Molecular Circuit Linking Abscisic Acid Signaling to Tanshinone Production Uncovered

Salvia miltiorrhiza, also known as Danshen, is a highly regarded traditional Chinese medicine widely used for treating cardiovascular and cerebrovascular diseases. Its medicinal properties are largely attributed to tanshinones-a group of more than 40 diterpenoid quinone compounds, including tanshinone I, tanshinone IIA, and cryptotanshinone, which predominantly accumulate in the plant's roots.

The biosynthetic pathway involves a complex cascade starting from isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP), proceeding through geranylgeranyl diphosphate (GGPP), and culminating in modifications by specific cytochrome P450 enzymes. Although abscisic acid (ABA) is known to act as an elicitor that promotes tanshinone accumulation, the transcription factors that translate this hormonal signal into enhanced biosynthesis have remained largely unexplored. Based on these challenges, there is a pressing need to conduct in-depth research on the ABA-responsive transcription factors that bridge hormone signaling with secondary metabolism in S. miltiorrhiza.

A team led by researchers at Zhejiang Chinese Medical University in Hangzhou, China, reports (DOI: 10.1093/hr/uhag186) these findings on May 12, 2026, in Horticulture Research, a journal published by Oxford University Press on behalf of Nanjing Agricultural University. The study identifies SmMYB32 as an ABA-responsive R2R3-MYB transcription factor that directly activates two key tanshinone biosynthetic genes-SmCYP76AH3 and SmCYP71D411-by binding to MYB-binding sites (MBS) in their promoters. Perhaps most unexpectedly, the work also reveals that the ABA receptor SmPYL8 physically interacts with SmMYB32 and acts as a brake on its activity, exposing a previously unknown regulatory counterbalance.

The researchers first pinpointed SmMYB32 from an ABA-induced transcriptome of S. miltiorrhiza hairy roots, selecting it based on its strong responsiveness to hormone treatment and its tissue-specific expression pattern. Quantitative analysis showed that SmMYB32 transcript levels surged approximately six-fold within just one hour of ABA exposure. When the team overexpressed SmMYB32 in transgenic hairy roots, total tanshinone content increased by up to three times compared with controls, with the highest-producing line reaching 7.0 mg per gram dry weight. In contrast, RNA interference (RNAi)-mediated silencing of SmMYB32 reduced tanshinone accumulation by 30% to 70% and completely abolished the ABA-induced increase, confirming that SmMYB32 is essential for mediating the hormonal effect.

Mechanistically, a combination of yeast one-hybrid (Y1H), dual-luciferase reporter, and electrophoretic mobility shift assays (EMSA) demonstrated that SmMYB32 directly binds to the promoters of SmCYP76AH3 and SmCYP71D411 to activate their transcription. To understand how this activation is controlled, the team conducted a yeast two-hybrid (Y2H) screen and identified SmPYL8-an ABA receptor of the PYR/PYL/RCAR family-as a physical interaction partner of SmMYB32. The interaction was confirmed by pull-down assays and bimolecular fluorescence complementation (BiFC), with ABA treatment further strengthening the protein-protein association. Functional analysis revealed that overexpression of SmPYL8 reduced tanshinone content, while its silencing boosted accumulation. Crucially, when SmPYL8 was co-expressed with SmMYB32 in dual-luciferase assays, the transcriptional activation of SmCYP76AH3 and SmCYP71D411 was significantly attenuated, indicating that SmPYL8 directly represses SmMYB32's regulatory function.

The authors said that establishing a direct physical link between an ABA receptor and a biosynthetic regulator was the most striking part of their work. "We have known for years that ABA can push plants to produce more tanshinones, but the specific proteins that carry out this order have remained a black box," they explained. "SmMYB32 is the first ABA-responsive R2R3-MYB transcription factor shown to directly activate key downstream genes in this pathway. And discovering that SmPYL8 binds to SmMYB32 to dial down its activity reveals an elegant built-in feedback mechanism-when ABA levels drop, the receptor steps in to prevent overproduction. This gives us a very precise on-off switch to work with for engineering purposes."

These findings offer a clear roadmap for metabolic engineering strategies aimed at sustainable, high-yield tanshinone production. By manipulating SmMYB32 expression or strategically disrupting its interaction with the inhibitory SmPYL8 partner, researchers could significantly boost yields in hairy root culture systems-a platform already widely used for producing these medicinal compounds. Given the escalating global demand for tanshinones as therapeutic agents against cardiovascular disease, cancer, and atherosclerosis, this regulatory module provides a powerful new tool for synthetic biology and industrial-scale production.

Furthermore, the study's insights into how plants coordinate hormonal signals with secondary metabolism may serve as a valuable reference for enhancing the production of other high-value plant natural products.