Bradyrhizobium BclA is a peptide transporter required for bacterial differentiation in symbiosis with Aeschynomene legumes

ABSTRACT

Nodules of legume plants are highly integrated symbiotic systems shaped by millions of years of evolution. They harbor nitrogen fixing rhizobium bacteria called bacteroids. Several legume species produce peptides called NCRs in the symbiotic nodule cells housing the bacteroids. NCRs are related to antimicrobial peptides of plant innate immunity. They induce the endosymbionts into a differentiated, enlarged and polyploid state. The bacterial symbionts on their side evolved functions for the response to the NCR peptides. Here we identified the bclA gene of Bradyrhizobium strains ORS285 which is required for the formation of differentiated and functional bacteroids in the nodules of the NCR-producing Aeschynomene legumes. The BclA ABC transporter promotes the import of NCR peptides and provides protection against the antimicrobial activity of these peptides. Moreover, BclA can complement the role of the related BacA transporter of Sinorhizobium meliloti which has a similar symbiotic function in the interaction with Medicago legumes.