Last updated

Temporal range: OrosirianPresent
Scientific classification Red Pencil Icon.png
Domain: Eukaryota
(Chatton, 1925) Whittaker & Margulis, 1978
Supergroups and kingdoms [1] [2] [3]

Eukaryotic organisms that cannot be classified under the kingdoms Plantae, Animalia or Fungi are sometimes grouped in the paraphyletic Protista .


Eukaryota, whose members are known as eukaryotes ( /jˈkærits,-əts/ ), is a diverse domain of organisms whose cells have a nucleus. [4] All animals, plants, fungi, and many unicellular organisms, are eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacteria and Archaea (both prokaryotes) make up the other two domains. [5] [6]

The eukaryotes are usually now regarded as having emerged in the Archaea or as a sister of the Asgard archaea. [7] [8] This implies that there are only two domains of life, Bacteria and Archaea, with eukaryotes incorporated among archaea. [9] [10] Eukaryotes represent a small minority of the number of organisms, [11] but, due to their generally much larger size, their collective global biomass is estimated to be about equal to that of prokaryotes. [11] Eukaryotes emerged approximately 2.3–1.8 billion years ago, during the Proterozoic eon, likely as flagellated phagotrophs. [12] [1] Their name comes from the Greek εὖ (eu, "well" or "good") and κάρυον (karyon, "nut" or "kernel"). [13]

Eukaryotic cells typically contain other membrane-bound organelles such as mitochondria and Golgi apparatus. Chloroplasts can be found in plants and algae. Prokaryotic cells may contain primitive organelles. [14] Eukaryotes may be either unicellular or multicellular, and include many cell types forming different kinds of tissue. In comparison, prokaryotes are typically unicellular. Animals, plants, and fungi are the most familiar eukaryotes. Other eukaryotes are sometimes called protists. [15]

Eukaryotes can reproduce both asexually through mitosis and sexually through meiosis and gamete fusion. In mitosis, one cell divides to produce two genetically identical cells. In meiosis, DNA replication is followed by two rounds of cell division to produce four haploid daughter cells that act as sex cells or gametes. Each gamete has just one set of chromosomes, each a unique mix of the corresponding pair of parental chromosomes resulting from genetic recombination during meiosis. [16]

Cell features

Cytology Video, Cell Features

Eukaryotic cells are typically much larger than those of prokaryotes, having a volume of around 10,000 times greater than the prokaryotic cell. [17] They have a variety of internal membrane-bound structures, called organelles, and a cytoskeleton composed of microtubules, microfilaments, and intermediate filaments, which play an important role in defining the cell's organization and shape. Eukaryotic DNA is divided into several linear bundles called chromosomes, which are separated by a microtubular spindle during nuclear division.

Internal membranes

The endomembrane system and its components Endomembrane system diagram en (edit).svg
The endomembrane system and its components

Eukaryote cells include a variety of membrane-bound structures, collectively referred to as the endomembrane system. [18] Simple compartments, called vesicles and vacuoles, can form by budding off other membranes. Many cells ingest food and other materials through a process of endocytosis, where the outer membrane invaginates and then pinches off to form a vesicle. [19] It is probable[ citation needed ] that most other membrane-bound organelles are ultimately derived from such vesicles. Alternatively some products produced by the cell can leave in a vesicle through exocytosis.

The nucleus is surrounded by a double membrane known as the nuclear envelope, with nuclear pores that allow material to move in and out. [20] Various tube- and sheet-like extensions of the nuclear membrane form the endoplasmic reticulum, which is involved in protein transport and maturation. It includes the rough endoplasmic reticulum where ribosomes are attached to synthesize proteins, which enter the interior space or lumen. Subsequently, they generally enter vesicles, which bud off from the smooth endoplasmic reticulum. [21] In most eukaryotes, these protein-carrying vesicles are released and further modified in stacks of flattened vesicles (cisternae), the Golgi apparatus. [22]

Vesicles may be specialized for various purposes. For instance, lysosomes contain digestive enzymes that break down most biomolecules in the cytoplasm. [23] Peroxisomes are used to break down peroxide, which is otherwise toxic. Many protozoans have contractile vacuoles, which collect and expel excess water, and extrusomes, which expel material used to deflect predators or capture prey. In higher plants, most of a cell's volume is taken up by a central vacuole, which mostly contains water and primarily maintains its osmotic pressure.


Simplified structure of a mitochondrion Mitochondrion structure.svg
Simplified structure of a mitochondrion

Mitochondria are organelles found in all but one eukaryote, [note 1] and are commonly referred to as "the powerhouse of the cell". [25] Mitochondria provide energy to the eukaryote cell by oxidising sugars or fats and releasing energy as ATP. [26] They have two surrounding membranes, each a phospholipid bi-layer; the inner of which is folded into invaginations called cristae where aerobic respiration takes place.

The outer mitochondrial membrane is freely permeable and allows almost anything to enter into the intermembrane space while the inner mitochondrial membrane is semi permeable so allows only some required things into the mitochondrial matrix.

Mitochondria contain their own DNA, which has close structural similarities to bacterial DNA, and which encodes rRNA and tRNA genes that produce RNA which is closer in structure to bacterial RNA than to eukaryote RNA. [27] They are now generally held to have developed from endosymbiotic prokaryotes, probably Alphaproteobacteria.

Some eukaryotes, such as the metamonads such as Giardia and Trichomonas , and the amoebozoan Pelomyxa , appear to lack mitochondria, but all have been found to contain mitochondrion-derived organelles, such as hydrogenosomes and mitosomes, and thus have lost their mitochondria secondarily. [24] They obtain energy by enzymatic action on nutrients absorbed from the environment. The metamonad Monocercomonoides has also acquired, by lateral gene transfer, a cytosolic sulfur mobilisation system which provides the clusters of iron and sulfur required for protein synthesis. The normal mitochondrial iron-sulfur cluster pathway has been lost secondarily. [24] [28]


Plants and various groups of algae also have plastids. Plastids also have their own DNA and are developed from endosymbionts, in this case cyanobacteria. They usually take the form of chloroplasts which, like cyanobacteria, contain chlorophyll and produce organic compounds (such as glucose) through photosynthesis. Others are involved in storing food. Although plastids probably had a single origin, not all plastid-containing groups are closely related. Instead, some eukaryotes have obtained them from others through secondary endosymbiosis or ingestion. [29] The capture and sequestering of photosynthetic cells and chloroplasts occurs in many types of modern eukaryotic organisms and is known as kleptoplasty.

Endosymbiotic origins have also been proposed for the nucleus, and for eukaryotic flagella. [30]

Cytoskeletal structures

Longitudinal section through the flagellum of Chlamydomonas reinhardtii Chlamydomonas TEM 09.jpg
Longitudinal section through the flagellum of Chlamydomonas reinhardtii

Many eukaryotes have long slender motile cytoplasmic projections, called flagella, or similar structures called cilia. Flagella and cilia are sometimes referred to as undulipodia, [31] and are variously involved in movement, feeding, and sensation. They are composed mainly of tubulin. These are entirely distinct from prokaryotic flagellae. They are supported by a bundle of microtubules arising from a centriole, characteristically arranged as nine doublets surrounding two singlets. Flagella also may have hairs, or mastigonemes, and scales connecting membranes and internal rods. Their interior is continuous with the cell's cytoplasm.

Microfilamental structures composed of actin and actin binding proteins, e.g., α-actinin, fimbrin, filamin are present in submembranous cortical layers and bundles, as well. Motor proteins of microtubules, e.g., dynein or kinesin and actin, e.g., myosins provide dynamic character of the network.

Centrioles are often present even in cells and groups that do not have flagella, but conifers and flowering plants have neither. They generally occur in groups that give rise to various microtubular roots. These form a primary component of the cytoskeletal structure, and are often assembled over the course of several cell divisions, with one flagellum retained from the parent and the other derived from it. Centrioles produce the spindle during nuclear division. [32]

The significance of cytoskeletal structures is underlined in the determination of shape of the cells, as well as their being essential components of migratory responses like chemotaxis and chemokinesis. Some protists have various other microtubule-supported organelles. These include the radiolaria and heliozoa, which produce axopodia used in flotation or to capture prey, and the haptophytes, which have a peculiar flagellum-like organelle called the haptonema.

Cell wall

The cells of plants and algae, fungi and most chromalveolates have a cell wall, a layer outside the cell membrane, providing the cell with structural support, protection, and a filtering mechanism. The cell wall also prevents over-expansion when water enters the cell. [33]

The major polysaccharides making up the primary cell wall of land plants are cellulose, hemicellulose, and pectin. The cellulose microfibrils are linked via hemicellulosic tethers to form the cellulose-hemicellulose network, which is embedded in the pectin matrix. The most common hemicellulose in the primary cell wall is xyloglucan. [34]

Differences among eukaryotic cells

There are many different types of eukaryotic cells, though animals and plants are the most familiar eukaryotes, and thus provide an excellent starting point for understanding eukaryotic structure. Fungi and many protists have some substantial differences, however.

Animal cell

Structure of a typical animal cell Animal cell structure en.svg
Structure of a typical animal cell
Structure of a typical plant cell Plant cell structure-en.svg
Structure of a typical plant cell

All animals are eukaryotic. Animal cells are distinct from those of other eukaryotes, most notably plants, as they lack cell walls and chloroplasts and have smaller vacuoles. Due to the lack of a cell wall, animal cells can transform into a variety of shapes. A phagocytic cell can even engulf other structures.

Plant cell

Plant cells have a number of features that distinguish them from the cells of the other eukaryotic organisms. These include:

Fungal cell

Fungal Hyphae cells: 1 - hyphal wall, 2 - septum, 3 - mitochondrion, 4 - vacuole, 5 - ergosterol crystal, 6 - ribosome, 7 - nucleus, 8 - endoplasmic reticulum, 9 - lipid body, 10 - plasma membrane, 11 - spitzenkorper, 12 - Golgi apparatus HYPHAE.png
Fungal Hyphae cells: 1 – hyphal wall, 2 – septum, 3 – mitochondrion, 4 – vacuole, 5 – ergosterol crystal, 6 – ribosome, 7 – nucleus, 8 – endoplasmic reticulum, 9 – lipid body, 10 – plasma membrane, 11 – spitzenkörper, 12 – Golgi apparatus

The cells of fungi are similar to animal cells, with the following exceptions: [39]

Other eukaryotic cells

Some groups of eukaryotes have unique organelles, such as the cyanelles (unusual plastids) of the glaucophytes, [40] the haptonema of the haptophytes, or the ejectosomes of the cryptomonads. Other structures, such as pseudopodia, are found in various eukaryote groups in different forms, such as the lobose amoebozoans or the reticulose foraminiferans. [41] Structures known as cortical alveoli are vesicles present under the cell membrane of many protists such as dinoflagellates, ciliates and apicomplexan parasites. [42]


This diagram illustrates the twofold cost of sex. If each individual were to contribute the same number of offspring (two), (a) the sexual population remains the same size each generation, where the (b) asexual population doubles in size each generation. Evolsex-dia1a.png
This diagram illustrates the twofold cost of sex. If each individual were to contribute the same number of offspring (two), (a) the sexual population remains the same size each generation, where the (b) asexual population doubles in size each generation.

