Effects Of An Endophytic Streptomyces Sp. On Growth And Artemisinin Biosynthesis Of Artemisia Annua L.

Artemisinin, a sesquiterpene lactone, is the major secondary metabolite of Chinese traditional medicine Artemisia annua L.. It is an effective and low-toxic antimalarial drug and has excellent effect against multi-drug resistant strains of Plasmodium. Since extracting from the intact plant remains the main source of artemisinin, the low content in A. annua limits the commercial production. In recent years, various studies have found endophytes in plants could produce new functional metabolites and induce accumulation of plant secondary metabolites. Therefore, in the present study, we investigated the effect of endophytic actinomycetes(Streptomyces sp.) on growth, physiology and the accumulation of artemisinin in A. annua. The induction mechanism has also been investigated preliminarily.Firstly, we isolated an endophyte from wild A. annua plants. The results of morphological observation and molecular identification indicated the endophyte belonged to the Streptomyces and had 99% similarity with Streptomyces coelicolor, Streptomyces somaliensis and Streptomyces flavofungini. The 16 S rRNA sequence had submitted to Genbank(accession number KJ589646). The strain was named as Streptomyces sp.. We further investigated the phosphate solubilization and indole-acetic acid(IAA) production activity of Streptomyces sp. in vitro. It could not soluble inorganic phosphorus but had the activity to produce IAA which was mainly produced by L-tryptophan-dependent pathways.The strain was used to inoculate A. annua gnotobiotic seedlings. Re-isolation results indicated Streptomyces sp. could enter into the plants. Streptomyces sp. in the plants showed little effect on the growth of A. annua. The content of hydrogen peroxide(H2O2) was increased by 12% with the inoculation of Streptomyces sp.. Activity of superoxide dismutase(SOD) was decreased while activity of H2O2-scanvenging enzymes including catalase(CAT), peroxidase(POD) and ascorbate peroxidase(APX) was increased indicating the increase of defense reaction of A. annua after the inoculation.Finally, we explored the change of artemisinin content after 66 days inoculation and researched the mechanism in it. The stain induced the increase of artemisinin content, which was 1.98 fold to the control. Length of trichomes in leaves was increased but numbers of trichomes decreased. Expression of HMGR gene in the mevalonic acid pathway and DXS gene in methylerythritol phosphate(MEP) pathway was increased while expression of DXR gene in MEP pathway decreased. Gene expression in the biosynthesis downstream was not effected. That was to say, Streptomyces sp. increased content of artemisinin by inducing the MVA pathway.In summary, this study isolated an endophytic streptomces(Streptomyces sp.) from A. annua and inoculated the strain into A. annua gnotobiotic seedlings to research its effects on the growth and biosynthesis of artemisinin. The induction mechanism was elucidated preliminarily. This work will guide us to understand the relationship between endophyte and plants and increase artemisinin production with endophytes.