The life form is a dinoflagellate, a marine plankton parasite. From ScienceDaily:
The mitochondria of the dinoflagellate Amoebophrya ceratii appear to produce energy just like our own mitochondria, but without any genetic material, as the team reports in the journal Science Advances. …
In this context, the team sequenced the genome (all the genetic material) of Amoebophrya, which consists of roughly 100 million base pairs. That’s extremely low by dinoflagellate standards: other species have genome a thousand times larger, which is much larger than even the human genome. That being said, a small genome isn’t exactly unusual for a parasite. Many of those pursuing this lifestyle don’t produce all of the metabolic products they need to survive; they simply steal them from their host. Though this makes them host-dependent, it also means there are many genes they can simply do without. But that’s not the road that Amoebophrya ceratii chose to go down. “In this species, nearly all metabolic processes still work, so it should also be able to get by quite well on its own,” says Uwe John. And it can do so with significantly less genetic material than any other dinoflagellate.
This reduction is especially pronounced in that part of the genome that lies outside the nucleus. In plants and algae, their own DNA is not just found in the nucleus and mitochondria, but also in the plastids, which they need for photosynthesis. For dinoflagellates in general, this plastid DNA is fairly basic, and consists of only 14 genes. Yet Amoebophrya ceratii would appear to have done away with the plastids entirely, and with all but one of their genes.
Yet the ‘budget cuts’ that the parasite has pursued with regard to its mitochondria are even more impressive. In related species, these tiny power plants’ DNA still contains three genes, which experts have generally assumed to be indispensable. But Amoebophrya ceratii has apparently cut out the mitochondria genome entirely; despite painstaking efforts, the team was unable to find any trace of it. Two of the three genes are nowhere to be found, and the third, cytochrome c oxidase 1 (COX1 or COI), has migrated to the nucleus. “That absolutely amazed me,” says Uwe John, “because there’s no other oxygen-breathing life-form on record that has no genetic material of its own in its mitochondria.”
This downsizing could come in handy when the parasites need to rapidly form a large number of new dinospores… Paper. (open access) – Uwe John, Yameng Lu, Sylke Wohlrab, Marco Groth, Jan Janouškovec, Gurjeet S. Kohli, Felix C. Mark, Ulf Bickmeyer, Sarah Farhat, Marius Felder, Stephan Frickenhaus, Laure Guillou, Patrick J. Keeling, Ahmed Moustafa, Betina M. Porcel, Klaus Valentin, Gernot Glöckner. An aerobic eukaryotic parasite with functional mitochondria that likely lacks a mitochondrial genome. Science Advances, 2019; 5 (4): eaav1110 DOI: 10.1126/sciadv.aav1110 More.
Does anyone remember when genes were still a “thing”?
The researchers go on to speculate as to how, despite appearances, not having any mitochondrial DNA is an evolutionary advantage. But wait a minute. Maybe it isn’t. A large proportion of the types of life forms that have ever existed are extinct. Insisting on explanations that show how a given change is an example of fitness created by natural selection requires us to ignore the possibility that the life form may, in fact, be on the way out. As Colin Patterson used to say, we don’t know why most extinctions occur. As long as we keep mapping genomes, we are sure to find more odd stuff.
Maybe the next time something happens that requires the use of mitochondrial DNA, that particular species will disappear. No, we don’t know that but neither do the researchers know that whatever we find is an example of fitness. One wishes they felt free to say, maybe not. Time will tell.
See also: Researcher: “No Rhyme Or Reason” To Unexpected Sea Anemone Genome
Two Jellyfish Genomes Differ “As Drastically As Humans Do From Sea Urchins. ”
Follow UD News at Twitter!