To systemically understand the biosynthetic pathways of bioactive substances, including triterpenoids and polysaccharides, in Ganoderma lucidum, the correlation between substrate degradation, carbohydrate and triterpenoid metabolism during growth was analyzed by combining changes in metabolite content and changes in related enzyme expression in G. lucidum over 5 growth phases. Changes in low-polarity triterpenoid content were correlated with changes in glucose and mannitol content in fruiting bodies. Additionally, changes in medium-polarity triterpenoid content were correlated with changes in the lignocellulose content of the substrate and with the glucose, trehalose and mannitol contents of fruiting bodies. Weighted gene coexpression network analysis (WGCNA) indicated that changes in trehalose and polyol content were related to carbohydrate catabolism and polysaccharide synthesis. Changes in triterpenoid content were related to expression of the carbohydrate catabolic enzymes, laccase, cellulase, hemicellulase, and polysaccharide synthase and to the expression of several cytochrome P450 monooxygenases (CYPs). It was concluded that the products of cellulose and hemicellulose degradation participate in polyol, trehalose and polysaccharide synthesis during initial fruiting body formation. These carbohydrates accumulate in the early phase of fruiting body formation and are utilized when the fruiting bodies mature and a large number of spores are ejected. An increase in carbohydrate metabolism provides additional precursors for the synthesis of triterpenoids.
Importance
Most studies of G. lucidum have focused on its medicinal function and on the mechanism of its activity, whereas the physiological metabolism and synthesis of bioactive substances during the growth of this species have been less studied. Therefore, theoretical guidance for cultivation methods to increase the production of bioactive compounds remains lacking. This study integrated changes in the lignocellulose, carbohydrate and triterpenoid contents of G. lucidum with enzyme expression from transcriptomics data using WGCNA. The findings helped us better understand the connections between substrate utilization and the synthesis of polysaccharides and triterpenoids during the cultivation cycle of G. lucidum. The results of WGCNA suggest that the synthesis of triterpenoids can be enhanced not only through regulating the expression of enzymes in the triterpenoid pathway, but also through regulating carbohydrate metabolism and substrate degradation. This study provides a potential approach and identifies enzymes that can be targeted to regulate lignocellulose degradation and accelerate the accumulation of bioactive substances by regulating substrate degradation in G. lucidum.
Genetic and Metabolic Intraspecific Biodiversity ofGanoderma lucidum
