Integrated transcriptional and phytochemical analyses of the flavonoid biosynthesis pathway in Epimedium

Epimedium is a widely used traditional Chinese medicinal plant due to its high content of health-promoting components such as epimedin A, epimedin B, epimedin C, and icariin (hereafter designated as bioactive compounds); however, the biosynthesis of these bioactive compounds in Epimedium remains to be elucidated. In this study, E. sagitattum flavonoid genes, including three copies of chalcone synthase, two copies of dihydroflavonol 4-reductase, and a single copy of each of chalcone isomerase, flavanone 3 hydroxylase, flavonol synthase, and anthocyanidin synthase, have been isolated. In addition, several transcription factors involved in flavonol, anthocyanin, and proanthocyanin pathways, were identified from an Epimedium 454 EST database. Gene expression profiles and the levels of bioactive compounds in light-stressed E. pubescens leaves in response to phytohormones [abscisic acid (ABA), gibberellic acid (GA(3)), indole-3-acetic acid (IAA), salicylic acid (SA)] and sucrose were investigated. All bioactive compounds were significantly elevated by phytohormone and sucrose application except for epimedin B in SA-treated samples and epimedin C following GA(3) and sucrose treatment. Our results suggest that phytohormone and sucrose treatments offer a method for promoting the accumulation of bioactive compounds in Epimedium.