Suppressing calcineurin activity increases the toxicity of Cry2Ab to Helicoverpa armigera

Abstract

BACKGROUND Extensive planting of transgenetic Bacillus thuringiensis crops has driven the evolution of pest resistance to Cry1Ac. Adjustment of cropping structures has promoted further outbreak of Helicoverpa armigera in China. To control this pest, a combination of pyramiding RNA interference (RNAi) and Cry2Ab is considered a promising strategy for countering cross‐resistance and enhancing the toxicity of Cry2Ab to cotton bollworm. We explored the possibility of using calcineurin (CAN) as a target RNAi gene, because it is involved in cotton bollworm responses to the toxicity of Cry2Ab. RESULTS Cry2Ab treatment led to a significant increase in HaCAN mRNA level and HaCAN activity. Suppression of HaCAN activity due to RNAi‐mediated knockdown of HaCAN increased the susceptibility of midgut cells to Cry2Ab. The increase in HaCAN activity shown by heterologous expression of HaCAN reduced the cytotoxicity of Cry2Ab to Sf9 cells. Moreover, ingestion of HaCAN‐specific inhibitor FK506 increased the toxicity of Cry2Ab in larvae. Interestingly, HaCAN does not function as a Cry2Ab direct binding protein that participates in Cry2Ab toxicity. CONCLUSIONS The results in this study provide evidence that suppression of HaCAN not only affected the development of the cotton bollworm, but also enhanced the toxicity of Cry2Ab to the pest. HaCAN is therefore an important candidate gene in cotton bollworm that can be targeted for pest control when the pest infests RNAi+Cry2Ab crops. Meanwhile, the mechanism of action of HaCAN in Cry2Ab toxicity suggested that protein dephosphorylation was involved. © 2020 Society of Chemical Industry

Cyclosporin A as a Source for a Novel Insecticidal Product for Controlling Spodoptera frugiperda

“…CaN is an important immune-regulated enzyme that regulates the expression of antimicrobial peptides and immune-related genes in insects through Toll or IMD pathways [ 21 , 22 , 23 ]. Suppression of CaN activity by FK506 increased the toxicity of Cry1Ac and Cry2Ab in Helicoverpa armigera Hubner (Lepidoptera: Noctuidae) larvae in our previous studies [ 24 , 25 ]. CaN is an important Ca 2+ -dependent phosphatase in animals, and it has a high amino acid identity among different species, indicating the conservation of CaN function [ 26 , 27 ].…”

“…For each combination, we calculated the mortality of CsA (50 μg/g, 100 μg/g, and 200 μg/g) against third instar larvae. The expected mortality was calculated as described previously [ 24 , 25 ], and as explained in detail in the Supplementary Information . Each treatment group consisted of 72 newly molted third instar larvae of the same size (three biological replicates).…”

Cyclosporin A as a Potential Insecticide to Control the Asian Corn Borer Ostrinia furnacalis Guenée (Lepidoptera: Pyralidae)

“…Mortality was recorded after 2 (for the combination of CsA and β-cypermethrin), 3 (for CsA and indoxacarb and CsA and emamectin benzoate), or 5 (for CsA and azadirachtin and CsA and Cry1Ac) days. The expected mortality for each combination of the two toxins was calculated following a reported method [ 27 , 32 , 33 ] as follows: Expected mortality = (1 − S A × S B ) × 100% where S A /S B is the observed survival rate of larvae treated with toxin A/B. Expected mortality > observed mortality ( p < 0.05, analyzed by independent samples t -test) indicates that the combined toxicity is synergistic; expected mortality < observed mortality ( p < 0.05) indicates that the combined toxicity is antergic; expected mortality = observed mortality ( p > 0.05) indicates that the combined toxicity is independent.…”

Involvement of an Enhanced Immunity Mechanism in the Resistance to Bacillus thuringiensis in Lepidopteran Pests

“…CaN serves as an immune activator by interacting with Relish to regulate AMP (gloverin, cecropin D, and attacin) expression in H. armigera ( Figure 1 ) [ 105 ]. Importantly, CaN activity could be induced by Cry1Ac and Cry2Ab [ 40 , 41 ]. Consequently, AMP expression was promoted.…”

“…Currently, the response mechanisms and immune resistance of insects is attracting worldwide attention to improve the insecticidal activity of Bt and managing insect resistance to Bt . In fact, understanding the host response mechanisms and immune resistance to Bt and Bt proteins will enable us to identify more ways of pest control and resistance management [ 40 , 41 , 42 , 43 , 44 , 45 ]. In this review, we will focus on the involvement of enhanced immune defense of insects against Bt , including the pattern recognition proteins for recognizing Bt , AMPs and their synthetic signaling pathways, the prophenoloxidase system, ROS generation, nodulation, encapsulation, phagocytosis, and cell-free aggregates.…”