Establishment of a marine nematode model for animal functional genomics, environmental adaptation and developmental evolution

Nematodes play key roles in marine ecosystem. Although oceans cover 71% of the Earths surface, none of marine model nematode has been reported. Here, we constructed the first inbred line of free-living marine nematode Litoditis marina, sequenced and assembled its genome. Furthermore, we successfully applied CRISPR/Cas9 genome editing in L. marina. Comparative genomics revealed that immunity and oxygen regulation genes are expanded, which is probably central to its sediment adaptation. While L. marina exhibits massive gene contractions in NHRs, chemoreceptors, xenobiotics detoxification and core histones, which could explain the more defined marine environment. Our experiments showed that dozens of H4 genes in Caenorhabditis elegans might contribute to its adaptation to the complex terrestrial environments, while two H4 genes in L. marina are involved in salinity stress adaptation. Additionally, ninety-two conserved genes appear to be positively selected in L. marina, which may underpin its osmotic, neuronal and epigenetic changes in the sea. With short generation time, highly inbred lines, and genomic resources, our report brings L. marina a promising marine animal model, and a unique satellite marine model to the well-known biomedical model nematode C. elegans. This study will underpin ongoing work on animal functional genomics, environmental adaptation and developmental evolution.