Evidence of artemisinin production from IPP stemming from both the mevalonate and the nonmevalonate pathways
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The potent antimalarial sesquiterpene lactone, artemisinin, is produced in low quantities by the plant Artemisia annua L. The source and regulation of the isopentenyl diphosphate (IPP) used in the biosynthesis of artemisinin has not been completely characterized. Terpenoid biosynthesis occurs in plants via two IPP-generating pathways: the mevalonate pathway in the cytosol, and the non-mevalonate pathway in plastids. Using inhibitors specific to each pathway, it is possible to resolve which supplies the IPP precursor to the end product. Here, we show the effects of inhibition on the two pathways leading to IPP for artemisinin production in plants. We grew young (7–14 days post cotyledon) plants in liquid culture, and added mevinolin to the medium to inhibit the mevalonate pathway, or fosmidomycin to inhibit the non-mevalonate pathway. Artemisinin levels were measured after 7–14 days incubation, and production was significantly reduced by each inhibitor compared to controls, thus, it appears that IPP from both pathways is used in artemisinin production. Also when grown in miconazole, an inhibitor of sterol biosynthesis, there was a significant increase in artemisinin compared to controls suggesting that carbon was shifted from sterols into sesquiterpenes. Collectively these results indicate that artemisinin is probably biosynthesized from IPP pools from both the plastid and the cytosol, and that carbon from competing pathways can be channeled toward sesquiterpenes. This information will help advance our understanding of the regulation of in planta production of artemisinin.
KeywordsArtemisinin Mevalonate pathway Nonmevalonate pathway DMSO
Thanks to Brandon Matthews for some preliminary work. We also appreciate assistance with statistics by Professor Liz Ryder of WPI, and the critical reviews provided by Professors Kris Wobbe at WPI, and Fabricio Medina-Bolivar at the Arkansas Bioscience Institute. Financial support for this work was gratefully received from NIH 1R15GM 069562-01.
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