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Tom Beeckman - One of the best experts on this subject based on the ideXlab platform.
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RALFL34 regulates formative cell divisions in Arabidopsis Pericycle during lateral root initiation
Journal of experimental botany, 2016Co-Authors: Evan Murphy, Tatsuaki Goh, Lisa Van Den Broeck, Zhefeng Lin, Priya Ramakrishna, Brigitte Van De Cotte, Allison Gaudinier, Daniel Slane, Tom BeeckmanAbstract:In plants, many signalling molecules, such as phytohormones, miRNAs, transcription factors, and small signalling peptides, drive growth and development. However, very few small signalling peptides have been shown to be necessary for lateral root development. Here, we describe the role of the peptide RALFL34 during early events in lateral root development, and demonstrate its specific importance in orchestrating formative cell divisions in the Pericycle. Our results further suggest that this small signalling peptide acts on the transcriptional cascade leading to a new lateral root upstream of GATA23, an important player in lateral root formation. In addition, we describe a role for ETHYLENE RESPONSE FACTORs (ERFs) in regulating RALFL34 expression. Taken together, we put forward RALFL34 as a new, important player in lateral root initiation.
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auxin reflux between the endodermis and Pericycle promotes lateral root initiation
The EMBO Journal, 2012Co-Authors: Peter Marhavý, Tom Beeckman, Bert De Rybel, Marleen Vanstraelen, Ding Zhaojun, Malcolm J Bennett, Eva BenkovaAbstract:Lateral root (LR) formation is initiated when Pericycle cells accumulate auxin, thereby acquiring founder cell (FC) status and triggering asymmetric cell divisions, giving rise to a new primordium. How this auxin maximum in Pericycle cells builds up and remains focused is not understood. We report that the endodermis plays an active role in the regulation of auxin accumulation and is instructive for FCs to progress during the LR initiation (LRI) phase. We describe the functional importance of a PIN3 (PIN-formed) auxin efflux carrier-dependent hormone reflux pathway between overlaying endodermal and Pericycle FCs. Disrupting this reflux pathway causes dramatic defects in the progress of FCs towards the next initiation phase. Our data identify an unexpected regulatory function for the endodermis in LRI as part of the fine-tuning mechanism that appears to act as a check point in LR organogenesis after FCs are specified.
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Lateral Root Initiation or the Birth of a New Meristem
Plant Molecular Biology, 2006Co-Authors: Ive De Smet, Dirk Inze, Tom BeeckmanAbstract:Root branching happens through the formation of new meristems out of a limited number of Pericycle cells inside the parent root. As opposed to shoot branching, the study of lateral root formation has been complicated due to its internal nature, and a lot of questions remain unanswered. However, due to the availability of new molecular tools and more complete genomic data in the model species Arabidopsis , the probability to find new and crucial elements in the lateral root formation pathway has increased. Increasingly more data are supporting the idea that lateral root founder cells become specified in young root parts before differentiation is accomplished. Next, Pericycle founder cells undergo anticlinal asymmetric, divisions followed by an organized cell division pattern resulting in the formation of a new organ. The whole process of cell cycle progression and stimulation of the molecular pathway towards lateral root initiation is triggered by the plant hormone auxin. In this review, we aim to give an overview on the developmental events taking place from the very early specification of founder cells in the Pericycle until the first anticlinal divisions by combining the knowledge originating from classical physiology studies with new insights from genetic-molecular analyses. Based on the current knowledge derived from recent genetic and developmental studies, we propose here a hypothetical model for LRI.
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Transcript profiling of early lateral root initiation.
