Volatile organic compounds from Bacillus velezensis FZB42 remodel Arabidopsis root architecture by an auxin-dependent mechanism.

Volatile organic compounds produced by plant growth-promoting rhizobacteria promote lateral root development by modulating the auxin signaling pathway in Arabidopsis thaliana, thereby remodeling root architecture. Volatile organic compounds (VOCs) emitted by plant growth-promoting rhizobacteria (PGPR) have been shown to promote both shoot and root growth in plants. While VOCs are known to modulate root architecture, the underlying mechanisms remain poorly understood. In this study, we demonstrate that VOCs released by Bacillus velezensis FZB42 significantly promote primary root elongation and increase lateral root (LR) development in Arabidopsis thaliana, thereby altering root architecture. This study indicates that VOC-mediated modulation of root architecture is closely associated with auxin signaling, particularly its polar transport. Notably, the promotive effects of VOCs on lateral root formation were nearly abolished in auxin signaling mutants, including pin2 and axr1-12. Our results further demonstrate that treatment with FZB42-VOCs does not rescue the lateral root deficiency phenotype in the auxin core components arf7 arf19 double mutants. VOCs were found to stimulate the emergence of lateral root primordia (LRP) and to induce the expression of the auxin-responsive marker DR5:GFP in pre-existing LRPs. Additionally, VOCs were found to modulate the expression of auxin efflux carriers, such as PIN1 and PIN2, and to induce DR5:GFP expression in both primary and lateral roots. Treatment with NPA, an auxin transport inhibitor, further confirmed that VOC-mediated remodeling of root architecture is dependent on auxin polar transport. In conclusion, these findings suggest that VOCs enhance auxin response during early lateral root development by modulating auxin distribution and downstream signaling, thereby stimulating lateral root formation. These findings provide valuable insights into microbe-mediated root development and could inform sustainable agricultural practices involving PGPR.