miR-13a-3p regulates susceptibility to Bacillus thuringiensis Cry1Ac protoxin in Ostrinia furnacalis by targeting...

The melanization cascade, activated by pattern recognition receptors such as β-1,3-glucan recognition proteins (βGRPs), is a key insect immune response implicated in resistance to pathogenic bacteria. However, its post-transcriptional regulation in response to Bacillus thuringiensis (Bt) infection remains poorly characterized. Here, we report that in the Asian corn borer, Ostrinia furnacalis, the core immune receptor gene OfβGRP3 is a direct target of miR-13a-3p. OfβGRP3 expression was induced by Bt Cry1Ac protoxin and functioned as a positive regulator of hemolymph phenoloxidase (PO) activity. In contrast, miR-13a-3p was suppressed by Cry1Ac protoxin and post-transcriptionally downregulated OfβGRP3 via binding to its coding sequence. Functionally, knockdown of OfβGRP3 or overexpression of miR-13a-3p significantly decreased PO activity and increased larval susceptibility to Cry1Ac protoxin. Conversely, inhibition of miR-13a-3p enhanced PO activity and Cry1Ac tolerance. Our findings reveal a novel miRNA-mediated regulatory circuit that fine-tunes the melanization response, significantly influencing Bt Cry1Ac toxicity and offering a potential target for improving pest control strategies.