Viruses are the most abundant biological entities in the world's oceans, where they play important ecological and biogeochemical roles. Metagenomics is revealing new groups of eukaryotic viruses, although disconnected from known hosts. Among these are the recently described mirusviruses, which share some similarities with herpesviruses.1 50 years ago, "herpes-type" viral particles2 were found in a thraustochytrid member of the labyrinthulomycetes, a diverse group of abundant and ecologically important marine eukaryotes,3,4 but could not be further characterized by methods then available. Long-read sequencing has allowed us to connect the biology of mirusviruses and thraustochytrids. We sequenced the genome of the genetically tractable model thraustochytrid Aurantiochytrium limacinum ATCC MYA-1381 and found that its 26 linear chromosomes have an extraordinary configuration. Subtelomeric ribosomal DNAs (rDNAs) found at all chromosome ends are interspersed with long repeated sequence elements denoted as long repeated-telomere and rDNA spacers (LORE-TEARS). We identified two genomic elements that are related to mirusvirus genomes. The first is a ∼300-kbp episome (circular element 1 [CE1]) present at a high copy number. Strikingly, the second, distinct, mirusvirus-like element is integrated between two sets of rDNAs and LORE-TEARS at the left end of chromosome 15 (LE-Chr15). Similar to metagenomically derived mirusviruses, these putative A. limacinum mirusviruses have a virion module related to that of herpesviruses along with an informational module related to nucleocytoplasmic large DNA viruses (NCLDVs). CE1 and LE-Chr15 bear striking similarities to episomal and endogenous latent forms of herpesviruses, respectively, and open new avenues of research into marine virus-host interactions.

• Klíčová slova
• LORE-TEARS, duplodnaviria, endogenous viruses, host-virus co-evolution, labyrinthulomycetes, long repeated-telomere and rDNA spacers, protist genome assembly, subtelomeric rDNAs, thraustochytrids, varidnaviria, viral episome,
• MeSH
• Eukaryota MeSH
• fylogeneze MeSH
• genom MeSH
• heterochromatin MeSH
• ribozomální DNA MeSH
• telomery MeSH
• viry * MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH
• Názvy látek
• heterochromatin MeSH
• ribozomální DNA MeSH

Thraustochytrids (phylum: Labyrinthulomycota) are nonphotosynthetic marine protists. Some thraustochytrids have crtIBY, a trifunctional fusion gene encoding a protein capable of β-carotene biosynthesis from geranylgeranyl pyrophosphate. Here we show that crtIBY is essential in, and encodes the sole pathway for, carotenoid biosynthesis in the thraustochytrid Aurantiochytrium limacinum ATCC MYA-1381. We explore the evolutionary origins of CrtIBY and discover that the closest related protein domains are present in a small but diverse group of other heterotrophic protists, including the apusomonad Thecamonas trahens and the dinoflagellates Oxyrrhis marina and Noctiluca scintillans. Each organism within this cluster also contains one or more β-carotene 15-15' oxygenase genes (blh and rpe65), suggesting that the acquisition of β-carotene biosynthesis genes may have been related to the production of retinal. Our findings support a novel origin of eukaryotic (apo)carotenoid biosynthesis by horizontal gene transfer from Actinobacteria, Bacteroidetes, and/or Archaea. This reveals a remarkable case of parallel evolution of eukaryotic (apo)carotenogenesis in divergent protistan lineages by repeated gene transfers.

• Klíčová slova
• carotenoid oxygenase, lycopene cyclase, phylogenetics, phytoene desaturase, phytoene synthase, thraustochytrids,
• MeSH
• Bacteria genetika   MeSH
• beta-karoten genetika   MeSH
• Heterokontophyta * MeSH
• karotenoidy * MeSH
• přenos genů horizontální MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH
• Názvy látek
• beta-karoten MeSH
• karotenoidy * MeSH

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

• Publikační typ
• časopisecké články MeSH
• tisková chyba MeSH

Diverse microbial ecosystems underpin life in the sea. Among these microbes are many unicellular eukaryotes that span the diversity of the eukaryotic tree of life. However, genetic tractability has been limited to a few species, which do not represent eukaryotic diversity or environmentally relevant taxa. Here, we report on the development of genetic tools in a range of protists primarily from marine environments. We present evidence for foreign DNA delivery and expression in 13 species never before transformed and for advancement of tools for eight other species, as well as potential reasons for why transformation of yet another 17 species tested was not achieved. Our resource in genetic manipulation will provide insights into the ancestral eukaryotic lifeforms, general eukaryote cell biology, protein diversification and the evolution of cellular pathways.

• MeSH
• biodiverzita MeSH
• biologické modely * MeSH
• DNA aplikace a dávkování   MeSH
• druhová specificita MeSH
• ekosystém MeSH
• Eukaryota klasifikace   fyziologie   MeSH
• mořská biologie * MeSH
• transformace genetická * MeSH
• zelené fluorescenční proteiny metabolismus   MeSH
• životní prostředí MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• DNA MeSH
• zelené fluorescenční proteiny MeSH