Abstract
Glutaredoxins (GRXs) belong to the antioxidants involved in the cellular stress responses. In spite of the identification 48 GRX genes in rice genomes, the biological functions of most of them remain unknown. Especially, the biological roles of members of GRX family in disease resistance are still lacking. Our proteomic analysis found that OsGRX20 increased by 2.7-fold after infection by bacterial blight. In this study, we isolated and characterized the full-length nucleotide sequences of the rice OsGRX20 gene, which encodes a GRX family protein with CPFC active site of CPYC-type class. OsGRX20 protein was localized in nucleus and cytosol, and its transcripts were expressed predominantly in leaves. Several stress- and hormone-related motifs putatively acting as regulatory elements were found in the OsGRX20 promoter. Real-time quantitative PCR analysis indicated that OsGRX20 was expressed at a significantly higher level in leaves of a resistant or tolerant rice genotype, Yongjing 50A, than in a sensitive genotype, Xiushui 11, exposed to bacterial blight, methyl viologen, heat, and cold. Its expression could be induced by salt, PEG-6000, 2,4-D, salicylic acid, jasmonic acid, and abscisic acid treatments in Yongjing 50A. Overexpression of OsGRX20 in rice Xiushui 11 significantly enhanced its resistance to bacterial blight attack, and tolerance to methyl viologen and salt stresses. In contrast, interference of OsGRX20 in Yongjing 50A led to increased susceptibility to bacterial blight, methyl viologen and salt stresses. OsGRX20 restrained accumulation of superoxide radicals in aerial tissue during methyl viologen treatment. Consistently, alterations in OsGRX20 expression affect the ascorbate/dehydroascorbate ratio and the abundance of transcripts encoding four reactive oxygen species scavenging enzymes after methyl viologen-induced stress. Our results demonstrate that OsGRX20 functioned as a positive regulator in rice tolerance to multiple stresses, which may be of significant use in the genetic improvement of rice resistance.
Highlights
A variety of environmental stresses, including pathogen attack, photooxidation, salinity, abnormal temperature, and drought, stimulate the production of reactive oxygen species (ROS)
The seedling leaves per tank were sprayed with 100 mL of 100 μM methyl viologen (MeV), 20 μM 2,4-D, 2 mM salicylic acid (SA), 100 μM jasmonic acid (JA), and 100 μM abscisic acid (ABA) in 0.02% Tween-20, while mock controls were sprayed with 0.02% Tween20 solution without addition of MeV or growth regulators
Our previous studies have demonstrated that rice variety Yongjing 50A exhibits the broad-spectrum resistance to Xanthomonas oryzae pv. oryzae (Xoo) strains, while Xiushui 11 is susceptible to Xoo strains (Huang et al, 2008; Zhang et al, 2015)
Summary
A variety of environmental stresses, including pathogen attack, photooxidation, salinity, abnormal temperature, and drought, stimulate the production of reactive oxygen species (ROS). Excessive ROS can induce macromolecular damage and change normal signal conduction (Fukao et al, 2011; Laporte et al, 2012) To cope with such oxidative toxicity, plant cells have developed. It has been reported recently that overexpression of a CC-type GRX gene, OsGRX8, in Arabidopsis plants reduced sensitivity to auxin and stress hormone, abscisic acid (ABA), and increased tolerance to various abiotic stresses, including oxidative stress, osmotic and salinity. The roles of members of GRX family in disease resistance remain unknown
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