<i>SmGA2ox4</i> Plays a Positive Role in Improving the Salt Tolerance and Tanshinone Accumulation of <i>Salvia miltiorrhiza</i>

Abstract Salvia miltiorrhiza, a medicinal plant of high value, faces significant yield and quality losses due to salt stress. Identifying salt tolerance genes is therefore essential for breeding resilient varieties. Gibberellin (GA) metabolism and signaling are modulated by diverse factors, with GA 2-oxidase (GA2ox) playing a key role in stress adaptation by inactivating GA and fine-tuning growth under adverse conditions. In this work, we identified 12 GA2ox genes in S. miltiorrhiza and generated a SmGA2ox4 transgenic line. Heterologous expression in Arabidopsis thaliana improved salt tolerance through enhanced germination, root growth, antioxidant activity, and stress-related physiological markers. Similar results were observed in transgenic hairy roots of S. miltiorrhiza. HPLC analysis further showed that SmGA2ox4 overexpression promoted tanshinone accumulation but suppressed salvianolic acid biosynthesis, whereas RNAi-mediated silencing had the opposite effect. Thus, SmGA2ox4 acts as a dual-function regulator, enhancing both salt tolerance and tanshinone production. This study establishes a novel link between GA2ox-mediated stress response and secondary metabolism in S. miltiorrhiza, providing a basis for engineering stress-resistant, high-quality varieties.