Opisthokont

The opisthokonts (Greek: ὀπίσθιος (opísthios)="rear, posterior" + κοντός (kontós)="pole" i.e. "flagellum") are a broad group of eukaryotes, including both the animal and fungus kingdoms.[5] The opisthokonts, previously called the "Fungi/Metazoa group",[6] are generally recognized as a clade. Opisthokonts together with Apusomonadida and Breviata comprise the larger clade Obazoa.[7][8][9][10][11]

Opisthokont
Temporal range: 1010 –0 Ma[1]
Clockwise, from top left: Abeoforma whisleri (Ichthyosporea); Amanita muscaria (Fungi); Desmarella moniliformis (Choanoflagellatea); Bonnet Macaque (Metazoa); Nuclearia thermophila (Nucleariida); Ministeria vibrans (Filozoa)
Scientific classification
(unranked): Unikonta
(unranked): Obazoa
(unranked): Opisthokonta
Copeland 1956,[2] emend. Cavalier-Smith 1987,[3] emend. Adl et al., 2005[4]
Subgroups

Flagella and other characteristics

A common characteristic of opisthokonts is that flagellate cells, such as the sperm of most animals and the spores of the chytrid fungi, 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.[7]

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.[12]

History

The close relationship between animals and fungi was suggested by Thomas Cavalier-Smith in 1987,[3] who used the informal name opisthokonta (the formal name has been used for the chytrids by Copeland in 1956), and was supported by later genetic studies.[13]

Early phylogenies placed fungi near the plants and other groups that have mitochondria with flat cristae, 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, 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 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 evolved.[14]

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.[15] Holomycota and Holozoa are composed of the following groups.

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 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.[17]

Eukaryotes
Bikonta
 

Archaeplastida (Plantae sensu lato)

 
 

Hacrobia

 
 

SAR supergroup

 
 
 

Excavata

 
Podiata
 

CRuMs

 
Amorphea/
 

Amoebozoa

 
Obazoa
 

Breviatea

 
 
 

Apusomonadida

 
Opisthokonts
Holomycota
Cristidiscoidea
 

Fonticulida

 
 

Nucleariida

 
 
Fungi/
 

BCG2

 
 
 
 

True Fungi

410 mya
 

Aphelida

 
 
 
 

BCG1

 
Rozellomyceta/
 

Rozella

 
 
 

Namako-37

 
 

Microsporidia

 
 
Cryptomycota
 
 
Opisthosporidia
 
Holozoa
 

Ichthyosporea

 
 
Pluriformea
 

Corallochytrium

 
 

Syssomonas

 
 
Filozoa
 

Filasterea

 
Choanozoa
 

Choanoflagellatea

 
 

Animalia

760 mya
950 mya
 
 
 
1300 mya
 
 
Unikonts
 
1850 mya

One view of the great kingdoms and their stem groups. Phylogeny based on Steenkamp et al 2005,[7] and Eichinger et al, 2005.[18]

References
  1. Loron, Corentin C.; François, Camille; Rainbird, Robert H.; Turner, Elizabeth C.; Borensztajn, Stephen; Javaux, Emmanuelle J. (May 22, 2019). "Early fungi from the Proterozoic era in Arctic Canada". Nature. 570 (7760): 232–235. Bibcode:2019Natur.570..232L. doi:10.1038/s41586-019-1217-0. PMID 31118507.
  2. Copeland, H. F. (1956). The Classification of Lower Organisms. Palo Alto: Pacific Books.
  3. Cavalier-Smith, T. (1987). "The origin of fungi and pseudofungi". In Rayner, Alan D. M. (ed.). Evolutionary biology of Fungi. Cambridge: Cambridge University Press. pp. 339–353. ISBN 0-521-33050-5.
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  6. "Fungi/Metazoa group". Retrieved 2009-03-08.
  7. Steenkamp, E.T.; Wright, J.; Baldauf, S.L. (January 2006). "The protistan origins of animals and fungi". Molecular Biology and Evolution. 23 (1): 93–106. doi:10.1093/molbev/msj011. PMID 16151185.
  8. Huang, Jinling; Xu, Ying; Gogarten, Johann Peter (November 2005). "The presence of a haloarchaeal type tyrosyl-tRNA synthetase marks the opisthokonts as monophyletic". Molecular Biology and Evolution. 22 (11): 2142–2146. doi:10.1093/molbev/msi221. PMID 16049196.
  9. Laura Wegener Parfrey; Erika Barbero; Elyse Lasser; Micah Dunthorn; Debashish Bhattacharya; David J Patterson; Laura A Katz (December 2006). "Evaluating support for the current classification of eukaryotic diversity". PLOS Genetics. 2 (12): e220. doi:10.1371/JOURNAL.PGEN.0020220. ISSN 1553-7390. PMC 1713255. PMID 17194223. Wikidata Q21090155.
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  11. Eme, Laura; Sharpe, Susan C.; Brown, Matthew W.; Roger, Andrew J. (August 2014). "On the Age of Eukaryotes: Evaluating Evidence from Fossils and Molecular Clocks". Cold Spring Harbor Perspectives in Biology. 6 (8): a016139. doi:10.1101/cshperspect.a016139. ISSN 1943-0264. PMC 4107988. PMID 25085908.
  12. Adl, Sina M.; Bass, David; Lane, Christopher E.; Lukeš, Julius; Schoch, Conrad L.; Smirnov, Alexey; Agatha, Sabine; Berney, Cedric; Brown, Matthew W. (2018-09-26). "Revisions to the Classification, Nomenclature, and Diversity of Eukaryotes". Journal of Eukaryotic Microbiology. 66 (1): 4–119. doi:10.1111/jeu.12691. ISSN 1066-5234. PMC 6492006. PMID 30257078.
  13. Wainright, P.O.; Hinkle, G.; Sogin, M.L.; Stickel, S.K. (April 1993). "Monophyletic origins of the metazoa: an evolutionary link with fungi". Science. 260 (5106): 340–342. Bibcode:1993Sci...260..340W. doi:10.1126/science.8469985. PMID 8469985.
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  15. Torruella, Guifré; Mendoza, Alex de; Grau-Bové, Xavier; Antó, Meritxell; Chaplin, Mark A.; Campo, Javier del; Eme, Laura; Pérez-Cordón, Gregorio; Whipps, Christopher M. (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.
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