Towards an understanding of the molecular basis of effective RNAi against a global insect pest, the whitefly Bemisia tabaci

Yuan Luo,Qingguo Chen,Junbo Luan,Seung Ho Chung,Joyce Van Eck,R Turgeon,Angela E Douglas

doi:10.1016/j.ibmb.2017.07.005

Yuan Luo, Qingguo Chen + Show 5 more

Open Access

https://doi.org/10.1016/j.ibmb.2017.07.005

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Abstract

In planta RNAi against essential insect genes offers a promising route to control insect crop pests, but is constrained for many insect groups, notably phloem sap-feeding hemipterans, by poor RNAi efficacy. This study conducted on the phloem-feeding whitefly Bemisia tabaci reared on tomato plants investigated the causes of low RNAi efficacy and routes to ameliorate the problem. Experiments using tomato transgenic lines containing ds-GFP (green fluorescent protein) revealed that full-length dsRNA is phloem-mobile, ingested by the insects, and degraded in the insect. We identified B. tabaci homologs of nuclease genes (dsRNases) in other insects that degrade dsRNA, and demonstrated that degradation of ds-GFP in B. tabaci is suppressed by administration of dsRNA against these genes. dsRNA against the nuclease genes was co-administered with dsRNA against two insect genes, an aquaporin AQP1 and sucrase SUC1, that are predicted to protect B. tabaci against osmotic collapse. When dsRNA constructs for AQP1, SUC1, dsRNase1 and dsRNase2 were stacked, insect mortality was significantly elevated to 50% over 6 days on artificial diets. This effect was accompanied by significant reduction in gene expression of the target genes in surviving diet-fed insects. This study offers proof-of-principle that the efficacy of RNAi against insect pests can be enhanced by using dsRNA to suppress the activity of RNAi-suppressing nuclease genes, especially where multiple genes with related physiological function but different molecular function are targeted.

Highlights

RNA interference (RNAi) holds great promise as a novel strategy against insect pests of agricultural crops (Scott et al, 2013; Whyard et al, 2009; Xue et al, 2012)
This study demonstrates the complexity of these processes, and identifies a strategy that improves the efficacy of RNAi against the globally-important insect pest, the whitefly B. tabaci
A critical factor determining the efficacy of in planta RNAi against phloem-feeding insects is the molecular identity of the phloem-mobile doublestranded RNA molecules (dsRNA) molecules

Summary

Introduction

RNA interference (RNAi) holds great promise as a novel strategy against insect pests of agricultural crops (Scott et al, 2013; Whyard et al, 2009; Xue et al, 2012). This is because, in principle, the only information needed to target an essential insect gene with exquisite specificity is the insect gene sequence; and the doublestranded RNA molecules (dsRNA) can be delivered via transgenesis of the crop plant. On ingestion by the insect, the dsRNA is internalized into cells, where it is cleaved by an insect dsRNA-specific enzyme, Dicer-2, into small interfering RNA Luo et al / Insect Biochemistry and Molecular Biology 88 (2017) 21e29 often reduces growth or reproduction, but has small or no effect on survivorship (Coleman et al, 2015; Pitino et al, 2011; Thakur et al, 2014; Tzin et al, 2015; Zha et al, 2011)

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