Auxin Transport, but in Which Direction?
Tobias Sieberer and Ottoline Leyser
Many aspects of plant growth depend on transport of the hormone auxin across tissues, directed by specific transporter proteins.
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The authors are in the Department of Biology, University of York, York YO10 4YW, UK. E-mail: ts20@york.ac.uk ; hmol1@york.ac.uk
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Abstract 2 of 16
The plant hormone auxin regulates a variety of growth and developmental responses and must be transported within the plant in an organized fashion. Petrášek et al. (p. 914, published online 6 April; see the Brevia by Wiśniewska et al. and the Perspective by Sieberer and Leyser) now show, by using inducible overexpression in plant cells and expression in human and yeast cells, that the protein PIN is responsible for the direction in which auxin flows out of the cell.
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Abstract 3 of 16
The "where" of auxin signaling is critical to regulating developmental responses during plant growth. Auxin is shunted through cells from one place to the next using influx and efflux carriers. The localization of these carriers thus has a direct effect on auxin signaling. Dharmasiri et al. (p. 1218, published online 11 May) have now cloned the AXR4 gene and show that the auxin influx carrier is localized according to directions provided by the AXR4 protein.
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Abstract 4 of 16
Auxin is an essential plant hormone that is involved in regulation of plant growth and development, however the mechanism of auxin biosynthesis in plants is poorly understood. Now Zhao et al. (p. 306) show that the Arabidopsis gene YUCCA encodes a flavin monooxygenase-like enzyme that catalyzes hydroxylation of the amino group of tryptamine. The step appears to be rate-limiting in auxin biosynthesis via a tryptophan-dependent pathway.
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Abstract 5 of 16
Polar PIN Localization Directs Auxin Flow in Plants
Justyna Winiewska,1,3 Jian Xu,2 Daniela Seifertová,1 Philip B. Brewer,1 Kamil Rika,1 Ikram Blilou,2 David Rouquié,1* Eva Benková,1 Ben Scheres,2 Jií Friml1
Polar flow of the phytohormone auxin requires plasma membrane-associated PIN proteins and underlies multiple developmental processes in plants. Here we address the importance of the polarity of subcellular PIN localization for the directionality of auxin transport in Arabidopsis thaliana. Expression of different PINs in the root epidermis revealed the importance of PIN polar positions for directional auxin flow and root gravitropic growth. Interfering with sequence-embedded polarity signals directly demonstrates that PIN polarity is a primary factor in determining the direction of auxin flow in meristematic tissues. This finding provides a crucial piece in the puzzle of how auxin flow can be redirected via rapid changes in PIN polarity.
1 Center for Plant Molecular Biology (ZMBP), Tübingen University, D-72076 Tübingen, Germany.
2 Department of Molecular Genetics, Utrecht University, 3584CH Utrecht, Netherlands.
3 Department of Biotechnology, Institute of General and Molecular Biology, 87-100 Toru, Poland.
* Present address: Bayer CropScience, F-06560 Sophia Antipolis Cedex, France.
To whom correspondence should be addressed. E-mail: jiri.friml@zmbp.uni-tuebingen.de
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Abstract 6 of 16
PIN Proteins Perform a Rate-Limiting Function in Cellular Auxin Efflux
Jan Petráek,1,2 Jozef Mravec,3 Rodolphe Bouchard,4 Joshua J. Blakeslee,5 Melinda Abas,6 Daniela Seifertová,1,2,3 Justyna Winiewska,3,7 Zerihun Tadele,8 Martin Kube,1,2 Milada ovanová,1,2 Pankaj Dhonukshe,3 Petr Skpa,1,2 Eva Benková,3 Lucie Perry,1 Pavel Keek,1,2 Ok Ran Lee,5 Gerald R. Fink,9 Markus Geisler,4 Angus S. Murphy,5 Christian Luschnig,6 Eva Zaímalová,1* Jií Friml3,10
Intercellular flow of the phytohormone auxin underpins multiple developmental processes in plants. Plant-specific pin-formed (PIN) proteins and several phosphoglycoprotein (PGP) transporters are crucial factors in auxin transport–related development, yet the molecular function of PINs remains unknown. Here, we show that PINs mediate auxin efflux from mammalian and yeast cells without needing additional plant-specific factors. Conditional gain-of-function alleles and quantitative measurements of auxin accumulation in Arabidopsis and tobacco cultured cells revealed that the action of PINs in auxin efflux is distinct from PGP, rate-limiting, specific to auxins, and sensitive to auxin transport inhibitors. This suggests a direct involvement of PINs in catalyzing cellular auxin efflux.
