PI CBGP: Luis Rey /José M Palacios

Associations of symbiotic bacteria with plants

PI CEPLAS: Ruben Garrido-Oter

Co-PI CEPLAS: Kathrin Wippel

Project summary:

Legumes interact symbiotically with nitrogen-fixing bacteria through a complex mechanism that has attracted much research. It has mostly focused on binary host-symbiont interactions and largely ignored the role that other surrounding microbes play in this process. Recently, using host symbiosis mutants, we showed an impact on the assembly of microbial communities in the root or rhizosphere, suggesting an interaction between commensal microbiota members and host-symbiont associations. However, the directionality, causality and mechanisms by which commensal bacteria interact with the symbiotic process is not yet understood. The bacterial type VI secretion system (T6SS) proved to be important for plant protection against pathogens and establishment of nitrogen fixing symbiosis. Analyzing genomes from the Arabidopsis thaliana and Lotus japonicus culture collections, we found T6SS genes present in rhizobial symbionts and other members of the commensal root and rhizosphere microbiota. Gnotobiotic experiments with L. japonicus and T6SS Mesorhizobium mutants showed a complete loss of nodulation in binary associations, which was partially restored by co-inoculation of a commensal SynCom, suggesting that members of the plant microbiota complement the mechanisms required to drive these associations. The aim of this proposal is to explore these mechanisms.