Bacterial community maintenance of plant root development

Plants grow within a complex web of species interacting with each other and with the plant. Much of these interactions take place via a wide repertoire of chemical signals, and the resulting chemical landscape of the rhizosphere can strongly affect root health and development. To understand how microbe-microbe interactions influence root development in Arabidopsis, we established a model system for plant-microbe-microbe-environment interactions. We inoculated seedlings with a 185-member bacterial synthetic community (SynCom), and manipulated the abiotic environment, enabling classification of the SynCom to modules of co-occurring strains. Based on these modules, iterative deconstruction of the SynCom identified multiple microbe-microbe interactions that determine root phenotypes. A primary player in these interactions is the genus Variovorax, which reverts phenotypic effects on root development that are induced by a wide diversity of bacterial strains as well as by the entire 185-member community. Variovorax manipulate plant hormone levels to balance this ecologically realistic root community’s effects on root development. Therefore, metabolic signal interference shapes bacteria-plant communication networks and is essential for maintaining the root’s developmental program.