Molecular Cloning and Characterization of a Trichome-Specific Promoter of Artemisinic Aldehyde Δ11(13) Reductase (DBR2) in Artemisia annua

Artemisinin is widely used as an antimalarial drug around the world. Artemisinic aldehyde Delta 11(13) reductase (DBR2) is a key enzyme which reduces artemisinic aldehyde to dihydroartemisinic aldehyde in the biosynthesis of artemisinin. In this study, two fragments encompassing a putative promoter of DBR2, designated as DBR2pro1 and DBR2pro2, were isolated using genomic DNA walking. The transcription start site and the putative cis-elements of each version of promoter were predicted using bioinformatic analysis. In order to study the function of the cloned promoter, Artemisia annua was transformed with beta-glucuronidase (GUS) reporter gene driven by DBR2pro1 and DBR2pro2, respectively. GUS staining results demonstrated that both DBR2pro1 and DBR2pro2 were strongly expressed in glandular secretory trichomes (GSTs) of leaf primordia and flower buds, but were not obviously expressed in roots, stems, old leaves, and fully developed flowers, thus indicating that the two versions of promoter were functional and specifically expressed in GSTs.