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Katharina Pawlowski - One of the best experts on this subject based on the ideXlab platform.
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accumulation of and response to auxins in roots and nodules of the actinorhizal plant datisca glomerata compared to the model legume medicago truncatula
Frontiers in Plant Science, 2019Co-Authors: Irina V Demina, Pooja Jha Maity, Anurupa Nagchowdhury, Eric Van Der Graaff, Kirill N Demchenko, Thomas Roitsch, Ulrike Mathesius, Katharina PawlowskiAbstract:Actinorhizal nodules are structurally different from legume nodules and show a greater similarity to lateral roots. Because of the important role of auxins in lateral root and nodule formation, auxin profiles were examined in roots and nodules of the actinorhizal species Datisca glomerata and the model legume Medicago truncatula. The auxin response in roots and nodules of both species was analyzed in transgenic root systems expressing a beta-glucuronidase gene under control of the synthetic auxin-responsive promoter DR5. The effects of two different auxin on root development were compared for both species. The auxin present in nodules at the highest levels was phenylacetic acid (PAA). No differences were found between the concentrations of active auxins of roots vs. nodules, while levels of the auxin conjugate indole-3-acetic acid-alanine were increased in nodules compared to roots of both species. Because auxins typically act in concert with cytokinins, cytokinins were also quantified. Concentrations of cis-zeatin and some glycosylated cytokinins were dramatically increased in nodules compared to roots of D. glomerata, but not of M. truncatula. The ratio of active auxins to cytokinins remained similar in nodules compared to roots in both species. The auxin response, as shown by the activation of the DR5 promoter, seemed significantly reduced in nodules compared to roots of both species, suggesting the accumulation of auxins in cell types that do not express the signal transduction pathway leading to DR5 activation. Effects on root development were analyzed for the synthetic auxin naphthaleneacetic acid (NAA) and PAA, the dominant auxin in nodules. Both auxins had similar effects, except that the sensitivity of roots to PAA was lower than to NAA. However, while the effects of both auxins on primary root growth were similar for both species, effects on root branching were different: both auxins had the classical positive effect on root branching in M. truncatula, but a negative effect in D. glomerata. Such a negative effect of exogenous auxin on root branching has previously been found for a cucurbit that forms lateral root primordia in the meristem of the parental root; however, root branching in D. glomerata does not follow that pattern.
Richard M Napier - One of the best experts on this subject based on the ideXlab platform.
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defining binding efficiency and specificity of auxins for scftir1 afb aux iaa co receptor complex formation
ACS Chemical Biology, 2014Co-Authors: Sarah Lee, Stefan Kepinski, Shanthy Sundaram, Lynne Armitage, John Paul Evans, Tim Hawkes, Noel Ferro, Richard M NapierAbstract:Structure-activity profiles for the phytohormone auxin have been collected for over 70 years, and a number of synthetic auxins are used in agriculture. Auxin classification schemes and binding models followed from understanding auxin structures. However, all of the data came from whole plant bioassays, meaning the output was the integral of many different processes. The discovery of Transport Inhibitor-Response 1 (TIR1) and the Auxin F-Box (AFB) proteins as sites of auxin perception and the role of auxin as molecular glue in the assembly of co-receptor complexes has allowed the development of a definitive quantitative structure-activity relationship for TIR1 and AFB5. Factorial analysis of binding activities offered two uncorrelated factors associated with binding efficiency and binding selectivity. The six maximum-likelihood estimators of Efficiency are changes in the overlap matrixes, inferring that Efficiency is related to the volume of the electronic system. Using the subset of compounds that bound strongly, chemometric analyses based on quantum chemical calculations and similarity and self-similarity indices yielded three classes of Specificity that relate to differential binding. Specificity may not be defined by any one specific atom or position and is influenced by coulomb matrixes, suggesting that it is driven by electrostatic forces. These analyses give the first receptor-specific classification of auxins and indicate that AFB5 is the preferred site for a number of auxinic herbicides by allowing interactions with analogues having van der Waals surfaces larger than that of indole-3-acetic acid. The quality factors are also examined in terms of long-standing models for the mechanism of auxin binding.
