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Review
. 2022 Mar 3:13:866282.
doi: 10.3389/fpls.2022.866282. eCollection 2022.

Specific Flavonoids and Their Biosynthetic Pathway in Scutellaria baicalensis

Tianlin Pei  1   2 , Mengxiao Yan  1 , Yanbo Huang  1 , Yukun Wei  1 , Cathie Martin  3 , Qing Zhao  1   2
Affiliations
Review

Specific Flavonoids and Their Biosynthetic Pathway in Scutellaria baicalensis

Tianlin Pei et al. Front Plant Sci. .

Abstract

Scutellaria baicalensis, is one of the most traditional medicinal plants in the Lamiaceae family, and has been widely used to treat liver and lung complaints and as a complementary cancer treatment in traditional Chinese medicine. The preparation from its roots, called "Huang Qin," is rich in specialized flavones such as baicalein, wogonin, and their glycosides which lack a 4'-hydroxyl group on the B ring (4'-deoxyflavones), with anti-tumor, antioxidant, and antiviral activities. Baicalein has recently been reported to inhibit the replication of the COVID-19 virus. These 4'-deoxyflavones are found only in the order Lamiales and were discovered in the genus Scutellaria, suggesting that a new metabolic pathway synthesizing 4'-deoxyflavones evolved recently in this genus. In this review, we focus on the class of 4'-deoxyflavones in S. baicalensis and their pharmacological properties. We also describe the apparent evolutionary route taken by the genes encoding enzymes involved in the novel, root-specific, biosynthetic pathway for baicalein and wogonin, which provides insights into the evolution of specific flavone biosynthetic pathways in the mint family.

Keywords: 4′-deoxyflavones; Scutellaria baicalensis; biosynthetic pathways; evolutionary mechanisms; flavonoids.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

FIGURE 1
FIGURE 1
The medicinal plant Scutellaria baicalensis and its major flavones. (A) S. baicalensis plant. (B) The dried roots of S. baicalensis used in traditional Chinese medicine. (C) Structure of flavones produced from naringenin. (D) Structure of 4′-deoxyflavones derived from pinocembrin.
FIGURE 2
FIGURE 2
Two pathways responsible for biosynthesis of flavones in Scutellaria baicalensis. The classic flavone pathway makes scutellarein in aerial tissues (left hand), while 4′-deoxyRSFs are produced by a newly evolved pathway in roots (right hand). PAL, phenylalanine ammonialyase; C4H, cinnamate 4-hydroxylase; CLL-7, cinnamate-CoA ligase; CLL-1, 4-coumarate CoA ligase; CHS, chalcone synthase; CHI, chalcone isomerase; FNSII, flavone synthase II; F6H, flavone 6-hydroxylase; F8H, flavone 8-hydroxylase; PFOMT, flavonoid O-methyltransferases; UBGAT, baicalein 7-O-glucuronosyltransferase.
FIGURE 3
FIGURE 3
Evolutionary paths of SbCHS2 and SbFNSII-2. (A) Syntenic analysis of SbCHS2s genes in Scutellaria baicalensis, Scutellaria barbata, and Salvia splendens. The multiplications of SbCHS2 are mostly late at the species level for S. baicalensis. (B) Syntenic analysis of SbFNSII-1 and SbFNSII-2 genes in S. baicalensis, S. barbata, and S. splendens. The duplication of SbFNSII-2 is earlier before the species divergence within Scutellaria.
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