Development of single nucleotide polymorphisms in key genes of taurine and betaine metabolism in Crassostrea hongkongensis and their association with content-related traits.

Background: Taurine and betaine are important nutrients in and have many important biological properties. To investigate the characteristics of taurine and betaine contents and identify SNPs associated with traits in the , we cloned the full-length cDNA of key genes in taurine and betaine (unpublished data) metabolism, determined taurine and betaine content and gene expression in different tissues and months of specimen collection, and developed SNPs in the gene coding region.

Results: We cloned the full-length cDNA of cysteine dioxygenase () and cysteine sulfite decarboxylase (), which are key genes involved in taurine metabolism in , and found that betaine and taurine contents and the expression of key genes were regulated by seawater salinity. A total of 47 SNP markers were developed in the coding regions of , , , , and using gene fragment resequencing and FLDAS-PCR. Through association analysis in a population of in the Maowei Sea, Guangxi, nine SNPs were found to be associated with taurine content, and one SNP was associated with betaine content. Haploid and linkage disequilibrium analyses showed that SNPs in formed one linkage group with three haplotypes: ACACA, GTTTG, and GTACA. The average taurine content of the corresponding individuals was 873.88, 838.99, and 930.72 ng/g, respectively, indicating the GTACA haplotype has a significant advantage in terms of taurine content.

Conclusions: We identified SNPs associated with taurine and betaine contents in for the first time, and found the GTACA haplotype in the coding region has a significant advantage in taurine content. These loci and haplotypes can serve as potential molecular markers for the molecular breeding of .