Diterpenoids from Scutellaria barbata induce tumour-selective cytotoxicity by taking the brakes off apoptosis

Medicinal plants are an excellent source of structurally diverse,bio-active compounds with potential in the fight against cancer.One of the most promising is Scutellaria barbata,prescribed traditionally for the treatment of cancers.Scutebarbatine A is the major diterpenoid,produced in specialized large,peltate trichomes on leaves of S.barbata.It induces dose-dependent apoptosis,specifically in cancer cells.The major class of proteins down-regulated are pro-survival proteins,the Inhibitors of Apoptosis(IAPs),and IAP regulating proteins.We propose that scutebarbatine A works by releasing the molecular brakes(the IAPs)on apoptosis in cell death-evading cancer cells.Comparison between the cytotoxicity of methanolic extracts of S.barbata leaves and decoctions(Ban Zhi Lian)prepared traditionally,showed substantially different chemical compositions and differential induction of apoptosis.Analyses suggest polyvalency between the constituents in both extracts,and ways to produce enhanced chemopreventive preparations for the treatment of cancer.

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.

Single-cell RNA sequencing facilitates the elucidation of the complete biosynthesis of the antidepressant hyperforin in St. John's wort

Hyperforin is the compound responsible for the effectiveness of St.John's wort(Hypericum perforatum)as an antidepressant,but its complete biosynthetic pathway remains unknown.Gene discovery based on co-expression analysis of bulk RNA-sequencing data or genome mining failed to discover the missing steps in hyperforin biosynthesis.In this study,we sequenced the 1.54-Gb tetraploid H.perforatum genome assem-bled into 32 chromosomes with the scaffold N50 value of 42.44 Mb.By single-cell RNA sequencing,we iden-tified a type of cell,“Hyper cells”,wherein hyperforin biosynthesis de novo takes place in both the leaves and flowers.Through pathway reconstitution in yeast and tobacco,we identified and characterized four transmembrane prenyltransferases(HpPT1-4)that are localized at the plastid envelope and complete the hyperforin biosynthetic pathway.The hyperforin polycyclic scaffold is created by a reaction cascade involving an irregular isoprenoid coupling and a tandem cyclization.Our findings reveal how and where hy-perforin is biosynthesized,enabling synthetic-biology reconstitution of the complete pathway.Thus,this study not only deepens our comprehension of specialized metabolism at the cellularlevel but also provides strategic guidance for elucidation of the biosynthetic pathways of other specializied metabolites in plants.