Archaeal Diversity Sheds New Light on the Origin of the Eukaryotic Endomembrane System

The emergence of the endomembrane system marks a pivotal milestone in eukaryogenesis, transforming a primitive prokaryotic cell into a highly intracellular, compartmentalized eukaryotic cell. The molecular machinery underlying the endomembrane system has been considered a defining feature of eukaryotes. Yet its evolutionary origin remains elusive. Over the past decade, the rapid expansion of archaeal diversity, coupled with advancements in metagenomic technologies and cell biological characterization, has revealed that many key protein components of the endomembrane system likely originated from the archaeal ancestors of eukaryotes, a specific archaeal lineage that underwent a symbiotic fusion with the mitochondrial ancestor. This review summarizes and discusses the remarkable progress made in these research fields, offering a refined perspective on the origin of the eukaryotic endomembrane system within an updated tree of life.