DMSO triggers the generation of ROS leading to an increase in artemisinin and dihydroartemisinic acid in Artemisia annua shoot cultures

The antimalarial sesquiterpene, artemisinin, is in short supply; demand is not being met, and the role of artemisinin in the plant is not well established. Prior work showed that addition of dimethyl sulfoxide (DMSO) to seedlings increased artemisinin in their shoots and this study further investigated that serendipitous observation. When in vitro-cultured Artemisia annua rooted shoots were fed different amounts of DMSO (0-2.0% v/v), artemisinin levels doubled and showed biphasic optima at 0.25 and 2.0% DMSO. Both artemisinin and its precursor, dihydroartemisinic acid, increased with the former continuing 7 days after DMSO treatment. There was no stimulation of artemisinin production in DMSO-treated unrooted shoots. The first gene in the artemisinin biosynthetic pathway, amorphadiene synthase, showed no increase in transcript level in response to DMSO compared to controls. In contrast, the second gene in the pathway, CYP71AV1, did respond to DMSO but at a level of transcripts inverse to artemisinin levels. When rooted shoots were stained for the reactive oxygen species (ROS), H2O2, ROS increased with increasing DMSO concentration; unrooted shoots produced no ROS in response to DMSO. Both the increases in DMSO-induced ROS response and corresponding artemisinin levels were inhibited by addition of vitamin C. Together these data show that at least in response to DMSO, artemisinin production and ROS increase and that when ROS is reduced, so also is artemisinin suggesting that ROS may play a role in artemisinin production in A. annua.