Over-expression of RNA interference (RNAi)core machinery improves susceptibility toRNAiin silkworm larvae

RNA interference (RNAi), one of the strategies that organisms use to defend against invading viruses, is an important tool for functional genomic analysis. In insects, the efficacy of RNAi varies amongst taxa. Lepidopteran insects are, in large part, recalcitrant to RNAi. The overall goal of this study is to overcome such insensitivity in lepidopterans to RNAi. We hypothesize that over-expression of core RNAi machinery enzymes can improve RNAi efficacy in traditionally recalcitrant species. A transgenicBombyx moristrain,Baculovirus Immediate-Early Gene, ie1, promoter driven expression of silkworm Dicer2 coding sequence(IE1-BmDicer2), which over-expressesBmDicer2, was generated bypiggyBactransposon-mediated transgenesis. Two indexes, the ratio of animals that showed a silencing phenotype and the duration of silencing, were used to evaluate silencing efficiency. Significant knockdown of target gene expression was observed at 48 h postinjection at both the transcriptional and translational levels. Furthermore, we coexpressedB. mori Argonaute 2BmAgo2?andBmDicer 2and found that 22% of the animals (n= 18) showed an obvious silencing effect even at 72 h, suggesting that coexpression of these two RNAi core machinery enzymes further increased the susceptibility ofB. morito injected double-stranded RNAs. This study offers a new strategy for functional genomics research in RNAi-refractory insect taxa in general and for lepidopterans in particular.