Transcriptome Analysis of Mantle Tissues Reveals Potential Shell-Matrix-Protein Genes in Gigantidas haimaensis.

Haima cold seep ecosystem is on the northwestern slope of the South China Sea, which is characterised by high pressure, low temperature, hypoxia, and low pH value. The deep-sea mussel Gigantidas haimaensis is distributed in this ecosystem. Previous studies have focused on its adaptation to abiotic stress, biogeography, ecotoxicology, genomes, immunity and symbiosis, but knowledge on biomineralisation remains lacking. Herein, we generated a comprehensive transcript dataset from G. haimaensis mantle tissue, and 30255 unigenes were assembled. The top 20 most highly expressed genes are related to energy supply, such as mitochondrial genes, suggesting they may mediate the adaptability of this deep-sea mussel to the high pressure and hypoxia environment. Eleven shell matrix protein (SMP)-related genes were identified from the transcriptome data. Quantitative PCR analyses showed that five of ten acidic SMPs and nacreous-layer-matrix-protein genes (nacrein, perlucin, perlwapin, pif and mantle protein) were highly expressed in mantle tissue, while the expressions of other five genes (chitinase, SPARC, TRY, papilin and calmodulin) were low. Scanning electron microscopy showed that the shell was composed of a prismatic layer and a nacreous layer, and every nacreous layer was made of the whole pieces of aragonite that stacked on top of each other. These results indicated the conservation of the structure and functions of nacreous matrix genes in G. haimaensis. Moreover, the nacreous layer was made of whole pieces of aragonite that were not quadrilateral or polygonal pieces. Studying these genes will likely reveal the molecular mechanisms of biomineralisation in G. haimaensis and other deep-sea mussels. [ABSTRACT FROM AUTHOR]