Antimicrobial peptide SCY2 with its interacting proteins Scyreprocin mediate the innate immune defense of Scylla paramamosain against Pseudomonas putida infection.

Pseudomonas putida was identified in the testis of Scylla paramamosain, where it induced elevated expression of two interacting antimicrobial peptides (AMPs), SCY2 and Scyreprocin, in the gonad, indicating their potential role in reproductive immunity. In this study, we demonstrate that both peptides exerted systemic immune protection in males against this pathogen, which colonizes multiple host tissues and causes substantial mortality. Furthermore, they also mediate reproductive-specific immune functions in females. Administration of recombinant SCY2 or Scyreprocin (8 μg per crab, average weight 250 g ± 10 g) in vivo increased the survival of P. putida-infected males by 40-50 %. In addition, both peptides promoted bacterial clearance in key immune-related tissues, including the hepatopancreas, gills, hemocytes, testis, and ejaculatory duct, and modulated the expression of immune-related genes. Subsequently, the peptides' function in mated females was examined through in vivo blockade, with the efficacy validated by immunofluorescence and flow cytometry. As expected, the in vivo blockade of SCY2 and Scyreprocin in female crabs resulted in increased bacterial colonization and a significant reduction in survival rates, which declined to only 5-10 % within 96 h post-reinfection. Taken together, this study reveals a dual function for the male-derived AMPs SCY2 and Scyreprocin: they not only mediate systemic innate immunity in males but are also transferred to females to establish reproductive immunity. Consequently, this establishes a direct correlation between male immune competence and the reproductive success of the species.