Exploiting a second mode of gene silencing in Hemiptera: RNAi triggered by piRNAs

RNA interference (RNAi) has the potential to revolutionize pest control technologies because of its non-toxic, biodegradable, and species-specific features. However, RNAi biology is fluid across animal species, including arthropods, which produce substantially variable responses to exogenous RNAi trigger. For optimal efficacy of RNAi as a biopesticide for insect pest and vector management, it has become necessary to discover and design new approaches to manipulate the most lucrative RNAi-triggers, and to design species-specific targets. Three endogenous small RNA pathways and processing of exogenous RNAi trigger molecules were investigated for the whitefly
Bemisia tabaci

(Genn.), B biotype. Whitefly and other hemipteran insects have abundant somatic piwi-associated RNAs (piRNAs) that silence protein-coding genes. Because piRNAs were previously thought to be germline-specific, their potential in pest-control biotechnology has not been explored until now. The key feature of piRNA production is recruitment of the precursor RNA into the piRNA biogenesis pathway. To test for a piRNA response, synthetic RNAs were designed with complementarity to selected annotated piRNA loci. Feeding of the synthetic piRNA triggers produced gene-silencing that was as robust as a ‘conventional’ siRNA-only approaches. These results demonstrate the potential for a new strategy for RNAi biopesticide technology, applicable to other pest species having a whitefly-like piRNA biology. Exploitation of piRNAs in parallel with siRNAs, could offer a means of eliciting gene-knockdown that in some instances will be critical to realizing RNAi for crop protection.