Project description:12plex_medicago_2014_02 - nar nodule vs root transcriptome - which are the genes differentially expressed in alfalfa spontaneous (non rhizobium-infected) nodules vs. control roots? - biological material: aeroponically grown cuttings of a Medicago sativa (alfalfa) accession that produces empty nodules when nitrogen-starved. Samples for transcriptome comparison: isolated NAR nodules (10 days post N-starvation) vs. roots of the same plants (pools of 3 roots).
Project description:In order to better understand the commonalities and differences in lateral root and nodule development, we compared their organogenesis and correlated this with changes in gene expression. To initiate lateral roots in Medicago truncatula we turned 2-day-old seedlings 135°, before returning them to their original axis of growth, while for nodule initiation we applied droplets of Sinorhizobium meliloti on the susceptibility zone of the root.
Project description:Legumes perform symbiotic nitrogen fixation through rhizobial bacteroids housed in specialised root nodules. The biochemical process is energy‐intensive and consumes a huge carbon source to generate sufficient reducing power. To maintain the symbiosis, malate is supplied by legume nodules to bacteroids as their major carbon and energy source in return for ammonium ions and nitrogenous compounds. To sustain the carbon supply to bacteroids, nodule cells undergo drastic reorganisation of carbon metabolism. Here, a comprehensive quantitative comparison of the mitochondrial proteomes between root nodules and uninoculated roots was performed using data‐independent acquisition proteomics, revealing the modulations in nodule mitochondrial proteins and pathways in response to carbon reallocation. Corroborated our findings with that from the literature, we believe nodules preferably allocate cytosolic phosphoenolpyruvates towards malate synthesis in lieu of pyruvate synthesis, and nodule mitochondria prefer malate over pyruvate as the primary source of NADH for ATP production. Moreover, the differential regulation of respiratory chain‐associated proteins suggests that nodule mitochondria could enhance the efficiencies of complexes I and IV for ATP synthesis. This study highlighted a quantitative proteomic view of the mitochondrial adaptation in soybean nodules.
Project description:Biological nitrogen fixation (BNF) is a primary input of nitrogen to natural and agricultural systems globally. BNF is a temperature-dependant enzymatic process and can be conducted by microbes (including Rhizobia) hosted symbiotically in root nodules of some plants. Heat shock proteins (Hsps) have been implicated in the process of acquiring thermotolerance or acclimating to elevated temperature, as they play a vital role in maintaining cell integrity and homeostasis during heat stress. Although the BNF response to temperature may crucially impact future ecosystem productivity in the face of global climate change, little is known about Hsp expression in nodules of N-fixing non-agricultural species, such as tropical N-fixing trees in the Fabaceae family. This project aimed to characterize small (15-20kDa) Hsp (sHsp) expression in nodule tissue to examine the biochemical mechanisms of heat response in these tissues. To first identify Hsps in nodule tissues, Vachellia farnesiana and Acacia confusa nodules were excised, heat shock was induced, and protein content was isolated via chemical treatment before separation of protein species and analysis with SDS-PAGE. Two polyacrylamide gels yielded bands in the 15-20 kDa region that displayed differential Coomassie staining, which were sent for further characterization by HPLC-MS analysis for protein sequencing. Ten rhizobial sHsps were detected in these samples in addition to seven Acacia sHsps when compared independently to reference rhizobial and plant proteome databases. In an attempt quantify relative expression of Hsps in nodule and root tissue, we performed western blot experiments using Anti-Hsp20 antibodies raised against human and mouse Hsp proteins, with anti-beta actin loading control. While nonuniform beta-actin expression across tissue types (A. confusa nodules versus root control) prevented quantitative analysis, the experiments validated that Hsp20s are expressed in Acacia nodules as well as in root tissue. These experiments could provide a foundation for future studies that aim to determine variation in responses to key stressors predicted to increase with global climate change and help determine the implications of warming across the tropics and beyond.