Al. Jones et al., DE-NOVO METHYLATION AND CO-SUPPRESSION INDUCED BY A CYTOPLASMICALLY REPLICATING PLANT RNA VIRUS, EMBO journal (Print), 17(21), 1998, pp. 6385-6393
The relationship between co-suppression and DNA methylation was explor
ed in transgenic plants showing inducible co-suppression following inf
ection with a cytoplasmically replicating RNA virus. Induction resulte
d in a loss of transgene mRNA and resistance to further infection, fac
tors typical of post-transcriptional gene silencing. In infected plant
s, de novo methylation of the transgene appeared to precede the onset
of resistance and only occurred in plants where the outcome was co-sup
pression. The methylation was limited to sequences homologous to the v
iral RNA and occurred at both symmetric and non-symmetric sites on the
DNA. Although methylation is predicted to occur in mitotic cells, the
virus was found not to access the meristem. A diffusible sequence-spe
cific signal may account for the epigenetic changes in those tissues.