Bush of life: giant virus DNA hiding in Algae (Introduction)

by David Turell , Thursday, November 19, 2020, 14:49 (1464 days ago) @ David Turell

What is it doing there?:

https://www.sciencemag.org/news/2020/11/giant-virus-genomes-discovered-lurking-dna-comm...

"In 2003, scientists discovered something huge, literally, in the virus world: viruses so big they could be seen with a standard microscope. These massive parasites were considered rare at the time, but they’ve since proved more common than anyone expected. Now, researchers have found entire giant virus genomes embedded in the genomes of several common algae. The find suggests this strange viral group is even more prolific—and potentially influential—than scientists thought.

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"Viral matches “kept popping up in algal genomes,” Aylward recalls. So the duo and their colleagues systematically looked through genomes representing all of the sequenced DNA from the group of algae called Chlorophytes. An entire giant virus was genetically present in the DNA of a dozen of these species, the team reports today in Nature.

"In all, the viruses added between 78 and 1782 genes to the algae. Two algae even had the whole genomes of two giant viruses in their DNA, in one case making up 10% of the algae’s total gene count.

"It’s not clear why these viruses sneak their DNA into their host’s genome, instead of just replicating inside the cell. It may be a way for the virus to ensure that its genetic material will be passed down from generation to generation. HIV and other viruses also integrate their genes into human DNA—one reason they are difficult to eliminate by the immune system or drugs.

"Some of these giant viruses have likely been part of the algae for a long time, the researchers found, perhaps millions of years. Indeed, some viral DNA has acquired noncoding DNA called introns within their genes. And some of their genes are now duplicated or missing, changes that are unlikely to occur in viruses simply floating around inside algal cells.

“'They make a solid case that the viral sequences they identified are, in all likelihood, part of their host genomes,” says Matthias Fischer, an environmental virologist at the Max Planck Institute for Medical Research.

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"The viral DNA present in algae can even include genes hijacked from other algae. The giant viruses may therefore be a way to transfer genes among species, says Andrew Roger, an evolutionary biologist at Dalhousie University. All of this new DNA can enable the host genome to take on new functions that improve the alga’s ability to survive and may have shaped the group’s diversity and distribution, he says.

“'These interactions have been going on since the origins of life,” Fischer adds. “And they continue to play a big role in cellular evolution.'”

Comment: Note the bold. This is a mystery, but perhaps the key is the role in evolution.