The relevance of genetic factors in conferring protection to severe malaria has been demonstrated, as in the case of sickle cell trait and G6PD deficiency . However, it remains unknown whether environmental components, such as dietary or metabolic variations, can contribute to the outcome of infection . Here, we show that administration of a high-fat diet to mice for a period as short as 4 days impairs Plasmodium liver infection by over 90%. Plasmodium sporozoites can successfully invade and initiate replication but die inside hepatocytes, thereby are unable to cause severe disease. Transcriptional analyses combined with genetic and chemical approaches reveal that this impairment of infection is mediated by oxidative stress. We show that reactive oxygen species, probably spawned from fatty acid β-oxidation, directly impact Plasmodium survival inside hepatocytes, and parasite load can be rescued by exogenous administration of the antioxidant N-acetylcysteine or the β-oxidation inhibitor etomoxir. Together, these data reveal that acute and transient dietary alterations markedly impact the establishment of a Plasmodium infection and disease outcome.

Like most pathogens, malaria parasites balance persistence in the current host with transmission to the next. For Plasmodium falciparum, the most widespread and virulent human malaria parasite, persistence depends on continuous asexual replication in red blood cells while transmission requires differentiation into non-replicating gametocytes, the male and female cells able to infect the mosquito vector. This developmental decision is controlled via stochastic derepression of a heterochromatin-silenced locus encoding the transcription factor PfAP2-G, which acts as the master switch for sexual differentiation. Recent work showed that the frequency of pfap2-g derepression is responsive to extracellular levels of phospholipid precursors. However, the regulatory mechanisms linking these metabolites to epigenetic regulation of pfap2-g was hitherto unknown. Using chemical, metabolomic, and genetic approaches, we show that this response is mediated by metabolic competition for the methyl donor S-adenosylmethionine between histone methyltransferases and phosphoethanolamine methyltransferase, a critical enzyme in the parasite pathway for de novo phosphatidylcholine synthesis. When phosphatidylcholine precursors are scarce, increased consumption of S-adenosylmethionine for de novo synthesis of phosphatidylcholine results in a decrease in histone methylation marks that mediate silencing of pfap2-g, thereby up-regulating its transcription and increasing the frequency of sexual differentiation. Our findings reveal a key connection between metabolite utilization and gene expression in malaria parasites that forms the mechanistic link between phosphatidylcholine metabolism and the frequency of sexual commitment.

Eukaryotes have canonical pathways for responding to amino acid (AA) availability. Under AA-limiting conditions, the TOR complex is repressed, whereas the sensor kinase GCN2 is activated. While these pathways have been highly conserved throughout evolution, malaria parasites are a rare exception. Despite auxotrophic for most AA, Plasmodium does not have either a TOR complex nor the GCN2-downstream transcription factors. While Ile starvation has been shown to trigger eIF2α phosphorylation and a hibernation-like response, the overall mechanisms mediating detection and response to AA fluctuation in the absence of such pathways has remained elusive. Here we show that Plasmodium parasites rely on an efficient sensing pathway to respond to AA fluctuations. A phenotypic screen of kinase knockout mutant parasites identified nek4, eIK1 and eIK2—the last two clustering with the eukaryotic eIF2α kinases—as critical for Plasmodium to sense and respond to distinct AA-limiting conditions. Such AA-sensing pathway is temporally regulated at distinct life cycle stages, allowing parasites to actively fine-tune replication and development in response to AA availability. Collectively, our data disclose a set of heterogeneous responses to AA depletion in malaria parasites, mediated by a complex mechanism that is critical for modulating parasite growth and survival.