Bikont

{{short description|Group of eukaryotes}} {{other uses}} {{Automatic taxobox | name = Bikonts | fossil_range = {{Long fossil range|1600|0|Mesoproterozoic  – present}} | image = Aulacanthas 01.jpg | image_caption = A radiolarian | display_parents = 2 | taxon = Bikonta | authority = Cavalier-Smith, 1993 | subdivision_ranks = Subgroups | subdivision = *Diaphoretickes *Excavata *Hemimastigophora | 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 and multi-celled organisms are members of the group, and these, as well as the presumed ancestor, have two flagella.<ref name="pmid16829542">{{cite journal |vauthors=Burki F, Pawlowski J |title=Monophyly of Rhizaria and multigene phylogeny of unicellular bikonts |journal=Mol. Biol. Evol. |volume=23 |issue=10 |pages=1922–30 |date=October 2006 |pmid=16829542 |doi=10.1093/molbev/msl055 |doi-access=free }}</ref>

==Enzymes== 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.<ref>{{cite journal | author=Thomas Cavalier-Smith | title=Protist phylogeny and the high-level classification of Protozoa | journal=European Journal of Protistology | year=2003 | volume=39 | issue=4 |pages=338–348 | doi=10.1078/0932-4739-00002 }}</ref>

The genes are separately translated in unikonts.

==Relationships== 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.<ref>{{cite journal |last1=Cavalier-Smith |first1=Thomas |title=Protist phylogeny and the high-level classification of Protozoa |journal=European Journal of Protistology |date=1 January 2003 |volume=39 |issue=4 |pages=338–348 |doi=10.1078/0932-4739-00002 }}</ref>

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.<ref>{{cite journal|vauthors=Burki F, Shalchian-Tabrizi K, Minge M, Skjæveland Å, Nikolaev SI|year=2007|title=Phylogenomics Reshuffles the Eukaryotic Supergroups|journal=PLOS ONE |volume=2|issue=8: e790|doi=10.1371/journal.pone.0000790|pages=e790|pmid=17726520|pmc=1949142|bibcode=2007PLoSO...2..790B|editor1-last=Butler|editor1-first=Geraldine|display-authors=etal|doi-access=free}}</ref>

An alternative to the Unikont–Bikont division was suggested by Derelle ''et al.'' in 2015,<ref name="Derelle2015"/> where they proposed the acronyms Opimoda–'''Diphoda''' respectively, as substitutes to the older terms. The name Diphoda is formed from the letters of DIscoba and diaPHOretickes (shown in capitals). {{cn-span|[suggested singular forms are Opneme-Dipheme respectively]|reason=I found no source in Google, Google Scholar or PubMed that these are suggested singular forms.|date=August 2024}}

==Cladogram== A "classical" cladogram (data from 2012, 2015) is:<ref>{{Cite journal|title = The Glaucophyta: the blue-green plants in a nutshell|journal = Acta Societatis Botanicorum Poloniae|date = 2015|volume = 84|issue = 2|doi = 10.5586/asbp.2015.020|first1 = Christopher|last1 = Jackson|first2 = Susan|last2 = Clayden|first3 = Adrian|last3 = Reyes-Prieto|pages=149–165|doi-access = free| bibcode=2015AcSBP..84..149J }}</ref><ref>{{Cite journal|title = The evolutionary history of haptophytes and cryptophytes: phylogenomic evidence for separate origins|journal = Proceedings of the Royal Society of London B: Biological Sciences|date = 7 June 2012 |pmc = 3321700|pmid = 22298847|pages = 2246–2254|volume = 279|issue = 1736|doi = 10.1098/rspb.2011.2301 |first1 = Fabien|last1 = Burki|first2 = Noriko|last2 = Okamoto|first3 = Jean-François|last3 = Pombert|first4 = Patrick J.|last4 = Keeling}}</ref>

{{clade |label1=Eukaryotes |1={{clade |label1=Bikonta |1={{clade |label1=SAR/HA Supergroup |1={{clade |2={{clade |label2=SAR supergroup |2={{clade |1=Rhizaria |label2=Halvaria |2={{clade |Heterokont |Alveolata }} }} |1=Haptophyta }} |1={{clade |1=Archaeplastida (inc. land plants) |2=Cryptophyta }} }} |2=Excavata |3=Unikonta }} }} }}

