Forward genetic screening identifies a link between Plasmodium falciparum fever response, artemisinin resistance and the algal origins of the apicoplast

Background: The emergence and spread of Plasmodium falciparum parasites that are resistant to front-line antimalarial artemisinin-combination therapies (ACT) threatens to erase the considerable gains against the disease of the last decade. We developed a new large-scale phenotypic screening pipeline and used it to carry out the first large-scale forward-genetic phenotype screen in Plasmodium falciparum in order to identify genes that allow parasites to survive febrile temperatures.

Results: Screening identified more than 200 P. falciparum mutants with differential responses to increased temperature. These mutants were more likely to be sensitive to artemisinin-derivatives as well as to heightened oxidative stress. Major processes critical for P. falciparum tolerance to febrile temperatures and artemisinin included highly essential, conserved pathways associated with protein-folding, heat-shock and proteasome-mediated degradation, but also, unexpectedly, isoprenoid biosynthesis, which originated from the parasite’s ancient endosymbiotic plastid, the apicoplast. Apicoplast-associated genes in general were up-regulated in response to heat shock, as were other Plasmodium genes with orthologs in plant and algal genomes.

Conclusions: Plasmodium falciparum parasites appear to exploit their innate febrile-response mechanisms to mediate resistance to artemisinin, and both responses depend on some of the most ancient genes in the parasite’s genome, suggesting a link to the evolutionary origins of Plasmodium parasites in free-living ancestors.