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

Jinxi Huo ,Bing Du ,Shaozhen He ,Jian Xu ,Sifan Sun ,Qingchang Liu ,Hong Lin Zhai

doi:10.15302/j-fase-2018225

Abstract

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 IbAKR was isolated from sweet potato. The relative expression levels of IbAKR increased significantly (approximately 3-fold) after exposure to 200 mmol·L−1 CdCl2 or 10 mmol·L−1 H2O2. A subcellular localization assay showed that IbAKR is predominantly located in the nucleus and cytoplasm. IbAKR-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 H2O2 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 IbAKR enhances tolerance to Cd stress via the scavenging of cytotoxic aldehydes and the activation of the ROS scavenging system.

Highlights

The heavy metal, Cd, is considered to be biologicallyReceived March 7, 2018; accepted April 8, 2018The aldo-keto reductase (AKR) protein superfamily contains > 190 members and is found in all phyla
BLAST showed that the AKR protein contained typical AKR signature motifs (Fig. S1a), including an (α/β)8-barrel motif and catalytic tetrad (Asp63, Tyr-68, Lys-94, and His-135), which are conserved in the AKR superfamily
Proline content and superoxide dismutase (SOD) activity were significantly higher and H2O2 levels were significantly lower in the transgenic plants than in the WT

Summary

Introduction

The heavy metal, Cd, is considered to be biologicallyReceived March 7, 2018; accepted April 8, 2018The aldo-keto reductase (AKR) protein superfamily contains > 190 members and is found in all phyla. The AKR superfamily comprises 18 families and includes mainly NAD(P)(H)-dependent oxidoreductases. These enzymes reduce carbonyl substrates, such as lipid peroxidation byproducts, keto-steroids, keto-prostaglandins, retinals and quinones[4]. The overexpression of a novel alfalfa aldose/aldehyde reductase gene in transgenic tobacco plants enhanced tolerance to oxidative damage caused by paraquat, heavy metals, UV-B (280–320 nm) irradiation, drought and low temperature[5,6,7]. The overexpression of a rice AKR increased tolerance to oxidative stress, heat and glyphosate in transgenic rice[8,9]. The expression of an Arabidopsis thaliana-encoded AKR protein in transgenic barley increased tolerance to oxidative stress, Cd stress and freezing stress[11,12]. A novel member of the AKR superfamily was cloned from a soil

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