An extensible RNAi platform based on Piwi-Interacting RNA-based gene silencing

As arthropod pests develop resistance to conventional pesticides there is a need for development of new control strategies. A technology that shows promise is RNA interference (RNAi) which offers species-specificity that avoids negative impacts on beneficial organisms and risk to human health. Unfortunately, effectiveness is limited due to differences in sensitivity. This work investigates the potential for using specially designed, single-stranded RNA (ssRNA) molecules to elicit gene silencing in the cosmopolitan lepidopteran crop pest, Spodoptera frugiperda (Fall armyworm). This approach exploits piwi-interacting RNA (piRNA) instead of the double-stranded dsRNA derived small-interfering RNA (siRNA). Unlike dsRNA, ssRNA can be engineered through the inclusion of sequence-based motifs that can form advantageous, complex structures. RNAs tested in this study substantially improve resistance to digestion by midgut nucleases. Inclusion of these structures also leads to greater knockdown of a target gene and induces the expected cellular phenotype. Collectively, this work demonstrates that piRNA-producing ssRNA can be used to induce RNAi in S. frugiperda and highlights its highly customizable nature which may be the key to overcoming challenges associated with typical dsRNA-mediated RNAi approaches.