Comparative genomics of an Antarctic sea-ice diatom (<i>Nitzschia</i> sp.) provides insights into potential polar adaptation

Sea-ice diatoms are key primary producers in Antarctic sea-ice ecosystems and the Southern Ocean. However, the genomic features that characterize these organisms remain incompletely understood. Here, we present a high-quality draft genome assembly of an Antarctic sea-ice diatom, <i>Nitzschia</i> sp. (most likely <i>Nitzschia stellata</i>), and examine its genomic characteristics using comparative analyses. We found that <i>Nitzschia</i> sp. and <i>Fragilariopsis cylindrus</i>, another Antarctic sea-ice diatom, share numerous orthologous genes that are absent from temperate diatoms. These shared genes are associated with biological processes such as oxidative stress response, DNA repair, protein quality control, osmotic regulation, and nutrient acquisition and transport-functions that may be relevant for coping with the combined stresses of the sea-ice environment. In addition, <i>Nitzschia</i> sp. shows contraction in several gene families, including those involved in proprotein convertase activity, clathrin-mediated endocytosis, BTB/POZ domain-containing proteins, solute carrier transporters, and voltage-gated potassium channels. We also identified a high-quality endogenous viral element (EVE) related to the viral family <i>Metaviridae</i>, as well as a high proportion of transposable elements (TEs), accounting for 27.25% of the genome assembly. Together, our results characterize the genomic features of <i>Nitzschia</i> sp. and highlight potential genomic strategies that may contribute to survival in sea-ice environments.