Genome-Wide Identification of the Wheat GAD Gene Family Reveals TaGAD1-Mediated Salt Tolerance via GABA-Dependent ROS Homeostasis

Wheat (Triticum aestivum L.) is a major food crop that is severely affected by salt stress, resulting in significant yield losses. Glutamic acid decarboxylase (GAD) catalyzes the irreversible conversion of glutamic acid to γ-aminobutyric acid (GABA) and plays key roles in plant growth, development, and stress responses. However, the GAD gene family in hexaploid wheat and its role in salt tolerance remain poorly understood. In this study, the wheat GAD gene family was systematically identified. Genome-wide analysis revealed seven TaGAD genes with 19 gene copies. A Ka/Ks ratio < 1 indicates strong evolutionary conservation of this family. All TaGAD proteins contain a conserved Glu-decarb-GAD domain with similar motif composition and structural organization. Promoter analysis showed enrichment of stress-responsive cis-elements. Expression profiling demonstrated tissue-specific patterns, with several TaGAD genes significantly induced under salt stress. CRISPR/Cas9-mediated knockout of TaGAD1 led to markedly reduced salt tolerance, accompanied by decreased GABA content and GAD activity, reduced activities of antioxidant enzymes (SOD, POD, and CAT), and excessive accumulation of reactive oxygen species (ROS). These results demonstrate that TaGAD1 positively regulates salt tolerance in wheat through GABA-mediated ROS homeostasis. This study provides a systematic characterization of the wheat TaGAD gene family in the context of salt stress, laying a theoretical foundation for understanding GABA-mediated tolerance mechanisms and identifying TaGAD1 as a potential molecular breeding target for improving salt tolerance in wheat.