Auxin fluxes in the root apex co-regulate gravitropism and lateral root initiation

International audienceRoot architecture plays an important role in water and nutrient acquisition and in the ability of the plant to adapt to the soil. Lateral root development is the main determinant of the shape of the root system and is controlled by external factors such as nutrient concentration. Here it is shown that lateral root initiation and root gravitropism, two processes that are regulated by auxin, are co-regulated in Arabidopsis. A mathematical model was generated that can predict the effects of gravistimulations on lateral root initiation density and suggests that lateral root initiation is controlled by an inhibitory fields mechanism. Moreover, gene transactivation experiments suggest a mechanism involving a single auxin transport route for both responses. Finally, co-regulation may offer a selective advantage by optimizing soil exploration as supported by a simple quantitative analysis

Modeling auxin fluxes and Arabidopsis root ramification at different scales

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An Auxin Transport-Based Model of Root Branching in Arabidopsis thaliana

Root architecture is a crucial part of plant adaptation to soil heterogeneity and is mainly controlled by root branching. The process of root system development can be divided into two successive steps: lateral root initiation and lateral root development/emergence which are controlled by different fluxes of the plant hormone auxin. While shoot architecture appears to be highly regular, following rules such as the phyllotactic spiral, root architecture appears more chaotic. We used stochastic modeling to extract hidden rules regulating root branching in Arabidopsis thaliana. These rules were used to build an integrative mechanistic model of root ramification based on auxin. This model was experimentally tested using plants with modified rhythm of lateral root initiation or mutants perturbed in auxin transport. Our analysis revealed that lateral root initiation and lateral root development/emergence are interacting with each other to create a global balance between the respective ratio of initiation and emergence. A mechanistic model based on auxin fluxes successfully predicted this property and the phenotype alteration of auxin transport mutants or plants with modified rythms of lateral root initiation. This suggests that root branching is controlled by mechanisms of lateral inhibition due to a competition between initiation and development/emergence for auxin

Caractérisation moléculaire et biochimique de la formation du bois de coeur chez le noyer noir (Juglans nigra L.) (accumulation des flavonoïdes et expression des gènes contrôlant leur biosynthèse)

NANCY1-SCD Sciences & Techniques (545782101) / SudocSudocFranceF

Exodermis structure controls fungal invasion in the leafless epiphytic orchid Dendrophylax lindenii (Lindl.) Benth. ex Rolfe

Leafless and shootless epiphytic orchids rely essentially on CAM photosynthesis in roots for carbon gain. However, it is believed that a proportion of carbon is obtained by endomycorrhizal associations. In this study, we show that Dendrophylax lindenii possesses a dimorphic exodermis with smaller, thin-walled passage cells that are depleted in flavonoids. No hyphae succeeded in penetrating into the cortex from a non-passage cell, but 20% of the hyphae in contact with a passage cell managed to penetrate into the cortex. The passage cells represent 40% of the amount of cells in the centre of the side that touches the substrate, but no passage cells are observed in the upper side of the root. This distribution and density of exodermal passage cells define a strategy for controlling the extent and location of fungal invasion in the orchid root. This strategy provides a mechanism for restricting fungal growth to the lower cortex and thus maximising carbon gain from photosynthesis while enabling further trophic exchanges from mycorrhizal associations. (C) 2014 Elsevier GmbH. All rights reserved

Transcription Factor Networks. Pathways to the Knowledge of Root Development

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Etude fonctionnelle des facteurs de transcription AGL12 et CrMYC2 dans les processus de différenciation morphologique et de différenciation métabolique de racines et de cellules végétales cultivées in vitro

Ce travail de thèse a consisté à étudier les rôles joués par les facteurs de transcription AGL12 et CrMYC2 dans les processus de différenciation morphologique et/ou métabolique au niveau d'embryons somatiques de noyer et de suspensions cellulaires de Catharanthus roseus.L'expression du gène Agl12 d'Arabidospis thaliana stimule le développement des racines des embryons somatiques de noyer. Les cellules de C. roseus exprimant Agl12 permet s'organisent en pseudo-tissu et synthétisent de l'ajmalicine. Ces résultats assignent un rôle important à AGL12 lors de la différenciation racinaire.CrMYC2 est capable d'interagir avec la G-box du promoteur du gène Str, et est rapidement et transitoirement induit dans des cellules de C. roseus en réponse à un eliciteur fongique et au méthyl jasmonate. La sur-expression de CrMYC2 dans les suspensions cellulaires n'a pas d'effet sur la régulation de l'expression du gène Str, mais semble avoir un effet inhibiteur sur l'expression des gènes Dxs et Chs.The goal of this work was to characterize the roles of two transcription factors (AGL12 and CrMYC2) during the morphological and metabolic differentiation occuring in walnut somatic embryos and Catharanthus roseus cell suspensions.Overexpression of the Agl12 gene from Arabidopsis thaliana enhances the rooting abilities of walnut somatic embryos. C. roseus transgenic cells expressing this gene are grouped in globular body and biosynthetize ajmalicine. Taken together, these results suggest that AGL12 plays an important role in root differentiation processes.The CrMYC2 transcription factor, which interact with the G-box localized within the Str gene promoter, is rapidly and transiently induced in C. roseus cells in response to a treatment with a fungal elicitor or methyl jasmonate. The expression of CrMYC2 in transgenic cells has no significant impact on the regulation of the Str gene expression but seems to have an inhibitory effect on the expression of the Dxs and Chs.TOURS-BU Sciences Pharmacie (372612104) / SudocSudocFranceF

Auxin fluxes and root branching in Arabidopsis thaliana (toward a virtual root)

Les plantes dépendent de leur système racinaire pour leur ancrage au substrat et leur nutrition hydrique et minérale. La bonne réalisation de ces fonctions dépend fortement de l'architecture du système racinaire dans son ensemble. Dans la plante modèle Arabidopsis thaliana, la ramification racinaire est la résultante d'événements d'initiation et d'émergence de nouvelles racines latérales, et présente un fort lien avec l'hormone végétale auxine. Le déroulement des événements d'initiation et d'émergence est aujourd'hui bien décrit aux échelles moléculaire et cellulaire, mais peu de données sont disponible pour expliciter la régulation globale de ces événements. A l'aide d'une approche mêlant biologie, analyse mathématique et modélisation informatique, cette thèse s'est attachée à élucider les mécanismes de régulation de ces événements chez Arabidopsis, afin de proposer une vue intégrée de la ramification racinairePlants depend on their roots for anchorage and nutrition. The architecture of the root system a key factor for these two functions. In the model plant Arabidopsis thaliana, root branching is the composotion of events of initiation and emergence of new lateral roots. While individuals events of initiation and emergence are well described at the cellular and molecular level in Arabidopsis and are known to be linked with the plant hormone auxin, little is known about the precise mechanisms regulating those events. Using an approach combining biology, mathematical analyses and computer modelling, this thesis project aimed to elucidate those mechanisms in Arabidopis, and to propose an integrated view of root branchingMONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF