TaSTG4B enhances wheat salt tolerance via regulation of antioxidant and photosynthetic protection pathways.

Soil salinization represents a major abiotic stress constraining wheat yield. Identifying key salt tolerance-related genes and unraveling their regulatory mechanisms is critical for breeding salt-tolerant wheat varieties. In this study, TaSTG4B (Triticum aestivum Salt-Tolerant Gene on 4B, gene ID: TraesCS4B02G042300), a key regulatory gene encoding an oxysterol-binding protein homolog, was jointly identified by ethyl methanesulfonate (EMS)-induced mutagenesis screening and genome-wide association study (GWAS), and systematically elucidated its salt tolerance mechanisms. TaSTG4B exhibits relatively higher expression in wheat roots, suggesting that it primarily functions in this organ. Under 200 mM NaCl treatment (simulating moderate salt stress in saline-alkali soils), TaSTG4B overexpression (OE) lines exhibited significantly greater shoot and root biomass, and elevated activities of antioxidant enzymes compared to the wild type (Fielder). In contrast, TaSTG4B knockout (KO) lines showed markedly reduced salt tolerance. Physiological analysis revealed that TaSTG4B overexpression enhances wheat's antioxidant capacity, maintains ion homeostasis, and mitigates membrane damage under salt stress. RNA sequencing (RNA-seq) analysis revealed that under non-stress conditions, TaSTG4B primarily regulates pathways such as secondary metabolite biosynthesis-including key salt-stress-related pathways like proline (PRO), polyamine, and flavonoid biosynthesis-as well as glutathione metabolism, collectively establishing a "primed state of defense." Under salt stress, it activates glutathione metabolism, photosynthesis-antenna proteins, and ion homeostasis pathways, coordinating antioxidant defense and photosynthetic protection. This study demonstrates that TaSTG4B enhances wheat salt tolerance through a hierarchical regulatory mode of pre-adaptation and stress-specific induction, providing valuable genetic resources and a theoretical basis for the breeding of salt-tolerant wheat varieties.