Fig. 6: Distribution of ERP genes and the hypothesized HDH model for eukaryotic origin.
a, Presence of various ERP gene families across the selected representatives as shown in Fig. 1d, which belong to five candidate Asgard archaeal phyla—Heimdallarchaeota, Gerdarchaeota, Lokiarchaeota, Thorarchaeota and Odinarchaeota. Inset, Total gene numbers belonging to the gene families shown in a. b, Venn diagrams showing the ERP gene families shared between lineages of different phylogenetic distances, including three circular genomes (left), two Thorarchaeota members related at the family level (middle) and two members of the Lokiarchaeota related at the family level (right). c, The proposed HDH model provides a conceptual framework for the process of genome acquisition during early eukaryotic evolution. Key steps include a Heimdall-like ancestral archaeon with a simple genome engaged in endosymbiosis with a bacterium to establish the FECA. FECA then acquired innovations across the tree of life via an extensive gene import, most frequently, and often indirectly, through close closely related Asgard archaea, to ultimately orchestrate the LECA. The pink arrows indicate several major phases during early eukaryotic evolution. The dark arrows indicate horizontal transfer events from or via Asgard archaea into the eukaryotic genomes. The grey arrows indicate other horizontal transfer events that occurred and contributed to the eukaryotic genomes, although to a lesser extent.
