IN INOCULANTS Nodulaid - 17th International Nitrogen Fixation ...

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17 th International Congress on Nitrogen Fixation Fremantle, Western Australia 27 November – 1 December 2011 Session Details: Monday 28 November 2011 Plenary Session 1 1100 - 1230 Authors: Fang Xie, Giulia Morieri, Jeremy Murray, Anne L. Heckmann, Anne Edwards, Jiyoung Kim, Giles E. D. Oldroyd and J. Allan Downie John Innes Centre Norwich Research Park, Colney, Norwich, NR4 7UH, UK Presentation Title: Characterisation of a legume pectate lyase required for initiation and growth of infection threads during nodule infection by rhizobia Presentation Time: 1100 - 1130 It has long been recognised that nodule infection by rhizobia requires localised degradation of plant cell walls to enable infection threads to initiate and grow. In root hair infection foci, the cell wall is locally degraded enabling penetration by the bacteria, and this is coupled with the synthesis of a new infection thread wall, but relatively little is known about the proteins required for these processes. A microarray analysis identified Medicago truncatula genes more strongly induced by Nod factors from WT than a (nodL) mutant of Sinorhizobium meliloti, which is reduced for infection. Among the genes identified was a predicted pectate lyase. In parallel work we identified two allelic Lotus japonicus mutants, which are defective for infection thread growth and nodule infection. Fine mapping indicated that the mutation was located in a region of about 38 genes. Analysis of the equivalent region of M. truncatula showed that the pectate lyase gene identified from the transcriptomics was one of these 38 genes. Sequencing of the orthologous gene from the two L. japonicus mutants identified different mutations in each, and the cloned WT allele complemented the mutant phenotype. Therefore the mutations in this pectate lyase gene caused the infection defect. In vitro biochemical assays with the purified WT and mutant protein demonstrated that the gene encodes a plant pectinase and we conclude that this activity contributes to the cell-wall degradation that is required to initiate infection thread growth in root hairs. It also appears to be required for subsequent extension of the infection thread across cell-cell junctions. The pectate lyase gene is induced following Nod-factor activation of the common symbiosis pathway and requires the transcriptional regulators NIN and NSP1 for its normal induction. Chromosome immunoprecipitation and promoter binding experiments indicated that the pectate lyase gene is directly regulated by NIN. These results show that there is specific Nod-factor induction of genes that play a role in initiating root infection by rhizobia. 16 2011
17 th International Congress on Nitrogen Fixation Fremantle, Western Australia 27 November – 1 December 2011 Session Details: Monday 28 November 2011 Plenary Session 1 1100 - 1230 Authors: Luis M. Rubio, Emilio Jiménez-Vicente, César Poza-Carrión, Carlos Echavarri-Erasun, Alessandro Scandurra & Elena Moreno-Urbano Universidad Politécnica de Madrid. Centro de Biotecnología y Genómica de Plantas Pozuelo de Alarcón, 28223 Madrid (Spain). Presentation Title: Changes in nif gene expression profiles during nitrogenase biogenesis Presentation Time: 1130-1200 A number of nitrogen fixation (nif) genes (10-20 depending on the organism) are involved in the assembly of a functional nitrogenase enzyme. Changes in the levels of nif gene products over time are required to obtain appropriate balances during nitrogenase biogenesis. In the model organism Azotobacter vinelandii nif gene expression exhibits exquisite regulation at least at the transcriptional and post-translational levels. We report here the changes over time of the cellular levels of nif mRNAs and Nif proteins with key functions in nitrogenase biosynthesis. Expression of nifH, nifD, nifK, nifY, nifE, nifN, nifX, nifU, nifS, nifV, nifA, nifB, FdxN, nifQ, and nafY genes was quantified by using real-time quantitative PCR. In addition, cellular accumulation of each one of the corresponding Nif proteins was determined by immunoblot analysis and quantified against standards obtained with purified protein preparations. The results will be analyzed in the context of observed in vivo nitrogenase activitiy development over time. The implications to constructing nitrogenase enzymes through synthetic biology techniques will be discussed. 17 2011
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IN INOCULANTS Nodulaid - 17th International Nitrogen Fixation ...

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