Loss of a conserved MAPK causes catastrophic failure in assembly of a specialized cilium-like structure in .

Primary cilia are important organizing centers that control diverse cellular processes. Apicomplexan parasites like have a specialized cilium-like structure called the conoid that organizes the secretory and invasion machinery critical for the parasites' lifestyle. The proteins that initiate the biogenesis of this structure are largely unknown. We identified the orthologue of the conserved kinase ERK7 as essential to conoid assembly. Parasites in which ERK7 has been depleted lose their conoids late during maturation and are immotile and thus unable to invade new host cells. This is the most severe phenotype to conoid biogenesis yet reported, and is made more striking by the fact that ERK7 is not a conoid protein, as it localizes just basal to the structure. ERK7 has been recently implicated in ciliogenesis in metazoan cells, and our data suggest that this kinase has an ancient and central role in regulating ciliogenesis throughout Eukaryota.