Eukaryogenesis

Last updated

LUCA and LECA: the origins of the eukaryotes. The point of fusion (marked "?") below LECA is the FECA, the first eukaryotic common ancestor, some 2.2 billion years ago. Much earlier, some 4 billion years ago, the LUCA gave rise to the two domains of prokaryotes, the bacteria and the archaea. After the LECA, some 2 billion years ago, the eukaryotes diversified into a crown group, which gave rise to animals, plants, fungi, and protists. LUCA and LECA McGrath 2022.jpg
LUCA and LECA: the origins of the eukaryotes. The point of fusion (marked "?") below LECA is the FECA, the first eukaryotic common ancestor, some 2.2 billion years ago. Much earlier, some 4 billion years ago, the LUCA gave rise to the two domains of prokaryotes, the bacteria and the archaea. After the LECA, some 2 billion years ago, the eukaryotes diversified into a crown group, which gave rise to animals, plants, fungi, and protists.

Eukaryogenesis, the process which created the eukaryotic cell and lineage, is a milestone in the evolution of life, since eukaryotes include all complex cells and almost all multicellular organisms. The process is widely agreed to have involved symbiogenesis, in which an archeon and a bacterium came together to create the first eukaryotic common ancestor (FECA). This cell had a new level of complexity and capability, with a nucleus, at least one centriole and cilium, facultatively aerobic mitochondria, sex (meiosis and syngamy), a dormant cyst with a cell wall of chitin and/or cellulose and peroxisomes. It evolved into a population of single-celled organisms that included the last eukaryotic common ancestor (LECA), gaining capabilities along the way, though the sequence of the steps involved has been disputed, and may not have started with symbiogenesis. In turn, the LECA gave rise to the eukaryotes' crown group, containing the ancestors of animals, fungi, plants, and a diverse range of single-celled organisms.

Contents

Context

Life arose on Earth once it had cooled enough for oceans to form. The last universal common ancestor (LUCA) was an organism which had ribosomes and the genetic code; it lived some 4 billion years ago. It gave rise to two main branches of prokaryotic life, the bacteria and the archaea. From among these small-celled, rapidly-dividing ancestors arose the Eukaryotes, with much larger cells, nuclei, and distinctive biochemistry. [1] [2] The eukaryotes form a domain that contains all complex cells and most types of multicellular organism, including the animals, plants, and fungi. [3] [4]

Symbiogenesis

In the theory of symbiogenesis, a merger of an archaean and an aerobic bacterium created the eukaryotes, with aerobic mitochondria, some 2.2 billion years ago. A second merger, 1.6 billion years ago, added chloroplasts, creating the green plants. Symbiogenesis 2 mergers.svg
In the theory of symbiogenesis, a merger of an archaean and an aerobic bacterium created the eukaryotes, with aerobic mitochondria, some 2.2 billion years ago. A second merger, 1.6 billion years ago, added chloroplasts, creating the green plants.

According to the theory of symbiogenesis (also known as the endosymbiotic theory) championed by Lynn Margulis, a member of the archaea gained a bacterial cell as a component. The archaeal cell was a member of the Asgard group. The bacterium was one of the Alphaproteobacteria, which had the ability to use oxygen in its respiration. This enabled it – and the archaeal cells that included it – to survive in the presence of oxygen, which was poisonous to other organisms adapted to reducing conditions. The endosymbiotic bacteria became the eukaryotic cell's mitochondria, providing most of the energy of the cell. [1] [5] Lynn Margulis and colleagues have suggested that the cell also acquired a Spirochaete bacterium as a symbiont, providing the cell skeleton of microtubules and the ability to move, including the ability to pull chromosomes into two sets during mitosis, cell division. [6] More recently, the Asgard archaean has been identified as belonging to the Heimdallarchaeota. [7]

Last eukaryotic common ancestor (LECA)

The last eukaryotic common ancestor (LECA) is the hypothetical last common ancestor of all living eukaryotes, around 2 billion years ago, [3] [4] and was most likely a biological population. [8] It is believed to have been a protist with a nucleus, at least one centriole and cilium, facultatively aerobic mitochondria, sex (meiosis and syngamy), a dormant cyst with a cell wall of chitin and/or cellulose, and peroxisomes. [9] [10]

