摘要
Major histocompatibility complex （MHC） genes are critical members in both innate and adaptive immunity, and the association between their polymorphism and disease resistance has been reported in many teleosts. In the present study, we first investigated the genetic variation at the MHC II β gene in orange-spotted grouper （Epinephelus coioides） after a challenge with Singapore grouper iridovirus （SGIV）. The results reveal that a high polymorphism level of the MHC II β gene （H = 1.000; K = 20.206; π=0.081） and at least three loci exist in grouper. The rate of dN/dS in the peptide-binding region （PBR） and non-PBR were both 〉1, suggesting the loci were evolving under positive selection. A high ratio of heterozygous individuals （37.26 %） and high rate of dN/dS were discovered, suggesting that both heterozygote advantage and frequency-dependent selection might result in the high polymorphism levels in MHC II β genes in grouper. A total of 33 MHC II β alleles were identified from 40 high-susceptibility （HS） and 40 high-re- sistance group （HR） individuals, and 15 alleles were used in the association analysis. Three alleles, EPCO-DBB＊0302, EPCO-DBB＊0307, EPCO-DBB＊0603, and EPCO- DBB＊1001 were significantly associated with resistance ability to SG1V, and the EPCO-DBB＊0607 and EPCO-DBB＊1303 alleles were associated with susceptibility （P 〈 0.05）. To further confirm the association, another independent challenge experiment was performed. The result of association analysis in the verification test found that only EPCO-DBB＊1001 alleles were significantly asso- ciated with resistance to SGIV （P 〈 0.05）, while the other alleles showed no significance （P 〉 0.05） in the frequency distribution between HR and HS groups. Therefore, the EPCO-DBB＊ 1001 alleles could be used as a disease resis- tance-related MHC marker in the molecular marker-assisted selective breeding program of grouper.
MHC基因是鱼类先天性和适应性免疫系统中的关键基因.在许多硬骨鱼的研究中表明,MHC基因的多态性与鱼体对某些疾病的抗病性存在显著关联性.本文以感染虹彩病毒的石斑鱼(Epinephelus coioides)群体为研究对象,分析石斑鱼MHC IIβ基因多态性与虹彩病毒抗性的相关性.结果表明,MHC IIβ基因在该群体内呈现出高度基因多态性(H=1.000;K=20.206;π=0.081),且石斑鱼基因组中至少存在2个MHC基因位点;MHC基因条带EPCO-DBB*1001与虹彩病毒抗性显著关联(P<0.05).因此条带EPCO-DBB*1001可以作为候选分子标记应用到石斑鱼抗病分子标记育种中.
基金
supported by China Postdoctoral Science Foundation Funded Project(2015M572380)
National Basic Research Program of China(973)(2012CB114402)
