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Significance: Eukaryotes, which include diverse species like animals, fungi, and plants, have cells that are fundamentally more complex than prokaryotic cells, such as bacteria. However, eukaryotes did evolve from prokaryotes, so they must have acquired this cellular complexity after they diverged from prokaryotes. A key cellular feature unique to eukaryotes is the kinetochore, a large, multiprotein structure that plays an essential role in cell division. Here we shed light on the origination of the kinetochore by studying the evolution of its proteins. We find that the kinetochore has diverse evolutionary roots and that it expanded via gene duplications. We present a mode by which eukaryotic systems originated and illuminate the prokaryote-to-eukaryote transition.

The apical complex is the instrument of invasion used by apicomplexan parasites, and the conoid is a conspicuous feature of this apparatus found throughout this phylum. The conoid, however, is believed to be heavily reduced or missing fromPlasmodiumspecies and other members of the class Aconoidasida. Relatively few conoid proteins have previously been identified, making it difficult to address how conserved this feature is throughout the phylum, and whether it is genuinely missing from some major groups. Moreover, parasites such asPlasmodiumspecies cycle through 3 invasive forms, and there is the possibility of differential presence of the conoid between these stages. We have applied spatial proteomics and high-resolution microscopy to develop a more complete molecular inventory and understanding of the organisation of conoid-associated proteins in the model apicomplexanToxoplasma gondii. These data revealed molecular conservation of all conoid substructures throughout Apicomplexa, includingPlasmodium, and even in allied Myzozoa such asChromeraand dinoflagellates. We reporter-tagged and observed the expression and location of several conoid complex proteins in the malaria modelP.bergheiand revealed equivalent structures in all of its zoite forms, as well as evidence of molecular differentiation between blood-stage merozoites and the ookinetes and sporozoites of the mosquito vector. Collectively, we show that the conoid is a conserved apicomplexan element at the heart of the invasion mechanisms of these highly successful and often devastating parasites.