1 Institute of Experimental Botany, the Academy of Sciences of the Czech Republic, 165 02 Prague 6, Czech Republic.
2 Department of Plant Physiology, Faculty of Science, Charles University, 128 44 Prague 2, Czech Republic.
3 Center for Plant Molecular Biology (ZMBP), University Tübingen, D-72076 Tübingen, Germany.
4 Zurich-Basel Plant Science Center, University of Zurich, Institute of Plant Biology, CH 8007 Zurich, Switzerland.
5 Department of Horticulture, Purdue University, West Lafayette, IN 47907, USA.
6 Institute for Applied Genetics and Cell Biology, University of Natural Resources and Applied Life Sciences–Universität für Bodenkultur, A-1190 Wien, Austria.
7 Department of Biotechnology, Institute of General and Molecular Biology, 87-100 Toru, Poland.
8 Institute of Plant Sciences, University of Bern, 3013 Bern, Switzerland.
9 Whitehead Institute for Biomedical Research, Nine Cambridge Center, Cambridge, MA 02142, USA.
10 Masaryk University, Department of Functional Genomics and Proteomics, Laboratory of Molecular Plant Physiology, Kamenice 5, 625 00 Brno, Czech Republic.
* To whom correspondence should be addressed. E-mail: eva.zazim@ueb.cas.cz
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Abstract 7 of 16
PLANT SCIENCE:
Auxin Begins to Give Up Its Secrets
Gretchen Vogel
Auxin controls the growth of plants and their interactions with their environment, but only now are researchers understanding the basics of this hormone. (Read more.)
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Abstract 8 of 16
The plant hormone auxin is a key regulator of growth and development. Zhao et al. (p. 1107) identified a compound, sirtinol, that stimulates biological responses similar to those initiated by auxin. They then screened for mutants of Arabidopsis that did not respond to sirtinol and identified a mutant they called sir1 that encodes a protein with similarity to a ubiquitin-activating E1-like protein. This result may help explain how auxin can rapidly degrade negative regulators as part of its mechanism of action.
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Abstract 9 of 16
PLANT BIOLOGY:
Growth by Auxin: When a Weed Needs Acid
Markus Grebe
In his Perspective, Grebe discusses how a plant proton pump residing in intracellular compartments, rather than in the plasma membrane of the cell surface, regulates growth and development. The pump modulates the expression at the plasma membrane of both a transporter for the hormone auxin and another proton pump. These findings open new views on how plants regulate cell wall acidity and hormone transport during development.
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The author is at the Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, 90 183 Umeå, Sweden. E-mail: markus.grebe@genfys.slu.se
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Abstract 10 of 16
Arabidopsis H+-PPase AVP1 Regulates Auxin-Mediated Organ Development
Jisheng Li,1* Haibing Yang,1* Wendy Ann Peer,3 Gregory Richter,2 Joshua Blakeslee,3 Anindita Bandyopadhyay,3 Boosaree Titapiwantakun,3 Soledad Undurraga,1 Mariya Khodakovskaya,1 Elizabeth L. Richards,3 Beth Krizek,4 Angus S. Murphy,3 Simon Gilroy,2 Roberto Gaxiola1
The transport of auxin controls developmental events in plants. Here, we report that in addition to maintaining vacuolar pH, the H+-pyrophosphatase, AVP1, controls auxin transport and consequently auxin-dependent development. AVP1 overexpression results in increased cell division at the onset of organ formation, hyperplasia, and increased auxin transport. In contrast, avp1-1 null mutants have severely disrupted root and shoot development and reduced auxin transport. Changes in the expression of AVP1 affect the distribution and abundance of the P–adenosine triphosphatase and Pinformed 1 auxin efflux facilitator, two proteins implicated in auxin distribution. Thus, AVP1 facilitates the auxin fluxes that regulate organogenesis.
1 Department of Plant Science, University of Connecticut, Storrs, CT 06268, USA.
2 Biology Department, Pennsylvania State University, University Park, PA 16802, USA.
3 Horticulture Department, Purdue University, West Lafayette, IN 47907, USA.
4 Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA.
* These authors contributed equally to this work.
To whom correspondence should be addressed. E-mail: roberto.gaxiola@uconn.edu
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Abstract 11 of 16
SIR1, an Upstream Component in Auxin Signaling Identified by Chemical Genetics
Yunde Zhao,1* Xinhua Dai,1 Helen E. Blackwell,2 Stuart L. Schreiber,2 Joanne Chory3
Auxin is a plant hormone that regulates many aspects of plant growth and development. We used a chemical genetics approach to identify SIR1, a regulator of many auxin-inducible genes. The sir1 mutant was resistant to sirtinol, a small molecule that activates many auxin-inducible genes and promotes auxin-related developmental phenotypes. SIR1 is predicted to encode a protein composed of a ubiquitin-activating enzyme E1–like domain and a Rhodanese-like domain homologous to that of prolyl isomerase. We suggest a molecular context for how the auxin signal is propagated to exert its biological effects.
