Flavonoid Versus Artemisinin Anti-malarial Activity in Whole-Leaf Extracts.

Artemisinin, a sesquiterpene lactone produced by glandular secretory trichomes, is the active ingredient in the most effective treatment for uncomplicated malaria caused by parasites. Other metabolites in or related species, particularly flavonoids, have been proposed to either act as antimalarials on their own or act synergistically with artemisinin to enhance antimalarial activity. We identified a mutation that disrupts the CHALCONE ISOMERASE 1 (CHI1) enzyme that is responsible for the second committed step of flavonoid biosynthesis. Detailed metabolite profiling revealed that lacks all major flavonoids but produces wild-type artemisinin levels, making this mutant a useful tool to test the antiplasmodial effects of flavonoids. We used whole-leaf extracts from and mutant lines impaired in artemisinin production in bioactivity assays against intraerythrocytic Dd2. We found that extracts did not differ from wild-type extracts in antiplasmodial efficacy nor initial rate of cytocidal action. Furthermore, extracts from the mutant and RNAi lines impaired in amorpha-4,11-diene synthase gene expression, which are both severely compromised in artemisinin biosynthesis but unaffected in flavonoid metabolism, showed very low or no antiplasmodial activity. These results demonstrate that bioactivity against of flavonoids is negligible when compared to that of artemisinin.