Expression of artemisinin biosynthesis and trichome formation genes in five Artemisia species

Artemisinin, a sesquiterpene lactone produced by some Artemisia species, is an efficacious anti-malarial drug, effective against cancer, hepatitis, and schistosomiasis. A. annua is a main source of artemisinin while other Artemisia species produce less artemisinin content. The aim of the current study was to identify the limiting factor of artemisinin biosynthesis in studied Artemisia species, compared to A. annua. The specialized 10-celled biseriate glandular trichomes on the leaves, stems, and inflorescences of some Artemisia species are as a site of artemisinin synthesis. The leaves of five Artemisia species, having different artemisinin contents were assessed in terms of the glandular trichomes density, and area per leaf, and the expression of artemisinin biosynthesis genes and two genes (Aa-TTG1 and Aa-TFAR1) involved in trichome formation. This study identified one novel plant sources of artemisinin (A. deserti, 5.30 mg g−1 DW) that statistically performed as well as A. annua of Iran (6.27 mg g−1 DW), but inferior to A. annua cv. Anamed (14.50 mg g−1 DW) at the flowering stage. A. deserti had the highest trichome area per leaf area accompanied with a high expression of Aa-ADS, Aa-AlDH1, Aa-CYP71AV1, Aa-TTG1, and Aa-TFAR1 genes. A. persica with low artemisinin content had a high density of glandular trichome, high expression of TTG1 and TFAR1, but low expression of artemisinin biosynthetic genes. A. khorassanica with no artemisinin content had a very low density of glandular trichome and gene expression. The artemisinin content of A. deserti is significantly as same as A. annua of Iran and inferior to A. annua cv. Anamed despite having the highest glandular trichome area per leaf, and high relative expression of Aa-ADS, Aa-ALDH1, Aa-CYP71AV1, Aa-TTG1, and Aa-TFAR1. We suggest that it is related to the preferential oxidation of artemisinic aldehyde to artemisinic acid than the reduction of the artemisinic aldehyde to dihydroartemisinic aldehyde, due to the very high expression of Aa-ALDH1 and Aa-CYP71AV1, and the low expression of Aa-DBR2. It is possible to develop high artemisinin producer plant by overexpression of Aa-DBR2 in A. deserti. It is concluded that there is a relationship between the enhancement of artemisinin content and increased expression of some genes.