However, a cladogram (data from 2015, 2016) with the root in Excavata is<ref name="Derelle2015">{{Cite journal|title = Bacterial proteins pinpoint a single eukaryotic root|journal = Proceedings of the National Academy of Sciences|date = 17 February 2015 |pmc = 4343179|pmid = 25646484|pages = E693–E699|volume = 112|issue = 7|doi = 10.1073/pnas.1420657112|language = en|first1 = Romain|last1 = Derelle|first2 = Guifré|last2 = Torruella|first3 = Vladimír|last3 = Klimeš|first4 = Henner|last4 = Brinkmann|first5 = Eunsoo|last5 = Kim|first6 = Čestmír|last6 = Vlček|first7 = B. Franz|last7 = Lang|first8 = Marek|last8 = Eliáš|bibcode = 2015PNAS..112E.693D|doi-access = free}}</ref><ref>{{Cite journal|title = Multiple origins of Heliozoa from flagellate ancestors: New cryptist subphylum Corbihelia, superclass Corbistoma, and monophyly of Haptista, Cryptista, Hacrobia and Chromista|journal = Molecular Phylogenetics and Evolution|date = December 2015|pages = 331–362|volume = 93|doi = 10.1016/j.ympev.2015.07.004|first1 = Thomas|last1 = Cavalier-Smith |authorlink=Thomas Cavalier-Smith |first2 = Ema E.|last2 = Chao|first3 = Rhodri|last3 = Lewis|pmid=26234272|doi-access = free| bibcode=2015MolPE..93..331C }}</ref><ref name=Elias2016>{{cite journal |title=A paneukaryotic genomic analysis of the small GTPase RABL2 underscores the significance of recurrent gene loss in eukaryote evolution |date=2016 |journal=Biology Direct | volume=11 |issue=1 |pages=5 |doi=10.1186/s13062-016-0107-8|pmid=26832778 |pmc=4736243 |last1 = Eliáš|first1 = Marek|last2=Klimeš |first2=Vladimír |last3=Derelle |first3=Romain |last4=Petrželková |first4=Romana |last5=Tachezy |first5=Jan |doi-access=free }}</ref>

{{clade |label1=Eukaryotes |1={{clade |label3=Opimoda (Unikonts) |3={{clade |1=Metamonada? |label2=podiates |2={{clade |1=Neolouka |2=Collodictyon |3={{clade |1=Varisulca |2={{clade |1=Amoebozoa |label2=Obazoa |2={{clade |1={{clade |1=Apusomonadida |2=Breviata }} |2=Opisthokonta }} }} }} }} }} |2=Metamonada? |label1=Diphoda (Bikonts) |1={{clade |label1=SAR/HA Supergroup |1={{clade |1=Archaeplastida (inc. land plants) |label2=Chromista |2={{clade |label1=Hacrobia |1={{clade |1=Cryptista |2=Haptista }} |label2=SAR supergroup |2={{clade |1=Rhizaria |label2=Halvaria |2={{clade |1=Heterokonta |2=Alveolata }} }} }} }} |2=Discoba }} }} }}

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 relationships between these phyla are still to be fully resolved.

Recent reconstructions placed Archaeplastida and Hacrobia together in an "HA supergroup" or "AH supergroup", which was a sister clade to the SAR supergroup within the SAR/HA supergroup. However, this seems to have fallen out of favor as the monophyly of hacrobia has come under dispute.

== See also == * Corticata

==References== {{Reflist|30em}}

==Further reading== *{{Wikispecies-inline|Bikonta}} *{{Commons category-inline|Bikonta}} * {{cite journal |vauthors=Stechmann A, Cavalier-Smith T |title=The root of the eukaryote tree pinpointed |journal=Curr. Biol. |volume=13 |issue=17 |pages=R665–6 |date=September 2003 |pmid=12956967 |doi= 10.1016/S0960-9822(03)00602-X|doi-access=free |bibcode=2003CBio...13.R665S }} * [http://tolweb.org/Eukaryotes/3 Tree of Life Eukaryotes]

Category:Bikonts Category:Eukaryote taxa Category:Taxa named by Thomas Cavalier-Smith