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1.
Science ; 375(6583): 806-810, 2022 Feb 25.
Article in English | MEDLINE | ID: mdl-35201865

ABSTRACT

Finland is set to open the world's first permanent repository for high-level nuclear waste. How did it succeed when other countries stumbled?

2.
Science ; 369(6500): 127, 2020 07 10.
Article in English | MEDLINE | ID: mdl-32646978
3.
5.
Nature ; 571(7766): S10-S11, 2019 07.
Article in English | MEDLINE | ID: mdl-31341308
6.
Nat Plants ; 5(6): 604-615, 2019 06.
Article in English | MEDLINE | ID: mdl-31182845

ABSTRACT

During phloem unloading, multiple cell-to-cell transport events move organic substances to the root meristem. Although the primary unloading event from the sieve elements to the phloem pole pericycle has been characterized to some extent, little is known about post-sieve element unloading. Here, we report a novel gene, PHLOEM UNLOADING MODULATOR (PLM), in the absence of which plasmodesmata-mediated symplastic transport through the phloem pole pericycle-endodermis interface is specifically enhanced. Increased unloading is attributable to a defect in the formation of the endoplasmic reticulum-plasma membrane tethers during plasmodesmal morphogenesis, resulting in the majority of pores lacking a visible cytoplasmic sleeve. PLM encodes a putative enzyme required for the biosynthesis of sphingolipids with very-long-chain fatty acid. Taken together, our results indicate that post-sieve element unloading involves sphingolipid metabolism, which affects plasmodesmal ultrastructure. They also raise the question of how and why plasmodesmata with no cytoplasmic sleeve facilitate molecular trafficking.


Subject(s)
Arabidopsis Proteins/metabolism , Arabidopsis/metabolism , Membrane Proteins/metabolism , Phloem/metabolism , Plasmodesmata/ultrastructure , Sphingolipids/biosynthesis , Arabidopsis/genetics , Arabidopsis/ultrastructure , Arabidopsis Proteins/genetics , Genes, Plant , Glucans/metabolism , Green Fluorescent Proteins/metabolism , Membrane Proteins/genetics , Mutation , Plant Roots/metabolism , Plasmodesmata/metabolism , Transferases (Other Substituted Phosphate Groups)/genetics , Transferases (Other Substituted Phosphate Groups)/metabolism
8.
Nature ; 555(7697): 454-455, 2018 03 22.
Article in English | MEDLINE | ID: mdl-29565372
9.
Nature ; 555(7697): 454-455, 2018 Mar.
Article in English | MEDLINE | ID: mdl-32034372
10.
New Phytol ; 215(1): 157-172, 2017 07.
Article in English | MEDLINE | ID: mdl-28503769

ABSTRACT

N6-adenosine methylation (m6 A) of mRNA is an essential process in most eukaryotes, but its role and the status of factors accompanying this modification are still poorly understood. Using combined methods of genetics, proteomics and RNA biochemistry, we identified a core set of mRNA m6 A writer proteins in Arabidopsis thaliana. The components required for m6 A in Arabidopsis included MTA, MTB, FIP37, VIRILIZER and the E3 ubiquitin ligase HAKAI. Downregulation of these proteins led to reduced relative m6 A levels and shared pleiotropic phenotypes, which included aberrant vascular formation in the root, indicating that correct m6 A methylation plays a role in developmental decisions during pattern formation. The conservation of these proteins amongst eukaryotes and the demonstration of a role in writing m6 A for the E3 ubiquitin ligase HAKAI is likely to be of considerable relevance beyond the plant sciences.


Subject(s)
Arabidopsis Proteins/physiology , Arabidopsis/metabolism , Methyltransferases/physiology , RNA, Messenger/metabolism , Ubiquitin-Protein Ligases/physiology , Adenosine/metabolism , Arabidopsis Proteins/genetics , Arabidopsis Proteins/metabolism , Conserved Sequence , Methylation , Methyltransferases/genetics , Methyltransferases/metabolism , Plants, Genetically Modified/metabolism , Sequence Alignment , Ubiquitin-Protein Ligases/genetics , Ubiquitin-Protein Ligases/metabolism
11.
Science ; 355(6320): 12, 2017 Jan 06.
Article in English | MEDLINE | ID: mdl-28059720
12.
J Exp Bot ; 68(1): 5-16, 2017 01.
Article in English | MEDLINE | ID: mdl-27837006

