Timing the origin of eukaryotic cellular complexity with ancient duplications

Area of Science:

• Evolutionary biology
• Genomics
• Cell biology

Background:

• Eukaryogenesis, the origin of eukaryotic cells from prokaryotic ancestors, remains a major evolutionary puzzle.
• Direct evidence of evolutionary intermediates is scarce, necessitating indirect methods to reconstruct this transition.
• Gene duplication events offer insights into the chronological order of events during eukaryogenesis.

Purpose of the Study:

• To reconstruct the successive steps of eukaryogenesis using a phylogenomics approach.
• To investigate the role and timing of gene duplications in the evolution of early eukaryotes.
• To understand the contribution of host complexity and mitochondrial endosymbiosis to eukaryogenesis.

Main Methods:

• Phylogenomics analysis to reconstruct evolutionary relationships.
• Comparative genomics to identify gene duplication events.
• Phylogenetic distance-based methods for relative event timing.

Main Results:

• Gene duplications approximately doubled the proto-eukaryotic gene repertoire.
• Gene families inherited from Asgard archaea-related hosts showed the highest duplication rates.
• Duplications in cytoskeletal and membrane-trafficking gene families were among the earliest events.
• Most other gene families expanded significantly after mitochondrial endosymbiosis.

Conclusions:

• The host cell possessed pre-existing eukaryote-like complexity before engulfing the proto- mitochondrion.
• Mitochondrial acquisition dramatically amplified cellular complexity, driving eukaryogenesis.
• This model reconciles the complexity seen in Asgard archaea with the role of mitochondria in eukaryotic evolution.