Publications by authors named "Steffen Abel"

40 Publications

Modulation of Phosphate Deficiency-Induced Metabolic Changes by Iron Availability in .

Int J Mol Sci 2021 Jul 16;22(14). Epub 2021 Jul 16.

Department of Molecular Signal Processing, Leibniz Institute of Plant Biochemistry, Weinberg 3, D-06120 Halle, Germany.

Concurrent suboptimal supply of several nutrients requires the coordination of nutrient-specific transcriptional, phenotypic, and metabolic changes in plants in order to optimize growth and development in most agricultural and natural ecosystems. Phosphate (P) and iron (Fe) deficiency induce overlapping but mostly opposing transcriptional and root growth responses in . On the metabolite level, P deficiency negatively modulates Fe deficiency-induced coumarin accumulation, which is controlled by Fe as well as P deficiency response regulators. Here, we report the impact of Fe availability on seedling growth under P limiting conditions and on P deficiency-induced accumulation of amino acids and organic acids, which play important roles in P use efficiency. Fe deficiency in P replete conditions hardly changed growth and metabolite profiles in roots and shoots of , but partially rescued growth under conditions of P starvation and severely modulated P deficiency-induced metabolic adjustments. Analysis of T-DNA insertion lines revealed the concerted coordination of metabolic profiles by regulators of Fe (FIT, bHLH104, BRUTUS, PYE) as well as of P (SPX1, PHR1, PHL1, bHLH32) starvation responses. The results show the interdependency of P and Fe availability and the interplay between P and Fe starvation signaling on the generation of plant metabolite profiles.
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http://dx.doi.org/10.3390/ijms22147609DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8306678PMC
July 2021

IQ67 DOMAIN proteins facilitate preprophase band formation and division-plane orientation.

Nat Plants 2021 Jun 24;7(6):739-747. Epub 2021 May 24.

Department of Molecular Signal Processing, Leibniz Institute of Plant Biochemistry, Halle (Saale), Germany.

Spatiotemporal control of cell division is essential for the growth and development of multicellular organisms. In plant cells, proper cell plate insertion during cytokinesis relies on the premitotic establishment of the division plane at the cell cortex. Two plant-specific cytoskeleton arrays, the preprophase band (PPB) and the phragmoplast, play important roles in division-plane orientation and cell plate formation, respectively. Microtubule organization and dynamics and their communication with membranes at the cortex and cell plate are coordinated by multiple, mostly distinct microtubule-associated proteins. How division-plane selection and establishment are linked, however, is still unknown. Here, we report members of the Arabidopsis IQ67 DOMAIN (IQD) family as microtubule-targeted proteins that localize to the PPB and phragmoplast and additionally reside at the cell plate and a polarized cortical region including the cortical division zone (CDZ). IQDs physically interact with PHRAGMOPLAST ORIENTING KINESIN (POK) proteins and PLECKSTRIN HOMOLOGY GTPase ACTIVATING (PHGAP) proteins, which are core components of the CDZ. The loss of IQD function impairs PPB formation and affects CDZ recruitment of POKs and PHGAPs, resulting in division-plane positioning defects. We propose that IQDs act as cellular scaffolds that facilitate PPB formation and CDZ set-up during symmetric cell division.
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http://dx.doi.org/10.1038/s41477-021-00923-zDOI Listing
June 2021

Guidelines for the use and interpretation of assays for monitoring autophagy (4th edition).

Autophagy 2021 Jan 8;17(1):1-382. Epub 2021 Feb 8.

University of Crete, School of Medicine, Laboratory of Clinical Microbiology and Microbial Pathogenesis, Voutes, Heraklion, Crete, Greece; Foundation for Research and Technology, Institute of Molecular Biology and Biotechnology (IMBB), Heraklion, Crete, Greece.

In 2008, we published the first set of guidelines for standardizing research in autophagy. Since then, this topic has received increasing attention, and many scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Thus, it is important to formulate on a regular basis updated guidelines for monitoring autophagy in different organisms. Despite numerous reviews, there continues to be confusion regarding acceptable methods to evaluate autophagy, especially in multicellular eukaryotes. Here, we present a set of guidelines for investigators to select and interpret methods to examine autophagy and related processes, and for reviewers to provide realistic and reasonable critiques of reports that are focused on these processes. These guidelines are not meant to be a dogmatic set of rules, because the appropriateness of any assay largely depends on the question being asked and the system being used. Moreover, no individual assay is perfect for every situation, calling for the use of multiple techniques to properly monitor autophagy in each experimental setting. Finally, several core components of the autophagy machinery have been implicated in distinct autophagic processes (canonical and noncanonical autophagy), implying that genetic approaches to block autophagy should rely on targeting two or more autophagy-related genes that ideally participate in distinct steps of the pathway. Along similar lines, because multiple proteins involved in autophagy also regulate other cellular pathways including apoptosis, not all of them can be used as a specific marker for autophagic responses. Here, we critically discuss current methods of assessing autophagy and the information they can, or cannot, provide. Our ultimate goal is to encourage intellectual and technical innovation in the field.
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http://dx.doi.org/10.1080/15548627.2020.1797280DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7996087PMC
January 2021

A cross-kingdom conserved ER-phagy receptor maintains endoplasmic reticulum homeostasis during stress.

Elife 2020 08 27;9. Epub 2020 Aug 27.

Gregor Mendel Institute (GMI), Austrian Academy of Sciences, Vienna BioCenter (VBC), Vienna, Austria.

