Characterization of the Promoter of Artemisia annua Amorpha-4,11-diene Synthase (ADS) Gene Using Homologous and Heterologous Expression as well as Deletion Analysis

Amorpha-4,11-diene synthase (ADS) is the first key enzyme of artemisinin biosynthetic pathway in Artemisia annua L. In this study, the promoter region of the ADS gene has been cloned and used to demonstrate the expression of GUS reporter gene in both glandular trichomes of A. annua and non-glandular trichomes of Arabidopsis thaliana following homologous and heterologous expression of ADS promoter-GUS fusion. Subsequently, 5' sequential deletion analysis of the ADS promoter revealed that a short sequence, -350 upstream of the transcription start site, was sufficient for trichome-specific expression in A. thaliana and that the region from -350 to -300 contained essential elements for this observed specificity. However, frequencies of transgenic A. thaliana plants displaying trichome-specific expressions varied between different lines, and all the lines with deleted fragments of the ADS promoter showed lower frequencies than the line with full-length ADS promoter. Most lines with deleted ADS promoter-GUS fusions showed GUS expressions in the guard cells of stomata as well, which was not observed in A. thaliana plants transformed with the full-length ADS promoter. GUS activities varied among different transgenic lines as well, both in transiently transformed Nicotiana benthamiana and stably transformed A. thaliana, with promoter-deletion lines exhibiting higher GUS activities than the full-length ADS promoter line.