The Experts below are selected from a list of 264 Experts worldwide ranked by ideXlab platform
Teva Vernoux - One of the best experts on this subject based on the ideXlab platform.
-
patterning at the shoot apical meristem and Phyllotaxis
Current Topics in Developmental Biology, 2019Co-Authors: Teva VernouxAbstract:Abstract The shoot apical meristem (SAM) generates all above-ground organs throughout the life of plants. The development and maintenance of the SAM are crucial for building the plant architecture. The spatiotemporal patterning of lateral organs (leaves and flowers), called Phyllotaxis, is one of the best-characterized self-organizing systems and has long been proposed to be driven by inhibitory fields generated by the existing organs and blocking new initiations in their vicinity. Recent years have seen impressive progress in our understanding of the molecular mechanisms controlling SAM function, and on how these mechanisms act in phyllotactic patterning. In this chapter, we first review the regulation of SAM stem cell activity and discuss how feedback signals coming from the differentiated organs affect stem cell homeostasis. Then we highlight experimental and theoretical works that have revealed the chemical and biophysical factors acting in the regulation of Phyllotaxis. Finally, we summarize the important roles of SAM geometry in Phyllotaxis.
-
a stochastic multicellular model identifies biological watermarks from disorders in self organized patterns of Phyllotaxis
eLife, 2016Co-Authors: Yassin Refahi, Geraldine Brunoud, Etienne Farcot, Alain Jeanmarie, Minna Pulkkinen, Teva Vernoux, Christophe GodinAbstract:Exploration of developmental mechanisms classically relies on analysis of pattern regularities. Whether disorders induced by biological noise may carry information on building principles of developmental systems is an important debated question. Here, we addressed theoretically this question using Phyllotaxis, the geometric arrangement of plant aerial organs, as a model system. Phyllotaxis arises from reiterative organogenesis driven by lateral inhibitions at the shoot apex. Motivated by recurrent observations of disorders in Phyllotaxis patterns, we revisited in depth the classical deterministic view of Phyllotaxis. We developed a stochastic model of primordia initiation at the shoot apex, integrating locality and stochasticity in the patterning system. This stochastic model recapitulates phyllotactic patterns, both regular and irregular, and makes quantitative predictions on the nature of disorders arising from noise. We further show that disorders in Phyllotaxis instruct us on the parameters governing Phyllotaxis dynamics, thus that disorders can reveal biological watermarks of developmental systems.
-
Phyllotaxis from patterns of organogenesis at the meristem to shoot architecture
Wiley Interdisciplinary Reviews-Developmental Biology, 2016Co-Authors: Carlos S Galvanampudia, Christophe Godin, Anais M Chaumeret, Teva VernouxAbstract:The primary architecture of the aerial part of plants is controlled by the shoot apical meristem, a specialized tissue containing a stem cell niche. The iterative generation of new aerial organs, (leaves, lateral inflorescences and flowers) at the meristem follows regular patterns, called Phyllotaxis. Phyllotaxis has long been proposed to self-‐organize from the combined action of growth and of inhibitory fields blocking organogenesis in the vicinity of existing organs in the meristem. In this review we will highlight how a combination of mathematical/computational modeling and experimental biology has demonstrated that the spatio-‐temporal distribution of the plant hormone auxin controls both organogenesis and the establishment of inhibitory fields. We will discuss recent advances showing that auxin likely acts through a combination of biochemical and mechanical regulatory mechanisms that control not only the pattern of organogenesis in the meristem but also post-‐meristematic growth, to shape the shoot.
-
meristem size contributes to the robustness of Phyllotaxis in arabidopsis
Journal of Experimental Botany, 2015Co-Authors: Benoit Landrein, Yassin Refahi, Teva Vernoux, Fabrice Besnard, Vincent Mirabet, Arezki Boudaoud, Nathan Hervieux, Olivier HamantAbstract:Using the plant model Arabidopsis, the relationship between day length, the size of the shoot apical meristem, and the robustness of phyllotactic patterns were analysed. First, it was found that reducing day length leads to an increased meristem size and an increased number of alterations in the final positions of organs along the stem. Most of the phyllotactic defects could be related to an altered tempo of organ emergence, while not affecting the spatial positions of organ initiations at the meristem. A correlation was also found between meristem size and the robustness of Phyllotaxis in two accessions (Col-0 and WS-4) and a mutant (clasp-1), independent of growth conditions. A reduced meristem size in clasp-1 was even associated with an increased robustness of the phyllotactic pattern, beyond what is observed in the wild type. Interestingly it was also possible to modulate the robustness of Phyllotaxis in these different genotypes by changing day length. To conclude, it is shown first that robustness of the phyllotactic pattern is not maximal in the wild type, suggesting that, beyond its apparent stereotypical order, the robustness of Phyllotaxis is regulated. Secondly, a role for day length in the robustness of the Phyllotaxis was also identified, thus providing a new example of a link between patterning and environment in plants. Thirdly, the experimental results validate previous model predictions suggesting a contribution of meristem size in the robustness of Phyllotaxis via the coupling between the temporal sequence and spatial pattern of organ initiations.
