Characterization of the pearl oyster (Pinctada martensii) mantle transcriptome unravels biomineralization genes.

Pearl oyster, Pinctada martensii, is a marine bivalve species widely distributed in tropic and subtropic marine coasts. Mantle is the special tissue of P. martensii that secretes biomineralization proteins inducing shell deposition as well as iridescent nacre both in the inner shell and artificial nucleus. The pearl oyster is very efficient for artificial pearl production and is therefore an ideal organism for studies into the processes of biomineralization. However, deficiency of transcriptome information limits the insight into biomineralization mechanisms and pearl formation. In this study, we sequenced and characterized the P. martensii mantle transcriptome using 454 pyrosequencing. A total of 25,723 unique transcripts were assembled from 220,824 quality reads, followed by annotation and Gene Ontology classification analysis. A total of 146 unique transcript segments homologous to 49 reference biomineralization genes were identified, including calcineurin-binding protein, amorphous calcium carbonate binding protein 1, calmodulin, calponin-like protein, carbonic anhydrase 1, glycine-rich shell matrix protein, lysine-rich matrix protein, mantle gene or protein, nacrein, pearlin, PIF, regucalcin, and shematrin. The sequence data enabled the identification of 10,285 potential single nucleotide polymorphism loci and 7,836 putative indels, providing a resource for molecular biomarker, population genetics, and functional genomic studies. A large number of candidate genes for biomineralization were identified, considerably enriching resources for the study of shell formation. These sequence data will notably advance biomineralization and transcriptome study in pearl oyster and other Pinctada species.