Squalene epoxidase (also called squalene monooxygenase) catalyses the conversion of squalene into 2,3-oxidosqualene by epoxidation and is regarded as the rate-limiting enzyme for sterol and saponin biosynthesis. However, the role of the squalene epoxidase gene in saponin biosynthesis in plants is not yet well understood. Here, we investigated the effects of overexpression of a Panax ginseng squalene epoxidase gene (PgSE1) on the production of phytosterols and ginsenoside saponins in ginseng adventitious roots. For the functional complementation test, the two squalene epoxidase sequences (PgSE1 and PgSE2) of P. ginseng were expressed in a yeast erg1 mutant (ergosterol auxotroph). The yeast mutant expressing PgSE1 or PgSE2 can restore growth on medium lacking ergosterol. Transgenic ginseng roots overexpressing the PgSE1 gene were constructed by Agrobacterium-mediated genetic transformation. The transgenic ginseng roots resulted in the enhanced production of both ginsenosides (ginsenoside Rg1, Re, Rf, Rc, Rb1, Rb2, and Rd) and phytosterols (campesterol, stigmasterol, and β-sitosterol). qPCR analysis revealed that overexpression of PgSE1 in transgenic ginseng roots clearly enhanced the expression of dammarenediol-II synthase (PgDDS) and cycloartenol synthase (PgPNX), which are key enzymes for ginsenoside and phytosterol biosynthesis in P. ginseng. This result indicates that the P. ginseng squalene epoxidase gene (PgSE1) encodes an efficient enzyme responsible for not only phytosterol production but also ginsenoside production in P. ginseng.

角鲨烯环氧酶（也称为角鲨烯单加氧酶）通过环氧化催化角鲨烯向2，3-氧化角鲨烯的转化，并且被认为是固醇和皂苷生物合成的限速酶。然而，关于角鲨烯环氧酶基因在植物皂素生物合成中的作用尚不清楚。在这里，我们调查了人参不定根中人参角鲨烯环氧酶基因（PgSE1）的过量表达对植物甾醇和人参皂甙皂苷生产的影响。为了进行功能互补测试，人参假单胞菌的两个角鲨烯环氧酶序列（PgSE1和PgSE2）在酵母erg1中表达 突变体（麦角固醇营养缺陷型）。表达PgSE1或PgSE2的酵母突变体可以在缺少麦角固醇的培养基上恢复生长。通过农杆菌介导的遗传转化构建了过量表达PgSE1基因的人参根。转基因人参根导致人参皂甙（人参皂甙Rg1，Re，Rf，Rc，Rb1，Rb2和Rd）和植物甾醇（菜油甾醇，豆甾醇和β-谷甾醇）的产量均增加。qPCR分析揭示的过表达PgSE1在转基因人参根明显增强dammarenediol-II合酶（表达PgDDS）和环木菠萝烯醇合酶（PgPNX），其是用于在人参皂甙和植物甾醇的生物合成的关键酶P.人参。该结果表明，该P.人参角鲨烯环氧酶基因（PgSE1）编码负责不仅植物甾醇生产，而且生产人参以高效的酶P.人参。