Orange-shell phenotype regulated by CgABCG2-mediated protoporphyrin IX transport in Pacific oyster (Crassostrea gigas)

Animal body coloration, governed by pigment synthesis and transport dynamics, carries ecological and commercial significance in aquaculture species. In molluscs, appealing shell color directly enhances market value of commercially important species and reflects physiological status, yet molecular mechanisms underlying pigment transportation remain unresolved. While porphyrins serve as primary pigments driving coloration, their transport pathways and deposition processes are poorly characterized. The Pacific oyster (Crassostrea gigas), with heritable shell color diversity, provides an ideal model for deciphering pigment transport mechanisms and improving color-trait-based breeding. Here, we identify ATP binding cassette subfamily G member 2 (CgABCG2) as the transporter mediating cytoplasmic Protoporphyrin IX (PPIX) efflux. Multi-omics analyses revealed stage specific synchronization between PPIX accumulation and CgABCG2 upregulation during shell formation. Western blotting, quantitative real-time PCR, and immunofluorescence demonstrated positive correlations between CgABCG2 expression levels and orange hue intensity, while structural modeling confirmed high PPIX binding affinity. Furthermore, CgABCG2 knockdown experiments impact porphyrin metabolism and PPIX accumulation, compromising orange-shell coloration. This study provides the first experimental evidence of ABCG2 mediated PPIX transmembrane transport in mollusc, extends the established regulatory network of shell coloration and offers potential molecular targets for genetically enhancing color traits in aquaculture species