Cell division generally takes place asexually by mitosis, a process that allows each daughter nucleus to receive one copy of each chromosome. Most eukaryotes also have a life cycle that involves sexual reproduction, alternating between a haploid phase, where only one copy of each chromosome is present in each cell and a diploid phase, wherein two copies of each chromosome are present in each cell. The diploid phase is formed by fusion of two haploid gametes to form a zygote, which may divide by mitosis or undergo chromosome reduction by meiosis. There is considerable variation in this pattern. Animals have no multicellular haploid phase, but each plant generation can consist of haploid and diploid multicellular phases.

Eukaryotes have a smaller surface area to volume ratio than prokaryotes, and thus have lower metabolic rates and longer generation times. [43]

The evolution of sexual reproduction may be a primordial and fundamental characteristic of eukaryotes. Based on a phylogenetic analysis, Dacks and Roger proposed that facultative sex was present in the common ancestor of all eukaryotes. [44] A core set of genes that function in meiosis is present in both Trichomonas vaginalis and Giardia intestinalis , two organisms previously thought to be asexual. [45] [46] Since these two species are descendants of lineages that diverged early from the eukaryotic evolutionary tree, it was inferred that core meiotic genes, and hence sex, were likely present in a common ancestor of all eukaryotes. [45] [46] Eukaryotic species once thought to be asexual, such as parasitic protozoa of the genus Leishmania , have been shown to have a sexual cycle. [47] Also, evidence now indicates that amoebae, previously regarded as asexual, are anciently sexual and that the majority of present-day asexual groups likely arose recently and independently. [48]


Phylogenetic and symbiogenetic tree of living organisms, showing a view of the origins of eukaryotes and prokaryotes Tree of Living Organisms 2.png
Phylogenetic and symbiogenetic tree of living organisms, showing a view of the origins of eukaryotes and prokaryotes
One hypothesis of eukaryotic relationships - the Opisthokonta group includes both animals (Metazoa) and fungi, plants (Plantae) are placed in Archaeplastida. Eukaryote Phylogeny.png
One hypothesis of eukaryotic relationships – the Opisthokonta group includes both animals (Metazoa) and fungi, plants (Plantae) are placed in Archaeplastida.
A pie chart of described eukaryote species (except for Excavata), together with a tree showing possible relationships between the groups Eukaryote species pie tree.png
A pie chart of described eukaryote species (except for Excavata), together with a tree showing possible relationships between the groups

In antiquity, the two lineages of animals and plants were recognized. They were given the taxonomic rank of Kingdom by Linnaeus. Though he included the fungi with plants with some reservations, it was later realized that they are quite distinct and warrant a separate kingdom, the composition of which was not entirely clear until the 1980s. [49] The various single-cell eukaryotes were originally placed with plants or animals when they became known. In 1818, the German biologist Georg A. Goldfuss coined the word protozoa to refer to organisms such as ciliates, [50] and this group was expanded until it encompassed all single-celled eukaryotes, and given their own kingdom, the Protista, by Ernst Haeckel in 1866. [51] [52] The eukaryotes thus came to be composed of four kingdoms:

The protists were understood to be "primitive forms", and thus an evolutionary grade, united by their primitive unicellular nature. [52] The disentanglement of the deep splits in the tree of life only really started with DNA sequencing, leading to a system of domains rather than kingdoms as top level rank being put forward by Carl Woese, uniting all the eukaryote kingdoms under the eukaryote domain. [6] At the same time, work on the protist tree intensified, and is still actively going on today. Several alternative classifications have been forwarded, though there is no consensus in the field.

Eukaryotes are a clade usually assessed to be sister to Heimdallarchaeota in the Asgard grouping in the Archaea. [53] [54] [55] In one proposed system[ which? ], the basal groupings are the Opimoda, Diphoda, the Discoba, and the Loukozoa. The Eukaryote root is usually assessed to be near or even in Discoba[ citation needed ].

A classification produced in 2005 for the International Society of Protistologists, [56] which reflected the consensus of the time, divided the eukaryotes into six supposedly monophyletic 'supergroups'. However, in the same year (2005), doubts were expressed as to whether some of these supergroups were monophyletic, particularly the Chromalveolata, [57] and a review in 2006 noted the lack of evidence for several of the supposed six supergroups. [58] A revised classification in 2012 [59] recognizes five supergroups.

(or Primoplantae)
Land plants, green algae, red algae, and glaucophytes
SAR supergroup Stramenopiles (brown algae, diatoms, etc.),
Alveolata, and Rhizaria (Foraminifera, Radiolaria,
and various other amoeboid protozoa)
Excavata Various flagellate protozoa
Amoebozoa Most lobose amoeboids and slime molds
Opisthokonta Animals, fungi, choanoflagellates, etc.

There are also smaller groups of eukaryotes whose position is uncertain or seems to fall outside the major groups [60]  – in particular, Haptophyta, Cryptophyta, Centrohelida, Telonemia, Picozoa, [61] Apusomonadida, Ancyromonadida, Breviatea, and the genus Collodictyon . [62] Overall, it seems that, although progress has been made, there are still very significant uncertainties in the evolutionary history and classification of eukaryotes. As Roger & Simpson said in 2009 "with the current pace of change in our understanding of the eukaryote tree of life, we should proceed with caution." [63] Newly identified protists, purported to represent novel, deep-branching lineages, continue to be described well into the 21st century; recent examples including Rhodelphis , putative sister group to Rhodophyta, and Anaeramoeba , anaerobic amoebaflagellates of uncertain placement. [64]


The rRNA trees constructed during the 1980s and 1990s left most eukaryotes in an unresolved "crown" group (not technically a true crown), which was usually divided by the form of the mitochondrial cristae; see crown eukaryotes. The few groups that lack mitochondria branched separately, and so the absence was believed to be primitive; but this is now considered an artifact of long-branch attraction, and they are known to have lost them secondarily. [65] [66]

It has been estimated that there may be 75 distinct lineages of eukaryotes. [67] Most of these lineages are protists.

The known eukaryote genome sizes vary from 8.2 megabases (Mb) in Babesia bovis to 112,000–220,050 Mb in the dinoflagellate Prorocentrum micans , showing that the genome of the ancestral eukaryote has undergone considerable variation during its evolution. [67] The last common ancestor of all eukaryotes is believed to have been a phagotrophic 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. [67] Later endosymbiosis led to the spread of plastids in some lineages.

Although there is still considerable uncertainty in global eukaryote phylogeny, particularly regarding the position of the root, a rough consensus has started to emerge from the phylogenomic studies of the past two decades. [60] [68] [69] [70] [2] [24] [71] [1] [64] [3] The majority of eukaryotes can be placed in one of two large clades dubbed Amorphea (similar in composition to the unikont hypothesis) and the Diaphoretickes, which includes plants and most algal lineages. A third major grouping, the Excavata, has been abandoned as a formal group in the most recent classification of the International Society of Protistologists due to growing uncertainty as to whether its constituent groups belong together. [72] The proposed phylogeny below includes only one group of excavates (Discoba), and incorporates the recent proposal that picozoans are close relatives of rhodophytes. [73]




Red algae (Rhodophyta) Bangia.jpg


Glaucophyta Glaucocystis sp.jpg

Green plants (Viridiplantae) Pediastrum (cropped).jpg

 (+  Gloeomargarita lithophora ) 

Haptista Raphidiophrys contractilis.jpg




Stramenopiles Ochromonas.png

Alveolata Ceratium furca.jpg

Rhizaria Ammonia tepida.jpg



Discoba (Excavata) Euglena mutabilis - 400x - 1 (10388739803) (cropped).jpg


Amoebozoa Chaos carolinensis Wilson 1900.jpg


Apusomonadida Apusomonas.png


Holomycota (inc. fungi) Asco1013.jpg

Holozoa (inc. animals) Comb jelly.jpg

In some analyses, the Hacrobia group (Haptophyta + Cryptophyta) is placed next to Archaeplastida, [74] but in others it is nested inside the Archaeplastida. [75] However, several recent studies have concluded that Haptophyta and Cryptophyta do not form a monophyletic group. [76] The former could be a sister group to the SAR group, the latter cluster with the Archaeplastida (plants in the broad sense). [77]

The division of the eukaryotes into two primary clades, bikonts (Archaeplastida + SAR + Excavata) and unikonts (Amoebozoa + Opisthokonta), derived from an ancestral biflagellar organism and an ancestral uniflagellar organism, respectively, had been suggested earlier. [75] [78] [79] A 2012 study produced a somewhat similar division, although noting that the terms "unikonts" and "bikonts" were not used in the original sense. [61]

A highly converged and congruent set of trees appears in Derelle et al. (2015), Ren et al. (2016), Yang et al. (2017) and Cavalier-Smith (2015) including the supplementary information, resulting in a more conservative and consolidated tree. It is combined with some results from Cavalier-Smith for the basal Opimoda. [80] [81] [82] [83] [84] [2] [85] The main remaining controversies are the root, and the exact positioning of the Rhodophyta and the bikonts Rhizaria, Haptista, Cryptista, Picozoa and Telonemia, many of which may be endosymbiotic eukaryote-eukaryote hybrids. [86] Archaeplastida acquired chloroplasts probably by endosymbiosis of a prokaryotic ancestor related to a currently extant cyanobacterium, Gloeomargarita lithophora . [87] [88] [86]





 (+  Gloeomargarita lithophora ) 












Diphyllatea, Rigifilida, Mantamonas







Cavalier-Smith's tree

Thomas Cavalier-Smith 2010, [89] 2013, [90] 2014, [91] 2017 [81] and 2018 [92] places the eukaryotic tree's root between Excavata (with ventral feeding groove supported by a microtubular root) and the grooveless Euglenozoa, and monophyletic Chromista, correlated to a single endosymbiotic event of capturing a red-algae. He et al. [93] specifically supports rooting the eukaryotic tree between a monophyletic Discoba (Discicristata + Jakobida) and an Amorphea-Diaphoretickes clade.





