Isoprene‐Emitting Transgenic Tobacco Shapes Root Microbiome and Enhances Growth of Co‐Cultivated Non‐Emitting Plants

Isoprene is the most abundant biogenic volatile organic compound emitted by terrestrial vegetation. Here we report the impact of isoprene on root-associated microbiomes. Using isoprene-emitting (IE) transgenic tobacco and isogenic non-emitting (NE) controls, we performed co-cultivation experiments in natural soil and analysed plant phenotypes and growth alongside bacterial and fungal communities across root, rhizosphere, and soil niches. NE plants co-cultivated with IE neighbours displayed increased shoot and root biomass, suggesting interactive belowground functions of isoprene. Amplicon sequencing revealed more growth-promoting microbiota in root and rhizosphere of IE plants than NE plants. Both bacterial and fungal growth-promoting microbiota were enriched in IE and NE plants grown in the same pot. However, isoprene-fumigated plant-free soils did not replicate these shifts, indicating that plant-microbe interactions are required for the modulation of the soil microbiome. Our results suggest that isoprene acts as a belowground cue influencing microbiome assembly and indirectly enhancing growth in neighbouring plants. This work uncovers a potential ecological role for isoprene, highlighting how plant-derived isoprene can mediate plant-plant-microbiome interactions and contribute to community-level processes in the rhizosphere.