Chimeric Double-Stranded RNAs Could Act as Tailor-Made Pesticides for Controlling Storage Insects

Functional Characterization and Putative Regulatory Mechanism of an RNAi Efficiency-Related Nuclease (REase) in the Fall Armyworm, Spodoptera frugiperda

The lepidopteran-specific RNAi efficiency-related nuclease (REase) has been shown to contribute to double-strand RNA (dsRNA) degradation in several lepidopteran insects. However, little is known about its regulatory mechanism. In this study, we identified and characterized SfREase in Spodoptera frugiperda. The exposure of the third-instar larvae to dsEGFP and high temperature led to the upregulation of SfREase, whereas starvation treatment resulted in the downregulation of SfREase. Further experiments revealed that dsRNA degraded more slowly in the hemolymph or midgut fluid extracted from dsSfREase-injected or dsSfREase-ingested larvae compared with those from dsEGFP-treated larvae, and the recombinant SfREase degraded dsRNA in a concentration-dependent manner. Additionally, the knockdown of SfREase improved RNAi efficiency. Finally, both RNAi and dual-luciferase reporter assay in Sf9 cells revealed that SfREase is negatively regulated by FOXO. These data provide insights into the function and regulatory mechanism of REase and have applied implications for the development of an RNAi-based control strategy of S. frugiperda.

Binding Properties of Odorant-Binding Protein 7 to Host Volatiles in Larvae of Spodoptera frugiperda

The chemosensory system is crucial during the growth and development of the moths. Spodoptera frugiperda (Lepidoptera: Noctuidae) is one of the most destructive insect pests. However, there is little functional research on odorant-binding proteins (OBPs) in the larval stage of S. frugiperda. Here, we obtained SfruOBP7 from transcriptomics and conducted the sequence analysis. We used quantitative real-time PCR to explore the expression profiles of SfruOBP7. The function identification showed that SfruOBP7 has a binding ability to 18 plant volatiles. Further molecular docking and site-directed mutant assay revealed that Lys45 and Phe110 were the key binding sites for SfruOBP7 interacting with linalool. In the behavior assays, linalool could attract the larvae, and dsOBP7-treated larvae lost their attraction to linalool. Our results help to reveal the essential molecular mechanism of the olfactory perception in the larvae and design an attractant based on the host volatiles.

Improving RNA-based crop protection through nanotechnology and insights from cross-kingdom RNA trafficking

Spray-induced gene silencing (SIGS) is a powerful and eco-friendly method for crop protection. Based off the discovery of RNA uptake ability in many fungal pathogens, the application of exogenous RNAs targeting pathogen/pest genes results in gene silencing and infection inhibition. However, SIGS remains hindered by the rapid degradation of RNA in the environment. As extracellular vesicles are used by plants, animals, and microbes in nature to transport RNAs for cross-kingdom/species RNA interference between hosts and microbes/pests, nanovesicles and other nanoparticles have been used to prevent RNA degradation. Efforts examining the effect of nanoparticles on RNA stability and internalization have identified key attributes that can inform better nanocarrier designs for SIGS. Understanding sRNA biogenesis, cross-kingdom/species RNAi, and how plants and pathogens/pests naturally interact are paramount for the design of SIGS strategies. Here, we focus on nanotechnology advancements for the engineering of innovative RNA-based disease control strategies against eukaryotic pathogens and pests.

Inefficient uptake of small interfering RNAs is responsible for their inability to trigger RNA interference in Colorado potato beetle cells

There has been limited success in the usage of exogenous small interference RNA (siRNA) or small hairpin RNA (shRNA) to trigger RNA interference (RNAi) in insects. Instead, long double-stranded RNAs (dsRNA) are used to induce knockdown of target genes in insects. Here, we compared the potency of si/sh RNAs and dsRNA in Colorado potato beetle (CPB) cells. CPB cells showed highly efficient RNAi response to dsRNA. However, si/sh RNAs were inefficient in triggering RNAi in CPB cells. Confocal microscopy observations of Cy3 labeled-si/sh RNA cellular uptake revealed reduced si/sh RNA uptake compared to dsRNA. si/sh RNAs were stable in the conditioned media of CPB cells. Although in a small amount, when internalized by CPB cells, the si/sh RNAs were processed by the Dicer enzyme. Lipid-mediated transfection and chimeric dsRNA approaches were used to improve the delivery of si/sh RNAs. Our results suggest that the uptake of si/sh RNAs is inefficient in CPB cells, resulting in ineffective RNAi response. However, with the help of effective delivery methods, si/sh RNA could be a useful option for developing target-specific RNAi-mediated biopesticides.

Key factors determining competitions between double-stranded RNAs in Tribolium castaneum

Combinatorial delivery of different double-stranded RNAs (dsRNAs) can result in competitive inhibition in insect pests and remains one of the obstacles in the way of future applications of the RNA interference (RNAi)-based pest control. In this study, we attempted to discover the basic competition characteristics between dsRNAs and provided insight into the solutions of competitive inhibition. RNAi sensitive insect species Tribolium castaneum were treated, and competitions between dsRNA fragments influencing the effectiveness of RNAi response could be measured. A chimeric dsRNA strategy for conjugating different dsRNA fragments into a single molecule and a nanoparticle carbon quantum dots-mediated dsRNA delivery were confirmed as efficient methods to knock down multiple target genes simultaneously. Furthermore, in vitro assays were conducted for determining the accumulation speed of serially diluted and incubated dsRNA in the midgut tissues. Our data showed that the accumulation of dsRNAs of different treated amounts was 0.25 μg ≈ 0.5 μg > 1 μg ≥ 2 μg > 4 μg, indicating that accumulation speed would be affected by treated dsRNA. Overall, our results strongly suggest that endocytic components influencing cellular uptake might be oversaturated when an excess amount of dsRNAs were treated, thereby causing competitive inhibition of target genes.