Endosymbiosis and Eukaryotic Cell Evolution

Abstract

Understanding the evolution of eukaryotic cellular complexity is one of the grand challenges of modern biology. It has now been firmly established that mitochondria and plastids, the classical membrane-bound organelles of eukaryotic cells, evolved from bacteria by endosymbiosis. In the case of mitochondria, evidence points very clearly to an endosymbiont of α-proteobacterial ancestry. The precise nature of the host cell that partnered with this endosymbiont is, however, very much an open question. And while the host for the cyanobacterial progenitor of the plastid was undoubtedly a fully-fledged eukaryote, how - and how often - plastids moved from one eukaryote to another during algal diversification is vigorously debated. In this article I frame modern views on endosymbiotic theory in a historical context, highlighting the transformative role DNA sequencing played in solving early problems in eukaryotic cell evolution, and posing key unanswered questions emerging from the age of comparative genomics.

Polyamines in Eukaryotes, Bacteria, and Archaea

“…9). Furthermore, heterotrophic singlecelled eukaryotes subsequently took up and assimilated red or green algal cells in independent secondary endosymbioses (10), and even tertiary endosymbioses in dinoflagellates (11).…”

Recent Advances in Mitochondrial Disease

“…Mitochondria, essential organelles that are present in almost all eukaryotic cells (8,49), are thought to have originated from free-living bacteria following a symbiotic event with a host cell approximately two billion years ago (4). In this hypothesis, known as the endosymbiotic theory, a proteobacterium was engulfed by endocytosis, providing the host with the ability to produce cellular energy in the form of ATP.…”

Symbiogenesis, gradualism, and mitochondrial energy in eukaryote origin

“…Current debate on symbiogenesis has focused on the role of mitochondria at the origin of eukaryotes. Proponents of symbiogenesis, or endosymbiotic theory, have it that symbiosis is a rare but crucial mechanism of evolution (7,8,9,10,11,12,13,14). Proponents of the opposing gradualist view admit that endosymbiosis occurred when mitochondria arose, but hold that it had no impact on the evolutionary process (15,16,17).…”

“…Those special issues underscore broad interest in the question. Other reviews and papers dedicated to the topic have also appeared recently (10,11,14,20,21,22,23,24). Why is so much being written on eukaryote origins?…”

“…ii) One more symbiogenic association gave rise to the first cell with plastids (7,9,10,11), from which all plants (now called archaeplastida) descend. iii) Secondary symbioses occurred among eukaryotes to give rise to algae with secondary plastids (83).…”