MtTGA1 Transcription Factor Enhances Salt Tolerance through Hormonal Regulation and Antioxidant Enzyme Activity in Medicago truncatula

The TGACG motif-binding factor1 (TGA1) transcription factor, in which belongs to the bZIP transcription factor family and has vast application potential in plant growth and development. Here, we cloned the gene of the MtTGA1 transcription factor from Medicago truncatula. The MtTGA1 promoter region contains a diverse range of photoregulatory and hormonal regulatory elements. The expression profile of MtTGA1 indicated its highest expression in the root. Additionally, the expression level of MtTGA1 was significantly upregulated after SA and BR treatments and showed a downward trend after GA and ABA treatments. To explore the potential function of MtTGA1, we treated the transgenic plants with salt treatment for 15 days, and the results showed that transgenic plants demonstrated significantly longer root lengths and heightened activities of antioxidant enzymes such as ascorbic acid catalase (APX), peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD) in their roots and leaves. The levels of endogenous hormones, including ABA and BR were improved in transgenic plants, with a marked change in the morphology of their leaf cells. Transcriptome analysis identified a total of 193 differentially expressed genes, which were significantly enriched in the pathways of "Brassinosteroid biosynthesis", "Ascorbate and aldarate metabolism", and "Plant hormone signal transduction". Furthermore, MtTGA1 was found to interact with the SPX domain-containing protein 1 (SPX1) in Medicago truncatula. In conclusion, these results are beneficial for further studies about the plant growth and development regulatory network mediated by the TGA1 transcription factor family.