Brassinosteroids control meristem size by promoting cell cycle progression in Arabidopsis roots

Brassinosteroids (BRs) play crucial roles in plant growth and development. Previous studies have shown that BRs promote cell elongation in vegetative organs in several plant species, but their contribution to meristem homeostasis remains unexplored. Our analyses report that both loss- and gain-of-function BR-related mutants in Arabidopsis thaliana have reduced meristem size, indicating that balanced BR signalling is needed for the optimal root growth. In the BR-insensitive bri1-116 mutant, the expression pattern of the cell division markers CYCB1;1, ICK2/KRP2 and KNOLLE revealed that a decreased mitotic activity accounts for the reduced meristem size; accordingly, this defect could be overcome by the overexpression of CYCD3;1. The activity of the quiescent centre (QC) was low in the short roots of bri1-116, as reported by cell type-specific markers and differentiation phenotypes of distal stem cells. Conversely, plants treated with the most active BR, brassinolide, or mutants with enhanced BR signalling, such as bes1-D, show a premature cell cycle exit that results in early differentiation of meristematic cells, which also negatively influence meristem size and overall root growth. In the stem cell niche, BRs promote the QC renewal and differentiation of distal stem cells. Together, our results provide evidence that BRs play a regulatory role in the control of cell-cycle progression and differentiation in the Arabidopsis root meristem.Fil: González García, Mary Paz. Centre for Research in Agricultural Genomics. Molecular Genetics Department; EspañaFil: Vilarrasa Blasi, Josep. Centre for Research in Agricultural Genomics. Molecular Genetics Department; EspañaFil: Zhiponova, Miroslava. Ghent University. Department of Plant Biotechnology and Genetics; Bélgica. Vlaams Instituut voor Biotechnologie; BélgicaFil: Divol, Fanchon. Centre for Research in Agricultural Genomics. Molecular Genetics Department; EspañaFil: Mora Garcia, Santiago. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquimicas de Buenos Aires; Argentina. Fundación Instituto Leloir; Argentina. Centre for Research in Agricultural Genomics. Molecular Genetics Department; EspañaFil: Russinova, Eugenia. Ghent University. Department of Plant Biotechnology and Genetics; Bélgica. Vlaams Instituut voor Biotechnologie; BélgicaFil: Caño Delgado, Ana I. Centre for Research in Agricultural Genomics. Molecular Genetics Department; Españ

Analyse de la réponse phloèmienne de la plante à l'infestation par Myzus persicae