-
pattern identification and characterization reveal permutations of organs as a key genetically controlled property of post meristematic Phyllotaxis
Journal of Theoretical Biology, 2013Co-Authors: Yann Guedon, Yassin Refahi, Etienne Farcot, Christophe Godin, Fabrice Besnard, Teva VernouxAbstract:In vascular plants, the arrangement of organs around the stem generates geometric patterns called Phyllotaxis. In the model plant, Arabidopsis thaliana, as in the majority of species, single organs are initiated successively at a divergence angle from the previous organ close to the canonical angle of 137.5°, producing a Fibonacci spiral. Given that little is known about the robustness of these geometric arrangements, we undertook to characterize Phyllotaxis by measuring divergence angles between organs along the stems of wild-type and specific mutant plants with obvious defects in Phyllotaxis. Sequences of measured divergence angles exhibit segments of non-canonical angles in both genotypes, albeit to a far greater extent in the mutant. We thus designed a pipeline of methods for analyzing these perturbations. The latent structure models used in this pipeline combine a non-observable model representing perturbation patterns (either a variable-order Markov chain or a combinatorial model) with von Mises distributions representing divergence angle uncertainty. We show that the segments of non-canonical angles in both wild-type and mutant plants can be explained by permutations in the order of insertion along the stem of two or three consecutive organs. The number of successive organs between two permutations reveals specific patterns that depend on the nature of the preceding permutation (2- or 3-permutation). We also highlight significant individual deviations from 137.5° in the level of baseline segments and a marked relationship between permutation of organs and defects in the elongation of the internodes between these organs. These results demonstrate that permutations are an intrinsic property of spiral Phyllotaxis and that their occurrence is genetically regulated.
Didier Reinhardt - One of the best experts on this subject based on the ideXlab platform.
-
Phyllotaxis involves auxin drainage through leaf primordia
Development, 2015Co-Authors: Dominik Marti, Cris Kuhlemeier, Martin Frenz, Didier ReinhardtAbstract:ABSTRACT The spatial arrangement of leaves and flowers around the stem, known as Phyllotaxis, is controlled by an auxin-dependent reiterative mechanism that leads to regular spacing of the organs and thereby to remarkably precise phyllotactic patterns. The mechanism is based on the active cellular transport of the phytohormone auxin by cellular influx and efflux carriers, such as AUX1 and PIN1. Their important role in Phyllotaxis is evident from mutant phenotypes, but their exact roles in space and time are difficult to address due to the strong pleiotropic phenotypes of most mutants in Phyllotaxis. Models of Phyllotaxis invoke the accumulation of auxin at leaf initials and removal of auxin through their developing vascular strand, the midvein. We have developed a precise microsurgical tool to ablate the midvein at high spatial and temporal resolution in order to test its function in leaf formation and Phyllotaxis. Using amplified femtosecond laser pulses, we ablated the internal tissues in young leaf primordia of tomato (Solanum lycopersicum) without damaging the overlying L1 and L2 layers. Our results show that ablation of the future midvein leads to a transient accumulation of auxin in the primordia and to an increase in their width. Phyllotaxis was transiently affected after midvein ablations, but readjusted after two plastochrons. These results indicate that the developing midvein is involved in the basipetal transport of auxin through young primordia, which contributes to phyllotactic spacing and stability.
