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Galectins are protein that participates in a variety of immune responses in the process of pathogenic infections. In the present study, a chimera galectin gene was screened from the transcriptome database of Nibea albiflora, which was named as YdGal-3. The results of qRT-PCR showed that the mRNA transcripts of YdGal-3 were ubiquitously distributed in all the detected tissues. After infection with Vibrio harveyi, the expression of YdGal-3 in liver, spleen, and head kidney increased significantly. Immunohistochemistry showed that YdGal-3 protein was widely expressed in the head kidney. The purified YdGal-3 protein by prokaryotic expression agglutinated red blood cells. Sugar inhibition assay showed that the agglutinating activity of YdGal-3 protein was inhibited by different sugars including lactose, D-galactose, and lipopolysaccharide. In addition, we mutated YdGal-3 His 294 into proline (P), alanine (A), glycine (G), and aspartic acid (D), it was further proved that the residue plays a key role in agglutination. YdGal-3 agglutinated some gram-negative bacteria including Pseudomonas plecoglossicida, Vibrio parahemolyticus, V. harveyi, and Aeromonas hydrophila, and exhibited antibacterial activity. These results suggested that YdGal-3 protein played an important role in the innate immunity of N. albiflora., (Copyright © 2021. Published by Elsevier B.V.)

Phosphoribosyl pyrophosphate synthetases (EC 2.7.6.1) are key enzymes in the biological synthesis of phosphoribosyl pyrophosphate and are involved in diverse developmental processes. In our previous study, the PRPS1 gene was discovered as a key disease-resistance candidate gene in yellow drum, Nibea albiflora, in response to the infection of Vibrio harveyi, through genome-wide association analysis. This study mainly focused on the characteristics and its roles in immune responses of the PRPS1 gene in yellow drum. In the present study, the NaPRPS1 gene was cloned from yellow drum, encoding a protein of 320 amino acids. Bioinformatic analysis showed that NaPRPS1 was highly conserved during evolution. Quantitative RT-PCR demonstrated that NaPRPS1 was highly expressed in the head-kidney and brain, and its transcription and translation were significantly activated by V. harveyi infection examined by RT-qPCR and immunohistochemistry analysis, respectively. Subcellular localization revealed that NaPRPS1 was localized in cytoplasm. In addition, semi-in vivo pull-down assay coupled with mass spectrometry identified myeloid differentiation factor 88 (MyD88) as an NaPRPS1-interacting patterner, and their interaction was further supported by reciprocal pull-down assay and co-immunoprecipitation. The inducible expression of MyD88 by V. harveyi suggested that the linker molecule MyD88 in innate immune response may play together with NaPRPS1 to coordinate the immune signaling in yellow drum in response to the pathogenic infection. We provide new insights into important functions of PRPS1, especially PRPS1 in the innate immunity of teleost fishes, which will benefit the development of marine fish aquaculture. [ABSTRACT FROM AUTHOR]

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]

Yellow drum (Nibea albiflora), a commercially important fish species in the coastal regions of southeast China, suffers greatly from attacks from bacteria, viruses, and parasites. To uncover their immune responses, the yellow drums were artificially challenged with the pathogenic Vibrio harveyi , and genome-wide association study (GWAS) was performed to identify the associated SNPs and genetic loci for disease resistance trait. Sequence analysis in 197 susceptible and 148 resistant fish identified 23 significantly associated SNPs and 8 candidate genes distributed in chromosome 14. The estimated proportion of phenotypic variance explained (PVE) by SNPs ranged from 10.64% to 13.68%. The discovery of sphingosine kinase (SPHK), CACNA1H , and MGAT5B harboring or within the flanking region of trait-associated SNPs may account for the underlying antibacterial mechanism in yellow drum. These results provide molecular basis for prevention of disease spread and a reference for genetic breeding in fish aquaculture. • The genomic loci conferring resistance against Vibrio harveyi infection, explained 13.68% phenotypic variances, was mapped in the yellow drum. • A total of 54 significantly associated SNPs and 8 candidate genes located on chromosome 14 were identified. • SPHK1 , CACNA1H and MGAT5B within the flanking region of top associated SNPs may play important roles in antibacterial mechanism in the yellow drum. [ABSTRACT FROM AUTHOR]