Hypothetical models on early eukaryotic history and origin of kinetoplastid kinetochores.
(A) The earliest-branching kinetoplastid hypothesis. In this scenario, LECA may have had KKT kinetochores (i), conventional kinetochores (ii), or unknown type of kinetochores (iii). Conventional and KKT-based kinetochores are shown in blue and red, respectively. Note that this is a highly simplified and non-comprehensive set of possibilities of early eukaryotic history and origins of kinetoplastid kinetochores. (B) The earliest-branching Euglenozoa hypothesis based on their unique cytochrome c biogenesis machinery. In this scenario, either kinetoplastids (i) or euglenids (ii) could be the earliest-branching eukaryotes.