New Findings about the Evolution of Complex Cellular Life

[Ygggdrasil]

Humans, other animals, plants, fungi and almost all other forms of complex, multi-cellular life are known as eukaryotes. How eukaryotes evolved from simpler prokaryotic organisms is a major question in evolutionary biology. The current view is that eukaryotes evolved from the fusion between a bacterium (which would eventually become the mitochondrion) and an archaeal host through a process called endosymbiosis. Until recently, the identity of the archaeal host had been mysterious. In 2015, a group of researchers led by Thijs Ettema and Lionel Guy in Sweden discovered lokiarchaeota, a phylum of archaea that shares many features with eukaryotes and was likely a close relative of the archaon that evolved into eukaryotes. Today, in the journal Nature, Ettema and co-workers report on the discovery of a larger superphylum of archaea related to lokiarchaeota, which sheds more light on the evolution of eukaryotes:

Abstract:The origin and cellular complexity of eukaryotes represent a major enigma in biology. Current data support scenarios in which an archaeal host cell and an alphaproteobacterial (mitochondrial) endosymbiont merged together, resulting in the first eukaryotic cell. The host cell is related to Lokiarchaeota, an archaeal phylum with many eukaryotic features. The emergence of the structural complexity that characterizes eukaryotic cells remains unclear. Here we describe the ‘Asgard’ superphylum, a group of uncultivated archaea that, as well as Lokiarchaeota, includes Thor-, Odin- and Heimdallarchaeota. Asgard archaea affiliate with eukaryotes in phylogenomic analyses, and their genomes are enriched for proteins formerly considered specific to eukaryotes. Notably, thorarchaeal genomes encode several homologues of eukaryotic membrane-trafficking machinery components, including Sec23/24 and TRAPP domains. Furthermore, we identify thorarchaeal proteins with similar features to eukaryotic coat proteins involved in vesicle biogenesis. Our results expand the known repertoire of ‘eukaryote-specific’ proteins in Archaea, indicating that the archaeal host cell already contained many key components that govern eukaryotic cellular complexity.

Zaremba-Niedzwiedzka et al. 2017. Asgard archaea illuminate the origin of eukaryotic cellular complexity. Nature. Published online 11 January 2017. doi:10.1038/nature21031[/PLAIN]

Popular press summary: https://www.theatlantic.com/science/archive/2017/01/our-origins-in-asgard/512645/

Thanks to a team of scientists led by http://www.ettemalab.org/thijs-ettema/, Asgard is now also the name of a large clan of microbes. Its members, which are named after Norse gods like Odin, Thor, Loki, and Heimdall, are found all over the world. Many of them are rare and no one has actually seen them under a microscope. But thanks to their DNA, we know they exist. And we know that they are singularly important to us, because they may well be the group from which we evolved.

http://nature.com/articles/doi:10.1038/nature21031 , then around two billion years ago, an Asgardian microbe (or an incredibly close relative) took part in a unique event that gave rise to the eukaryotes. That’s the group which includes humans, our fellow animals, plants, fungi, and every living thing made from large, complex cells—all the living things we’re most familiar with, and all the ones we can actually see. Our origins lie either in Asgard, or next door to it.

 

[BillTre]

Very cool!
I like the Asgard motif.

I also like that the unseen thing is important.
Kind of like the Denisovans. Similar to the Neanderthals but known only from DNA from a small finger bone (no whole fossils).

 

[DrClaude]

Popular press summary: https://www.theatlantic.com/science/archive/2017/01/our-origins-in-asgard/512645/

A more scientific summary can be found here: http://www.nature.com/nature/journal/vaop/ncurrent/full/nature21113.html

 

[jim mcnamara]

@DrClaude - the nature article is behind a paywall.

This is a really interesting finding. Thanks. It also hints strongly at why we had not seen the link before.

 

[Carlos L. Janer]

It is a real shame that Lynn Margullis has not lived long enough to see her bold proposal finally vindicated.

 

[atyy]

It is a real shame that Lynn Margullis has not lived long enough to see her bold proposal finally vindicated.

I think there was plenty of evidence before this to support her proposal. I would say she lived long enough to see her proposal become the main contender, and to the point where it is discussed in textbooks, eg. https://openstax.org/details/books/biology.

 

[Carlos L. Janer]

I think there was plenty of evidence before this to support her proposal. I would say she lived long enough to see her proposal become the main contender, and to the point where it is discussed in textbooks, eg. https://openstax.org/details/books/biology.

You may be right. The orthodox neodarwinism was the only contender in my generation and it did not allow for any deviation from it. People like Margullis and Gould were deemed as anathema for the comunity.