Eukaryotes have evolved various quality control mechanisms to promote proteostasis in the endoplasmic reticulum (ER). Selective removal of certain ER domains via autophagy (termed as ER-phagy) has emerged as a major quality control mechanism. However, the degree to which ER-phagy is employed by other branches of ER-quality control remains largely elusive. Here, we identify a cytosolic protein, C53, that is specifically recruited to autophagosomes during ER-stress, in both plant and mammalian cells. C53 interacts with ATG8 via a distinct binding epitope, featuring a shuffled ATG8 interacting motif (sAIM). C53 senses proteotoxic stress in the ER lumen by forming a tripartite receptor complex with the ER-associated ufmylation ligase UFL1 and its membrane adaptor DDRGK1. The C53/UFL1/DDRGK1 receptor complex is activated by stalled ribosomes and induces the degradation of internal or passenger proteins in the ER. Consistently, the C53 receptor complex and ufmylation mutants are highly susceptible to ER stress. Thus, C53 forms an ancient quality control pathway that bridges selective autophagy with ribosome-associated quality control in the ER.
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http://dx.doi.org/10.7554/eLife.58396DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7515635PMC
August 2020

Sensitive and Selective Amino Acid Profiling of Minute Tissue Amounts by HPLC/Electrospray Negative Tandem Mass Spectrometry Using 9-Fluorenylmethoxycarbonyl (Fmoc-Cl) Derivatization.

Methods Mol Biol 2019 ;2030:365-379

Department of Molecular Signal Processing, Leibniz Institute of Plant Biochemistry, Halle, Germany.

A method for selective and sensitive quantification of amino acids is described. The combination of established derivatization procedures of secondary and primary amino groups with 9-fluorenylmethoxycarbonyl chloride (Fmoc-Cl) and subsequent detection of derivatized amino acids by LC-ESI-MS/MS using multiple reaction monitoring provides high selectivity. The attachment of an apolar moiety enables purification of derivatized amino acids from matrix by a single solid-phase extraction step, which increases sensitivity by reduced ion suppression during LC-ESI-MS/MS detection. Additionally, chromatography of all amino acids can be performed on reversed-phase HPLC columns using eluents without additives, which are known to cause significant decreases in signal to noise ratios. The method has been routinely applied for amino acid profiling of low amounts of liquids and tissues of various origins with a sample throughput of about 50-100 samples a day. In addition to a detailed description of the method, some representative examples are presented.
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http://dx.doi.org/10.1007/978-1-4939-9639-1_27DOI Listing
April 2020

Iron and Phosphate Deficiency Regulators Concertedly Control Coumarin Profiles in Roots During Iron, Phosphate, and Combined Deficiencies.

Front Plant Sci 2019 11;10:113. Epub 2019 Feb 11.

Department of Molecular Signal Processing, Leibniz Institute of Plant Biochemistry, Halle, Germany.

Plants face varying nutrient conditions, to which they have to adapt to. Adaptive responses are nutrient-specific and strategies to ensure supply and homeostasis for one nutrient might be opposite to another one, as shown for phosphate (P) and iron (Fe) deficiency responses, where many genes are regulated in an opposing manner. This was also observed on the metabolite levels. Whereas root and exudate levels of catechol-type coumarins, phenylpropanoid-derived 2-benzopyranones, which facilitate Fe acquisition, are elevated after Fe deficiency, they are decreased after P deficiency. Exposing plants to combined P and Fe deficiency showed that the generation of coumarin profiles in roots by P deficiency considerably depends on the availability of Fe. Similarly, the effect of Fe deficiency on coumarin profiles is different at low compared to high P availability. These findings suggest a fine-tuning of coumarin profiles, which depends on Fe and P availability. T-DNA insertion lines exhibiting aberrant expression of genes involved in the regulation of P starvation responses () and Fe starvation responses () were used to analyze the regulation of the generation of coumarin profiles in roots by P, Fe, and combined P and Fe deficiency. The analysis revealed a role of several Fe-deficiency response regulators in the regulation of Fe and of P deficiency-induced coumarin profiles as well as for P deficiency response regulators in the regulation of P and of Fe deficiency-induced coumarin profiles. Additionally, the regulation of Fe deficiency-induced coumarin profiles by Fe deficiency response regulators is influenced by P availability. Conversely, regulation of P deficiency-induced coumarin profiles by P deficiency response regulators is modified by Fe availability.
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http://dx.doi.org/10.3389/fpls.2019.00113DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6378295PMC
February 2019

The Local Phosphate Deficiency Response Activates Endoplasmic Reticulum Stress-Dependent Autophagy.

Plant Physiol 2019 02 3;179(2):460-476. Epub 2018 Dec 3.

Department of Molecular Signal Processing, Leibniz Institute of Plant Biochemistry, 06120 Halle (Saale), Germany

Inorganic phosphate (Pi) is often a limiting plant nutrient. In members of the Brassicaceae family, such as Arabidopsis (), Pi deprivation reshapes root system architecture to favor topsoil foraging. It does so by inhibiting primary root extension and stimulating lateral root formation. Root growth inhibition from phosphate (Pi) deficiency is triggered by iron-stimulated, apoplastic reactive oxygen species generation and cell wall modifications, which impair cell-to-cell communication and meristem maintenance. These processes require LOW PHOSPHATE RESPONSE1 (LPR1), a cell wall-targeted ferroxidase, and PHOSPHATE DEFICIENCY RESPONSE2 (PDR2), the single endoplasmic reticulum (ER)-resident P5-type ATPase (AtP5A), which is thought to control LPR1 secretion or activity. Autophagy is a conserved process involving the vacuolar degradation of cellular components. While the function of autophagy is well established under nutrient starvation (C, N, or S), it remains to be explored under Pi deprivation. Because AtP5A/PDR2 likely functions in the ER stress response, we analyzed the effect of Pi limitation on autophagy. Our comparative study of mutants defective in the local Pi deficiency response, ER stress response, and autophagy demonstrated that ER stress-dependent autophagy is rapidly activated as part of the developmental root response to Pi limitation and requires the genetic module. We conclude that Pi-dependent activation of autophagy in the root apex is a consequence of local Pi sensing and the associated ER stress response, rather than a means for systemic recycling of the macronutrient.
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http://dx.doi.org/10.1104/pp.18.01379DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6426416PMC
February 2019

Microtubule-associated protein IQ67 DOMAIN5 regulates morphogenesis of leaf pavement cells in Arabidopsis thaliana.

