GABA Mediates the Enhancement of Maize (Zea mays L.) Saline-Alkali Tolerance Through DJ Bacterium

Soil salinization is considered a major abiotic stress limiting the sustainable development of agriculture globally. Utilizing plant growth-promoting rhizobacteria (PGPR) to enhance crop tolerance under saline-alkali stress constitutes a sustainable and promising strategy. This study focuses on Enterobacter cloacae strain DJ, isolated from the rhizosphere of Leymus chinensis in saline-alkali soil. This study aims to investigate the role of gamma-aminobutyric acid (GABA)metabolism in regulating the saline-alkali adaptation of strain DJ and its growth-promoting effects on maize under such stress. The results indicated that under saline-alkali conditions, strain DJ upregulated genes associated with GABA metabolism, energizing ion transport and motility. Furthermore, the extracellular GABA concentration in the culture medium of strain DJ rose from 4.04 μmol L^-1 at 4 h to 11.65 μmol L^-1 at 12 h, followed by a decline to 7.00 μmol L^-1 at 24 h, suggesting that GABA potentially promotes cellular growth and physiological activities. Exogenous GABA further enhanced the ion transport capacity, motility, and biomass of strain DJ, confirming the contribution of GABA to improving its saline-alkali adaptability. In maize, strain DJ improved germination (by 7-10%) and seedling growth under saline-alkali conditions, as evidenced by increases in primary radicle length (+2.8 cm), shoot height (+2 cm), and fibrous root number (+4). It upregulated root expression of GAT1 (threefold), GABA-T (1.3-fold), and SSADH (1.5-fold), and increased antioxidant enzyme activities (SOD/POD: 1.5-fold; CAT: 1.8-fold). These findings demonstrate that strain DJ enhances the antioxidant capacity of maize through a GABA-mediated pathway and supports energy metabolism for improving tolerance under saline-alkali conditions.