The generation of the first chromosome-level de-novo genome assembly and the development and validation of a 50K SNP array for North American Atlantic salmon

Given the genetic and genomic differences between Atlantic salmon of European origin and North American (N.A.) origin, it is crucial to develop unique genomic resources for each lineage. Here we describe the resources that we recently developed for genomic and genetic research in N.A. Atlantic salmon. Firstly, a new single nucleotide polymorphism (SNP) database for N.A. Atlantic salmon consisting of 3.1 million putative SNPs was generated using data from whole genome resequencing of 80 N.A. Atlantic salmon individuals; Secondly, a high density 50K SNP array enriched for the genic regions of the genome and containing three sex determination and 61 continent of origin markers was developed and validated; Thirdly, a genetic map composed of 27 linkage groups with 36K SNP markers, was generated from 2,512 individuals in 141 full-sib families; Finally, a chromosome level de-novo assembly of a male N.A. Atlantic salmon genome was generated using PacBio long-reads. Information from Hi-C proximity ligation sequences and Bionano optical mapping was used to concatenate the contigs into scaffolds. The assembly contains 1,755 scaffolds and only 1,253 gaps, with a total length of 2.83 Gb and N50 of 17.2 Mb. A BUSCO analysis detected 96.2% of conserved Actinopterygii genes in the assembly and the genetic linkage information was used to guide the formation of 27 chromosome sequences. In contrast, the karyotype of the European Atlantic salmon lineage is composed of 29 chromosomes. Comparative analysis with the reference genome assembly of the European Atlantic salmon confirmed that the karyotype differences between the two linages are caused by a fission in chromosome Ssa01 and three chromosome fusions including the p arm of chromosome Ssa01 with Ssa23, Ssa08 with Ssa29 and Ssa26 with Ssa28. The genomic resources we have generated for Atlantic salmon provide a crucial boost for genetic research and for management of farmed and wild populations in this highly valued species.