Comparative Genome Analysis of Scutellaria baicalensis and Scutellaria barbata Reveals the Evolution of Active Flavonoid Biosynthesis

Abstract

Scutellaria baicalensis and Scutellaria barbata, common medicinal plants of the Lamiaceae family, produce specific flavonoid compounds with antioxidant and antitumor activities, including baicalein, scutellarein, norwogonin, wogonin, and their glycosides. Here, we reported two chromosome-level genome assemblies of S. baicalensis and S. barbata with significant quantitative chromosomal variation (2n = 18 and 2n = 26, respectively). The divergence of S. baicalensis and S. barbata occurred far earlier than previously reported, and a whole-genome duplication event was identified. The insertion of long terminal repeat elements after speciation might be responsible for the observed chromosomal expansion and rearrangement. The comparative genome analysis of congeneric species elucidated the species-specific evolution of chrysin and apigenin biosynthetic genes, such as the S. baicalensis-specific tandem duplication of the phenylalanine ammonia lyase (PAL) and chalcone synthase (CHS) genes, and the S. barbata-specific duplication of 4-CoA ligase (4CL) genes. In addition, the paralogous duplication, collinearity, and expression diversity of CYP82D subfamily members revealed the functional divergence of flavone hydroxylase genes between S. baicalensis and S. barbata. These Scutellaria genomes highlight the common and species-specific evolution of flavone biosynthetic genes, promoting the development of molecular breeding and the study of the biosynthesis and regulation of bioactive compounds.