RNA Interference-Mediated Knockdown of Bombyx mori Haemocyte-Specific Cathepsin L (Cat L)-Like Cysteine Protease Gene Increases Bacillus thuringiensis kurstaki Toxicity and Reproduction in Insect Cadavers

Abstract

The silkworm’s Cat L-like gene, which encodes a lysosomal cathepsin L-like cysteine protease, is thought to be part of the insect’s innate immunity via an as-yet-undetermined mechanism. Assuming that the primary function of Cat L-like is microbial degradation in mature phagosomes, we hypothesise that the suppression of the Cat L-like gene expression would increase Bacillus thuringiensis (Bt) bacteraemia and toxicity in knockdown insects. Here, we performed a functional analysis of Cat L-like in larvae that were fed mulberry leaves contaminated with a commercial biopesticide formulation based on Bt kurstaki (Btk) (i.e., Dipel) to investigate its role in insect defence against a known entomopathogen. Exposure to sublethal doses of Dipel resulted in overexpression of the Cat L-like gene in insect haemolymph 24 and 48 h after exposure. RNA interference (RNAi)-mediated suppression of Cat L-like expression significantly increased the toxicity of Dipel to exposed larvae. Moreover, Btk replication was higher in RNAi insects, suggesting that Cat L-like cathepsin may be involved in a bacterial killing mechanism of haemocytes. Finally, our results confirm that Cat L-like protease is part of the antimicrobial defence of insects and suggest that it could be used as a target to increase the insecticidal efficacy of Bt-based biopesticides.

Transcriptomic Analysis of Metarhizium anisopliae-Induced Immune-Related Long Non-Coding RNAs in Polymorphic Worker Castes of Solenopsis invicta

“…In contrast, fungus-infected minor worker ants demonstrated that cis -acting lncRNAs regulated apoptosis-related genes, including caspase , TRAF , JNK-1 , etc. Cathepsin L , a gene involved in antimicrobial autophagy [ 77 , 78 ], was also identified as the cis -regulatory target of lncRNA in minor worker ants.…”

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

“…Sl102 downregulation in S. littoralis larvae and feeding bacteria expressing dsRNA enhanced the insecticidal activity of Bt kurstaki [ 44 ]. RNAi-mediated knockdown of the hemocyte-specific cathepsin L-like cysteine protease gene in B. mori can enhance the toxicity of Bt -based biopesticides [ 165 ]. In addition, a pyramid combining the protection from RNAi and Bt toxins is also recommended as a next-generation transgenic to counter insect resistance [ 166 , 167 ].…”

Common strategies in silkworm disease resistance breeding research

“…As an autoimmune mechanism, it has an important role in suppressing viral infestation and in antiviral immunity. RNAi is a specific degradation of messenger RNA (mRNA) mediated by double‐stranded non‐coding RNA (dsRNA), which is widely present in various organisms, and is an important mechanism by which organisms to respond to external environmental stress and regulate their development 3–5 . Because of its specificity, stability, high efficiency, and selectivity, RNAi technology has an important role in virus resistance research.…”