Transcriptome profiling suggests roles of innate immunity and digestion metabolism in purplish Washington clam

The purplish Washington clam (Saxidomus purpuratus) in the family Veneridae is distributed widely along the intertidal zones of northeast Asia and is increasingly being utilized as a commercially important food resource. Bivalves maintain homeostasis by regulating their food intake and digestion, innate immunity, and biotransformation in a mollusk-specific organ, the digestive gland. To understand digestive gland-specific pathways, we generated a high-quality de novo assembly of the digestive gland transcriptome of this clam using the Illumina Miseq platform. A total of 9.9 million raw reads were obtained and assembled using the Oases assembly platform, resulting in 27,358 contigs with an N50 of 433 bp. Functional gene annotations were performed using Gene Ontology, Eukaryotic Orthologous Groups, and Kyoto Encyclopedia of Genes and Genomes pathway analyses. In the transcriptome, many crucial genes involved in innate immunity and digestion metabolism were detected. A number of enzymes associated with drug metabolism were annotated, as much as that identified from the whole transcriptome of the Pacific oyster Crassostrea gigas. We provide valuable sequence information of S. purpuratus to predict functional understandings of the bivalve-specific digestive gland. This resource will be valuable for researchers comparing gene compositions and their expression levels in the digestive glands of bivalves.