Tsukubamonas globosa














Mantamonas plastica









Evolutionary history

Origin of eukaryotes

The three-domains tree and the Eocyte hypothesis Eocyte hypothesis.png
The three-domains tree and the Eocyte hypothesis
Phylogenetic tree showing a possible relationship between the eukaryotes and other forms of life; eukaryotes are colored red, archaea green and bacteria blue Collapsed tree labels simplified.png
Phylogenetic tree showing a possible relationship between the eukaryotes and other forms of life; eukaryotes are colored red, archaea green and bacteria blue
Eocyte tree. Phylogenetic Tree of Life.png
Eocyte tree.

The origin of the eukaryotic cell, also known as eukaryogenesis, is a milestone in the evolution of life, since eukaryotes include all complex cells and almost all multicellular organisms. A number of approaches have been used to find the first eukaryote and their closest relatives. The last eukaryotic common ancestor (LECA) is the hypothetical last common ancestor of all living eukaryotes, [5] and was most likely a biological population. [97]

Eukaryotes have a number of features that differentiate them from prokaryotes, including an endomembrane system, and unique biochemical pathways such as sterane synthesis. [98] A set of proteins called eukaryotic signature proteins (ESPs) was proposed to identify eukaryotic relatives in 2002: They have no homology to proteins known in other domains of life by then, but they appear to be universal among eukaryotes. They include proteins that make up the cytoskeleton, the complex transcription machinery, membrane-sorting systems, the nuclear pore, as well as some enzymes in the biochemical pathways. [99]


The timing of this series of events is hard to determine; Knoll (2006) suggests they developed approximately 1.6–2.1 billion years ago. Some acritarchs are known from at least 1.65 billion years ago, and the possible alga Grypania has been found as far back as 2.1 billion years ago. [100] The Geosiphon -like fossil fungus Diskagma has been found in paleosols 2.2 billion years old. [101]

Organized living structures have been found in the black shales of the Palaeoproterozoic Francevillian B Formation in Gabon, dated at 2.1 billion years old. Eukaryotic life could have evolved at that time. [102] Fossils that are clearly related to modern groups start appearing an estimated 1.2 billion years ago, in the form of a red algae, though recent work suggests the existence of fossilized filamentous algae in the Vindhya basin dating back perhaps to 1.6 to 1.7 billion years ago. [103]

The presence of eukaryotic-specific biomarkers (steranes) in Australian shales previously indicated that eukaryotes were present in these rocks dated at 2.7 billion years old, [98] [104] which was even 300 million years older than the first geological records of the appreciable amount of molecular oxygen during the Great Oxidation Event. However, these Archaean biomarkers were eventually rebutted as later contaminants. [105] Currently, putatively the oldest biomarker records are only ~800 million years old. [106] In contrast, a molecular clock analysis suggests the emergence of sterol biosynthesis as early as 2.3 billion years ago, [107] and thus there is a huge gap between molecular data and geological data, which hinders a reasonable inference of the eukaryotic evolution through biomarker records before 800 million years ago. The nature of steranes as eukaryotic biomarkers is further complicated by the production of sterols by some bacteria. [108] [109]

Whenever their origins, eukaryotes may not have become ecologically dominant until much later; a massive uptick in the zinc composition of marine sediments 800  million years ago has been attributed to the rise of substantial populations of eukaryotes, which preferentially consume and incorporate zinc relative to prokaryotes, approximately a billion years after their origin (at the latest). [110]

In April 2019, biologists reported that the very large medusavirus, or a relative, may have been responsible, at least in part, for the evolutionary emergence of complex eukaryotic cells from simpler prokaryotic cells. [111]

Relationship to Archaea

The nuclear DNA and genetic machinery of eukaryotes is more similar to Archaea than Bacteria, leading to a controversial suggestion that eukaryotes should be grouped with Archaea in the clade Neomura. In other respects, such as membrane composition, eukaryotes are similar to Bacteria. Three main explanations for this have been proposed:

Diagram of the origin of life with the Eukaryotes appearing early, not derived from Prokaryotes, as proposed by Richard Egel in 2012. This view implies that the UCA was relatively large and complex. Primordial biogenesis.svg
Diagram of the origin of life with the Eukaryotes appearing early, not derived from Prokaryotes, as proposed by Richard Egel in 2012. This view implies that the UCA was relatively large and complex.

Alternative proposals include:

  • The chronocyte hypothesis postulates that a primitive eukaryotic cell was formed by the endosymbiosis of both archaea and bacteria by a third type of cell, termed a chronocyte. This is mainly to account for the fact that eukaryotic signature proteins were not found anywhere else by 2002. [99]
  • The universal common ancestor (UCA) of the current tree of life was a complex organism that survived a mass extinction event rather than an early stage in the evolution of life. Eukaryotes and in particular akaryotes (Bacteria and Archaea) evolved through reductive loss, so that similarities result from differential retention of original features. [119]

Assuming no other group is involved, there are three possible phylogenies for the Bacteria, Archaea, and Eukaryota in which each is monophyletic. These are labelled 1 to 3 in the table below, with a modification of hypothesis 2 making the 4th column: The eocyte hypothesis, in which the Archaea are paraphyletic. (The table and the names for the hypotheses are based on Harish & Kurland, 2017. [120] )

Alternative hypotheses for the base of the tree of life
1 – Two empires2 – Three domains3 – Gupta4 – Eocyte


















In recent years, most researchers have favoured either the three domains (3D) or the eocyte hypothesis. An rRNA analysis supports the eocyte scenario, apparently with the Eukaryote root in Excavata. [96] [89] [90] [91] [81] A cladogram supporting the eocyte hypothesis, positioning eukaryotes within Archaea, based on phylogenomic analyses of the Asgard archaea, is: [53] [54] [55] [10]














 (+Alphaproteobacteria )

In this scenario, the Asgard group is seen as a sister taxon of the TACK group, which comprises Thermoproteota (formerly named eocytes or Crenarchaeota), Nitrososphaerota (formerly Thaumarchaeota), and others. This group is reported contain many of the eukaryotic signature proteins and produce vesicles. [121]

In 2017, there was significant pushback against this scenario, arguing that the eukaryotes did not emerge within the Archaea. Cunha et al. produced analyses supporting the three domains (3D) or Woese hypothesis (2 in the table above) and rejecting the eocyte hypothesis (4 above). [122] Harish and Kurland found strong support for the earlier two empires (2D) or Mayr hypothesis (1 in the table above), based on analyses of the coding sequences of protein domains. They rejected the eocyte hypothesis as the least likely. [123] [120] A possible interpretation of their analysis is that the universal common ancestor (UCA) of the current tree of life was a complex organism that survived an evolutionary bottleneck, rather than a simpler organism arising early in the history of life. [119] On the other hand, the researchers who came up with Asgard re-affirmed their hypothesis with additional Asgard samples. [124] Since then, the publication of additional Asgard archaeal genomes and the independent reconstruction of phylogenomic trees by multiple independent laboratories have provided additional support for an Asgard archaeal origin of eukaryotes.

Details of the relation of Asgard archaea members and eukaryotes are still under consideration, [125] although, in January 2020, scientists reported that Candidatus Prometheoarchaeum syntrophicum , a type of cultured Asgard archaea, may be a possible link between simple prokaryotic and complex eukaryotic microorganisms about two billion years ago. [126] [121]

Endomembrane system and mitochondria

The origins of the endomembrane system and mitochondria are also unclear. [127] The phagotrophic hypothesis proposes that eukaryotic-type membranes lacking a cell wall originated first, with the development of endocytosis, whereas mitochondria were acquired by ingestion as endosymbionts. [128] The syntrophic hypothesis proposes that the proto-eukaryote relied on the proto-mitochondrion for food, and so ultimately grew to surround it. Here the membranes originated after the engulfment of the mitochondrion, in part thanks to mitochondrial genes (the hydrogen hypothesis is one particular version). [129]

In a study using genomes to construct supertrees, Pisani et al. (2007) suggest that, along with evidence that there was never a mitochondrion-less eukaryote, eukaryotes evolved from a syntrophy between an archaea closely related to Thermoplasmatales and an alphaproteobacterium, likely a symbiosis driven by sulfur or hydrogen. The mitochondrion and its genome is a remnant of the alphaproteobacterial endosymbiont. [130] The majority of the genes from the symbiont have been transferred to the nucleus. They make up most of the metabolic and energy-related pathways of the eukaryotic cell, while the information system (DNA polymerase, transcription, translation) is retained from archaea. [131]


Different hypotheses have been proposed as to how eukaryotic cells came into existence. These hypotheses can be classified into two distinct classes – autogenous models and chimeric models.

Autogenous models
Serial endosymbiosis.svg
An autogenous model for the origin of eukaryotes.

Autogenous models propose that a proto-eukaryotic cell containing a nucleus existed first, and later acquired mitochondria. [132] According to this model, a large prokaryote developed invaginations in its plasma membrane in order to obtain enough surface area to service its cytoplasmic volume. As the invaginations differentiated in function, some became separate compartments – giving rise to the endomembrane system, including the endoplasmic reticulum, golgi apparatus, nuclear membrane, and single membrane structures such as lysosomes. [133]

Mitochondria are proposed to come from the endosymbiosis of an aerobic proteobacterium after a eukaryote with a nucleus has evolved. This theory is less held onto because it requires extra assumptions to explain current conditions. For example, as every known eukaryote has a mitochondrion (or at least show signs of having an ancestor that had), one must assumed that all the eukaryotic lineages that did not acquire mitochondria became extinct. The theory also does not explain why anaerobic variants of mitochondria have evolved. [134]

Chimeric models

Chimeric models claim that two prokaryotic cells existed initially – an archaeon and a bacterium. The closest living relatives of these appears to be Asgardarchaeota and (distantly related) the alphaproteobacteria called the proto-mitochondrion. [135] [136] These cells underwent a merging process, either by a physical fusion or by endosymbiosis, thereby leading to the formation of a eukaryotic cell. Within these chimeric models, some studies further claim that mitochondria originated from a bacterial ancestor while others emphasize the role of endosymbiotic processes behind the origin of mitochondria.

