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 SA190s beneficial effects remained unclear. Given the pivotal role of sulfur-containing compounds in abiotic stress responses, we investigated multiple sulfur-related Arabidopsis mutants under drought stress. We found that SA190 enhances sulfate uptake and promotes glutathione (GSH) accumulation in shoots under stress conditions. SA190 treatment improved the GSH/GSSG ratio, indicating an enhanced redox balance under drought. Selective inhibition of Arabidopsis GSH biosynthesis using buthionine sulfoximine (BSO) confirmed the essential contribution of bacterial GSH to drought stress. In addition, by generation and use of bacterial mutants deficient in the GSH synthesis pathway, we show that the bacteria directly provide Arabidopsis with either GSH or its precursor {gamma}-EC. In summary, SA190 promotes drought tolerance by supplying the host plant with additional GSH thereby maintaining cellular redox homeostasis and enhancing drought stress resilience.