Endogenous γ-Aminobutyric Acid Accumulation Enhances Salinity Tolerance in Rice

Rice is an important food crop worldwide but is usually susceptible to saline stress. When grown on soil with excessive salt, rice plants experience osmotic, ionic, and oxidative stresses that adversely affect growth performance. γ-Aminobutyric acid (GABA) is a nonproteinogenic amino acid that plays an important role in the metabolic activities of organisms. Glutamate decarboxylase (GAD) is the rate-limiting enzyme in GABA metabolism. Here, we genetically modified rice GAD by overexpression or CRISPR-mediated genome editing. These lines, named gad3-ox1 and gad3-ox2 or gad1/3-ko, were used to explore the effects of endogenous GABA accumulation on salt tolerance in rice. Both the gad3-ox1 and gad3-ox2 lines exhibited significant accumulation of the GABA content, whereas the gad1/3-ko line presented a reduced GABA content in vivo. Notably, the two overexpression lines were markedly resistant to salt stress compared with the wild-type and knockout lines. Furthermore, our results demonstrated that endogenous GABA accumulation in the gad3-ox1 and gad3-ox2 lines increased the contents of antioxidant substances and osmotic regulators, decreased the content of membrane lipid peroxidation products and the Na⁺ content, and resulted in strong tolerance to salt stress. Together, these data provide a theoretical basis for cultivating rice varieties with strong salt tolerance.