The short-rooted phenotype of the brevis radix mutant partly reflects root abscisic acid hypersensitivity.

To gain further insight into abscisic acid (ABA) signaling and its role in growth regulation, we have screened for Arabidopsis (Arabidopsis thaliana) mutants hypersensitive to ABA-mediated root growth inhibition. As a result, we have identified a loss-of-function allele of BREVIS RADIX (BRX) in the Columbia background, named brx-2, which shows enhanced response to ABA-mediated inhibition of root growth. BRX encodes a key regulator of cell proliferation and elongation in the root, which has been implicated in the brassinosteroid (BR) pathway as well as in the regulation of auxin-responsive gene expression. Mutants affected in BR signaling that are not impaired in root growth, such as bes1-D, bzr1-D, and bsu1-D, also showed enhanced sensitivity to ABA-mediated inhibition of root growth. Triple loss-of-function mutants affected in PP2Cs, which act as negative regulators of ABA signaling, showed impaired root growth in the absence of exogenous ABA, indicating that disturbed regulation of ABA sensitivity impairs root growth. In agreement with this result, diminishing ABA sensitivity of brx-2 by crossing it with a 35S:HAB1 ABA-insensitive line allowed significantly higher recovery of root growth after brassinolide treatment. Finally, transcriptomic analysis revealed that ABA treatment negatively affects auxin signaling in wild-type and brx-2 roots and that ABA response is globally altered in brx-2. Taken together, our results reveal an interaction between BRs, auxin, and ABA in the control of root growth and indicate that altered sensitivity to ABA is partly responsible for the brx short-root phenotype.

Cervical nerve root synovial sarcoma in a child with chromosomal (X;18) translocation. Case report and review of the literature.

We report on an 11-year-old female with a history of cervicobrachialgia and progressive weakness of the right arm. Cervical spine MRI showed an enhancing heterogeneous intradural mass occupying the right C6-C7 foramen. She underwent a right C6-C7 foraminotomy with a complete macroscopic removal of the lesion. Pathological examination revealed a synovial sarcoma. Treatment was completed by chemotherapy and proton radiotherapy, and the girl remained free of symptoms for 3 years. After appearance of new symptoms, a local recurrence was confirmed, and despite aggressive treatment with salvage chemotherapy and radiotherapy, the disease progressed beyond medical control, and the child died, 6 years after diagnosis. Early recognition of this rare entity compared to its more benign differential diagnosis is crucial, as an aggressive management is needed.

Rab3D is critical for secretory granule maturation in PC12 cells.

Neuropeptide- and hormone-containing secretory granules (SGs) are synthesized at the trans-Golgi network (TGN) as immature secretory granules (ISGs) and complete their maturation in the F-actin-rich cell cortex. This maturation process is characterized by acidification-dependent processing of cargo proteins, condensation of the SG matrix and removal of membrane and proteins not destined to mature secretory granules (MSGs). Here we addressed a potential role of Rab3 isoforms in these maturation steps by expressing their nucleotide-binding deficient mutants in PC12 cells. Our data show that the presence of Rab3D(N135I) decreases the restriction of maturing SGs to the F-actin-rich cell cortex, blocks the removal of the endoprotease furin from SGs and impedes the processing of the luminal SG protein secretogranin II. This strongly suggests that Rab3D is implicated in the subcellular localization and maturation of ISGs.

Increased axonal regrowth of lesioned rat sciatic nerve by veratrylguanidine methane sulfonate.

Neurotrophic factors appear as essential factors for normal development and repair of the nervous tissue. Veratrylguanidine methane sulfonate, has been shown to induce important neurite outgrowth of cultured dorsal root ganglia isolated from newborn rats. Its action was similar to that of NGF and was found to be additive to that of NGF. In order to see if this compound was able to stimulate axonal growth in adult animals, we examined the effect of this substance on the regeneration of the lesioned sciatic nerve. Using histochemical, immunohistochemical and ultrastructural studies, it is shown that a single intraperitoneal injection of veratrylguanidine methane sulfonate significantly increases the axonal growth during repair of the adult rat sciatic nerve. The efficiency of this substance is explained by its good targeting and long life time in the sciatic nerve.

