First report on the regulation and function of carbon metabolism during large sclerotia formation in medicinal fungus Wolfiporia cocos

The medicinal fungus Wolfiporia cocos colonizes and then grows on the wood of Pinus species, and utilizes a variety of Carbohydrate Active Enzymes (CAZymes) to degrades wood for the development of large sclerotia that is mostly built up of beta-glucans. Some differentially expressed CAZymes were revealed by comparisons between the mycelia cultured on potato dextrose agar (PDA) and sclerotia formed on pine logs in previous studies. Here, different profile of expressed CAZymes were revealed by comparisons between the mycelia colonization on pine logs (Myc.) and sclerotia (Scl.b). To further explore the regulation and function of carbon metabolism in the conversion of carbohydrates from Pine species by W. cocos, the transcript profile of core carbon metabolism was firstly analyzed, and it was characterized by the up-regulated expression of genes in the glycolysis pathway (EMP) and pentose phosphate pathway (PPP) in Scl.b, as well as high expression of genes in the tricarboxylic acid cycle (TCA) in both Myc. and Scl.b stages. The conversion between glucose and glycogen and between glucose and β-glucan was firstly identified as the main carbon flow in the differentiation process of W. cocos sclerotia, with a gradual increase in the content of β-glucan, trehalose and polysaccharide during this process. Additionally, gene functional analysis revealed that the two key genes (PGM and UGP1) may mediate the formation and development of W. cocos sclerotia possibly by regulating β-glucan synthesis and hyphal branching. This study has shed light on the regulation and function of carbon metabolism during large W. cocos sclerotium formation and may facilitate its commercial production.