Abstract
Dinoflagellates are taxonomically diverse, ecologically important phytoplankton in marine and freshwater environments. Here, we present two draft diploid genome assemblies of the free-living dinoflagellate Polarella glacialis, isolated from the Arctic and Antarctica. For each genome, guided using full-length transcriptome data, we predicted >50,000 high-quality genes. About 68% of the genome is repetitive sequence; long terminal repeats likely contribute to intra-species structural divergence and distinct genome sizes (3.0 and 2.7 Gbp). Of all genes, ∼40% are encoded unidirectionally, ∼25% comprised of single exons. Multi-genome comparison unveiled genes specific to P. glacialis and a common, putatively bacterial, origin of ice-binding domains in cold-adapted dinoflagellates. Our results elucidate how selection acts within the context of a complex genome structure to facilitate local adaptation. Since most dinoflagellate genes are constitutively expressed, Polarella glacialis has enhanced transcriptional responses via unidirectional, tandem duplication of single-exon genes that encode functions critical to survival in cold, low-light environments.
Footnotes
Main text revised; Figures 1, 2, 3 and 4 revised; new Figure 6 added; Supplemental files updated with new Supplementary Note and new Supplementary Tables; authorship revised.
