Study On The Mechanism Of Fungal Polysaccharide Elicitor Mediating The Biosynthesis Of Ganoderma Triterpenes

Ganoderma triterpenes have been found to have various biological activities such as antioxidation,anti-tumor and immune regulation,but their biosynthesis efficiency using conventional fermentation methods is low.Fungal elicitors can induce specific gene expression and promote secondary metabolism by activating the immune defense response of cells.For this reason,Penicillium rolfsii,which was isolated from the soil where G.lucidum was cultivated and can promote the synthesis of Ganoderma triterpenes,made into fungal polysaccharide elicitor(FPE).This thesis first optimized the conditions for FPE to induce triterpene formation,focusing on the FPE-induced primary metabolism of G.lucidum,the triterpene biosynthesis pathway and the response of reactive oxygen species(ROS)signaling pathways,thus revealing the regulation mechanism of FPE-mediated Ganoderma triterpene biosynthesis.The main findings are as follows:1.FPE can obviously promote the growth and the triterpenoid synthesis of liquid fermented G.lucidum.The concentration effect of FPE-induced Ganoderma triterpene synthesis is the optimal concentration type,and its optimal concentration is 75 mg/L.The G.lucidum mycelium that changes from the exponential growth phase to the plateau phase is most sensitive to FPE.Adding 75 mg/L FPE on the 4th day is the best induction condition for the elicitor.Under this treatment,the biomass and triterpene content of G.lucidum are 14.20 g/L and 75.01 mg/g,which are 1.50 times and 2.07 times that of the control group.2.FPE promotes the transformation of primary metabolism to Ganoderma triterpene synthesis metabolism in submerged G.lucidum.After 24 hours of FPE treatment,it was found that the G.lucidum mycelium consumed more reducing sugars and free amino acids,and activated the triterpene synthesis pathway,leading to the up-regulation of the key enzyme gene expression of triterpene synthesis,and the intermediate metabolites such as squalene and lanosterol increased significantly.The content of Ganoderma triterpenes is significantly increased.However,the content of intracellular polysaccharides and protein did not increase significantly.3.FPE regulates the synthesis of Ganoderma triterpene through ROS signaling pathway.FPE promoted the accumulation of ROS in G.lucidum cells,leading to aggravation of lipid peroxidation damage of cell membrane,up-regulation of antioxidant enzyme gene expression,and enhanced antioxidant enzyme activity,indicating that FPE activates the ROS signal pathway of G.lucidum.At the same time,it was found that adding ROS scavengers(NAC,VC)can reduce the influence of FPE on ROS signal transduction pathway,but also inhibit the activation effect of FPE on the Ganoderma triterpene synthesis pathway.These mean that ROS signal transduction pathway plays an important role in the Ganoderma triterpene biosynthesis induced by FPE.