The opisthokonts () are a broad group of

eukaryote Eukaryotes () are organisms whose cells have a nucleus. 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. Bacter ...

s, including both the

animal Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage ...

and

fungus A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately fr ...

kingdoms. The opisthokonts, previously called the "Fungi/Metazoa group", are generally recognized as a

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English ter ...

. Opisthokonts together with

Apusomonadida The Apusomonadida are a group of protozoan zooflagellates that glide on surfaces, and mostly consume prokaryotes. They are of particular evolutionary interest because they appear to be the sister group to the Opisthokonts, the clade that inclu ...

and

Breviata ''Breviata anathema'' is a single-celled flagellate amoeboid eukaryote, previously studied under the name '' Mastigamoeba invertens''. The cell lacks mitochondria but has remnant mitochondrial genes, and possesses an organelle believed to be a modi ...

comprise the larger clade

Obazoa Obazoa (Brown et al., 2013) is a proposed sister clade of Amoebozoa (which together form Amorphea). Obazoa is composed of Breviatea, Apusomonadida and Opisthokonta. The term Obazoa is based on the OBA acronym for Opisthokonta, Breviatea, and A ...

Flagella and other characteristics

A common characteristic of opisthokonts is that

flagellate A flagellate is a cell or organism with one or more whip-like appendages called flagella. The word ''flagellate'' also describes a particular construction (or level of organization) characteristic of many prokaryotes and eukaryotes and thei ...

cells, such as the

sperm Sperm is the male reproductive cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as a flagellum, ...

of most animals and the

spores In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, ...

of the

chytrid Chytridiomycota are a division of zoosporic organisms in the kingdom Fungi, informally known as chytrids. The name is derived from the Ancient Greek ('), meaning "little pot", describing the structure containing unreleased zoöspores. Chytrid ...

fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately fr ...

, propel themselves with a single ''posterior'' flagellum. It is this feature that gives the group its name. In contrast, flagellate cells in other eukaryote groups propel themselves with one or more ''anterior'' flagella. However, in some opisthokont groups, including most of the fungi, flagellate cells have been lost. Opisthokont characteristics include synthesis of extracellular chitin in exoskeleton, cyst/spore wall, or cell wall of filamentous growth and hyphae; the extracellular digestion of substrates with osmotrophic absorption of nutrients; and other cell biosynthetic and metabolic pathways. Genera at the base of each clade are amoeboid and phagotrophic.

History

The close relationship between animals and fungi was suggested by

Thomas Cavalier-Smith Thomas (Tom) Cavalier-Smith, FRS, FRSC, NERC Professorial Fellow (21 October 1942 – 19 March 2021), was a professor of evolutionary biology in the Department of Zoology, at the University of Oxford. His research has led to discov ...

in 1987, who used the informal name opisthokonta (the formal name has been used for the

chytrids Chytridiomycota are a division of zoosporic organisms in the kingdom Fungi, informally known as chytrids. The name is derived from the Ancient Greek ('), meaning "little pot", describing the structure containing unreleased zoöspores. Chytr ...

by Copeland in 1956), and was supported by later genetic studies. Early phylogenies placed fungi near the

plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae excl ...

s and other groups that have

mitochondria A mitochondrion (; ) is an organelle found in the cells of most Eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is used ...

with flat

cristae A crista (; plural cristae) is a fold in the inner membrane of a mitochondrion. The name is from the Latin for ''crest'' or ''plume'', and it gives the inner membrane its characteristic wrinkled shape, providing a large amount of surface area fo ...

, but this character varies. More recently, it has been said that holozoa (animals) and holomycota (fungi) are much more closely related to each other than either is to plants, because opisthokonts have a triple fusion of

carbamoyl phosphate synthetase Carbamoyl phosphate synthetase catalyzes the ATP-dependent synthesis of carbamoyl phosphate from glutamine () or ammonia () and bicarbonate. This enzyme catalyzes the reaction of ATP and bicarbonate to produce carboxy phosphate and ADP. Carb ...

