Abstract
Salvia miltiorrhiza is known for tanshinones and salvianolic acids, which have been shown to have a protective effect against ROS, especially for cardiovascular diseases and other various ailments of human organs. Due to the low yield of tanshinones and their analogs in S. miltiorrhiza, multiple stimulation strategies have been developed to improve tanshinones production in plant tissue cultures. Endophytic fungi have been reported to form different relationships with their host plants, including symbiotic, mutualistic, commensalistic, and parasitic interactions. Thus we take the assumption that endophytic fungi may be a potential microbial tool for secondary metabolism promotion in medicinal plants. We recently isolated Chaetomium globosum D38 from the roots of S. miltiorrhiza and our study aimed to examine the effects of this live endophytic fungus D38 and its elicitor on the accumulation of tanshinones in the hairy root cultures of S. miltiorrhiza. Our results revealed that C. globosum D38 mainly colonized in the intercellular gap of xylem parenchyma cells of S. miltiorrhiza hairy roots during the long term co-existence without any toxicity. Moreover, both of the live fungus and its mycelia extract could increase the production of tanshinones, especially for dihydrotanshinone I and cryptotanshinone. The effect of the mycelia extract was much stronger than that of the live fungus on tanshinones synthesis, which significantly increased the transcriptional activity of those key genes in tanshinone biosynthetic pathway. Furthermore, the live C. globosum D38 could also be made into biotic fertilizer used for S. miltiorrhiza seedlings culture, which not only significantly promoted the growth of the host plant, but also notably enhanced the accumulation of tanshinones and salvianolic acids. We thus speculated that, in the soil environment D38 could form bitrophic and mutual beneficial interactions with the host and enhance the plant growth and its secondary metabolism on the whole so as to have facilitative effects on both tanshinones and salvianolic acids accumulation. In conclusion, Chaetomium globosum D38 was a highly beneficial endophytic fungus for the growth and metabolism of S. miltiorrhiza.
Highlights
Herbal medicines consumption has been increasing steadily and plant-derived secondary metabolites have become an important part for human health and nutrition
Though most plants are infested by a group of fungi that will not cause obvious disease symptoms, these fungi may trigger a complex network of reactions leading to the biosynthesis and accumulation of secondary metabolites (Zhao et al, 2010)
Fungal endophytes could act as a zoetic elicitor to multiply and persistently stimulate the plant tissue (Saikkonen et al, 2004; Rusch, 2016), there are few reported endophytes from the host plant can be co-cultured with their host plant tissue for a long time
Summary
Herbal medicines consumption has been increasing steadily and plant-derived secondary metabolites have become an important part for human health and nutrition. It is known that elicitation can enhance the biosynthesis of secondary metabolites and biotic elicitors (Thwe et al, 2016) have been used to induce the secondary metabolites accumulation in medicinal plants (Bahabadi et al, 2014) It is one of the most effective means to stimulate secondary metabolites biosynthesis in plant tissue cultures, such as hairy roots and plant cells, using pathogenic and nonpathogenic fungi as biotic elicitors (Huang et al, 2016). Not all the endophytes have the ability to coculture with their host plant tissues for a long time, which depends on the toxicity of the fungal isolate In most cases, those fungi were fabricated into elicitors with their toxicity removed, which can stimulate the secondary metabolism of the host plants (Giauque and Hawkes, 2013). Fully elucidation of above-mentioned host–microbe interactions, may provide solid evidence for the favorable effects of long-term microbial beneficially colonization on herbal plants (Guo et al, 2015)
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