Transcriptome and exosome proteome analyses provide insights into the mantle exosome involved in nacre color formation of pearl oyster Pinctada fucata martensii.

Color polymorphisms in molluscan shells play an important economic in the aquaculture industry. Among bivalves, shell color diversity can reflect properties such as growth rate and tolerance. In pearl oysters, the nacre color of the donor is closely related to the pearl color. Numerous genes and proteins involved in nacre color formation have been identified within the exosomes of the mantle. In this study, we analyzed the carotenoids present in the mantle of gold- and silver-lipped pearl oysters, identifying capsanthin and xanthophyll as crucial pigments contributing to coloration. Transcriptome analysis of the mantle revealed several differentially expressed genes (DEGs) involved in color formation, including ferric-chelate reductase, mantle genes, and larval shell matrix proteins. We also isolated and identified exosomes from the mantles of both gold- and silver-lipped strains of the pearl oyster Pinctada fucata martensii, revealing the extracellular transition mechanism of coloration-related proteins. From these exosomes, we obtained a total of 1223 proteins, with 126 differentially expressed proteins (DEPs) identified. These proteins include those associated with carotenoid metabolism and Fe(III) metabolism, such as apolipoproteins, scavenger receptor proteins, β,β-carotene-15,15'-dioxygenase, ferritin, and ferritin heavy chains. This study may provide a new perspective on the nacre color formation process and the pathways involved in deposition within the pearl oyster P. f. martensii.