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 the Hong Kong oyster (Crassostrea hongkongensis) and have many important biological properties. To investigate the characteristics of taurine and betaine and identify single nucleotide polymorphisms (SNPs) associated with traits in C. hongkongensis, we cloned the full-length cDNA of key genes involved in taurine and betaine metabolism (unpublished data), determined taurine and betaine content and gene expression in different tissues and months of the oyster specimen collection, and developed SNPs in the gene coding region.

Results: We cloned the full-length cDNA of the genes that express cysteine dioxygenase and cysteine sulfite decarboxylase (ChCSAD and ChCDO, respectively), which are key genes involved in taurine metabolism in C. hongkongensis, 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 ChCSAD, ChCDO, choline dehydrogenase (ChCDH), betaine aldehyde dehydrogenase (ChBADH), and betaine homocysteine methyltransferase (ChBHMT) using gene fragment resequencing and FLDAS-PCR. Through association analysis of a population of C. hongkongensis 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 ChCDO formed one linkage group with three haplotypes: ACACA, GTACA and GTTTG. The average taurine content of the corresponding individuals was 873.88, 838.99, and 930.72 μg/g, respectively, indicating the GTTTG haplotype has a significant advantage in terms of taurine content.

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