initiation codon, was cloned into an Agrobacterium tumefaciens transformation vector. The regenerated transgenic tobacco plants were analyzed for the presence of the CP gene. Although transgene transcripts were observed in all transgenic lines tested, three different phenotypes of resistance were observed, including high resistance, partial resistance, and susceptibility. An inverse correlation between the transgene transcript steady-state levels and resistance of transgenic plants to PVY^o was observed. The results obtained suggest that the resistance observed in the transgenic plants is essentially due to the presence of multiple PVY transgenes that accumulate low levels of the transgene transcript. A post-transcriptional RNA degradation process appears to support the transgene transcript reduction within the RNA-mediated resistance mechanism.