J Exp Bot 2019 01;70(2):529-543

Department of Molecular Signal Processing, Leibniz Institute of Plant Biochemistry (IPB),Halle (Saale), Germany.

Plant microtubules form a highly dynamic intracellular network with important roles for regulating cell division, cell proliferation, and cell morphology. Their organization and dynamics are co-ordinated by various microtubule-associated proteins (MAPs) that integrate environmental and developmental stimuli to fine-tune and adjust cytoskeletal arrays. IQ67 DOMAIN (IQD) proteins recently emerged as a class of plant-specific MAPs with largely unknown functions. Here, using a reverse genetics approach, we characterize Arabidopsis IQD5 in terms of its expression domains, subcellular localization, and biological functions. We show that IQD5 is expressed mostly in vegetative tissues, where it localizes to cortical microtubule arrays. Our phenotypic analysis of iqd5 loss-of-function lines reveals functions of IQD5 in pavement cell (PC) shape morphogenesis. Histochemical analysis of cell wall composition further suggests reduced rates of cellulose deposition in anticlinal cell walls, which correlate with reduced anisotropic expansion. Lastly, we demonstrate IQD5-dependent recruitment of calmodulin calcium sensors to cortical microtubule arrays and provide first evidence for important roles for calcium in regulation of PC morphogenesis. Our work identifies IQD5 as a novel player in PC shape regulation and, for the first time, links calcium signaling to developmental processes that regulate anisotropic growth in PCs.
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http://dx.doi.org/10.1093/jxb/ery395DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6322583PMC
January 2019

Arabidopsis Transporter ABCG37/PDR9 contributes primarily highly oxygenated Coumarins to Root Exudation.

Sci Rep 2017 06 16;7(1):3704. Epub 2017 Jun 16.

Department of Molecular Signal Processing, Leibniz Institute of Plant Biochemistry, D-06120, Halle (Saale), Germany.

The chemical composition of root exudates strongly impacts the interactions of plants with microorganisms in the rhizosphere and the efficiency of nutrient acquisition. Exudation of metabolites is in part mediated by ATP-binding cassette (ABC) transporters. In order to assess the contribution of individual ABC transporters to root exudation, we performed an LC-MS based non-targeted metabolite profiling of semi-polar metabolites accumulating in root exudates of Arabidopsis thaliana plants and mutants deficient in the expression of ABCG36 (PDR8/PEN3), ABCG37 (PDR9) or both transporters. Comparison of the metabolite profiles indicated distinct roles for each ABC transporter in root exudation. Thymidine exudation could be attributed to ABCG36 function, whereas coumarin exudation was strongly reduced only in ABCG37 deficient plants. However, coumarin exudation was compromised in abcg37 mutants only with respect to certain metabolites of this substance class. The specificity of ABCG37 for individual coumarins was further verified by a targeted LC-MS based coumarin profiling method. The response to iron deficiency, which is known to strongly induce coumarin exudation, was also investigated. In either treatment, the distribution of individual coumarins between roots and exudates in the investigated genotypes suggested the involvement of ABCG37 in the exudation specifically of highly oxygenated rather than monohydroxylated coumarins.
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http://dx.doi.org/10.1038/s41598-017-03250-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5473935PMC
June 2017

Phosphate scouting by root tips.

Authors:
Steffen Abel

Curr Opin Plant Biol 2017 10 17;39:168-177. Epub 2017 May 17.

Department of Molecular Signal Processing, Leibniz Institute of Plant Biochemistry, 06120 Halle, Germany; Department of Plant Sciences, University of California, Davis, CA 95616, USA. Electronic address:

Chemistry assigns phosphate (Pi) dominant roles in metabolism; however, it also renders the macronutrient a genuinely limiting factor of plant productivity. Pi bioavailability is restricted by low Pi mobility in soil and antagonized by metallic toxicities, which force roots to actively seek and selectively acquire the vital element. During the past few years, a first conceptual outline has emerged of the sensory mechanisms at root tips, which monitor external Pi and transmit the edaphic cue to inform root development. This review highlights new aspects of the Pi acquisition strategy of Arabidopsis roots, as well as a framework of local Pi sensing in the context of antagonistic interactions between Pi and its major associated metallic cations, Fe and Al.
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http://dx.doi.org/10.1016/j.pbi.2017.04.016DOI Listing
October 2017

Low phosphate activates STOP1-ALMT1 to rapidly inhibit root cell elongation.

Nat Commun 2017 05 15;8:15300. Epub 2017 May 15.

Laboratoire de Biologie du Développement des Plantes, Institut de Biosciences et Biotechnology Aix-Marseille, Commissariat à l'Energie Atomique et aux énergies alternatives, Saint-Paul-Lez-Durance 13108, France.

Environmental cues profoundly modulate cell proliferation and cell elongation to inform and direct plant growth and development. External phosphate (Pi) limitation inhibits primary root growth in many plant species. However, the underlying Pi sensory mechanisms are unknown. Here we genetically uncouple two Pi sensing pathways in the root apex of Arabidopsis thaliana. First, the rapid inhibition of cell elongation in the transition zone is controlled by transcription factor STOP1, by its direct target, ALMT1, encoding a malate channel, and by ferroxidase LPR1, which together mediate Fe and peroxidase-dependent cell wall stiffening. Second, during the subsequent slow inhibition of cell proliferation in the apical meristem, which is mediated by LPR1-dependent, but largely STOP1-ALMT1-independent, Fe and callose accumulate in the stem cell niche, leading to meristem reduction. Our work uncovers STOP1 and ALMT1 as a signalling pathway of low Pi availability and exuded malate as an unexpected apoplastic inhibitor of root cell wall expansion.
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http://dx.doi.org/10.1038/ncomms15300DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5440667PMC
May 2017

The IQD Family of Calmodulin-Binding Proteins Links Calcium Signaling to Microtubules, Membrane Subdomains, and the Nucleus.

Plant Physiol 2017 03 23;173(3):1692-1708. Epub 2017 Jan 23.

Department of Molecular Signal Processing, Leibniz Institute of Plant Biochemistry, 06120 Halle (Saale), Germany (K.B., R.P., G.S., D.M., S.A.).

