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Opisthokonts

Opisthokonta

Description of Opisthokonts

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Circumscription: This group contains the true fungi and their protist relatives (the chytrids) and the animals and their protist relatives (the choanoflagellates). The close relationship of the multicellular taxa was initially indicated by molecular means. The group contains uniflagellated solitary and colonial protists with one flagellum at some stage in their life history, phagotrophs, saprophytes, mycelial organisms with spore-forming bodies but no flagella, multicellular heterotrophs formed from layers of cells (epithelia), and the sponges with a less structured arrangement of cells. Collagen, one of the components of the extracellular matrix of the animals has also been reported from some fungi. All of the flagellated taxa and flagellated cells swim with a single flagellum beating behind the cell. The term opisthokonta has been applied to this grouping (Cavalier-Smith and Chao 1995; Cavalier-Smith 1996). However, Cavalier-Smith and Chao do not use the term as a formal taxon because it would require that more important taxa are subordinated to less important taxa. Here, the opisthokonts is a taxon with the composition as indicated. The name may need to be revisited as the term Opisthokonta has previously been used by Copeland (1956) for the chytrids. Some other permanently or temporarily opisthokont protists-such as several nominal pelobionts or the unassigned Phalansterium or Pseudaphelidium-are not included, and it is not yet known if they form part of this group. Ultrastructural identity: The diversity of organization within this group is great, extending from uniflagellated protists with or without the ability to make siliceous products to multicellular myeelial or epitheliate organisms. Apart from having platycristate mitochondria and being dictyosomate, this group has few discriminating characters that extend throughout this group. Nuclear division is variable within the fungi but in the animals, the envelope breaks down during mitosis. Synapomorphy: Unspecified but probably may relate to the radiating and arcing anchorage structures associated with the single flagellum. Very few studies of the protistan (ancestral) members have been conducted, and until more detailed ultrastructural studies are carried Out, such a determination would probably be premature. Most included taxa have secondarily lost this character. Composition: The largest of the major eukaryote lineages with probably in excess of 1,000,000 species, in two major clusters: (chytrids + true fungi) + (choanoflagellates + Metazoa). These two clusters themselves require appropriately defined names. This taxon includes the Myxospora (previously thought of as a group of protozoa) as a subset of the Cnidaria; and the Microspora are placed with the fungi in line with recent molecular evidence.
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Opisthokont

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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]

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[14] 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.

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) Pediastrum (cropped).jpg

   

Hacrobia Coccolithus pelagicus.jpg

   

SAR supergroup Ochromonas.png

     

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

Podiata

CRuMs Collodictyon anterior view, showing sulcus, nucleus, blepharoplast, rhizoplast, and four flagella..jpg

Amorphea/  

Amoebozoa Chaos carolinensis Wilson 1900.jpg

Obazoa

Breviatea Mastigamoeba invertens.jpg

     

Apusomonadida Apusomonas.png

Opisthokonts Holomycota Cristidiscoidea

Fonticulida

   

Nucleariida Nuclearia sp Nikko.jpg

    Fungi/  

BCG2

       

True Fungi Asco1013.jpg

   

Aphelida

       

BCG1

Rozellomyceta/  

Rozella Rozella allomycis2.jpg

     

Namako-37

   

Microsporidia Fibrillanosema spore.jpg

    Cryptomycota     OpisthosporidiaHolozoa

Ichthyosporea Abeoforma whisleri-2.jpg

    Pluriformea

Corallochytrium Corallochytrium limacisporum.png

   

Syssomonas

    Filozoa

Filasterea Ministeria vibrans.jpeg

Choanozoa

Choanoflagellatea Desmarella moniliformis.jpg

   

Animalia Comb jelly.jpg

          1300 mya     Unikonts    

One view of the great kingdoms and their stem groups.[18]

Gallery

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. doi:10.1038/s41586-019-1217-0. PMID 31118507.
  2. ^ Copeland, H. F. (1956). The Classification of Lower Organisms. Palo Alto: Pacific Books.
  3. ^ a b Cavalier-Smith, T. (1987). "The origin of fungi and pseudofungi". In Rayner, Alan D. M. (ed.). Evolutionary biology of Fungi. Cambridge: Cambridge Univ. Press. pp. 339–353. ISBN 0-521-33050-5.
  4. ^ Adl, S.M.; et al. (September–October 2005). "The new higher level classification of eukaryotes with emphasis on the taxonomy of protists". Journal of Eukaryotic Microbiology. 52 (5): 399–451. doi:10.1111/j.1550-7408.2005.00053.x. PMID 16248873.
  5. ^ Shalchian-Tabrizi K, Minge MA, Espelund M, et al. (7 May 2008). Aramayo R (ed.). "Multigene phylogeny of choanozoa and the origin of animals". PLoS ONE. 3 (5): e2098. Bibcode:2008PLoSO...3.2098S. doi:10.1371/journal.pone.0002098. PMC 2346548. PMID 18461162.
  6. ^ "Fungi/Metazoa group". Retrieved 2009-03-08.
  7. ^ a b Steenkamp ET, Wright J, Baldauf SL (January 2006). "The protistan origins of animals and fungi". Mol. Biol. Evol. 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. ^ Parfrey, Laura Wegener; et al. (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.
  10. ^ Torruella, Guifré; et al. (February 2012). "Phylogenetic relationships within the Opisthokonta based on phylogenomic analyses of conserved single-copy protein domains". Molecular Biology and Evolution. 29 (2): 531–544. doi:10.1093/molbev/msr185. PMC 3350318. PMID 21771718.
  11. ^ Eme, Laura; Sharpe, Susan C.; Brown, Matthew W.; Roger, Andrew J. (2014-08-01). "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 PO, Hinkle G, Sogin ML, Stickel SK (April 1993). "Monophyletic origins of the metazoa: an evolutionary link with fungi". Science. 260 (5106): 340–2. Bibcode:1993Sci...260..340W. doi:10.1126/science.8469985. PMID 8469985.
  14. ^ Stechmann, A.; Cavalier-Smith, T. (5 July 2002). "Rooting the eukaryote tree by using a derived gene fusion". Science. 297 (5578): 89–91. Bibcode:2002Sci...297...89S. doi:10.1126/science.1071196. PMID 12098695.
  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.
  16. ^ Matthew W. Brown, Frederick W. Spiegel and Jeffrey D. Silberman (2009), "Phylogeny of the "Forgotten" Cellular Slime Mold, Fonticula alba, Reveals a Key Evolutionary Branch within Opisthokonta", Molecular Biology and Evolution, 26 (12): 2699–2709, doi:10.1093/molbev/msp185, PMID 19692665
  17. ^ Tedersoo, Leho; Sánchez-Ramírez, Santiago; Kõljalg, Urmas; Bahram, Mohammad; Döring, Markus; Schigel, Dmitry; May, Tom; Ryberg, Martin; Abarenkov, Kessy (2018). "High-level classification of the Fungi and a tool for evolutionary ecological analyses". Fungal Diversity. 90 (1): 135–159. doi:10.1007/s13225-018-0401-0. ISSN 1560-2745.
  18. ^ Phylogeny based on:

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Opisthokont: Brief Summary

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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. The opisthokonts, previously called the "Fungi/Metazoa group", are generally recognized as a clade. Opisthokonts together with Apusomonadida and Breviata comprise the larger clade Obazoa.

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