1 Section of Cell and Developmental Biology, Division of Biological Sciences, University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093–0116, USA.
2 Department of Chemistry and Chemical Biology, Howard Hughes Medical Institute (HHMI), Harvard University, 12 Oxford Street, Cambridge, MA 02138, USA.
3 The Plant Biology Laboratory, HHMI and The Salk Institute, 10010 North Torrey Pines Road, La Jolla, CA 92037, USA.
Present address: Department of Chemistry, University of Wisconsin–Madison, 1101 University Avenue, Madison, WI 53706–1396, USA.
* To whom correspondence should be addressed. E-mail: yzhao@biomail.ucsd.edu
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Abstract 12 of 16
AXR4 Is Required for Localization of the Auxin Influx Facilitator AUX1
S. Dharmasiri,1* R. Swarup,2* K. Mockaitis,1* N. Dharmasiri,1 S. K. Singh,3 M. Kowalchyk,3 A. Marchant,3 S. Mills,4 G. Sandberg,3 M. J. Bennett,2 M. Estelle1
The AUX1 and PIN auxin influx and efflux facilitators are key regulators of root growth and development. For root gravitropism to occur, AUX1 and PIN2 must transport auxin via the lateral root cap to elongating epidermal cells. Genetic studies suggest that AXR4 functions in the same pathway as AUX1. Here we show that AXR4 is a previously unidentified accessory protein of the endoplasmic reticulum (ER) that regulates localization of AUX1 but not of PIN proteins. Loss of AXR4 resulted in abnormal accumulation of AUX1 in the ER of epidermal cells, indicating that the axr4 agravitropic phenotype is caused by defective AUX1 trafficking in the root epidermis.
1 Department of Biology, Indiana University, Bloomington, IN 47405, USA.
2 School of Biosciences, University of Nottingham, Loughborough LE12 5RD, UK.
3 Umeå Plant Science Centre, SLU, Umeå, Sweden.
4 School of Computer Science and Information Technology, University of Nottingham, Nottingham NG7 2UH, UK.
* These authors contributed equally to this work.
Present address: Department of Biology, Texas State University–San Marcos, San Marcos, TX 78666, USA.
To whom correspondence should be addressed. E-mail: malcolm.bennett@nottingham.ac.uk (M.J.B.), maestell@indiana.edu (M.E.)
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Abstract 13 of 16
A Role for Flavin Monooxygenase-Like Enzymes in Auxin Biosynthesis
Yunde Zhao,12 Sioux K. Christensen,2* Christian Fankhauser,2 John R. Cashman,3 Jerry D. Cohen,4 Detlef Weigel,2 Joanne Chory12
Although auxin is known to regulate many processes in plant development and has been studied for over a century, the mechanisms whereby plants produce it have remained elusive. Here we report the characterization of a dominant Arabidopsis mutant, yucca, which contains elevated levels of free auxin. YUCCA encodes a flavin monooxygenase-like enzyme and belongs to a family that includes at least nine other homologous Arabidopsis genes, a subset of which appears to have redundant functions. Results from tryptophan analog feeding experiments and biochemical assays indicate that YUCCA catalyzes hydroxylation of the amino group of tryptamine, a rate-limiting step in tryptophan-dependent auxin biosynthesis.
1 Howard Hughes Medical Institute,
2 Plant Biology Laboratory, The Salk Institute for Biological Studies, La Jolla, CA 92037, USA.
3 The Human BioMolecular Research Institute, 5310 Eastgate Mall, San Diego, CA 92121, USA.
4 Department of Horticultural Science, University of Minnesota, Saint Paul, MN 55108, USA.
* Present address: Department of Molecular, Cell, and Developmental Biology, University of California, Los Angeles, 2124 Life Sciences Box 951606, Los Angeles, CA 90095-1606, USA.
Present address: Department of Molecular Biology, 30 quai Ernest Ansermet, 1211 Geneve 4, Switzerland.
To whom correspondence should be addressed. E-mail: chory@salk.edu
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Abstract 14 of 16
A Plant miRNA Contributes to Antibacterial Resistance by Repressing Auxin Signaling
Lionel Navarro,1,2 Patrice Dunoyer,2 Florence Jay,2 Benedict Arnold,3 Nihal Dharmasiri,4 Mark Estelle,4 Olivier Voinnet,2* Jonathan D. G. Jones1*
Plants and animals activate defenses after perceiving pathogen-associated molecular patterns (PAMPs) such as bacterial flagellin. In Arabidopsis, perception of flagellin increases resistance to the bacterium Pseudomonas syringae, although the molecular mechanisms involved remain elusive. Here, we show that a flagellin-derived peptide induces a plant microRNA (miRNA) that negatively regulates messenger RNAs for the F-box auxin receptors TIR1, AFB2, and AFB3. Repression of auxin signaling restricts P. syringae growth, implicating auxin in disease susceptibility and miRNA-mediated suppression of auxin signaling in resistance.