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defining binding efficiency and specificity of auxins for scf tir1 afb aux iaa co receptor complex formation
ACS Chemical Biology, 2014Co-Authors: Sarah Lee, Stefan Kepinski, Shanthy Sundaram, Lynne Armitage, John Paul Evans, Noel Ferro, Tim R Hawkes, Richard M NapierAbstract:Structure-activity profiles for the phytohormone auxin have been collected for over 70 years, and a number of synthetic auxins are used in agriculture. Auxin classification schemes and binding models followed from understanding auxin structures. However, all of the data came from whole plant bioassays, meaning the output was the integral of many different processes. The discovery of Transport Inhibitor-Response 1 (TIR1) and the Auxin F-Box (AFB) proteins as sites of auxin perception and the role of auxin as molecular glue in the assembly of co-receptor complexes has allowed the development of a definitive quantitative structure-activity relationship for TIR1 and AFB5. Factorial analysis of binding activities offered two uncorrelated factors associated with binding efficiency and binding selectivity. The six maximum-likelihood estimators of Efficiency are changes in the overlap matrixes, inferring that Efficiency is related to the volume of the electronic system. Using the subset of compounds that bound strongly, chemometric analyses based on quantum chemical calculations and similarity and self-similarity indices yielded three classes of Specificity that relate to differential binding. Specificity may not be defined by any one specific atom or position and is influenced by coulomb matrixes, suggesting that it is driven by electrostatic forces. These analyses give the first receptor-specific classification of auxins and indicate that AFB5 is the preferred site for a number of auxinic herbicides by allowing interactions with analogues having van der Waals surfaces larger than that of indole-3-acetic acid. The quality factors are also examined in terms of long-standing models for the mechanism of auxin binding.
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Patch-clamp analysis establishes a role for an auxin binding protein in the auxin stimulation of plasma membrane current in Zea mays protoplasts
The Plant Journal, 1993Co-Authors: Annegret Ruck, Klaus Palme, Richard M Napier, Michael A. Venis, Hubert H. FelleAbstract:The electrical response of Zea mays protoplasts to different auxins and to antibodies raised against an ER-located auxin binding protein from maize (Zm-ERabp1), was investigated using the patch-clamp technique (whole-cell configuration). Following a lag-phase of 30–40 seconds, indole-3-acetic acid and 1-naphthylacetic acid induced an outwardly directed current of positive charge in a concentration-dependent manner. This current was further increased by the fungal toxin fusicoccin (FC). The current was observed only in the presence of Mg2+-ATP in the patch-pipette and was abolished after addition of erythrosin B, an inhibitor of H+-ATPase, to the protoplasts indicating that the plasma membrane H+-ATPase is activated by auxins and fusicoccin. Addition of antibodies directed against Zm-ERabp1 abolished the current induced by auxins, without affecting the response of protoplasts to fusicoccin. Antibodies directed against a peptide representing part of the putative auxin binding domain of Zm-ERabp1 showed auxin agonist activity, stimulating an outwardly directed membrane current in the absence of auxin. These results suggest that (i) Zm-ERabp1 or antigenically related proteins represent a site for auxin perception through which the plasma membrane H+-ATPase is activated, and (ii) that the activation of the H+-ATPase by such proteins is initiated from outside the plasma membrane.
Irina V Demina - One of the best experts on this subject based on the ideXlab platform.
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accumulation of and response to auxins in roots and nodules of the actinorhizal plant datisca glomerata compared to the model legume medicago truncatula
Frontiers in Plant Science, 2019Co-Authors: Irina V Demina, Pooja Jha Maity, Anurupa Nagchowdhury, Eric Van Der Graaff, Kirill N Demchenko, Thomas Roitsch, Ulrike Mathesius, Katharina PawlowskiAbstract:Actinorhizal nodules are structurally different from legume nodules and show a greater similarity to lateral roots. Because of the important role of auxins in lateral root and nodule formation, auxin profiles were examined in roots and nodules of the actinorhizal species Datisca glomerata and the model legume Medicago truncatula. The auxin response in roots and nodules of both species was analyzed in transgenic root systems expressing a beta-glucuronidase gene under control of the synthetic auxin-responsive promoter DR5. The effects of two different auxin on root development were compared for both species. The auxin present in nodules at the highest levels was phenylacetic acid (PAA). No differences were found between the concentrations of active auxins of roots vs. nodules, while levels of the auxin conjugate indole-3-acetic acid-alanine were increased in nodules compared to roots of both species. Because auxins typically act in concert with cytokinins, cytokinins were also quantified. Concentrations of cis-zeatin and some glycosylated cytokinins were dramatically increased in nodules compared to roots of D. glomerata, but not of M. truncatula. The ratio of active auxins to cytokinins remained similar in nodules compared to roots in both species. The auxin response, as shown by the activation of the DR5 promoter, seemed significantly reduced in nodules compared to roots of both species, suggesting the accumulation of auxins in cell types that do not express the signal transduction pathway leading to DR5 activation. Effects on root development were analyzed for the synthetic auxin naphthaleneacetic acid (NAA) and PAA, the dominant auxin in nodules. Both auxins had similar effects, except that the sensitivity of roots to PAA was lower than to NAA. However, while the effects of both auxins on primary root growth were similar for both species, effects on root branching were different: both auxins had the classical positive effect on root branching in M. truncatula, but a negative effect in D. glomerata. Such a negative effect of exogenous auxin on root branching has previously been found for a cucurbit that forms lateral root primordia in the meristem of the parental root; however, root branching in D. glomerata does not follow that pattern.
