Identification of Galectin 9 and its antibacterial function in yellow drum (Nibea albiflora).

Galectins are a family of evolutionarily conserved lectins that contain carbohydrate recognition domains (CRDs) specifically recognizing β-galactoside. Galectin-9 plays a crucial role in various biological processes during pathogenic infections. In a previous study, galectin-9 was identified as a candidate gene for resistance to Vibrio harveyi disease in yellow drum using a genome-wide association study (GWAS) analysis. In this study, a galectin-9 gene was identified from Nibea albiflora and named YdGal-9. The mRNA transcripts of YdGal-9 were distributed in all the detected tissues and the highest level was found in the kidney. The subcellular localization of YdGal-9-EGFP proteins was observed in both nucleus and cytoplasm in the kidney cells of N. albiflora. The expression of YdGal-9 in the brain increased significantly after infection with Vibrio harveyi. The red blood cells from rabbits, Larimichthys crocea , and N. albiflora were agglutinated by the purified recombinant YdGal-9 proteins. The results of the agglutination activity of deletion mutants of YdGal-9 proved that the conserved sugar binding motifs (H-NPR and WG-EE-) were critical for YdGal-9's agglutination activity. In addition, YdGal-9 killed some gram-negative bacteria by inducing cell wall destruction including Pseudomonas plecoglossicida , Aeromonas hydrophila , Escherichia coli , V. parahemolyticus , V. harveyi , and V. alginolyticus. Taken together, these results suggested that the YdGal-9 protein of N. albiflora played a vital role in fighting bacterial infections. • A galectin-9 was identified from Nibea albiflora and named YdGal-9. • YdGal-9 was ubiquitously distributed in all the detected tissues. • YdGal-9 expression in the brain significantly increased after Vibrio harveyi infection. • YdGal-9 had agglutination activity towards red blood cells. • YdGal-9 killed some gram-negative bacteria and resisted bacterial infections. [ABSTRACT FROM AUTHOR]