Project description:The bacterium, Sinorhizobium meliloti, interacts symbiotically with leguminous plants such as Medicago truncatula to form nitrogen-fixing root nodules. During symbiosis, plant and bacterial cells differentiate in a coordinated manner, resulting in specialized plant cells that contain nitrogen-fixing bacteroids. Medicago nodules are organized in structurally distinct tissue zones, representing different stages of bacterial and plant differentiation. We used laser-capture microdissection (LCM) to analyze bacterial and plant gene expression in four root nodule regions. In parallel, we analyzed gene expression in nodules formed by wild type bacteria on six plant mutants with nitrogen fixation deficiencies (dnf). We found that bacteroid metabolism is drastically remodeled during bacteroid differentiation. Many processes required for bacterial growth are down-regulated in the nitrogen fixation zone. The overall transcriptional changes are similar to those occurring during nutrient limitation by the stringent response. We also observed differential expression of bacterial genes involved in nitrogen fixation, cell envelope homeostasis, cell division, stress response and polyamine biosynthesis at distinct stages of nodule development. In M. truncatula we observed the differential regulation of several host processes that may trigger bacteroid differentiation and control bacterial infection. We analyzed plant and bacterial gene expression simultaneously, which allowed us to correlate processes in both organisms.
Project description:To investigate the effect that biological nitrogen fixation will have on plant responses to nitrogen dose at elevated CO2, alfalfa (Medicago sativa) lines were grown at three nitrogen doses and ambient or elevated CO2. Four lines were used in the study, two lines that can form nodules capable of fixing nitrogen (effective lines) and two lines that can not form nodules capable of nitrogen fixation (ineffective lines). The ineffective lines are the result of a complementary mutation in the same gene.
Project description:The experiment aims to identify the response of mature nodules and denodulated roots of Medicago truncatula /Sinorhizobium medicae md4 to the systemic signaling of plant N deficit. The root systems of nodulated symbiotic plants were divided into two compartments. The N source of N2 fixing plants was exclusively the air. To reduce the plant nitrogen (N) supply (N-deficient conditions), we flushed one half root system with Ar/O2 (80/20 v/v) while the other half root system was kept on control conditions (Air). To characterize the systemic responses of the transcriptome to plant N deficit , nodules and roots of the non-treated half root system were harvested and total RNA isolated for RNAseq analysis. We performed a time-course (6 hours, 1-, 3- and 5-days treatment).
Project description:With a view to re-annotate the genome sequence of the nitrogen fixing bacterium Sinorhizobium meliloti, we generated oriented sequences of transcripts. To cover a large number of expressed genes we prepared RNA from bacteria grown in three very different physiological conditions including bacteria grown in liquid cultures (in both exponential and stationary growth phases) and from 10-day-old nodules in which bacteria were differentiated in nitrogen fixing bacteroids. The transcripts sequences were then integrated into EuGene-P, a new prokaryotic genome annotation tool able to integrate high throughput data including oriented RNA-Seq data directly into the prediction process, which led to the production of an accurate and complete annotation of the genome of S. meliloti strain 2011.
Project description:The experiment aims to identify the response of the mature nodules and denodulated roots of Medicago truncatula /Sinorhizobium medicae md4 to the systemic signaling of plant water deficit. The root systems of nodulated symbiotic plants were divided into two compartments. The N source of N2 fixing plants was exclusively the air. To apply the water stress, we treated half root system with PEG while the other was kept on control conditions. To characterize the systemic responses of the transcriptome to the PEG treatment , nodules and roots of the non-treated half root system were harvested and total RNA isolated for RNAseq analysis. We performed a time-course (6 hours, 1-, 3- and 5-days treatment) .
Project description:Root nodules of the medicago truncatula-sinorhizobium meliloti plant-bacterail symbiotic model system were hand sectioned followed by LCMS. Sections were made to separate different developmental zones along the nodules longitudinal axis.
Project description:Transcriptome analysis in nodules of Medicago truncatula with customn 2.3K cDNA arrays.<br><br>Study of different nodule developmental stages in wild type.<br><br>Study of various mutants forming non-functional nodules.
Project description:The RNA-binding protein Hfq is a global regulator, which controls diverse cellular processes in bacteria. To begin understanding the role of Hfq in the Sinorhizobium meliloti-Medicago truncatula nitrogen-fixing symbiosis, we defined free-living and symbiotic phenotypes of an hfq mutant. Over 500 transcripts were differentially accumulated in the hfq mutant of S. meliloti Rm1021 when grown in a shaking culture.