It had been proposed that the LECA fed by phagocytosis, engulfing other organisms. [9] [10] However, in 2022, Nico Bremer and colleagues confirmed that the LECA had mitochondria, and stated that it had multiple nuclei, but disputed that it was phagotrophic. This would mean that the ability found in many eukaryotes to engulf materials developed later, rather than being acquired first and then used to engulf the alphaproteobacteria that became mitochondria. [11]

The LECA has been described as having "spectacular cellular complexity". [12] Its cell was divided into compartments. [12] It appears to have inherited a set of endosomal sorting complex proteins that enable membranes to be remodelled, including pinching off vesicles to form endosomes. [13] Its apparatuses for transcribing DNA into RNA, and then for translating the RNA into proteins, were separated, permitting extensive RNA processing and allowing the expression of genes to become more complex. [14] It had mechanisms for reshuffling its genetic material, and possibly for manipulating its own evolvability. All of these gave the LECA "a compelling cohort of selective advantages". [12]

Eukaryotic sex

Sex in eukaryotes is a composite process, consisting of meiosis and fertilisation, which can be coupled to reproduction. [15] Dacks and Roger [16] proposed on the basis of a phylogenetic analysis that facultative sex was likely present in the common ancestor of all eukaryotes. Early in eukaryotic evolution, about 2 billion years ago, organisms needed a solution to the major problem that oxidative metabolism releases reactive oxygen species that damage the genetic material, DNA. [15] Eukaryotic sex provides a process, homologous recombination during meiosis, for using informational redundancy to repair such DNA damage. [15]

Scenarios

Biologists have proposed multiple scenarios for the creation of the eukaryotes. While there is broad agreement that the LECA must have had a nucleus, mitochondria, and internal membranes, the order in which these were acquired has been disputed. In the syntrophic model, the first eukaryotic common ancestor (FECA, around 2.2 gya) gained mitochondria, then membranes, then a nucleus. In the phagotrophic model, it gained a nucleus, then membranes, then mitochondria. In a more complex process, it gained all three in short order, then other capabilities. Other models have been proposed. Whatever happened, many lineages must have been created, but the LECA either out-competed or came together with the other lineages to form a single point of origin for the eukaryotes. [12] Nick Lane and William Martin have argued that mitochondria came first, on the grounds that energy had been the limiting factor on the size of the prokaryotic cell. [17] The phagotrophic model presupposes the ability to engulf food, enabling the cell to engulf the aerobic bacterium that became the mitochondrion. [12]

Eugene Koonin and others, noting that the archaea share many features with eukaryotes, argue that rudimentary eukaryotic traits such as membrane-lined compartments were acquired before endosymbiosis added mitochondria to the early eukaryotic cell, while the cell wall was lost. In the same way, mitochondrial acquisition must not be regarded as the end of the process, for still new complex families of genes had to be developed after or during the endosymbiotic exchange. In this way, from FECA to LECA, we can think of organisms that can be considered as protoeukaryotes. At the end of the process, LECA was already a complex organism with the presence of protein families involved in cellular compartmentalization. [18] [19]

Diversification: crown eukaryotes

In turn, the LECA gave rise to the eukaryotes' crown group, containing the ancestors of animals, fungi, plants, and a diverse range of single-celled organisms with the new capabilities and complexity of the eukaryotic cell. [20] [21] Single cells without cell walls are fragile and have a low probability of being fossilised. If fossilised, they have few features to distinguish them clearly from prokaryotes: size, morphological complexity, and (eventually) multicellularity. Early eukaryote fossils, from the late Paleoproterozoic, include acritarch microfossils with relatively robust ornate carbonaceous vesicles of Tappania from 1.63 gya and Shuiyousphaeridium from 1.8 gya. [21]

Related Research Articles

<span class="mw-page-title-main">Cell (biology)</span> Basic unit of many life forms

The cell is the basic structural and functional unit of all forms of life. Every cell consists of cytoplasm enclosed within a membrane; many cells contain organelles, each with a specific function. The term comes from the Latin word cellula meaning 'small room'. Most cells are only visible under a microscope. Cells emerged on Earth about 4 billion years ago. All cells are capable of replication, protein synthesis, and motility.

