Conservation of the Toxoplasma conoid proteome in Plasmodium reveals a cryptic conoid feature that differentiates between blood- and vector-stage zoite

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 from Plasmodium species and other members of the Class Aconoidasida. Relatively few conoid proteins have been previously identified making it difficult to address the question of how conserved this feature is throughout the phylum, and whether it is truly missing from some major groups. Moreover, parasites such as Plasmodium species cycle through multiple invasive forms raising the question of differential presence of the conoid between these stages. We have applied spatial proteomics methods and high-resolution microscopy to develop a more complete molecular inventory and organisation of conoid-associated proteins in the model apicomplexan Toxoplasma gondii. These data revealed conservation of the molecules of all substructures of the conoid throughout Apicomplexa including Plasmodium and even in allied Myzozoa such as Chromera. We reporter-tagged and observed the expression and location of several conoid proteins in the malaria model P. berghei and revealed equivalent structures in all 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.