Potato virus X amplicon-mediated silencing of nuclear genes

Transgenic expression of a replicating potato virus X (PVX) construct (term ed an 'amplicon') reproducibly and consistently activates post-transcriptio nal gene silencing (PTGS) in every plant. The amplicon-mediated PTGS mechan ism can target transiently expressed RNAs that share homology with the ampl icon transgene. We show that amplicons can also be used to silence stably i ntegrated transgenes and endogenous genes. Plants expressing both a transge ne and an amplicon targeting part of the transgene show low accumulation of the transgene RNA. Similarly, plants expressing an amplicon targeting an e ndogenous gene show low accumulation of the endogenous RNA and display a mu tant phenotype matching a previously characterised mutation. These data dem onstrate that PVX amplicons present a novel approach for the consistent act ivation of PTGS that can be used to specifically target and suppress gene e xpression in plants.