Evolution and sedimentology of a channel fill in the sandy braided South Saskatchewan River and its comparison to the deposits of an adjacent compound bar

The depositional stratigraphy of within-channel deposits in sandy braided rivers is dominated by a variety of barforms (both singular `unit' bars and complex `compound' bars), as well as the infill of individual channels (herein termed `channel fills'). The deposits of bars and channel fills define the key components of facies models for braided rivers and their within-channel heterogeneity, knowledge of which is important for reservoir characterization. However, few studies have sought to address the question of whether the deposits of bars and channel fills can be readily differentiated from each other. This paper presents the first quantitative study to achieve this aim, using aerial images of an evolving modern sandy braided river and geophysical imaging of its subsurface deposits. Aerial photographs taken between 2000 and 2004 document the abandonment and fill of a 1 3 km long, 80 m wide anabranch channel in the sandy braided South Saskatchewan River, Canada. Upstream river regulation traps the majority of very fine sediment and there is little clay (<1%) in the bed sediments. Channel abandonment was initiated by a series of unit bars that stalled and progressively blocked the anabranch entrance, together with dune deposition and stacking at the anabranch entrance and exit. Complete channel abandonment and subsequent fill of up to 3 m of sediment took approximately two years. Thirteen kilometres of ground-penetrating radar surveys, coupled with 18 cores, were obtained over the channel fill and an adjacent 750 m long, 400 m wide, compound bar, enabling a quantitative analysis of the channel and bar deposits. Results show that, in terms of grain-size trends, facies proportions and scale of deposits, there are only subtle differences between the channel fill and bar deposits which, therefore, renders them indistinguishable. Thus, it may be inappropriate to assign different geometric and sedimentological attributes to channel fill and bar facies in object-based models of sandy braided river alluvial architecture.

Primary root protophloem differentiation requires balanced phosphatidylinositol-4,5-biphosphate levels and systemically affects root branching.

Protophloem is a specialized vascular tissue in growing plant organs, such as root meristems. In Arabidopsis mutants with impaired primary root protophloem differentiation, brevis radix (brx) and octopus (ops), meristematic activity and consequently overall root growth are strongly reduced. Second site mutation in the protophloem-specific presumed phosphoinositide 5-phosphatase COTYLEDON VASCULAR PATTERN 2 (CVP2), but not in its homolog CVP2-LIKE 1 (CVL1), partially rescues brx defects. Consistent with this finding, CVP2 hyperactivity in a wild-type background recreates a brx phenotype. Paradoxically, however, while cvp2 or cvl1 single mutants display no apparent root defects, the root phenotype of cvp2 cvl1 double mutants is similar to brx or ops, although, as expected, cvp2 cvl1 seedlings contain more phosphatidylinositol-4,5-biphosphate. Thus, tightly balanced phosphatidylinositol-4,5-biphosphate levels appear essential for proper protophloem differentiation. Genetically, OPS acts downstream of phosphatidylinositol-4,5-biphosphate levels, as cvp2 mutation cannot rescue ops defects, whereas increased OPS dose rescues cvp2 cvl1 defects. Finally, all three mutants display higher density and accelerated emergence of lateral roots, which correlates with increased auxin response in the root differentiation zone. This phenotype is also created by application of peptides that suppress protophloem differentiation, CLAVATA3/EMBRYO SURROUNDING REGION 26 (CLE26) and CLE45. Thus, local changes in the primary root protophloem systemically shape overall root system architecture.

Transcriptome diversity among rice root types during asymbiosis and interaction with arbuscular mycorrhizal fungi.

Root systems consist of different root types (RTs) with distinct developmental and functional characteristics. RTs may be individually reprogrammed in response to their microenvironment to maximize adaptive plasticity. Molecular understanding of such specific remodeling-although crucial for crop improvement-is limited. Here, RT-specific transcriptomes of adult rice crown, large and fine lateral roots were assessed, revealing molecular evidence for functional diversity among individual RTs. Of the three rice RTs, crown roots displayed a significant enrichment of transcripts associated with phytohormones and secondary cell wall (SCW) metabolism, whereas lateral RTs showed a greater accumulation of transcripts related to mineral transport. In nature, arbuscular mycorrhizal (AM) symbiosis represents the default state of most root systems and is known to modify root system architecture. Rice RTs become heterogeneously colonized by AM fungi, with large laterals preferentially entering into the association. However, RT-specific transcriptional responses to AM symbiosis were quantitatively most pronounced for crown roots despite their modest physical engagement in the interaction. Furthermore, colonized crown roots adopted an expression profile more related to mycorrhizal large lateral than to noncolonized crown roots, suggesting a fundamental reprogramming of crown root character. Among these changes, a significant reduction in SCW transcripts was observed that was correlated with an alteration of SCW composition as determined by mass spectrometry. The combined change in SCW, hormone- and transport-related transcript profiles across the RTs indicates a previously overlooked switch of functional relationships among RTs during AM symbiosis, with a potential impact on root system architecture and functioning.

