Lipid kinases are essential for apicoplast homeostasis in T oxoplasma gondii

Summary Phosphoinositides regulate numerous cellular processes by recruiting cytosolic effector proteins and acting as membrane signalling entities. The cellular metabolism and localization of phosphoinositides are tightly regulated by distinct lipid kinases and phosphatases. Here, we identify and characterize a unique phosphatidylinositol 3 kinase ( PI 3 K ) in T oxoplasma gondii , a protozoan parasite belonging to the phylum Apicomplexa. Conditional depletion of this enzyme and subsequently of its product, PI (3) P , drastically alters the morphology and inheritance of the apicoplast, an endosymbiotic organelle of algal origin that is a unique feature of many Apicomplexa. We searched the T . gondii genome for PI (3) P ‐binding proteins and identified in total six PX and FYVE domain‐containing proteins including a PIK fyve lipid kinase, which phosphorylates PI (3) P into PI (3,5) P 2 . Although depletion of putative PI (3) P ‐binding proteins shows that they are not essential for parasite growth and apicoplast biology, conditional disruption of PIK fyve induces enlarged apicoplasts, as observed upon loss of PI (3) P . A similar defect of apicoplast homeostasis was also observed by knocking down the PIK fyve regulatory protein A r PIK fyve, suggesting that in T . gondii , PI (3) P ‐related function for the apicoplast might mainly be to serve as a precursor for the synthesis of PI (3,5) P 2 . Accordingly, PI 3 K is conserved in all apicomplexan parasites whereas PIK fyve and A r PIK fyve are absent in C ryptosporidium species that lack an apicoplast, supporting a direct role of PI (3,5) P 2 in apicoplast homeostasis. This study enriches the already diverse functions attributed to PI (3,5) P 2 in eukaryotic cells and highlights these parasite lipid kinases as potential drug targets.