Proceedings of the National Academy of Sciences of the United States of America, 2004Co-Authors: Kristiina Himanen, Dirk Inze, Marnik Vuylsteke, Steven Vercruysse, Elodie Boucheron, Philippe Alard, Dominique Chriqui, Marc Van Montagu, Tom BeeckmanAbstract:At the onset of lateral root initiation in Arabidopsis thaliana, the phytohormone auxin activates xylem pole Pericycle cells for asymmetric cell division. However, the molecular events leading from auxin to lateral root initiation are poorly understood, in part because the few responsive cells in the process are embedded in the root and are thus difficult to access. A lateral root induction system, in which most xylem pole Pericycle cells were synchronously activated by auxin transport inhibition followed by auxin application, was used for microarray transcript profiling. Of 4,600 genes analyzed, 906 significantly differentially regulated genes were identified that could be grouped into six major clusters. Basically, three major patterns were discerned representing induced, repressed, and transiently expressed genes. Analysis of the coregulated genes, which were specific for each time point, provided new insight into the molecular regulation and signal transduction preceding lateral root initiation in Arabidopsis. The reproducible expression profiles during a time course allowed us to define four stages that precede the cell division in the Pericycle. These early stages were characterized by G1 cell cycle block, auxin perception, and signal transduction, followed by progression over G1/S transition and G2/M transition. All these processes took place within 6 h after transfer from N-1-naphthylphthalamic acid to 1-naphthalene acetic acid. These results indicate that this lateral root induction system represents a unique synchronized system that allows the systematic study of the developmental program upstream of the cell cycle activation during lateral root initiation.
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dissecting arabidopsis lateral root development
Trends in Plant Science, 2003Co-Authors: Ilda Casimiro, Rishikesh P Bhalerao, Pedro J. Casero, Göran Sandberg, Tom Beeckman, Neil S Graham, Hanma Zhang, Malcolm J BennettAbstract:Recent studies in the model plant Arabidopsis provide new insight into the regulation of root architecture, a key determinant of nutrient- and water-use efficiency in crops. Lateral root (LR) primordia originate from a subset of Pericycle founder cells. Sophisticated mass-spectroscopy-based techniques have been used to map the sites of biosynthesis of auxin and its distribution in Arabidopsis seedlings, highlighting the importance of the phytohormone during LR initiation and emergence. Key components of the cell cycle and signal-transduction pathway(s) that promote and attenuate auxin-dependent LR initiation have recently been identified. Additional signals, such as abscisic acid and nitrate, also regulate LR emergence, raising intriguing questions about the cross-talk between their transduction pathways.
Laurent Laplaze - One of the best experts on this subject based on the ideXlab platform.
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Cytokinins Act Directly on Lateral Root Founder Cells to Inhibit Root Initiation
The Plant cell, 2007Co-Authors: Laurent Laplaze, Eva Benkova, Ranjan Swarup, Ilda Casimiro, Steffen Vanneste, Boris Parizot, Lies Maes, Dolf Weijers, Vanessa Calvo, Maria Begoña Herrera-rodriguezAbstract:In Arabidopsis thaliana, lateral roots are formed from root Pericycle cells adjacent to the xylem poles. Lateral root development is regulated antagonistically by the plant hormones auxin and cytokinin. While a great deal is known about how auxin promotes lateral root development, the mechanism of cytokinin repression is still unclear. Elevating cytokinin levels was observed to disrupt lateral root initiation and the regular pattern of divisions that characterizes lateral root development in Arabidopsis. To identify the stage of lateral root development that is sensitive to cytokinins, we targeted the expression of the Agrobacterium tumefaciens cytokinin biosynthesis enzyme isopentenyltransferase to either xylem-pole Pericycle cells or young lateral root primordia using GAL4-GFP enhancer trap lines. Transactivation experiments revealed that xylem-pole Pericycle cells are sensitive to cytokinins, whereas young lateral root primordia are not. This effect is physiologically significant because transactivation of the Arabidopsis cytokinin degrading enzyme cytokinin oxidase 1 in lateral root founder cells results in increased lateral root formation. We observed that cytokinins perturb the expression of PIN genes in lateral root founder cells and prevent the formation of an auxin gradient that is required to pattern lateral root primordia.
