Freshwater mussel Hyriopsis cumingii is ubiquitous in China and commercially valuable for freshwater
pearl production. Donor pearl mussel or oyster shell nacre color considerably affects pearl color, but the molecular
mechanism underlying pearl color remains unclear. Mussels with purple and white inner-shell colors were selected,
and five genes related to nacreous layer color formation were identified through comparative transcriptome analysis.
Real-time quantitative analysis indicated that HcTyr1 encoding tyrosinase is involved in black pigment synthesis. HcTyr1
expression in rear edge films was higher in the purple mussels (p < 0.05). The expression in the posterior and anterior
mantle pallial of HcAst, which encodes shrimp erythropoietin, was higher in the purple mussels (p < 0.01). HcAst
expression in the central membrane was also higher in the purple mussels (p < 0.05). The expression of HcCyt, which
encodes cytochrome P450, was higher in the central membranes of the purple mussels than in the posterior and anterior
mantle pallial and the central membranes of the white mussels (p <0.01). The expression in the posterior mantle pallial
of HcTDO, which encodes tryptophan oxygenase involving in ophthalmic lutein synthesis, was significantly higher in
the purple mussels (p < 0.01). No difference in expression regularity in the outer mantle of HcUROD which encodes
urine porphyrin decarboxylase participating in heme synthesis was observed among the mussels, and the expression
was higher in the posterior marginal membrane than in the central membrane (p < 0.01). These studied genes are
involved in nacre color formation in H. cumingii.