Transcriptome analysis of 1- and 3-year-old Panax notoginseng roots and functional characterization of saponin biosynthetic genes DS and CYP716A47-like

Transcriptome analysis revealed high expression of saponin biosynthetic genes may account for highly accumulated saponins in 3-year-old Panax notoginseng roots and DS and CYP716A47 - like were functionally verified by transgenic tobacco. Panax notoginseng is a well-known traditional medical herb that contains bioactive compounds known as saponins. Three major dammarene-type triterpene saponins including R1, Rb1, and Rg1 were found to be highly accumulated in the roots of 3-year-old plants when compared to those of 1-year-old plants. However, the underlying cellular mechanism is poorly understood. In this study, transcriptome analysis revealed that most genes involved in saponin biosynthesis in P. notoginseng roots augmented during their growth periods. The analysis of the KEGG pathway indicated that the primary metabolism, cell growth, and differentiation were less active in the roots of 3-year-old plant; however, secondary metabolisms were enhanced, thus providing molecular evidence for the harvesting of P. notoginseng roots in the 3rd year of growth. Furthermore, the functional role of DS and CYP716A47-like, two of the candidate genes involved in saponin biosynthesis isolated from P. notoginseng, were verified via overexpression in cultivated tobacco. Approximately, 0.325 µg g−1 of dammarenediol-II and 0.320 µg g−1 of protopanaxadiol were recorded in the dry leaves of transgenic tobacco overexpressed with DS and both DS and CYP716A47-like, respectively. This study provides insights into the molecular mechanisms for saponin accumulation in P. notoginseng roots during its growth period and paves a promising way to produce dammarenediol-II and protopanaxadiol via transgenic techniques.