Multilayered organization of jasmonate signalling in the regulation of root growth.

Physical damage can strongly affect plant growth, reducing the biomass of developing organs situated at a distance from wounds. These effects, previously studied in leaves, require the activation of jasmonate (JA) signalling. Using a novel assay involving repetitive cotyledon wounding in Arabidopsis seedlings, we uncovered a function of JA in suppressing cell division and elongation in roots. Regulatory JA signalling components were then manipulated to delineate their relative impacts on root growth. The new transcription factor mutant myc2-322B was isolated. In vitro transcription assays and whole-plant approaches revealed that myc2-322B is a dosage-dependent gain-of-function mutant that can amplify JA growth responses. Moreover, myc2-322B displayed extreme hypersensitivity to JA that totally suppressed root elongation. The mutation weakly reduced root growth in undamaged plants but, when the upstream negative regulator NINJA was genetically removed, myc2-322B powerfully repressed root growth through its effects on cell division and cell elongation. Furthermore, in a JA-deficient mutant background, ninja1 myc2-322B still repressed root elongation, indicating that it is possible to generate JA-responses in the absence of JA. We show that NINJA forms a broadly expressed regulatory layer that is required to inhibit JA signalling in the apex of roots grown under basal conditions. By contrast, MYC2, MYC3 and MYC4 displayed cell layer-specific localisations and MYC3 and MYC4 were expressed in mutually exclusive regions. In nature, growing roots are likely subjected to constant mechanical stress during soil penetration that could lead to JA production and subsequent detrimental effects on growth. Our data reveal how distinct negative regulatory layers, including both NINJA-dependent and -independent mechanisms, restrain JA responses to allow normal root growth. Mechanistic insights from this work underline the importance of mapping JA signalling components to specific cell types in order to understand and potentially engineer the growth reduction that follows physical damage.

Subcellular Redistribution of Root Aquaporins Induced by Hydrogen Peroxide.

Aquaporins are water channel proteins that mediate the fine-tuning of cell membrane water permeability during development or in response to environmental stresses. The present work focuses on the oxidative stress-induced redistribution of plasma membrane intrinsic protein (PIP) aquaporins from the plasma membrane (PM) to intracellular membranes. This process was investigated in the Arabidopsis root. Sucrose density gradient centrifugation showed that exposure of roots to 0.5 mM H2O2 induces significant depletion in PM fractions of several abundant PIP homologs after 15 min. Analyses by single-particle tracking and fluorescence correlative spectroscopy showed that, in the PM of epidermal cells, H2O2 treatment induces an increase in lateral motion and a reduction in the density of a fluorescently tagged form of the prototypal AtPIP2;1 isoform, respectively. Co-expression analyses of AtPIP2;1 with endomembrane markers revealed that H2O2 triggers AtPIP2;1 accumulation in the late endosomal compartments. Life-time analyses established that the high stability of PIPs was maintained under oxidative stress conditions, suggesting that H2O2 triggers a mechanism for intracellular sequestration of PM aquaporins without further degradation. In addition to information on cellular regulation of aquaporins, this study provides novel and complementary insights into the dynamic remodeling of plant internal membranes during oxidative stress responses.

