LAUSR

ABSTRACT Defensins are a group of small cationic and cysteine‐rich peptides that are important components of the innate immune system. However, studies on defensins in teleosts are very limited, particularly studies on defensin functions through in vivo assays. In this study, we cloned and identified one &bgr;‐defensin (TroBD) the golden pompano, Trachinotus ovatus, and analyzed the functions of TroBD in both in vivo and in vitro assays. TroBD is composed of 63 amino acids and shares high sequence identities (27.27–98.41%) with known &bgr;‐defensins of other teleosts. The protein has a signature motif of six conserved cysteine residues within the mature peptide. The expression of TroBD was most abundant in the head kidney and spleen and was significantly upregulated following infection by Vibrio harveyi and viral nervous necrosis virus (VNNV). Purified recombinant TroBD (rTroBD) inhibited the growth of V. harveyi, and its antimicrobial activity was influenced by salt concentration. TroBD was found to have a chemotactic effect on macrophages in vitro. The results of an in vivo study demonstrated that TroBD overexpression/knockdown in T. ovatus significantly reduced/increased bacterial colonization or viral copy numbers in tissues. Taken together, these results indicate that TroBD plays a significant role in both antibacterial and antiviral immunity and provide new avenues for protection against pathogen infection in the aquaculture industry. HighlightsWe identified and characterized a &bgr;‐Defensin (TroBD) in golden pompano (Trachinotus ovatus).The activity against V. harveyi of recombinant TroBD was influenced by salt concentration.TroBD was found to have a chemotactic effect on macrophages in vitro.TroBD had antibacterial and antiviral properties through overexpression and knockdown assays.