Origin and Early Evolution of the Eukaryotic Cell
Annual Review of Microbiology
Vol. 75:631-647 (Volume publication date October 2021)
First published as a Review in Advance on August 3, 2021
https://doi.org/10.1146/annurev-micro-090817-062213
Toni Gabaldón1,2,3
1Barcelona Supercomputing Centre (BCS-CNS), 08034 Barcelona, Spain; email: toni.gabaldon.bcn@gmail.com
2Institute for Research in Biomedicine (IRB), The Barcelona Institute of Science and Technology (BIST), 08028 Barcelona, Spain
3Catalan Institution for Research and Advanced Studies (ICREA), 08010 Barcelona, Spain
Abstract
The origin of eukaryotes has been defined as the major evolutionary transition since the origin of life itself. Most hallmark traits of eukaryotes, such as their intricate intracellular organization, can be traced back to a putative common ancestor that predated the broad diversity of extant eukaryotes. However, little is known about the nature and relative order of events that occurred in the path from preexisting prokaryotes to this already sophisticated ancestor. The origin of mitochondria from the endosymbiosis of an alphaproteobacterium is one of the few robustly established events to which most hypotheses on the origin of eukaryotes are anchored, but the debate is still open regarding the time of this acquisition, the nature of the host, and the ecological and metabolic interactions between the symbiotic partners. After the acquisition of mitochondria, eukaryotes underwent a fast radiation into several major clades whose phylogenetic relationships have been largely elusive. Recent progress in the comparative analyses of a growing number of genomes is shedding light on the early events of eukaryotic evolution as well as on the root and branching patterns of the tree of eukaryotes. Here I discuss current knowledge and debates on the origin and early evolution of eukaryotes. I focus particularly on how phylogenomic analyses have challenged some of the early assumptions about eukaryotic evolution, including the widespread idea that mitochondrial symbiosis in an archaeal host was the earliest event in eukaryogenesis.
Keywords eukaryogenesis, mitochondria, endosymbiosis, eukaryotic evolution, LECA
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