The inside-out hypothesis

The inside-out hypothesis suggests that the fusion between free-living mitochondria-like bacteria, and an archaeon into a eukaryotic cell happened gradually over a long period of time, instead of in a single phagocytotic event. In this scenario, an archaeon would trap aerobic bacteria with cell protrusions, and then keep them alive to draw energy from them instead of digesting them. During the early stages the bacteria would still be partly in direct contact with the environment, and the archaeon would not have to provide them with all the required nutrients. But eventually the archaeon would engulf the bacteria completely, creating the internal membrane structures and nucleus membrane in the process. [137]

It is assumed the archaean group called halophiles went through a similar procedure, where they acquired as much as a thousand genes from a bacterium, way more than through the conventional horizontal gene transfer that often occurs in the microbial world, but that the two microbes separated again before they had fused into a single eukaryote-like cell. [138]

An expanded version of the inside-out hypothesis proposes that the eukaryotic cell was created by physical interactions between two prokaryotic organisms and that the last common ancestor of eukaryotes got its genome from a whole population or community of microbes participating in cooperative relationships to thrive and survive in their environment. The genome from the various types of microbes would complement each other, and occasional horizontal gene transfer between them would be largely to their own benefit. This accumulation of beneficial genes gave rise to the genome of the eukaryotic cell, which contained all the genes required for independence. [139] [140] [141]

The serial endosymbiotic hypothesis

According to serial endosymbiotic theory (championed by Lynn Margulis), a union between a motile anaerobic bacterium (like Spirochaeta) and a thermoacidophilic crenarchaeon (like Thermoplasma which is sulfidogenic in nature) gave rise to the present day eukaryotes. This union established a motile organism capable of living in the already existing acidic and sulfurous waters. Oxygen is known to cause toxicity to organisms that lack the required metabolic machinery. Thus, the archaeon provided the bacterium with a highly beneficial reduced environment (sulfur and sulfate were reduced to sulfide). In microaerophilic conditions, oxygen was reduced to water thereby creating a mutual benefit platform. The bacterium on the other hand, contributed the necessary fermentation products and electron acceptors along with its motility feature to the archaeon thereby gaining a swimming motility for the organism.

From a consortium of bacterial and archaeal DNA originated the nuclear genome of eukaryotic cells. Spirochetes gave rise to the motile features of eukaryotic cells. Endosymbiotic unifications of the ancestors of alphaproteobacteria and cyanobacteria, led to the origin of mitochondria and plastids respectively. For example, Thiodendron has been known to have originated via an ectosymbiotic process based on a similar syntrophy of sulfur existing between the two types of bacteria – Desulfobacter and Spirochaeta.

However, such an association based on motile symbiosis has never been observed practically. Also there is no evidence of archaeans and spirochetes adapting to intense acid-based environments. In addition, the theory posits that mitochondrion-less eukaryotes have existed, tying back to the problem in the autogenous model. [132]

The hydrogen hypothesis

In the hydrogen hypothesis, the symbiotic linkage of an anaerobic and autotrophic methanogenic archaeon (host) with an alphaproteobacterium (the symbiont) gave rise to the eukaryotes. The host used hydrogen (H2) and carbon dioxide (CO2) to produce methane while the symbiont, capable of aerobic respiration, expelled H2 and CO2 as byproducts of anaerobic fermentation process. The host's methanogenic environment worked as a sink for H2, which resulted in heightened bacterial fermentation.

Endosymbiotic gene transfer acted as a catalyst for the host to acquire the symbionts' carbohydrate metabolism and turn heterotrophic in nature. Subsequently, the host's methane forming capability was lost. Thus, the origins of the heterotrophic organelle (symbiont) are identical to the origins of the eukaryotic lineage. In this hypothesis, the presence of H2 represents the selective force that forged eukaryotes out of prokaryotes. [129]

The syntrophy hypothesis

The syntrophy hypothesis was developed in contrast to the hydrogen hypothesis and proposes the existence of two symbiotic events. According to this model, the origin of eukaryotic cells was based on metabolic symbiosis (syntrophy) between a methanogenic archaeon and a deltaproteobacterium. This syntrophic symbiosis was initially facilitated by H2 transfer between different species under anaerobic environments. In earlier stages, an alphaproteobacterium became a member of this integration, and later developed into the mitochondrion. Gene transfer from a deltaproteobacterium to an archaeon led to the methanogenic archaeon developing into a nucleus. The archaeon constituted the genetic apparatus, while the deltaproteobacterium contributed towards the cytoplasmic features.

This theory incorporates two selective forces at the time of nucleus evolution

6+ serial endosymbiosis scenario

A complex scenario of 6+ serial endosymbiotic events of archaea and bacteria has been proposed in which mitochondria and an asgard related archaeota were acquired at a late stage of eukaryogenesis, possibly in combination, as a secondary endosymbiont. [142] [143] The findings have been rebuked as an artifact. [144]

See also


  1. To date, only one eukaryote, Monocercomonoides , is known to have completely lost its mitochondria. [24]

Related Research Articles

<span class="mw-page-title-main">Cell (biology)</span> Basic unit of all known organisms

The cell is the basic structural and functional unit of life forms. Every cell consists of a cytoplasm enclosed within a membrane, and contains many biomolecules such as proteins, DNA and RNA, as well as many small molecules of nutrients and metabolites. The term comes from the Latin word cellula meaning 'small room'.

In cell biology, an organelle is a specialized subunit, usually within a cell, that has a specific function. The name organelle comes from the idea that these structures are parts of cells, as organs are to the body, hence organelle, the suffix -elle being a diminutive. Organelles are either separately enclosed within their own lipid bilayers or are spatially distinct functional units without a surrounding lipid bilayer. Although most organelles are functional units within cells, some function units that extend outside of cells are often termed organelles, such as cilia, the flagellum and archaellum, and the trichocyst.

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.

In biological taxonomy, a domain, also dominion, superkingdom, realm, or empire, is the highest taxonomic rank of all organisms taken together. It was introduced in the three-domain system of taxonomy devised by Carl Woese, Otto Kandler and Mark Wheelis in 1990.

<span class="mw-page-title-main">Plastid</span> Plant cell organelles that perform photosynthesis and store starch

The plastid is a membrane-bound organelle found in the cells of plants, algae, and some other eukaryotic organisms. They are considered to be intracellular endosymbiotic cyanobacteria. Examples include chloroplasts, chromoplasts, and leucoplasts.

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

The three-domain system is a biological classification introduced by Carl Woese, Otto Kandler, and Mark Wheelis in 1990 that divides cellular life forms into three domains, namely Archaea, Bacteria, and Eukaryota or Eukarya. 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 organism. It has been challenged by the two-domain system that divides organisms into Bacteria and Archaea only, as eukaryotes are considered as one group 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. All 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 3.8–4.0 billion years ago.

Archezoa was a kingdom proposed in the 20th century by Thomas Cavalier-Smith (1942–2021), and was believed to encompass eukaryotes which did not have mitochondria or peroxisomes. The category was dropped after it was discovered that all the amitochondriates were descendants of eukaryotes with mitochondria that had lost them.

<span class="mw-page-title-main">Crown eukaryotes</span>

Taking into account the definition of a crown group, crown eukaryotes could be seen as the aggrupation of all lineages descending from LECA. This comprises a huge ensemble of taxa that seemingly diverged simultaneously and that conform the vast majority of the eukaryotic life, plants, fungi, animals and the variety of protist lineages. According to ribosomal RNA data, the radiation of eukaryotes from LECA would have originated from a series of basal lineages that branched off successively at this early stage. The hallmark of these organisms pertaining to crown eukaryotes is a higher complexity of their genetic and cellular machinery as compared with prokaryotes, enabled by their cellular compartmentalization. This complexity is accompanied by others extra cell-morphological features: endo/exocytosis, sexual reproduction, multicellularity, and vertical inheritance, that have led to the current morphological, behavioral and macroecological complexity of eukaryotes

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">Nuclear gene</span> Gene located in the cell nucleus of a eukaryote

A nuclear gene is a gene whose physical DNA nucleotide sequence is located in the cell nucleus of a eukaryote. The term is used to distinguish nuclear genes from genes found in mitochondria or chloroplasts. The vast majority of genes in eukaryotes are nuclear.

<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 that lacks a membrane-bound nucleus

A prokaryote is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word prokaryote comes from the Greek πρό and κάρυον. 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. In biological evolution, prokaryotes are deemed to have arisen before eukaryotes.

<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 prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria, but this term has fallen out of use.

<span class="mw-page-title-main">Evolution of cells</span> Evolutionary origin and subsequent development of cells

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.

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

The eocyte hypothesis in evolutionary biology proposes the origin of eukaryotes 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: Parkaryoates that 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 (DSAG), also known as Marine Benthic Group B (MBG-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.

A plastid is a membrane-bound organelle found in plants, algae and other eukaryotic organisms that contribute to the production of pigment molecules. Most plastids are photosynthetic, thus leading to color production and energy storage or production. There are many types of plastids in plants alone, but all plastids can be separated based on the number of times they have undergone endosymbiotic events. Currently there are three types of plastids; primary, secondary and tertiary. Endosymbiosis is reputed to have led to the evolution of eukaryotic organisms today, although the timeline is highly debated.

<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 big domains, Bacteria and Archaea. It emerged from development in the knowledge of archaea diversity and challenge over the widely accepted three-domain system that defines life into Bacteria, Archaea, and Eukarya. It was predicted by the eocyte hypothesis of James A. Lake in the 1980s, which was largely superseded by the three-domain system due to better compelling evidences at the time. Better understanding of archaea, especially in their roles in the origin of eukaryotes by symbiogenesis with bacteria, led to the revival of the eocyte hypothesis in the 2000s. The two-domain system became widely appreciated after the discovery of a large group (superphylum) of archaea called Asgard in 2017, evidences of which suggest to be the evolutionary root of eukaryotes – implying that eukaryotes are members of the domain Archaea.


