Sequestosome 1 in Autophagy Regulates a Defense Response of the Striped Stem Borer to the Cry9Aa Protein

Bacillus thuringiensis produces insecticidal crystal (Cry) proteins that target and destroy insect pest midgut epithelial cells, ultimately leading to larval death. However, exposure to sublethal concentrations of Cry proteins can activate defense responses to counteract toxicity. Here, we revealed a moderate autophagy response to a sublethal dose of Cry9Aa in the larval midgut of Chilo suppressalis through autophagosome detection by electron microscopy, Western blot analysis of the Atg8-PE/Atg8 ratio, and visualization of Atg8-PE puncta. Additionally, differential gene expression analysis showed significant upregulation of the autophagy receptor genes sequestosome 1 (sqstm1) and atg12, supporting a potential role for autophagy in the response to Cry9Aa intoxication. Knocking down sqstm1 increased larval susceptibility to Cry9Aa by 30%, highlighting its role in defense, whereas atg12 knockdown increased susceptibility by only 8%. Our findings suggest that sqstm1 contributes to C. suppressalis defense against Cry9Aa intoxication through a mechanism response that may not be strictly dependent on canonical autophagy.