Le phloème a comme fonction première le transport des photoassimilats des organes sources aux organes puits. Il est également impliqué dans la signalisation à longue distance et dans la coordination du développement. Les éléments conducteurs de la sève constituent le site alimentaire des insectes phloèmophages tels que les pucerons. Lors des interactions plante / pucerons, les mécanismes de défense associés aux processus de réponse des plantes aux pathogènes et à la blessure, sont induits au niveau local. Par contre, très peu de données sont disponibles quand aux processus implique s dans la réponse systémique du tissu phloémien. Pour apporter des éléments de compréhension, nous avons utilisé deux approches en réponse à une infestation par le puceron Myzus persicae. Une analyse trancriptomique comparative a été réalisée avec des macroarrays d'ADNc thématiques construits à partir de deux banques soustraites SSH contenant 1632 ADNc de phloème isolé d'Apium graveolens. Puis une caractérisation fonctionnelle de quelques gènes a été entreprise chez Arabidopsis thaliana, basée sur l'étude de lignées recombinantes exprimant des fusions transcriptionnelles avec un gène rapporteur. Cette caractérisation a été complétée par des bio-essais sur des mutants d'inactivation (lignées K.O.). La première approche a permis d'identifier 516 gènes induits de façon systémique dans le phloème 3 et/ou 7 jours après infestation. Ces gènes sont impliqués dans la modification des parois, le métabolisme carboné, azoté, la biosynthèse de la vitamine B1, l'homéostasie des métaux et les flux hydriques. L'analyse plus fine par northern blot et hybridation in situ, de quelques uns de ces gènes a permis de démontrer l'existence de régulations tissulaire et cellulaire différentielles dans cette réponse. Ces résultats suggèrent que le phloème réajuste de façon complexe et systémique, l'expression de nombreux gènes en réponse à une infestation. Par l'identification et l'étude des orthologues potentiels les plus proche chez A. thaliana, la conservation de cette réponse entre espèce a été abordée. Ainsi il a pu être démontré que la spécificité tissulaire de l'expression de ces gènes, en particulier dans le phloème, était le plus souvent conservée entre espèces, mais que les dérégulations en réponse aux pucerons l'étaient moins. Une analyse plus fine des gènes AgXTH1 de céleri et de son orthologue AtXTH33 d' A. thaliana codant une xyloglucane endotransglycosylase / hydrolase, induits de façon systémique lors d'une infestation, ont montré qu'ils sont régulés différentiellement en réponse à un insecte phloèmophage et à la blessure. Ces observations ont été complétées par les données de l'analyse fonctionnelle qui suggèrent un rôle de AtXTH33 dans les mécanismes de protection vis à vis de l'infestation par les pucerons.The primary function of phloem is the transport of photoassimilates from source to sink organs, in addition to long distance signalling and to the coordination of the development. The conducting elements, the sieve elements, are the feeding sites for phloem feeding insects, such as aphids. This interaction induces locally a response similar to those associated with pathogen infection and wounding.. However, little information exists about the molecular processes involved during the systemic phloem response to feeding. To decopher the participation of the phloem in this response, we used two approaches in response to a infestation by the aphid Myzus persicae. A first trancriptomics comparative analysis was performed on celery (Apium graveolens) using thematic cDNA macroarrays prepared with 1632 cDNA clones from specific subtractive SSH cDNA libraries. This was completed by functional analysis based on the study of several Arabidopsis thaliana recombinant lines expressing reporter-gene transcriptional fusions and the realization of bioassays with knock-out (K.O.) mutants. We were able to identify 516 genes that were systemically induced in the phloem at 3 and/or 7 days after infestation. These genes are implied in the modification of the walls, nitrogen and carbon metabolism, the biosynthesis of the vitamin B1, the homeostasis of metals and water exchanges. A more precise analysis of some of these of genes, using northern blot analysis and in situ hybridization, made it possible to show the existence of differential tissue and cellular regulations in this response. These results suggest that the phloem response is set upt by fine tuning readjustments of many genes in a complex and systemic way. By the identification and the study of the potential orthologs in A. thaliana, the conservation of this response between species was then examined. This demonstrated that the tissue specificity of the expression of these genes, in particular in the phloem, was generally conserved between species, but that the regulations in response to aphids were less conserved. A finer analysis of the celery AgXTH1 genes and of its ortholog in Arabidopsis, AtXTH33, encoding a xyloglucane endotransglycosilase/hydrolase, that are induced in a systemic way following infestation, revealed that these genes present a differential response of the plant the insects and the wound. These observations were completed by results of the functional analysis which suggest a role of AtXTH33 in the mechanisms of protection against aphid infestation.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Protophloem differentiation in early Arabidopsis thaliana development

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The Arabidopsis Yellow Stripe LIKE4 and 6 transporters control iron release from the chloroplast.

International audienceIn most plant cell types, the chloroplast represents the largest sink for iron, which is both essential for chloroplast metabolism and prone to cause oxidative damage. Here, we show that to buffer the potentially harmful effects of iron, besides ferritins for storage, the chloroplast is equipped with specific iron transporters that respond to iron toxicity by removing iron from the chloroplast. We describe two transporters of the YELLOW STRIPE1-LIKE family from Arabidopsis thaliana, YSL4 and YSL6, which are likely to fulfill this function. Knocking out both YSL4 and YSL6 greatly reduces the plant's ability to cope with excess iron. Biochemical and immunolocalization analyses showed that YSL6 resides in the chloroplast envelope. Elemental analysis and histochemical staining indicate that iron is trapped in the chloroplasts of the ysl4 ysl6 double mutants, which also accumulate ferritins. Also, vacuolar iron remobilization and NRAMP3/4 expression are inhibited. Furthermore, ubiquitous expression of YSL4 or YSL6 dramatically reduces plant tolerance to iron deficiency and decreases chloroplastic iron content. These data demonstrate a fundamental role for YSL4 and YSL6 in managing chloroplastic iron. YSL4 and YSL6 expression patterns support their physiological role in detoxifying iron during plastid dedifferentiation occurring in embryogenesis and senescence

