Transgenic potato overexpressing Arabidopsis cytosolic AtDHAR1 showed higher tolerance to herbicide, drought and salt stresses

Abstract

Ascorbate (vitamin C) is a powerful antioxidant and scavenger of free radicals that protects plants against oxidative damage caused by adverse environmental conditions such as drought, salt stress, and herbicide use. Dehydroascorbate reductase (DHAR; EC 1.8.5.1) and monodehydroascorbate reductase (MDAR; EC 1.6.5.4) are crucial for ascorbate regeneration and the maintenance of a pool of the reduced form. In this study, we report the development of transgenic potato (Solanum tuberosum L.) that overexpresses the Arabidopsis thaliana DHAR gene (AtDHAR1) in the cytosol. The transgenic plants exhibited up to 4.5 times the DHAR activity and up to 2.8 times the level of reduced ascorbate found in the wild-type plants. When subjected to methylviologen treatment, the transgenic plants exhibited enhanced tolerance in terms of less ion leakage, greater chlorophyll contents, less accumulation of hydrogen peroxide, and less severe visual injury symptoms. Moreover, the transgenic plants exhibited faster growth under drought and salt stress. Our results demonstrate that elevating ascorbate contents by overproducing DHAR represents a viable approach for the development of herbicide-tolerant potato.Key Words: ascorbate, potato, vitamin C, dehydroascorbate, methylviologen. IntroductionAdverse environmental conditions such as drought, salt stress, and use of herbicide promote the overproduction of reactive oxygen species (ROS) in plant cells. ROS such as singlet oxygen (O 2 1 ), superoxide radicals (O 2 ⋅), hydrogen peroxide (H 2 O 2 ), and hydroxyl radicals (OH⋅) are believed to be the major factor responsible for rapid cellular damage due to their high reactivity with membrane lipids, proteins, and DNA (Asada and Takahashi 1987, Hung et al. 2005, Mittler 2002). Scavenging and reducing the deleterious effects of ROS is performed by several enzymatic and nonenzymatic systems in plant cells. A network of low-molecularweight antioxidants, such as ascorbate (AsA), glutathione (GSH), and α-tocopherol, and antioxidative enzymes such as superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT) are crucial for preventing and controlling the dangerous affects of ROS (Noctor and Foyer 1998). Specifically, enzymes involved in catalyzing redox reactions and in maintaining pools of reduced AsA and GSH in the AsA-GSH pathway, mainly monodehydroascorbate reductase (MDAR; EC 1.6.5.4), dehydroascorbate reductase (DHAR; EC 1.8.5.1), and glutathione reductase, are considered of paramount importance in plant antioxidant defense mechanisms.The antioxidant AsA can directly scavenge free radicals (Halliwell and Gutteridge 2000), and is particularly important as an electron donor for detoxification of H 2 O 2 via ascorbate peroxidase in plant cells (Noctor and Foyer 1998). Moreover, AsA is a major redox buffer in plants , a cofactor of many enzymes (Smirnoff and Wheeler 2000), a regulator of cell division and growth (Kerk and Feldman 1995), and a molecule used in signal transduction in plants (Noctor et al. 2000). AsA is synthesized in t...

Elevating vitamin C content via overexpression of myo-inositol oxygenase and l-gulono-1,4-lactone oxidase in Arabidopsis leads to enhanced biomass and tolerance to abiotic stresses

“…4 a, c, d ). This result is in agreement with previous studies in Arabidopsis (Ushimaru et al 2006), potato (Upadhyaya et al 2010; Eltayeb et al 2011), soybean (Hamada and Al-Hakimi 2009), tobacco (Kwon et al 2003; Eltayeb et al 2006; Eltayeb et al 2007; Lee et al 2007), tomato (Shalata and Neumann 2001; Zhang et al 2011), and wheat (Athar et al 2008) that also support the positive role of elevated AsA in conferring tolerance to salt stress. Total AsA content of seedlings grown on MS plates plus NaCl declined as salt concentration increased, however, AsA levels of MIOX4 and GLOase remained higher than with WT and pCAMBIA lines at all NaCl concentrations tested (Fig.4 b ).…”

Reactive Oxygen Species, Oxidative Damage, and Antioxidative Defense Mechanism in Plants under Stressful Conditions

“…This upregulation of DHAR was correlated to its role in AsA recycling in the apoplast [224]. Transgenic potato overexpressing Arabidopsis cytosolic AtDHAR1 showed higher tolerance to herbicide, drought, and salt stresses [225].…”

Manipulation of Ascorbate Biosynthetic, Recycling, and Regulatory Pathways for Improved Abiotic Stress Tolerance in Plants

“…Increased expression of the DHAR gene has increased the concentrations of reduced ascorbate in a wide range of species, including 1.1to 3.3-fold in Arabidopsis [34,90-94], 1.9-to 6.1-fold in maize (Zea mays L.) [95,96] [85,95,[101][102][103][104][105][106], and 1.5-fold to 1.9-fold in tomato [88,107,108] (Table 2). Increased expression of the DHAR gene in plants has been associated with enhanced tolerance to salt, drought, high light, heat, ozone, cold, aluminum, hydrogen peroxide, and methyl viologen-induced stress [85,[90][91][92][93][94]98,[101][102][103][104][105][106][107][108] (Table 2).…”