Differentiation of Symbiotic Cells and Endosymbionts in Medicago truncatula Nodulation Are Coupled to Two Transcriptome-Switches

The legume plant Medicago truncatula establishes a symbiosis with the nitrogen-fixing bacterium Sinorhizobium meliloti which takes place in root nodules. The formation of nodules employs a complex developmental program involving organogenesis, specific cellular differentiation of the host cells and the endosymbiotic bacteria, called bacteroids, as well as the specific activation of a large number of plant genes. By using a collection of plant and bacterial mutants inducing non-functional, Fix− nodules, we studied the differentiation processes of the symbiotic partners together with the nodule transcriptome, with the aim of unravelling links between cell differentiation and transcriptome activation. Two waves of transcriptional reprogramming involving the repression and the massive induction of hundreds of genes were observed during wild-type nodule formation. The dominant features of this “nodule-specific transcriptome” were the repression of plant defense-related genes, the transient activation of cell cycle and protein synthesis genes at the early stage of nodule development and the activation of the secretory pathway along with a large number of transmembrane and secretory proteins or peptides throughout organogenesis. The fifteen plant and bacterial mutants that were analyzed fell into four major categories. Members of the first category of mutants formed non-functional nodules although they had differentiated nodule cells and bacteroids. This group passed the two transcriptome switch-points similarly to the wild type. The second category, which formed nodules in which the plant cells were differentiated and infected but the bacteroids did not differentiate, passed the first transcriptome switch but not the second one. Nodules in the third category contained infection threads but were devoid of differentiated symbiotic cells and displayed a root-like transcriptome. Nodules in the fourth category were free of bacteria, devoid of differentiated symbiotic cells and also displayed a root-like transcriptome. A correlation thus exists between the differentiation of symbiotic nodule cells and the first wave of nodule specific gene activation and between differentiation of rhizobia to bacteroids and the second transcriptome wave in nodules. The differentiation of symbiotic cells and of bacteroids may therefore constitute signals for the execution of these transcriptome-switches

AGO1 and AGO2 Act Redundantly in miR408-Mediated Plantacyanin Regulation

Background: In Arabidopsis, AGO1 and AGO2 associate with small RNAs that exhibit a Uridine and an Adenosine at their 59 end, respectively. Because most plant miRNAs have a 59U, AGO1 plays many essential roles in miRNA-mediated regulation of development and stress responses. In contrast, AGO2 has only been implicated in antibacterial defense in association with miR393*, which has a 59A. AGO2 also participates in antiviral defense in association with viral siRNAs. Principal Findings: This study reveals that miR408, which has a 59A, regulates its target Plantacyanin through either AGO1 or AGO2. Indeed, neither ago1 nor ago2 single mutations abolish miR408-mediated regulation of Plantacyanin. Only an ago1 ago2 double mutant appears compromised in miR408-mediated regulation of Plantacyanin, suggesting that AGO1 and AGO2 have redundant roles in this regulation. Moreover, the nature of the 59 nucleotide of miR408 does not appear essential for its regulatory role because both a wildtype 59A-MIR408 and a mutant 59U-MIR408 gene complement a mir408 mutant. Conclusions/Significance: These results suggest that miR408 associates with both AGO1 and AGO2 based on criteria that differ from the 59 end rule, reminiscent of miR390-AGO7 and miR165/166-AGO10 associations, which are not based on the nature of the 59 nucleotide

Analyse du transcriptome de Medicago truncatula lors de l'organogenèse de la nodosité induite par Sinorhizobium melitoti

