The polymorphisms of MHCIIß gene of Trachinotus ovatus and their association with resistance/susceptibility to Photobacterium damsela

Trachinotus ovatus is an important economic species in China, with an annual output of over 100,000 tons (FAO). The major histocompatibility complex (MHC) genes, which are a highly polymorphic gene superfamily, play a vital role in the adaptive immune system. In our study, due to the threat caused by Photobacterium damselae, the associations between polymorphisms of exon 2 of MHC IIß and disease resistance/susceptibility were analysed in Trachinotus ovatus. The gene structure of MHC IIß was composed of six exons and five introns in T. ovatus, similar to Hippocampus erectus MHC IIß. Among the forty-three alleles, high levels of polymorphism were found (24.8% of nucleotide positions were variable). In the peptide-binding region (PBR) and non-PBR sites, the value of dN was 6.60 and 12.22 (> 1) times higher than the value of dS, respectively. Six alleles were chosen to calculate their distributions in the high-resistance (HR) and high-susceptibility (HS) groups. The analysis of the associations between alleles and resistance/susceptibility to P. damselae indicated that the TO-DAB-01 allele was associated with immunity to P. damselae and the TO-DAB-04, TO-DAB-05 and TO-DAB-10 alleles were associated with its sensitivity to P. damselae. The results suggest that the diversity of exon 2 of MHC IIß alleles could be used to explore the association between disease susceptibility/resistance and the multiformity of MHC IIß and to achieve the molecular-assisted selection of T. ovatus with enhanced disease resistance.