Expressed sequence tags 454 sequencing and biomineralization gene expression for pearl sac of the pearl oyster,Pinctada fucata martensii

Abstract

Pearl sac is the tissue that secretes proteins resulting into artificial pearl formation, a highly controlled biomineralization process similar to development of inner shell regulated by the mantle. We present here the pearl sac transcriptome of Pinctada fucata martensii using massively parallel pyrosequencing. A total of 21 729 putative unique transcripts were assembled and annotated. Twenty-three candidate biomineralization genes were identified, such as calmodulin, calponin-like protein (CLP), mantle gene, pearlin, nacrein and Pif. The sequence data contained 4303 potential SNP loci and 4291 probable indels, providing a resource for molecular biomarker, population genetics and gene function. Expression levels of six potential biomineralization genes were also characterized with real-time PCR. The expression level of mantle gene 4 was the highest, followed by lysine-rich matrix protein 4. Nearly all detected genes maintained the highest expression levels in mantle edge and the lowest in pearl sac. In both tissues of mantle centre and pearl sac, the six genes had an obvious higher expression activity in host oyster producing nacre pearls than those producing plain nuclei, but the expression level of CLP was similar in the two host groups. These results will notably advance biomineralization and transcript-wide study in P. fucata martensii and other Pinctada species.