ABSTRACT

The root vascular tissues provide an excellent system for studying organ patterning, as the specification of these tissues signals a transition from radial symmetry to bisymmetric patterns. The patterning process is controlled by the combined action of hormonal signaling/transport pathways, transcription factors, and miRNA that operate through a series of non-linear pathways to drive pattern formation collectively. With the discovery of multiple components and feedback loops controlling patterning, it has become increasingly difficult to understand how these interactions act in unison to determine pattern formation in multicellular tissues. Three independent mathematical models of root vascular patterning have been formulated in the last few years, providing an excellent example of how theoretical approaches can complement experimental studies to provide new insights into complex systems. In many aspects these models support each other; however, each study also provides its own novel findings and unique viewpoints. Here we reconcile these models by identifying the commonalities and exploring the differences between them by testing how transferable findings are between models. New simulations herein support the hypothesis that an asymmetry in auxin input can direct the formation of vascular pattern. We show that the xylem axis can act as a sole source of cytokinin and specify the correct pattern, but also that broader patterns of cytokinin production are also able to pattern the root. By comparing the three modeling approaches, we gain further insight into vascular patterning and identify several key areas for experimental investigation.


Subject(s)
Phloem/anatomy & histology , Plant Roots/anatomy & histology , Xylem/anatomy & histology , Cytokinins/metabolism , Cytokinins/physiology , Indoleacetic Acids/metabolism , Models, Biological , Phloem/physiology , Plant Growth Regulators/physiology , Plant Roots/physiology , Xylem/physiology
14.
PLoS Comput Biol ; 11(10): e1004450, 2015 Oct.
Article in English | MEDLINE | ID: mdl-26505899

ABSTRACT

An auxin maximum is positioned along the xylem axis of the Arabidopsis root tip. The pattern depends on mutual feedback between auxin and cytokinins mediated by the PIN class of auxin efflux transporters and AHP6, an inhibitor of cytokinin signalling. This interaction has been proposed to regulate the size and the position of the hormones' respective signalling domains and specify distinct boundaries between them. To understand the dynamics of this regulatory network, we implemented a parsimonious computational model of auxin transport that considers hormonal regulation of the auxin transporters within a spatial context, explicitly taking into account cell shape and polarity and the presence of cell walls. Our analysis reveals that an informative spatial pattern in cytokinin levels generated by diffusion is a theoretically unlikely scenario. Furthermore, our model shows that such a pattern is not required for correct and robust auxin patterning. Instead, auxin-dependent modifications of cytokinin response, rather than variations in cytokinin levels, allow for the necessary feedbacks, which can amplify and stabilise the auxin maximum. Our simulations demonstrate the importance of hormonal regulation of auxin efflux for pattern robustness. While involvement of the PIN proteins in vascular patterning is well established, we predict and experimentally verify a role of AUX1 and LAX1/2 auxin influx transporters in this process. Furthermore, we show that polar localisation of PIN1 generates an auxin flux circuit that not only stabilises the accumulation of auxin within the xylem axis, but also provides a mechanism for auxin to accumulate specifically in the xylem-pole pericycle cells, an important early step in lateral root initiation. The model also revealed that pericycle cells on opposite xylem poles compete for auxin accumulation, consistent with the observation that lateral roots are not initiated opposite to each other.


Subject(s)
Arabidopsis/physiology , Cytokinins/metabolism , Indoleacetic Acids/metabolism , Models, Biological , Plant Roots/growth & development , Plant Vascular Bundle/growth & development , Arabidopsis Proteins/metabolism , Computer Simulation , Membrane Transport Proteins , Plant Growth Regulators/metabolism
15.
Development ; 140(7): 1373-83, 2013 Apr.
Article in English | MEDLINE | ID: mdl-23482484

ABSTRACT

Cytokinins are a major class of plant hormones that are involved in various aspects of plant development, ranging from organ formation and apical dominance to leaf senescence. Cytokinin and auxin have long been known to interact antagonistically, and more recent studies have shown that cytokinins also interact with other plant hormones to regulate plant development. A growing body of research has begun to elucidate the molecular and genetic underpinnings of this extensive crosstalk. The rich interconnections between the synthesis, perception and transport networks of these plant hormones provide a wide range of opportunities for them to modulate, amplify or buffer one another. Here, we review this exciting and rapidly growing area of cytokinin research.