  1. 1 2 3 Strassert JF, Irisarri I, Williams TA, Burki F (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.
  2. 1 2 3 Brown MW, Heiss AA, Kamikawa R, Inagaki Y, Yabuki A, Tice AK, et al. (February 2018). "Phylogenomics Places Orphan Protistan Lineages in a Novel Eukaryotic Super-Group". Genome Biology and Evolution. 10 (2): 427–433. doi:10.1093/gbe/evy014. PMC   5793813 . PMID   29360967.
  3. 1 2 Tikhonenkov DV, Mikhailov KV, Gawryluk RM, Belyaev AO, Mathur V, Karpov SA, et al. (December 2022). "Microbial predators form a new supergroup of eukaryotes". Nature. 612 (7941): 714–719. doi:10.1038/s41586-022-05511-5. PMID   36477531. S2CID   254436650.
  4. "Definition of EUKARYOTE". Retrieved 12 December 2022.
  5. 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.
  6. 1 2 Woese CR, Kandler O, Wheelis ML (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.
  7. Zimmer C (11 April 2016). "Scientists Unveil New 'Tree of Life'". The New York Times. Archived from the original on 24 March 2019. Retrieved 11 April 2016.
  8. Gribaldo S, Brochier-Armanet C (January 2020). "Evolutionary relationships between archaea and eukaryotes". Nature Ecology & Evolution. 4 (1): 20–21. doi: 10.1038/s41559-019-1073-1 . PMID   31836857.
  9. Doolittle WF (February 2020). "Evolution: Two Domains of Life or Three?". Current Biology. 30 (4): R177–R179. doi: 10.1016/j.cub.2020.01.010 . PMID   32097647.
  10. 1 2 Williams TA, Cox CJ, Foster PG, Szöllősi GJ, Embley TM (January 2020). "Phylogenomics provides robust support for a two-domains tree of life". Nature Ecology & Evolution. 4 (1): 138–147. doi:10.1038/s41559-019-1040-x. PMC   6942926 . PMID   31819234.
  11. 1 2 Whitman WB, Coleman DC, Wiebe WJ (June 1998). "Prokaryotes: the unseen majority" (PDF). Proceedings of the National Academy of Sciences of the United States of America. 95 (12): 6578–6583. Bibcode:1998PNAS...95.6578W. doi: 10.1073/pnas.95.12.6578 . PMC   33863 . PMID   9618454. Archived (PDF) from the original on 20 August 2008. Retrieved 16 September 2011.
  12. Leander BS (May 2020). "Predatory protists". Current Biology. 30 (10): R510–R516. doi: 10.1016/j.cub.2020.03.052 . PMID   32428491. S2CID   218710816.
  13. Harper, Douglas. "eukaryotic". Online Etymology Dictionary .
  14. Murat D, Byrne M, Komeili A (October 2010). "Cell biology of prokaryotic organelles". Cold Spring Harbor Perspectives in Biology. 2 (10): a000422. doi:10.1101/cshperspect.a000422. PMC   2944366 . PMID   20739411.
  15. Whittaker RH (January 1969). "New concepts of kingdoms or organisms. Evolutionary relations are better represented by new classifications than by the traditional two kingdoms". Science. 163 (3863): 150–60. Bibcode:1969Sci...163..150W. CiteSeerX . doi:10.1126/science.163.3863.150. PMID   5762760.
  16. Campbell NA, Cain ML, Minorsky PV, Reece JB, Urry LA (2018). "Chapter 13: Sexual Life Cycles and Meiosis". Biology: A Global Approach (11th ed.). New York: Pearson Education. ISBN   978-1-292-17043-5.
  17. Yamaguchi M, Worman CO (2014). "Deep-sea microorganisms and the origin of the eukaryotic cell" (PDF). Jpn. J. Protozool. 47 (1, 2): 29–48. Archived from the original (PDF) on 9 August 2017. Retrieved 24 October 2017.
  18. Linka M, Weber AP (2011). "Evolutionary Integration of Chloroplast Metabolism with the Metabolic Networks of the Cells". In Burnap RL, Vermaas WF (eds.). Functional Genomics and Evolution of Photosynthetic Systems. Springer. p. 215. ISBN   978-94-007-1533-2. Archived from the original on 29 May 2016. Retrieved 27 October 2015.
  19. Marsh M (2001). Endocytosis. Oxford University Press. p. vii. ISBN   978-0-19-963851-2.
  20. Hetzer MW (March 2010). "The nuclear envelope". Cold Spring Harbor Perspectives in Biology. 2 (3): a000539. doi:10.1101/cshperspect.a000539. PMC   2829960 . PMID   20300205.
  21. "Endoplasmic Reticulum (Rough and Smooth)". British Society for Cell Biology. Archived from the original on 24 March 2019. Retrieved 12 November 2017.
  22. "Golgi Apparatus". British Society for Cell Biology. Archived from the original on 13 November 2017. Retrieved 12 November 2017.
  23. "Lysosome". British Society for Cell Biology. Archived from the original on 13 November 2017. Retrieved 12 November 2017.
  24. 1 2 3 4 Karnkowska A, Vacek V, Zubáčová Z, Treitli SC, Petrželková R, Eme L, et al. (May 2016). "A Eukaryote without a Mitochondrial Organelle". Current Biology. 26 (10): 1274–1284. doi: 10.1016/j.cub.2016.03.053 . PMID   27185558.
  25. Saygin D, Tabib T, Bittar HE, Valenzi E, Sembrat J, Chan SY, et al. (July 1957). "Transcriptional profiling of lung cell populations in idiopathic pulmonary arterial hypertension". Pulmonary Circulation. 10 (1): 131–144. Bibcode:1957SciAm.197a.131S. doi:10.1038/scientificamerican0757-131. PMID   32166015.
  26. Mack S (1 May 2006). "Re: Are there eukaryotic cells without mitochondria?". Archived from the original on 24 April 2014. Retrieved 24 April 2014.
  27. Watson J, Hopkins N, Roberts J, Steitz JA, Weiner A (1988). "28: The Origins of Life". Molecular Biology of the Gene (Fourth ed.). Menlo Park, CA: The Benjamin/Cummings Publishing Company, Inc. p.  1154. ISBN   978-0-8053-9614-0.
  28. Davis JL (13 May 2016). "Scientists Shocked To Discover Eukaryote With NO Mitochondria". IFL Science. Archived from the original on 17 February 2019. Retrieved 13 May 2016.
  29. Sato N (2006). "Origin and Evolution of Plastids: Genomic View on the Unification and Diversity of Plastids". In Wise RR, Hoober JK (eds.). The Structure and Function of Plastids. Advances in Photosynthesis and Respiration. Vol. 23. Springer Netherlands. pp. 75–102. doi:10.1007/978-1-4020-4061-0_4. ISBN   978-1-4020-4060-3.
  30. Margulis L (1998). Symbiotic planet: a new look at evolution. New York: Basic Books. ISBN   978-0-465-07271-2. OCLC   39700477.[ page needed ]
  31. Lynn Margulis, Heather I. McKhann & Lorraine Olendzenski (ed.), Illustrated Glossary of Protoctista, Jones and Bartlett Publishers, Boston, 1993, p. xviii. ISBN   0-86720-081-2
  32. Vorobjev IA, Nadezhdina ES (1987). The centrosome and its role in the organization of microtubules. International Review of Cytology. Vol. 106. pp. 227–293. doi:10.1016/S0074-7696(08)61714-3. ISBN   978-0-12-364506-7. PMID   3294718.
  33. Howland JL (2000). The Surprising Archaea: Discovering Another Domain of Life. Oxford: Oxford University Press. pp. 69–71. ISBN   978-0-19-511183-5.
  34. Fry SC (1989). "The Structure and Functions of Xyloglucan". Journal of Experimental Botany. 40 (1): 1–11. doi:10.1093/jxb/40.1.1.
  35. Raven JA (July 1987). "The role of vacuoles". New Phytologist. 106 (3): 357–422. doi: 10.1111/j.1469-8137.1987.tb00149.x .
  36. Oparka K (2005). Plasmodesmata. Oxford, UK: Blackwell Publishing.
  37. Raven PH, Evert RF, Eichorm SE (1999). Biology of Plants. New York: W.H. Freeman.
  38. Silflow CD, Lefebvre PA (December 2001). "Assembly and motility of eukaryotic cilia and flagella. Lessons from Chlamydomonas reinhardtii". Plant Physiology. 127 (4): 1500–1507. doi:10.1104/pp.010807. PMC   1540183 . PMID   11743094.
  39. Deacon J (2005). Fungal Biology. Cambridge, Massachusetts: Blackwell Publishers. pp. 4 and passim. ISBN   978-1-4051-3066-0.
  40. Keeling PJ (October 2004). "Diversity and evolutionary history of plastids and their hosts". American Journal of Botany. 91 (10): 1481–1493. doi: 10.3732/ajb.91.10.1481 . PMID   21652304.
  41. Patterson DJ. "Amoebae: Protists Which Move and Feed Using Pseudopodia". Tree of Life Web Project. Archived from the original on 15 June 2010. Retrieved 12 November 2017.
  42. Gould SB, Tham WH, Cowman AF, McFadden GI, Waller RF (2008). "Alveolins, a new family of cortical proteins that define the protist infrakingdom Alveolata". Molecular Biology and Evolution. 25 (6): 1219–1230. doi:10.1093/molbev/msn070. PMID   18359944.
  43. Lane N (June 2011). "Energetics and genetics across the prokaryote-eukaryote divide". Biology Direct. 6 (1): 35. doi:10.1186/1745-6150-6-35. PMC   3152533 . PMID   21714941.
  44. Dacks J, Roger AJ (June 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.
  45. 1 2 Ramesh MA, Malik SB, Logsdon JM (January 2005). "A phylogenomic inventory of meiotic genes; evidence for sex in Giardia and an early eukaryotic origin of meiosis". Current Biology. 15 (2): 185–191. doi: 10.1016/j.cub.2005.01.003 . PMID   15668177. S2CID   17013247.
  46. 1 2 Malik SB, Pightling AW, Stefaniak LM, Schurko AM, Logsdon JM (August 2007). Hahn MW (ed.). "An expanded inventory of conserved meiotic genes provides evidence for sex in Trichomonas vaginalis". PLOS ONE. 3 (8): e2879. Bibcode:2008PLoSO...3.2879M. doi: 10.1371/journal.pone.0002879 . PMC   2488364 . PMID   18663385.
  47. Akopyants NS, Kimblin N, Secundino N, Patrick R, Peters N, Lawyer P, Dobson DE, Beverley SM, Sacks DL (April 2009). "Demonstration of genetic exchange during cyclical development of Leishmania in the sand fly vector". Science. 324 (5924): 265–268. Bibcode:2009Sci...324..265A. doi:10.1126/science.1169464. PMC   2729066 . PMID   19359589.
