Effect of down-regulating 1-deoxy-<Emphasis Type="SmallCaps">d</Emphasis>-xylulose-5-phosphate reductoisomerase by RNAi on growth and artemisinin biosynthesis in <Emphasis Type="Italic">Artemisia annua</Emphasis> L.

1-Deoxy-d-xylulose-5-phosphate reductoisomerase (DXR), an important enzyme in the 2-c-methyl-d-erythritol-4-phosphate (MEP) pathway in plant plastids, provides the basic five-carbon units for isoprenoid biosynthesis. To investigate the roles of the MEP pathway in regulating growth, development and artemisinin biosynthesis of Artemisia annua L., we used RNA interference technology to generate transgenic plants with suppressed expression of DXR in A. annua (AaDXR). Suppression of AaDXR resulted in shorter stems, decreased branch numbers and leaf area, lower density of leaf trichomes. Although AaDXR-RNAi plants had no significant changes on the stomatal conductance, the net photosynthesis rate was decreased by 20.0–31.4% due to the marked decline in the contents of chlorophyll. Decreased levels of endogenous gibberellic acid (GA₃) and abscisic acid were also detected in the transgenic lines. The artemisinin contents in leaves of all tested transgenic lines declined by 41.8–73.4% at the vegetative stage and 61.5–63.6% at the stages of flowering. The enhancement of artemisinin contents by methyl jasmonate at 300 µM has been abolished at seedling and vegetative stages in AaDXR-RNAi plants. These results demonstrate that AaDXR play import roles in the control of plan vegetative growth and artemisinin biosynthesis in A. annua.