A novel aldo-keto reductase gene, IbAKR, from sweet potato confers higher tolerance to cadmium stress in tobacco

High concentrations of Cd can inhibit growth and reduce the activity of the photosynthetic apparatus in plants. In several plant species, aldo-keto reductases(AKRs) have been shown to enhance tolerance to various abiotic stresses by scavenging cytotoxic aldehydes;however, few AKRs have been reported to enhance Cd stress tolerance. In this study, the gene Ib AKR was isolated from sweet potato. The relative expression levels of Ib AKR increased significantly(approximately 3-fold) after exposure to 200 mmol$L–1 Cd Cl2 or 10 mmol$L–1 H2 O2. A subcellular localization assay showed that Ib AKR is predominantly located in the nucleus and cytoplasm.Ib AKR-overexpressing tobacco plants showed higher tolerance to Cd stress than wild-type(WT). Transgenic lines showed a significant ability to scavenge malondialdehyde(MDA) and methylglyoxal(MG). In addition,proline content and superoxide dismutase activity were significantly higher and H2 O2 levels were significantly lower in the transgenic plants than in the WT. Quantitative real-time PCR analysis showed that the reactive oxygen species(ROS) scavenging genes encoding guaiacol peroxidase(GPX), ascorbate peroxidase(APX), monodehydroascorbate reductase(MDHAR) and peroxidase(POD) were significantly upregulated in transgenic plants compared to WT under Cd stress. These findings suggest that overexpressing Ib AKR enhances tolerance to Cd stress via the scavenging of cytotoxic aldehydes and the activation of the ROS scavenging system.