γ-aminobutyric acid mitigates manganese toxicity in soybean by regulating GmNAC022: Insights from biochemical and transcriptomic analyses

Manganese (Mn) stress severely impairs plant growth and productivity. γ-aminobutyric acid (GABA) plays an essential role in counteracting various abiotic stresses. However, its involvement in regulating soybean responses to Mn stress remains largely unexplored. In this study, we conducted integrated biochemical and transcriptomic analyses on soybean seedlings subjected to Mn stress alone or in combination with GABA treatment. The results showed that an appropriate concentration of GABA can mitigate the detrimental effects of excess Mn on soybean seedlings by modulating the antioxidant defense system, amino acid contents, and mineral nutrient homeostasis. These physiological changes were corroborated by differentially expressed genes (DEGs) enriched in oxidation-reduction processes and amino acid metabolism pathways. Moreover, weighted gene co-expression network analysis (WGCNA) identified GmNAC022 as a hub gene, encoding a nuclear-localized transcription factor. Yeast one-hybrid (Y1H) and Dual-Luciferase (Dual-LUC) assays revealed that GmNAC022 directly binds to the promoters of ROS-scavenging genes, including GmGSTU1 and GmPRX1, to activate their expression. Collectively, these results suggest that GmNAC022-regulated transcriptional modules play essential roles in enhancing GABA-mediated Mn stress tolerance in soybean. These findings offer a promising strategy for GABA application in agricultural practices and identify a new molecular marker for breeding soybean varieties with improved Mn tolerance.