Project summary Severe malaria due to infection by Plasmodium falciparum is a serious threat to global health with over a million deaths per year. New antimalarial agents are needed due to widespread resistance to existing therapies. A promising antimalarial drug target is the MEP pathway of isoprenoid biosynthesis, which is not found in humans. This pathway is the target of an antimalarial agent, fosmidomycin, which is currently in Phase II clinical trials in combination therapies for malaria. We have used forward genetic screening to identify fosmidomycin-resistant malaria parasites, in order to investigate the genetic mechanisms of fosmidomycin resistance and advance our basic understanding of isoprenoid biology. We have thus identified a new family of metabolic regulators in malaria, the HAD proteins. Our approach consists of two specific aims: (1) Establish the mechanisms of HAD-mediated drug resistance, and (2) Characterize the genetic and metabolic mechanisms that underlie enhanced drug resistance in malaria strains lacking HADs. We will identify P. falciparum genes and pathways that genetically interact with the essential MEP pathway and our strong preliminary results support this approach. Our results will identify molecular biomarkers of fosmidomycin resistance and identify new targets for much needed antimalarial drug development.