Asgard Archaea and all eukaryotes share a common ancestor, says study | Ski.News

Understanding how complex eukaryotic cells emerged from prokaryotic ancestors represents a major challenge in biology. A major point of contention in refining eukaryogenesis scenarios revolves around the exact relationship between Archaea and eukaryotes. In new research, scientists at the University of Texas at Austin and elsewhere have generated 63 new Asgard archaea genomes from samples obtained from 11 locations around the world. Analyzing the expanded genomic sampling of Asgard archaea using state-of-the-art analyses, they firmly place eukaryotes as a nested clade within Asgard archaea, similar to how birds are one of several groups within a larger group called dinosaurs, sharing a common ancestor. By revealing key features regarding the identity, nature and physiology of the last common ancestor of the archaea and Asgard’s eukaryotes, their results represent important, hitherto missing pieces of the eukaryotic puzzle.

Archaeon of Asgard.  Scale bar - 500 nm.  Image credit: Imachi et al., doi: 10.1038/s41586-019-1916-6.

Archaeon of Asgard. Scale bar – 500 nm. Image credit: Imachi et al., doi: 10.1038/s41586-019-1916-6.

No eukaryotic fossils have been found from further than about 2 billion years ago, suggesting that only various types of microbes existed before, said co-senior author Dr. Brett Baker, a researcher in the university’s Department of Integrative Biology. of Texas in Austin.

So what events led microbes to evolve into eukaryotes? This is a big question. Having this common ancestor is a big step towards understanding this.

In their study, Dr. Baker and colleagues identified the closest microbial relative of all complex life forms on the tree of life as a newly described order called Hodarchaeales.

The Hodarchaeales, found in marine sediments, are one of several subgroups within the larger group of Asgard archaea.

The archaea of ​​Asgard evolved more than 2 billion years ago and their descendants are still alive.

Some have been discovered in deep marine sediments and hot springs around the world, but so far only two strains have been successfully grown in the laboratory.

To identify them, researchers harvest their genetic material from the environment and then piece their genomes together.

Based on genetic similarities to other organisms that can be grown in the laboratory and studied, they can infer the metabolism and other characteristics of the Asgard archaea.

Imagine a time machine, not to explore the realms of dinosaurs or ancient civilizations, but to travel deep into potential metabolic reactions that could have triggered the dawn of complex life, said co-author Dr. Valerie De Anda, also she from the Department of Integrative Biology at the University of Texas at Austin.

Instead of fossils or ancient artifacts, we look to the genetic blueprints of modern microbes to piece together their past.

The origin of the eukaryotic cell is one of the most puzzling events in the evolution of life on Earth and includes many important details that remain poorly understood, said co-senior author Dr. Thijs Ettema, a researcher at Wageningen University.

In particular, how eukaryotic cells obtained their complex and compartmentalized nature is a matter of debate.

In this study, we identified a specific archaic group from Asgard – the Hodarchaeales – as the closest relatives of eukaryotes and provided evidence that the genetic basis of some of the eukaryotic complexity can be traced back to the archaea of ​​Asgard.

Our study involved many detailed phylogenetic analyzes of genomic data to determine which microbial group represented the closest relatives of eukaryotes in the tree of life.

Resolving such evolutionary relationships is extremely complicated as their last common ancestor dates back to about 2 billion years ago.

Since then, the evolutionary signal needed to resolve their relationship has eroded due to the accumulation of mutations in their genomes.

Scientists expanded Asgard’s known genomic diversity, adding 63 undescribed Asgardian genomes as input to their modeling.

Their analysis indicates that the ancestor of all modern Asgards appears to have lived in warm environments, consuming carbon dioxide and chemicals to live.

Meanwhile, Hodarchaeales, which are more closely related to eukaryotes, are metabolically more similar to us, eat carbon, and live in colder environments.

We found that the archaic ancestor Asgard of eukaryotes already possessed multiple genes for complex cellular processes that had previously only been found in eukaryotes, said co-author Dr. Daniel Tamarit, a researcher at Utrecht University.

Furthermore, we found that many of its genes evolved via gene duplication events.

This is surprising, as archaea and bacteria, unlike eukaryotes, are known to primarily acquire genes from other microbes in a process called horizontal gene transfer.

The high rates of gene duplication observed in Asgard’s archaea suggest that their genomes have already evolved in a way somewhat similar to that of eukaryotes.

The study was published in the journal Nature.

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L.Eme et al. Inference and reconstruction of the heimdallarchaeial ancestry of eukaryotes. Nature, published online June 14, 2023; doi: 10.1038/s41586-023-06186-2

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