Abstract
BackgroundThe pearl oyster Pinctada fucata martensii (Pfu.), widely cultured in the South China Sea, is a precious source of sea pearls and calcifying materials. A yellow shell variety of Pfu. was obtained after years of artificial breeding. To identify differentially expressed genes between yellow shell and normal black shell pearl oysters, we performed transcriptomic sequencing and proteomic analyses using mantle edge tissues.ResultsA total of 56,969 unigenes were obtained from transcriptomic, of which 21,610 were annotated, including 385 annotated significant up-regulated genes and 227 significant down-regulated genes in yellow shell oysters (| log2 (fold change) | ≥2 and false discovery rate < 0.001). Tyrosine metabolism, calcium signalling pathway, phototransduction, melanogenesis pathways and rhodopsin related Gene Ontology (GO) terms were enriched with significant differentially expressed genes (DEGs) in transcriptomic. Proteomic sequencing identified 1769 proteins, of which 51 were significantly differentially expressed in yellow shell oysters. Calmodulin, N66 matrix protein, nacre protein and Kazal-type serine protease inhibitor were up-regulated in yellow shell oysters at both mRNA and protein levels, while glycine-rich protein shematrin-2, mantle gene 4, and sulphide: quinone oxidoreductase were down-regulated at two omics levels. Particularly, calmodulin, nacre protein N16.3, mantle gene 4, sulphide: quinone oxidoreductase, tyrosinase-like protein 3, cytochrome P450 3A were confirmed by quantitative real-time PCR. Yellow shell oysters possessed higher total carotenoid content (TCC) compared than black shell oyster based on spectrophotography.ConclusionsThe yellow phenotype of pearl oysters, characterised by higher total carotenoids content, may reflect differences in retinal and rhodopsin metabolism, melanogenesis, calcium signalling pathway and biomineralisation. These results provide insights for exploring the relationships between calcium regulation, biomineralisation and yellow shell colour pigmentation.
Highlights
The pearl oyster Pinctada fucata martensii (Pfu.), widely cultured in the South China Sea, is a precious source of sea pearls and calcifying materials
Pigments in higher molluscs such as bivalves are thought to be tightly attached to conchiolins in the shell, similar to gastropods and pulmonarias [7], while the periostracum layer is composed of conchiolins and calcium salts
Sun et al [8] found that calmodulin-related protein, adenylate cyclase, and tyrosinase family members are involved in both biomineralisation and melanin biosynthesis in scallop Patinopecten yessoensis
Summary
The pearl oyster Pinctada fucata martensii (Pfu.), widely cultured in the South China Sea, is a precious source of sea pearls and calcifying materials. To identify differentially expressed genes between yellow shell and normal black shell pearl oysters, we performed transcriptomic sequencing and proteomic analyses using mantle edge tissues. The. Xu et al BMC Genomics (2019) 20:469 mantle protein, and nacrein are related to shell colour [5]. Pigments in higher molluscs such as bivalves are thought to be tightly attached to conchiolins (organic matrix proteins) in the shell, similar to gastropods and pulmonarias [7], while the periostracum layer is composed of conchiolins and calcium salts. Sequential layer-by-layer mineralisation is directed by cells of the mantle edge in Pfu., and pigments, glycoproteins and polysaccharides in the periostracum layer are secreted by the mantle or foot tissue in molluscs [13, 14]. There may be a close relationship between biomineralisation and pigment deposition, with some genes acting as a bridge between these two biological phenomena
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