ABSTRACT
RNA silencing is a mechanism that results in sequence-specifi c degradation of RNA in eukaryotes. This phenomenon has been termed RNA interference ( RNAi) in animals, quelling in fungi and post-transcriptional gene silencing ( PTGS) in plants (Baulcombe 2004, Fulci and Macino 2007, Umbach and Cullen 2009). A common feature of RNA silencing is that it is
most strongly triggered by double-stranded RNA (dsRNA); however, it is also triggered by aberrant RNAs associated with transposons, transgenes and viruses. RNAs with hairpin structures are particularly effective inducers of PTGS in plants. All of these RNAs are cleaved by Dicer and dicer-like (DCL) enzymes, which are members of the RNase III family of dsRNA-specifi c endonucleases, to generate RNAs of 21-25 nucleotides (nt). These are generally referred to as small interfering RNAs (siRNAs) (Chapman and Carrington 2007). siRNAs become incorporated into an RNA-induced silencing complex ( RISC), which includes Argonaute (AGO)-type family proteins that contain small RNA-binding PAZ and RNaseH-like PIWI domains. The RISC/ siRNA complex binds and degrades RNA that is complementary in sequence to the bound siRNA (Matranga et al. 2005, Vaucheret 2008).