<span class="mw-page-title-main">Kingdom (biology)</span> Taxonomic rank

In biology, a kingdom is the second highest taxonomic rank, just below domain. Kingdoms are divided into smaller groups called phyla.

<span class="mw-page-title-main">Symbiogenesis</span> Evolutionary theory holding that eukaryotic organelles evolved through symbiosis with prokaryotes

Symbiogenesis is the leading evolutionary theory of the origin of eukaryotic cells from prokaryotic organisms. The theory holds that mitochondria, plastids such as chloroplasts, and possibly other organelles of eukaryotic cells are descended from formerly free-living prokaryotes taken one inside the other in endosymbiosis. Mitochondria appear to be phylogenetically related to Rickettsiales bacteria, while chloroplasts are thought to be related to cyanobacteria.

<span class="mw-page-title-main">Three-domain system</span> Hypothesis for classification of life

The three-domain system is a taxonomic classification system that groups all cellular life into three domains, namely Archaea, Bacteria and Eukarya, introduced by Carl Woese, Otto Kandler and Mark Wheelis in 1990. The key difference from earlier classifications such as the two-empire system and the five-kingdom classification is the splitting of Archaea from Bacteria as completely different organisms. It has been challenged by the two-domain system that divides organisms into Bacteria and Archaea only, as Eukaryotes are considered as a clade of Archaea.

<span class="mw-page-title-main">Unicellular organism</span> Organism that consists of only one cell

A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic organisms and eukaryotic organisms. Most prokaryotes are unicellular and are classified into bacteria and archaea. Many eukaryotes are multicellular, but some are unicellular such as protozoa, unicellular algae, and unicellular fungi. Unicellular organisms are thought to be the oldest form of life, with early protocells possibly emerging 3.8–4.8 billion years ago.

<span class="mw-page-title-main">Mating</span> Process of pairing in biology

In biology, mating is the pairing of either opposite-sex or hermaphroditic organisms for the purposes of sexual reproduction. Fertilization is the fusion of two gametes. Copulation is the union of the sex organs of two sexually reproducing animals for insemination and subsequent internal fertilization. Mating may also lead to external fertilization, as seen in amphibians, fishes and plants. For most species, mating is between two individuals of opposite sexes. However, for some hermaphroditic species, copulation is not required because the parent organism is capable of self-fertilization (autogamy); for example, banana slugs.

The hydrogen hypothesis is a model proposed by William F. Martin and Miklós Müller in 1998 that describes a possible way in which the mitochondrion arose as an endosymbiont within a prokaryotic host in the archaea, giving rise to a symbiotic association of two cells from which the first eukaryotic cell could have arisen (symbiogenesis).

<span class="mw-page-title-main">Genome size</span> Amount of DNA contained in a genome

Genome size is the total amount of DNA contained within one copy of a single complete genome. It is typically measured in terms of mass in picograms or less frequently in daltons, or as the total number of nucleotide base pairs, usually in megabases. One picogram is equal to 978 megabases. In diploid organisms, genome size is often used interchangeably with the term C-value.

Viral eukaryogenesis is the hypothesis that the cell nucleus of eukaryotic life forms evolved from a large DNA virus in a form of endosymbiosis within a methanogenic archaeon or a bacterium. The virus later evolved into the eukaryotic nucleus by acquiring genes from the host genome and eventually usurping its role. The hypothesis was first proposed by Philip Bell in 2001 and was further popularized with the discovery of large, complex DNA viruses that are capable of protein biosynthesis.

<span class="mw-page-title-main">Cellular compartment</span> Closed part in cytosol

Cellular compartments in cell biology comprise all of the closed parts within the cytosol of a eukaryotic cell, usually surrounded by a single or double lipid layer membrane. These compartments are often, but not always, defined as membrane-bound organelles. The formation of cellular compartments is called compartmentalization.

