Transcriptomic analysis reveals the preliminary molecular mechanism of pigmentation of the Corbicula fluminea

Bivalves are one of the more diverse and economically valuable groups of the Mollusca phylum, and they occupy an important position in fisheries and aquaculture. The diversity of bivalve shell colouration is of interest for its breeding potential and relevance for species formation and adaptation studies. To gain more information on the potential mechanisms of shell pigmentation, in this study, the transcriptome of Corbicula fluminea, with different mantle regions with two shell colours (yellow and black), was sequenced and differential colouration-related specific genes were investigated using RNA sequencing and time-course quantitative polymerase chain reaction analysis of the expression patterns. Based on the transcript assembly, a total of 24174 annotated genes and 2234 novel genes were detected. The results of the transcriptome analysis showed that there were 460 differentially expressed genes (DEGs) in the edge mantle tissues of the yellow vs the black-shelled strains, significant enrichment of the DEGs in melanogenesis, and a possible role of melanogenesis in the process of the outer shell pigmentation. There were 575 DEGs in the central mantle tissues, including many genes associated with metal ions that may be related to shell colour formation in the inner shell of Corbicula fluminea. Our results suggest that different crustal mantle tissue regions play different roles in shell pigmentation; FSS may act as an external pressure on shell color formation. This study reveals the mechanism of colouration in C. fluminea.