This study aims to find genes related to the formation of nacre color.According to the sequence annotated from the transcriptome,the full-length cDNA sequence of HcCUBDC gene was cloned from Hyriopsis cumingii by using rapid amplification of cDNA ends(RACE)approaches.The entire HcCUBDC cDNA was 5 158 bp,including a 1 902 bp open reading frame(ORF) encoding a polypeptide of 639 amino acids,a 576 bp 5'UTR,and a 2 622 bp 3'UTR(GenBank accession number is KP067952).Bioinformatics analysis showed that the HcCUBDC gene had a signal peptide of 19 amino acids,and four CUB domains,but shared no identity with known proteins.Real-time Q-PCR revealed that HcCUBDC gene was ubiquitously expressed in all tissues,including anterior mantle pallial(aMP),posterior mantle pallial(pMP),mantle center(M),gill(G),foot(F),hepatopancreas(H),intestine(I)and kidney(K),with the lowest level of transcripts in H.In the purple mussels,the expression level of pMP was significantly higher compared with aMP.In the white mussels,there was no difference between aMP and pMP.HcCUBDC gene expression level of the pMP in purple mussels was significantly higher than that of white mussels,and there was no difference about the mRNA levels of aMP between the purple and white mussels.In situ hybridization showed that HcCUBDC mRNA was mainly expressed in outer epithelial cells at the mantle pallial.The results showed that HcCUBDC gene played important roles in the inner- shell color formation of H.cumingii,and may provide useful information for further studies on function and regulation mechanism of HcCUBDC gene in the color formation of the pearls.