Seasonal and differential sesquiterpene accumulation in artemisia annua suggest selection based on both artemisinin and dihydroartemisinic acid may increase artemisinin in planta

Authors: Ferreira, Jorge; BENEDITO, VAGNER - West Virginia State University; Sandhu, Devinder; MARCHESE, JOSE - The Federal University Of Technology; LIU, SHUOQIAN - Hunan Agricultural University

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/6/2018
Publication Date: 8/13/2018
Publication URL: https://handle.nal.usda.gov/10113/6496456
Citation: Ferreira, J.F., Benedito, V.A., Sandhu, D., Marchese, J.A., Liu, S. 2018. Seasonal and differential sesquiterpene accumulation in artemisia annua suggest selection based on both artemisinin and dihydroartemisinic acid may increase artemisinin in planta. Frontiers in Plant Science. 9:1096. https://doi.org/10.3389/fpls.2018.01096.
DOI: https://doi.org/10.3389/fpls.2018.01096

Interpretive Summary: The worldwide supply of the antimalarial artemisinin (ART) for the production of ARTcombination therapies (ACT), relies solely on commercial plantings of ART source plant Artemisia. Although plant ART increased considerably in the past 20 years, further increase is needed to decrease ACT global prices and make it affordable for developing countries afflicted by malaria. There is no study on the seasonal peak of ART or its main precursor (DHAA) in the plant, and plant selection has focused only on increased ART and biomass. Our results show that ART daily concentration varies little in the plant, but greatly during the season. Our seasonal studies of elite Brazilian, Chinese, and Swiss germplasms in eastern USA established that ART peaks in vegetative plants of all germplasms in late August to early September. While the main ART biochemical precursor peaks with ART in Chinese and Swiss plants, it decreases, as ART increases, in the Brazilian plants. Chinese plants produced up to 0.9% ART and 1.6% DHAA; Brazilian plants produced up to 0.9% ART, but less than 0.4% DHAA; Swiss plants produced 0.8% ART and up to 1% DHAA. Field studies using Brazilian and Swiss seeded plants showed that ART ranged from 0.55-1.2% (Swiss) with all plants being higher in DHAA than ART, and from 0.33-1.5% ART (Brazilian), with most plants being higher in ART than DHAA, reflecting the ART variability that occurs in commercial crops. One germplasm from the UK produced from less than 0.2% of ART and DHAA, but 0.4-1.1% of artemisinic acid, a biochemically competing precursor to ART and DHAA. Plants that are high in artemisinic acid, but low in ART and DHAA, have no commercial value. Our data indicates that differing pathways between Brazilian and both Swiss and Chinese plants may be explored by crossing Chinese or Swiss DHAA-rich plants with Brazilian ART-rich plants to obtain new crosses that are higher in ART than currently available commercial germplasm. Selection for both ART and DHAA can be a valuable approach for future selection and breeding to generate both high-ART and high-DHAA hybrids and that may convert DHAA into ART during commercial drying. If proven successful, this approach will change the focus of breeding of Artemisia and other pharmaceutical crops. The attainment of natural variants with high ART concentration will empower the countries and farmers who select, improve, and cultivate Artemisia plants as a commercial pharmaceutical crop. This approach will also make sure that ART will be produced in places where it is needed to fight malaria and other parasitic neglected diseases.

Technical Abstract: Commercial Artemisia annua crops are the sole source of artemisinin (ART) worldwide. Data on seasonal accumulation and peak of sesquiterpenes, especially ART in commercial A. annua, is lacking while current breeding programs focus only on ART and plant biomass, but ignores dihydroartemisinic acid (DHAA) and artemisinic acid (AA). Despite past breeding successes, plants richer in ART are needed to decrease prices of artemisinin-combination therapy (ACT). Our results show that sesquiterpene concentrations vary greatly along the growing season and that sesquiterpene profiles differ widely among chemotypes. Field studies with elite Brazilian, Chinese, and Swiss germplasms established that ART peaked in vegetative plants from late August to early September, suggesting that ART is related to the photoperiod, not flowering. DHAA peaks with ART in Chinese and Swiss plants, but decreases, as ART increases, in Brazilian plants, while AA remained stable through the season in these genotypes. Chinese plants peaked at 0.9% ART, 1.6% DHAA; Brazilian plants at 0.9% ART, with less than 0.4% DHAA; Swiss plants at 0.8% ART and 1% DHAA. At single-date harvests, seeded Swiss plants produced 0.55–1.2% ART, with plants being higher in DHAA than ART; Brazilian plants produced 0.33–1.5% ART, with most having higher ART than DHAA. Elite germplasms produced from 0.02–0.43% AA, except Sandeman-UK (0.4–1.1% AA). Our data suggest that different chemotypes, high in ART and DHAA, have complementary pathways, while competing with AA. Crossing plants high in ART and DHAA may generate hybrids with higher ART than currently available in commercial germplasms. Selecting for high ART and DHAA (and low AA) can be a valuable approach for future selection and breeding to produce plants more efficient in transforming DHAA into ART in planta and during post-harvest. This novel approach could change the breeding focus of A. annua and other pharmaceutical species that produce more than one desired metabolite in the same pathway. Obtaining natural variants with high ART content will empower countries and farmers who select, improve, and cultivate A. annua as a commercial pharmaceutical crop. This selection approach could enable ART to be produced locally where it is most needed to fight malaria and other parasitic neglected diseases.