Evolution horizontal gene transfer Tree of life

Giant virus shares genes (core histones) with complex life forms. But what exactly does that imply?

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cryo-frozen Marseilleviridae/Kenta Okamoto et al, CC

From ScienceDaily:

“It’s exciting and significant to find a living family of giant viruses with eukaryote-specific genes in a form that predates the latest common ancestor of all eukaryotes,” says Albert Erives, associate professor in the Department of Biology. “These viruses are like time machines that tell us more about how life on our planet came to be.”

In the study, Erives analyzed the genome of a virus family called Marseilleviridae and found it shares a similar set of genes, called core histones, with eukaryotes.

That places Marseilleviridae, and perhaps its viral relatives, somewhere along eukaryotes’ evolutionary journey.

“We now know that eukaryotes are more closely related to viruses,” says Erives, “and the reason is because they share core histones, which are fundamental to eukaryotes.”

“So, when I saw this, it was wild,” Erives says. “No one has ever seen a virus with his tones.”

Moreover, he realized Marseilleviridae “did not get these genes from any one eukaryotic lineage living, but rather from some ancestor who was proto-eukaryotic — that is, on its way to becoming a eukaryote. Until now, no ‘organism’ was known to have core histone genes besides eukaryotic cells,” he says.

The discovery begs a larger question about the role giant viruses have played in the evolution of all life on Earth. Erives likens giant viruses to vines spreading out into the cellular tree of life — sampling here, borrowing there, and sharing genetic material among the branches of archaea, bacteria, and eukaryotes. Paper. (public access) – Albert J. Erives. Phylogenetic analysis of the core histone doublet and DNA topo II genes of Marseilleviridae: evidence of proto-eukaryotic provenance. Epigenetics & Chromatin, 2017; 10 (1) DOI: 10.1186/s13072-017-0162-0 More.

Before we get too carried away, how do we know that the genetic similarity is not better explained by horizontal gene transfer? Why not investigate that before we resort to Tree of Life claims? Or if there is a good reason for Darwinsplaining, let’s hear it.

Note: Didn’t a Marseillevirus pioneer get into trouble for doubting Darwin? There’s stuff we just daren’t think these days, no matter what the evidence or how well we are placed …

See also: Researchers ask: Do viruses share genes across the kingdoms of life?

and

Horizontal gene transfer: Virus carries DNA of black widow spider toxin

2 Replies to “Giant virus shares genes (core histones) with complex life forms. But what exactly does that imply?

  1. 1
    Peer says:

    It is very easy and straightforward: Giant viruses are nothing but degenerate bacteria that acquired a virus coat. The only criterium to call them viruses is their coat (and they are parasites, usually). Mimivirus, for instance, can be traced back simply to soil bacteria based on their genes.

    That the M-Virus carries histone genes is best explained by HGT, indeed. They simply picked them up from the Genome of their “Hosts”.

    As usual, these darwinos have the order of events upsidedown.

  2. 2
    critical rationalist says:

    Before we get too carried away, how do we know that the genetic similarity is not better explained by horizontal gene transfer? Why not investigate that before we resort to Tree of Life claims? Or if there is a good reason for Darwinsplaining, let’s hear it.

    Do you mean, transfer from a proto-eukaryotic ancestor of eukaryotic cells?
    You quoted just that…

    Erives likens giant viruses to vines spreading out into the cellular tree of life — sampling here, borrowing there, and sharing genetic material among the branches of archaea, bacteria, and eukaryotes.

    The exciting thing here is this virus seems to indicate the existence of proto-eukaryotic cells that are transitioning between being prokaryotic and eukaryotic by sampling / sharing genetic material from them. it’s like sampling from a transitional fossil. Or collecting and sharing that material with prokaryotic cells, resulting in them transitioning into eukaryotic cells.

    Core histones are packagers, like professional gift-wrappers. They’re proteins that, in humans, coil DNA in the chromosomes so vital genetic information is compact and protected. Prokaryotes don’t have core histones, so somehow, somewhere, eukaryotes picked them up.

    Viruses like Marseilleviridae may have been the source. (An alternative and equally fascinating explanation is that an ancestor of the Marseilleviridae picked up this gene from a proto-eukaryotic organism, an intermediate between prokaryotes and eukaryotes.)

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