-
a plausible model of Phyllotaxis
Proceedings of the National Academy of Sciences of the United States of America, 2006Co-Authors: Richard S Smith, Therese Mandel, Cris Kuhlemeier, Didier Reinhardt, Soazig Guyomarch, Przemyslaw PrusinkiewiczAbstract:A striking phenomenon unique to the kingdom of plants is the regular arrangement of lateral organs around a central axis, known as Phyllotaxis. Recent molecular-genetic experiments indicate that active transport of the plant hormone auxin is the key process regulating Phyllotaxis. A conceptual model based on these experiments, introduced by Reinhardt et al. [Reinhardt, D., Pesce, E. R., Stieger, P., Mandel, T., Baltensperger, K., et al. (2003) Nature 426, 255–260], provides an intuitively plausible interpretation of the data, but raises questions of whether the proposed mechanism is, in fact, capable of producing the observed temporal and spatial patterns, is robust, can start de novo, and can account for phyllotactic transitions, such as the frequently observed transition from decussate to spiral Phyllotaxis. To answer these questions, we created a computer simulation model based on data described previously or in this paper and reasonable hypotheses. The model reproduces, within the standard error, the divergence angles measured in Arabidopsis seedlings and the effects of selected experimental manipulations. It also reproduces distichous, decussate, and tricussate patterns. The model thus offers a plausible link between molecular mechanisms of morphogenesis and the geometry of Phyllotaxis.
-
Phyllotaxis a new chapter in an old tale about beauty and magic numbers
Current Opinion in Plant Biology, 2005Co-Authors: Didier ReinhardtAbstract:Phyllotaxis, the regular arrangement of leaves and flowers around the stem, is one of the most fascinating patterning phenomena in biology. Numerous theoretical models, that are based on biochemical, biophysical and other principles, have been proposed to explain the development of the patterns. Recently, auxin has been identified as the inducer of organ formation. An emerging model for Phyllotaxis states that polar auxin transport in the plant apex generates local peaks in auxin concentration that determine the site of organ formation and thereby the different phyllotactic patterns found in nature. The PIN proteins play a primary role in auxin transport. These proteins are localized in a polar fashion, reflecting the directionality of polar auxin transport. Recent evidence shows that most aspects of Phyllotaxis can be explained by the expression pattern and the dynamic subcellular localization of PIN1.
-
regulation of Phyllotaxis
The International Journal of Developmental Biology, 2005Co-Authors: Didier ReinhardtAbstract:Plant architecture is characterized by a high degree of regularity. Leaves, flowers and floral organs are arranged in regular patterns, a phenomenon referred to as Phyllotaxis. Regular Phyllotaxis is found in virtually all higher plants, from mosses, over ferns, to gymnosperms and angiosperms. Due to its remarkable precision, its beauty and its accessibility, Phyllotaxis has for centuries been the object of admiration and scientific examination. There have been numerous hypotheses to explain the nature of the mechanistic principle behind Phyllotaxis, however, not all of them have been amenable to experimental examination. This is due mainly to the delicacy and small size of the shoot apical meristem, where plant organs are formed and the phyllotactic patterns are laid down. Recently, the combination of genetics, molecular tools and micromanipulation has resulted in the identification of auxin as a central player in organ formation and positioning. This paper discusses some aspects of phyllotactic patterns found in nature and summarizes our current understanding of the regulatory mechanism behind Phyllotaxis.
-
auxin and Phyllotaxis
Trends in Plant Science, 2001Co-Authors: Cris Kuhlemeier, Didier ReinhardtAbstract:Our understanding of Phyllotaxis is still largely based on surgical and pharmacological experiments carried out before 1970. Recent experiments implicate the plant hormone auxin in the regulation of Phyllotaxis. A recent paper shows how the polar auxin transport mutant, pin1-1, which fails to make flowers, affects the expression of well known meristem genes. This work opens the door for the genetic analysis of Phyllotaxis.
Yassin Refahi - One of the best experts on this subject based on the ideXlab platform.
-
a stochastic multicellular model identifies biological watermarks from disorders in self organized patterns of Phyllotaxis
eLife, 2016Co-Authors: Yassin Refahi, Geraldine Brunoud, Etienne Farcot, Alain Jeanmarie, Minna Pulkkinen, Teva Vernoux, Christophe GodinAbstract:Exploration of developmental mechanisms classically relies on analysis of pattern regularities. Whether disorders induced by biological noise may carry information on building principles of developmental systems is an important debated question. Here, we addressed theoretically this question using Phyllotaxis, the geometric arrangement of plant aerial organs, as a model system. Phyllotaxis arises from reiterative organogenesis driven by lateral inhibitions at the shoot apex. Motivated by recurrent observations of disorders in Phyllotaxis patterns, we revisited in depth the classical deterministic view of Phyllotaxis. We developed a stochastic model of primordia initiation at the shoot apex, integrating locality and stochasticity in the patterning system. This stochastic model recapitulates phyllotactic patterns, both regular and irregular, and makes quantitative predictions on the nature of disorders arising from noise. We further show that disorders in Phyllotaxis instruct us on the parameters governing Phyllotaxis dynamics, thus that disorders can reveal biological watermarks of developmental systems.
