nucleation

LIT-1558: Dominant contribution of Asgard archaea to eukaryogenesis

2 min read

Properties5
StatusActive — read in full 2026-10-27 (NOTE-1242) from the PubMed Central copy of the version of record (PMC12872458, open access); worth reading as the largest survey so far of where the last eukaryotic common ancestor's genes came from, finding Asgard archaea the largest single source in nearly every functional system, the alphaproteobacterial share small and mitochondrial, and other bacteria diffuse (THEORY-1104), and for its test of the stem-length method, which it finds does not behave as a clock (THEORY-1101). Read it knowing that "dominant" means about half of likelihood weight among well-resolved families, not a count of genes; that the paper is itself mitochondrion-late; that its denial of further symbioses is read off the diffuseness of the bacterial signal, not shown; and that it rests on sparse, biased genome sampling, as the authors stress.
Version3
Tagsendosymbiosis, natural-sciences
Cited as “paper” byNOTE-1242 — Tobiasson, Luo, Wolf & Koonin — Dominant contribution of Asgard archaea to eukaryogenesis
Cited as “source” byTHEORY-1101 — Tobiasson, Luo, Wolf and Koonin find, on 5,850 eukaryotic gene stems, that normalized stem length does not behave as a clock of acquisition time: alphaproteobacterial stems are longer than Asgard ones for the 70% of stems below 0.3 and shorter only above 0.35, oxidative-phosphorylation genes presumed acquired together vary by more than two orders of magnitude, and information-processing genes have short stems; they conclude that even normalized stem lengths are set primarily by factors other than acquisition time, at least over the long timescales analysed, and suggest that adaptation after acquisition lengthens stems, THEORY-1104 — In Tobiasson, Luo, Wolf and Koonin's constrained-tree survey of widespread eukaryotic protein families, Asgard archaea are the largest single prokaryotic source, with about half the likelihood weight in the best-resolved families and the lead in nearly every functional system, while Alphaproteobacteria contribute a small, coherent set centred on the mitochondrion and other bacteria about a third of families, scattered across functions with no pathway led by one donor except a narrow Myxococcota signal in nucleotide-sugar and nicotinate metabolism; the authors read this as one Asgard host lineage, one endosymbiont and piecemeal gene transfer rather than further symbioses, THEORY-1197 — Eukaryogenesis involved one archaeal host lineage, of Asgard descent, and one bacterial endosymbiont, the alphaproteobacterial ancestor of mitochondria; the eukaryotic genes from other bacteria came by piecemeal gene transfer, not from further symbiotic partners, THEORY-1201 — Normalized stem length is not a clock of gene acquisition time: it is set mainly by factors other than when a gene was acquired, such as adaptation to the new cell after acquisition, so relative timings of eukaryogenesis drawn from stem lengths alone are not supported

Graph View

Tobiasson, V., Luo, J., Wolf, Y. I. & Koonin, E. V. (2026). Dominant contribution of Asgard archaea to eukaryogenesis. Nature 650(8100): 141–149. doi:10.1038/s41586-025-09960-6.

Key takeaways

From the reading, NOTE-1242.

  • Asgard first, by likelihood weight. In 4,290 well-resolved clusters, Asgard takes 50% of the weight and leads in nearly every functional class. Information processing is “almost exclusively of Asgard descent” (THEORY-1104).
  • The mitochondrion’s share is small and coherent. Alphaproteobacteria lead only in oxidative phosphorylation, ubiquinone, 4Fe-4S assembly and mitochondrial translation.
  • Other bacteria are diffuse. About a third of families point elsewhere, with no pathway from one donor apart from a narrow Myxococcota signal. The authors read this as transfer, with “no indication of another symbiotic event”. That is an interpretation.
  • Stem length is not a clock. The mitochondrion-late stem-length signal reproduces only for long stems and reverses for short ones, and co-acquired genes scatter widely (THEORY-1101).
  • Mitochondrion-late all the same. The authors favour an Asgard ancestor with a cytoskeleton and endomembranes before the endosymbiont, inferred from gene ancestry, not timed.

Why this is here

A1 ranked it sixth; A2 sets it beside LIT-1566 and LIT-1561 as one side of a live disagreement on whether eukaryogenesis was one two-partner merger or a distributed history of associations.

The reading corrects that placement in part. This work is the two-partner side only on symbiosis: it accepts many bacterial gene donors before and after the endosymbiosis and denies only that any was a further partner. On the timing of the mitochondrion it agrees with LIT-1566 as the record summarizes it. Its disagreement with LIT-1561 is about whether the non-alphaproteobacterial genes are diffuse or come from a few donors in waves, and whether stem lengths can time them (NOTE-1242).

Backlinks