Endosymbiotic selective pressure at the origin of eukaryotic cell biology

Abstract

The dichotomy that separates prokaryotic from eukaryotic cells runs deep. The transition from pro- to eukaryote evolution is poorly understood due to a lack of reliable intermediate forms and definitions regarding the nature of the first host that could no longer be considered a prokaryote, the first eukaryotic common ancestor, FECA. The last eukaryotic common ancestor, LECA, was a complex cell that united all traits characterising eukaryotic biology including a mitochondrion. The role of the endosymbiotic organelle in this radical transition towards complex life forms is, however, sometimes questioned. In particular the discovery of the asgard archaea has stimulated discussions regarding the pre-endosymbiotic complexity of FECA. Here we review differences and similarities among models that view eukaryotic traits as isolated coincidental events in asgard archaeal evolution or, on the contrary, as a result of and in response to endosymbiosis. Inspecting eukaryotic traits from the perspective of the endosymbiont uncovers that eukaryotic cell biology can be explained as having evolved as a solution to housing a semi-autonomous organelle and why the addition of another endosymbiont, the plastid, added no extra compartments. Mitochondria provided the selective pressures for the origin (and continued maintenance) of eukaryotic cell complexity. Moreover, they also provided the energetic benefit throughout eukaryogenesis for evolving thousands of gene families unique to eukaryotes. Hence, a synthesis of the current data lets us conclude that traits such as the Golgi apparatus, the nucleus, autophagosomes, and meiosis and sex evolved as a response to the selective pressures an endosymbiont imposes.

How mitochondrial cristae illuminate the important role of oxygen during eukaryogenesis

“…The bacterium, upon merging with an archaeon lost all independence, but played a crucial role, as a highly efficient ATP generator, internal ROS source, and wellspring of membranes. [ 74,75 ]…”

“…The bacterium, upon merging with an archaeon lost all independence, but played a crucial role, as a highly efficient ATP generator, internal ROS source, and wellspring of membranes. [74,75] Two other questions remain (though only indirectly connected with cristae, our main focus so far). Recently, Al Jewari & Baldauf claimed that modern eukaryotes actually arose under anoxic conditions, citing the absence of aerobic mitochondria in three of the earliest branching lineages.…”

Performance of localization prediction algorithms decreases rapidly with the evolutionary distance to the training set increasing

“…A plant encodes 20-30,000 proteins on average, of which many thousand are targeted to intracellular membrane bound compartments after or during translation [1][2][3] . The compartments owe their origins to bacterial ancestors directly or indirectly [4][5][6][7][8][9][10][11][12] . Mitochondria and plastids are of endosymbiotic origin and have transferred a majority of their coding capacity to the nuclear genome in the course of their transition from bacterium to organelle [13][14][15] .…”

Editorial: Algal symbiotic relationships in freshwater and marine environments

“…Living organisms have never been solitary individuals and symbiotic relationships are challenging our very conception of the individual. Symbiosis, initially defined as a living together of different organisms ( De Bary, 1879 ; Raval et al., 2022 ) represents a range of complex and intermingled relationships (mutualism, commensalism amensalism and parasitism). Although actively debated with numerous theories on the origin of eukaryotes, it is widely accepted that a metabolic symbiosis and successive endosymbioses were important in the evolution of eukaryotes and their diversification ( Hartman and Fedorov, 2002 ; Sapp, 2004 ; Embley and Martin, 2006 ; Cenci et al., 2017 ; Sibbald and Archibald, 2020 ; Gabaldon, 2021 ).…”