-
meristem size contributes to the robustness of Phyllotaxis in arabidopsis
Journal of Experimental Botany, 2015Co-Authors: Benoit Landrein, Yassin Refahi, Teva Vernoux, Fabrice Besnard, Vincent Mirabet, Arezki Boudaoud, Nathan Hervieux, Olivier HamantAbstract:Using the plant model Arabidopsis, the relationship between day length, the size of the shoot apical meristem, and the robustness of phyllotactic patterns were analysed. First, it was found that reducing day length leads to an increased meristem size and an increased number of alterations in the final positions of organs along the stem. Most of the phyllotactic defects could be related to an altered tempo of organ emergence, while not affecting the spatial positions of organ initiations at the meristem. A correlation was also found between meristem size and the robustness of Phyllotaxis in two accessions (Col-0 and WS-4) and a mutant (clasp-1), independent of growth conditions. A reduced meristem size in clasp-1 was even associated with an increased robustness of the phyllotactic pattern, beyond what is observed in the wild type. Interestingly it was also possible to modulate the robustness of Phyllotaxis in these different genotypes by changing day length. To conclude, it is shown first that robustness of the phyllotactic pattern is not maximal in the wild type, suggesting that, beyond its apparent stereotypical order, the robustness of Phyllotaxis is regulated. Secondly, a role for day length in the robustness of the Phyllotaxis was also identified, thus providing a new example of a link between patterning and environment in plants. Thirdly, the experimental results validate previous model predictions suggesting a contribution of meristem size in the robustness of Phyllotaxis via the coupling between the temporal sequence and spatial pattern of organ initiations.
-
pattern identification and characterization reveal permutations of organs as a key genetically controlled property of post meristematic Phyllotaxis
Journal of Theoretical Biology, 2013Co-Authors: Yann Guedon, Yassin Refahi, Etienne Farcot, Christophe Godin, Fabrice Besnard, Teva VernouxAbstract:In vascular plants, the arrangement of organs around the stem generates geometric patterns called Phyllotaxis. In the model plant, Arabidopsis thaliana, as in the majority of species, single organs are initiated successively at a divergence angle from the previous organ close to the canonical angle of 137.5°, producing a Fibonacci spiral. Given that little is known about the robustness of these geometric arrangements, we undertook to characterize Phyllotaxis by measuring divergence angles between organs along the stems of wild-type and specific mutant plants with obvious defects in Phyllotaxis. Sequences of measured divergence angles exhibit segments of non-canonical angles in both genotypes, albeit to a far greater extent in the mutant. We thus designed a pipeline of methods for analyzing these perturbations. The latent structure models used in this pipeline combine a non-observable model representing perturbation patterns (either a variable-order Markov chain or a combinatorial model) with von Mises distributions representing divergence angle uncertainty. We show that the segments of non-canonical angles in both wild-type and mutant plants can be explained by permutations in the order of insertion along the stem of two or three consecutive organs. The number of successive organs between two permutations reveals specific patterns that depend on the nature of the preceding permutation (2- or 3-permutation). We also highlight significant individual deviations from 137.5° in the level of baseline segments and a marked relationship between permutation of organs and defects in the elongation of the internodes between these organs. These results demonstrate that permutations are an intrinsic property of spiral Phyllotaxis and that their occurrence is genetically regulated.
