Successes of artemisinin elicitation in low-artemisinin producing Artemisia annua cell cultures constrained by repression of biosynthetic genes

The sesquiterpene phytolactone derived from Artemisia annua, artemisinin is associated with a variety of novel biological properties, such as immunoregulatory and anticancer effects, and therapeutic applications, apart from its main function as an antimalarial drug. Emerging from the fact that artemisinin production in planta occurs in trace amounts and its compartmentalized synthesis, the irregular agricultural supply often results in market fluctuations and reductions in artemisinin inventory. Further improvement in artemisinin production calls for approaches that act in a supplementary manner, filling the agricultural production gap. Here we investigated the elicitation efficiency of ultraviolet B (UV-B) and dimethyl sulfoxide (DMSO) independently on a low-artemisinin producing (LAP) chemotype of the species A. annua. The exposure of cell suspension cultures to short-term UV-B radiation and DMSO treatment did not result in significant changes in artemisinin yield. The lack of stimulation has been associated with: (i) the general lack of cytodifferentiation of cell cultures; (ii) negative feedback regulation of artemisinin biosynthesis; and (iii) artemisinin sequestration by cellular detoxification. Further molecular analysis revealed the repression of key genes ADS, DBR2 and ALDH1 which affected artemisinin synthesis. This study provides insights into the complexity of stress-induced responses of A. annua cell suspension cultures in relation to metabolic processes (transportation, accumulation and degradation of secondary products) which are important for artemisinin formation.