Genome-wide analysis reveals expansion and structural rearrangements of the attacin gene family in saturniid silkmoths

Antimicrobial peptides (AMPs) are essential components of insect immunity, yet the attacin gene family remains poorly studied in Saturniidae. Despite comprehensive functional studies on AMPs across various lepidopteran taxa, the attacin gene family remains insufficiently characterized in Antheraea assamensis (A. assamensis) and related saturniid silkmoths. Here, we present a comprehensive genome-wide analysis across five saturniid silkmoths, identifying 10 attacin genes in A. assamensis, 9 in Antheraea pernyi (A. pernyi), 5 in Antheraea mylitta (A. mylitta), 4 in Antheraea yamamai (A. yamamai), and 10 in Samia ricini (S. ricini). Domain analysis revealed that while most Attacins possess both N- and C-terminal glycine-rich domains, several encode truncated isoforms and some with extended polypeptide lengths. Phylogenetic analysis demonstrated lineage-specific expansions, and aBSREL analysis identified positive selection acting on certain clades, particularly those encoding C-terminal-only isoforms. Conserved microsynteny with Bombyx mori (B. mori) supports a shared evolutionary origin despite scaffold variation. In silico structural modelling and molecular docking predicted high-affinity interactions between Attacin peptides and bacterial lipopolysaccharides (LPS), implicating their role in membrane disruption. Finally, qRT-PCR analysis revealed that several attacin paralogs, particularly attacin5 to attacin8, were significantly upregulated in both the fat body and midgut of A. assamensis following E. coli infection. Notably, attacin2 and attacin10 exhibited higher expression levels in the midgut, highlighting their potential roles in both systemic and gut-localized immune responses.