Cold stress improves the production of artemisinin depending on the increase in endogenous jasmonate

Previous publications reported that the artemisinin level was increased in Artemisia annua following a night-frost period. However, the molecular mechanism was not clear. In this study, we found that exogenous jasmonate (JA) effectively enhanced the freezing tolerance of A. annua. The JA biosynthetic genes (LOX1, LOX2, allene oxide cyclase [AOC], and jasmonate resistant 1 [JAR1]) were induced by cold stress, leading to an increase in endogenous JA in cold-treated A. annua. Increased endogenous JA enhanced the expression of three JA-responsive transcription factors, ethylene response factor 1, ethylene response factor 2, and octadecanoid-responsive AP2/ERF, all of which were reported to transcriptionally activate the expression of artemisinin biosynthetic genes, such as amorpha-4,11-diene synthase (ADS), CYP71AV1, DBR2, and aldehyde dehydrogenase 1 (ALDH1). Furthermore, the expression levels of the four artemisinin biosynthetic genes were also significantly increased under cold stress. Consequently, the levels of artemisinin and related secondary metabolites, such as dihydroartemisinic acid, artemisinin B, and artemisinic acid, were increased in A. annua under cold stress. Our study points to a molecular mechanism in which the production of artemisinin is regulated by cold stress in A. annua.