11 research outputs found
Association préférentielle entre les mycorhizes à arbuscules et les <em>pseudomonas</em> saprophytes présentant des systÚmes de sécrétion de type III
National audienceLes systĂšmes de sĂ©crĂ©tion de type III (SST3) permettent aux bactĂ©ries Ă Gram nĂ©gatif d'Ă©tablir des interactions cellulaires avec des organismes eucaryotes. La plus grande frĂ©quence de Pseudomonas spp. fluorescents saprophytes prĂ©sentant des SST3 dans la rhizosphĂšre (Mazurier et al., 2004) comparĂ©e au sol suggĂšre leur possible rĂŽle dans les interactions entre ces bactĂ©ries et les eucaryotes prĂ©sents dans la rhizosphĂšre, en particulier plante et champignon. Lâobjectif de cette Ă©tude Ă©tait de diffĂ©rencier lâeffet des racines et des mycorhizes Ă arbuscules (MA) sur la densitĂ© et la diversitĂ© des populations de Pseudomonas prĂ©sentant des SST3. La stratĂ©gie adoptĂ©e a consistĂ© Ă comparer les populations de Pseudomonas associĂ©es (i) aux racines mycorhizĂ©es de Medicago truncatula J5 (Myc+ Nod+ ) et du mutant TRV48 (Myc+ Nod- ), (ii) aux racines non mycorhizĂ©es du mutant TRV25 (Myc- Nod- ) cultivĂ©s dans le sol de ChĂąteaurenard (France) et (iii) au sol nu correspondant. Cette comparaison a portĂ© sur (i) la frĂ©quence des isolats portant des gĂšnes codant des SST3 (hrcRST), (ii) la diversitĂ© de ces sĂ©quences et de celle du fond gĂ©nĂ©tique des isolats (BOX-PCR). Les rĂ©sultats indiquent que la frĂ©quence des isolats prĂ©sentant des SST3 est significativement plus Ă©levĂ©e sur les racines mycorhizĂ©es (J5 et TRV48) que sur les racines non mycorhizĂ©es (TRV25) ou dans le sol nu. LâĂ©tude de diversitĂ© des sĂ©quences hrcRST a rĂ©vĂ©lĂ© la prĂ©sence de quatre gĂ©notypes dont deux spĂ©cifiquement associĂ©s aux racines mycorhizĂ©es. Les isolats prĂ©sentant des SST3 ne sont repartis que dans 10 des 65 gĂ©notypes BOX-PCR dĂ©crits. Les MA ont donc un effet marquĂ© sur les populations prĂ©sentant des SST3, suggĂ©rant leur rĂŽle dans lâinteraction bactĂ©ries-mycorhizes. Pivato et coll. ont rĂ©cemment montrĂ© quâune souche modĂšle de P. fluorescens (C7R12) prĂ©sentant un SST3 amĂ©liore la mycorhization. La contribution du SST3 dans cet effet bĂ©nĂ©fique est en cours dâĂ©valuation
Fluorescent pseudomonads harboring type III secretion genes are enriched in the mycorrhizosphere of Medicago truncatula
International audienceType III secretion systems (T3SSs) of Gram-negative bacteria mediate direct interactions with eukaryotic cells. Pseudomonas spp. harboring T3SS genes (T3SS+) were previously shown to be more abundant in the rhizosphere than in bulk soil. To discriminate the contribution of roots and associated arbuscular mycorrhizal fungi (AMF) on the enrichment of T3SS+ fluorescent pseudomonads in the rhizosphere of Medicago truncatula, their frequency was assessed among pseudomonads isolated from mycorrhizal and nonmycorrhizal roots and from bulk soil. T3SS genes were identified by PCR targeting a conserved hrcRST DNA fragment. Polymorphism of hrcRST in T3SS+ isolates was assessed by PCR-restriction fragment length polymorphism and sequencing. Genotypic diversity of all pseudomonads isolated, whether or not harboring T3SS, was described by BOX-PCR. T3SS+ pseudomonads were significantly more abundant in mycorrhizal than in nonmycorrhizal roots and in bulk soil, and all were shown to belong to the phylogenetic group of Pseudomonas fluorescens on the basis of 16S rRNA gene identity. Four hrcRST genotypes were described; two only included isolates from mycorrhizal roots. T3SS+ and T3SSâ pseudomonads showed different genetic backgrounds as indicated by their different BOX-PCR types. Taken together, these data suggest that T3SSs are implicated in interactions between fluorescent pseudomonads and AM in medic rhizosphere
Dynamics and Differential Proliferation of Transposable Elements During the Evolution of the B and A Genomes of Wheat
Chromatin redistribution of the DEK oncoprotein represses hTERT transcription in leukemias.
