Expression profiles of antimicrobial peptides in Mytilus coruscus

Antimicrobial peptides (AMPs) play a fundamental role in mussels' innate immunity, preventing the invasion of potential pathogens. Previous research has shown that AMPs are abundant in Mytilus species. A mussel with important economic value and limited distribution in the East China Sea, M. coruscus, also contains abundant AMPs, including the mytichitin and myticusin identified previously in this species. However, the molecular diversity and expression pattern of M. coruscus AMPs remain largely unknown. Based on the dataset of the M. coruscus hemocyte transcriptome, we identified twelve AMPs representing the main AMP families present in M. coruscus, including three novel AMPs (two arthropod-like and one crustin-like). The variations in the expression of the genes encoding these AMPs have been analyzed in different tissues, different larval development stages, and different M. coruscus individuals, as well as in hemocytes and gonads under the threat of different microbes. The results suggest that in adult M. coruscus, the gonads and hemocytes are the sources of AMPs for mussels collected in winter and summer, respectively. The expression of AMPs is developmentally regulated, and most AMPs are undetectable in larvae until after larval settlement and metamorphosis. In vivo microbial challenges significantly increased the expression of AMPs in M. coruscus hemocytes, and different AMP response patterns under challenges from different microbes were observed, showing a rapid, strong response to gram-positive strains, a weak response to gram-negative strains, and a long-term response to fungus. While the gonads showed a different response pattern than the hemocytes, with stronger changes in expression relative to the control and stronger fluctuation in the expression level of some AMPs. Finally, LC-MS/MS was used for peptidomic analysis of the AMPs in M. coruscus, and the results confirmed the presence of several AMP families in the mussel serum