Calcium (Ca) signaling and dynamic reorganization of the cytoskeleton are essential processes for the coordination and control of plant cell shape and cell growth. Calmodulin (CaM) and closely related calmodulin-like (CML) polypeptides are principal sensors of Ca signals. CaM/CMLs decode and relay information encrypted by the second messenger via differential interactions with a wide spectrum of targets to modulate their diverse biochemical activities. The plant-specific IQ67 DOMAIN (IQD) family emerged as possibly the largest class of CaM-interacting proteins with undefined molecular functions and biological roles. Here, we show that the 33 members of the IQD family in Arabidopsis () differentially localize, using green fluorescent protein (GFP)-tagged proteins, to multiple and distinct subcellular sites, including microtubule (MT) arrays, plasma membrane subdomains, and nuclear compartments. Intriguingly, the various IQD-specific localization patterns coincide with the subcellular patterns of IQD-dependent recruitment of CaM, suggesting that the diverse IQD members sequester Ca-CaM signaling modules to specific subcellular sites for precise regulation of Ca-dependent processes. Because MT localization is a hallmark of most IQD family members, we quantitatively analyzed GFP-labeled MT arrays in cells transiently expressing GFP-IQD fusions and observed IQD-specific MT patterns, which point to a role of IQDs in MT organization and dynamics. Indeed, stable overexpression of select IQD proteins in Arabidopsis altered cellular MT orientation, cell shape, and organ morphology. Because IQDs share biochemical properties with scaffold proteins, we propose that IQD families provide an assortment of platform proteins for integrating CaM-dependent Ca signaling at multiple cellular sites to regulate cell function, shape, and growth.
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http://dx.doi.org/10.1104/pp.16.01743DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5338658PMC
March 2017

Comparative expression profiling reveals a role of the root apoplast in local phosphate response.

BMC Plant Biol 2016 Apr 28;16:106. Epub 2016 Apr 28.

Department of Molecular Signal Processing, Leibniz Institute of Plant Biochemistry, D-06120, Halle (Saale), Germany.

Background: Plant adaptation to limited phosphate availability comprises a wide range of responses to conserve and remobilize internal phosphate sources and to enhance phosphate acquisition. Vigorous restructuring of root system architecture provides a developmental strategy for topsoil exploration and phosphate scavenging. Changes in external phosphate availability are locally sensed at root tips and adjust root growth by modulating cell expansion and cell division. The functionally interacting Arabidopsis genes, LOW PHOSPHATE RESPONSE 1 and 2 (LPR1/LPR2) and PHOSPHATE DEFICIENCY RESPONSE 2 (PDR2), are key components of root phosphate sensing. We recently demonstrated that the LOW PHOSPHATE RESPONSE 1 - PHOSPHATE DEFICIENCY RESPONSE 2 (LPR1-PDR2) module mediates apoplastic deposition of ferric iron (Fe(3+)) in the growing root tip during phosphate limitation. Iron deposition coincides with sites of reactive oxygen species generation and triggers cell wall thickening and callose accumulation, which interfere with cell-to-cell communication and inhibit root growth.

Results: We took advantage of the opposite phosphate-conditional root phenotype of the phosphate deficiency response 2 mutant (hypersensitive) and low phosphate response 1 and 2 double mutant (insensitive) to investigate the phosphate dependent regulation of gene and protein expression in roots using genome-wide transcriptome and proteome analysis. We observed an overrepresentation of genes and proteins that are involved in the regulation of iron homeostasis, cell wall remodeling and reactive oxygen species formation, and we highlight a number of candidate genes with a potential function in root adaptation to limited phosphate availability. Our experiments reveal that FERRIC REDUCTASE DEFECTIVE 3 mediated, apoplastic iron redistribution, but not intracellular iron uptake and iron storage, triggers phosphate-dependent root growth modulation. We further highlight expressional changes of several cell wall-modifying enzymes and provide evidence for adjustment of the pectin network at sites of iron accumulation in the root.

Conclusion: Our study reveals new aspects of the elaborate interplay between phosphate starvation responses and changes in iron homeostasis. The results emphasize the importance of apoplastic iron redistribution to mediate phosphate-dependent root growth adjustment and suggest an important role for citrate in phosphate-dependent apoplastic iron transport. We further demonstrate that root growth modulation correlates with an altered expression of cell wall modifying enzymes and changes in the pectin network of the phosphate-deprived root tip, supporting the hypothesis that pectins are involved in iron binding and/or phosphate mobilization.
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http://dx.doi.org/10.1186/s12870-016-0790-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4849097PMC
April 2016

Non-targeted profiling of semi-polar metabolites in Arabidopsis root exudates uncovers a role for coumarin secretion and lignification during the local response to phosphate limitation.

J Exp Bot 2016 Mar 17;67(5):1421-32. Epub 2015 Dec 17.

Department of Molecular Signal Processing, Leibniz Institute of Plant Biochemistry, D-06120 Halle (Saale), Germany Institute of Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, D-06120 Halle (Saale), Germany Department of Plant Sciences, University of California-Davis, Davis, CA 95616, USA.

Plants have evolved two major strategies to cope with phosphate (Pi) limitation. The systemic response, mainly comprising increased Pi uptake and metabolic adjustments for more efficient Pi use, and the local response, enabling plants to explore Pi-rich soil patches by reorganization of the root system architecture. Unlike previous reports, this study focused on root exudation controlled by the local response to Pi deficiency. To approach this, a hydroponic system separating the local and systemic responses was developed. Arabidopsis thaliana genotypes exhibiting distinct sensitivities to Pi deficiency could be clearly distinguished by their root exudate composition as determined by non-targeted reversed-phase ultraperformance liquid chromatography electrospray ionization quadrupole-time-of-flight mass spectrometry metabolite profiling. Compared with wild-type plants or insensitive low phosphate root 1 and 2 (lpr1 lpr2) double mutant plants, the hypersensitive phosphate deficiency response 2 (pdr2) mutant exhibited a reduced number of differential features in root exudates after Pi starvation, suggesting the involvement of PDR2-encoded P5-type ATPase in root exudation. Identification and analysis of coumarins revealed common and antagonistic regulatory pathways between Pi and Fe deficiency-induced coumarin secretion. The accumulation of oligolignols in root exudates after Pi deficiency was inversely correlated with Pi starvation-induced lignification at the root tips. The strongest oligolignol accumulation in root exudates was observed for the insensitive lpr1 lpr2 double mutant, which was accompanied by the absence of Pi deficiency-induced lignin deposition, suggesting a role of LPR ferroxidases in lignin polymerization during Pi starvation.
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http://dx.doi.org/10.1093/jxb/erv539DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4762384PMC
March 2016

Structural Biology of Nuclear Auxin Action.

