To artificially enhance antimicrobial peptide expression in Bombyx mori, we constructed genetically engineered silkworms overexpressing Rel family transcription factor, truncated BmRelish1 (BmRelish1t) and BmRelish2 genes controlled by B. mori cytoplasmic actin 3 promoter by using the piggyBac transposon vector. The BmRelish1t gene contained a Rel homolog domain (RHD), nuclear localization signal (NLS), acidic and hydrophobic amino acid (AHAA) rich region, and death domain (DD), but no ankyrin repeat (ANK) domain. The BmRelish2 gene had RHD and NLS, but no AHAA, ANK, or DD. Chromosome analysis of G1 generations of a transgenic silkworm with EGFP expression confirmed stable insertion of BmRelish1t and BmRelish2. BmRelish1t gene overexpression in transgenic silkworms resulted in higher mRNA expression levels of B. mori antimicrobial peptides and proteins such as lebocin (~19.6-fold), moricin (~9.8-fold), and nuecin (~16.4-fold) than those in normal silkworms. However, transgenic silkworms overexpressing BmRelish2 showed mRNA expression patterns of antimicrobial peptides similar to those of normal silkworms, excluding that of lebocin (~3.9-fold). Moreover, transgenic silkworms overexpressing BmRelish1t showed antibacterial activity against various pathogenic bacteria, while those with the BmRelish2 gene showed no antibacterial activity. Therefore, we suggest that BmRelish1t expression could be useful for the simultaneous production of various antimicrobial peptides in transgenic silkworms.

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