黑鲷耐低温和耐低氧性状的QTL定位及候选基因筛选OA

Water temperature and dissolved oxygen are critical environmental factors for fish survival,directly affecting growth,development,and reproduction.Unsuitable temperatures can cause tissue damage or mortality,whereas hypoxia leads to growth retardation,immune suppression,and economic losses.Black seabream(Acanthopagrus schlegelii)faces substantial overwintering costs and hypoxia risks in aquaculture,making the improvement of stress tolerance through genetic breeding an urgent priority.Understanding the genetic basis of stress tolerance in this species is essential for developing resilient strains through marker-assisted selection(MAS).This study aimed to map quantitative trait loci(QTLs)and screen candidate genes associated with cold tolerance(CT)and hypoxia tolerance(HT)in black seabream,thereby providing a theoretical basis for MAS breeding.A full-sib F1 family comprising 158 eight-month-old individuals was generated from a cross between wild Fujian(♀)and Shandong(♂)black seabream.Phenotyping for CT and HT was based on the time to loss of equilibrium during controlled temperature reduction and progressive oxygen depletion,respectively.Body length and head length were measured in accordance with national standards.All phenotypic data were Box-Cox transformed to achieve normality,and Pearson correlation analysis was used to evaluate relationships among traits.A previously constructed high-density genetic linkage map containing 4212 SNP markers,with an average spacing 0.42 cM,was used for QTL analysis.Interval mapping was performed using MapQTL 6.0,with 1000 permutation tests applied to determine LOD thresholds(α=0.05)and a 1 cM step-size for interval mapping(IM)-based QTL scanning.Candidate genes located within QTL confidence intervals were identified based on the reference genome.Correlation analysis revealed a significant positive relationship between HT and body length(r=0.326,P<0.01),whereas CT showed no significant correlation with body size.Three QTLs associated with CT were detected on LG1,LG15,and LG16.Notably,qCT-1 on LG1 reached genome-wide significance(LOD=5.07,PVE=13.8%).Eight QTLs associated with HT were identified on LG1,LG13,and LG19,all reaching chromosome-wide significance,with PVE values ranging from 8.7%to 13.2%.A cluster of five QTLs was observed on LG19(14.74-15.13 cM).Within the QTL intervals,13 candidate genes associated with CT(e.g.,Usp53,Dusp8,Ube2h)and 13 associated with HT(e.g.,Rfxank,Mef2c,Slc25a42,Cers1)were identified.The significant positive correlation between HT and body length supports a size-dependent hypoxia tolerance mechanism in fish,emphasizing the need to control body size or include body length as a covariate in HT-related QTL analyses to avoid confounding effects.In contrast,the independence of CT from growth traits suggests regulation by intrinsic factors such as cell membrane lipid composition or antioxidant enzyme activity,reflecting distinct physiological mechanisms underlying the two stress traits.The genome-wide significant CT-QTL(qCT-1)and clustered HT-QTLs on LG19 provide key genetic loci for stress tolerance,while candidate genes involved in ubiquitin-mediated proteolysis,MAPK signaling,and HIF regulation clarify potential molecular regulatory mechanisms.Notably,the overlapping CT/HT-QTL region on LG1 implies a genetic hotspot associated with multi-stress responses.These findings not only advance our understanding of the molecular mechanisms underlying stress responses in teleosts but also provide crucial genetic markers and candidate genes for MAS breeding programs aimed at improving the environmental resilience of black seabream.