-
analyzing perturbations in Phyllotaxis of arabidopsis thaliana
Proceedings of the 6th International Workshop on Functional-Structural Plant Models FSPM 2010 September 12-17 2010 University of California Davis (USA, 2010Co-Authors: Yassin Refahi, Etienne Farcot, Christophe Godin, Yann Guedon, Fabrice Besnard, Teva VernouxAbstract:Vascular plants produce new organs at the tip of the stem in a very organized fashion. This patterning process occurs in small groups of stem cells, the so-called shoot apical meristems (SAM), and generates regular patterns called Phyllotaxis. The Phyllotaxis of the model plant Arabidopsis thaliana follows a Fibonacci spiral, the most frequent phyllotactic pattern found in nature. In this phyllotactic mode, single organs are initiated successively at a divergence angle from the previous organ close to 137.5°, the golden angle. Cytokinins, a class of plant hormones, is involved in the control of Phyllotaxis but its role has remained elusive (Vernoux et al., 2010). By analyzing the expression of several cytokinin signaling regulators in the meristem, we found that the pseudo-phosphotransfer protein AHP6 is expressed specifically during early organogenesis (unpublished results). AHP6 has been demonstrated to act as an inhibitor of cytokinin signaling (Mahonen et al., 2006) and we further observed a destabilization of Phyllotaxis in ahp6 null mutant. To understand how AHP6 acts in the control of Arabidopsis Phyllotaxis, we analyzed sequences of divergence angles in both wild-type and ahp6 mutant plants. We thus measured the divergence angle between successive flowers on a stem from the base (older flowers) to the top (younger flowers).
Cris Kuhlemeier - One of the best experts on this subject based on the ideXlab platform.
-
Phyllotaxis.
Current biology : CB, 2017Co-Authors: Cris KuhlemeierAbstract:Leaves and flowers are arranged in regular patterns around the stem of a plant, a phenomenon known as Phyllotaxis. Different arrangements occur, such as distichous, decussate or spiral (Figure 1). Most prevalent in nature are spirals in which the average divergence angles between successive organs are close to 137.5°, the so-called 'golden angle'. It is this exact number that has given Phyllotaxis its special flavor as a quantitative developmental problem, and over the centuries, it has enjoyed the attention of scientists far beyond botany. In the 1830s mathematicians described the spirals as they related to the Fibonacci numbers, and in the 1860s improved microscopes made it possible for botanists to observe the initiation of leaf and flower primordia in a diversity of plants. This descriptive work led to the conclusion that new organ primordia form in the first available space between existing primordia, a conclusion still valid today. But how does it work? Ideas from the early 20th century suggested that an inhibitor produced by existing primordia diffuses towards the shoot apical meristem: where the concentration of the inhibitor falls below a threshold value, an organ is initiated. Other models dating back to the 1870s have tried to explain phyllotactic patterning by applying the laws of mechanics. Such models went through a long period of marginal interest, but have experienced a remarkable renaissance over the past 20 years. In this Primer I will give a broad overview of Phyllotaxis, its emergence from the shoot apical meristem, how auxin and its transporter function as a 'pattern generator', and the role of tissue mechanics and computational modeling.
-
Phyllotaxis involves auxin drainage through leaf primordia
Development, 2015Co-Authors: Dominik Marti, Cris Kuhlemeier, Martin Frenz, Didier ReinhardtAbstract:ABSTRACT The spatial arrangement of leaves and flowers around the stem, known as Phyllotaxis, is controlled by an auxin-dependent reiterative mechanism that leads to regular spacing of the organs and thereby to remarkably precise phyllotactic patterns. The mechanism is based on the active cellular transport of the phytohormone auxin by cellular influx and efflux carriers, such as AUX1 and PIN1. Their important role in Phyllotaxis is evident from mutant phenotypes, but their exact roles in space and time are difficult to address due to the strong pleiotropic phenotypes of most mutants in Phyllotaxis. Models of Phyllotaxis invoke the accumulation of auxin at leaf initials and removal of auxin through their developing vascular strand, the midvein. We have developed a precise microsurgical tool to ablate the midvein at high spatial and temporal resolution in order to test its function in leaf formation and Phyllotaxis. Using amplified femtosecond laser pulses, we ablated the internal tissues in young leaf primordia of tomato (Solanum lycopersicum) without damaging the overlying L1 and L2 layers. Our results show that ablation of the future midvein leads to a transient accumulation of auxin in the primordia and to an increase in their width. Phyllotaxis was transiently affected after midvein ablations, but readjusted after two plastochrons. These results indicate that the developing midvein is involved in the basipetal transport of auxin through young primordia, which contributes to phyllotactic spacing and stability.
-
Phyllotaxis.
