Homologous expression of γ-glutamylcysteine synthetase increases grain yield and tolerance of transgenic rice plants to environmental stresses.

Various environmental stresses induce reactive oxygen species (ROS), causing deleterious effects on plant cells. Glutathione (GSH), a critical antioxidant, is used to combat ROS. GSH is produced by γ-glutamylcysteine synthetase (γ-ECS) and glutathione synthetase (GS). To evaluate the functional roles of the Oryza sativa L. Japonica cv. Ilmi ECS (OsECS) gene, we generated transgenic rice plants overexpressing OsECS under the control of an inducible promoter (Rab21). When grown under saline conditions (100mM) for 4 weeks, 2-independent transgenic (TGR1 and TGR2) rice plants remained bright green in comparison to control wild-type (WT) rice plants. TGR1 and TGR2 rice plants also showed a higher GSH/GSSG ratio than did WT rice plants in the presence of 100mM NaCl, which led to enhanced redox homeostasis. TGR1 and TGR2 rice plants also showed lower ion leakage and higher chlorophyll-fluorescence when exposed to 10μM methyl viologen (MV). Furthermore, the TGR1 and TGR2 rice seeds had approximately 1.5-fold higher germination rates in the presence of 200mM salt. Under paddy field conditions, OsECS-overexpression in transgenic rice plants increased rice grain yield (TGW) and improved biomass. Overall, our results show that OsECS overexpression in transgenic rice increases tolerance and germination rate in the presence of abiotic stress by improving redox homeostasis via an enhanced GSH pool. Our findings suggest that increases in grain yield by OsECS overexpression could improve crop yields under natural environmental conditions.