Jiři Friml - One of the best experts on this subject based on the ideXlab platform.
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plant embryogenesis requires aux lax mediated auxin influx
Development, 2015Co-Authors: Hélène S. Robert, Dolf Weijers, Malcolm J Bennett, Kim Boutilier, Ranjan Swarup, Wim Grunewald, Michael Sauer, Bernard Cannoot, Mercedes Soriano, Jiři FrimlAbstract:The plant hormone auxin and its directional transport are known to play a crucial role in defining the embryonic axis and subsequent development of the body plan. Although the role of PIN auxin efflux transporters has been clearly assigned during embryonic shoot and root specification, the role of the auxin influx carriers AUX1 and LIKE-AUX1 (LAX) proteins is not well established. Here, we used chemical and genetic tools on Brassica napus microspore-derived embryos and Arabidopsis thaliana zygotic embryos, and demonstrate that AUX1, LAX1 and LAX2 are required for both shoot and root pole formation, in concert with PIN efflux carriers. Furthermore, we uncovered a positive-feedback loop between MONOPTEROS (ARF5)-dependent auxin signalling and auxin transport. This MONOPTEROS-dependent transcriptional regulation of auxin influx (AUX1, LAX1 and LAX2) and auxin efflux (PIN1 and PIN4) carriers by MONOPTEROS helps to maintain proper auxin transport to the root tip. These results indicate that auxin-dependent cell specification during embryo development requires balanced auxin transport involving both influx and efflux mechanisms, and that this transport is maintained by a positive transcriptional feedback on auxin signalling.
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cytokinin controls polarity of pin1 dependent auxin transport during lateral root organogenesis
Current Biology, 2014Co-Authors: Jiři Friml, Remko Offringa, Peter Marhavý, Jerome Duclercq, Benjamin Weller, Elena Feraru, Agnieszka Bielach, Claus SchwechheimerAbstract:Summary The plant hormones auxin and cytokinin mutually coordinate their activities to control various aspects of development [1–9], and their crosstalk occurs at multiple levels [10, 11]. Cytokinin-mediated modulation of auxin transport provides an efficient means to regulate auxin distribution in plant organs. Here, we demonstrate that cytokinin does not merely control the overall auxin flow capacity, but might also act as a polarizing cue and control the auxin stream directionality during plant organogenesis. Cytokinin enhances the PIN-FORMED1 (PIN1) auxin transporter depletion at specific polar domains, thus rearranging the cellular PIN polarities and directly regulating the auxin flow direction. This selective cytokinin sensitivity correlates with the PIN protein phosphorylation degree. PIN1 phosphomimicking mutations, as well as enhanced phosphorylation in plants with modulated activities of PIN-specific kinases and phosphatases, desensitize PIN1 to cytokinin. Our results reveal conceptually novel, cytokinin-driven polarization mechanism that operates in developmental processes involving rapid auxin stream redirection, such as lateral root organogenesis, in which a gradual PIN polarity switch defines the growth axis of the newly formed organ.
