Dated gene duplications elucidate the evolutionary assembly of eukaryotes

Area of Science:

• Evolutionary biology
• Molecular evolution
• Cell biology

Background:

• The origin of eukaryotic cells (eukaryogenesis) is a pivotal event in life's history, with key hypotheses differing on the timing of mitochondrial acquisition.
• Understanding eukaryogenesis is challenging due to the lack of intermediate lineages.
• Gene duplication events during eukaryogenesis offer insights into the evolutionary timeline of eukaryotic cell assembly.

Purpose of the Study:

• To determine the evolutionary timeline of gene duplications during eukaryogenesis.
• To test hypotheses regarding the sequence of events in eukaryotic cell evolution, particularly the timing of mitochondrial endosymbiosis.
• To infer the characteristics of the archaeal host cell prior to endosymbiosis.

Main Methods:

• Utilized a relaxed molecular clock approach to date gene duplication events.
• Analyzed gene duplication timescales to reconstruct the sequence of eukaryogenesis.
• Integrated findings with geological eras (Mesoarchaean to Palaeoproterozoic) for temporal constraints.

Main Results:

• Eukaryogenesis occurred between the Mesoarchaean and late Palaeoproterozoic eras.
• Complex cellular features, including a cytoskeleton, nucleus, and endomembrane system, predated mitochondrial endosymbiosis.
• Gene duplications indicate these complex features arose between 3.0 and 2.25 billion years ago.

Conclusions:

• Rejects "mitochondrion-early" models of eukaryogenesis.
• Supports a "complexified-archaean, late-mitochondrion" model for eukaryotic evolution.
• Suggests an archaeal host cell with advanced features existed in anoxic oceans, potentially benefiting from syntrophy.