1 The Sainsbury Laboratory, John Innes Centre, Colney Lane, Norwich NR4 7UH, UK.
2 Institut de Biologie Molèculaire des Plantes du Centre National de la Recherche Scientifique, 67084 Strasbourg Cedex, France.
3 John Innes Centre, Colney Lane, Norwich NR4 7UH, UK.
4 Department of Biology, Indiana University, Bloomington, IN 47405, USA.
* These authors contributed equally to this work.
To whom correspondence should be addressed. E-mail: jonathan.jones@sainsbury-laboratory.ac.uk (J.D.G.J.); olivier.voinnet@ibmp-ulp.u-strasbg.fr (O.V.)
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Abstract 15 of 16
A PINOID-Dependent Binary Switch in Apical-Basal PIN Polar Targeting Directs Auxin Efflux
Jií Friml,1 Xiong Yang,2,3 Marta Michniewicz,1 Dolf Weijers,1,2 Ab Quint,2 Olaf Tietz,4 René Benjamins,2,6 Pieter B. F. Ouwerkerk,2 Karin Ljung,5 Göran Sandberg,5 Paul J. J. Hooykaas,2 Klaus Palme,4 Remko Offringa2*
Polar transport–dependent local accumulation of auxin provides positional cues for multiple plant patterning processes. This directional auxin flow depends on the polar subcellular localization of the PIN auxin efflux regulators. Overexpression of the PINOID protein kinase induces a basal-to-apical shift in PIN localization, resulting in the loss of auxin gradients and strong defects in embryo and seedling roots. Conversely, pid loss of function induces an apical-to-basal shift in PIN1 polar targeting at the inflorescence apex, accompanied by defective organogenesis. Our results show that a PINOID-dependent binary switch controls PIN polarity and mediates changes in auxin flow to create local gradients for patterning processes.
1 Developmental Genetics, Center for Molecular Biology of Plants, University Tübingen, Auf der Morgenstelle 3, D-72076 Tübingen, Germany.
2 Developmental Genetics, Institute of Biology, Leiden University, Clusius Laboratory, Wassenaarseweg 64, 2333 AL Leiden, Netherlands.
3 College of Life Sciences, Peking University, Beijing 100871, China.
4 Albert-Ludwigs-Universität, Biologie II, Schaenzlestrasse 1, D-79104 Freiburg, Germany.
5 Umeå Plant Science Center, Department of Forest and Plant Physiology, Swedish University of Agricultural Sciences, S 901 83 Umeå, Sweden.
6 Institute of Applied Genetics and Cell Biology, BOKU–University of Natural Resources and Applied Life Sciences, Muthgasse 8, A-1190 Vienna, Austria.
* To whom correspondence should be addressed. E-mail: offringa@rulbim.leidenuniv.nl
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Abstract 16 of 16
Interactions of the COP9 Signalosome with the E3 Ubiquitin Ligase SCFTIR1 in Mediating Auxin Response
Claus Schwechheimer,1* Giovanna Serino,1* Judy Callis,2 William L. Crosby,3 Svetlana Lyapina,4 Raymond J. Deshaies,4 William M. Gray,5 Mark Estelle,5 Xing-Wang Deng1
The COP9 signalosome is an evolutionary conserved multiprotein complex of unknown function that acts as a negative regulator of photomorphogenic seedling development in Arabidopsis. Here, we show that plants with reduced COP9 signalosome levels had decreased auxin response similar to loss-of-function mutants of the E3 ubiquitin ligase SCFTIR1. Furthermore, we found that the COP9 signalosome and SCFTIR1 interacted in vivo and that the COP9 signalosome was required for efficient degradation of PSIAA6, a candidate substrate of SCFTIR1. Thus, the COP9 signalosome may play an important role in mediating E3 ubiquitin ligase-mediated responses.
1 Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT 06520-8104, USA.
2 Section of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA.
3 Plant Biotechnology Institute, National Research Council, Saskatoon SK S7N OW9, Canada.
4 Division of Biology, California Institute of Technology, Pasadena, CA 91125, USA.
5 Institute for Molecular and Cellular Biology, Section of Molecular, Cellular, and Developmental Biology, University of Texas, Austin, TX 78712, USA.
* These authors contributed equally to this work.
To whom correspondence should be addressed. E-mail: xingwang.deng@yale.edu
