The Timing of Pre-LECA Gene Duplications and the resulting implications for Eukaryogenesis

Abstract

The sequence of events that gave rise to eukaryotic complexity has remained a pertinent question due to its importance in understanding the origin of complex life and that of fundamental cellular processes such as organelle formation, development of the endomembrane system and the establishment of cellular compartmentalization as well as the likely timing of the endosymbiosis event that gave rise to early mitochondria and plastids and also the degree to which eukaryotic complexity had progressed before this event. This question is complicated by conflicting results indicating different relative timing of this endosymbiosis event and different relative contributions of archaea and bacteria to the genome of early eukaryotes (Tria et al., 2021; Vosseberg et al., 2021). Under the assumption that the evolution of cellular complexity was enabled by the genetic material created by gene duplication, gene duplications can be used as a metric for the potential onset of eukaryotic cellular complexity when duplicated gene families are analysed using the molecular clock hypothesis. We ran molecular clock analyses on a sample of previously inferred paralogous gene families that were deemed to have duplicated before the Last Eukaryotic Common Ancestor (LECA) (Tria et al., 2021; Vosseberg et al., 2021). Results indicate a ‘mitochondria early’ scenario for the onset of eukaryotic complexity based on marginally older maximum age for gene duplications of bacterial origin. This implies that the mitochondrial endosymbiosis may have happened before the gene duplications began, therefore giving a potential minimum date for mitochondrial endosymbiosis. Results broadly agree that most genes sampled duplicated in the late Archean Eon and that LECA likely occurred in the early Proterozoic Eon, therefore suggesting that mitochondrial endosymbiosis may have occurred either in or before the late Archean Eon and have provided the energetic foundation for most of the subsequent genomic innovation and cellular complexity.

Date of Award	1 Oct 2024
Original language	English
Awarding Institution	University of Bristol
Supervisor	Tom Williams (Supervisor)