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efflux dependent auxin gradients establish the apical basal axis of arabidopsis
Nature, 2003Co-Authors: Jiři Friml, Dolf Weijers, Michael Sauer, Anne Vieten, Heinz Schwarz, Thorsten Hamann, Remko Offringa, Gerd JurgensAbstract:Axis formation occurs in plants, as in animals, during early embryogenesis. However, the underlying mechanism is not known. Here we show that the first manifestation of the apical–basal axis in plants, the asymmetric division of the zygote, produces a basal cell that transports and an apical cell that responds to the signalling molecule auxin. This apical–basal auxin activity gradient triggers the specification of apical embryo structures and is actively maintained by a novel component of auxin efflux, PIN7, which is located apically in the basal cell. Later, the developmentally regulated reversal of PIN7 and onset of PIN1 polar localization reorganize the auxin gradient for specification of the basal root pole. An analysis of pin quadruple mutants identifies PIN-dependent transport as an essential part of the mechanism for embryo axis formation. Our results indicate how the establishment of cell polarity, polar auxin efflux and local auxin response result in apical–basal axis formation of the embryo, and thus determine the axiality of the adult plant.
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localization of the auxin permease aux1 suggests two functionally distinct hormone transport pathways operate in the arabidopsis root apex
Genes & Development, 2001Co-Authors: Ranjan Swarup, Klaus Palme, Alan Marchant, Jiři Friml, Göran Sandberg, Karin Ljung, Malcolm J BennettAbstract:Auxins represent an important class of plant hormone that regulate plant development. Plants use specialized carrier proteins to transport the auxin indole-3-acetic acid (IAA) to target tissues. To date, efflux carrier-mediated polar auxin transport has been assumed to represent the sole mode of long distance IAA movement. Localization of the auxin permease AUX1 in the Arabidopsis root apex has revealed a novel phloem-based IAA transport pathway. AUX1, asymmetrically localized to the plasma membrane of root protophloem cells, is proposed to promote the acropetal, post-phloem movement of auxin to the root apex. MS analysis shows that IAA accumulation in aux1 mutant root apices is impaired, consistent with an AUX1 phloem unloading function. AUX1 localization to columella and lateral root cap tissues of the Arabidopsis root apex reveals that the auxin permease regulates a second IAA transport pathway. Expression studies using an auxin-regulated reporter suggest that AUX1 is necessary for root gravitropism by facilitating basipetal auxin transport to distal elongation zone tissues.
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auxin transport inhibitors block pin1 cycling and vesicle trafficking
Nature, 2001Co-Authors: Niko Geldner, Gerd Jurgens, Jiři Friml, York-dieter Stierhof, Klaus PalmeAbstract:Polar transport of the phytohormone auxin mediates various processes in plant growth and development, such as apical dominance, tropisms, vascular patterning and axis formation1,2. This view is based largely on the effects of polar auxin transport inhibitors. These compounds disrupt auxin efflux from the cell but their mode of action is unknown3. It is thought that polar auxin flux is caused by the asymmetric distribution of efflux carriers acting at the plasma membrane4. The polar localization of efflux carrier candidate PIN1 supports this model4. Here we show that the seemingly static localization of PIN1 results from rapid actin-dependent cycling between the plasma membrane and endosomal compartments. Auxin transport inhibitors block PIN1 cycling and inhibit trafficking of membrane proteins that are unrelated to auxin transport. Our data suggest that PIN1 cycling is of central importance for auxin transport and that auxin transport inhibitors affect efflux by generally interfering with membrane-trafficking processes. In support of our conclusion, the vesicle-trafficking inhibitor brefeldin A mimics physiological effects of auxin transport inhibitors.
Gerd Jurgens - One of the best experts on this subject based on the ideXlab platform.
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auxin inhibits endocytosis and promotes its own efflux from cells
Nature, 2005Co-Authors: Tomasz Paciorek, Jan Petrášek, Gerd Jurgens, York-dieter Stierhof, Eva Zazimalova, Nadia Ruthardt, Jurgen Kleinevehn, David A Morris, Neil Emans, Niko GeldnerAbstract:One of the mechanisms by which signalling molecules regulate cellular behaviour is modulating subcellular protein translocation. This mode of regulation is often based on specialized vesicle trafficking, termed constitutive cycling, which consists of repeated internalization and recycling of proteins to and from the plasma membrane. No such mechanism of hormone action has been shown in plants although several proteins, including the PIN auxin efflux facilitators, exhibit constitutive cycling. Here we show that a major regulator of plant development, auxin, inhibits endocytosis. This effect is specific to biologically active auxins and requires activity of the Calossin-like protein BIG. By inhibiting the internalization step of PIN constitutive cycling, auxin increases levels of PINs at the plasma membrane. Concomitantly, auxin promotes its own efflux from cells by a vesicle-trafficking-dependent mechanism. Furthermore, asymmetric auxin translocation during gravitropism is correlated with decreased PIN internalization. Our data imply a previously undescribed mode of plant hormone action: by modulating PIN protein trafficking, auxin regulates PIN abundance and activity at the cell surface, providing a mechanism for the feedback regulation of auxin transport.
