Development of expressed sequence tags from the pearl oyster, Pinctada martensii Dunker

The pearl oyster, Pinctada martensii, is the primary species used for the aquaculture production of marine pearls in China and Japan. Genetic tools and resources are needed to study the genome of this species and to understand the molecular basis of development, growth, host defense, pearl formation, and other important traits. In this study, we developed a set of expressed sequence tags (ESTs) for P. martensii. We constructed cDNA libraries from adult tissues and sequenced 7,128 ESTs. Clustering analysis identified 788 contigs (covering 5,769 ESTs) and 1,351 singletons, yielding a total of 2,139 unique genes. Of these unique genes, only 935 had significant (E-value ≤ 0.005) hits in GenBank, and the remaining 1,204 (56.3%) were novel. Most of the known genes are related to cellular structure, protein binding, and metabolic processes. Putative host-defense genes (86) were identified including C-type lectin, ferritin, polyubiquitin, proteases, protease inhibitors, scavenger receptors, heat shock proteins, and RAS oncogenes. The EST sequences developed in this study provide a valuable resource for future efforts on gene identification, marker development, and studies on molecular mechanism of host defense in pearl oysters.