Lupeol is a pentacyclic triterpene which possesses many pharmacological activities. It has been found in many plants but generally with low content. Specifically, castor bean (Ricinus communis L.) contains high amounts of lupeol deposited on the outer surface, which is the major composition of epidermal wax. However, the biochemical pathways or regulatory genes responsible for lupeol accumulation in castor are largely unknown. In this study, a comparative transcriptome study was performed between the epidermis and stele of castor hypocotyl. Thirty-nine candidate genes involved in lupeol biosynthesis were identified and their expressions were analyzed. In particular, five selected genes associated with the mevalonate (MVA) pathway and triterpene downstream biosynthesis showed high correlation between their expression levels and the lupeol contents. Furthermore, several kinds of transcription factors were found to be specifically expressed in the epidermis. Especially, four transcription factors could activate the expression of Lupeol Synthase (RcLUS) in vivo, which is a key gene involved in lupeol synthesis. Taken together, these data will not only advance our understanding of triterpenoid synthesis in plants, but also provides potential candidate genes for enhancing lupeol biosynthesis by genetic engineering.

羽扇豆酚是具有许多药理活性的五环三萜。它已在许多植物中发现，但含量通常较低。具体来说，蓖麻子（蓖麻）L.）含有大量沉积在外表面的卢比欧酚，这是表皮蜡的主要成分。然而，很大程度上未知负责腰果酚的积累的生化途径或调控基因。在这项研究中，在蓖麻下胚轴的表皮和石碑之间进行了比较转录组研究。鉴定了与羽扇豆酚生物合成有关的39个候选基因，并分析了它们的表达。特别是，与甲羟戊酸（MVA）途径和三萜下游生物合成相关的五个选定基因显示出它们的表达水平与羽扇豆酚含量之间的高度相关性。此外，发现几种转录因子在表皮中特异性表达。特别是四个转录因子可以激活体内Lupeol合酶（RcLUS），是参与Lupeol合成的关键基因。综上所述，这些数据不仅将促进我们对植物中三萜类化合物合成的理解，而且还将提供通过基因工程增强羽扇豆酚生物合成的潜在候选基因。