Trends in plant science, 2007Co-Authors: Cris KuhlemeierAbstract:Phyllotaxis, the regular arrangement of leaves or flowers around a plant stem, is an example of developmental pattern formation and organogenesis. Phyllotaxis is characterized by the divergence angles between the organs, the most common angle being 137.5 degrees , the golden angle. The quantitative aspects of Phyllotaxis have stimulated research at the interface between molecular biology, physics and mathematics. This review documents the rich history of different approaches and conflicting hypotheses, and then focuses on recent molecular work that establishes a novel patterning mechanism based on active transport of the plant hormone auxin. Finally, it shows how computer simulations can help to formulate quantitative models that in turn can be tested by experiment. The accumulation of ever increasing amounts of experimental data makes quantitative modeling of interest for many developmental systems.
-
a plausible model of Phyllotaxis
Proceedings of the National Academy of Sciences of the United States of America, 2006Co-Authors: Richard S Smith, Therese Mandel, Cris Kuhlemeier, Didier Reinhardt, Soazig Guyomarch, Przemyslaw PrusinkiewiczAbstract:A striking phenomenon unique to the kingdom of plants is the regular arrangement of lateral organs around a central axis, known as Phyllotaxis. Recent molecular-genetic experiments indicate that active transport of the plant hormone auxin is the key process regulating Phyllotaxis. A conceptual model based on these experiments, introduced by Reinhardt et al. [Reinhardt, D., Pesce, E. R., Stieger, P., Mandel, T., Baltensperger, K., et al. (2003) Nature 426, 255–260], provides an intuitively plausible interpretation of the data, but raises questions of whether the proposed mechanism is, in fact, capable of producing the observed temporal and spatial patterns, is robust, can start de novo, and can account for phyllotactic transitions, such as the frequently observed transition from decussate to spiral Phyllotaxis. To answer these questions, we created a computer simulation model based on data described previously or in this paper and reasonable hypotheses. The model reproduces, within the standard error, the divergence angles measured in Arabidopsis seedlings and the effects of selected experimental manipulations. It also reproduces distichous, decussate, and tricussate patterns. The model thus offers a plausible link between molecular mechanisms of morphogenesis and the geometry of Phyllotaxis.
-
Regulation of Phyllotaxis by polar auxin transport
Nature, 2003Co-Authors: Delphine Reinhardt, Pia Stieger, Kurt Baltensperger, Malcolm Bennett, Jan Traas, Therese Mandel, Eva-rachele Pesce, Jiří Friml, Cris KuhlemeierAbstract:The regular arrangement of leaves around a plant's stem, called Phyllotaxis, has for centuries attracted the attention of philosophers, mathematicians and natural scientists; however, to date, studies of Phyllotaxis have been largely theoretical. Leaves and flowers are formed from the shoot apical meristem, triggered by the plant hormone auxin. Auxin is transported through plant tissues by specific cellular influx and efflux carrier proteins. Here we show that proteins involved in auxin transport regulate Phyllotaxis. Our data indicate that auxin is transported upwards into the meristem through the epidermis and the outermost meristem cell layer. Existing leaf primordia act as sinks, redistributing auxin and creating its heterogeneous distribution in the meristem. Auxin accumulation occurs only at certain minimal distances from existing primordia, defining the position of future primordia. This model for Phyllotaxis accounts for its reiterative nature, as well as its regularity and stability.
Christophe Godin - One of the best experts on this subject based on the ideXlab platform.
-
a stochastic multicellular model identifies biological watermarks from disorders in self organized patterns of Phyllotaxis
eLife, 2016Co-Authors: Yassin Refahi, Geraldine Brunoud, Etienne Farcot, Alain Jeanmarie, Minna Pulkkinen, Teva Vernoux, Christophe GodinAbstract:Exploration of developmental mechanisms classically relies on analysis of pattern regularities. Whether disorders induced by biological noise may carry information on building principles of developmental systems is an important debated question. Here, we addressed theoretically this question using Phyllotaxis, the geometric arrangement of plant aerial organs, as a model system. Phyllotaxis arises from reiterative organogenesis driven by lateral inhibitions at the shoot apex. Motivated by recurrent observations of disorders in Phyllotaxis patterns, we revisited in depth the classical deterministic view of Phyllotaxis. We developed a stochastic model of primordia initiation at the shoot apex, integrating locality and stochasticity in the patterning system. This stochastic model recapitulates phyllotactic patterns, both regular and irregular, and makes quantitative predictions on the nature of disorders arising from noise. We further show that disorders in Phyllotaxis instruct us on the parameters governing Phyllotaxis dynamics, thus that disorders can reveal biological watermarks of developmental systems.
-
Phyllotaxis from patterns of organogenesis at the meristem to shoot architecture
Wiley Interdisciplinary Reviews-Developmental Biology, 2016Co-Authors: Carlos S Galvanampudia, Christophe Godin, Anais M Chaumeret, Teva VernouxAbstract:The primary architecture of the aerial part of plants is controlled by the shoot apical meristem, a specialized tissue containing a stem cell niche. The iterative generation of new aerial organs, (leaves, lateral inflorescences and flowers) at the meristem follows regular patterns, called Phyllotaxis. Phyllotaxis has long been proposed to self-‐organize from the combined action of growth and of inhibitory fields blocking organogenesis in the vicinity of existing organs in the meristem. In this review we will highlight how a combination of mathematical/computational modeling and experimental biology has demonstrated that the spatio-‐temporal distribution of the plant hormone auxin controls both organogenesis and the establishment of inhibitory fields. We will discuss recent advances showing that auxin likely acts through a combination of biochemical and mechanical regulatory mechanisms that control not only the pattern of organogenesis in the meristem but also post-‐meristematic growth, to shape the shoot.
-
pattern identification and characterization reveal permutations of organs as a key genetically controlled property of post meristematic Phyllotaxis
Journal of Theoretical Biology, 2013Co-Authors: Yann Guedon, Yassin Refahi, Etienne Farcot, Christophe Godin, Fabrice Besnard, Teva VernouxAbstract:In vascular plants, the arrangement of organs around the stem generates geometric patterns called Phyllotaxis. In the model plant, Arabidopsis thaliana, as in the majority of species, single organs are initiated successively at a divergence angle from the previous organ close to the canonical angle of 137.5°, producing a Fibonacci spiral. Given that little is known about the robustness of these geometric arrangements, we undertook to characterize Phyllotaxis by measuring divergence angles between organs along the stems of wild-type and specific mutant plants with obvious defects in Phyllotaxis. Sequences of measured divergence angles exhibit segments of non-canonical angles in both genotypes, albeit to a far greater extent in the mutant. We thus designed a pipeline of methods for analyzing these perturbations. The latent structure models used in this pipeline combine a non-observable model representing perturbation patterns (either a variable-order Markov chain or a combinatorial model) with von Mises distributions representing divergence angle uncertainty. We show that the segments of non-canonical angles in both wild-type and mutant plants can be explained by permutations in the order of insertion along the stem of two or three consecutive organs. The number of successive organs between two permutations reveals specific patterns that depend on the nature of the preceding permutation (2- or 3-permutation). We also highlight significant individual deviations from 137.5° in the level of baseline segments and a marked relationship between permutation of organs and defects in the elongation of the internodes between these organs. These results demonstrate that permutations are an intrinsic property of spiral Phyllotaxis and that their occurrence is genetically regulated.
-
analyzing perturbations in Phyllotaxis of arabidopsis thaliana
Proceedings of the 6th International Workshop on Functional-Structural Plant Models FSPM 2010 September 12-17 2010 University of California Davis (USA, 2010Co-Authors: Yassin Refahi, Etienne Farcot, Christophe Godin, Yann Guedon, Fabrice Besnard, Teva VernouxAbstract:Vascular plants produce new organs at the tip of the stem in a very organized fashion. This patterning process occurs in small groups of stem cells, the so-called shoot apical meristems (SAM), and generates regular patterns called Phyllotaxis. The Phyllotaxis of the model plant Arabidopsis thaliana follows a Fibonacci spiral, the most frequent phyllotactic pattern found in nature. In this phyllotactic mode, single organs are initiated successively at a divergence angle from the previous organ close to 137.5°, the golden angle. Cytokinins, a class of plant hormones, is involved in the control of Phyllotaxis but its role has remained elusive (Vernoux et al., 2010). By analyzing the expression of several cytokinin signaling regulators in the meristem, we found that the pseudo-phosphotransfer protein AHP6 is expressed specifically during early organogenesis (unpublished results). AHP6 has been demonstrated to act as an inhibitor of cytokinin signaling (Mahonen et al., 2006) and we further observed a destabilization of Phyllotaxis in ahp6 null mutant. To understand how AHP6 acts in the control of Arabidopsis Phyllotaxis, we analyzed sequences of divergence angles in both wild-type and ahp6 mutant plants. We thus measured the divergence angle between successive flowers on a stem from the base (older flowers) to the top (younger flowers).