APETALA2/ethylene-responsive factor (AP2/ERF) transcription factors integrate phytohormone signalling with developmental programmes and specialised metabolism, yet their family-wide features and potential contributions to phenolic-acid biosynthesis remain to be systematically clarified in Salvia miltiorrhiza. In this study, we conducted a comprehensive genome-wide analysis and identified 169 SmAP2/ERF genes, which were classified into five subfamilies (AP2, ERF, DREB, RAV and Soloist). SmAP2/ERFs were unevenly distributed across chromosomes and expanded predominantly through tandem and segmental duplication, and Ka/Ks analysis indicated that tandem-duplicated pairs have mainly undergone purifying selection. Promoter analysis revealed abundant cis-acting elements related to light, phytohormones and stress responses, indicating extensive regulatory potential. Comparative phylogenetic analysis with Arabidopsis thaliana prioritised four candidates (SmAP2/ERF88, SmAP2/ERF110, SmAP2/ERF121 and SmAP2/ERF122) closely associated with specialised-metabolism regulators. These genes exhibited distinct tissue-preferential expression patterns and divergent hormone responsiveness: SmAP2/ERF88/110 were broadly inducible, whereas SmAP2/ERF121/122 responded mainly to abscisic acid and were repressed by brassinosteroids. Confocal imaging of GFP fusions confirmed nuclear localisation of all four proteins. Phytohormone treatments differentially regulated key phenolic-acid pathway genes (PAL, C4H, 4CL, TAT, HPPR, RAS and CYP98A14) and altered rosmarinic acid and salvianolic acid B accumulation. These results broaden the genome-wide understanding of the SmAP2/ERF family in Salvia miltiorrhiza. Hormone-responsive SmAP2/ERFs show expression patterns associated with hormone-dependent transcriptional changes in phenolic-acid pathway genes and with RA and SAB accumulation, providing candidates for future functional validation and metabolic engineering.

Salvia miltiorrhiza Bunge is a traditional Chinese medicinal plant whose roots are rich in water-soluble phenolic acids. Rosmarinic acid and salvianolic acid B are representative components that confer antibacterial, antioxidant, and cardio-cerebrovascular protective activities. However, these metabolites often accumulate at low and unstable levels in planta, which limits their efficient development and use. This review summarises recent advances in understanding salvianolic acid biosynthesis and its transcriptional regulation in S. miltiorrhiza. Current evidence supports a coordinated pathway composed of the phenylpropanoid route and a tyrosine-derived branch, which converge to generate rosmarinic acid and subsequently more complex derivatives through oxidative coupling reactions. Key findings on transcription factor families that fine-tune pathway flux by regulating core structural genes are synthesised. Representative positive regulators such as SmMYB111, SmMYC2, and SmTGA2 activate key nodes (e.g., PAL, TAT/HPPR, RAS, and CYP98A14) to promote phenolic acid accumulation. Conversely, negative regulators such as SmMYB4 and SmMYB39 repress pathway genes and/or interfere with activator complexes. Major regulatory features include hormone-inducible signalling, cooperative regulation through transcription factor complexes, and emerging post-transcriptional and post-translational controls. Future directions and challenges are discussed, including overcoming regulatory redundancy and strong spatiotemporal specificity of transcriptional control. Integrating spatial and single-cell omics with functional genomics (e.g., genome editing and rational TF stacking) is highlighted as a promising strategy to enable predictive metabolic engineering for the stable, high-yield production of salvianolic acid-type compounds.