Biosynthetic Gene Expression and Tissue Distribution of Diosgenin in Dioscorea japonica .

Diosgenin is an aglycone of dioscin, a major bioactive steroidal saponin found in plants, including Himalayan Paris (), fenugreek (), and yam ( spp.). We have previously demonstrated that a species of natural yam, , contains a promising bioactive compound diosgenin, which induces anti-carcinogenic and anti-hypertriacylglycerolemic activities. Here, we found for the first time that Japanese yam () bulbils are richer in diosgenin than the edible tubers (rhizomes) and leaves. LC-MS and imaging-MS analyses revealed that diosgenin accumulated in the peripheral region of bulbils. Additionally, we performed RNA-seq analysis of , and multiple sequence alignment identified (CYP90), the orthologous gene of CYP90G4 in , CYP90B50 in , CYP90G6 in , and CYP90G in , which encodes a diosgenin biosynthetic rate-limiting enzyme. The expression levels of CYP90 were significantly upregulated in bulbils than in its rhizomes and leaves. Since diosgenin is one of the most promising functional food factors executing several favorable bioactivities, bulbils rich in diosgenin would be a beneficial natural resource.