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diarch symmetry of the vascular bundle in arabidopsis root encompasses the Pericycle and is reflected in distich lateral root initiation
Plant Physiology, 2007Co-Authors: Boris Parizot, Laurent Laplaze, Ive De Smet, Lilian Ricaud, Elodie Boucherondubuisson, Vincent Bayle, Martin Bonke, Scott R Poethig, Yrjo Helariutta, Jim HaseloffAbstract:The outer tissues of dicotyledonous plant roots (i.e. epidermis, cortex, and endodermis) are clearly organized in distinct concentric layers in contrast to the diarch to polyarch vascular tissues of the central stele. Up to now, the outermost layer of the stele, the Pericycle, has always been regarded, in accordance with the outer tissue layers, as one uniform concentric layer. However, considering its lateral root-forming competence, the Pericycle is composed of two different cell types, with one subset of cells being associated with the xylem, showing strong competence to initiate cell division, whereas another group of cells, associated with the phloem, appears to remain quiescent. Here, we established, using detailed microscopy and specific Arabidopsis thaliana reporter lines, the existence of two distinct Pericycle cell types. Analysis of two enhancer trap reporter lines further suggests that the specification between these two subsets takes place early during development, in relation with the determination of the vascular tissues. A genetic screen resulted in the isolation of mutants perturbed in Pericycle differentiation. Detailed phenotypical analyses of two of these mutants, combined with observations made in known vascular mutants, revealed an intimate correlation between vascular organization, Pericycle fate, and lateral root initiation potency, and illustrated the independence of Pericycle differentiation and lateral root initiation from protoxylem differentiation. Taken together, our data show that the Pericycle is a heterogeneous cell layer with two groups of cells set up in the root meristem by the same genetic pathway controlling the diarch organization of the vasculature.
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the cell cycle promoter cdc2aat from arabidopsis thaliana is induced in the lateral roots of the actinorhizal tree allocasuarina verticillata during the early stages of the symbiotic interaction with frankia
Physiologia Plantarum, 2007Co-Authors: Valerie Hocher, Didier Bogusz, Florence Auguy, Laurent Laplaze, H. Gherbi, Claudine FrancheAbstract:The symbiosis between the actinorhizal tree Allocasuarina verticillata and the actinomycete Frankia leads to the formation of root nodules inside which bacteria fix atmospheric nitrogen. Actinorhizal nodule organogenesis starts with the induction of cell divisions in the root cortex and in the Pericycle cells opposite protoxylem poles near Frankia-infected root hairs. To study the ability of Frankia to induce progression through the cell cycle, we monitored the expression of the β-glucuronidase (gus) gene driven by the promoter from cdc2aAt, an Arabidopsis cyclin-dependent kinase gene that displays competence for cell division, during plant growth and nodule ontogenesis. In non-symbiotic tissues, the gus gene was mainly expressed in primary and secondary meristems of roots and shoots. Auxins and cytokinins were found to induce reporter gene activity in the root system of whole plants, showing that the promoter cdc2aAt displayed the same regulation by hormones in Allocasuarina as that reported in Arabidopsis. In transgenic nodules, gus expression was found to be restricted to the phellogen. During the early stages of the interaction between Frankia and the plant root system, cdc2aAt was strongly induced in the lateral roots surrounded by hyphae of the actinomycete. Histochemical analysis of β-glucuronidase activity revealed that cells from the Pericycle opposite protoxylem poles were very deeply stained. These data indicate that upon Frankia infection, cells from the lateral roots, and notably Pericycle cells that can give rise to a nodule or a root primordium, prepare to re-enter the cell cycle.
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Auxin-dependent regulation of lateral root positioning in the basal meristem of Arabidopsis.
