Construction of a high-density genetic map and fine QTL mapping for growth and nutritional traits of Crassostrea gigas.

BACKGROUND: Both growth and nutritional traits are important economic traits of Crassostrea gigas (C. gigas) in industry. But few work has been done to study the genetic architecture of nutritional traits of the oyster. In this study, we constructed a high-density genetic map of C. gigas to help assemble the genome sequence onto chromosomes, meanwhile explore the genetic basis for nutritional traits via quantitative trait loci (QTL) mapping.

RESULTS: The constructed genetic map contained 5024 evenly distributed markers, with an average marker interval of 0.68 cM, thus representing the densest genetic map produced for the oyster. According to the high collinearity between the consensus map and the oyster genome, 1574 scaffold (about 70%) of the genome sequence of C. gigas were successfully anchored to 10 linkage groups (LGs) of the consensus map. Using this high-qualified genetic map, we then conducted QTL analysis for growth and nutritional traits, the latter of which includes glycogen, amino acid (AA), and fatty acid (FA). Overall, 41 QTLs were detected for 17 traits. In addition, six candidate genes identified in the QTL interval showed significant correlation with the traits on transcriptional levels. These genes include growth-related genes AMY and BMP1, AA metabolism related genes PLSCR and GR, and FA metabolism regulation genes DYRK and ADAMTS.

CONCLUSION: Using the constructed high-qualified linkage map, this study not only assembled nearly 70% of the oyster genome sequence onto chromosomes, but also identified valuable markers and candidate genes for growth and nutritional traits, especially for AA and FA that undergone few studies before. These findings will facilitate genome assembly and molecular breeding of important economic traits in C. gigas.