Propiedades ópticas de los materiales activos en diodos láser con confinamiento cuántico

En esta tesis se recoge el trabajo experimental realizado para la caracterización de las propiedades ópticas en diodos láser construidos con estructuras basadas en pozos cuánticos (QW) y puntos cuánticos (QD). Las propiedades que se han estudiado en estos dispositivos son los espectros de ganancia, ganancia diferencial, índice diferencial y factor de ensanchamiento de línea (LEF). La comprensión de estas propiedades es de especial importancia para el diseño de nuevos diodos láser destinados a ser utilizados en aplicaciones exigentes como son las comunicaciones ópticas o aplicaciones médicas. El estudio se ha llevado a cabo en muestras de diodos láser suministrados por diferentes fabricantes: Ferdinand Braun Institut für Hóchstfrequenztechnik, Thales Research and Technology y la Universidad de Würzburg. Debido a esto las muestras de los láseres se han suministrado en diferentes configuraciones, utilizándose tanto dispositivos con cavidades de área ancha como de tipo caballete (“ridge”). En los trabajos se ha realizado el diseño y la construcción de los montajes experimentales y la implementación de los métodos analíticos necesarios para el estudio de las diferentes muestras. En los montajes experimentales se han implementado procesos para el filtrado espacial de los modos laterales de la cavidad presentes en los láseres de área ancha. Los métodos analíticos implementados se han utilizado para reducir los errores existentes en los sistemas de medida, mejorar su precisión y para separar la variación de índice en debida al calentamiento y la variación de corriente cuando los láseres operan en continua. El estudio sistemático de las propiedades de ópticas de los diodos láser basados en QW y QD ha permitido concluir que propiedades como el factor de ensanchamiento de línea no tienen por qué ser necesariamente inferiores en estos últimos, ya que dependen de las condiciones de inyección. En los láseres de QW se ha observado experimentalmente una reducción del factor de ensanchamiento de línea al alcanzarse la segunda transición, debido al aumento de la ganancia diferencial. ABSTRACT This thesis includes the experimental work for the characterization of optical properties of quantum well (QW) and quantum dot (QD) laser diodes. The properties that have been studied in these devices are the gain, differential gain, differential index and the linewith enhancement factor (LEF). The understating of these properties is of special importance for the design of new laser diodes to be used in exigent applications such as optical communications or medical applications. The study has been carried out using laser samples supplied by different manufacturers: Ferdinand Braun Institut fu¨r H¨ochstfrequenztechnik, Thales Research and Technology and the University of Wu¨rzburg. Because of this the laser samples were supplied in various configurations, using both broad area and ridge devices. In the work it has been done the design and construction of the experimental setups and implementation of analytical methods required for the study of the different devices. In the experimental set-ups it has been implemented a spatial filtering process to remove the lateral modes present in broad area lasers. The implemented analytical methods has been used to reduce the experimental errors in the measurement systems, improve the accuracy and separate the index variation caused by heating and current variation when the lasers operated on continuous wave. The systematic study of the optical properties of the QW and QD laser diodes has allowed concluding that properties such the linewith enhancement factor does not have to be necessary to be lower in the QD devices, since it is dependent on the injections conditions. In this work it has been experimentally observed a reduction of the linewith enhancement factor where the second transition has been reached mainly due to in the increased of the differential gain which is observed in this situation

Transcriptome analysis of the phloem of in the plant response to aphid feeding

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Involvement of the xyloglucan endotransglycosylase/hydrolases encoded by celery XTH1 and Arabidopsis XTH33 in the phloem response to aphids

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New insights on phloem processes provided by transcriptome analysis

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