In plants, double-stranded RNA that is processed to short RNAs approximately 21-24 nt in length can trigger two types of epigenetic gene silencing. Posttranscriptional gene silencing, which is related to RNA interference in animals and quelling in fungi, involves targeted elimination of homologous mRNA in the cytoplasm. RNA-directed DNA methylation involves de novo methylation of almost all cyt...

Considerable effort has been devoted to the characterization of RNA interference (RNAi), a posttranscriptional gene silencing mechanism involving small RNA-containing effector complexes. Recent studies have revealed that components of the RNAi machinery are associated not only with target RNA cleavage and impairment of target RNA translation but also with the formation of heterochromatin. There...

Cellular RNA-dependent RNA polymerases (RDRs) are fundamental components of RNA silencing in plants and many other eukaryotes. In Arabidopsis thaliana genetic studies have demonstrated that RDR2 and RDR6 are involved in the synthesis of double stranded RNA (dsRNA) from single stranded RNA (ssRNA) targeted by RNA silencing. The dsRNA is subsequently cleaved by the ribonuclease DICER-like into se...

'RNA silencing' is the suppression of gene expression through nucleotide sequence-specific interactions that are mediated by RNA. Initially identified as an immune system that is targeted against transposons and viruses, RNA silencing is emerging as a fundamental regulatory process that is likely to affect many layers of endogenous gene expression in most, if not all, eukaryotes.

RNA interference (RNAi) is a post-transcriptional gene silencing mechanism that widely exists in eukaryotes. RNAi is initiated by double-stranded RNA (dsRNA) or microRNA (miRNA) and degrades specific messenger RNAs (mRNAs) by RNA-induced silencing complex (RISC), and then it specifically impairs the expression of target genes [1,2]. Therefore, RNAi has been becoming an effective tool to explore...

A mutation that disrupts post-transcriptional gene silencing in Neurospora crassa has been found to affect the homologue of a plant-encoded RNA-dependent RNA polymerase. This enzyme may produce a specificity determinant of gene silencing and mediate an epigenetic conversion at the RNA level.

Just fourteen years ago, Victor Ambros and coworkers discovered the first microRNA (miRNA). And just eight years ago, small interfering RNAs (siRNAs), the small silencing RNAs that mediate RNA interference (RNAi), were identified and subsequently shown in animals to be derived from a longer double-stranded RNA trigger and to serve as guides for the destruction of complementary mRNAs. The discov...

Genetic studies are revealing the pathway for RNA-mediated gene silencing. Short RNA molecules are the key, giving sequence specificity for RNA degradation and mediating communication within and between cells; these short RNAs are common to transcriptional and post-transcriptional silencing pathways.