Abstract
Double-stranded RNAs (dsRNA) that contain promoter sequences can trigger transcriptional inactivation in trans of gene driven by a homologous promoter. Small RNAs derived from dsRNA are implicated in this dsRNA-mediated transcriptional gene silencing phenomenon and in de novo methylation of the target promoter, but the molecular mechanism(s) is still unclear. To investigate the silencing machinery, a tissue specific promoter system was developed. From a mutant screen, 3 mutants, drd1, drd2, drd3 (defective in RNA-directed DNA methylation), which show a reactivation of the silenced promoter activity were obtained. In all of these mutants, non-CpG methylation of the target promoter is almost eliminated while CpG methylation is unaffected. DRD1 was identified as a novel putative chromatin remodeling factor that belongs to a plant specific subfamily of SWI2/SNF2-like proteins most similar to the RAD54/ATRX subfamily. The possible role(s) of DRD1 in the RNA-directed de novo DNA methylation pathway will be discussed.