Trends Plant Sci 2016 04 1;21(4):302-316. Epub 2015 Dec 1.

Department of Molecular Signal Processing, Leibniz Institute of Plant Biochemistry, Weinberg 3, D-06120 Halle (Saale), Germany; Institute of Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, Kurt-Mothes-Strasse 3, D-06120 Halle (Saale), Germany; Department of Plant Sciences, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA. Electronic address:

Auxin coordinates plant development largely via hierarchical control of gene expression. During the past decades, the study of early auxin genes paired with the power of Arabidopsis genetics have unraveled key nuclear components and molecular interactions that perceive the hormone and activate primary response genes. Recent research in the realm of structural biology allowed unprecedented insight into: (i) the recognition of auxin-responsive DNA elements by auxin transcription factors; (ii) the inactivation of those auxin response factors by early auxin-inducible repressors; and (iii) the activation of target genes by auxin-triggered repressor degradation. The biophysical studies reviewed here provide an impetus for elucidating the molecular determinants of the intricate interactions between core components of the nuclear auxin response module.
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http://dx.doi.org/10.1016/j.tplants.2015.10.019DOI Listing
April 2016

Perturbations in the Primary Metabolism of Tomato and Arabidopsis thaliana Plants Infected with the Soil-Borne Fungus Verticillium dahliae.

PLoS One 2015 18;10(9):e0138242. Epub 2015 Sep 18.

Leibniz Institute of Vegetable and Ornamental Crops, Theodor-Echtermeyer-Weg 1, 14979 Grossbeeren, Germany.

The hemibiotrophic soil-borne fungus Verticillium dahliae is a major pathogen of a number of economically important crop species. Here, the metabolic response of both tomato and Arabidopsis thaliana to V. dahliae infection was analysed by first using non-targeted GC-MS profiling. The leaf content of both major cell wall components glucuronic acid and xylose was reduced in the presence of the pathogen in tomato but enhanced in A. thaliana. The leaf content of the two tricarboxylic acid cycle intermediates fumaric acid and succinic acid was increased in the leaf of both species, reflecting a likely higher demand for reducing equivalents required for defence responses. A prominent group of affected compounds was amino acids and based on the targeted analysis in the root, it was shown that the level of 12 and four free amino acids was enhanced by the infection in, respectively, tomato and A. thaliana, with leucine and histidine being represented in both host species. The leaf content of six free amino acids was reduced in the leaf tissue of diseased A. thaliana plants, while that of two free amino acids was raised in the tomato plants. This study emphasizes the role of primary plant metabolites in adaptive responses when the fungus has colonized the plant.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0138242PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4575037PMC
June 2016

Solution structure of the PsIAA4 oligomerization domain reveals interaction modes for transcription factors in early auxin response.

Proc Natl Acad Sci U S A 2015 May 27;112(19):6230-5. Epub 2015 Apr 27.

Department of Molecular Signal Processing, Leibniz Institute of Plant Biochemistry, D-06120 Halle, Germany; Institute of Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, D-06120 Halle, Germany; and Department of Plant Sciences, University of California, Davis, CA 95616

The plant hormone auxin activates primary response genes by facilitating proteolytic removal of auxin/indole-3-acetic acid (AUX/IAA)-inducible repressors, which directly bind to transcriptional auxin response factors (ARF). Most AUX/IAA and ARF proteins share highly conserved C-termini mediating homotypic and heterotypic interactions within and between both protein families. The high-resolution NMR structure of C-terminal domains III and IV of the AUX/IAA protein PsIAA4 from pea (Pisum sativum) revealed a globular ubiquitin-like β-grasp fold with homologies to the Phox and Bem1p (PB1) domain. The PB1 domain of wild-type PsIAA4 features two distinct surface patches of oppositely charged amino acid residues, mediating front-to-back multimerization via electrostatic interactions. Mutations of conserved basic or acidic residues on either face suppressed PsIAA4 PB1 homo-oligomerization in vitro and confirmed directional interaction of full-length PsIAA4 in vivo (yeast two-hybrid system). Mixing of oppositely mutated PsIAA4 PB1 monomers enabled NMR mapping of the negatively charged interface of the reconstituted PsIAA4 PB1 homodimer variant, whose stoichiometry (1:1) and equilibrium binding constant (KD ∼ 6.4 μM) were determined by isothermal titration calorimetry. In silico protein-protein docking studies based on NMR and yeast interaction data derived a model of the PsIAA4 PB1 homodimer, which is comparable with other PB1 domain dimers, but indicated considerable differences between the homodimeric interfaces of AUX/IAA and ARF PB1 domains. Our study provides an impetus for elucidating the molecular determinants that confer specificity to complex protein-protein interaction circuits between members of the two central families of transcription factors important to the regulation of auxin-responsive gene expression.
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http://dx.doi.org/10.1073/pnas.1424077112DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4434759PMC
May 2015

Iron-dependent callose deposition adjusts root meristem maintenance to phosphate availability.

