(660g) Signal Transduction Engineering As a Powerful Tool for Enhancing Valuable Secondary Metabolite Production By Plant Cells and Higher Fungi

Plant cells and medicinal mushrooms are a treasury of therapeutically bioactive agents. Ginsenosides are an important group of tetracyclic triterpene glycosides produced by Panax ginseng, a well-known traditional Chinese medicinal plant, and the versatile pharmacological activities of ginsenosides include hypocholesterolemic, antitumor, immunoadjuvant and anti-inflammatory functions. Ganoderic acids (GAs) produced by Ganoderma lucidum, a traditional Chinese medicinal mushroom, have significant pharmacological activities such as anti-tumor, anti-metastasis and anti-HIV. Both ginsenosides and GAs are synthesized through the mevalonate/isopenoid pathway, but the details of later steps in their biosynthetic pathways are yet unclear. The fact implies that construction of heterologous biosynthetic pathway of them in other hosts is not feasible at this stage, although a few di/tri-terpenoids-derived natural products have been produced in microorganisms.

Signal transduction engineering is important to improve secondary metabolite production. In this work, the effects of heavy metals and other elicitors on the ginsenoside and GAs biosynthesis in liquid cultures of P. ginseng and G. lucidum were investigated. The optimal concentration and time of vanadate addition for ginsenoside biosynthesis and Mn²⁺ addition for GAs biosynthesis were identified. The increased activities of key enzymes and up-regulation of transcriptional levels of genes encoding enzymes in the triterpenes’ biosynthesis were observed. Further investigation by intracellular Ca²⁺ imaging and calcineurin inhibitor study revealed that addition of Mn²⁺ led to Ca²⁺ influx from medium to the cells to trigger calcineurin signals. The regulation mechanism of Mn²⁺ on the GA biosynthesis was considered through calcineurin signaling transduction. For the ginseng cell culture, our results indicated that vanadate stimulated the ginsenoside biosynthesis by inducing the signal molecule jasmonic acid. This work demonstrated that elicitors manipulation, as efficient induction strategy, significantly improved the production of ginsenosides and GAs in the cell cultures. The approach of signal transduction engineering proposed here is very useful for large-scale production of ginsenosides, GAs, and other important secondary metabolites in plant-cell/mushroom cultures.