Genome-Wide QTL Analysis Identified Significant Associations Between Hypoxia Tolerance and Mutations in the GPR132 and ABCG4 Genes in Nile Tilapia.

Exposure to hypoxia induces both acute and chronic stress responses, which plays an important role in health of cultured organisms including growth, reproduction, immunity, and other energy demanding activities. Application of advanced genomic technologies allows rapid identification of hypoxia trait-associated genes and precise selection of superior brood stocks with high tolerance in tilapia. By applying QTL-seq and double-digest restriction-site associated DNA sequencing (ddRAD-seq) techniques, we identified four genome-wide significant quantitative trait loci (QTLs) for hypoxia tolerance and many suggestive QTLs in Nile tilapia. These QTLs explained 6.6-14.7% of the phenotypic variance. Further analysis revealed that single nucleotide polymorphisms (SNPs) in exons of both GPR132 and ABCG4 genes located in genome-wide QTL intervals were significantly associated with hypoxia-tolerant traits. Expression analysis of both genes suggested that they were strong candidate genes involved into hypoxia tolerance in tilapia. Our findings suggest that both QTL-seq and ddRAD-seq techniques can be effectively utilized in QTL mapping of hypoxia traits in fish. Our data supply a basis for further marker-assisted selection of super lines with a high level of tolerance against low oxygen stress in the tilapia.