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 aMDHARgene from a sugar beet M14 line (BvM14). The full-lengthBvM14-MDHARwas 1737 bp, and its ORF contained 1059 bp encoding the MDHAR of 352 amino acids. In addition, we expressed the coding sequence ofBvM14-MDHAR inEscherichia coliand purified theBvM14-MDHAR protein with high enzymatic activity. Quantitative real-time PCR analysis revealed that theBvM14-MDHARwas up-regulated in theBvM14roots under salt stress. To investigate the functions of theBvM14-MDHAR, it was constitutively expressed inArabidopsis 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 theBvM14-MDHARconfers 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.