Dev Cell 2015 Apr;33(2):216-30

Department of Molecular Signal Processing, Leibniz Institute of Plant Biochemistry, 06120 Halle (Saale), Germany; Institute of Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, 06120 Halle (Saale), Germany; Department of Plant Sciences, University of California, Davis, Davis, CA 95616, USA. Electronic address:

Plant root development is informed by numerous edaphic cues. Phosphate (Pi) availability impacts the root system architecture by adjusting meristem activity. However, the sensory mechanisms monitoring external Pi status are elusive. Two functionally interacting Arabidopsis genes, LPR1 (ferroxidase) and PDR2 (P5-type ATPase), are key players in root Pi sensing, which is modified by iron (Fe) availability. We show that the LPR1-PDR2 module facilitates, upon Pi limitation, cell-specific apoplastic Fe and callose deposition in the meristem and elongation zone of primary roots. Expression of cell-wall-targeted LPR1 determines the sites of Fe accumulation as well as callose production, which interferes with symplastic communication in the stem cell niche, as demonstrated by impaired SHORT-ROOT movement. Antagonistic interactions of Pi and Fe availability control primary root growth via meristem-specific callose formation, likely triggered by LPR1-dependent redox signaling. Our results link callose-regulated cell-to-cell signaling in root meristems to the perception of an abiotic cue.
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http://dx.doi.org/10.1016/j.devcel.2015.02.007DOI Listing
April 2015

Analysis of amino acids by HPLC/electrospray negative ion tandem mass spectrometry using 9-fluorenylmethoxycarbonyl chloride (Fmoc-Cl) derivatization.

Amino Acids 2014 Dec 14;46(12):2799-808. Epub 2014 Sep 14.

Department of Molecular Signal Processing, Institute of Plant Biochemistry, Weinberg 3, 06120, Halle, Germany,

A new method for the determination of amino acids is presented. It combines established methods for the derivatization of primary and secondary amino groups with 9-fluorenylmethoxycarbonyl chloride (Fmoc-Cl) with the subsequent amino acid specific detection of the derivatives by LC-ESI-MS/MS using multiple reaction monitoring (MRM). The derivatization proceeds within 5 min, and the resulting amino acid derivatives can be rapidly purified from matrix by solid-phase extraction (SPE) on HR-X resin and separated by reversed-phase HPLC. The Fmoc derivatives yield several amino acid specific fragment ions which opened the possibility to select amino acid specific MRM transitions. The method was applied to all 20 proteinogenic amino acids, and the quantification was performed using L-norvaline as standard. A limit of detection as low as 1 fmol/µl with a linear range of up to 125 pmol/µl could be obtained. Intraday and interday precisions were lower than 10 % relative standard deviations for most of the amino acids. Quantification using L-norvaline as internal standard gave very similar results compared to the quantification using deuterated amino acid as internal standards. Using this protocol, it was possible to record the amino acid profiles of only a single root from Arabidopsis thaliana seedlings and to compare it with the amino acid profiles of 20 dissected root meristems (200 μm).
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http://dx.doi.org/10.1007/s00726-014-1837-5DOI Listing
December 2014

Simultaneous analysis of apolar phytohormones and 1-aminocyclopropan-1-carboxylic acid by high performance liquid chromatography/electrospray negative ion tandem mass spectrometry via 9-fluorenylmethoxycarbonyl chloride derivatization.

J Chromatogr A 2014 Oct 14;1362:102-9. Epub 2014 Aug 14.

Department of Molecular Signal Processing, Leibniz-Institute of Plant Biochemistry, Weinberg 3, D-06120 Halle, Germany. Electronic address:

A strategy to detect and quantify the polar ethylene precursor 1-aminocyclopropan-1-carboxylic acid (ACC) along with the more apolar phytohormones abscisic acid (ABA), indole-3-acetic acid (IAA), jasmonic acid (JA), jasmonic acid-isoleucine conjugate (JA-Ile), 12-oxo-phytodienoic acid (OPDA), trans-zeatin, and trans-zeatin 9-riboside using a single extraction is presented. Solid phase resins commonly employed for extraction of phytohormones do not allow the recovery of ACC. We circumvent this problem by attaching an apolar group to ACC via derivatization with the amino group specific reagent 9-fluorenylmethoxycarbonyl chloride (Fmoc-Cl). Derivatization in the methanolic crude extract does not modify other phytohormones. The derivatized ACC could be purified and detected together with the more apolar phytohormones using common solid phase extraction resins and reverse phase HPLC/electrospray negative ion tandem mass spectrometry. The limit of detection was in the low nanomolar range for all phytohormones, a sensitivity sufficient to accurately determine the phytohormone levels from less than 50mg (fresh weight) of Arabidopsis thaliana and Nicotiana benthamiana tissues. Comparison with previously published phytohormone levels and the reported changes in phytohormone levels after stress treatments confirmed the accuracy of the method.
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http://dx.doi.org/10.1016/j.chroma.2014.08.029DOI Listing
October 2014

Agrobacterium-derived cytokinin influences plastid morphology and starch accumulation in Nicotiana benthamiana during transient assays.

BMC Plant Biol 2014 May 9;14:127. Epub 2014 May 9.

Abteilung Pflanzen Physiologie, Institut für Biologie-Pflanzenphysiologie, Martin-Luther-Universität Halle-Wittenberg, Weinbergweg 10, Halle/Saale 06120, Germany.

Background: Agrobacterium tumefaciens-based transient assays have become a common tool for answering questions related to protein localization and gene expression in a cellular context. The use of these assays assumes that the transiently transformed cells are observed under relatively authentic physiological conditions and maintain 'normal' sub-cellular behaviour. Although this premise is widely accepted, the question of whether cellular organization and organelle morphology is altered in Agrobacterium-infiltrated cells has not been examined in detail. The first indications of an altered sub-cellular environment came from our observation that a common laboratory strain, GV3101(pMP90), caused a drastic increase in stromule frequency. Stromules, or 'stroma-filled-tubules' emanate from the surface of plastids and are sensitive to a variety of biotic and abiotic stresses. Starting from this observation, the goal of our experiments was to further characterize the changes to the cell resulting from short-term bacterial infestation, and to identify the factor responsible for eliciting these changes.