An overview of the metabolic differences between Bradyrhizobium japonicum 110 bacteria and differentiated bacteroids from soybean (Glycine max) root nodules: An in vitro 13C-and 31P-nuclear magnetic resonance spectroscopy study

Bradyrhizobium japonicum is a symbiotic nitrogen-fixing soil bacteria that induce root nodules formation in legume soybean (Glycine max.). Using 13C- and 31P-nuclear magnetic resonance (NMR) spectroscopy, we have analysed the metabolite profiles of cultivated B.japonicum cells and bacteroids isolated from soybean nodules. Our results revealed some quantitative and qualitative differences between the metabolite profiles of bacteroids and their vegetative state. This includes in bacteroids a huge accumulation of soluble carbohydrates such as trehalose, glutamate, myo-inositol and homospermidine as well as Pi, nucleotide pools and intermediates of the primary carbon metabolism. Using this novel approach, these data show that most of the compounds detected in bacteroids reflect the metabolic adaptation of rhizobia to the surrounding microenvironment with its host plant cells.

Changes of Root Length and Root-to-Crown Ratio after Apical Surgery: An Analysis by Using Cone-beam Computed Tomography.

INTRODUCTION: Apical surgery is an important treatment option for teeth with post-treatment periodontitis. Although apical surgery involves root-end resection, no morphometric data are yet available about root-end resection and its impact on the root-to-crown ratio (RCR). The present study assessed the length of apicectomy and calculated the loss of root length and changes of RCR after apical surgery. METHODS: In a prospective clinical study, cone-beam computed tomography scans were taken preoperatively and postoperatively. From these images, the crown and root lengths of 61 roots (54 teeth in 47 patients) were measured before and after apical surgery. Data were collected relative to the cementoenamel junction (CEJ) as well as to the crestal bone level (CBL). One observer took all measurements twice (to calculate the intraobserver variability), and the means were used for further analysis. The following parameters were assessed for all treated teeth as well as for specific tooth groups: length of root-end resection and percentage change of root length, preoperative and postoperative RCRs, and percentage change of RCR after apical surgery. RESULTS: The mean length of root-end resection was 3.58 ± 1.43 mm (relative to the CBL). This amounted to a loss of 33.2% of clinical and 26% of anatomic root length. There was an overall significant difference between the tooth groups (P < .05). There was also a statistically significant difference comparing mandibular and maxillary teeth (P < .05), but not for incisors/canines versus premolars/molars (P = .125). The mean preoperative and postoperative RCRs (relative to CEJ) were 1.83 and 1.35, respectively (P < .001). With regard to the CBL reference, the mean preoperative and postoperative RCRs were 1.08 and 0.71 (CBL), respectively (P < .001). The calculated changes of RCR after apical surgery were 24.8% relative to CEJ and 33.3% relative to CBL (P < .001). Across the different tooth groups, the mean RCR was not significantly different (P = .244 for CEJ and 0.114 for CBL). CONCLUSIONS: This CBCT-based study demonstrated that the RCR is significantly changed after root-end resection in apical surgery irrespective of the clinical (CBL) or anatomic (CEJ) reference levels. The lowest, and thus clinically most critical, postoperative RCR was observed in maxillary incisors. Future clinical studies need to show the impact of resection length and RCR changes on the outcome of apical surgery.

Role of an LRR receptor-like kinase in the establishment of a functional root endodermal barrier

