LAUSR

Abstract Beta 2-microglobulin (β2m), an essential subunit of major histocompatibility complex protein (MHC) class I molecule, plays an important role in the immune system of vertebrates, but has very limited information in fish. In order to understand the expression pattern of β2m gene and its association with antibacterial trait in Megalobrama amblycephala, in the present study, the sequence of β2m gene was obtained from the genome database, and its expression pattern was studied by quantitative real-time PCR, SNPs were screened and genotyped by High Resolution Melting method. The results showed that the β2m gene was located in the genomic Linkage Group 14 of M. amblycephala, and its ORF was 351 bp, encoding 116 amino acids. The β2m gene is widely expression in various tissues of healthy fish. After Aeromonas hydrophila infection, the expression of β2m significantly increased at 24 hpi (hours post injection) in the liver and reached a peak at 72 hpi. Moreover, the β2m expression in the spleen increased significantly and peaked at 4 hpi, followed by a slow decline, but still higher than the control. Four SNPs were screened from the β2m gene, which are located in exons SNP-β2m + 1042 A/T and SNP-β2m + 1438C/T, and introns SNP-β2m + 198 A/G and SNP-β2m + 408 A/C, respectively. The genotype and the alleles frequency of SNP-β2m + 408 A/C were significantly different between the resistant and susceptible groups. The genotype frequency of SNP-β2m + 1042 A/T was not significant different, but the alleles were significantly different between the resistant and susceptible groups. The results of this study provide certain theoretical support for the further functional study of the β2m gene and for the selection breeding of new resistant strains of M. amblycephala.