Bikont

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For an explanation of very similar terms, see Corticata.
Bikonts
Aulacanthas 01.jpg
A radiolarian
Scientific classification e
Domain: Eukaryota
(unranked): Bikonta
Cavalier-Smith, 1993
Subgroups

Apusozoa
Rhizaria
Excavata
Archaeplastida
Chromalveolata

Synonyms
  • Biciliata Cavalier-Smith, 1993
  • Diaphoretickes Adl et al., 2012
  • Diphoda Derelle et al., 2015

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.[1]

Enzymes[edit]

Another shared trait of bikonts is the fusion of two genes into a single unit: the genes for thymidylate synthase (TS) and dihydrofolate reductase (DHFR) encode a single protein with two functions.[2]

The genes are separately translated in unikonts.

Relationships[edit]

Some research suggests that a unikont (a eukaryotic cell with a single flagellum) was the ancestor of opisthokonts (Animals, Fungi, and related forms) and Amoebozoa, and a bikont was the ancestor of Archaeplastida (Plants and relatives), Excavata, Rhizaria, and Chromalveolata. Cavalier-Smith has suggested that Apusozoa, which are typically considered incertae sedis, are in fact bikonts.

Relationships within the bikonts are not yet clear. Cavalier-Smith has grouped the Excavata and Rhizaria into the Cabozoa and the Archaeplastida and Chromalveolata into the Corticata, but at least one other study has suggested that the Rhizaria and Chromalveolata form a clade.[3]

Cladogram[edit]

An up to date "classical" cladogram is[4][5][6]

Eukaryote
Bikonta

Chromalveolata (+ Archaeplastida and Rhizaria)


Archaeplastida



Cryptophyta





Haptophyta


SAR supergroup

Rhizaria


Halvaria

Heterokont



Alveolata








Excavata




Unikonta



However, an even more up-to date cladogram with the root in Excavata is[7][8]

Eukaryotes
Diphoda
Diaphoretickes/corticata

Archaeplastida


Chromista
Hacrobia

Cryptista



Haptista



Harosa

Rhizaria


Halvaria

Heterokonta



Alveolata






Discoba



Jakobea + Tsukubea




Percolozoa




Euglenozoa




Metamonada?




Metamonada?


Opimoda

Metamonada?


podiates

Neolouka



Collodictyon




Varisulca




Amoebozoa


Obazoa

Breviata




Apusomonadida



Opisthokont









The corticates correspond roughly to the bikonts. While Haptophyta, Cryptophyta, Glaucophyta, Rhodophyta, the SAR supergroup and viridiplantae are usually considered monophyletic, Archaeplastida may be paraphyletic, and the mutual relationship between these phyla are still to be fully resolved.

References[edit]

  1. ^ Burki F, Pawlowski J (October 2006). "Monophyly of Rhizaria and multigene phylogeny of unicellular bikonts". Mol. Biol. Evol. 23 (10): 1922–30. doi:10.1093/molbev/msl055. PMID 16829542. 
  2. ^ Thomas Cavalier-Smith (2003). "Protist phylogeny and the high-level classification of Protozoa". European Journal of Protistology. 39 (4): 338–348. doi:10.1078/0932-4739-00002. 
  3. ^ Burki F, Shalchian-Tabrizi K, Minge M, Skjæveland Å, Nikolaev SI, et al. (2007). Butler G, ed. "Phylogenomics Reshuffles the Eukaryotic Supergroups". PLoS ONE. 2 (8: e790): e790. doi:10.1371/journal.pone.0000790. PMC 1949142free to read. PMID 17726520. 
  4. ^ Jackson, Christopher; Clayden, Susan; Reyes-Prieto, Adrian (2015). "The Glaucophyta: the blue-green plants in a nutshell". Acta Societatis Botanicorum Poloniae. 84 (2). doi:10.5586/asbp.2015.020. 
  5. ^ Derelle, Romain; Torruella, Guifré; Klimeš, Vladimír; Brinkmann, Henner; Kim, Eunsoo; Vlček, Čestmír; Lang, B. Franz; Eliáš, Marek (17 February 2015). "Bacterial proteins pinpoint a single eukaryotic root". Proceedings of the National Academy of Sciences. 112 (7): E693–E699. doi:10.1073/pnas.1420657112. ISSN 0027-8424. PMC 4343179free to read. PMID 25646484. 
  6. ^ Burki, Fabien; Okamoto, Noriko; Pombert, Jean-François; Keeling, Patrick J. (7 June 2012). "The evolutionary history of haptophytes and cryptophytes: phylogenomic evidence for separate origins". Proceedings of the Royal Society of London B: Biological Sciences. 279 (1736): 2246–2254. doi:10.1098/rspb.2011.2301. ISSN 0962-8452. PMC 3321700free to read. PMID 22298847. 
  7. ^ Cavalier-Smith, Thomas; Chao, Ema E.; Lewis, Rhodri (December 2015). "Multiple origins of Heliozoa from flagellate ancestors: New cryptist subphylum Corbihelia, superclass Corbistoma, and monophyly of Haptista, Cryptista, Hacrobia and Chromista". Molecular Phylogenetics and Evolution. 93: 331–362. doi:10.1016/j.ympev.2015.07.004. 
  8. ^ "A paneukaryotic genomic analysis of the small GTPase RABL2 underscores the significance of recurrent gene loss in eukaryote evolution". doi:10.1186/s13062-016-0107-8. 

Further reading[edit]