Multiomics provided insights into the molecular mechanisms underlying black-colored mantle in scallops

In our previous studies, we obtained scallops with black mantles by treating fertilized eggs with EMS (ethylmethane sulfonate) in the Argopecten scallop variety “Bohai”. While scallops that are potentially rich in melanin may have higher market values, the mechanisms underlying the occurrence of these black-mantled are largely unknown. We sequenced and compared the transcriptomes and metabolomes of the mantles from the black-mantled “Bohai Red” scallops and those from the scallops with normal-colored (white) mantles. Results reveal that the pigment component in the black mantle of scallops was melanin indeed. Based on the transcriptome data, 1 314 differentially expressed genes were obtained and subjected to the gene ontology (GO) enrichment analysis. The upregulated genes in the black mantle were mainly enriched in transition metal ion binding, hydrolytic enzyme activity, and copper ion binding. Several candidate genes associated with black mantle formation in scallops were identified. Among them, the downregulation of monoamine oxidase (MAO) and glutathione S-transferases (GST) genes and upregulation of cytochrome P450 family 3 subfamily A (CYP3A) and protein kinase A (PKA) genes may have a positive effect on the formation of black mantle in scallops. The differentially expressed metabolites were mainly enriched in metabolism-related biological pathways, suggesting that the formation of black mantle in scallops may affect physiological functions related to metabolism in scallops. This study provided new evidence for understanding the mechanisms of coloration in scallop tissues, which eventually benefit the selection of new scallop strain with high melanin content.