Transcriptomics and metabolomics provide the difference of unique odor between natural and cultivated Ophiocordyceps sinensis and the biosynthetic pathway of key volatile compounds

Abstract

Ophiocordyceps sinensis has a unique fishy odor, but its chemical composition and biosynthesis process have not been paid attention to. In this study, HS-SPME-GC/MS and transcriptome were integrated to explore the differences in volatile compounds (VOCs) and their formation mechanisms between natural and cultivated O. sinensis. We qualitatively and quantitatively analyzed the VOCs in natural and cultivated O. sinensis, and identified 17 key volatile compounds (KOCs) by multivariate statistical analysis combined with relative odor activity (ROVA) value. They identified similar but heterogeneously accumulated fishy odor characteristics in natural and cultivated O. sinensis and their different tissues. Among them, 10 KOCs such as acetic acid, 2-ethylhexyl ester, 1-butanol, 3-methyl-propanoate, 2-n-butyl furan, 2-octanone, 2-butanone,4-(2,6,6-trimethyl-2-cyclohexen-1-yl), 3-mercapto-3-methylbutanol, 1-octen-3-ol, benzeneacetaldehyde, p-cymene, β-damascone and naphthalene, 2-methyl were abundantly enriched in natural O. sinensis, forming woody, balsamic and mushroom-like woody aromas. In cultivated O. sinensis, higher levels of styrene, isophorone and 1h-pyrrole, 1-(2-furanylmethyl) (3 KOCs) form fruity, floral and berry aromas and sweetness similar to honey and rose. These KOCs are more enriched in sclerotia, which means that sclerotia contributes more to the overall odor than stroma. Transcriptome analysis showed that the heterogeneous accumulation of metabolic flux in monoterpenoid biosynthesis and sesquiterpenoid and triterpenoid biosynthesis regulated by core genes such as Zn_clus, psiD, Gpd-2 and chol-2 in the sample explained the biosynthesis process of fishy gas. These results reveal the chemical composition and biosynthesis basis of O. sinensis odor, expand our understanding of the synthesis process of filamentous fungi odor substances, and provide a new strategy for rapid identification of natural and cultivated O. sinensis.