Abstract: The silkworm, Bombyx mori, has been a domesticated, economically important insect for 5 000 years. Recent accomplishments in molecular immunology have revealed just a preliminary outline for silkworm innate immunity. The acquisition of the updated silkworm genome has enabled a comparative analysis of the silkworm immune-related genes and signaling pathways. In this study, through comparing with the sequenced Drosophila melanogaster, Anopheles gambiae, Apis mellifera and Tribolium castaneum genomes, we identified over 218 genes in the silkworm that fall into 21 families involved in immune defense, including pattern recognition receptors, signaling transducers, effectors and oxidative defense enzymes. Phylogenetic analysis showed that the signal transducers have remarkable orthologous relationships between different insect species in spite of the divergent sequences. In contrast, gene families associated with recognition, modulation and effectors exhibit more significant sequence conservation. However, the orthologs of these families are remarkably absent, presumably attributable to the lineage-specific gene duplication. Our results suggest that common mechanisms may be responsible for innate-immunity responses to pathogens via signaling pathways in the silkworm. Furthermore, hosts may adjust their defensive strategies by gene duplication and sequence divergence to kill pathogens.

Key words: Bombyx mori, innate immunity, antimicrobial peptide, oxidative defense, gene expression, signaling pathways