Functional divergence and patterns of inductive expression of three multi-gene families of antimicrobial peptides in the silkworm, Bombyx mori

Three multi-gene families of the antimicrobial peptides, Cecropins, Moricins and Attacins, in Bombyx mori were investigated for their inductive expression and functional divergence. Fifteen genes were cloned and expressed in vitro. Antimicrobial activity of the peptides was assayed by agar diffusion and minimum inhibitory concentration. Gene expression of the four Cecropin subfamilies was examined by quantitative RT-PCR. Strong antibacterial activity in Cecropin D and BmcecB1 and high transcriptional levels in Cecropin D and BmcecB1-B5 were found, whereas BmcecD1 transcripts were not detected, indicating that dominant inducible genes are present in this family. Antibacterial activity and high transcription levels were detected in the Moricins A, but not Moricins B subfamily, suggesting that Moricins A subfamily is dominant in the Moricins family. Antibacterial activity of Bmatt1 and Nuecin in the Attacins family displayed similar antibacterial spectrum. This study was supported by the “973 Program” (2005CB121000), the “863 Program”（2006AA10A119）and the NNSF of Guangdong Province of China (032256, 04020553).