Opisthokont

Lore & Background

The close relationship between animals and fungi was suggested by Thomas Cavalier-Smith in 1987, who used the informal name opisthokonta. This was supported by later genetic studies. Early phylogenies placed fungi near plants, but more recent work shows that holozoa (animals) and holomycota (fungi) are much more closely related to each other than either is to plants. This is supported by a triple fusion of carbamoyl phosphate synthetase, dihydroorotase, and aspartate carbamoyltransferase present in opisthokonts but not in plants, while plants have a fusion of thymidylate synthase and dihydrofolate reductase not present in opisthokonts.

Reader's Guide

Opisthokonts are significant because they represent a major branch of eukaryotic life, encompassing all animals and fungi. Their defining characteristic is the presence of a single posterior flagellum in flagellate cells, such as sperm in most animals and spores of chytrid fungi, which gives the group its name. This feature contrasts with other eukaryotes that have one or more anterior flagella. The group also shares other characteristics, including synthesis of extracellular chitin, extracellular digestion with osmotrophic absorption, and likely an early amoeboid and phagotrophic lifestyle. The opisthokont clade is divided into Holomycota (fungus-like organisms) and Holozoa (animal-like organisms), with no basal opisthokonts identified as of 2020. The phylogeny of opisthokonts has been largely resolved using phylogenomics, and the group is part of the larger unikont hypothesis, which posits that uniciliate eukaryotes split from biciliate eukaryotes shortly after they evolved.

Did You Know?

• The name opisthokont comes from Ancient Greek for 'rear, posterior' and 'pole, flagellum', referring to the single posterior flagellum.
• Flagellate cells have been secondarily lost in some opisthokont groups, including most of the fungi.
• Animals and fungi are both heterotrophs, unlike plants, and while most fungi are sessile like plants, there are also sessile animals.
• Opisthokonts together with Apusomonadida and Breviata make up the larger clade Obazoa.