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 and dihydrofolate reductase 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 of protists than to animals or fungi. Animals and fungi are both heterotrophs, unlike plants, and while fungi are sessility (motility), sessile like plants, there are also sessile animals. Cavalier-Smith and Stechmann argue that the uniciliate eukaryotes such as opisthokonts and Amoebozoa, collectively called unikonts, split off from the other biciliate eukaryotes, called bikonts, shortly after they Evolution, evolved.

Taxonomy

Opisthokonts are divided into Holomycota or Nucletmycea (fungi and all organisms more closely related to fungi than to animals) and Holozoa (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. * Holomycota (Fungus-like) ** Fungi *** Includes: ****

s (flagellated, zoosporic fungi) **** ''Fonticula'' (#Phylogeny , more recent work considers this to be part of Cristidiscoidea, a sister group to the fungi) **** ''Hyaloraphidium'' (previously thought to be a Chlorophyta, green alga, now considered a fungus) **** microsporidia (previously thought to be apicomplexia) **** Nucleariida (#Phylogeny , more recent work considers this to be part of Cristidiscoidea, a sister group to the fungi) *** Excludes: **** labyrinthulomycetes (slime nets) (now included in the SAR supergroup) **** Myxogastria, myxomycetes (now included in amoebozoans) **** oomycetes (water molds) (now included in the SAR supergroup) ** Rozellida (placement uncertain) * Holozoa (Animal-like) ** ''Corallochytrium'' (formerly considered a Heterokont) ** Filozoa *** Animalia (including myxozoa) *** Choanoflagellata (flagellates formerly included in protozoa) *** Filasterea ** Mesomycetozoea *** Amoebidiales (formerly considered trichomycetes) *** Dermocystida (formerly considered parasitic fungi or sporozoans) *** Eccrinales (formerly considered fungi) *** Ichthyophonida (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. ''Corallochytrium'' seem likely to be more closely related to the fungi than to the animals on the basis of the presence of ergosterol in their membranes and being capable of synthesis of lysine via the Alpha-aminoadipate pathway, 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 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'' (Nucleariida) File:Rozella allomycis2.jpg, ''Rozella'' sp. (Rozellida) File:Msp tubule EM.jpg, Microsporidian spore (Microsporidia) File:CSIRO ScienceImage 1392 Scanning Electron Micrograph of Chytrid Fungus.jpg, Chytrid (flagellated fungus) File:Sphaeroforma arctica.jpg, ''Sphaeroforma'' sp. (Mesomycetozoea) File:Ministeria vibrans.jpeg, ''Ministeria'' sp. (Filasterea) File:Capsaspora owczarzaki.jpeg, ''Capsaspora'' sp. (Filasterea) File:Protero-7.png, ''Salpingoeca'' (Choanoflagellatea) File:Desmarella moniliformis.jpg, ''Desmarella'' sp. colony (Choanoflagellatea) File:Matsutakeredpinemushroomhunting.jpg, Two opisthokonts: a human (Metazoa) and a mushroom (Fungi)

References

External links

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