ABSTRACT
OBJECTIVE: To study the relative expression of the genes involved in artemisinin biosynthesis in different tissues including roots, stems, leaves and flowers of Artemisia annua, and establish the relationship between gene expression and artemisinin accumulation, eventually leading to discover the mainly effective genes involved in artemisinin biosynthesis. METHOD: The 7 functional genes involved in artemisinin biosynthesis were detected at the level of expression by using qRT-PCR, and simultaneously the content of artemisinin in the 4 investigated tissues was detected in parallel. RESULT: The 3 genes including HMGR, DXR and FPS which were involved in the upstream pathway of artemisinin biosynthesis showed the highest expression levels in flowers, and the 4 functional genes including ADS, CYP71AV1, CPR and AAR which were involved in the artemisinin-specific biosynthetic pathway were found to be expressed in all the 4 detected tissues. The highest expression level of ADS was found in leaves, then followed by flowers, and the lowest expression level of ADS was found in roots and stems. CYP71AV1 had highest expression level in flowers and lowest in leaves. CPR showed highest expression level in flowers, and AAR had lower expression levels in the other 3 artemisinin-specific pathway genes in all the tissues. The highest content of artemisinin was found in leaves (0.343 mg x g(-1)), then followed by flowers (0.152 mg x g(-1)), roots (0.062 mg x g(-1)) and stems (0.060 mg x g(-1)). CONCLUSION: In the biosynthesis of artemisinin, the upstream genes including HMGR from the MVA pathway, DXR from the MEP pathway and the checkpoint gene FPS were much more active in flowers, and this suggested that flowers might be the tissues of artemisinin precursor biosynthesis, and further DXR contributed more to artemisinin biosynthesis. The positive correlation of ADS expression and artemisinin content in tissues demonstrated that ADS played a very important role in artemisinin biosynthesis, which was the ideal target for engineering the artemisinin biosynthetic pathway. In summary, the functional genes involved in artemisinin biosynthesis do not express at the same level but synergistically.