Phloem: the integrative avenue for resource distribution, signaling, and defense.

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Phloem sap intricacy and interplay with aphid feeding

Aphididae feed upon the plant sieve elements (SE), where they ingest sugars, nitrogen compounds and other nutrients. For ingestion, aphid stylets penetrate SE, and because of the high hydrostatic pressure in SE, phloem sap exudes out into the stylets. Severing stylets to sample phloem exudates (i.e. stylectomy) has been used extensively for the study of phloem contents. Alternative sampling techniques are spontaneous exudation upon wounding that only works in a few plant species, and the popular EDTA-facilitated exudation technique. These approaches have allowed fundamental advances on the understanding of phloem sap composition and sieve tube physiology, which are surveyed in this review. A more complete picture of metabolites, ions, proteins and RNAs present in phloem sap is now available, which has provided large evidence for the phloem role as a signalling network in addition to its primary role in partitioning of photo-assimilates. Thus, phloem sap sampling methods can have remarkable applications to analyse plant nutrition, physiology and defence responses. Since aphid behaviour is suspected to be affected by phloem sap quality, attempts to manipulate phloem sap content were recently undertaken based on deregulation in mutant plants of genes controlling amino acid or sugar content of phloem sap. This opens up new strategies to control aphid settlement on a plant host

La proteine capsidade d'un potyvirus, le virus de la mosaique de la laitue (LMV), aspects moleculaires et structuraux, utilisation dans le recherche de resistance aux virus

* Station de Pathologie vegetale - INRA Versailles Diffusion du document : Station de Pathologie vegetale - INRA Versailles Diplôme : Dr. Ing.absentabsen

Des ponts entre les cellules végétales (plasmdesmes)

National audienc

Contrôle des potyvirus par transgénose

National audienc

The phloem pathway: New issues and old debates

International audienceThe phloem is a central actor in plant development and nutrition, providing nutrients and energy to sink organs and integrating interorgan communication. A comprehensive picture of the molecules trafficking in phloem sap is being made available, with recent surveys of proteins, RNAs, sugars, and other metabolites, some of which are potentially acting as signals. In this review, we focus on recent breakthroughs on phloem transport and signalling. A case study was phloem loading of sucrose, acting both as a nutrient and as a signal, whose activity was shown to be tightly regulated. Recent advances also described actors of macromolecular trafficking in sieve elements, including chaperones and RNA binding proteins, involved potentially in the formation of ribonucleoprotein complexes. Likewise, long distance signalling appeared to integrate electrical potential waves, calcium bursts and potentially the generation of reactive oxygen species. The ubiquitin-proteasome system was also proposed to be on action in sieve elements for signalling and protein turnover. Surprisingly, several basic processes of phloem physiology are still under debate. Hence, the absence in phloem sap of reducing sugar species, such as hexoses, was recently challenged with observations based on an analysis of the sap from Ranunculaceae and Papaveraceae. The possibility that protein synthesis might occur in sieve elements was again questioned with the identification of components of the translational machinery in Pumpkin phloem sap. Altogether, these new findings strengthen the idea that phloem is playing a central role in interorgan nutrient exchanges and communication and demonstrate that the ways by which this is achieved can obey various patterns among species

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

Sampling and analysis of phloem sap

Chapitre 12The transport tubes of the phloem are essential for higher plants. They not only provide the route for the distribution of assimilates produced during photosynthesis from source to sink organs but also (re-) distribute mineral nutrients. Additionally, the phloem is essential for sending information between distant plant organs and steering developmental and defense processes. For example, flowering and tuberization time are controlled by phloem-mobile signals and important defense reactions on the whole plant level, like systemic acquired resistance or systemic gene silencing, are spread through the phloem. In addition, recent results demonstrate that also the allocation of mineral nutrients is coordinated by phloem mobile signaling molecules.However, in many studies the important analysis of phloem sap is neglected, probably because the content of sieve tubes is not easy to access. This chapter will describe the current methods for sampling and analysis of phloem sap in order to encourage researchers to include the analysis of this crucial compartment in their relevant studies

Delving deeper into the link between sugar transport, sugar signaling and vascular system development

International audiencePlant growth and development rely on the transport and use of sugars produced during photosynthesis. Sugars have a dual function as nutrients and signal molecules in the cell. Many factors maintaining sugar homeostasis and signaling are now identified, but our understanding of the mechanisms involved in coordinating intracellular and intercellular sugar translocation is still limited. We also know little about the interplay between sugar transport and signaling and the formation of the vascular system, which controls long-distance sugar translocation. Sugar signaling has been proposed to play a role; however, evidence to support this hypothesis is still limited. Here, we exploited recent transcriptomics datasets produced in aerial organs of Arabidopsis to identify genes coding for sugar transporters or signaling components expressed in the vascular cells. We identified genes belonging to sugar transport and signaling for which no information is available regarding a role in vasculature development. In addition, the transcriptomics datasets obtained from sugar-treated Arabidopsis seedlings were used to assess the sugar-responsiveness of known genes involved in vascular differentiation. Interestingly, several key regulators of vascular development were found to be regulated by either sucrose or glucose. Especially CLE41, which controls the procambial cell fate, was oppositely regulated by sucrose or glucose in these datasets. Even if more experimental data are necessary to confirm these findings, this survey supports a link between sugar transport/signaling and vascular system development. This article is protected by copyright. All rights reserved