Development (Cambridge England), 2007Co-Authors: Ive De Smet, Ranjan Swarup, Ilda Casimiro, Laurent Laplaze, Bert De Rybel, Dominique Audenaert, Takuya Tetsumura, Nicolas Frei Dit Frey, Mirande NaudtsAbstract:In plants, the developmental mechanisms that regulate the positioning of lateral organs along the primary root are currently unknown. We present evidence on how lateral root initiation is controlled in a spatiotemporal manner in the model plant Arabidopsis thaliana. First, lateral roots are spaced along the main axis in a regular left-right alternating pattern that correlates with gravity-induced waving and depends on AUX1, an auxin influx carrier essential for gravitropic response. Second, we found evidence that the priming of Pericycle cells for lateral root initiation might take place in the basal meristem, correlating with elevated auxin sensitivity in this part of the root. This local auxin responsiveness oscillates with peaks of expression at regular intervals of 15 hours. Each peak in the auxin-reporter maximum correlates with the formation of a consecutive lateral root. Third, auxin signaling in the basal meristem triggers Pericycle cells for lateral root initiation prior to the action of INDOLE-3-ACETIC ACID14 (SOLITARY ROOT).
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gal4 gfp enhancer trap lines for genetic manipulation of lateral root development in arabidopsis thaliana
Journal of Experimental Botany, 2005Co-Authors: Laurent Laplaze, Claudine Franche, Didier Bogusz, Andrew J Baker, Florence Auguy, Boris Parizot, Lilian Ricaud, Alexandre Martiniere, Laurent Nussaume, Jim HaseloffAbstract:Lateral root development occurs throughout the life of the plant and is responsible for the plasticity of the root system. In Arabidopsis thaliana, lateral root founder cells originate from Pericycle cells adjacent to xylem poles. In order to study the mechanisms of lateral root development, a population of Arabidopsis GAL4-GFP enhancer trap lines were screened and two lines were isolated with GAL4 expression in root xylempole Pericycle cells (J0121), i.e. in cells competent to become lateral root founder cells, and in young lateral root primordia (J0192). These two enhancer trap lines are very useful tools with which to study the molecular and cellular bases of lateral root development using targeted gene expression. These lines were used for genetic ablation experiments by targeting the expression of a toxin-encoding gene. Moreover, the molecular bases of the enhancer trap expression pattern were characterized. These results suggest that the lateral-root-specific GAL4 expression pattern in J0192 is due to a strong enhancer in the promoter of the LOB-domain protein gene LBD16.
Ive De Smet - One of the best experts on this subject based on the ideXlab platform.
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Lateral root initiation: one step at a time
The New phytologist, 2011Co-Authors: Ive De SmetAbstract:Plant growth relies heavily on a root system that is hidden belowground, which develops post-embryonically through the formation of lateral roots. The de novo formation of lateral root organs requires tightly coordinated asymmetric cell division of a limited number of Pericycle cells located at the xylem pole. This typically involves the formation of founder cells, followed by a number of cellular changes until the cells divide and give rise to two unequally sized daughter cells. Over the past few years, our knowledge of the regulatory mechanisms behind lateral root initiation has increased dramatically. Here, I will summarize these recent advances, focusing on the prominent role of auxin and cell cycle activity, and elaborating on the three key steps of Pericycle cell priming, founder cell establishment and asymmetric cell division. Taken together, recent findings suggest a tentative model in which successive auxin response modules are crucial for lateral root initiation, and additional factors provide more layers of control.
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receptor like kinase acr4 restricts formative cell divisions in the arabidopsis root
Science, 2008Co-Authors: Bert De Rybel, Ive De Smet, Valya Vassileva, Mitchell P Levesque, Wim GrunewaldAbstract:During the development of multicellular organisms, organogenesis and pattern formation depend on formative divisions to specify and maintain pools of stem cells. In higher plants, these activities are essential to shape the final root architecture because the functioning of root apical meristems and the de novo formation of lateral roots entirely rely on it. We used transcript profiling on sorted Pericycle cells undergoing lateral root initiation to identify the receptor-like kinase ACR4 of Arabidopsis as a key factor both in promoting formative cell divisions in the Pericycle and in constraining the number of these divisions once organogenesis has been started. In the root tip meristem, ACR4 shows a similar action by controlling cell proliferation activity in the columella cell lineage. Thus, ACR4 function reveals a common mechanism of formative cell division control in the main root tip meristem and during lateral root initiation.
