Root endophyte sulfur metabolites enhance redox balance and drought tolerance in Arabidopsis

Drought is a major consequence of climate change and significantly limits crop productivity. Plant growth-promoting bacteria offer a promising solution to mitigate drought stress. The root endophyte Pseudomonas argentinensis SA190 has been shown to enhance plant performance under drought stress conditions, but the mechanistic basis of SA190's beneficial effects remained unclear. Given the pivotal role of sulfur-containing compounds in abiotic stress responses, we investigated multiple sulfur-related Arabidopsis mutants under PEG-induced drought stress. We found that SA190 enhances sulfate uptake and promotes glutathione (GSH) accumulation in shoots under stress conditions. SA190 treatment increased the GSH/GSSG ratio, providing an enhanced redox resilience under PEG stress. Inhibition of GSH biosynthesis in Arabidopsis with buthionine sulfoximine (BSO) provided evidence that SA190 contributes to elevated GSH levels under PEG-induced drought stress. Using bacterial mutants defective in GSH biosynthesis, we further show that SA190 contributes to Arabidopsis growth under PEG-induced stress, potentially through a mechanism involving bacterial GSH itself or its precursor, γ -glutamylcysteine (γ-EC). In summary, SA190 enhances tolerance to PEG-induced drought stress by modulating host sulfur metabolism and improving cellular redox homeostasis.