<span class="mw-page-title-main">Prokaryote</span> Unicellular organism lacking a membrane-bound nucleus

A prokaryote is a single-cell organism whose cell lacks a nucleus and other membrane-bound organelles. The word prokaryote comes from the Ancient Greek πρό 'before' and κάρυον 'nut, kernel'. In the two-empire system arising from the work of Édouard Chatton, prokaryotes were classified within the empire Prokaryota. But in the three-domain system, based upon molecular analysis, prokaryotes are divided into two domains: Bacteria and Archaea. Organisms with nuclei are placed in a third domain, Eukaryota.

<span class="mw-page-title-main">Archaea</span> Domain of single-celled organisms

Archaea is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotic. Archaea were initially classified as bacteria, receiving the name archaebacteria, but this term has fallen out of use.

<span class="mw-page-title-main">Eukaryote</span> Domain of life whose cells have nuclei

The eukaryotes constitute the domain of Eukarya or Eukaryota, organisms whose cells have a membrane-bound nucleus. All animals, plants, fungi, and many unicellular organisms are eukaryotes. They constitute a major group of life forms alongside the two groups of prokaryotes: the Bacteria and the Archaea. Eukaryotes represent a small minority of the number of organisms, but given their generally much larger size, their collective global biomass is much larger than that of prokaryotes.

Evolution of cells refers to the evolutionary origin and subsequent evolutionary development of cells. Cells first emerged at least 3.8 billion years ago approximately 750 million years after Earth was formed.

The origin and function of meiosis are currently not well understood scientifically, and would provide fundamental insight into the evolution of sexual reproduction in eukaryotes. There is no current consensus among biologists on the questions of how sex in eukaryotes arose in evolution, what basic function sexual reproduction serves, and why it is maintained, given the basic two-fold cost of sex. It is clear that it evolved over 1.2 billion years ago, and that almost all species which are descendants of the original sexually reproducing species are still sexual reproducers, including plants, fungi, and animals.

<span class="mw-page-title-main">Eocyte hypothesis</span> Hypothesis in evolutionary biology

The eocyte hypothesis in evolutionary biology proposes that the eukaryotes originated from a group of prokaryotes called eocytes. After his team at the University of California, Los Angeles discovered eocytes in 1984, James A. Lake formulated the hypothesis as "eocyte tree" that proposed eukaryotes as part of archaea. Lake hypothesised the tree of life as having only two primary branches: prokaryotes, which include Bacteria and Archaea, and karyotes, that comprise Eukaryotes and eocytes. Parts of this early hypothesis were revived in a newer two-domain system of biological classification which named the primary domains as Archaea and Bacteria.

<span class="mw-page-title-main">Lokiarchaeota</span> Phylum of archaea

Lokiarchaeota is a proposed phylum of the Archaea. The phylum includes all members of the group previously named Deep Sea Archaeal Group, also known as Marine Benthic Group B. Lokiarchaeota is part of the superphylum Asgard containing the phyla: Lokiarchaeota, Thorarchaeota, Odinarchaeota, Heimdallarchaeota, and Helarchaeota. A phylogenetic analysis disclosed a monophyletic grouping of the Lokiarchaeota with the eukaryotes. The analysis revealed several genes with cell membrane-related functions. The presence of such genes support the hypothesis of an archaeal host for the emergence of the eukaryotes; the eocyte-like scenarios.

<span class="mw-page-title-main">Proteoarchaeota</span> Proposed kingdom of archaea

"Proteoarchaeota" are a proposed archaeal kingdom thought to be closely related and possibly ancestral to the Eukaryotes.

<span class="mw-page-title-main">Marine prokaryotes</span> Marine bacteria and marine archaea

Marine prokaryotes are marine bacteria and marine archaea. They are defined by their habitat as prokaryotes that live in marine environments, that is, in the saltwater of seas or oceans or the brackish water of coastal estuaries. All cellular life forms can be divided into prokaryotes and eukaryotes. Eukaryotes are organisms whose cells have a nucleus enclosed within membranes, whereas prokaryotes are the organisms that do not have a nucleus enclosed within a membrane. The three-domain system of classifying life adds another division: the prokaryotes are divided into two domains of life, the microscopic bacteria and the microscopic archaea, while everything else, the eukaryotes, become the third domain.

