A platform for anti-pest nucleic acid engineering based on piRNA-mediated gene silencing.

Arthropod cells generate a variety of small regulatory RNAs that enact RNAi-based gene silencing. Biopesticide technology is typically designed to exploit the small-interfering RNA (siRNA) pathway where precursor double-stranded RNAs are processed into siRNAs that guide repression of complementary mRNAs. The siRNA pathway is an anti-viral response though a variety of endogenous siRNAs have been annotated. Most species of arthropods express an additional type of small RNA-based defense pathway–the piwi-interacting RNA (piRNA) pathway. This mechanism does rely on a specific structure to trigger small RNA production, like double-stranded RNA. Instead, an existing pool of piRNAs recognize complementary transcripts directing its conversion into piRNAs. Endogenous targets of piRNAs are often parasitic elements such as transposons, though some genic transcripts also appear to be subject to regulation. As piRNA mechanisms allow gene targeting based on sequence rather than structure this presents opportunities for nucleic acid engineering. Here we provide an update on our efforts to translate this approach to enable RNAi-based pesticides that exploit piRNA biogenesis. Synthetic piRNA triggers fed to whiteflies (Bemisia tabaci) not only silence target genes in whiteflies but also induce significant mortality. This is demonstrated both in artificial feeding and from plant transgenes. We also discuss the extensible nature of piRNA-based technology where addition of motifs can enable cell uptake, stability, and organelle targeting. As many major pest species exhibit somatic piRNAs further development of the platform may provide an opportunity for applying RNAi biopesticides where challenges with using siRNA have limited application.