Although numerous factors have been found to modulate hTERT transcription, the mechanism of its repression in certain leukemias remains unknown. We show here that DEK represses hTERT transcription through its enrichment on the hTERT promoter in cells from chronic and acute myeloid leukemias, chronic lymphocytic leukemia, but not acute lymphocytic leukemias where hTERT is overexpressed. We isolated DEK from the hTERT promoter incubated with nuclear extracts derived from fresh acute myelogenous leukemia (AML) cells and from cells expressing Tax, an hTERT repressor encoded by the human T cell leukemia virus type 1. In addition to the recruitment of DEK, the displacement of two potent known hTERT transactivators from the hTERT promoter characterized both AML cells and Tax-expressing cells. Reporter and chromatin immunoprecipitation assays permitted to map the region that supports the repressive effect of DEK on hTERT transcription, which was proportionate to the level of DEK-promoter association but not with the level of DEK expression. Besides hTERT repression, this context of chromatin redistribution of DEK was found to govern about 40% of overall transcriptional modifications, including those of cancer-prone genes. In conclusion, DEK emerges as an hTERT repressor shared by various leukemia subtypes and seems involved in the deregulation of numerous genes associated with leukemogenesis
Chromatin Redistribution of the DEK Oncoprotein Represses hTERT Transcription in Leukemias
Development of genomic resources for <em>Medicago truncatula</em> and related legume crops
National audienc
Les intermittences du sujet
Cent ans aprĂšs Ă la Recherche du temps perdu de Marcel Proust, les intermittences du cĆur demeurent, mais les mots pour le dire s'inscrivent dans un nouveau paradigme, celui du discontinu. L'Ă©criture de soi ne cesse d'imploser dans d'infinies intermittences gĂ©nĂ©riques et scripturales qui tĂ©moignent d'un sujet dĂ©sireux moins de se prendre intus et in cute que de se dĂ©prendre en privilĂ©giant la recherche d'un soi Ă travers ses mĂ©tamorphoses et ses virtualitĂ©s. La notion de vĂ©ritĂ© se dĂ©place, comme le montre dĂ©jĂ Michel Leiris cherchant sa vĂ©ritĂ© dans les tableaux de Cranach, ou Serge Doubrovsky, inventeur du terme « autofiction ». Si la psychanalyse change la donne de la recherche de soi, la grande hache de l'Histoire entre pour une large part dans cette nouvelle Ă©criture d'un soi comme expropriĂ© de lui-mĂȘme, notamment de son passĂ© et de sa filiation, contraint, comme Jorge Semprun ou Alain Fleischer, Ă s'inventer. ThĂ©Ăątre, cinĂ©ma, arts plastiques et multimĂ©dias s'en font l'Ă©cho dans des pratiques comparables de bricolage et de recomposition, Ă l'image d'AgnĂšs Varda, qui, dans ses films ou ses installations, met en scĂšne l'Ă©phĂ©mĂšre et le prĂ©caire. L'originalitĂ© de cet ouvrage tient Ă sa problĂ©matique audacieuse, urgente, complexe autant que mouvante, Ă laquelle elle tente de rĂ©pondre en interrogeant des Ćuvres canoniques aussi bien que rĂ©centes grĂące Ă des approches multiples et diverses qui mettent la littĂ©rature au cĆur d'un dialogue avec les arts et la pensĂ©e de son temps
Fluorescent pseudomonads harboring type III secretion genes are enriched in the mycorrhizosphere of Medicago truncatula
The Medicago genome provides insight into the evolution of rhizobial symbioses
Legumes (Fabaceae or Leguminosae) are unique among cultivated plants for their ability to carry out endosymbiotic nitrogen fixation with rhizobial bacteria, a process that takes place in a specialized structure known as the nodule. Legumes belong to one of the two main groups of eurosids, the Fabidae, which includes most species capable of endosymbiotic nitrogen fixation(1). Legumes comprise several evolutionary lineages derived from a common ancestor 60 million years ago (Myr ago). Papilionoids are the largest clade, dating nearly to the origin of legumes and containing most cultivated species(2). Medicago truncatula is a long-established model for the study of legume biology. Here we describe the draft sequence of the M. truncatula euchromatin based on a recently completed BAC assembly supplemented with Illumina shotgun sequence, together capturing similar to 94% of all M. truncatula genes. A whole-genome duplication (WGD) approximately 58 Myr ago had a major role in shaping the M. truncatula genome and thereby contributed to the evolution of endosymbiotic nitrogen fixation. Subsequent to the WGD, the M. truncatula genome experienced higher levels of rearrangement than two other sequenced legumes, Glycine max and Lotus japonicus. M. truncatula is a close relative of alfalfa (Medicago sativa), a widely cultivated crop with limited genomics tools and complex autotetraploid genetics. As such, the M. truncatula genome sequence provides significant opportunities to expand alfalfa's genomic toolbox