Genome Report: A chromosome-scale Mytilus edulis genome assembly for aquaculture, marine ecology and evolution.

The smooth-shelled blue mussel, Mytilus edulis is part of the Mytilus species complex, encompassing at least three putative species: M. edulis, M. galloprovincialis and M. trossulus. These three species occur on both sides of the Atlantic and hybridize in nature, and both M. edulis and M. galloprovincialis are important aquaculture species. They are also invasive species in many parts of the world. Here, we present a chromosome-level assembly of Mytilus edulis. We used a combination of PacBio sequencing and Dovetail's Omni-C technology to generate an assembly with 14 long scaffolds containing 94% of the predicted length of the M. edulis genome (1.6 out of 1.7 Gb). Assembly statistics were total length 1.65 Gb, N50 = 116 Mb, L50 = 7 and, L90 = 13. BUSCO analysis showed 92.55% eukaryote BUSCOs identified. AB-Initio annotation using RNA-seq from mantle, gills, muscle and foot predicted 47,128 genes. These gene models were combined with IsoSeq validation resulting in 45,379 full CDS protein sequences and 129,708 isoforms. Using GBS and shotgun sequencing, we also sequenced several eastern Canadian populations of Mytilus to characterize single-nucleotide as well as structural variance. This high-quality genome for M. edulis provides a platform to develop tools that can be used in breeding, molecular ecology and evolution to address questions of both commercial and environmental perspectives.