Overexpression of SbMYB38 from Sorghum bicolor Enhances Saline–Alkali Stress Tolerance in Arabidopsis thaliana

Saline–alkali stress is a major environmental factor limiting plant growth and development, primarily because it causes ion toxicity, oxidative damage, and osmotic stress. Studies have shown that some members of the MYB gene family in Sorghum bicolor can enhance plant tolerance to saline–alkali stress. To clarify the specific function of the MYB family member SbMYB38 under saline–alkali stress, we cloned the coding sequence of SbMYB38 and successfully transformed it into Arabidopsis thaliana. Subcellular localization results showed that SbMYB38 was located in the nucleus. Overexpression of SbMYB38 in transgenic Arabidopsis thaliana (OE) increased plant tolerance to saline–alkali stress. After treatment with 150 mM NaHCO3, the activities of the antioxidant enzymes superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were significantly higher in the OE lines than in the wild type (WT). Under 150 mM NaHCO3 stress, the expression levels of genes related to the absorption and transport of protons, sodium ions, and potassium ions, such as AtAHA2, AtSOS1 and AtNHX1, showed different changes. Physiological and biochemical analyses indicated that following NaHCO3 treatment, the transgenic lines had significantly increased proline and chlorophyll contents and decreased malondialdehyde (MDA) content. In addition, transcriptomic data showed that the key genes involved in flavonoid biosynthesis, including FLS, 4CL3, and CYP75B1, were differentially upregulated, whereas key genes involved in lignin biosynthesis, such as HCT, CCoAOMT, CAD, and CCR, were downregulated. This suggests that SbMYB38 may enhance plant tolerance to saline–alkali stress by participating in flavonoid biosynthesis. However, this hypothesis requires further verification. Collectively, these findings provide a basis for understanding the molecular mechanisms of plant saline–alkali tolerance and offer valuable resources for breeding tolerant crops and for the phytoremediation of saline–alkali land.