Microbial Volatile 3-Methyl-1-Butanol Enhances Stomatal Closure and Salt Stress Tolerance via Ethylene and Jasmonate Pathways in Arabidopsis

Microbial biostimulants can be applied to reliably improve crop productivity and quality. One such biostimulant is 3-methyl-1-butanol (3MB), a microbial volatile compound released by various plant growth-promoting microbes, which has gained recent attention due to its ability to promote plant growth and enhance stress tolerance. Previous studies have shown that 3MB induces stomatal closure and enhances salt stress tolerance in plants; however, its mode of action in these processes remains poorly understood. In this study, 6-day-old Arabidopsis seedlings were fumigated with 3MB (1 mg L-1) for 3 days, resulting in significant transcriptomic changes compared to untreated controls. Transcriptome analysis revealed 452 differentially expressed genes (256 upregulated and 196 downregulated by 3MB), among which several ethylene (ET)- and jasmonate (JA)-related genes were upregulated. Interestingly, 3MB induced stomatal closure and salt stress tolerance in wild-type plants but not in ethylene-responsive factor 4 (erf4) and jasmonate resistant1 (jar1-1) mutants. A metabolomic analysis further revealed a significant increase in JA and anthocyanin contents following 3MB treatment. Together, these findings suggest that 3MB-induced stomatal closure and salt stress tolerance are mediated by ET and JA signaling pathways in Arabidopsis, with potential involvement of anthocyanins. This study deepens our understanding of plant immune responses and highlights the potential of microbial biostimulants for sustainable crop improvement strategies.