  48. Lahr DJ, Parfrey LW, Mitchell EA, Katz LA, Lara E (July 2011). "The chastity of amoebae: re-evaluating evidence for sex in amoeboid organisms". Proceedings: Biological Sciences. 278 (1715): 2081–2090. doi:10.1098/rspb.2011.0289. PMC   3107637 . PMID   21429931.
  49. Moore RT (1980). "Taxonomic proposals for the classification of marine yeasts and other yeast-like fungi including the smuts". Botanica Marina. 23: 361–373.
  50. Goldfuß (1818). "Ueber die Classification der Zoophyten" [On the classification of zoophytes]. Isis, Oder, Encyclopädische Zeitung von Oken (in German). 2 (6): 1008–1019. Archived from the original on 24 March 2019. Retrieved 15 March 2019. From p. 1008: "Erste Klasse. Urthiere. Protozoa." (First class. Primordial animals. Protozoa.) [Note: each column of each page of this journal is numbered; there are two columns per page.]
  51. Scamardella JM (1999). "Not plants or animals: a brief history of the origin of Kingdoms Protozoa, Protista and Protoctista" (PDF). International Microbiology . 2 (4): 207–221. PMID   10943416. Archived from the original (PDF) on 14 June 2011.
  52. 1 2 Rothschild LJ (1989). "Protozoa, Protista, Protoctista: what's in a name?". Journal of the History of Biology. 22 (2): 277–305. doi:10.1007/BF00139515. PMID   11542176. S2CID   32462158. Archived from the original on 4 February 2020. Retrieved 4 February 2020.
  53. 1 2 Spang A, Saw JH, Jørgensen SL, Zaremba-Niedzwiedzka K, Martijn J, Lind AE, van Eijk R, Schleper C, Guy L, Ettema TJ (May 2015). "Complex archaea that bridge the gap between prokaryotes and eukaryotes". Nature. 521 (7551): 173–179. Bibcode:2015Natur.521..173S. doi:10.1038/nature14447. PMC   4444528 . PMID   25945739.
  54. 1 2 Zaremba-Niedzwiedzka K, Caceres EF, Saw JH, Bäckström D, Juzokaite L, Vancaester E, Seitz KW, Anantharaman K, Starnawski P, Kjeldsen KU, Stott MB, Nunoura T, Banfield JF, Schramm A, Baker BJ, Spang A, Ettema TJ (January 2017). "Asgard archaea illuminate the origin of eukaryotic cellular complexity". Nature. 541 (7637): 353–358. Bibcode:2017Natur.541..353Z. doi:10.1038/nature21031. OSTI   1580084. PMID   28077874. S2CID   4458094. Archived from the original on 5 December 2019. Retrieved 28 June 2019.
  55. 1 2 Liu Y, Zhou Z, Pan J, Baker BJ, Gu JD, Li M (April 2018). "Comparative genomic inference suggests mixotrophic lifestyle for Thorarchaeota". The ISME Journal. 12 (4): 1021–1031. doi:10.1038/s41396-018-0060-x. PMC   5864231 . PMID   29445130.
  56. Adl SM, Simpson AG, Farmer MA, Andersen RA, Anderson OR, Barta JR, et al. (2005). "The new higher level classification of eukaryotes with emphasis on the taxonomy of protists". The Journal of Eukaryotic Microbiology. 52 (5): 399–451. doi: 10.1111/j.1550-7408.2005.00053.x . PMID   16248873. S2CID   8060916.
  57. Harper JT, Waanders E, Keeling PJ (January 2005). "On the monophyly of chromalveolates using a six-protein phylogeny of eukaryotes" (PDF). International Journal of Systematic and Evolutionary Microbiology. 55 (Pt 1): 487–496. doi: 10.1099/ijs.0.63216-0 . PMID   15653923. Archived from the original (PDF) on 17 December 2008.
  58. Parfrey LW, Barbero E, Lasser E, Dunthorn M, Bhattacharya D, Patterson DJ, Katz LA (December 2006). "Evaluating support for the current classification of eukaryotic diversity". PLOS Genetics. 2 (12): e220. doi:10.1371/journal.pgen.0020220. PMC   1713255 . PMID   17194223.
  59. Adl SM, Simpson AG, Lane CE, Lukeš J, Bass D, Bowser SS, et al. (September 2012). "The revised classification of eukaryotes" (PDF). The Journal of Eukaryotic Microbiology. 59 (5): 429–93. doi:10.1111/j.1550-7408.2012.00644.x. PMC   3483872 . PMID   23020233. Archived from the original (PDF) on 16 June 2016.
  60. 1 2 Burki F (May 2014). "The eukaryotic tree of life from a global phylogenomic perspective". Cold Spring Harbor Perspectives in Biology. 6 (5): a016147. doi:10.1101/cshperspect.a016147. PMC   3996474 . PMID   24789819.
  61. 1 2 Zhao S, Burki F, Bråte J, Keeling PJ, Klaveness D, Shalchian-Tabrizi K (June 2012). "Collodictyon – an ancient lineage in the tree of eukaryotes". Molecular Biology and Evolution. 29 (6): 1557–1568. doi:10.1093/molbev/mss001. PMC   3351787 . PMID   22319147.
  62. Romari K, Vaulot D (2004). "Composition and temporal variability of picoeukaryote communities at a coastal site of the English Channel from 18S rDNA sequences". Limnol Oceanogr. 49 (3): 784–798. Bibcode:2004LimOc..49..784R. doi: 10.4319/lo.2004.49.3.0784 . S2CID   86718111.
  63. Roger AJ, Simpson AG (February 2009). "Evolution: revisiting the root of the eukaryote tree". Current Biology. 19 (4): R165–67. doi: 10.1016/j.cub.2008.12.032 . PMID   19243692. S2CID   13172971.
  64. 1 2 Burki F, Roger AJ, Brown MW, Simpson AG (January 2020). "The New Tree of Eukaryotes". Trends in Ecology & Evolution. 35 (1): 43–55. doi: 10.1016/j.tree.2019.08.008 . PMID   31606140.
  65. Tovar J, Fischer A, Clark CG (June 1999). "The mitosome, a novel organelle related to mitochondria in the amitochondrial parasite Entamoeba histolytica". Molecular Microbiology. 32 (5): 1013–1021. doi: 10.1046/j.1365-2958.1999.01414.x . PMID   10361303. S2CID   22805284.
  66. Boxma B, de Graaf RM, van der Staay GW, van Alen TA, Ricard G, Gabaldón T, van Hoek AH, Moon-van der Staay SY, Koopman WJ, van Hellemond JJ, Tielens AG, Friedrich T, Veenhuis M, Huynen MA, Hackstein JH (March 2005). "An anaerobic mitochondrion that produces hydrogen" (PDF). Nature. 434 (7029): 74–79. Bibcode:2005Natur.434...74B. doi:10.1038/nature03343. PMID   15744302. S2CID   4401178. Archived (PDF) from the original on 24 January 2019. Retrieved 24 January 2019.
  67. 1 2 3 Jagus R, Bachvaroff TR, Joshi B, Place AR (2012). "Diversity of Eukaryotic Translational Initiation Factor eIF4E in Protists". Comparative and Functional Genomics. 2012: 1–21. doi: 10.1155/2012/134839 . PMC   3388326 . PMID   22778692.
  68. Burki F, Kaplan M, Tikhonenkov DV, Zlatogursky V, Minh BQ, Radaykina LV, Smirnov A, Mylnikov AP, Keeling PJ (January 2016). "Untangling the early diversification of eukaryotes: a phylogenomic study of the evolutionary origins of Centrohelida, Haptophyta and Cryptista". Proceedings: Biological Sciences. 283 (1823): 20152802. doi:10.1098/rspb.2015.2802. PMC   4795036 . PMID   26817772.
  69. Janouškovec J, Tikhonenkov DV, Burki F, Howe AT, Rohwer FL, Mylnikov AP, Keeling PJ (December 2017). "A New Lineage of Eukaryotes Illuminates Early Mitochondrial Genome Reduction" (PDF). Current Biology. 27 (23): 3717–24.e5. doi: 10.1016/j.cub.2017.10.051 . PMID   29174886. S2CID   37933928. Archived (PDF) from the original on 27 April 2019. Retrieved 2 September 2019.
  70. Bodył A (February 2018). "Did some red alga-derived plastids evolve via kleptoplastidy? A hypothesis". Biological Reviews of the Cambridge Philosophical Society. 93 (1): 201–222. doi:10.1111/brv.12340. PMID   28544184. S2CID   24613863.
  71. Lax G, Eglit Y, Eme L, Bertrand EM, Roger AJ, Simpson AG (November 2018). "Hemimastigophora is a novel supra-kingdom-level lineage of eukaryotes". Nature. 564 (7736): 410–414. Bibcode:2018Natur.564..410L. doi:10.1038/s41586-018-0708-8. PMID   30429611. S2CID   205570993.
  72. Adl SM, Bass D, Lane CE, Lukeš J, Schoch CL, Smirnov A, et al. (January 2019). "Revisions to the Classification, Nomenclature, and Diversity of Eukaryotes". The Journal of Eukaryotic Microbiology. 66 (1): 4–119. doi:10.1111/jeu.12691. PMC   6492006 . PMID   30257078.
  73. Schön ME, Zlatogursky VV, Singh RP, Poirier C, Wilken S, Mathur V, et al. (2021). "Picozoa are archaeplastids without plastid". Nature Communications. 12 (1): 6651. bioRxiv   10.1101/2021.04.14.439778 . doi:10.1038/s41467-021-26918-0. PMC   8599508 . PMID   34789758. S2CID   233328713.
  74. Burki F, Shalchian-Tabrizi K, Minge M, Skjaeveland A, Nikolaev SI, Jakobsen KS, Pawlowski J (August 2007). Butler G (ed.). "Phylogenomics reshuffles the eukaryotic supergroups". PLOS ONE. 2 (8): e790. Bibcode:2007PLoSO...2..790B. doi: 10.1371/journal.pone.0000790 . PMC   1949142 . PMID   17726520.
  75. 1 2 Kim E, Graham LE (July 2008). Redfield RJ (ed.). "EEF2 analysis challenges the monophyly of Archaeplastida and Chromalveolata". PLOS ONE. 3 (7): e2621. Bibcode:2008PLoSO...3.2621K. doi: 10.1371/journal.pone.0002621 . PMC   2440802 . PMID   18612431.
  76. Baurain D, Brinkmann H, Petersen J, Rodríguez-Ezpeleta N, Stechmann A, Demoulin V, Roger AJ, Burger G, Lang BF, Philippe H (July 2010). "Phylogenomic evidence for separate acquisition of plastids in cryptophytes, haptophytes, and stramenopiles". Molecular Biology and Evolution. 27 (7): 1698–1709. doi: 10.1093/molbev/msq059 . PMID   20194427.
  77. Burki F, Okamoto N, Pombert JF, Keeling PJ (June 2012). "The evolutionary history of haptophytes and cryptophytes: phylogenomic evidence for separate origins". Proceedings: Biological Sciences. 279 (1736): 2246–2254. doi:10.1098/rspb.2011.2301. PMC   3321700 . PMID   22298847.
