Natural lupeol level variation among castor accessions and the upregulation of lupeol synthesis in response to light

Lupeol, a plant-derived lupane-type pentacyclic triterpenoid, has many pharmacological activities. Although lupeol is found widely in many fruits, vegetables, and medicinal plants, its low content and difficult extraction limit its current applications. The castor plant (Ricinus communis L.) is a potential candidate plant for producing lupeol because it accumulates at high levels as a dominant wax component in the epidermal surface. The lupeol content varies significantly among castor individuals/cultivars. To identify castor lines for further breeding and uncover the molecular mechanism of lupeol biosynthesis and regulation, several castor varieties with various lupeol levels were identified, including 26 lines with higher lupeol contents and 12 glossy lines with very low lupeol contents. A deletion of the coding sequence of castor lupeol synthase RcLUS-1 was identified in glossy1, which possibly affects the binding ability of the substrate. The role of RcLUS-1 in lupeol production was determined using a virus-induced gene silencing (VIGS) assay. The promoter region of RcLUS-1 was analyzed further to uncover the factors affecting lupeol synthesis. Several potential cis-acting elements responding to light present were enriched in this region. Further study showed that light intensity affects RcLUS-1 expression and lupeol production. Overall, this study evaluated several potential castor resources for future breeding and expanded the knowledge of the lupeol regulation mechanism.