Characterization of a trichome-specific promoter of the aldehyde dehydrogenase 1 (ALDH1) gene in Artemisia annua

Artemisinin is a frequently used anti-malaria drug extracted from glandular trichomes (GSTs) in Artemisia annua L. In this study, we report on the characterization of the promoter of aldehyde dehydrogenase 1 (ALDH1) involved in the biosynthesis of artemisinin. A 1620-bp promoter fragment was cloned upstream of the ALDH1 start codon. Putative regulatory cis-acting elements are predicted by software, revealing that this gene is affected by complex factors. The activity of the ALDH1 promoter was analyzed using a reporter gene GUS. GUS expression showed a spatial difference in leaves at different ages. In young leaves, GUS staining was exclusively discovered in GSTs. In older leaves, both GSTs and T-shaped trichomes (TSTs) showed GUS signals. Only TSTs showed GUS staining in lower leaves. No GUS staining was detected in the bottom leaves. The result demonstrates that the ALDH1 promoter is trichome-specific. The RT-Q-PCR analysis revealed that both wild-type and recombinant promoters showed similar activity in A. annua. After application of exogenous 100 μM methyl jasmonate, 100 μM gibberellin and 100 μM salicylic acid separately, the transcript levels were increased significantly, indicating that ALDH1 may play an important role in the response to hormones in A. annua.