BacterialPxRdl2dsRNA increased the insecticidal activities of GABAR-targeting compounds againstPlutella xylostella

Abstract

BACKGROUND: The application of RNAi to control pests has attracted the attention of researchers. Our results indicated that knockout of PxRdl2 can decrease resistance to fipronil in Plutella xylostella, providing a suitable target gene for RNAi-based pest control. RESULTS: The differences in the sensitivity of two established homozygous knockout strains of P. xylostella. (Rdl1KO and Rdl2KO) and susceptible P. xylostella to a series of compounds were evaluated. Quinazolines and isoxazolines both showed stronger efficacy in the Rdl2KO strain. Therefore, we proposed a method based on the knockdown of the P. xylostella Rdl2 gene as a tactic to enhance the toxicity of quinazolines and isoxazolines. To reduce costs and protect dsRNA against degradation, we applied a bacterial expression system using the L4440 vector to express PxRdl2 dsRNA in HT115 Escherichia coli. Transformed bacteria (dsRNA-Bac) fed through leaves combined with quinazoline and isoxazolines proved to be more effective in both the susceptible and fipronil-resistant P. xylostella. CONCLUSION: Our results provide a strategy for the development of novel insecticide spray formulations containing dsRNA-Bac, which synergize with insecticide toxins by suppressing PxRdl2, reducing the use of pesticides in the field.

Lab-to-Field Transition of RNA Spray Applications – How Far Are We?

“…Beyond shielding dsRNA from RNase degradation, the silencing of a dsRNA ribonuclease improved oral RNAi efficacy in the southern green stinkbug (Sharma et al, 2021). This finding indicates that the simultaneous application of protective agents such as RNase inhibitors or the silencing of dsRNases might encourage targeted detoxification mediated by P450s, ABC transporters and others (Wang et al, 2021). Notably, a nanomaterial-based formulation may help to increase selectivity not only by shielding dsRNA from the environment but also by providing target-site-specific RNA release (e.g., pH-dependent release kinetics), or selectivity facilitated by attractants that are incorporated in the envelope of (nano)-capsules following the proven attract and kill principle.…”

“…For these purposes, encapsulation is pursued to guarantee and prolong the longevity of RNA sprays in the field. For example, E. coli is not only utilized for cost-effective dsRNA production but also represents a protective envelope for efficient dsRNA delivery (Lü et al, 2020;Máximo et al, 2020;Wang et al, 2021;Wu et al, 2021). Interestingly, encapsulation of dsRNA, if large enough, may prevent cellular uptake (plant intake) and thus shield dsRNA from plant DCL processing, as indicated by previous breakthroughs demonstrating that the expression of dsRNA in chloroplasts (DCL-free organelles) targeting the ßactin gene of L. decemlineata (Colorado potato beetle) caused larval lethality (Zhang et al, 2015).…”