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

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 (ELF alpha) 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.