The genomes of medicinal skullcaps reveal the polyphyletic origins of clerodane diterpene biosynthesis in the family Lamiaceae.

The presence of anticancer clerodane diterpenoids is a chemotaxonomic marker for the traditional Chinese medicinal plant Scutellaria barbata, although the molecular mechanisms behind clerodane biosynthesis are unknown. Here, we report a high-quality assembly of the 414.98 Mb genome of S. barbata into 13 pseudochromosomes. Using phylogenomic and biochemical data, we mapped the plastidial metabolism of kaurene (gibberellins), abietane, and clerodane diterpenes in three species of the family Lamiaceae (Scutellaria barbata, Scutellaria baicalensis, and Salvia splendens), facilitating the identification of genes involved in the biosynthesis of the clerodanes, kolavenol, and isokolavenol. We show that clerodane biosynthesis evolved through recruitment and neofunctionalization of genes from gibberellin and abietane metabolism. Despite the assumed monophyletic origin of clerodane biosynthesis, which is widespread in species of the Lamiaceae, our data show distinct evolutionary lineages and suggest polyphyletic origins of clerodane biosynthesis in the family Lamiaceae. Our study not only provides significant insights into the evolution of clerodane biosynthetic pathways in the mint family, Lamiaceae, but also will facilitate the production of anticancer clerodanes through future metabolic engineering efforts.

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

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.

Transcriptomic Insight into Terpenoid Biosynthesis and Functional Characterization of Three Diterpene Synthases in Scutellaria barbata.

Scutellaria barbata (Lamiaceae) is an important medicinal herb widely used in China, Korea, India, and other Asian countries. Neo-clerodane diterpenoids are the largest known group of Scutellaria diterpenoids and show promising cytotoxic activity against several cancer cell lines. Here, Illumina-based deep transcriptome analysis of flowers, the aerial parts (leaf and stem), and roots of S. barbata was used to explore terpenoid-related genes. In total, 121,958,564 clean RNA-sequence reads were assembled into 88,980 transcripts, with an average length of 1370 nt and N50 length of 2144 nt, indicating high assembly quality. We identified nearly all known terpenoid-related genes (33 genes) involved in biosynthesis of the terpenoid backbone and 14 terpene synthase genes which generate skeletons for different terpenoids. Three full length diterpene synthase genes were functionally identified using an in vitro assay. SbTPS8 and SbTPS9 were identified as normal-CPP and ent-CPP synthase, respectively. SbTPS12 reacts with SbTPS8 to produce miltiradiene. Furthermore, SbTPS12 was proven to be a less promiscuous class I diterpene synthase. These results give a comprehensive understanding of the terpenoid biosynthesis in S. barbata and provide useful information for enhancing the production of bioactive neo-clerodane diterpenoids through genetic engineering.

An Untapped Resource in the Spotlight of Medicinal Biotechnology: The Genus Scutellaria.

BACKGROUND: This review is intended to draw the attention of pharmaceutical and biotechnological communities to the untapped potential of the Scutellaria genus. Skullcaps, as they are more widely known, are found in one of the oldest materia medica in the world, that of ancient Chinese pharmacology, and their numerous wide range of medicinal bioactivities have been studied both in vivo and in vitro. For thousands of years, chemical compounds from the Scutellaria species have been safely used as antitumor, antibacterial, antiviral, anti-inflammatory, antioxidant or hepatoprotective factors. OBJECTIVE: As these effects are well known, reflected in the presence of Scutellaria plants in national pharmacopoeias, it is clear that the plant has yet enormous unexploited potential. The European pharmacological market has turned to the resources of Scutellaria only in the last two decades, and although the construction and clinical processing of a new drug is a long process, the general impression is that very few medical products in pharmacies have been inspired by the phytochemistry of skullcaps. CONCLUSION: This paper presents the current state of knowledge on the wealth of Scutellaria chemical compounds with treatment applications, its tissue culture and biotechnological achievements, especially in the context of the production of secondary metabolites.

[Oryzalin-induced chromosome doubling of Scutellaria barbata].

OBJECTIVE: To obtain polyploidy Scutellaria barbata. METHODS: Explants of stem segment of Scutellaria barbata were treated with oryzalin at various concentration and time duration in vitro. RESULTS: Comparing with the characteristics of diploid, mutant plants had significant changes in plant morphology inducing compact plant, darker leaf color, smaller leaf index, thicken stem, significantly larger stomata, guard cells and chloroplasts in stomata guard cells and significantly lower stomata density. Mutant plants were plant chimera of diploid and tetraploid assessed by chromosome counting and flow cytometry. CONCLUSION: The technique could be used for chromosome doubling in Scutellaria barbata.

Comparisons of Scutellaria baicalensis, Scutellaria lateriflora and Scutellaria racemosa: genome size, antioxidant potential and phytochemistry.

The genus Scutellaria in the family Lamiaceae has over 350 species, many of which are medicinally active. One species, Scutellaria baicalensis, is one of the most widely prescribed plants in Traditional Chinese Medicine, used for neurological disorders, cancer and inflammatory diseases and has been the subject of detailed scientific study but little is known about the phytochemistry of other Scutellaria. The current study was designed to compare the medicinal phytochemistry of 3 species of Scutellaria used to treat neurological disorders. To accomplish this objective, the specific objectives were (a) to establish an in vitro collection of the South American native; S. racemosa, (b) to botanically characterize S. racemosa and (c) to compare the phytochemistry of S. racemosa with S. baicalensis and S. lateriflora. S. racemosa was established in vitro from wild populations in Florida. Botanically, S. racemosa is diploid with 18 chromosomes, and flow cytometry data indicated that S. baicalensis and S. racemosa have small nuclei with estimated small genomes (377 mbp and 411 mbp respectively). Antioxidant potential studies showed that there were no significant differences in the 3 Scutellaria species. Phytochemical analyses detected and quantified the flavonoids baicalin, baicalein, scutellarin, and wogonin as well as the human neurohormones melatonin and serotonin in leaf and stem tissues from S. baicalensis, S. lateriflora, and S. racemosa. These findings represent the first phytochemical analysis of S. racemosa and establish S. racemosa as a model system for study of medicinal plant secondary metabolism and as a potential source of important phytopharmaceuticals for treatment of human disease.