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auxin and embryo axis formation the ends in sight
Current Opinion in Plant Biology, 2005Co-Authors: Dolf Weijers, Gerd JurgensAbstract:The major axis of polarity of the plant embryo serves as a reference for the formation of meristems and, thus, for all subsequent development. Mechanisms underlying the establishment of the embryo axis itself have remained elusive. This is now changing with recent reports documenting a role for auxin in embryo axis formation. Auxin accumulates dynamically at specific positions that correlate with developmental decisions in early embryogenesis, and this ties developmental decisions to both transport regulators and components of the response machinery. A major challenge for the future is to determine how auxin-dependent processes interact with other as yet unknown factors to mediate differential gene expression patterns in early embryogenesis.
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partial loss of function alleles reveal a role for gnom in auxin transport related post embryonic development of arabidopsis
Development, 2003Co-Authors: Niko Geldner, Anne Vieten, Sandra Richter, Sebastian Marquardt, Ramon A Torresruiz, Ulrike Mayer, Gerd JurgensAbstract:The Arabidopsis GNOM gene encodes an ARF GDP/GTP exchange factor involved in embryonic axis formation and polar localisation of the auxin efflux regulator PIN1. To examine whether GNOM also plays a role in post-embryonic development and to clarify its involvement in auxin transport, we have characterised newly isolated weak gnom alleles as well as trans-heterozygotes of complementing strong alleles. These genotypes form a phenotypic series of GNOM activity in post-embryonic development, with auxin-related defects, especially in the maintenance of primary root meristem activity and in the initiation and organisation of lateral root primordia. Our results suggest a model for GNOM action mediating auxin transport in both embryogenesis and post-embryonic organ development.
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efflux dependent auxin gradients establish the apical basal axis of arabidopsis
Nature, 2003Co-Authors: Jiři Friml, Dolf Weijers, Michael Sauer, Anne Vieten, Heinz Schwarz, Thorsten Hamann, Remko Offringa, Gerd JurgensAbstract:Axis formation occurs in plants, as in animals, during early embryogenesis. However, the underlying mechanism is not known. Here we show that the first manifestation of the apical–basal axis in plants, the asymmetric division of the zygote, produces a basal cell that transports and an apical cell that responds to the signalling molecule auxin. This apical–basal auxin activity gradient triggers the specification of apical embryo structures and is actively maintained by a novel component of auxin efflux, PIN7, which is located apically in the basal cell. Later, the developmentally regulated reversal of PIN7 and onset of PIN1 polar localization reorganize the auxin gradient for specification of the basal root pole. An analysis of pin quadruple mutants identifies PIN-dependent transport as an essential part of the mechanism for embryo axis formation. Our results indicate how the establishment of cell polarity, polar auxin efflux and local auxin response result in apical–basal axis formation of the embryo, and thus determine the axiality of the adult plant.
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auxin transport inhibitors block pin1 cycling and vesicle trafficking
Nature, 2001Co-Authors: Niko Geldner, Gerd Jurgens, Jiři Friml, York-dieter Stierhof, Klaus PalmeAbstract:Polar transport of the phytohormone auxin mediates various processes in plant growth and development, such as apical dominance, tropisms, vascular patterning and axis formation1,2. This view is based largely on the effects of polar auxin transport inhibitors. These compounds disrupt auxin efflux from the cell but their mode of action is unknown3. It is thought that polar auxin flux is caused by the asymmetric distribution of efflux carriers acting at the plasma membrane4. The polar localization of efflux carrier candidate PIN1 supports this model4. Here we show that the seemingly static localization of PIN1 results from rapid actin-dependent cycling between the plasma membrane and endosomal compartments. Auxin transport inhibitors block PIN1 cycling and inhibit trafficking of membrane proteins that are unrelated to auxin transport. Our data suggest that PIN1 cycling is of central importance for auxin transport and that auxin transport inhibitors affect efflux by generally interfering with membrane-trafficking processes. In support of our conclusion, the vesicle-trafficking inhibitor brefeldin A mimics physiological effects of auxin transport inhibitors.