Plasma membrane recycling drives reservoir formation during Toxoplasma gondii intracellular replication

Abstract

During intracellular development, apicomplexan parasites reside within a parasito phorous vacuole largely derived from the host plasma membrane (PM) and rendered nonfusogenic with the host endolysosomal system. Yet, the parasite is capable of protein uptake from the host cell via endocytosis, which occurs via a conserved structure, the micropore. Recently the composition of the micropore was charac terized and its stability was shown to depend on the presence of the kelch-domain protein K13 which is also central to malarial drug-resistance to artemisinin. Interest ingly, depletion of K13 also resulted in an impressive accumulation of PM attached to or between individual parasites, suggesting that the micropore plays a critical role in PM homoeostasis. Here, we characterized the dynamics and recycling of the PM in Toxoplasma gondii. In intracellular parasites, the PM is shared between individual parasites and undergoes a cycle of endocytosis and exocytosis during replication, similar to what has been previously demonstrated for extracellular parasites. This cycle appears to depend on Rab5b and MyoF. Interestingly, in contrast to Plasmo dium falciparum, Rab5b is dispensable for the lytic cycle of T. gondii. During repli cation, parasites establish an extracellular plasma membrane reservoir (PMR) prior to daughter cell formation. The PMR is a dynamic membranous structure that varies in size and position throughout replication and disappears after daughter cell bud ding. Perturbation of the endo-exocytic balance disrupts PMR formation, leading to increased number and size of PMRs and, ultimately, to a complete loss of membrane organization directly linking endocytosis to the regulation of PMR formation.