Enzymes involved in plastid-targeted phosphatidic acid synthesis are essential for Plasmodium yoelii liver-stage development

Malaria parasites scavenge nutrients from their host but also harbour enzymatic pathways for de novo macromolecule synthesis. One such pathway is apicoplast-targeted type II fatty acid synthesis, which is essential for late liver-stage development in rodent malaria. It is likely that fatty acids synthesized in the apicoplast are ultimately incorporated into membrane phospholipids necessary for exoerythrocytic merozoite formation. We hypothesized that these synthesized fatty acids are being utilized for apicoplast-targeted phosphatidic acid synthesis, the phospholipid precursor. Phosphatidic acid is typically synthesized in a three-step reaction utilizing three enzymes: glycerol 3-phosphate dehydrogenase, glycerol 3-phosphate acyltransferase and lysophosphatidic acid acyltransferase. The Plasmodium genome is predicted to harbour genes for both apicoplast- and cytosol/endoplasmic reticulum-targeted phosphatidic acid synthesis. Our research shows that apicoplast-targeted Plasmodium yoelii glycerol 3-phosphate dehydrogenase and glycerol 3-phosphate acyltransferase are expressed only during liver-stage development and deletion of the encoding genes resulted in late liver-stage growth arrest and lack of merozoite differentiation. However, the predicted apicoplast-targeted lysophosphatidic acid acyltransferase gene was refractory to deletion and was expressed solely in the endoplasmic reticulum throughout the parasite life cycle. Our results suggest that P.yoelii has an incomplete apicoplast-targeted phosphatidic acid synthesis pathway that is essential for liver-stage maturation.