RNA interference(RNAi)is a highly conserved posttranscriptional gene regulatory mechanism that controls gene expression at the mRNA level within living cells(Fire et al.,1998;Bellés,2010;Zhuang & Hunter,2012).RNAi is triggered by small interfering RNA(siRNA),which is processed by Dicer,an endoribonuclease in the RNase Ⅲ family,from either exogenous(e.g.,infection by a virus or laboratory manipulations)or endogenous(e.g.,premicroRNA)double-stranded RNA(dsRNA).The siRNAs are short dsRNA fragments of about 20-25 base pairs and carry two base extensions at the 3 end of each strand.In the RNAi pathway,siRNAs are incorporated into an RNA-induced silencing complex(RISC)in conjunction with an Argonaute(Ago)multidomain protein.Ago which contains an RNase H-like domain responsible for target degradation cleaves and discards the passenger(sense)strand of the siRNA duplex leading to an active RISC.The remaining(antisense)strand of the siRNA duplex serves as the guide strand and guides the RISC to its homologous target mRNA.The active RISC degrades the mRNA,which shares sequence-specific homology to the siRNA,resulting in the diminishment or abolishment of the gene expression.