Au cœur de la symbiose entre les légumineuses et les rhizobia se trouve un échange de nutriments. Cette interaction se déroule dans un organe racinaire spécifique : la nodosité. Les bactéroïdes sont des rhizobia différenciés à l'intérieur des nodosités fixant l'azote pour l'usage de la plante hôte et la plante fourni des produits carbonés aux bactéries. Les mécanismes moléculaires et les gènes gouvernant l'organogenèse de la nodosité sont dans leur majorité peu connus. Pendant ce travail de thèse, une analyse transcriptomique a été utilisée pour la description de la formation des nodosités. A cette fin, une collection d'EST a été établie à partir d'une banque d'ADNc de nodosités puis des microarrays ont été créés. Un compendium de transcriptomes a été assemblé à partir de stades distincts du développement chez le sauvage, de tissus de nodosités disséquées et de nodosités induites par une collection de mutants bactériens ou végétaux, incapables de former une nodosité fonctionnelle. Environ 500 gènes sur les 2400 testés sont induits au cours de la nodulation. Parmi ces gènes, une nouvelle famille a été identifiée de plus de 300 gènes (les ncrs) qui sont exclusivement exprimés dans les nodosités. Sur la base d'une variété de critères, il est proposé que les NCRs jouent un rôle dans la différentiation des rhizobia pour former des bactéroïdes fixateurs d'azote. D'autres gènes importants identifiés codent des facteurs de transcription et sont des bons candidats pour orchestrer le transcriptome dans les nodosités. Des gènes candidats qui organisent et exécutent la sénescence des nodosités ont également été identifiés. L'analyse statistique du compendium a permis d'organiser les gènes en clusters et de prédire pour un grand nombre d'entre eux leur profil d'expression spatiale dans les nodosités. Cela a également permis de classer les mutants de nodulation en fonction de leur transcriptome et de le corréler avec leur phénotype morphologique. Il est démontré que le transcriptome spécifique des nodosités n'est atteint que lorsque les cellules végétales symbiotiques et les bactéroïdes sont différenciés mais qu'il est indépendant de la fixation d'azote.At the heart of the Rhizobium-legume symbiosis is the exchange of nutrients between the two symbionts. This interaction takes place in specialized organs, the nodules, on the roots of the plant. Bacteroids are differentiated rhizobia inside the nodules that fix nitrogen for plant use and plants in turn provide photosynthates to the bacteria. The molecular mechanisms and the plant genes that govern nodule organogenesis are only partially understood. During this thesis work, transcriptome analysis was used to describe the nodule formation. For this purpose, an EST collection was made from a nodule cDNA library and microarrays were constructed. A compendium of transcriptomes was assembled from distinct stages in wild type nodule development, dissected tissues of nodules and nodules induced by a collection of bacterial and plant mutants unable to form a functional nodule. About 500 from the 2400 tested genes were induced during nodule formation. Among these, a novel family was identified of more than 300 genes (the ncrs) which are exclusively expressed in nodules. Other important identified genes code for transcription factors and are good candidates to orchestrate the nodule transcriptome. Candidate genes orchestrating senescence of nodules were identified as well. Statistical analysis of the compendium data made it possible to create gene clusters and to predict spatial gene expression patterns in nodules for many of the nodule induced genes. It also allowed classifying the mutants in function of their transcriptome and correlating this with their morphological phenotype. It is demonstrate that the nodule specific transcriptome is established only when both, plant symbiotic cells and bacteroids are differentiated but it is independent of nitrogen fixation.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Jurisprudence française relative au droit international

Maziau Nicolas, Cazala Julien, Jambon Nicolas, Maunoury Myriam. Jurisprudence française relative au droit international. In: Annuaire français de droit international, volume 50, 2004. pp. 876-903

Jurisprudence française relative au droit international

Maziau Nicolas, Cazala Julien, Jambon Nicolas, Maunoury Myriam. Jurisprudence française relative au droit international. In: Annuaire français de droit international, volume 51, 2005. pp. 773-801

Jurisprudence française relative au droit international (2001)

Maziau Nicolas, Cazala Julien, Jambon Nicolas, Maunoury Myriam. Jurisprudence française relative au droit international (2001). In: Annuaire français de droit international, volume 48, 2002. pp. 725-761

Jurisprudence française relative au droit international

Maziau Nicolas, Cazala Julien, Jambon Nicolas, Maunoury Myriam. Jurisprudence française relative au droit international. In: Annuaire français de droit international, volume 49, 2003. pp. 699-731

Jurisprudence française relative au droit international - 2005

Maziau Nicolas, Cazala Julien, Jambon Nicolas, Maunoury Myriam. Jurisprudence française relative au droit international - 2005. In: Annuaire français de droit international, volume 52, 2006. pp. 764-793

Jurisprudence française relative au droit international – 2006

Maziau Nicolas, Cazala Julien, Jambon Nicolas, Maunoury Myriam. Jurisprudence française relative au droit international – 2006. In: Annuaire français de droit international, volume 53, 2007. pp. 846-871