Expression and Localization of Amorpha-4,11-diene Synthase in Artemisia annua L.

Artemisia annua L. is the only commercial source of the widely used antimalarial compound artemisinin. Biosynthesis of artemisinin has been proposed to take place in glandular trichomes. The first committed step in the conversion of farnesyl diphosphate (FDP) to artemisinin is conducted by the amorpha-4,11-diene synthase (ADS). To explore the organ-specific and developmental distributions of ADS, rabbit polyclonal antibodies were raised against recombinant ADS produced in Escherichia coli from the corresponding A. annua cDNA. Protein gel blot analysis of different A. annua organs showed that ADS was most abundant in young leaves and flower buds. Minor amounts of ADS were found in mature leaves. These findings were generally consistent with the analysis of the transcript level of the ADS gene. Immunolocalization of ADS showed strong positive staining in apical meristems, young leaves and glandular trichomes. No staining was observed in other cells of the leaf. The whole mount hybridization revealed that ADS was not expressed in all glandular trichomes of mature leaves. Specific staining of ADS could be detected in about 10–40 % of glandular trichomes.