Involvement of peroxinectin in the defence of red swamp crayfish Procambarus clarkii against pathogenic Aeromonas hydrophila.

Cell adhesion factors are important immune components for invertebrate to immobilize, phagocytose or encapsulate invasive microorganisms and foreign particles. In this study, a new cell adhesion factor, peroxinectin (refered as Pcpxin) was isolated from hemocytes of red swamp crayfish (Procambarus clarkii). The full-length cDNA of Pcpxin was 3014 bp encoding a protein of 819 amino acid residues with a predicted molecular weight of 89.0 kDa and a calculational isoelectric point of 6.93. The putative amino acid sequence contained a peroxidase domain and a signal peptide of 21 amino acid residues, and exhibited high identity to peroxinectin from Pacifastacus leniusculus (85%), Fenneropenaeus chinensis (62%) and Scylla serrata (58%), as well as peroxidase from Camponotus floridanus (40%), Pediculus humanus corporis (39%), and Culex quinquefasciatus (38%). Quantitative real time PCR revealed that mRNA expression of Pcpxin in hemocytes could be inhibited by challenge with heat-killed Aeromonas hydrophila, suggesting that Pcpxin was involved in immune responses to A. hydrophila. RNA interference (RNAi) experiment demonstrated that silencing Pcpxin significantly reduced the survival rate of red swamp crayfishes after challenge with A. hydrophila, which indicated that Pcpxin was important for P. clarkii to survive A. hydrophila infection. Moreover, silencing Pcpxin inhibited the up-regulation of crustin1 and lysozyme expression in response to challenge with heat-killed A. hydrophila. This result suggested that Pcpxin might participate in antibacterial peptide gene expression and thereby might be involved in signal transduction pathway regulating the expression of antibacterial peptide gene.