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diarch symmetry of the vascular bundle in arabidopsis root encompasses the Pericycle and is reflected in distich lateral root initiation
Plant Physiology, 2007Co-Authors: Boris Parizot, Laurent Laplaze, Ive De Smet, Lilian Ricaud, Elodie Boucherondubuisson, Vincent Bayle, Martin Bonke, Scott R Poethig, Yrjo Helariutta, Jim HaseloffAbstract:The outer tissues of dicotyledonous plant roots (i.e. epidermis, cortex, and endodermis) are clearly organized in distinct concentric layers in contrast to the diarch to polyarch vascular tissues of the central stele. Up to now, the outermost layer of the stele, the Pericycle, has always been regarded, in accordance with the outer tissue layers, as one uniform concentric layer. However, considering its lateral root-forming competence, the Pericycle is composed of two different cell types, with one subset of cells being associated with the xylem, showing strong competence to initiate cell division, whereas another group of cells, associated with the phloem, appears to remain quiescent. Here, we established, using detailed microscopy and specific Arabidopsis thaliana reporter lines, the existence of two distinct Pericycle cell types. Analysis of two enhancer trap reporter lines further suggests that the specification between these two subsets takes place early during development, in relation with the determination of the vascular tissues. A genetic screen resulted in the isolation of mutants perturbed in Pericycle differentiation. Detailed phenotypical analyses of two of these mutants, combined with observations made in known vascular mutants, revealed an intimate correlation between vascular organization, Pericycle fate, and lateral root initiation potency, and illustrated the independence of Pericycle differentiation and lateral root initiation from protoxylem differentiation. Taken together, our data show that the Pericycle is a heterogeneous cell layer with two groups of cells set up in the root meristem by the same genetic pathway controlling the diarch organization of the vasculature.
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Auxin-dependent regulation of lateral root positioning in the basal meristem of Arabidopsis.
Development (Cambridge England), 2007Co-Authors: Ive De Smet, Ranjan Swarup, Ilda Casimiro, Laurent Laplaze, Bert De Rybel, Dominique Audenaert, Takuya Tetsumura, Nicolas Frei Dit Frey, Mirande NaudtsAbstract:In plants, the developmental mechanisms that regulate the positioning of lateral organs along the primary root are currently unknown. We present evidence on how lateral root initiation is controlled in a spatiotemporal manner in the model plant Arabidopsis thaliana. First, lateral roots are spaced along the main axis in a regular left-right alternating pattern that correlates with gravity-induced waving and depends on AUX1, an auxin influx carrier essential for gravitropic response. Second, we found evidence that the priming of Pericycle cells for lateral root initiation might take place in the basal meristem, correlating with elevated auxin sensitivity in this part of the root. This local auxin responsiveness oscillates with peaks of expression at regular intervals of 15 hours. Each peak in the auxin-reporter maximum correlates with the formation of a consecutive lateral root. Third, auxin signaling in the basal meristem triggers Pericycle cells for lateral root initiation prior to the action of INDOLE-3-ACETIC ACID14 (SOLITARY ROOT).