, dihydroorotase, and aspartate carbamoyltransferase that is not present in plants, and plants have a fusion of

thymidylate synthase Thymidylate synthase (TS) () is an enzyme that catalyzes the conversion of deoxyuridine monophosphate (dUMP) to deoxythymidine monophosphate (dTMP). Thymidine is one of the nucleotides in DNA. With inhibition of TS, an imbalance of deoxynucle ...

and

dihydrofolate reductase Dihydrofolate reductase, or DHFR, is an enzyme that reduces dihydrofolic acid to tetrahydrofolic acid, using NADPH as an electron donor, which can be converted to the kinds of tetrahydrofolate cofactors used in 1-carbon transfer chemistry ...

not present in the opisthokonts. Animals and fungi are also more closely related to amoebas than to plants, and plants are more closely related to the

SAR supergroup The SAR supergroup, also just SAR or Harosa, is a clade that includes stramenopiles ( heterokonts), alveolates, and Rhizaria. The name is an acronym derived from the first letters of each of these clades; it has been alternatively spelled "RAS". ...

of protists than to animals or fungi. Animals and fungi are both heterotrophs, unlike plants, and while fungi are sessile like plants, there are also sessile animals. Cavalier-Smith and Stechmann argue that the uniciliate eukaryotes such as opisthokonts and

Amoebozoa Amoebozoa is a major taxonomic group containing about 2,400 described species of amoeboid protists, often possessing blunt, fingerlike, lobose pseudopods and tubular mitochondrial cristae. In traditional and currently no longer supported c ...

, collectively called unikonts, split off from the other biciliate eukaryotes, called

bikont A bikont ("two flagella") is any of the eukaryotic organisms classified in the group Bikonta. Many single-celled members of the group, and the presumed ancestor, have two flagella. Enzymes Another shared trait of bikonts is the fusion of two ge ...

s, shortly after they

evolved Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variati ...

Taxonomy

Opisthokonts are divided into

Holomycota Holomycota or Nucletmycea are a basal Opisthokont clade as sister of the Holozoa. It consists of the Cristidiscoidea and the kingdom Fungi. The position of nucleariids, unicellular free-living phagotrophic amoebae, as the earliest lineage of Hol ...

or Nucletmycea (fungi and all organisms more closely related to fungi than to animals) and

Holozoa Holozoa is a group of organisms that includes animals and their closest single-celled relatives, but excludes fungi. ''Holozoa'' is also an old name for the tunicate genus ''Distaplia''.'' Because Holozoa is a clade including all organisms mor ...

(animals and all organisms more closely related to animals than to fungi); no opisthokonts basal to the Holomycota/Holozoa split have yet been identified. The Opisthokonts was largely resolved by Torriella et al. Holomycota and Holozoa are composed of the following groups. *

(Fungus-like) **

Fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately fr ...

*** Includes: ****

s (flagellated, zoosporic fungi) **** ''

Fonticula ''Fonticula'' is a genus of cellular slime mold which forms a fruiting body in a volcano shape. As long ago as 1979 it has been known to not have a close relationship with either the Dictyosteliida or the Acrasidae, the two well-established gro ...

'' ( more recent work considers this to be part of

Cristidiscoidea Cristidiscoidea or Nucleariae is a proposed basal holomycota clade in which Fonticula and Nucleariida emerged, as sister of the fungi. Since it is close to the divergence between the main lineages of fungi and animals, the study of Cristidiscoi ...

, a sister group to the fungi) **** '' Hyaloraphidium'' (previously thought to be a

green alga The green algae (singular: green alga) are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/Streptophyta. The land plants (Embryophytes) have emerged deep in the Charophyte alga as ...

, now considered a fungus) ****

microsporidia Microsporidia are a group of spore-forming unicellular parasites. These spores contain an extrusion apparatus that has a coiled polar tube ending in an anchoring disc at the apical part of the spore. They were once considered protozoans or pr ...

