On the chimeric origin of eukaryotic genes

Abstract

The origin of eukaryotes is quite enigmatic and still poorly understood. It was previously thought that eukaryotes are the result of an endosymbiotic event between an Archaeal cell and an Alphaproteobacterium. However, many of the genes that were present in the last eukaryotic common ancestor (LECA) cannot be accounted for solely by Archaeal or Alphaproteobacterial contributions. Here we look at the literature regarding the origin of eukaryotic genes. It would currently appear like many additional prokaryotes contributed to eukaryogenesis. Viruses may have played a role in the horizontal gene transfer from these prokaryotes to the proto-eukaryote. Moreover, the influx of genetic material from various prokaryotes and viruses would have presented a significant source of genetic conflict to the proto-eukaryote, likely driving eukaryotic innovation, giving rise to complex eukaryotic features like the kinetochore. Based on our current view on the origin of eukaryotic genes, we propose a scenario for eukaryogenesis which emphasizes a gradual nature, being characterized by multiple consecutive (failed) symbiotic partners in a diverse syntrophic environment like a microbial mat.