<span class="mw-page-title-main">Two-domain system</span> Biological classification system

The two-domain system is a biological classification by which all organisms in the tree of life are classified into two domains, Bacteria and Archaea. It emerged from development of knowledge of archaea diversity and challenges to the widely accepted three-domain system that classifies life into Bacteria, Archaea, and Eukarya. It was preceded by the eocyte hypothesis of James A. Lake in the 1980s, which was largely superseded by the three-domain system, due to evidence at the time. Better understanding of archaea, especially of their roles in the origin of eukaryotes through symbiogenesis with bacteria, led to the revival of the eocyte hypothesis in the 2000s. The two-domain system became more widely accepted after the discovery of a large group (superphylum) of archaea called Asgard in 2017, which evidence suggests to be the evolutionary root of eukaryotes, thereby making eukaryotes members of the domain Archaea.

References

  1. 1 2 3 McGrath, Casey (31 May 2022). "Highlight: Unraveling the Origins of LUCA and LECA on the Tree of Life". Genome Biology and Evolution. 14 (6): evac072. doi:10.1093/gbe/evac072. PMC   9168435 .
  2. ↑ Weiss, Madeline C.; Sousa, F. L.; Mrnjavac, N.; et al. (2016). "The physiology and habitat of the last universal common ancestor" (PDF). Nature Microbiology. 1 (9): 16116. doi:10.1038/nmicrobiol.2016.116. PMID   27562259. S2CID   2997255.
  3. 1 2 Gabaldón, T. (October 2021). "Origin and Early Evolution of the Eukaryotic Cell". Annual Review of Microbiology. 75 (1): 631–647. doi:10.1146/annurev-micro-090817-062213. PMID   34343017. S2CID   236916203.
  4. 1 2 Woese, C.R.; Kandler, Otto; Wheelis, Mark L. (June 1990). "Towards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eucarya". Proceedings of the National Academy of Sciences of the United States of America. 87 (12): 4576–4579. Bibcode:1990PNAS...87.4576W. doi: 10.1073/pnas.87.12.4576 . PMC   54159 . PMID   2112744.
  5. 1 2 Latorre, A.; Durban, A; Moya, A.; Pereto, J. (2011). "The role of symbiosis in eukaryotic evolution". In Gargaud, Muriel; López-Garcìa, Purificacion; Martin H. (eds.). Origins and Evolution of Life: An astrobiological perspective. Cambridge: Cambridge University Press. pp. 326–339. ISBN   978-0-521-76131-4. Archived from the original on 24 March 2019. Retrieved 27 August 2017.
  6. ↑ Margulis, Lynn; Chapman, Michael; Guerrero, Ricardo; Hall, John (29 August 2006). "The last eukaryotic common ancestor (LECA): Acquisition of cytoskeletal motility from aerotolerant spirochetes in the Proterozoic Eon". Proceedings of the National Academy of Sciences. 103 (35): 13080–13085. Bibcode:2006PNAS..10313080M. doi: 10.1073/pnas.0604985103 . PMC   1559756 . PMID   16938841.
  7. ↑ Williams, Tom A.; Cox, Cymon J.; Foster, Peter G.; Szöllősi, Gergely J.; Embley, T. Martin (9 December 2019). "Phylogenomics provides robust support for a two-domains tree of life". Nature Ecology & Evolution. 4 (1): 138–147. Bibcode:2019NatEE...4..138W. doi:10.1038/s41559-019-1040-x. PMC   6942926 . PMID   31819234.
  8. ↑ O'Malley, Maureen A.; Leger, Michelle M.; Wideman, Jeremy G.; Ruiz-Trillo, Iñaki (18 February 2019). "Concepts of the last eukaryotic common ancestor". Nature Ecology & Evolution. 3 (3): 338–344. Bibcode:2019NatEE...3..338O. doi:10.1038/s41559-019-0796-3. hdl: 10261/201794 . PMID   30778187. S2CID   256718457.
