Overexpression of a Monodehydroascorbate Reductase Gene from Sugar Beet M14 Increased Salt Stress Tolerance

Monodehydroascorbate reductase (MDHAR), a key enzyme to reduce monodehydroascorbate (DHA) to ascorbic acid (AsA), plays an important role in maintaining the level of ascorbic acid in plant cells. It helps to remove reactive oxygen species and regulate cellular redox homeostasis. In this study, we cloned a MDHAR gene from a sugar beet M14 line ( BvM14 ). The full-length BvM14 - MDHAR was 1737 bp, and its ORF contained 1059 bp encoding the MDHAR of 352 amino acids. In addition, we expressed the coding sequence of BvM14 -MDHAR in Escherichia coli and purified the BvM14 -MDHAR protein with high enzymatic activity. Quantitative real-time PCR analysis revealed that the BvM14 - MDHAR was up-regulated in the BvM14 roots under salt stress. To investigate the functions of the BvM14 - MDHAR , it was constitutively expressed in Arabidopsis thaliana . The transgenic plants exhibited an obvious salt stress tolerance phenotype, as evidenced by longer roots, higher fresh weight and chlorophyll contents, as well as higher AsA/DHA levels than wild-type (WT) seedlings under salt stress. In addition, the overexpression seedlings showed higher activities of MDHAR and dehydroascorbate reductase (DHAR) and decreased cell membrane damage compared to WT. The results showed that the BvM14 - MDHAR confers salt tolerance through its activity in redox regulation. It is a potential target for enhancing crop salt stress tolerance through genetic engineering and molecular breeding effort.