Resistance to RNA interference by plant‐derived double‐stranded RNAs but not plant‐derived short interfering RNAs in Helicoverpa armigera

Abstract

Plant-mediated RNA interference (RNAi) has emerged as a promising technology for pest control through expression of double-stranded RNAs (dsRNAs) targeted against essential insect genes. However, little is known about the underlying molecular mechanisms and whether long dsRNA or short interfering RNAs (siRNAs) are the effective triggers of the RNAi response. Here we generated transplastomic and nuclear transgenic tobacco plants expressing dsRNA against the Helicoverpa armigera ATPaseH gene. We showed that expression of long dsRNA of HaATPaseH was at least three orders of magnitude higher in transplastomic plants than in transgenic plants.HaATPaseH-derived siRNAs are absent from transplastomic plants, while they are abundant in transgenic plants. Feeding transgenic plants to H. armigera larvae reduced gene expression of HaATPaseH and delayed growth. Surprisingly, no effect of transplastomic plants on insect growth was observed, despite efficient dsRNA expression in plastids. Furthermore, we found that dsRNA ingested by H. armigera feeding on transplastomic plants was rapidly degraded in the intestinal fluid. In contrast, siRNAs are relatively stable in the digestive system. These results suggest that plantderived siRNAs may be more effective triggers of RNAi in Lepidoptera than dsRNAs, which will aid the optimization of the strategies for plant-mediated RNAi to pest control.

Host-delivered RNAi mediated silencing of HaAce1, encoding the major isoform of acetylcholinesterase, imparts resistance against the polyphagous insect-pest, Helicoverpa armigera

“…Considering the efficacy and biosafety concerns, transplastomic expression of hpRNA is preferred as reported by Bally et al (2016Bally et al ( , 2020. However, the higher magnitude of target knockdown and greater stability of siRNAs derived from nuclear-transformed lines in the digestive system of H. armigera as compared to the transplastomically produced dsRNA, suggest that host-delivered siRNAs could be a more effective trigger of RNAi in Lepidoptera than host-delivered dsRNAs (Fu et al 2022). Moreover, the lack of efficient transformation, selection, and regeneration protocols for engineering fertile homoplastic lines across different crop species is the major limitation to the immediate application of this approach in major food crops (Wani et al 2015).…”

HDAC3 Knockdown Dysregulates Juvenile Hormone and Apoptosis-Related Genes in Helicoverpa armigera

“…For H. armigera , although growth was inhibited, the method did not achieve pest control and high mortality. Based on recent research, dsRNA produced by H. armigera after feeding on transgenic plants is rapidly degraded in the intestinal fluid, whereas siRNA is relatively stable in the digestive system; in lepidopteran insects, siRNAs may be more effective than dsRNAs in triggering RNAi [ 7 ]. Therefore, the findings could optimize plant-mediated RNAi pest-control strategies.…”

“…It has advantages such as high specificity, efficiency, stability, heritability, and transferability. In H. armigera , however, dsRNA silencing of target genes is inefficient, primarily because Lepidoptera have relatively high levels of dsRNase activity, which can lead to dsRNA degradation more easily than siRNA [ 7 , 8 ]. In the case of H. armigera , therefore, it is more effective to select siRNA that specifically silences target genes.…”

Complete protection from Henosepilachna vigintioctopunctata by expressing long double‐stranded RNAs in potato plastids

“…When expressed from the plastid genome, dsRNAs accumulate much more abundantly in the plastids due to the high polyploidy of the plastid genome (with up to 10 000 identical copies per cell), and remain intact owing to the absence of an RNAi machinery in plastids (there are no Dicer‐like endoribonucleases that could process dsRNAs into siRNAs). Plastid‐mediated RNAi (PM‐RNAi) technology has also been tested in Helicoverpa armigera (Bally et al, 2016; Fu et al, 2022), Frankliniella occidentalis (western flower thrip; Wu et al, 2022), Myzus persicae (green peach aphid; Dong et al, 2022), and Bemisia tabaci (whitefly; Dong et al, 2020), revealing that the feasibility and efficiency of PM‐RNAi varies between different insect orders. This is probably due to the wide differences in (i) RNAi susceptibility (Arraes et al, 2021) and/or (ii) feeding habit among insect orders.…”