CONICET | Buscador de Institutos y Recursos Humanos

Leguminous plants can develop a symbiotic interaction with compatible rhizobia that culminates in the formation of root nodules, where bacteria differentiate into bacteriods, which reduce atmospheric nitrogen to ammonium that is used by the host. Ensifer meliloti is the model of efficient rhizobia that establishes a highly specific symbiosis with Medicago truncatula, resulting in nodules with differentiated bacteroids. Rhizobium favelukesii LPU83 is an acid-tolerant rhizobia, which is also able to nodulate M. truncatula. However, this strain is inefficient in nitrogen fixation and bacteria differentiation into full bacteroids is diminished. There is a vast amount of information about the initial infection process and the development of the nodule but little is known about the determinants involved in the differentiation process. The comparison between the transcriptomes of the nodules infected by E. meliloti and R. favelukesii as a model of efficient and inefficient nodule in nitrogen fixation, respectively, could be key to find genes that may be involved in this process. Plant assays were done and after 10 and 31 days after inoculation (dpi), nodules were collected. RNA expression profiles of the nodules and those of these strains in free-living conditions were obtained by RNAseq. After performing a differential expression analysis, we obtained more than 3,000 differentially expressed genes (DEG) between free-living bacteria and bacteria inside the nodule (at 10 dpi and 31 dpi), for both E. meliloti and R. favelukesii. These DEGs where distributed among the chromosome and the plasmids that harbor each species. DEGs were categorized into cellular-functional groups according to each cluster of orthologous groups (COGs) and different functional categories were enriched depending on the bacteria. These results show that the behavior of the bacteria during the infection and differentiation process is far more complex than it was thought.