Single Nucleotide polymorphisms and their relationship to codon usage bias in the Pacific oyster Crassostrea gigas

• Published in: Gene
• Main Authors: Sauvage, C., Bierne, Nicolas, Lapegue, S., Boudry, Pierre
• Other Authors: Unité Amélioration génétique, Santé animale et Environnement (AGSAE), Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), Institut des Sciences de l'Evolution de Montpellier (UMR ISEM), Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-École Pratique des Hautes Études (EPHE), Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-Université de Montpellier (UM)-Institut de recherche pour le développement IRD : UR226-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2007
• Subjects: SNP; genetic diversity; codon bias; Crassostrea gigas; [SDE.BE]Environmental Sciences/Biodiversity and Ecology; Pacific oyster
• Online Access: https://hal.science/halsde-00450670; https://doi.org/10.1016/j.gene.2007.05.011

International audience DNA sequence polymorphism and codon usage bias were investigated in a set of 41 nuclear loci in the Pacific oyster Crassostrea gigas. Our results revealed a very high level of DNA polymorphism in oysters, in the order of magnitude of the highest levels reported in animals to date. A total of 290 single nucleotide polymorphisms (SNPs) were detected, 76 of which being localised in exons and 214 in non-coding regions. Average density of SNPs was estimated to be one SNP every 60 bp in coding regions and one every 40 bp in non-coding regions. Non-synonymous substitutions contributed substantially to the polymorphism observed in coding regions. The non-synonymous to silent diversity ratio was 0.16 on average, which is fairly higher to the ratio reported in other invertebrate species recognised to display large population sizes. Therefore, purifying selection does not appear to be as strong as it could have been expected for a species with a large effective population size. The level of non-synonymous diversity varied greatly from one gene to another, in accordance with varying selective constraints. We examined codon usage bias and its relationship with DNA polymorphism. The table of optimal codons was deduced from the analysis of an EST dataset, using EST counts as a rough assessment of gene expression. As recently observed in some other taxa, we found a strong and significant negative relationship between codon bias and non-synonymous diversity suggesting correlated selective constraints on synonymous and non-synonymous substitutions. Codon bias as measured by the frequency of optimal codons for expression might therefore provide a useful indicator of the level of constraint upon proteins in the oyster genome.