A Link between PVYN CP Gene-mediated Virus Resistance and Transgene Arrangement

RNA-mediated virus resistance is one kind of post-transcriptional gene silencing (PTGS). PTGS can be induced by transgenes or by viral infection that triggers the degradation of RNAs with homology or complementarity to the foreign genes transcript or viral RNA. In this study, tobacco plants transformed with untranslatable Potato virus YN (PVYN)-coated protein (CP) gene were used to examine the correlation between transgene integration patterns and RNAmediated resistance more directly. HindIII and EcoRI were used to digest genomic DNAs from progeny T1 transgenic plants with a range of responses to PVYN infection. Southern blot analysis indicated that nearly all of the highly resistant plants contained repeat foreign sequences, including direct repeat (DR) and inverted repeat (IR). Specifically, the highly resistant plants always contained both or one of these constructs, with the majority containing both constructs. Conversely, almost all of the susceptible transgenic plants contained neither construct, though some contained multiply copies. Our results show that transgene integration rather than copy number is the key factor for RNA-mediated virus resistance. Many researchers identified double-stranded RNA (dsRNA) as the common link for PTGS triggered by various events. Therefore, we suggest that only transgenes can make dsRNA, by transcription or other pathways, and either repeated constructs (IR or DR) or single copy will induce RNA-mediated PVYN resistance