## 3 Discussion  
### AtMYB2 Promotes Tolerance to Salt Stress by Improving Antioxidant System Function  
Gene expression in higher plants is commonly regulated through the interplay of specific transcription factors and cis-acting elements. Among these, the MYB2 protein stands out, playing a crucial role in regulating processes like secondary metabolism [26; 27], the meristem and pollen development [28; 29], and response to abiotic stress [30]. Many experiments have been conducted to study _Arabidopsis MYB2_, a typical R2R3-MYB gene, and have found that it is associated with improved plant resistance to hormone and environmental stress. [PERSON] et al. discovered that _AtMYB2_ expression increased in response to water stress, high-salt conditions, and ABA treatment at the transcriptional level, and serves as a crucial transcriptional activator in regulating gene expression in response to ABA under drought and salt stress [21; 31; 32]. Using domain mapping, a calmodulin (CaM) binding domain was identified in AtMYB2, and the specific CaM isoform GmCaM4 was found to enhance the DNA-binding activity of AtMYB2. Overexpression _GmCaM4_ in _Arabidopsis_ enhances the transcription rate of AtMYB2-regulated genes. This mechanism boosts salt tolerance by promoting the accumulation of proline [33]. When subjected to salt  
Figure 8: Hierarchical clustering of DEGs of _AtMYB2_ transgenic lines versus those of pCAMBIA1301 plants (**A**) and KEGG classification of DEGs of _AtMYB2_ transgenic lines versus those of pCAMBIA1301 plants (**B**). or drought stress, AtMYB2 suppresses the formation of axillary meristens in _Arabidopsis_ by downregulating the expression of the RAX1 (regulator of axillary meristem1) gene. This adaptation enables plants to undergo a shortened vegetative developmental stage in response to environmental stresses [28]. Choline monooxygenase (CMO) is an enzyme located in the chloroplast stroma that is responsible for catalyzing the initial step of glycine betaine synthesis in plants. AtMYB2 has the ability to directly interact with the CMO promoter, thereby enhancing plant adaptation to salinity by promoting the accumulation of glycine betaine [34]. In the present study, _AtMYB2_ transgenic plants showed a more resistant phenotype under high-salinity conditions compared to the wild-type plants by improving the antioxidant system's function under oxidative stress. Salt stress disrupted intracellular ROS homoeostasis, inducing excessive accumulation of ROS and causing oxidative stress to plants. Hence, maintaining low levels of ROS production and bolstering robust ROS-scavenging capabilities are crucial during salt stress. At this stage, the activity of antioxidant enzymes in plants increases to mitigate the damage caused by salt stress [35; 36; 37]. For instance, overexpression of _Tabzr1-1D_ enhances ROS scavenging capacity, thus improving the salt stress resistance in wheat [38]. _AtMYB49_ can function to alleviate oxidative damage induced by salinity by upregulating the expression of certain genes encoding POD in transgenic _Arabidopsis_ such as _Prx15_, _Prx24_, _Prx26_, _Prx32_, _Prx53_, and _Prx55_[39]. Meanwhile, _DcWRXY3_ positively contributes to the response to salt stress by enhancing the ability to scavge ROS and by maintaining osmotic pressure balance in plants [40]. Our results indicated that _AtMYB2_ transgenic _S. multiorrhiza_ plants exhibited significantly reduced ROS (O\({}_{2}\)\({}^{-}\) and H\({}_{2}\)O\({}_{2}\)) accumulation compared to WT plants under salt stress conditions (Figure 3), with higher enzymatic scavenger (SOD, POD, and CAT) activities (Figure 4). The NBT and DAB staining also supported the results of the O\({}_{2}\)\({}^{-}\) and H\({}_{2}\)O\({}_{2}\) content assay (Figure 3A,B). Meanwhile, compared with the WT, there were lower EL and MDA levels, accompanied by higher total chlorophyll content, in _AtMYB2_ transgenic _S. multiorrhiza_ (Figure 4).