Subject(s)
Cytokinins/physiology , Receptor Cross-Talk/physiology , Signal Transduction/genetics , Animals , Biological Transport/genetics , Cytokinins/genetics , Cytokinins/metabolism , Gene Expression Regulation, Plant , Histidine Kinase , Metabolic Networks and Pathways/genetics , Metabolic Networks and Pathways/physiology , Models, Biological , Protein Kinases/genetics , Protein Kinases/metabolism , Protein Kinases/physiology , Signal Transduction/physiology
16.
Curr Biol ; 21(11): 917-26, 2011 Jun 07.
Article in English | MEDLINE | ID: mdl-21620702

ABSTRACT

BACKGROUND: Whereas the majority of animals develop toward a predetermined body plan, plants show iterative growth and continually produce new organs and structures from actively dividing meristems. This raises an intriguing question: How are these newly developed organs patterned? In Arabidopsis embryos, radial symmetry is broken by the bisymmetric specification of the cotyledons in the apical domain. Subsequently, this bisymmetry is propagated to the root promeristem. RESULTS: Here we present a mutually inhibitory feedback loop between auxin and cytokinin that sets distinct boundaries of hormonal output. Cytokinins promote the bisymmetric distribution of the PIN-FORMED (PIN) auxin efflux proteins, which channel auxin toward a central domain. High auxin promotes transcription of the cytokinin signaling inhibitor AHP6, which closes the interaction loop. This bisymmetric auxin response domain specifies the differentiation of protoxylem in a bisymmetric pattern. In embryonic roots, cytokinin is required to translate a bisymmetric auxin response in the cotyledons to a bisymmetric vascular pattern in the root promeristem. CONCLUSIONS: Our results present an interactive feedback loop between hormonal signaling and transport by which small biases in hormonal input are propagated into distinct signaling domains to specify the vascular pattern in the root meristem. It is an intriguing possibility that such a mechanism could transform radial patterns and allow continuous vascular connections between other newly emerging organs.


Subject(s)
Arabidopsis Proteins/physiology , Arabidopsis/growth & development , Cytokinins/metabolism , Indoleacetic Acids/metabolism , Plant Growth Regulators/metabolism , Arabidopsis/anatomy & histology , Arabidopsis/metabolism , Arabidopsis Proteins/genetics , Arabidopsis Proteins/metabolism , Body Patterning , Feedback, Physiological , Meristem/physiology , Models, Biological , Plant Growth Regulators/physiology , Plant Roots/anatomy & histology , Plant Roots/growth & development , Plant Roots/metabolism , Xylem/growth & development , Xylem/metabolism
17.
Curr Biol ; 21(11): 927-32, 2011 Jun 07.
Article in English | MEDLINE | ID: mdl-21620705

ABSTRACT

Cytokinin phytohormones regulate a variety of developmental processes in the root such as meristem size, vascular pattern, and root architecture [1-3]. Long-distance transport of cytokinin is supported by the discovery of cytokinins in xylem and phloem sap [4] and by grafting experiments between wild-type and cytokinin biosynthesis mutants [5]. Acropetal transport of cytokinin (toward the shoot apex) has also been implicated in the control of shoot branching [6]. However, neither the mode of transport nor a developmental role has been shown for basipetal transport of cytokinin (toward the root apex). In this paper, we combine the use of a new technology that blocks symplastic connections in the phloem with a novel approach to visualize radiolabeled hormones in planta to examine the basipetal transport of cytokinin. We show that this occurs through symplastic connections in the phloem. The reduction of cytokinin levels in the phloem leads to a destabilization of the root vascular pattern in a manner similar to mutants affected in auxin transport or cytokinin signaling [7]. Together, our results demonstrate a role for long-distance basipetal transport of cytokinin in controlling polar auxin transport and maintaining the vascular pattern in the root meristem.


Subject(s)
Arabidopsis/metabolism , Cytokinins/metabolism , Indoleacetic Acids/metabolism , Meristem/metabolism , Phloem/metabolism , Plant Growth Regulators/metabolism , Arabidopsis/genetics , Arabidopsis/growth & development , Arabidopsis Proteins/genetics , Arabidopsis Proteins/metabolism , Arabidopsis Proteins/physiology , Biological Transport , Meristem/growth & development , Plant Roots/genetics , Plant Roots/growth & development , Plant Roots/metabolism , Plants, Genetically Modified/metabolism
18.
Biophys Chem ; 134(3): 232-8, 2008 May.
Article in English | MEDLINE | ID: mdl-18329784

ABSTRACT

Eukaryote genomes contain excessively introns, intergenic and other non-genic sequences that appear to have no vital functional role or phenotype manifestation. Their existence, a long-standing puzzle, is viewed from the principle of increasing entropy. According to thermodynamics of open systems, genomes evolve toward diversity by various mechanisms that increase, decrease and distribute genomic material in response to thermodynamic driving forces. Evolution results in an excessive genome, a high-entropy ecosystem of its own, where copious non-coding segments associate with low-level functions and conserved sequences code coordinated activities. The rate of entropy increase, equivalent to the rate of free energy decrease, is identified with the universal fitness criterion of natural selection that governs populations of genomic entities as well as other species.


Subject(s)
Evolution, Molecular , Genetic Variation , Genome/genetics , Models, Genetic , Computer Simulation , Ecosystem , Entropy
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