The endodermis is a highly conserved cell layer present in the root of all vascular plants, except Lycophytes. This tissue layer establishes a protective diffusion barrier surrounding the vasculature and is expected to prevent passive, uncontrolled flow of nutrients through the root. This barrier property is achieved by the production of Casparian strips (CS), a localized cell wall impregnation of lignin in the anticlinal walls of each endodermal cell, forming a belt-like structure sealing the extracellular space. The CS act as a selective barrier between the external cell layers and the vascular cylinder and are thought to be important in many aspects of root function. For instance, selective nutrient uptake and sequestration from the soil, resistance to different abiotic and biotic stresses are expected to involve functional CS. Although discovered 150 years ago, nothing was known about the genes involved in CS establishment until recently. The use of the model plant Arabidopsis thaliana together with both reverse and forward genetic approaches led to the discovery of an increasing number of genes involved in different steps of CS formation during the last few years. One of these genes encodes SCHENGEN3 (SGN3), a leucine-rich repeat receptor-like kinase (LRR-RLK). SGN3 was discovered first by reverse genetic due to its endodermis-enriched expression, and the corresponding mutant displays strong endodermal permeability of the apoplastic tracer Propidium Iodide (PI) indicative of defective CS. One aim of this thesis is to study the role of SGN3 at the molecular level in order to understand its involvement in establishing an impermeable CS. The endodermal permeability of sgn3 is shown to be the result of incorrect localization of key proteins involved in CS establishment (the "Casparian strip domain proteins", CASPs), leading to non-functional CS interrupted by discontinuities. CASPs localize in the plasma membrane domain subjacent to the CS, named the Casparian Strip membrane Domain (CSD). The CSD discontinuities in sgn3 together with SGN3 localization in close proximity to the CASPs lead to the assumption that SGN3 is involved in the formation of a continuous CSD. In addition, SGN3 might have a second role, acting as a kinase reporting CSD integrity leading to lignin and suberin production in CSD/CS defective plants. Up to now, sgn3 is the strongest and most specific CS mutant available, displaying tracer penetration along the whole length of the seedling root. For this reason, this mutant is well suited in order to characterize the physiological behaviour of CS affected plants. Due to the lack of such mutants in the past, it was not possible to test the presumed functions of CS by using plants lacking this structure. We decided to use sgn3 for this purpose. Surprisingly, sgn3 overall growth is only slightly affected. Nevertheless, processes expected to rely on functional CS, such as water transport through the root, nutrient homeostasis, salt tolerance and resistance to an excess of some nutrients are altered in this mutant. On the other hand, homeostasis for most elements and drought tolerance are not affected in sgn3. It is surprising to observe that homeostatic defects are specific, with a decrease in potassium and an increase in magnesium levels. It indicates a backup system, set up by the plant in order to counteract free diffusion of nutrients into the stele. For instance, potassium shortage in sgn3 upregulates the transcription of potassium influx transport proteins and genes known to be induced by potassium starvation. Moreover, sgn3 mutant is hypersensitive to low potassium conditions. Hopefully, these results about SGN3 will help our understanding of CS establishment at the molecular level. In addition, physiological experiments using sgn3 should give us a framework for future experiments and help us to understand the different roles of CS and their involvement during nutrient radial transport through the root. -- L'endoderme est un tissu présent dans les racines de toutes les plantes vasculaires à l'exception des Lycophytes. Ce tissu établit une barrière protectrice entourant les tissus vasculaires dans le but d'éviter la diffusion passive et incontrôlée des nutriments au travers de la racine. Cette propriété de barrière provient de la production des cadres de Caspary, une imprégnation localisée de lignine des parties anticlinales de la paroi de chaque cellule d'endoderme. Cela donne naissance à un anneau/cadre qui rend étanche l'espace extracellulaire. Les cadres de Caspary agissent comme une barrière sélective entre les couches externes de la racine et le cylindre central et sont supposés être importants dans beaucoup d'aspects du fonctionnement de la racine. Par exemple, l'absorption sélective de nutriments et leur séquestration à partir du sol ainsi que la résistance contre différents stress abiotiques et biotiques sont supposés impliquer des cadres de Caspary fonctionnels. Bien que découverts il y a 150 ans, rien n'était connu concernant les gènes impliqués dans Ja formation des cadres de Caspary jusqu'à récemment. Durant ces dernière années, l'utilisation de la plante modèle Arabidopsis thaliana ainsi que des approches de génétique inverse et classique ont permis la découverte d'un nombre croissant de gènes impliqués à différentes