The Transcription Factor MYB8 Positively Regulates Flavonoid Biosynthesis of Scutellaria baicalensis in Response to Drought Stress.

Abstract

Drought stress dynamically reprograms specialised metabolism in medicinal plants. However, the transcriptional regulatory modules governing stress-adaptive metabolite synthesis remain poorly characterised. Here, we identified SbMYB8 as a drought-responsive transcription factor showing nuclear localisation and dose-dependent induction under drought in Scutellaria baicalensis. SbMYB8 activation triggered coordinated upregulation of six baicalin biosynthetic genes, elevating total baicalin and aglycones. Heterologous overexpression in Arabidopsis thaliana revealed SbMYB8's conserved regulatory function, driving anthocyanin accumulation (2.3-fold), flavonoid hyperproduction (5.8-fold), and developmental plasticity through enhanced lateral root proliferation. Specifically, we established the first stable S. baicalensis genetic transformation system, enabling tissue-specific dissection of SbMYB8 function. Transgenic OE-SbMYB8 lines exhibited root architectural remodelling (thickened primary roots, increased lateral root density) and root-specific flavonoid amplification (baicalin 1.8-fold; total flavonoids 3.5-fold), coupled with hierarchical induction of 12 pathway genes. Low-dose PEG (2.5%) synergised with SbMYB8 to transiently boost aglycone synthesis, whereas high-dose stress (5%) disrupted this coordination, suppressing biosynthetic machinery and metabolite yields. Mechanistically, yeast one-hybrid and dual-luciferase assays revealed SbMYB8 directly binds cis-elements in target promoters to orchestrate pathway activation. Based on the above results, we propose a SbMYB8-mediated "drought perception - transcriptional activation - metabolic response" network and provide transformative tools for precision breeding of stress-resilient medicinal plants.