Stress-induced Bacillus subtilis DLD-8 volatiles enhance drought tolerance in mung bean via 2,3-butanediol-MYB interaction.

Drought is major abiotic constraint limiting mung bean (Vigna radiata L. Wilczek) productivity. Rhizobacterial volatile organic compounds (VOCs) are increasingly being recognized for their role in plant-microbe interactions including growth promotion and stress tolerance. This study evaluated the effects of VOCs on biometric and physiological responses of mung bean under osmotic stress and examined interaction of the most efficient VOC with a MYB protein. VOCs from five rhizobacterial cultures, grown under non-stress and osmotic stress conditions, were assessed in vitro and in vivo. VOCs from three cultures significantly enhanced plant biomass, proline accumulation, and SOD activity; with stronger responses observed for VOCs from stressed cultures. Based on its performance, Bacillus subtilis DLD-8 was selected for detailed analysis. GC-MS profiling detected 36 VOCs under stress and 24 under non-stress, with stressed cultures enriched in alkanes and alcohols. VIP-based analysis identified 2,3-butanediol, tetradecane, and octadecane as key volatiles. Pathway enrichment indicated stress-induced activation of tyrosine and benzoate metabolism, while non-stressed cultures showed enrichment in lipid and fatty acid metabolism. Network analysis suggested enhanced connectivity of 2,3 butanediol with pyruvate derived intermediates under stress indicating carbon flux redistribution towards the acetoin-2,3-butanediol pathway. In vivo validation, revealed that 2,3-butanediol and the blend of three predominant VOCs elicited the strongest plant responses. Notably, 2,3-butanediol alone outperformed the blend, and enhanced biomass, proline, chlorophyll, and SOD activity. Docking analysis provided preliminary computational evidence of a potential interaction between 2,3-butanediol and Vigna radiata MYB protein, suggesting possible link in MYB-mediated drought stress-responsive pathways.