Volatile organic compounds emitted by Bacillus sp. JC03 promote plant growth through the action of auxin and strigolactone

The volatile organic compounds (VOCs) emitted by plant rhizobacteria play a significant role in the promotion of plant growth. However, it is unclear how VOCs play a role in plant growth and which component participates in this process. In this study, we assessed the effect of the VOCs emitted by Bacillus sp. JC03 on the promotion of plant growth and identified the overall functional mechanism. The results indicated that the VOCs produced by JC03 could significantly promote the biomass accumulation of Arabidopsis and tomato. Furthermore, an analysis of Arabidopsis mutants perturbations in hormone production and signaling, in conjunction with analyses of hormone contents and gene expression levels, indicated that auxin and strigolactone played essential roles in the promotion of plant growth induced by the VOCs produced by JC03. The results showed that the ARF1 and CCD7 genes were significantly upregulated in the Arabidopsis seedlings exposed to the VOCs emitted by JC03 and the results of the endogenous hormone levels detection experiment reached the same conclusion. Furthermore, the VOC-induced phenotype was reduced or, even lost in the ARF1, and CCD7 mutant lines, while the phenotype remained in A. thaliana ecotype Col-0 seedlings and in other mutants, such as etr1, OST1 and gai1. Finally, GC-MS analysis results positively identified the compounds released from JC03, including 3-hydroxy-2-butanone, 1, 3-propanediol, 2-methyl-dipropanoate, tetrahydrofuran-3-ol, 2-heptanone, 2-ethyl-1-hexanol. Only tetrahydrofuran-3-ol, 2-heptanone and 2-ethyl-1-hexanol, at different concentrations, significantly promoted the growth of the Arabidopsis seedlings. In this study, we first demonstrated that the VOCs emitted by JC03 promoted plant growth through the action of auxin and strigolactone, and identified several new compounds, tetrahydrofuran-3-ol, 2-heptanone and 2-ethyl-1-hexanol, that could promote plant growth. The important achievement of our study is the further elucidation of the interacting mechanisms related to plant responses to the VOCs emitted by microbes.