étapes de la formation de cette structure. Un des ces gènes code pour SCHENGEN3 (SGN3), un récepteur kinase "leucine-rich repeat receptor-like kinase" (LRR-RLK). SGN3 a été découvert en premier par génétique inverse grâce à son expression enrichie dans l'endoderme. Les cadres de Caspary ne sont pas fonctionnels dans le mutant correspondant, ce qui est visible à cause de la perméabilité de l'endoderme au traceur apoplastique Propidium Iodide (PI). Un des objectifs de cette thèse est d'étudier la fonction de SGN3 au niveau moléculaire dans le but de comprendre son rôle dans la formation des cadres de Caspary. J'ai pu démontrer que la perméabilité de l'endoderme du mutant sgn3 est le résultat de la localisation incorrecte de protéines impliquées dans la formation des cadres de Caspary, les "Casparian strip domain proteins" (CASPs). Cela induit des cadres de Caspary non fonctionnels, contenant de nombreuses interruptions. Les CASPs sont localisés à la membrane plasmique dans un domaine sous-jacent les cadres de Caspary appelé Casparian Strip membrane Domain (CSD). Les interruptions du CSD dans le mutant sgn3, ainsi que la localisation de SGN3 à proximité des CASPs nous font penser à un rôle de SGN3 dans l'élaboration d'un CSD ininterrompu. De plus, SGN3 pourrait avoir un second rôle, agissant en tant que kinase reportant l'intégrité du CSD et induisant la production de lignine et de subérine dans des plantes contenant des cadres de Caspary non fonctionnels. Jusqu'à ce jour, sgn3 est le mutant en notre possession le plus fort et le plus spécifique, ayant un endoderme perméable tout le long de la racine. Pour cette raison, ce mutant est adéquat dans le but de caractériser la physiologie de plantes ayant des cadres de Caspary affectés. De manière surprenante, la croissance de sgn3 est seulement peu affectée. Néanmoins, des processus censés nécessiter des cadres de Caspary fonctionnels, comme le transport de l'eau au travers de la racine, l'homéostasie des nutriments, la tolérance au sel et la résistance à l'excès de certains nutriments sont altérés dans ce mutant. Malgré tout, l'homéostasie de la plupart des nutriments ainsi que la résistance au stress hydrique ne sont pas affectés dans sgn3. De manière surprenante, les altérations de l'ionome de sgn3 sont spécifiques, avec une diminution de potassium et un excès de magnésium. Cela implique un système de compensation établi par la plante dans le but d'éviter la diffusion passive des nutriments en direction du cylindre central. Par exemple, le manque de potassium dans sgn3 augmente la transcription de transporteurs permettant l'absorption de cet élément. De plus, des gènes connus pour être induits en cas de carence en potassium sont surexprimés dans sgn3 et la croissance de ce mutant est sévèrement affectée dans un substrat pauvre en potassium. Ces résultats concernant SGN3 vont, espérons-le, aider à la compréhension du processus de formation des cadres de Caspary au niveau moléculaire. De plus, les expériences de physiologie utilisant sgn3 présentées dans cette thèse devraient nous donner une base pour des expériences futures et nous permettre de comprendre mieux le rôle des cadres de Caspary, et plus particulièrement leur implication dans le transport radial des nutriments au travers de la racine. -- Les plantes terrestres sont des organismes puisant l'eau et les nutriments dont elles ont besoin pour leur croissance dans le sol grâce à leurs racines. De par leur immobilité, elles doivent s'adapter à des sols contenant des quantités variables de nutriments et il leur est crucial de sélectionner ce dont elles ont besoin afin de ne pas s'intoxiquer. Cette sélection est faite grâce à un filtre formé d'un tissu racinaire interne appelé endoderme. L'endoderme fabrique une barrière imperméable entourant chaque cellule appelée "cadre de Caspary". Ces cadres de Caspary empêchent le libre passage des nutriments, permettant un contrôle précis de leur passage. De plus, ils sont censés permettre de résister contre différents stress environnementaux comme la sécheresse, la salinité du sol ou l'excès de nutriments. Bien que découverts il y a 150 ans, rien n'était connu concernant les gènes impliqués dans la formation des cadres de Caspary jusqu'à récemment. Durant ces dernière années, l'utilisation de la plante modèle Arabidopsis thaliana a permis la découverte d'un nombre croissant de gènes impliqués à différentes étapes de la formation de cette structure. Un de ces gènes code pour SCHENGEN3 (SGN3), un récepteur kinase "leucine-rich repeat receptor-like kinase" (LRR- RLK). Nous montrons dans cette étude que le gène SGN3 est impliqué dans la formation des cadres de Caspary, et que le mutant correspondant sgn3 a des cadres de Caspary interrompus. Ces interruptions rendent l'endoderme perméable, l'empêchant de bloquer le passage des molécules depuis le sol vers le centre de la racine. En utilisant ce mutant, nous avons pu caractériser la physiologie de plantes ayant des cadres de Caspary affectés. Cela a permis de découvrir que le transport de l'eau au travers de la racine était affecté dans le mutant sgn3. De plus, l'accumulation de certains éléments dans les feuilles de ce mutant est altérée. Nous avons également pu montrer une sensibilité de ce mutant à un excès de sel ou de certains nutriments comme le fer et le manganèse.