Inducible overexpression of cecropin B decreases the susceptibility of the transgenic silkworm, Bombyx mori (Lepidoptera: Bombycidae), to bacteria

Abstract

Silkworms and other insects confer innate immunity by expressing antimicrobial peptides (AMPs) through the induction of Toll and IMD pathways. Cecropin B, an AMP from Bombyx mori L. (Lepidoptera: Bombycidae), has a broad range of antibacterial activity against both Gram-positive and -negative bacteria. Bacterial flacherie is one of the severe diseases in silkworms. In an attempt to develop silkworm strains expressing antibacterial properties, a transgenic vector, piggyBac overexpressing the cecropin B gene, was constructed under its promoter. The vector had GFP under the control of the elongation factor (ELFα) promoter as a marker for screening transgenic silkworms. Transgenic silkworms were generated by microinjecting the piggyBac vector along with the helper vector into the silkworm eggs. The mRNA level of cecropin B in the fat body of transgenic lines was higher than the non-transgenic lines in response to Escherichia coli and Staphylococcus aureus infections. The overexpression of cecropin B was confirmed by Western blot analysis. Transgenic lines' mortality was significantly decreased compared to non-transgenic lines’ post-bacterial infections. These results imply that overexpressing an endogenous AMP gene can enhance the resistance of silkworms in response to bacterial infections.