Single CRD containing lectin from Macrobrachium rosenbergii (MrLec) participates in innate immunity against pathogen infections

• A new C-type lectin gene (MrLec) was identified from M. rosenbergii.
• MrLec was regulated by Vibrio parahaemolyticus.
• The expression of Alf 1 and Lyso2 were markedly decreased after MrLec-RNAi.
• Recombinant MrLec-CRD can agglutinate (Ca2+-dependent) bacteria.
• Recombinant MrLec-CRD can bind bacteria.

As a type of pattern-recognition proteins, lectins perform important functions in the innate immunity of crustaceans, including prawns. Although several reports showed that C-type lectin domain family (CLEC) importantly functions in host–pathogen interactions, limited research has focused on CLEC in Macrobrachium rosenbergii. In the present study, a new single CRD containing CLEC (designated as MrLec) was reported in freshwater prawns, M. rosenbergii. The full-length cDNA of MrLec consisted of 1027 bp with an open reading frame of 801 bp, which encoded a peptide of 266 amino acid residues. Genomic sequence for MrLec was also obtained from the M. rosenbergii, which contain 4 exons and 3 introns. MrLec was found to contain a single carbohydrate-recognition domain with an EPN motif. MrLec was ubiquitously distributed in various tissues of a normal prawn, particularly in the hepatopancreas and gills. MrLec expression in the gills was significantly upregulated after a challenge with Vibrio parahaemolyticus and downregulated at 24 h after MrLec RNA interference (MrLec-RNAi). The expression levels of some AMPs, including antilipopolysaccharide factor 1 (Alf1) and lysozyme 2 (Lyso2), also markedly decreased after MrLec-RNAi. Recombinant MrLec can agglutinate (Ca2+-dependent) and bind both Gram-negative and Gram-positive bacteria. Results suggested that MrLec participates in the recognition of invading pathogens and functions in the immune response of prawn against pathogen infections.