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

Unikonta


Bikonta

Excavata



Chromalveolata (+ Archaeplastida)

SAR supergroup
Halvaria

Heterokont



Alveolata




Rhizaria




Haptophyta





Cryptophyta



Archaeplastida







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

Eukaryotes

Euglenozoa




Percolozoa




Tsukubamonadea




Jakobea




Metamonada



corticata

Archaeplastida


Chromista
Harosa

Rhizaria


Halvaria

Heterokonta



Alveolata




Hacrobia

Haptista



Cryptista





podiates


Amoebozoa


Obazoa

Breviata




Apusomonadida



Opisthokont






Neolouka



Collodictyon



Varisulca









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 (2006). "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, Geraldine, ed. "Phylogenomics Reshuffles the Eukaryotic Supergroups". PLoS ONE 2 (8: e790): e790. doi:10.1371/journal.pone.0000790. PMC 1949142. PMID 17726520. 
  4. ^ Jackson, Christopher; Clayden, Susan; Reyes-Prieto, Adrian (2015-01-01). "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 (2015-02-17). "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 4343179. PMID 25646484. 
  6. ^ Burki, Fabien; Okamoto, Noriko; Pombert, Jean-François; Keeling, Patrick J. (2012-06-07). "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 3321700. PMID 22298847. 
  7. ^ Cavalier-Smith, Thomas; Chao, Ema E.; Lewis, Rhodri (2015-12-01). "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. 

Further reading[edit]