Endophytes in Artemisia annua L.: new potential regulators for plant growth and artemisinin biosynthesis

The medicinal plant Artemisia annua L. is presently the sole plant source of artemisinin, the key ingredient of first-line antimalarial drug. As the content of artemisinin in the native plant is very low, the growth and artemisinin biosynthesis of A. annua attract extensive attentions. Endophytic microbes, which spend their entire life spans within plant tissue are widespread in healthy A. annua plants. Although endophytes have emerged in recent years as the novel resources for secondary metabolites of antioxidant, antimicrobial and anticancer activities, the roles of endophytes in plant growth and metabolism have not been fully understood. This review presents the current development of researches into endophytes in model medicinal herb A. annua and focuses on the regulatory roles of endophytes. We introduced the isolation, cultivation and identification method for endophytes in A. annua. Distribution, biodiversity and novel bioactive metabolites of the endophytes were presented. Endophytes promoted the growth of A. annua through the enhanced photosynthesis, nutrient acquisition and phytohormones. The defense resistance against microbial pathogens of A. annua was partially involved with endophyte metabolites. The development of glandular secretory trichomes and the oxidative stress induced by endophytes could be key factors for enhanced artemisinin production. Understanding the endophyte-host partnerships has the potential to improve agricultural practices for A. annua growth and artemisinin production. The aim of this review is to shed light on the importance of endophytes in plant growth and the production of medicinally important secondary metabolites.