Lokiarchaeota and the Evolution of Complex Cellular Life

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Biologists split life into two broad categories: prokaryotes and eukaryotes. Prokaryotes are relatively simple single-celled organisms and are split into two groups (bacteria and archaea). Eukaryotes, on the other hand, are much more complex cells containing specialized compartments such as the nucleus, mitochondria, and other membrane-bound organelles. All of what we consider complex life (e.g. plants, animals, fungi, protists) are eukaryotes. Scientists have long been interested in determining how eukarotes evolved from prokaryotes.

This week, researchers published the discovered a new species of archaea which shares many features with eukaryotes and is the closes known prokaryotic relative of all eukaryotes. The finding explains the evolutionary origins of many features once thought to be unique to eukaryotes, and strengthens the "two-domain" hypothesis of life:
The origin of the eukaryotic cell remains one of the most contentious puzzles in modern biology. Recent studies have provided support for the emergence of the eukaryotic host cell from within the archaeal domain of life, but the identity and nature of the putative archaeal ancestor remain a subject of debate. Here we describe the discovery of ‘Lokiarchaeota’, a novel candidate archaeal phylum, which forms a monophyletic group with eukaryotes in phylogenomic analyses, and whose genomes encode an expanded repertoire of eukaryotic signature proteins that are suggestive of sophisticated membrane remodelling capabilities. Our results provide strong support for hypotheses in which the eukaryotic host evolved from a bona fide archaeon, and demonstrate that many components that underpin eukaryote-specific features were already present in that ancestor. This provided the host with a rich genomic ‘starter-kit’ to support the increase in the cellular and genomic complexity that is characteristic of eukaryotes.
Sprang et al. 2015 Complex archaea that bridge the gap between prokaryotes and eukaryotes Nature. Published online 06 May 2015. http://dx.doi.org/10.1038/nature14447 [Broken]

See also this summary from National Geographic: http://phenomena.nationalgeographic...robe-is-closest-relative-to-all-complex-life/

Although this finding answers many questions about the evolution of eukaryotes, more work remains to be done to understand the evolution other features unique to eukaryotes, such as the evolution of the nucelus. However, because eukaryotes evolved from these "Loki" archaea after they endosymbioticallly captured an alphaproteobacterium, it would be a neat experiment to try to recreate this event in the lab.
 
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Nice news summary. Thanks for sharing.
 
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