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Lateral Root Initiation or the Birth of a New Meristem
Plant Molecular Biology, 2006Co-Authors: Ive De Smet, Dirk Inze, Tom BeeckmanAbstract:Root branching happens through the formation of new meristems out of a limited number of Pericycle cells inside the parent root. As opposed to shoot branching, the study of lateral root formation has been complicated due to its internal nature, and a lot of questions remain unanswered. However, due to the availability of new molecular tools and more complete genomic data in the model species Arabidopsis , the probability to find new and crucial elements in the lateral root formation pathway has increased. Increasingly more data are supporting the idea that lateral root founder cells become specified in young root parts before differentiation is accomplished. Next, Pericycle founder cells undergo anticlinal asymmetric, divisions followed by an organized cell division pattern resulting in the formation of a new organ. The whole process of cell cycle progression and stimulation of the molecular pathway towards lateral root initiation is triggered by the plant hormone auxin. In this review, we aim to give an overview on the developmental events taking place from the very early specification of founder cells in the Pericycle until the first anticlinal divisions by combining the knowledge originating from classical physiology studies with new insights from genetic-molecular analyses. Based on the current knowledge derived from recent genetic and developmental studies, we propose here a hypothetical model for LRI.
Ilda Casimiro - One of the best experts on this subject based on the ideXlab platform.
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Cytokinins Act Directly on Lateral Root Founder Cells to Inhibit Root Initiation
The Plant cell, 2007Co-Authors: Laurent Laplaze, Eva Benkova, Ranjan Swarup, Ilda Casimiro, Steffen Vanneste, Boris Parizot, Lies Maes, Dolf Weijers, Vanessa Calvo, Maria Begoña Herrera-rodriguezAbstract:In Arabidopsis thaliana, lateral roots are formed from root Pericycle cells adjacent to the xylem poles. Lateral root development is regulated antagonistically by the plant hormones auxin and cytokinin. While a great deal is known about how auxin promotes lateral root development, the mechanism of cytokinin repression is still unclear. Elevating cytokinin levels was observed to disrupt lateral root initiation and the regular pattern of divisions that characterizes lateral root development in Arabidopsis. To identify the stage of lateral root development that is sensitive to cytokinins, we targeted the expression of the Agrobacterium tumefaciens cytokinin biosynthesis enzyme isopentenyltransferase to either xylem-pole Pericycle cells or young lateral root primordia using GAL4-GFP enhancer trap lines. Transactivation experiments revealed that xylem-pole Pericycle cells are sensitive to cytokinins, whereas young lateral root primordia are not. This effect is physiologically significant because transactivation of the Arabidopsis cytokinin degrading enzyme cytokinin oxidase 1 in lateral root founder cells results in increased lateral root formation. We observed that cytokinins perturb the expression of PIN genes in lateral root founder cells and prevent the formation of an auxin gradient that is required to pattern lateral root primordia.
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Auxin-dependent regulation of lateral root positioning in the basal meristem of Arabidopsis.
Development (Cambridge England), 2007Co-Authors: Ive De Smet, Ranjan Swarup, Ilda Casimiro, Laurent Laplaze, Bert De Rybel, Dominique Audenaert, Takuya Tetsumura, Nicolas Frei Dit Frey, Mirande NaudtsAbstract:In plants, the developmental mechanisms that regulate the positioning of lateral organs along the primary root are currently unknown. We present evidence on how lateral root initiation is controlled in a spatiotemporal manner in the model plant Arabidopsis thaliana. First, lateral roots are spaced along the main axis in a regular left-right alternating pattern that correlates with gravity-induced waving and depends on AUX1, an auxin influx carrier essential for gravitropic response. Second, we found evidence that the priming of Pericycle cells for lateral root initiation might take place in the basal meristem, correlating with elevated auxin sensitivity in this part of the root. This local auxin responsiveness oscillates with peaks of expression at regular intervals of 15 hours. Each peak in the auxin-reporter maximum correlates with the formation of a consecutive lateral root. Third, auxin signaling in the basal meristem triggers Pericycle cells for lateral root initiation prior to the action of INDOLE-3-ACETIC ACID14 (SOLITARY ROOT).
