Genomes of the dinoflagellate Polarella glacialis encode tandemly repeated single-exon genes with adaptive functions

• Published in: BMC Biology
• Main Authors: Stephens, Timothy G., González-Pech, Raúl A., Cheng, Yuanyuan, Mohamed, Amin R., Burt, David W., Bhattacharya, Debashish, Ragan, Mark A., Chan, Cheong Xin
• Format: Article in Journal/Newspaper
• Language: English
• Published: BioMed Central 2020
• Subjects: Biotechnology; Plant Science; General Biochemistry; Genetics and Molecular Biology; Developmental Biology; Cell Biology; Physiology; Ecology; Evolution; Behavior and Systematics; Structural Biology; General Agricultural and Biological Sciences; 1100 Agricultural and Biological Sciences; 1300 Biochemistry; 1105 Ecology; 1110 Plant Science; 1305 Biotechnology; 1307 Cell Biology; 1309 Developmental Biology; 1314 Physiology; 1315 Structural Biology; Arctic; Antarc*; Antarctica; Phytoplankton
• Online Access: https://espace.library.uq.edu.au/view/UQ:9dda3cb

Dinoflagellates are taxonomically diverse and ecologically important phytoplankton that are ubiquitously present in marine and freshwater environments. Mostly photosynthetic, dinoflagellates provide the basis of aquatic primary production; most taxa are free-living, while some can form symbiotic and parasitic associations with other organisms. However, knowledge of the molecular mechanisms that underpin the adaptation of these organisms to diverse ecological niches is limited by the scarce availability of genomic data, partly due to their large genome sizes estimated up to 250 Gbp. Currently available dinoflagellate genome data are restricted to Symbiodiniaceae (particularly symbionts of reef-building corals) and parasitic lineages, from taxa that have smaller genome size ranges, while genomic information from more diverse free-living species is still lacking.Here, we present two draft diploid genome assemblies of the free-living dinoflagellate Polarella glacialis, isolated from the Arctic and Antarctica. We found that about 68% of the genomes are composed of repetitive sequence, with long terminal repeats likely contributing to intra-species structural divergence and distinct genome sizes (3.0 and 2.7 Gbp). For each genome, guided using full-length transcriptome data, we predicted > 50,000 high-quality protein-coding genes, of which ~40% are in unidirectional gene clusters and ~25% comprise 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. Because 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 polar environments. These genomes provide a foundational reference for future research on dinoflagellate evolution.