Overexpression of the CC-type glutaredoxin, OsGRX6 affects hormone and nitrogen status in rice plants.

Ashraf El-Kereamy,Eiji Nambara,Yong-Mei Bi,Mahmoud W Yaish,Steven J Rothstein,Kashif Mahmood,Kosala Ranathunge

doi:10.3389/fpls.2015.00934

Abstract

Glutaredoxins (GRXs) are small glutathione dependent oxidoreductases that belong to the Thioredoxin (TRX) superfamily and catalyze the reduction of disulfide bonds of their substrate proteins. Plant GRXs include three different groups based on the motif sequence, namely CPYC, CGFS, and CC-type proteins. The rice CC-type proteins, OsGRX6 was identified during the screening for genes whose expression changes depending on the level of available nitrate. Overexpression of OsGRX6 in rice displayed a semi-dwarf phenotype. The OsGRX6 overexpressors contain a higher nitrogen content than the wild type, indicating that OsGRX6 plays a role in homeostatic regulation of nitrogen use. Consistent with this, OsGRX6 overexpressors displayed delayed chlorophyll degradation and senescence compared to the wild type plants. To examine if the growth defect of these transgenic lines attribute to disturbed plant hormone actions, plant hormone levels were measured. The levels of two cytokinins (CKs), 2-isopentenyladenine and trans-zeatin, and gibberellin A1 (GA1) were increased in these lines. We also found that these transgenic lines were less sensitive to exogenously applied GA, suggesting that the increase in GA1 is a result of the feedback regulation. These data suggest that OsGRX6 affects hormone signaling and nitrogen status in rice plants.

Highlights

Glutaredoxin (GRXs) are small glutathione dependent oxidoreductases that belong to the Thioredoxin (TRX) superfamily and catalyze the reduction of disulfide bonds of their substrate proteins in the presence of glutathione
Plant GRXs include three different groups based on the motif sequence, CPYC, CGFS, and CC-type proteins (Ziemann et al, 2009) and a fourth group was added in rice containing the GRL-type (Garg et al, 2010)
We describe the functional analysis of the OSGRX6, a CC-type GRXs gene that was identified by Bi et al (2009), during the screening for genes involved in nitrogen use efficiency (NUE) in rice

Summary

Introduction

Glutaredoxin (GRXs) are small glutathione dependent oxidoreductases that belong to the Thioredoxin (TRX) superfamily and catalyze the reduction of disulfide bonds of their substrate proteins in the presence of glutathione. The dithiol reaction requires the presence of two conserved terminal cysteines in the motif (CXXC) while in the monothiol reaction the target protein is reduced only through one Nterminal cysteine that can be a part of the CXXC or CXXS motif Both reduction reactions result in a reversible posttranslational and structural modification of the target proteins (Xing et al, 2006). The plant glutaredoxins have been shown to be involved during various stress responses including Type II peroxiredoxins reduction, dehydroascorbate reduction, peroxidase activity, Overexpression of OsGRX6 in rice methylviologen response, methionine sulfoxide reductase regeneration and interaction with thioredoxins. The tomato glutaredoxin gene SlGRX1 has been reported to regulate plant responses to oxidative stress.

Methods

Results

Conclusion