ZmGAPB enhances the drought and salt stress tolerance in maize seedlings

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) B subunit (GAPB) is essential for photosynthetic CO₂ fixation and regulating GAPDH enzyme activity. However, its role in abiotic stress responses remains largely unexplored. We conducted a thorough investigation of ZmGAPB expression profiles and performed a comprehensive functional characterization using maize inbred line B73 (wild type, WT) and an EMS-induced zmgapb mutant line. Our findings demonstrate that ZmGAPB expression is significantly induced by salt or drought stress. Confocal microscopic analysis confirmed that ZmGAPB is localized to chloroplasts. Under stress conditions, the zmgapb mutant line exhibited markedly impaired growth phenotypes and reduced photosynthetic efficiency compared to WT plants. This was evidenced by significant decreases in plant biomass, chlorophyll accumulation, and osmotic adjustment capacity. Furthermore, the zmgapb mutant line displayed an elevated degree of cell membrane oxidative damage and markedly reduced antioxidant enzyme activity. Under conditions of salt stress, the zmgapb mutant line demonstrated an elevated Na ⁺ level and a significantly reduced K⁺/Na⁺ ratio, resulting in increased ionic toxicity relative to WT plants. Additionally, relevant stress genes in the zmgapb mutant line were down-regulated under stress conditions. Taken together, our results indicate that ZmGAPB could be a promising candidate gene for improving maize tolerance to abiotic stress.