The Opisthokonts

The Opisthokonts is a supergroup of eukaryotes that contains animals (Metazoa), Fungi and several unicellular lineages (for a review see 1). The name was first proposed by Tom Cavalier-Smith for a clade that included Metazoa, Fungi and Choanoflagellata (2). This was later on corroborated by ribosomal RNA gene phylogenies (3). Recent multi-gene phylogenies divide the Opisthokonta into two main clades: 1) the Holozoa, which includes animals and their closest unicellular relatives, which are Choanoflagellata, Filasterea, and Teretosoporea (Ichthyosporea + Corallochytrea); and 2) the Holomycota, which includes Fungi, Opisthosporidia, and Nucleariidae (4-11).
Etymology
The name Opisthokonta derives from the greek opisthen (posterior) and kontos (oar or pole); thus referring to a posterior flagellum, which supposedly had the common ancestor of all the Opisthokonts.
Diagnostic apomorphies
The only morphological apomorphy is the posterior insertion of the flagellum, as seen in the opisthokont taxa that have unicellular flagellated stages. This is rare in eukaryotes, given that most flagellated cells have anterior or lateral flagella .
Some molecular synapomorphies were proposed (12-14). However, the only molecular synapomorphy that seems to stand with the sequencing of more taxa is the approximately 12 amino acid insertion in the translation elongation factor 1α (EF-1α) gene (15-16).

References

  1. Paps, J., & Ruiz-Trillo, I. (2010). Animals and Their Unicellular Ancestors. In Encyclopedia of Life Sciences (ELS) DOI: 10.1002/9780470015902.a0022853. Chichester: John Wiley & Sons, Ltd.
  2. Cavalier-Smith, T. 1987. The origin of fungi and pseudofungi. Pages 339-353 in Evolutionary biology of the fungi. (A. D. M. Rayner, C. M. Brasier, and D. Moore, eds.) British Mycological Society Symposium 12. Cambridge University Press, Cambridge, U.K.
  3. Wainright, P. O., G. Hinkle, G., M. L. Sogin and S. K. Stickel. 1993. Monophyletic orgins of the Metazoa: an evolutionary link with Fungi. Science 260:340-342.
  4. Lang, B. F., C. J. O’Kelly, T. A. Nerad, M. W. Gray and G. Burger. 2002. The closest unicellular relatives of animals. Curr. Biol. 12:1773-1778.
  5. Baldauf, S. L. 2003. The deep roots of eukaryotes. Science 300:1703-1706.
  6. Ruiz-Trillo, I., Y. Inagaki, L. A. Davis, S. Sperstad, B. Landfald and A. J. Roger. 2004. Capsaspora owczarzaki is an independent opisthokont lineage. Curr. Biol. 14:R946-947.
  7. Ruiz-Trillo, I., C. E. Lane, J. M. Archibald and A. J. Roger. 2006. Insights into the evolutionary origin and genome architecture of the unicellular opisthokonts Capsaspora owczarzaki and Sphaeroforma arctica. J. Eukaryot. Microbiol. 53:379-384.
  8. Ruiz-Trillo, I. A. J. Roger, G. Burger, M. W. Gray and B. F. Lang. 2008. A phylogenomic investigation into the origin of Metazoa. Mol. Biol. Evol. 25:664-672.
  9. Shalchian-Tabrizi, K., M. A. Minge, M. Espelund, R. Orr, T. Ruden, K. S. Jakobsen and T. Cavalier-Smith. 2008. Multigene phylogeny of Choanozoa and the origin of animals. PLoS ONE 3:e2098.
  10. Torruella, G., Derelle, R., Paps, J., Lang, B. F., Roger, A. J., Shalchian-Tabrizi, K., & Ruiz-Trillo, I. (2012). Phylogenetic relationships within the Opisthokonta based on phylogenomic analyses of conserved single-copy protein domains. Mol Biol Evol, 29(2), 531–544. http://doi.org/10.1093/molbev/msr185
  11. Torruella, G., de Mendoza, A., Grau-Bové, X., Antó, M., Chaplin, M. A., del Campo, J., et al. (2015). Phylogenomics Reveals Convergent Evolution of Lifestyles in Close Relatives of Animals and Fungi. Current Biology : CB, 25(18), 2404–2410. http://doi.org/10.1016/j.cub.2015.07.053
  12. Huang,  J. Y. Xu and J. P. Gogarten. 2005. The presence of a haloarchaeal type tyrosyl-tRNA synthetase marks the opisthokonts as monophyletic. Mol. Biol. Evol. 22:2142-2146.
  13. Elias, M. 2008. The guanine nucleotide exchange factors Sec2 and PRONE: Candidate synapomorphies for the Opisthokonta and the Archaeplastida. Mol. Biol. Evol. 25:1526-1529.
  14. Shadwick, J. D., & Ruiz-Trillo, I. (2012). A genomic survey shows that the haloarchaeal type tyrosyl tRNA synthetase is not a synapomorphy of opisthokonts. Eur J Protistol, 48(1), 89–93. http://doi.org/10.1016/j.ejop.2011.10.003
  15. Baldauf, S. L. and J. D. Palmer. 1993. Animals and fungi are each other’s closest relatives: Congruent evidence from multiple proteins. Proc. Natl. Acad. Sci. USA 90:11558-11562.
  16. Steenkamp, E. T., J. Wright and S. L. Baldauf. 2006. The protistan origins of animals and fungi. Mol. Biol. Evol. 23:93-106.