TAR1 Is Required for Artemisinin Biosynthesis and Trichome Development in Artemisia Annua L

Trichomes, small protrusions on the surface of many plants, can produce and store various secondary metabolic products. Artemisinin, a famous and potent medicine for malaria, is synthesized, stored and secreted by Artemisia annua trichomes. However the molecular basis regulating the biosynthesis of artemisinin and the development of trichomes remains poorly understood. Here, we revealed the crucial role of an AP2 transcription factor, TRICHOME AND ARTEMISININ REGULATOR 1 (TAR1), in controlling the development of trichomes and the biosynthesis of artemisinin in A. annua. TAR1 is expressed mainly in young leaves, flower buds, and some trichomes, and its protein is specially located in cell nucleus. In TAR1-RNAi lines, the phenotype of trichomes and the composition of cuticular wax were altered. The content of artemisinin was dramatically reduced as well, which increased significantly when TAR1 was overexpressed. Furthermore, the expression of many genes that participate in artemisinin biosynthesis was changed when TAR1 was silenced or overexpressed, especially ADS and CYP71AV1, which were shown to be the likely direct targets of TAR1 through electrophoretic mobility shift, yeast one-hybrid and transient transformation GUS assay. These results indicate that TAR1 is a key component of the molecular network regulating A. annua trichome development and artemisinin biosynthesis.