Abstract
Scutellaria baicalensis (S. baicalensis) and Scutellaria barbata (S. barbata) are common medicinal plants of the Lamiaceae family. Both produce specific flavonoid compounds, including baicalein, scutellarein, norwogonin, and wogonin, as well as their glycosides, which exhibit antioxidant and antitumor activities. Here, we report chromosome-level genome assemblies of S. baicalensis and S. barbata with 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 (WGD) event was identified. The insertion of long terminal repeat elements after speciation might be responsible for the observed chromosomal expansion and rearrangement. Comparative genome analysis of the congeneric species revealed the species-specific evolution of chrysin and apigenin biosynthetic genes, such as the S. baicalensis-specific tandem duplication of genes encoding phenylalanine ammonia lyase and chalcone synthase, and the S. barbata-specific duplication of genes encoding 4-CoA ligase. In addition, the paralogous duplication, colinearity, and expression diversity of CYP82D subfamily members revealed the functional divergence of genes encoding flavone hydroxylase between S. baicalensis and S. barbata. Analyzing these Scutellaria genomes reveals the common and species-specific evolution of flavone biosynthetic genes. Thus, these findings would facilitate the development of molecular breeding and studies of biosynthesis and regulation of bioactive compounds.
Highlights
Plant-specific proanthocyanidins, and isoflavones, play important functions in plants, such as flower pigmentation, UV protection, and symbiotic nitrogen fixation [1−3]
The low-quality long reads were further corrected and trimmed to yield 20.2 Gb Oxford Nanopore technology (ONT) reads with an N50 of 35.5 kb from S. baicalensis and 18.0 Gb
The results indicated that baicalein, norwogonin, wogonin, baicalin, norwogonoside and wogonoside mainly accumulated in the roots of S. baicalensis and S. barbata, while scutellarin was distributed in the aerial parts of these species (Figure 1B, Figure S11, Table S12), providing a potential basis for the co-expression analysis of biosynthetic genes [23]
Summary
Plant-specific proanthocyanidins, and isoflavones, play important functions in plants, such as flower pigmentation, UV protection, and symbiotic nitrogen fixation [1−3]. Flavonoid metabolites have biological and pharmacological activities in human health, including antibacterial and antioxidant functions, and the treatment of cancer, inflammatory, and cardiovascular diseases [3]. The genus Scutellaria, belong to the Lamiaceae family, comprises common herbal plants enriched by bioactive flavonoids, and approximately 300 to 360 Scutellaria species have been documented as having the characteristic flower form of upper and lower lips [4,5]. The main biologically active compounds in Scutellaria are derivatives of chrysin and apigenin, such as baicalein, scutellarein, wogonin, and their glycosides (baicalin, scutellarin, and wogonoside) [7−10]. Baicalin has been confirmed to activate carnitine palmitoyltransferase 1 in the treatment of diet-induced obesity and hepatic steatosis, leading to extensive interest in the potential antilipemic effect of this compound [11,12]
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