Volatile organic compounds from the salt-tolerant Glutamicibacter halophytocola KLBMP 5180 enhance salt stress tolerance in tomato seedlings by regulating antioxidant defense, ion homeostasis, and auxin, jasmonic acid/ethylene signaling pathways.

The application of salt-tolerant plant growth-promoting rhizobacteria (PGPR) represents a promising strategy to alleviate salt stress in crops. However, the mechanisms by which volatile organic compounds (VOCs) from actinomycetes mitigate salinity stress remain unclear. In this study, exposure to VOCs from the halotolerant actinomycete Glutamicibacter halophytocola KLBMP 5180 significantly promotes the growth of tomato seedlings under salt stress, as evidenced by increased fresh weight, lateral root number, and chlorophyll content. Physiological analyses show that VOCs exposure reduces oxidative damage and enhances antioxidant enzyme activity. Furthermore, elevated levels of total phenolics and flavonoids are detected, along with decreased sodium ion accumulation and an improved Na⁺/K⁺ ratio. Transcriptome analysis reveales that VOCs treatment upregulates genes associated with pathways involved in phenylpropanoid biosynthesis, glutathione metabolism, MAPK signaling, plant hormone signal transduction, and plant-pathogen interactions under saline conditions. VOCs also increase levels of endogenous auxin, jasmonic acid (JA), and 1-aminocyclopropane-1-carboxylic acid (ACC), while activating genes related to their respective signaling pathways. The salt tolerance enhancement mediated by VOCs is compromised by ethylene and JA inhibitors, suggesting that KLBMP 5180-derived VOCs improve tomato salt tolerance by stimulating ethylene synthesis and signal transduction. Additional VOCs profiling identifies several key bioactive compounds, including 3-methyl-1-butanol, phenylethyl alcohol, 2-aminopropanediamide, and 2-undecanone. These findings demonstrate that VOCs from G. halophytocola KLBMP 5180 enhance tomato growth under salt stress and advance our understanding of the role of actinomycetes in pronoting plant growth and mitigating salinity stress.