SUPPRESSION OF VIRUS ACCUMULATION IN TRANSGENIC PLANTS EXHIBITING SILENCING OF NUCLEAR GENES

Homology-dependent gene silencing contributes to variation between tra nsgenic plants with respect to transgene and/or endogenous gene expres sion levels. Recent studies have linked post-transcriptional gene sile ncing and virus resistance in plants expressing virus-derived transgen es. Using a potato virus X vector, we present three examples in which silencing of nonviral transgenes prevented virus accumulation. This ef fect was dependent on sequence homology between the virus and the sile nced transgene. Analysis of potato virus X derivatives carrying bacter ial beta-glucuronidase (GUS) sequences showed that the 3' region of th e GUS coding sequence was a target of the silencing mechanism in two i ndependent tobacco lines. Methylation of the silenced GUS transgenes i n these lines was also concentrated in the 3' region of the GUS coding sequence. Based on this concurrence, we propose a link between the DN A-based transgene methylation and the RNA-based gene silencing process .