Abstract: C-type lectins (CTLs) are Ca2+-dependent carbohydrate-recognition proteins which are extensively present in plants, animals and microorganisms. CTLs were revealed to be able to recognize and bind the carbohydrate components on the cell surface of pathogenic microorganisms, and play crucial roles in innate immunity. To understand the molocular characterization of CTL and its potential function from a species of freshwater pearl mussel (Hyriopsis schlegelii), the cDNA sequence of one novel C-type lectin gene (named as HsCTL) in this study was cloned from H. Schlegelii for the first time by means of de novo transcriptome sequencing, combined with 5′ and 3′ rapid amplification of cDNA ends (RACE). The full-length cDNA consists of 1716 bp with one open reading frame (ORF) of 726 bp, encoding a polypeptide of 241 amino acids with 28 ku predicted molecular weight, one 5′-untranslated region (UTR) of 92 bp and one 3′-UTR of 898 bp. The HsCTL contained a typical signal peptide sequence with 23 amino acids and one carbohydrate recognition domain (CRD). The CRD of HsCTL was composed of 115 residues, including 6 conserved cysteine residues and a QPD (Gln-Pro-Asp) motif which has a predicted binding specificity for galactose-type sugarin immune reactions. BLASTP analysis showed that the HsCTL shared the highest identity (reaching 36%) with the ortholog in sugpo prawn (Penaeus monodon), and 9.7%-18.1% with other molluscon orthologs. The phylogenetic analysis showed that the HsCTL fell on the same branch with P. monodon and Fenneropenaeus chinensiss. And then they were clustered with Hyriopsis cumingii and Haliotis diversicolor in a big branch in the neighbor-joining tree. Tissue expression analysis showed that the HsCTL mRNA was expressed in hepatopancrea, hemocyte, mantle, gill, adductor muscle and gonad, with the highest expression in hemocyte and then in mantle, hepatopancreas, gill and adductor muscle, with the lowest expression in gonad. After challenge with lipopolysaccharide (LPS), HsCTL mRNA expression was upregulated significantly in the hemocytes and hepatopancreas. Our results implied that HsCTL plays an important role in the immune response in mussels and lays a foundation for studies on the H. schlegelii immune system.

Key words: Hyriopsis schlegelii, C-type lectin, cloning, sequence analysis, immune response, real-time PCR