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.