Adaptation to abiotic stress in the oyster Crassostrea angulata relays on genetic polymorphisms

Here we describe the whole genome re-sequencing of the Portuguese oyster Crassostrea angulata, an edible cupped oyster of major commercial importance with an important role as biosensor of coastal water pollution. We sequenced the genome of the C. angulata to 29.3-fold coverage using ABI SOLID system. Comparisons of the sequences with the reference assembly of the Pacific oyster (Crassostrea gigas), yielded 129 million SNPs, 151,620 from which were located in 20,908 genes from the C. gigas database. The analysis of Gene Ontology (GO) terms associated with gene regions containing SNPs, revealed that significant GO terms showing differences between the two oyster species, were related to activities of response to stress caused both by drying and by metal contamination. In the Biological Process domain, the GO terms ion transport, phosphorylation and proteolysis processes, among others, showed many polymorphic genes in C. angulata. These processes are related to combating genotoxic and hypo-osmotic stress in the oyster. It is noteworthy that more than 200 polymorphic genes were associated with DNA repair processes. These results reveal that most of the gene polymorphisms observed in C. angulata are associated with processes related to genome adaptation to abiotic stress in estuarine regions and support that genetic polymorphisms may be the base to the observed ability of C. angulata to retain the phenomenally high concentrations of toxic heavy metals. Our results also provide the framework for future investigations to establish the molecular basis of phenotypic variation of adaptive traits and should contribute to the management of the species' genetic resources.