  9. 1 2 Leander, B. S. (May 2020). "Predatory protists". Current Biology. 30 (10): R510–R516. doi: 10.1016/j.cub.2020.03.052 . PMID   32428491. S2CID   218710816.
  10. 1 2 Strassert, Jürgen F. H.; Irisarri, Iker; Williams, Tom A.; Burki, Fabien (25 March 2021). "A molecular timescale for eukaryote evolution with implications for the origin of red algal-derived plastids". Nature Communications. 12 (1): 1879. Bibcode:2021NatCo..12.1879S. doi:10.1038/s41467-021-22044-z. PMC   7994803 . PMID   33767194.
  11. ↑ Bremer, Nico; Tria, Fernando D. K.; Skejo, Josip; Garg, Sriram G.; Martin, William F. (31 May 2022). "Ancestral State Reconstructions Trace Mitochondria But Not Phagocytosis to the Last Eukaryotic Common Ancestor". Genome Biology and Evolution. 14 (6). doi:10.1093/gbe/evac079. PMC   9185374 . PMID   35642316.
  12. 1 2 3 4 5 Koumandou, V. Lila; Wickstead, Bill; Ginger, Michael L.; van der Giezen, Mark; Dacks, Joel B.; Field, Mark C. (2013). "Molecular paleontology and complexity in the last eukaryotic common ancestor". Critical Reviews in Biochemistry and Molecular Biology. 48 (4): 373–396. doi:10.3109/10409238.2013.821444. PMC   3791482 . PMID   23895660.
  13. ↑ Makarova, Kira S.; Yutin, Natalya; Bell, Stephen D.; Koonin, Eugene V. (6 September 2010). "Evolution of diverse cell division and vesicle formation systems in Archaea". Nature Reviews Microbiology. 8 (10): 731–741. doi:10.1038/nrmicro2406. PMC   3293450 . PMID   20818414.
  14. ↑ Martin, William; Koonin, Eugene V. (2006). "Introns and the origin of nucleus–cytosol compartmentalization". Nature. 440 (7080): 41–45. doi:10.1038/nature04531. ISSN   0028-0836.
  15. 1 2 3 Horandl, E.; Speijer, D. (7 February 2018). "How oxygen gave rise to eukaryotic sex". Proceedings of the Royal Society B: Biological Sciences. 285 (1872). The Royal Society. doi:10.1098/rspb.2017.2706. PMC   5829205 . PMID   29436502.
  16. ↑ Dacks, J.; Roger, A. J. (1999). "The first sexual lineage and the relevance of facultative sex". Journal of Molecular Evolution. 48 (6): 779–783. Bibcode:1999JMolE..48..779D. doi:10.1007/pl00013156. PMID   10229582. S2CID   9441768.
  17. ↑ Lane, Nick; Martin, William F. (2010). "The energetics of genome complexity". Nature. 467 (7318): 929–934. Bibcode:2010Natur.467..929L. doi:10.1038/nature09486. PMID   20962839. S2CID   17086117.
  18. ↑ Koonin, Eugene V. (March 2005). "The incredible expanding ancestor of eukaryotes". Cell. 140 (5): 606–608. doi:10.1016/j.cell.2010.02.022. PMC   3293451 . PMID   20211127.
  19. ↑ Martijn, J.; Ettema, T.J.G. (February 2013). "From archaeon to eukaryote: the evolutionary dark ages of the eukaryotic cell". Biochem Soc Trans. 41 (1): 451–7. doi:10.1042/BST20120292. PMID   23356327.
  20. ↑ Van de Peer, Yves; Baldaufrid, Sandra L.; Doolittle, W. Ford; Meyerid, Axel (2000). "An Updated and Comprehensive rRNA Phylogeny of (Crown) Eukaryotes Based on Rate-Calibrated Evolutionary Distances". Journal of Molecular Evolution. 51 (6): 565–576. Bibcode:2000JMolE..51..565V. doi:10.1007/s002390010120. PMID   11116330. S2CID   9400485.
  21. 1 2 Butterfield, N.J. (2015). "Early evolution of the Eukaryota". Palaeontology. 58 (1): 5–17. Bibcode:2015Palgy..58....5B. doi: 10.1111/pala.12139 .
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.