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dissecting arabidopsis lateral root development
Trends in Plant Science, 2003Co-Authors: Ilda Casimiro, Rishikesh P Bhalerao, Pedro J. Casero, Göran Sandberg, Tom Beeckman, Neil S Graham, Hanma Zhang, Malcolm J BennettAbstract:Recent studies in the model plant Arabidopsis provide new insight into the regulation of root architecture, a key determinant of nutrient- and water-use efficiency in crops. Lateral root (LR) primordia originate from a subset of Pericycle founder cells. Sophisticated mass-spectroscopy-based techniques have been used to map the sites of biosynthesis of auxin and its distribution in Arabidopsis seedlings, highlighting the importance of the phytohormone during LR initiation and emergence. Key components of the cell cycle and signal-transduction pathway(s) that promote and attenuate auxin-dependent LR initiation have recently been identified. Additional signals, such as abscisic acid and nitrate, also regulate LR emergence, raising intriguing questions about the cross-talk between their transduction pathways.
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Auxin Transport Promotes Arabidopsis Lateral Root Initiation
The Plant Cell, 2001Co-Authors: Ilda Casimiro, Sandra Dhooge, Neil Graham, Alan Marchant, Rishikesh P Bhalerao, Ranjan Swarup, Göran Sandberg, Dirk Inze, Tom Beeckman, Pedro J. CaseroAbstract:Lateral root development in Arabidopsis provides a model for the study of hormonal signals that regulate postembryonic organogenesis in higher plants. Lateral roots originate from pairs of Pericycle cells, in several cell files positioned opposite the xylem pole, that initiate a series of asymmetric, transverse divisions. The auxin transport inhibitor N-1-naphthylphthalamic acid (NPA) arrests lateral root development by blocking the first transverse division(s). We investigated the basis of NPA action by using a cell-specific reporter to demonstrate that xylem pole Pericycle cells retain their identity in the presence of the auxin transport inhibitor. However, NPA causes indoleacetic acid (IAA) to accumulate in the root apex while reducing levels in basal tissues critical for lateral root initiation. This pattern of IAA redistribution is consistent with NPA blocking basipetal IAA movement from the root tip. Characterization of lateral root development in the shoot meristemless1 mutant demonstrates that root basipetal and leaf acropetal auxin transport activities are required during the initiation and emergence phases, respectively, of lateral root development.
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occurrence of cell surface arabinogalactan protein and extensin epitopes in relation to Pericycle and vascular tissue development in the root apex of four species
Planta, 1998Co-Authors: Pedro J. Casero, Ilda Casimiro, Paul J KnoxAbstract:Monoclonal antibodies recognizing two classes of developmentally regulated plant cell surface components – arabinogalactan-proteins (AGPs) and extensins – have been used to immunolabel cells at the root apices of four species with different characteristics of Pericycle and vascular tissue development. Root apices of pea (Pisum sativum L.), radish (Raphanus sativus L.), carrot (Daucus carota L.) and onion (Allium cepa L.) were immunolabelled with the anti-AGP monoclonal antibodies JIM4 and JIM13 and anti-extensin monoclonal antibodies JIM11, JIM12, JIM19 and JIM20. All of these antibodies recognized subsets of Pericycle cells in at least one, but never all, of these species. The restricted patterns of epitope occurrence also reflected vascular cell development. The differences in patterns of antibody recognition in the four species are discussed in relation to the possible roles of these cell surface molecules in cell differentiation and root patterning events.
Eva Benkova - One of the best experts on this subject based on the ideXlab platform.