  78. Cavalier-Smith T (2003). "Protist phylogeny and the high-level classification of Protozoa". European Journal of Protistology. 39 (4): 338–348. doi:10.1078/0932-4739-00002. S2CID   84403388.
  79. Burki F, Pawlowski J (October 2006). "Monophyly of Rhizaria and multigene phylogeny of unicellular bikonts". Molecular Biology and Evolution. 23 (10): 1922–1930. doi: 10.1093/molbev/msl055 . PMID   16829542.
  80. Ren R, Sun Y, Zhao Y, Geiser D, Ma H, Zhou X (September 2016). "Phylogenetic Resolution of Deep Eukaryotic and Fungal Relationships Using Highly Conserved Low-Copy Nuclear Genes". Genome Biology and Evolution. 8 (9): 2683–2701. doi:10.1093/gbe/evw196. PMC   5631032 . PMID   27604879.
  81. 1 2 3 Cavalier-Smith T (January 2018). "Kingdom Chromista and its eight phyla: a new synthesis emphasising periplastid protein targeting, cytoskeletal and periplastid evolution, and ancient divergences". Protoplasma. 255 (1): 297–357. doi:10.1007/s00709-017-1147-3. PMC   5756292 . PMID   28875267.
  82. Derelle R, Torruella G, Klimeš V, Brinkmann H, Kim E, Vlček Č, Lang BF, Eliáš M (February 2015). "Bacterial proteins pinpoint a single eukaryotic root". Proceedings of the National Academy of Sciences of the United States of America. 112 (7): E693–699. Bibcode:2015PNAS..112E.693D. doi: 10.1073/pnas.1420657112 . PMC   4343179 . PMID   25646484.
  83. Yang J, Harding T, Kamikawa R, Simpson AG, Roger AJ (May 2017). "Mitochondrial Genome Evolution and a Novel RNA Editing System in Deep-Branching Heteroloboseids". Genome Biology and Evolution. 9 (5): 1161–1174. doi:10.1093/gbe/evx086. PMC   5421314 . PMID   28453770.
  84. Cavalier-Smith T, Fiore-Donno AM, Chao E, Kudryavtsev A, Berney C, Snell EA, Lewis R (February 2015). "Multigene phylogeny resolves deep branching of Amoebozoa". Molecular Phylogenetics and Evolution. 83: 293–304. doi: 10.1016/j.ympev.2014.08.011 . PMID   25150787.
  85. Torruella G, de Mendoza A, Grau-Bové X, Antó M, Chaplin MA, del Campo J, Eme L, Pérez-Cordón G, Whipps CM, Nichols KM, Paley R, Roger AJ, Sitjà-Bobadilla A, Donachie S, Ruiz-Trillo I (September 2015). "Phylogenomics Reveals Convergent Evolution of Lifestyles in Close Relatives of Animals and Fungi". Current Biology. 25 (18): 2404–2410. doi: 10.1016/j.cub.2015.07.053 . PMID   26365255.
  86. 1 2 López-García P, Eme L, Moreira D (December 2017). "Symbiosis in eukaryotic evolution". Journal of Theoretical Biology. 434: 20–33. Bibcode:2017JThBi.434...20L. doi:10.1016/j.jtbi.2017.02.031. PMC   5638015 . PMID   28254477.
  87. Ponce-Toledo RI, Deschamps P, López-García P, Zivanovic Y, Benzerara K, Moreira D (February 2017). "An Early-Branching Freshwater Cyanobacterium at the Origin of Plastids". Current Biology. 27 (3): 386–391. doi:10.1016/j.cub.2016.11.056. PMC   5650054 . PMID   28132810.
  88. de Vries J, Archibald JM (February 2017). "Endosymbiosis: Did Plastids Evolve from a Freshwater Cyanobacterium?". Current Biology. 27 (3): R103–105. doi: 10.1016/j.cub.2016.12.006 . PMID   28171752.
  89. 1 2 Cavalier-Smith T (June 2010). "Kingdoms Protozoa and Chromista and the eozoan root of the eukaryotic tree". Biology Letters. 6 (3): 342–345. doi:10.1098/rsbl.2009.0948. PMC   2880060 . PMID   20031978.
  90. 1 2 Cavalier-Smith T (May 2013). "Early evolution of eukaryote feeding modes, cell structural diversity, and classification of the protozoan phyla Loukozoa, Sulcozoa, and Choanozoa". European Journal of Protistology. 49 (2): 115–178. doi:10.1016/j.ejop.2012.06.001. PMID   23085100.
  91. 1 2 Cavalier-Smith T, Chao EE, Snell EA, Berney C, Fiore-Donno AM, Lewis R (December 2014). "Multigene eukaryote phylogeny reveals the likely protozoan ancestors of opisthokonts (animals, fungi, choanozoans) and Amoebozoa". Molecular Phylogenetics and Evolution. 81: 71–85. doi: 10.1016/j.ympev.2014.08.012 . PMID   25152275.
  92. Cavalier-Smith T, Chao EE, Lewis R (April 2018). "Multigene phylogeny and cell evolution of chromist infrakingdom Rhizaria: contrasting cell organisation of sister phyla Cercozoa and Retaria". Protoplasma. 255 (5): 1517–1574. doi:10.1007/s00709-018-1241-1. PMC   6133090 . PMID   29666938.
  93. He D, Fiz-Palacios O, Fu CJ, Fehling J, Tsai CC, Baldauf SL (February 2014). "An alternative root for the eukaryote tree of life". Current Biology. 24 (4): 465–470. doi: 10.1016/j.cub.2014.01.036 . PMID   24508168.
  94. Cox CJ, Foster PG, Hirt RP, Harris SR, Embley TM (December 2008). "The archaebacterial origin of eukaryotes". Proceedings of the National Academy of Sciences of the United States of America. 105 (51): 20356–20361. Bibcode:2008PNAS..10520356C. doi: 10.1073/pnas.0810647105 . PMC   2629343 . PMID   19073919.
  95. Ciccarelli FD, Doerks T, von Mering C, Creevey CJ, Snel B, Bork P (March 2006). "Toward automatic reconstruction of a highly resolved tree of life". Science. 311 (5765): 1283–1287. Bibcode:2006Sci...311.1283C. CiteSeerX . doi:10.1126/science.1123061. PMID   16513982. S2CID   1615592.
  96. 1 2 Hug LA, Baker BJ, Anantharaman K, Brown CT, Probst AJ, Castelle CJ, Butterfield CN, Hernsdorf AW, Amano Y, Ise K, Suzuki Y, Dudek N, Relman DA, Finstad KM, Amundson R, Thomas BC, Banfield JF (April 2016). "A new view of the tree of life". Nature Microbiology. 1 (5): 16048. doi: 10.1038/nmicrobiol.2016.48 . PMID   27572647.
  97. O'Malley MA, Leger MM, Wideman JG, Ruiz-Trillo I (March 2019). "Concepts of the last eukaryotic common ancestor". Nature Ecology & Evolution. Springer Science and Business Media LLC. 3 (3): 338–344. doi:10.1038/s41559-019-0796-3. hdl: 10261/201794 . PMID   30778187. S2CID   67790751.
  98. 1 2 Brocks JJ, Logan GA, Buick R, Summons RE (August 1999). "Archean molecular fossils and the early rise of eukaryotes". Science. 285 (5430): 1033–1036. Bibcode:1999Sci...285.1033B. CiteSeerX . doi:10.1126/science.285.5430.1033. PMID   10446042.
  99. 1 2 Hartman H, Fedorov A (February 2002). "The origin of the eukaryotic cell: a genomic investigation". Proceedings of the National Academy of Sciences of the United States of America. 99 (3): 1420–5. Bibcode:2002PNAS...99.1420H. doi: 10.1073/pnas.032658599 . PMC   122206 . PMID   11805300.
  100. Knoll AH, Javaux EJ, Hewitt D, Cohen P (June 2006). "Eukaryotic organisms in Proterozoic oceans". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 361 (1470): 1023–1038. doi:10.1098/rstb.2006.1843. PMC   1578724 . PMID   16754612.
  101. Retallack GJ, Krull ES, Thackray GD, Parkinson DH (2013). "Problematic urn-shaped fossils from a Paleoproterozoic (2.2 Ga) paleosol in South Africa". Precambrian Research. 235: 71–87. Bibcode:2013PreR..235...71R. doi:10.1016/j.precamres.2013.05.015.
  102. El Albani A, Bengtson S, Canfield DE, Bekker A, Macchiarelli R, Mazurier A, Hammarlund EU, Boulvais P, Dupuy JJ, Fontaine C, Fürsich FT, Gauthier-Lafaye F, Janvier P, Javaux E, Ossa FO, Pierson-Wickmann AC, Riboulleau A, Sardini P, Vachard D, Whitehouse M, Meunier A (July 2010). "Large colonial organisms with coordinated growth in oxygenated environments 2.1 Gyr ago". Nature. 466 (7302): 100–104. Bibcode:2010Natur.466..100A. doi:10.1038/nature09166. PMID   20596019. S2CID   4331375.
  103. Bengtson S, Belivanova V, Rasmussen B, Whitehouse M (May 2009). "The controversial "Cambrian" fossils of the Vindhyan are real but more than a billion years older". Proceedings of the National Academy of Sciences of the United States of America. 106 (19): 7729–7734. Bibcode:2009PNAS..106.7729B. doi: 10.1073/pnas.0812460106 . PMC   2683128 . PMID   19416859.
  104. Ward P (9 February 2008). "Mass extinctions: the microbes strike back". New Scientist . pp. 40–43. Archived from the original on 8 July 2008. Retrieved 27 August 2017.
  105. French KL, Hallmann C, Hope JM, Schoon PL, Zumberge JA, Hoshino Y, Peters CA, George SC, Love GD, Brocks JJ, Buick R, Summons RE (May 2015). "Reappraisal of hydrocarbon biomarkers in Archean rocks". Proceedings of the National Academy of Sciences of the United States of America. 112 (19): 5915–5920. Bibcode:2015PNAS..112.5915F. doi: 10.1073/pnas.1419563112 . PMC   4434754 . PMID   25918387.
  106. Brocks JJ, Jarrett AJ, Sirantoine E, Hallmann C, Hoshino Y, Liyanage T (August 2017). "The rise of algae in Cryogenian oceans and the emergence of animals". Nature. 548 (7669): 578–581. Bibcode:2017Natur.548..578B. doi:10.1038/nature23457. PMID   28813409. S2CID   205258987.
  107. Gold DA, Caron A, Fournier GP, Summons RE (March 2017). "Paleoproterozoic sterol biosynthesis and the rise of oxygen". Nature. 543 (7645): 420–423. Bibcode:2017Natur.543..420G. doi:10.1038/nature21412. hdl: 1721.1/128450 . PMID   28264195. S2CID   205254122.
  108. Wei JH, Yin X, Welander PV (24 June 2016). "Sterol Synthesis in Diverse Bacteria". Frontiers in Microbiology. 7: 990. doi: 10.3389/fmicb.2016.00990 . PMC   4919349 . PMID   27446030.
