Overexpression of Dehydroascorbate Reductase Confers Enhanced Tolerance to Salt Stress in Rice Plants (Oryza sativa L. japonica)

Dehydroascorbate reductase (DHAR, EC 1.8.5.1) helps to maintain redox pools of ascorbate (AsA) by recycling dehydroascorbate (DHA) to AsA. To investigate whether DHAR influences the acquired tolerance of rice plants to abiotic stresses, cDNA encoding DHAR (OsDHAR1) was isolated from rice and used to develop OsDHAR1-overexpressing transgenic rice plants regulated by a maize ubiquitin promoter. The incorporation and expression of the transgene was confirmed by polymerase chain reaction (PCR) and semi-quantitative reverse transcription PCR, real-time PCR, Western blot and enzyme activity. The overexpression of OsDHAR1 greatly increased the DHAR activity and the AsA/DHA ratio, following increase in AsA content and decrease in DHA content. In addition, the enzyme activity of monodehydroascorbate reductase, glutathione reductase and ascorbate peroxidase, which are related to the ascorbate-glutathione systems, was enhanced in the presence and the absence of salt stress in homozygous transgenic rice plants (OsDHAR1-OX1, -OX2) harbouring Ubi::OsDHAR1. In addition, OsDHAR1-expressing transgenic rice plants enhanced the redox state by reducing both hydroperoxide and malondialdehyde levels under salt and methyl viologen (MV) stress conditions, which led to better plant growth, ion leakage and quantum yield (Fv/Fm). Therefore, our results show that the overexpression of OsDHAR1 increases the adaptation of rice plants to salt stress, by maintaining the AsA pool, ion homoeostasis and redox homoeostasis. Finally, the findings of this study indicate that OsDHAR1 plays an important role in attenuating the deleterious effects of various abiotic stresses.