Brassinosteroid-related transcription factor BZR1 regulates vegetative development and flavonoids biosynthesis in Scutellaria baicalensis.

Scutellaria baicalensis Georgi is a traditional Chinese medicine known for its flavonoid and polysaccharide content, which offers significant pharmacological effects. However, the molecular mechanisms governing the biosynthesis of these phytochemicals are not fully understood. Here, we first identified the transcription factor BZR1 (~36 kDa) within the brassinosteroid (BR) pathway as a key regulator of active compound biosynthesis in S. baicalensis. Application of 24-epibrassinolide (eBL) significantly stimulated seedling development, increased fresh biomass, and enhanced key gene expression in baicalin biosynthesis pathway. Biochemical analyses indicated that BR promotes dephosphorylation and accumulation of SbBZR1. The constitutively active mutant Sbbzr1-D rescued the dwarf phenotype of the Arabidopsis BR-deficient mutant Atbri1-116. Overexpression of Sbbzr1-1D in Arabidopsis resulted in phenotypes similar to Atbzr1-1D, including curled leaves, darker pigmentation, and delayed flowering. Quantitative RT-PCR revealed significant upregulation of nine key enzymes in flavonoid biosynthetic pathway in Sbbzr1-1D/Col-0 lines, leading to increased total flavonoid content. Transient expression of SbBZR1 and Sbbzr1-1D upregulated nine key enzymes in baicalin biosynthesis. Yeast one-hybrid and bimolecular assays confirmed SbBZR1 binds the promoter region, regulating its gene expression. In conclusion, SbBZR1 is crucial for the growth of S. baicalensis and the regulation of flavonoid biosynthesis, enhancing the accumulation of bioactive compounds.