Project description:Plant-released flavonoids induce the transcription of symbiotic genes in rhizobia and one of the first bacterial responses is the synthesis of so called Nod factors. They are responsible for the initial root hair curling during onset of root nodule development. This signal exchange is believed to be essential for initiating the plant symbiosis with rhizobia affiliated with the alphaproteobacteria. Here, we provide evidence that in broad host range rhizobia the complete lack of quorum sensing molecules results in an elevated copy number of its symbiotic plasmid (pNGR234a). This in turn triggers the expression of symbiotic genes and the production of Nod factors in the absence of plant signals. Therefore, increasing the copy number of specific plasmids could be a widespread mechanism of specialized bacterial populations bridging gaps in signalling cascades and providing a competitive advantage.
Project description:NGS2013-04: Transcriptomic response to Nod Factor treatments on Medicago Role of the root hair in water and nutrient uptake and the establishment of the nitrogen-fixing symbiotic interaction with rhizobia.
Project description:NGS2013-04: Transcriptomic response to Nod Factor treatments on Medicago Role of the root hair in water and nutrient uptake and the establishment of the nitrogen-fixing symbiotic interaction with rhizobia. The RNA was extracted from root hairs of Medicago: control vs treated by nod factors (2 biological replicates)
Project description:Rhizobia are soil bacteria that can enter into complex symbiotic relationships with legumes, where rhizobia induce the formation of nodules on the plant root. Inside nodules, rhizobia differentiate into nitrogen-fixing bacteroids that reduce atmospheric nitrogen into ammonia, secreting it to the plant host in exchange for carbon. During the transition from free-living bacteria to bacteroids, rhizobial metabolism undergoes major changes. To investigate the metabolism of bacteroids and contrast it with the free-living state, we quantified the proteome of unlabelled bacteroids relative to 15N-labelled free-living rhizobia. The data were used to build a core metabolic model of pea bacteroids for the strain Rhizobium leguminosarum bv. viciae 3841.
Project description:Legume plants form symbiotic relationships with diazotrophic bacteria called rhizobia. During such symbiosis, plants provide bacteria with preferred carbon sources such as malate and succinate in return for essential reduced nitrogen. Compatible interactions result in a series of plant root modifications that eventually result in nodule formation. Bacteria living in the nodule cells fix nitrogen via the nitrogenase enzyme complex. Interestingly, as in plant-pathogen interactions, incompatibility in legume-rhizobia associations is also regulated in a genotype-specific manner. For example, the dominant Rj2 gene is presumed to help exclude poor nitrogen-fixing or less-beneficial rhizobia such as B. japonicum USDA122 (U122). The process likely involves recognition of bacterial effectors by host receptor proteins similar to the perception of pathogenic microbes. Our results show that genetic exclusion of incompatible rhizobia in the root requires conserved molecular components of the plant immune response pathway and results in the induction of systemic signaling in the distal tissue. To better understand the mechanism underlying incompatible rhizobia-induced systemic signaling, we compared the transcriptional changes in the foliar tissue of Rj2 plants inoculated with compatible or incompatible rhizobia strains, using RNA-Seq analysis.
Project description:Paraburkholderia phymatum belongs to the β-subclass of proteobacteria. It has recently been shown to be able to nodulate and fix nitrogen in symbiosis with several mimosoid and papillionoid legumes. In contrast to symbiosis of legumes with α-proteobacteria, very little is known about the molecular determinants underlying the successful establishment of this mutualistic relationship with β-proteobacteria. In this study, we analyzed RNA-seq data of free-living P. phymatum growing under nitrogen replete and limited conditions, the latter partially mimicking the situation in nitrogen deprived soils. Among the genes up-regulated under nitrogen limitation, we found genes involved in exopolysaccharide production and motility, two traits relevant for plant root infection. Next, RNA-seq data of P. phymatum grown under free-living conditions and from symbiotic root nodules of Phaseolus vulgaris (common bean) were generated and compared. Among the genes highly up-regulated during symbiosis, we identified an operon encoding a potential cytochrome o ubiquinol oxidase (Bphy_3646-49). Bean root nodules induced by a cyoB mutant strain showed reduced nitrogenase and nitrogen fixation abilities suggesting an important role of the cytochrome for respiration inside the nodule. Analysis of mutant strains for RNA polymerase transcription factor rpoN (σ54) and its activator NifA indicated that – similar to the situation in α-rhizobia – P. phymatum RpoN and NifA are key regulators during symbiosis with P. vulgaris.