## 2 Results
### AtMYB2 Promotes the Accumulation of Tanshinones and Salvianic Acid  
Compared to the wild type, the overexpression of _AtMYB2_ led to alterations in the secondary metabolite content of transgenic _S. milliorrhiza_ hairy roots and plants. The _AtMYB2_ transgenic hairy roots appeared much redder and thicker than those of the control plants (Figure 5A). In transgenic hairy roots, the content of Sal B was highest in _OE-AtMYB2-L4_, reaching 20.41 mg/g dw, which was 22.7% higher compared with the WT. Upon observation, it was noted that the tanshinone extracts from the _AtMYB2_ transgenic hairy root lines exhibited a deeper red color compared with the control lines (Figure 5D), suggesting a potential elevation in tanshinone concentration. Through high-performance liquid chromatography (HPLC) detection, the transgenic hairy root line with the highest content of each tanshinone was _OE-AtMYB2-L6_, which increased by 27.1% (TI), 24.6% (TIIA), and 20.6% (TT) compared with the WT, respectively. The content of CT in each transgenic hairy root line showed no significant differences (Figure 5G). As for the roots of plants, phenotypically, the roots of transgenic plants exhibited fewer fine branchings and a deeper red coloration (Figure 5B). The transgenic plant lines produced much higher levels of Sal B and total tanshinone than the WT. Meanwhile, the Sal B and total tanshinone content increased by 38.5% (40.5 mg/g dw) and 20.5% (11.29 mg/g dw) in _OE-AtMYB2-L5_ when compared with those in the WT, respectively. Similarly, compared to the control group, the tanshinone extract from transgenic _S. milliorrhiza_ roots also exhibited a deeper red color. However, _AtMYB2_ transgenic plant lines had more of an effect on the production of TI and TIIA than CT (Figure 5H). Figure 3: Accumulation of O\({}^{2-}\) (**A**,**C) and H\({}_{2}\)O\({}_{2}\) (**B**,**D) in all _S. milliorrhiza_ lines under salt stress. The localization and accumulation of O\({}^{2-}\) (**A**) and H\({}_{2}\)O\({}_{2}\) (**B**) were visualized by blue and brown staining. Control, plants grown under normal conditions; Salt, plants subjected to salt stress treatment for 7 days. **\(p<0.01\). AtMYB2 Promotes Tanshinones and Salvianolic Acid Content by Upregulationating the Expression of Biosynthesis Genes  
To elucidate the mechanisms underlying these changes in the contents of salvianolic acid and tanshinones, we first examined the transcript levels of eight key enzyme genes in the salvianolic acid biosynthesis pathway and eight enzyme genes in the tanshinone biosynthesis pathway in transgenic hairy roots. The results indicated that, compared to the wild type, the expression levels of _SmPAL1_, _SmC4H2_, _SmTAT1_, and _SmHPPR1_ in the salvianolic acid biosynthesis pathway were significantly increased (ranging from 1.30 to 4.15 times higher than the wild type) in transgenic hairy roots (\(p<0.05\)), while the expression levels of the remaining four genes showed no significant differences. The expression levels of all eight key enzyme genes involved in the tanshinone biosynthetic pathway were significantly upregulated, ranging from 1.42- to 6.69-fold higher in the transgenic hairy root lines compared to the wild type (Figure S4). Subsequently, we selected two _AtMYB2_ transgenic _S. miltiorrhiza_ lines, Line5 and Line7, with higher salvianolic acid and tanshinones content, and conducted a more detailed expression analysis of the key enzyme genes in both the salvianolic acid and tanshinone biosynthesis pathways. The results indicated that the transcript levels of seven out of the sixteen key enzyme genes in the salvianolic acid biosynthesis pathway were significantly increased, including _SmC4H1_, _SmC4H2_, _Sm4 CL1_, _Sm4 CL3_, _SmTAT1_, _SmTAT2_, and _SmHPPR1_ (Figure 6).