(previously thought to be

apicomplexia The Apicomplexa (also called Apicomplexia) are a large phylum of parasitic alveolates. Most of them possess a unique form of organelle that comprises a type of non-photosynthetic plastid called an apicoplast, and an apical complex structure. The ...

) **** Nucleariida ( more recent work considers this to be part of

, a sister group to the fungi) *** Excludes: **** labyrinthulomycetes (slime nets) (now included in the

) **** myxomycetes (now included in

amoebozoa Amoebozoa is a major taxonomic group containing about 2,400 described species of amoeboid protists, often possessing blunt, fingerlike, lobose pseudopods and tubular mitochondrial cristae. In traditional and currently no longer supported c ...

ns) **** oomycetes (water molds) (now included in the

) **

Rozellida Cryptomycota ('hidden fungi'), Rozellida, or Rozellomycota are a clade of micro-organisms that are either fungi or a sister group to fungi. They differ from classical fungi in that they lack chitinous cell walls at any trophic stage in their l ...

(placement uncertain) *

(Animal-like) ** ''

Corallochytrium ''Corallochytrium'' belongs to the class of Corallochytrea within Teretosporea and is a sister group to Ichthyosporea. ''C. limacisporum'' is the only species of Corallochytrium known so far. It was first discovered and named in the Arabian Se ...

'' (formerly considered a

Heterokont Heterokonts are a group of protists (formally referred to as Heterokonta, Heterokontae or Heterokontophyta). The group is a major line of eukaryotes. Most are algae, ranging from the giant multicellular kelp to the unicellular diatoms, which a ...

) **

Filozoa The Filozoa are a monophyletic grouping within the Opisthokonta. They include animals and their nearest unicellular relatives (those organisms which are more closely related to animals than to fungi or Mesomycetozoa). Three groups are current ...

***

Animalia Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in ...

(including

myxozoa Myxozoa (etymology: Greek: μύξα ''myxa'' "slime" or "mucus" + thematic vowel o + ζῷον ''zoon'' "animal") is a subphylum of aquatic cnidarian animals – all obligate parasites. It contains the smallest animals ever known to have lived. O ...

) *** Choanoflagellata (flagellates formerly included in protozoa) ***

Filasterea Filasterea is a proposed basal Filozoan clade that includes '' Ministeria'' and '' Capsaspora''. It is a sister clade to the Choanozoa in which the Choanoflagellatea and Animals appeared. Originally proposed by Shalchian-Tabrizi et al. in 2008, b ...

** Mesomycetozoea ***

Amoebidiales Amoebidiidae is a family of single-celled eukaryotes, previously thought to be zygomycete fungi belonging to the clasTrichomycetes but molecular phylogenetic analysesBenny, G. L., and O'Donnell, K. 2000. ''Amoebidium parasiticum'' is a protozoan ...

(formerly considered trichomycetes) ***

Dermocystida Dermocystida is an order of parasitic eukaryotes. Taxonomy * Family Rhinosporidiaceae Mendoza et al. 2001 ** Genus '' Amphibiocystidium'' Pascolini et al. 2003 ** Genus '' Chromosphaera'' Grau-Bové et al. 2017 ** Genus ''Dermocystidium ''De ...

(formerly considered parasitic fungi or sporozoans) *** Eccrinales (formerly considered fungi) ***

Ichthyophonida Ichthyophonida is an order of parasitic eukaryotes. Taxonomy Members of Ichthyophonida include: * Amoebidiaceae **''Amoebidium'' ***'' Amoebidium appalachense'' ***''Amoebidium parasiticum'' * Paramoebidiidae **''Paramoebidium'' ***'' Param ...