  109. Hoshino Y, Gaucher EA (June 2021). "Evolution of bacterial steroid biosynthesis and its impact on eukaryogenesis". Proceedings of the National Academy of Sciences of the United States of America. 118 (25): e2101276118. Bibcode:2021PNAS..11801276H. doi: 10.1073/pnas.2101276118 . PMC   8237579 . PMID   34131078.
  110. Isson TT, Love GD, Dupont CL, Reinhard CT, Zumberge AJ, Asael D, et al. (June 2018). "Tracking the rise of eukaryotes to ecological dominance with zinc isotopes". Geobiology. 16 (4): 341–352. doi: 10.1111/gbi.12289 . PMID   29869832.
  111. Yoshikawa G, Blanc-Mathieu R, Song C, Kayama Y, Mochizuki T, Murata K, Ogata H, Takemura M (April 2019). "Medusavirus, a Novel Large DNA Virus Discovered from Hot Spring Water". Journal of Virology. 93 (8). doi:10.1128/JVI.02130-18. PMC   6450098 . PMID   30728258. Archived from the original on 30 April 2019.
  112. Martin W (December 2005). "Archaebacteria (Archaea) and the origin of the eukaryotic nucleus". Current Opinion in Microbiology. 8 (6): 630–637. doi:10.1016/j.mib.2005.10.004. PMID   16242992.
  113. Takemura M (May 2001). "Poxviruses and the origin of the eukaryotic nucleus". Journal of Molecular Evolution. 52 (5): 419–425. Bibcode:2001JMolE..52..419T. doi:10.1007/s002390010171. PMID   11443345. S2CID   21200827.
  114. Bell PJ (September 2001). "Viral eukaryogenesis: was the ancestor of the nucleus a complex DNA virus?". Journal of Molecular Evolution. 53 (3): 251–256. Bibcode:2001JMolE..53..251L. doi: 10.1007/s002390010215 . PMID   11523012. S2CID   20542871.
  115. Wächtershäuser G (January 2003). "From pre-cells to Eukarya – a tale of two lipids". Molecular Microbiology. 47 (1): 13–22. doi: 10.1046/j.1365-2958.2003.03267.x . PMID   12492850. S2CID   37944519.
  116. Wächtershäuser G (October 2006). "From volcanic origins of chemoautotrophic life to Bacteria, Archaea and Eukarya". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 361 (1474): 1787–1806, discussion 1806–1808. doi:10.1098/rstb.2006.1904. PMC   1664677 . PMID   17008219.
  117. Lane N (2016). The Vital Question: Why is Life the Way it is? (paperback ed.). Profile Books. pp. 157–91. ISBN   978-1-781-25037-2.
  118. Egel R (January 2012). "Primal eukaryogenesis: on the communal nature of precellular States, ancestral to modern life". Life. Vol. 2, no. 1. pp. 170–212. doi: 10.3390/life2010170 . PMC   4187143 . PMID   25382122.
  119. 1 2 Harish A, Tunlid A, Kurland CG (August 2013). "Rooted phylogeny of the three superkingdoms". Biochimie. 95 (8): 1593–1604. doi:10.1016/j.biochi.2013.04.016. PMID   23669449.
  120. 1 2 Harish A, Kurland CG (July 2017). "Akaryotes and Eukaryotes are independent descendants of a universal common ancestor". Biochimie. 138: 168–183. doi:10.1016/j.biochi.2017.04.013. PMID   28461155.
  121. 1 2 Imachi H, Nobu MK, Nakahara N, Morono Y, Ogawara M, Takaki Y, et al. (January 2020). "Isolation of an archaeon at the prokaryote-eukaryote interface". Nature. 577 (7791): 519–525. Bibcode:2020Natur.577..519I. doi: 10.1038/s41586-019-1916-6 . PMC   7015854 . PMID   31942073.
  122. Da Cunha V, Gaia M, Gadelle D, Nasir A, Forterre P (June 2017). "Lokiarchaea are close relatives of Euryarchaeota, not bridging the gap between prokaryotes and eukaryotes". PLOS Genetics. 13 (6): e1006810. doi:10.1371/journal.pgen.1006810. PMC   5484517 . PMID   28604769.
  123. Harish A, Kurland CG (July 2017). "Empirical genome evolution models root the tree of life". Biochimie. 138: 137–155. doi:10.1016/j.biochi.2017.04.014. PMID   28478110.
  124. Spang A, Eme L, Saw JH, Caceres EF, Zaremba-Niedzwiedzka K, Lombard J, et al. (March 2018). "Asgard archaea are the closest prokaryotic relatives of eukaryotes". PLOS Genetics. 14 (3): e1007080. doi:10.1371/journal.pgen.1007080. PMC   5875740 . PMID   29596421.
  125. MacLeod F, Kindler GS, Wong HL, Chen R, Burns BP (2019). "Asgard archaea: Diversity, function, and evolutionary implications in a range of microbiomes". AIMS Microbiology. 5 (1): 48–61. doi:10.3934/microbiol.2019.1.48. PMC   6646929 . PMID   31384702.
  126. Zimmer C (15 January 2020). "This Strange Microbe May Mark One of Life's Great Leaps – A organism living in ocean muck offers clues to the origins of the complex cells of all animals and plants". The New York Times . Archived from the original on 16 January 2020. Retrieved 18 January 2020.
  127. Jékely G (2007). "Origin of Eukaryotic Endomembranes: A Critical Evaluation of Different Model Scenarios". Eukaryotic Membranes and Cytoskeleton. Advances in Experimental Medicine and Biology. Vol. 607. New York, N.Y. : Springer Science+Business Media; Austin, Tex. : Landes Bioscience. pp.  38–51. doi:10.1007/978-0-387-74021-8_3. ISBN   978-0-387-74020-1. PMID   17977457.
  128. Cavalier-Smith T (March 2002). "The phagotrophic origin of eukaryotes and phylogenetic classification of Protozoa". International Journal of Systematic and Evolutionary Microbiology. 52 (Pt 2): 297–354. doi:10.1099/00207713-52-2-297. PMID   11931142. Archived from the original on 29 July 2017. Retrieved 10 June 2008.
  129. 1 2 Martin W, Müller M (March 1998). "The hydrogen hypothesis for the first eukaryote". Nature. 392 (6671): 37–41. Bibcode:1998Natur.392...37M. doi:10.1038/32096. PMID   9510246. S2CID   338885.
  130. Pisani D, Cotton JA, McInerney JO (August 2007). "Supertrees disentangle the chimerical origin of eukaryotic genomes". Molecular Biology and Evolution. 24 (8): 1752–1760. doi: 10.1093/molbev/msm095 . PMID   17504772.
  131. Brueckner J, Martin WF (April 2020). "Bacterial Genes Outnumber Archaeal Genes in Eukaryotic Genomes". Genome Biology and Evolution. 12 (4): 282–292. doi: 10.1093/gbe/evaa047 . PMC   7151554 . PMID   32142116.
  132. 1 2 Latorre A, Durban A, Moya A, Pereto J (2011). "The role of symbiosis in eukaryotic evolution". In Gargaud M, López-Garcìa P, 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.
  133. Ayala J (April 1994). "Transport and internal organization of membranes: vesicles, membrane networks and GTP-binding proteins". Journal of Cell Science. 107 (Pt 4): 753–763. doi:10.1242/jcs.107.4.753. PMID   8056835. Archived from the original on 29 April 2012. Retrieved 27 March 2013.
  134. Martin WF. "The Origin of Mitochondria". Scitable. Nature education. Archived from the original on 16 June 2013. Retrieved 27 March 2013. That is, it entails a corollary assumption (an add–on to the theory that brings it into agreement with available observations) that all descendants of the initial host lineage, except the one that acquired mitochondria, went extinct.
  135. Dacks JB, Field MC (August 2018). "Evolutionary origins and specialisation of membrane transport". Current Opinion in Cell Biology. 53: 70–76. doi:10.1016/ PMC   6141808 . PMID   29929066.
  136. Martijn J, Vosseberg J, Guy L, Offre P, Ettema TJ (May 2018). "Deep mitochondrial origin outside the sampled alphaproteobacteria". Nature. 557 (7703): 101–105. Bibcode:2018Natur.557..101M. doi:10.1038/s41586-018-0059-5. PMID   29695865. S2CID   13740626. Archived from the original on 21 April 2019. Retrieved 21 April 2019.
  137. Baum DA, Baum B (October 2014). "An inside-out origin for the eukaryotic cell". BMC Biology. 12: 76. doi:10.1186/s12915-014-0076-2. PMC   4210606 . PMID   25350791.
  138. Brouwers L (12 April 2013). "How genetic plunder transformed a microbe into a pink, salt-loving scavenger". Scientific American. 109 (50): 20537–20542. Archived from the original on 10 October 2018. Retrieved 21 April 2019.
  139. Wilcox C (9 April 2019). "Rethinking the ancestry of the eukaryotes". Quanta Magazine. Archived from the original on 9 May 2019. Retrieved 8 May 2019.
  140. McCutcheon JP (October 2021). "The Genomics and Cell Biology of Host-Beneficial Intracellular Infections". Annual Review of Cell and Developmental Biology. 37 (1): 115–142. doi:10.1146/annurev-cellbio-120219-024122. PMID   34242059. S2CID   235786110.
  141. Saygin D, Tabib T, Bittar HE, Valenzi E, Sembrat J, Chan SY, et al. (8 June 2022). "Transcriptional profiling of lung cell populations in idiopathic pulmonary arterial hypertension". Pulmonary Circulation. 10 (1). doi: 10.1146/knowable-060822-2 . PMID   32166015.
  142. Pittis AA, Gabaldón T (March 2016). "Late acquisition of mitochondria by a host with chimaeric prokaryotic ancestry". Nature. 531 (7592): 101–104. Bibcode:2016Natur.531..101P. doi:10.1038/nature16941. PMC   4780264 . PMID   26840490.
  143. Burton ZF (1 August 2017). Evolution since coding: Cradles, halos, barrels, and wings. Academic Press. ISBN   978-0-12-813034-6. Archived from the original on 24 March 2019. Retrieved 27 November 2018.
  144. Martin WF, Roettger M, Ku C, Garg SG, Nelson-Sathi S, Landan G (February 2017). "Late mitochondrial origin is an artifact". Genome Biology and Evolution. 9 (2): 373–379. doi:10.1093/gbe/evx027. PMC   5516564 . PMID   28199635.

PD-icon.svg This article incorporates public domain material from Science Primer. NCBI. Archived from the original on 8 December 2009.