Amazing stuff!
"Genome forms of the single-cell, green algae called Chlamydomonas do just fine in polar waters despite the fierce cold, harsh UV radiation, and other extremes. Their success may stem in part from genes given them by so-called giant viruses.
Uncommonly large and complex, and often sporting unusual tendrils, giant viruses were first discovered in 2003. They most often infect algae or amoebae, but can invade more complex multicellular organisms, and are found throughout the world, including in marine, aquatic, and terrestrial habitats.
In Current Biology yesterday, a team reported that polar algae have hundreds of genes given to them by these viruses—roughly 5% of their genome. Further studies showed these genes, remnants of past infection, were active and made proteins that could help the algae—some of the genes encode ice-binding proteins, which help keep the algae from freezing in waters that can dip as low as –2°C. “ ..."
From the highlights and abstract:
"Highlights
• Diverse polar algal genomes harbor widespread endogenous giant virus elements
• Polar alga Chlamydomonas ICE-L shows extensive giant virus genome endogenization
• Many viral genes are expressed and respond to abiotic stress
• Co-expression patterns of viral genes suggest regulatory integration with host
Summary
Giant viruses, members of the phylum Nucleocytoviricota (NCV), possess exceptionally large genomes that encode hundreds of genes involved in replication, metabolism, and host manipulation. These viruses have emerged as major players in protist ecology and evolution. Recent studies reveal that their genomes are frequently endogenized in protists, contributing to structural innovation and functional novelty. Yet, the extent and impact of such events on genome architecture and physiological responses in algae inhabiting extreme polar environments remain unknown.
Here, we report widespread giant endogenous viral elements (GEVEs) in nine polar microalgae, revealing extensive viral integration. Most notably, Chlamydomonas sp. ICE-L, an Antarctic sea ice alga, harbors over 400 GEVE regions spanning more than 26 megabase pairs (Mbp)—the most extensive giant viral endogenization recorded in any eukaryote. These insertions, derived from multiple NCV lineages, encode >25,000 genes, including those associated with replication, chromatin remodeling, stress responses, and transposable elements.
Transcriptomic analyses show that ∼40% of GEVE genes are actively expressed, with hundreds being differentially regulated under UV radiation, salinity, and temperature stress. A co-expression network reveals modular regulation patterns, suggesting functional integration of viral genes into host transcriptional networks.
Additionally, phylogeny supports giant viruses as important mediators of horizontal gene transfer (HGT) of key freeze-tolerance proteins, such as ice-binding proteins (IBPs), in polar algae.
Our findings position giant viral endogenization as a key driver of genome content, regulatory complexity, and environmental adaptation in polar algae and establish Chlamydomonas sp. ICE-L as a model for studying virus-derived genomic innovation in extreme environments."
Genes from giant viruses help polar algae survive frigid waters and harsh sunlight "A prior infection may create lasting, beneficial evolutionary change in these hardy microbes"
Extensive array of endogenous giant viral elements in a polar alga shows dynamic transcriptional response to abiotic stress (open access)
Figure 1 GEVE statistics and distribution
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