De Novo Sequencing and Transcriptome Analysis of Wolfiporia cocos to Reveal Genes Related to Biosynthesis of Triterpenoids

Wolfiporia cocos Ryvarden et Gilbertson is a saprophytic fungus in the Basidiomycetes. Its dried sclerotium is widely used as a traditional crude drug in East Asia. Especially in China, the dried sclerotium is regarded as the silver of the Chinese traditional drugs, not only for its white color, but also its medicinal value. Furthermore, triterpenoids from W. cocos are the main active compounds with antitumor and anti-inflammatory activity. Biosynthesis of the triterpenoids has rarely been researched. In this study, the de novo sequencing of the mycelia and sclerotia of W. cocos were carried out by Illumina HiSeq 2000. A total of 3,484,996,740 bp from 38,722,186 sequence reads of mycelia, and 3,573,921,960 bp from 39,710,244 high quality sequence reads of sclerotium were obtained. These raw data were assembled into 60,354 contigs and 40,939 singletons, and 56,938 contigs and 37,220 singletons for mycelia and sclerotia, respectively. The transcriptomic data clearly showed that terpenoid biosynthesis was only via the MVA pathwayin W. cocos. The production of total triterpenoids and pachymic acid was examined in the dry mycelia and sclerotia. The content of total triterpenoids was 5.36% and 1.43% in mycelia and sclerotia, respectively, and the content of pachymic acid was 0.458% and 0.174%. Some genes involved in the triterpenoid biosynthetic pathway were chosen to be verified by qRT-PCR. The unigenes encoding diphosphomevalonate decarboxylase (Unigene 20430), farnesyl diphosphate synthase (Unigene 14106 and 21656), hydroxymethylglutaryl-CoA reductase (NADPH) (Unigene 6395_All) and lanosterol synthase (Unigene28001_All) were upregulated in the mycelia stage. It is likely that expression of these genes influences the biosynthesis of triterpenoids in the mycelia stage.