---

A specialized flavone biosynthetic pathway has evolved in the medicinal plant, Scutellaria baicalensis

Authors Zhao, Qing; Zhang, Yang; Wang, Gang; Hill, Lionel; Weng, Jing-Ke; Chen, Xiao-Ya; Xue, Hongwei; Martin, Cathie

Journal SCIENCE ADVANCES , APR 2016,4:2

DOI 10.1126/sciadv.1501780 PubMed 27152350

Abstract Wogonin and baicalein are bioactive flavones in the popular Chinese herbal remedy Huang-Qin (Scutellaria baicalensis Georgi). These specialized flavones lack a 4''-hydroxyl group on the B ring (4''-deoxyflavones) and induce apoptosis in a wide spectrum of human tumor cells in vitro and inhibit tumor growth in vivo in different mouse tumor models. Root-specific flavones (RSFs) from Scutellaria have a variety of reported additional beneficial effects including antioxidant and antiviral properties. We describe the characterization of a new pathway for the synthesis of these compounds, in which pinocembrin (a 4''-deoxyflavanone) serves as a key intermediate. Although two genes encoding flavone synthase II (FNSII) are expressed in the roots of S. baicalensis, FNSII-1 has broad specificity for flavanones as substrates, whereas FNSII-2 is specific for pinocembrin. FNSII-2 is responsible for the synthesis of 4''-deoxyRSFs, such as chrysin and wogonin, wogonoside, baicalein, and baicalin, which are synthesized from chrysin. A gene encoding a cinnamic acid-specific coenzyme A ligase (SbCLL-7), which is highly expressed in roots, is required for the synthesis of RSFs by FNSII-2, as demonstrated by gene silencing. A specific isoform of chalcone synthase (SbCHS-2) that is highly expressed in roots producing RSFs is also required for the synthesis of chrysin. Our studies reveal a recently evolved pathway for biosynthesis of specific, bioactive 4''-deoxyflavones in the roots of S. baicalensis.

Species covered 黄芩 Scutellaria baicalensis