Project description:Legume plants can form root organs called nodules where they house intracellular symbiotic rhizobium bacteria. Within nodule cells, rhizobia differentiate into bacteroids, which fix nitrogen for the benefit of the plant. Depending on the combination of host plants and rhizobial strains, the output of rhizobium-legume interactions is varying from non-fixing associations to symbioses that are highly beneficial for the plant. Bradyrhizobium diazoefficiens USDA110 was isolated as a soybean symbiont but it can also establish a functional symbiotic interaction with Aeschynomene afraspera. In contrast to soybean, A. afraspera triggers terminal bacteroid differentiation, a process involving bacterial cell elongation, polyploidy and membrane permeability leading to loss of bacterial viability while plants increase their symbiotic benefit. A combination of plant metabolomics, bacterial proteomics and transcriptomics along with cytological analyses was used to study the physiology of USDA110 bacteroids in these two host plants. We show that USDA110 establish a poorly efficient symbiosis with A. afraspera, despite the full activation of the bacterial symbiotic program. We found molecular signatures of high level of stress in A. afraspera bacteroids whereas those of terminal bacteroid differentiation were only partially activated. Finally, we show that in A. afraspera, USDA110 bacteroids undergo an atypical terminal differentiation hallmarked by the disconnection of the canonical features of this process. This study pinpoints how a rhizobium strain can adapt its physiology to a new host and cope with terminal differentiation when it did not co-evolve with such a host.
Project description:Rhizobia are soil bacteria that can associate with some legumes and participate in symbiotic nitrogen fixation. Bacterial CspA family members are small, single stranded nucleic acid binding proteins. Differentiation of rhizobial bacteria from a free-living to symbiotic state within legume root nodules follows a massive re-programming of bacterial gene expression. Here, the role of Sinorhizobium meliloti CspA family members in symbiotic development with Medicago sativa (alfalfa) was investigated. We defined expression patterns of CspA family members, identified CspA interacting RNAs, and investigated phenotypes and transcriptional defects associated with cspA deletion strains. We propose that these proteins affect rhizobial physiology through their global control of the cellular RNA secondary structure strength environment and through specific modulation of small non-coding RNA (sRNA) structures involved in cis-regulation of stress responsive sigma factor expression. This work describes an RNA structure mediated mechanism important for bacterial stress adaptation and symbiotic development within a plant host.
Project description:Rhizobia are soil bacteria that can associate with some legumes and participate in symbiotic nitrogen fixation. Bacterial CspA family members are small, single stranded nucleic acid binding proteins. Differentiation of rhizobial bacteria from a free-living to symbiotic state within legume root nodules follows a massive re-programming of bacterial gene expression. Here, the role of Sinorhizobium meliloti CspA family members in symbiotic development with Medicago sativa (alfalfa) was investigated. We defined expression patterns of CspA family members, identified CspA interacting RNAs, and investigated phenotypes and transcriptional defects associated with cspA deletion strains. We propose that these proteins affect rhizobial physiology through their global control of the cellular RNA secondary structure strength environment and through specific modulation of small non-coding RNA (sRNA) structures involved in cis-regulation of stress responsive sigma factor expression. This work describes an RNA structure mediated mechanism important for bacterial stress adaptation and symbiotic development within a plant host.
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:Green hydra (Hydra viridissima) harbors endosymbiotic Chlorella and have established a mutual relation. To identify the host hydra genes involved in the specific symbiotic relationship, transcriptomes of intact H. viridissima colonized with symbiotic Chlorella strain A99, aposymbiotic H.viridissima and H. viridissima artificially infected with other symbiotic Chlorella were compared by microarray analysis. The results indicated that genes involved in nutrition supply to Chlorella were upregulated in the symbiotic hydra. In addition, it was induced by supply of photosynthates from the symbiont to the host, suggesting cooperative metabolic interaction between the host and the symbiotic algae.