Effect of Antisense Squalene Synthase Gene Expression on the Increase of Artemisinin Content in Artemisia anuua

Artemisinin, a sesquiterpene lactone endoperoxide, is a valuable and powerful antimalarial drug obtained from the aerial parts of a Chinese herb, Artemisia annua (Liu et al., 1979). Artemisinin and its derivatives show few or no side effects with the existing antimalarial drugs, it has consequently been regarded as the next generation of antimalarial drugs (Looaresuwan, 1994). Currently, commercial production of artemisinin mainly based on its extraction and purification from plant material, however, the endogenous production of artemisinin is very low (0.01%-0.8% dry weight) (Wallaart et al., 1999). In view of the limited availability of artemisinin and the increased demand, the synthetic preparation of artemisinin becomes an attractive proposition. However due to its complex structure, the complete chemical synthesis is very difficult (Schmid & Hofheinz, 1983). Artemisia annua as the only valid source, many research groups have directed their investigations toward the enhancement of artemisinin production in A. annua cell cultures or whole plants by biotechnological approaches. However these approaches were still proved to be not successful (Ghingra et al., 2000). Recently, several genes in artemisinin biosynthesis have been cloned, and important advances in artemisinin biosynthesis have been achieved, which makes it possible to regulate artemisinin biosynthesis in a direct way, for example, by metabolic engineering (Abdin et al., 2003).