Sm. Angell et Dc. Baulcombe, CONSISTENT GENE SILENCING IN TRANSGENIC PLANTS EXPRESSING A REPLICATING POTATO-VIRUS-X RNA, EMBO journal, 16(12), 1997, pp. 3675-3684
Tobacco plants were transformed with constructs in which the transgene
was a cDNA of replicating potato virus X (PVX) RNA. The constructs, r
eferred to here as amplicons, were the intact genome of PVX and PVX co
nstructs modified to carry the beta-glucuronidiase (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 carryi
ng these constructs displayed several phenotypes that we attribute to
post-transcriptional gene silencing. These phenotypes include the abse
nce of viral symptoms, low accumulation of transgene-derived RNA, extr
eme strain-specific resistance against PVX, low and non-uniform GUS ex
pression (in the PVX/GUS and PVX/GUS/CP plants) and suppression of tra
nsiently expressed RNA sharing homology with the transgene. Importantl
y, the amplicon-mediated gene silencing was exhibited in all lines tes
ted. There was no evidence of gene silencing in seven lines expressing
a PVX RNA that was unable to replicate. From these data we conclude t
hat the replicating viral RNA is a potent trigger of gene silencing. M
oreover, amplicon-mediated gene silencing provides an important new st
rategy for the consistent activation of gene silencing in transgenic p
lants.