MHC class II alpha polymorphisms and their association with resistance/susceptibility to Singapore grouper iridovirus (SGIV) in orange-spotted grouper, Epinephelus coioides

摘要

The major histocompatibility complex (MHC) is a crucial component of the immune systems of vertebrate animals and is associated with their resistance/susceptibility to pathogenic diseases. In this study, the association between MHC II alpha gene polymorphisms and disease resistance/susceptibility was analyzed in the orange-spotted grouper (Epinephelus coioides), by challenging it with Singapore grouper iridovirus (SGIV). Thirty-seven alleles showing high levels of polymorphism (24.7% mutation sites) were isolated from 80 individuals. In the peptide-binding region, the ratio of nonsynonymous (dN) substitutions to synonymous (dS) substitutions was 1.427 (>1), suggesting that the loci are evolving under positive balancing selection. Eight alleles were selected to estimate their distributions in high-resistance (HR) and high-susceptibility (HS) groups of fish. The EPCO-DAA*0101 allelewas significantly associated with susceptibility to SGIV infection (P 0.05) and the EPCO-DAA*0104, EPCO-DAA* 0601, EPCO-DAA*1101, and EPCO-DAA*1201 alleles were significantly associated with resistance to SGIV (P 0.05 for each). To confirm these correlations, an additional independent challenge experiment was performed in the Wenchang population of the orange-spotted grouper. The frequency distribution showed that the EPCO-DAA*0101 allele was significantly more frequent in the Wenchang HS (WC-HS) group than in the WC-HR group (P 0.05), whereas the EPCO-DAA*1101 allele was significantly more frequent in the WC-HR group than in the WC-HS group (P 0.05), consistent with the first challenge. However, the frequency distributions of the EPCO-DAA*0104, EPCO-DAA*0601, and EPCO-DAA*1201 alleles did not differ significantly between the WC-HR and WC-HS groups (P > 0.05). These results indicate that the EPCO-DAA*0101 allele confers susceptibility to SGIV infection, whereas the EPCO-DAA*1101 allele confers resistance to it. These disease-resistance- related MHC markers could be useful for the molecular-marker-assisted selective breeding of the orange-spotted grouper. (C) 2016 Elsevier B.V. All rights reserved.