Consistent gene silencing in transgenic plants expressing a replicating potato virus X RNA

Abstract

Tobacco plants were transformed with constructs in which the transgene was a cDNA of replicating potato virus X (PVX) RNA. The constructs, referred to here as amplicons, were the intact genome of PVX and PVX constructs modified to carry the β‐glucuronidase (GUS) reporter gene either as an additional gene or as a replacement for the coat protein gene (PVX/GUS/CP and PVX/GUS respectively). Transformed plants carrying these constructs displayed several phenotypes that we attribute to post‐transcriptional gene silencing. These phenotypes include the absence of viral symptoms, low accumulation of transgene‐derived RNA, extreme strain‐specific resistance against PVX, low and non‐uniform GUS expression (in the PVX/GUS and PVX/GUS/CP plants) and suppression of transiently expressed RNA sharing homology with the transgene. Importantly, the amplicon‐mediated gene silencing was exhibited in all lines tested. There was no evidence of gene silencing in seven lines expressing a PVX RNA that was unable to replicate. From these data we conclude that the replicating viral RNA is a potent trigger of gene silencing. Moreover, amplicon‐mediated gene silencing provides an important new strategy for the consistent activation of gene silencing in transgenic plants.