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auxin reflux between the endodermis and Pericycle promotes lateral root initiation
The EMBO Journal, 2012Co-Authors: Peter Marhavý, Tom Beeckman, Bert De Rybel, Marleen Vanstraelen, Ding Zhaojun, Malcolm J Bennett, Eva BenkovaAbstract:Lateral root (LR) formation is initiated when Pericycle cells accumulate auxin, thereby acquiring founder cell (FC) status and triggering asymmetric cell divisions, giving rise to a new primordium. How this auxin maximum in Pericycle cells builds up and remains focused is not understood. We report that the endodermis plays an active role in the regulation of auxin accumulation and is instructive for FCs to progress during the LR initiation (LRI) phase. We describe the functional importance of a PIN3 (PIN-formed) auxin efflux carrier-dependent hormone reflux pathway between overlaying endodermal and Pericycle FCs. Disrupting this reflux pathway causes dramatic defects in the progress of FCs towards the next initiation phase. Our data identify an unexpected regulatory function for the endodermis in LRI as part of the fine-tuning mechanism that appears to act as a check point in LR organogenesis after FCs are specified.
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auxin acts as a local morphogenetic trigger to specify lateral root founder cells
Proceedings of the National Academy of Sciences of the United States of America, 2008Co-Authors: Joseph G Dubrovsky, Maria G Ivanchenko, Michael Sauer, Selene Napsucialymendivil, Jiři Friml, Svetlana Shishkova, John L Celenza, Eva BenkovaAbstract:Plants exhibit an exceptional adaptability to different environmental conditions. To a large extent, this adaptability depends on their ability to initiate and form new organs throughout their entire postembryonic life. Plant shoot and root systems unceasingly branch and form axillary shoots or lateral roots, respectively. The first event in the formation of a new organ is specification of founder cells. Several plant hormones, prominent among them auxin, have been implicated in the acquisition of founder cell identity by differentiated cells, but the mechanisms underlying this process are largely elusive. Here, we show that auxin and its local accumulation in root Pericycle cells is a necessary and sufficient signal to respecify these cells into lateral root founder cells. Analysis of the alf4-1 mutant suggests that specification of founder cells and the subsequent activation of cell division leading to primordium formation represent two genetically separable events. Time-lapse experiments show that the activation of an auxin response is the earliest detectable event in founder cell specification. Accordingly, local activation of auxin response correlates absolutely with the acquisition of founder cell identity and precedes the actual formation of a lateral root primordium through patterned cell division. Local production and subsequent accumulation of auxin in single Pericycle cells induced by Cre-Lox-based activation of auxin synthesis converts them into founder cells. Thus, auxin is the local instructive signal that is sufficient for acquisition of founder cell identity and can be considered a morphogenetic trigger in postembryonic plant organogenesis.
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Cytokinins Act Directly on Lateral Root Founder Cells to Inhibit Root Initiation
The Plant cell, 2007Co-Authors: Laurent Laplaze, Eva Benkova, Ranjan Swarup, Ilda Casimiro, Steffen Vanneste, Boris Parizot, Lies Maes, Dolf Weijers, Vanessa Calvo, Maria Begoña Herrera-rodriguezAbstract:In Arabidopsis thaliana, lateral roots are formed from root Pericycle cells adjacent to the xylem poles. Lateral root development is regulated antagonistically by the plant hormones auxin and cytokinin. While a great deal is known about how auxin promotes lateral root development, the mechanism of cytokinin repression is still unclear. Elevating cytokinin levels was observed to disrupt lateral root initiation and the regular pattern of divisions that characterizes lateral root development in Arabidopsis. To identify the stage of lateral root development that is sensitive to cytokinins, we targeted the expression of the Agrobacterium tumefaciens cytokinin biosynthesis enzyme isopentenyltransferase to either xylem-pole Pericycle cells or young lateral root primordia using GAL4-GFP enhancer trap lines. Transactivation experiments revealed that xylem-pole Pericycle cells are sensitive to cytokinins, whereas young lateral root primordia are not. This effect is physiologically significant because transactivation of the Arabidopsis cytokinin degrading enzyme cytokinin oxidase 1 in lateral root founder cells results in increased lateral root formation. We observed that cytokinins perturb the expression of PIN genes in lateral root founder cells and prevent the formation of an auxin gradient that is required to pattern lateral root primordia.
