Dominant contribution of Asgard archaea to eukaryogenesis

Area of Science:

• Evolutionary biology
• Genomics
• Microbiology

Background:

• The origin of eukaryotes (eukaryogenesis) remains a central question in evolutionary biology.
• The last eukaryotic common ancestor (LECA) possessed mitochondria, originating from alphaproteobacteria.
• Asgard archaea are identified as the closest archaeal relatives to eukaryotes.

Purpose of the Study:

• To comprehensively analyze the evolutionary origins of core eukaryotic genes present in the LECA.
• To test evolutionary hypotheses regarding eukaryogenesis using a robust statistical framework.
• To elucidate the contributions of different microbial lineages to the foundational eukaryotic genome.

Main Methods:

• Phylogenetic analysis of core eukaryotic genes.
• Rigorous statistical framework for evolutionary hypothesis testing.
• Constrained phylogenetic trees to infer ancestral gene origins.

Main Results:

• Asgard archaea provided the majority of conserved eukaryotic functional systems and pathways.
• Alphaproteobacteria contributed genes mainly related to energy transformation and Fe-S cluster biogenesis.
• Other bacterial phyla showed scattered, inconsistent gene contributions across the eukaryotic functional landscape.

Conclusions:

• Eukaryotic cell organization largely evolved within the Asgard archaeal lineage leading to the LECA.
• The alphaproteobacterial endosymbiont was acquired after the establishment of key eukaryotic features.
• Gene acquisitions from other bacteria occurred sporadically before and after endosymbiosis, shaping the eukaryotic genome.