Evidence for nod dependent and nod independent symbiotic interaction between different Cupriavidus species and legume hosts

Abstract

Rhizobia are soil bacteria belonging to the alpha and beta subclasses within proteobacteria that are able to establish symbiotic interaction with plants of the Legume family. During this interaction, the rhizobia reduce atmospheric dinitrogen to ammonia, in a process known as biological nitrogen fixation (BFN). Although the capital importance of FBN and that the existence of rhizobia has been documented more than 120 years ago, the mechanisms involved in the recognition and selection of the symbiotic partners has been documented in a limited number of studied models. Most of these include rhizobia belonging to the alpha proteobacteria, while scarce information is available for those belonging to the beta subclass. Our laboratory has two main interests; to analyze the diversity of rhizobia associated to legumes of the Mimosoid clade in Uruguay and to describe the main signal and responses involved in the molecular dialogue between beta-rhizobia and legume hosts. We have identified natural symbionts occurring at 20 Mimosa species, founding that most belongs to the Cupriavidus and Paraburkholderia genus. Two of the Cupriavidus strains were selected to analyze their behavior during their interaction with plant hots. Their genomes were sequenced, then the gene and proteins expression patterns were analyzed in the presence of flavonoids, plant exudates or co-culture conditions. We have designed and developed novel methods that could be applied for other bacteria models. Our results indicated that native Mimosa are reservoirs of novel Cupriavidus species and suggest that these beta-rhizobia relies both on conserved and innovating mechanisms for their interaction with plant hosts.