(formerly considered parasitic fungi ''incertae sedis'')

Phylogeny

The choanoflagellates have a circular mitochondrial DNA genome with long intergenic regions. This is four times as large as animal mitochondrial genomes and contains twice as many protein coding genes. ''

'' seem likely to be more closely related to the fungi than to the animals on the basis of the presence of

ergosterol Ergosterol (ergosta-5,7,22-trien-3β-ol) is a sterol found in cell membranes of fungi and protozoa, serving many of the same functions that cholesterol serves in animal cells. Because many fungi and protozoa cannot survive without ergosterol, t ...

in their membranes and being capable of synthesis of

lysine Lysine (symbol Lys or K) is an α-amino acid that is a precursor to many proteins. It contains an α-amino group (which is in the protonated form under biological conditions), an α-carboxylic acid group (which is in the deprotonated − ...

via the AAA pathway. The ichthyosporeans have a two amino acid deletion in their EEF1A1 gene that is considered characteristic of fungi. The ichthyosporean genome is >200 kilobase pairs in length and consists of several hundred linear chromosomes that share elaborate terminal-specific sequence patterns. In the following

phylogenetic tree A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spec ...

it is indicated how many millions of years ago (Mya) the clades diverged into newer clades. The holomycota tree is following Tedersoo et al. One view of the great kingdoms and their stem groups. Phylogeny based on Steenkamp et al 2005, and Eichinger et al, 2005.

Gallery

File:Nuclearia sp Nikko.jpg, ''

Nuclearia ''Nuclearia'' is a nucleariid Nucleariida is a group of amoebae with filose pseudopods, known mostly from soils and freshwater. They are distinguished from the superficially similar vampyrellids mainly by having mitochondria with discoid ...

'' ( Nucleariida) File:Rozella allomycis2.jpg, ''

Rozella ''Rozella'' is a fungal genus of obligate endoparasites of a variety of hosts, including Oomycota, Chytridiomycota, and Blastocladiomycota. ''Rozella'' was circumscribed by French mycologist Marie Maxime Cornu in 1872. Considered one of the ear ...

'' sp. (

) File:Msp tubule EM.jpg, Microsporidian spore (

Microsporidia Microsporidia are a group of spore-forming unicellular parasites. These spores contain an extrusion apparatus that has a coiled polar tube ending in an anchoring disc at the apical part of the spore. They were once considered protozoans or pr ...

) File:CSIRO ScienceImage 1392 Scanning Electron Micrograph of Chytrid Fungus.jpg,

Chytrid Chytridiomycota are a division of zoosporic organisms in the kingdom Fungi, informally known as chytrids. The name is derived from the Ancient Greek ('), meaning "little pot", describing the structure containing unreleased zoöspores. Chytrid ...

(flagellated fungus) File:Sphaeroforma arctica.jpg, ''

Sphaeroforma ''Sphaeroforma arctica'', is a unicellular eukaryote with a pivotal position in the tree of life. It was first isolated from the arctic marine amphipod '' Gammarus setosus''. Like other Ichthyosporeans such as ''Creolimax'' and ''Abeoforma'', ''S ...

'' sp. ( Mesomycetozoea) File:Ministeria vibrans.jpeg, ''

Ministeria ''Ministeria'' is a genus of Filasterea. The species can be found in the North Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and ...

'' sp. (

) File:Capsaspora owczarzaki.jpeg, ''

Capsaspora ''Capsaspora'' is a monotypic genus containing the single species ''Capsaspora owczarzaki. C. owczarzaki'' is a single-celled eukaryote that occupies a key phylogenetic position in our understanding of the origin of animal multicellularity, as o ...

'' sp. (

) File:Protero-7.png, ''

Salpingoeca ''Salpingoeca'' is a genus of Choanoflagellate The choanoflagellates are a group of free-living unicellular and colonial flagellate eukaryotes considered to be the closest living relatives of the animals. Choanoflagellates are collared flagell ...

'' ( Choanoflagellatea) File:Desmarella moniliformis.jpg, '' Desmarella'' sp. colony ( Choanoflagellatea) File:Matsutakeredpinemushroomhunting.jpg, Two opisthokonts: a human (

Metazoa Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in ...

) and a mushroom (

)

References

External links

Tree of Life Eukaryotes
{{Taxonbar, from=Q129021 Amorphea unranked clades