Results: Using a protocol typical of transient assays we evaluated the impact of GV3101(pMP90) infiltration on chloroplast behaviour and morphology in Nicotiana benthamiana. Our experiments confirmed that GV3101(pMP90) consistently induces stromules and alters plastid position relative to the nucleus. These effects were found to be the result of strain-dependant secretion of cytokinin and its accumulation in the plant tissue. Bacterial production of the hormone was found to be dependant on the presence of a trans-zeatin synthase gene (tzs) located on the Ti plasmid of GV3101(pMP90). Bacteria-derived cytokinins were also correlated with changes to both soluble sugar level and starch accumulation.

Conclusion: Although we have chosen to focus on how transient Agrobacterium infestation alters plastid based parameters, these changes to the morphology and position of a single organelle, combined with the measured increases in sugar and starch content, suggest global changes to cell physiology. This indicates that cells visualized during transient assays may not be as 'normal' as was previously assumed. Our results suggest that the impact of the bacteria can be minimized by choosing Agrobacterium strains devoid of the tzs gene, but that the alterations to sub-cellular organization and cell carbohydrate status cannot be completely avoided using this strategy.
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http://dx.doi.org/10.1186/1471-2229-14-127DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4062310PMC
May 2014

Comparative analysis of Arabidopsis UGT74 glucosyltransferases reveals a special role of UGT74C1 in glucosinolate biosynthesis.

Plant J 2014 Jul 13;79(1):92-105. Epub 2014 Jun 13.

Department of Molecular Signal Processing, Leibniz Institute of Plant Biochemistry, Weinberg 3, 06120, Halle, Germany.

The study of glucosinolates and their regulation has provided a powerful framework for the exploration of fundamental questions about the function, evolution, and ecological significance of plant natural products, but uncertainties about their metabolism remain. Previous work has identified one thiohydroximate S-glucosyltransferase, UGT74B1, with an important role in the core pathway, but also made clear that this enzyme functions redundantly and cannot be the sole UDP-glucose dependent glucosyltransferase (UGT) in glucosinolate synthesis. Here, we present the results of a nearly comprehensive in vitro activity screen of recombinant Arabidopsis Family 1 UGTs, which implicate other members of the UGT74 clade as candidate glucosinolate biosynthetic enzymes. Systematic genetic analysis of this clade indicates that UGT74C1 plays a special role in the synthesis of aliphatic glucosinolates, a conclusion strongly supported by phylogenetic and gene expression analyses. Finally, the ability of UGT74C1 to complement phenotypes and chemotypes of the ugt74b1-2 knockout mutant and to express thiohydroximate UGT activity in planta provides conclusive evidence for UGT74C1 being an accessory enzyme in glucosinolate biosynthesis with a potential function during plant adaptation to environmental challenge.
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http://dx.doi.org/10.1111/tpj.12541DOI Listing
July 2014

The emerging function of IQD proteins as scaffolds in cellular signaling and trafficking.

Plant Signal Behav 2013 Jun 26;8(6):e24369. Epub 2013 Mar 26.

Department of Molecular Signal Processing; Leibniz Institute of Plant Biochemistry; Halle, Germany; Institute of Biochemistry and Biotechnology; Martin-Luther-University Halle-Wittenberg; Halle, Germany; Department of Plant Sciences; University of California-Davis; Davis, USA.

Calcium (Ca(2+)) signaling modules are essential for adjusting plant growth and performance to environmental constraints. Differential interactions between sensors of Ca(2+) dynamics and their molecular targets are at the center of the transduction process. Calmodulin (CaM) and CaM-like (CML) proteins are principal Ca(2+)-sensors in plants that govern the activities of numerous downstream proteins with regulatory properties. The families of IQ67-Domain (IQD) proteins are a large class of plant-specific CaM/CML-targets (e.g., 33 members in A. thaliana) which share a unique domain of multiple varied CaM retention motifs in tandem orientation. Genetic studies in Arabidopsis and tomato revealed first roles for IQD proteins related to basal defense response and plant development. Molecular, biochemical and histochemical analysis of Arabidopsis IQD1 demonstrated association with microtubules as well as targeting to the cell nucleus and nucleolus. In vivo binding to CaM and kinesin light chain-related protein-1 (KLCR1) suggests a Ca(2+)-regulated scaffolding function of IQD1 in kinesin motor-dependent transport of multiprotein complexes. Furthermore, because IQD1 interacts in vitro with single-stranded nucleic acids, the prospect arises that IQD1 and other IQD family members facilitate cellular RNA localization as one mechanism to control and fine-tune gene expression and protein sorting.
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http://dx.doi.org/10.4161/psb.24369DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3909082PMC
June 2013

Arabidopsis calmodulin-binding protein IQ67-domain 1 localizes to microtubules and interacts with kinesin light chain-related protein-1.

J Biol Chem 2013 Jan 30;288(3):1871-82. Epub 2012 Nov 30.

Department of Molecular Signal Processing, Leibniz Institute of Plant Biochemistry, D-06120 Halle, Germany.

Calcium (Ca(2+)) is a key second messenger in eukaryotes and regulates diverse cellular processes, most notably via calmodulin (CaM). In Arabidopsis thaliana, IQD1 (IQ67 domain 1) is the founding member of the IQD family of putative CaM targets. The 33 predicted IQD proteins share a conserved domain of 67 amino acids that is characterized by a unique arrangement of multiple CaM recruitment motifs, including so-called IQ motifs. Whereas IQD1 has been implicated in the regulation of defense metabolism, the biochemical functions of IQD proteins remain to be elucidated. In this study we show that IQD1 binds to multiple Arabidopsis CaM and CaM-like (CML) proteins in vitro and in yeast two-hybrid interaction assays. CaM overlay assays revealed moderate affinity of IQD1 to CaM2 (K(d) ∼ 0.6 μm). Deletion mapping of IQD1 demonstrated the importance of the IQ67 domain for CaM2 binding in vitro, which is corroborated by interaction of the shortest IQD member, IQD20, with Arabidopsis CaM/CMLs in yeast. A genetic screen of a cDNA library identified Arabidopsis kinesin light chain-related protein-1 (KLCR1) as an IQD1 interactor. The subcellular localization of GFP-tagged IQD1 proteins to microtubules and the cell nucleus in transiently and stably transformed plant tissues (tobacco leaves and Arabidopsis seedlings) suggests direct interaction of IQD1 and KLCR1 in planta that is supported by GFP∼IQD1-dependent recruitment of RFP∼KLCR1 and RFP∼CaM2 to microtubules. Collectively, the prospect arises that IQD1 and related proteins provide Ca(2+)/CaM-regulated scaffolds for facilitating cellular transport of specific cargo along microtubular tracks via kinesin motor proteins.
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http://dx.doi.org/10.1074/jbc.M112.396200DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3548496PMC
January 2013

