Overexpression of BcERF3 increases the biosynthesis of saikosaponins in Bupleurum chinense.

Chaihu, the dried roots of some species of Bupleurum L., is a famous Chinese herbal medicine for treatment of liver- and cold-related diseases, in which saikosaponins (SSs) are the major active compounds. Many of the genetic components upstream of SS biosynthetic pathways have been characterized; however, the regulatory mechanisms remain elusive. In this study we identified the APETALA2/Ethylene Responsive Factor family transcription factor gene BcERF3 from B. chinense. The expression of BcERF3 was induced in methyl-jasmonate-treated adventitious root of B. chinense; it was also expressed at higher levels in roots than in other tissues (stem, leaf, flower, and tender fruit of early fruiting plants). Transient expression of BcERF3 in the leaves of Nicotiana benthamiana resulted in intracellular localization of the protein in the nucleus. It was also demonstrated that the number of SSs was greater in BcERF3-overexpressing hairy roots of B. chinense than in plants treated with empty vector controls. This coincided with upregulation of β-AS, which encodes a key enzyme involved with triterpenoid biosynthesis. In conclusion, BcERF3 plays a positive regulatory role in the biosynthesis of SSs.