PROJECT SUMMARY/ABSTRACT Inter-organellar communication is an essential process for cellular function. Inside the cell, organelles can interact through specialized microdomains called membrane contact sites (MCSs). These structures mediate the close apposition of two organellar membranes, allowing the exchange of metabolites. In doing so, MCSs are crucial for cellular homeostasis and metabolic plasticity. However, most of what is known about MCSs comes only from a handful of well-studied metazoans, particularly yeast and mammals. Studying the function and composition of MCSs in other eukaryotes—particularly in divergent lineages possessing phylum-specific organelles—is therefore crucial to gain insights into the mechanisms requiring an independent solution to inter- organellar communication. My group seeks to understand inter-organellar communication in apicomplexans, are a group of parasitic protists that include the causative agents of malaria and toxoplasmosis. In their complex life cycles, many of these organisms transition through a variety of environments as they enter and exit cells in different host species. The ability to propagate within a wide range of cell types relies on the capacity to access nutrients from diverse and changing environments, which underscores the metabolic plasticity of apicomplexans. Most apicomplexans possess a single mitochondrion and an apicoplast, a non-photosynthetic plastid that arose from a secondary endosymbiotic event at least 600 million years ago. Both organelles have been coevolving ever since, and now play crucial roles in the metabolic plasticity and survival of these parasites. Although a close physical interaction between the mitochondrion and the apicoplast has been observed, the molecular identity of this interaction remains elusive. Using the model apicomplexan Toxoplasma gondii, my laboratory aims to identify the molecular effectors mediating the mitochondrion-apicoplast interaction using two different, yet complementary approaches: proximity biotinylation and bimolecular complementation. As the apicoplast is an apicomplexan-specific organelle, the identification of proteins involved in mitochondrion-apicoplast MCSs could provide opportunities for the design of anti-parasitic therapies against these pathogens. Our work will open new scientific venues of apicomplexan biology, and yield insight into the evolution and organellar crosstalk in these organisms.

PROJECT NARRATIVE Within a cell, organelles can communicate with each other via specialized protein structures called membrane contact sites (MCSs). MCSs play a crucial role in cellular homeostasis, but our knowledge about them is limited to a very narrow group of organisms. This research seeks to characterize MCSs in a branch of pathogenic protists that cause significant human diseases—such as malaria and toxoplasmosis—to understand how their unique organelles communicate with each other, and identify new targets for the development of anti-parasitic therapies.