Kinetic analysis of Arabidopsis glucosyltransferase UGT74B1 illustrates a general mechanism by which enzymes can escape product inhibition.

Biochem J 2013 Feb;450(1):37-46

Department of Molecular Signal Processing, Leibniz Institute of Plant Biochemistry, Weinberg 3, 06120 Halle (Saale), Germany.

Plant genomes encode numerous small molecule glycosyltransferases which modulate the solubility, activity, immunogenicity and/or reactivity of hormones, xenobiotics and natural products. The products of these enzymes can accumulate to very high concentrations, yet somehow avoid inhibiting their own biosynthesis. Glucosyltransferase UGT74B1 (UDP-glycosyltransferase 74B1) catalyses the penultimate step in the core biosynthetic pathway of glucosinolates, a group of natural products with important functions in plant defence against pests and pathogens. We found that mutation of the highly conserved Ser284 to leucine [wei9-1 (weak ethylene insensitive)] caused only very mild morphological and metabolic phenotypes, in dramatic contrast with knockout mutants, indicating that steady state glucosinolate levels are actively regulated even in unchallenged plants. Analysis of the effects of the mutation via a structural modelling approach indicated that the affected serine interacts directly with UDP-glucose, but also predicted alterations in acceptor substrate affinity and the kcat value, sparking an interest in the kinetic behaviour of the wild-type enzyme. Initial velocity and inhibition studies revealed that UGT74B1 is not inhibited by its glycoside product. Together with the effects of the missense mutation, these findings are most consistent with a partial rapid equilibrium ordered mechanism. This model explains the lack of product inhibition observed both in vitro and in vivo, illustrating a general mechanism whereby enzymes can continue to function even at very high product/precursor ratios.
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http://dx.doi.org/10.1042/BJ20121403DOI Listing
February 2013

Phosphate sensing in root development.

Authors:
Steffen Abel

Curr Opin Plant Biol 2011 Jun 14;14(3):303-9. Epub 2011 May 14.

Leibniz-Institute of Plant Biochemistry, Halle (Saale), Germany.

Phosphate (Pi) and its anhydrides constitute major nodes in metabolism. Thus, plant performance depends directly on Pi nutrition. Inadequate Pi availability in the rhizosphere is a common challenge to plants, which activate metabolic and developmental responses to maximize Pi usage and acquisition. The sensory mechanisms that monitor environmental Pi and transmit the nutritional signal to adjust root development have increasingly come into focus. Recent transcriptomic analyses and genetic approaches have highlighted complex antagonistic interactions between external Pi and Fe bioavailability and have implicated the stem cell niche as a target of Pi sensing to regulate root meristem activity.
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http://dx.doi.org/10.1016/j.pbi.2011.04.007DOI Listing
June 2011

Chemoenzymatic synthesis of diverse thiohydroximates from glucosinolate-utilizing enzymes from Helix pomatia and Caldicellulosiruptor saccharolyticus.

Biotechnol Lett 2011 May 26;33(5):1039-46. Epub 2011 Jan 26.

Department of Molecular Signal Processing, Leibniz Institute for Plant Biochemistry, 06120 Halle (Saale), Germany.

Thiohydroximates comprise a diverse class of compounds important in both biological and industrial chemistry. Their syntheses are generally limited to simple alkyl and aryl compounds with few stereocenters and a narrow range of functional groups. We hypothesized that sequential action of two recombinant enzymes, a sulfatase from Helix pomatia and a β-O-glucosidase from Caldicellulosiruptor saccharolyticus, on glucosinolates would allow synthesis of thiohydroximates from a structurally broad array of abundant precursors. We report successful synthesis of thiohydroximates of varied chemical classes, including from homochiral compounds of demonstrated biological activity. The chemoenzymatic synthetic route reported here should allow access to many, if not all, of the thiohydroximate core structures of the ~200 known naturally occurring glucosinolates. The enrichment of this group for compounds with possible pharmacological potential is discussed.
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http://dx.doi.org/10.1007/s10529-011-0530-yDOI Listing
May 2011

Odyssey of auxin.

Cold Spring Harb Perspect Biol 2010 Oct 27;2(10):a004572. Epub 2010 Jan 27.

Department of Molecular Signal Processing, Leibniz-Institute of Plant Biochemistry, D-06120 Halle (Saale), Germany.

The history of plant biology is inexorably intertwined with the conception and discovery of auxin, followed by the many decades of research to comprehend its action during growth and development. Growth responses to auxin are complex and require the coordination of auxin production, transport, and perception. In this overview of past auxin research, we limit our discourse to the mechanism of auxin action. We attempt to trace the almost epic voyage from the birth of the hormonal concept in plants to the recent crystallographic studies that resolved the TIR1-auxin receptor complex, the first structural model of a plant hormone receptor. The century-long endeavor is a beautiful illustration of the power of scientific reasoning and human intuition, but it also brings to light the fact that decisive progress is made when new technologies emerge and disciplines unite.
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http://dx.doi.org/10.1101/cshperspect.a004572DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2944356PMC
October 2010

ER-resident proteins PDR2 and LPR1 mediate the developmental response of root meristems to phosphate availability.

Proc Natl Acad Sci U S A 2009 Aug 7;106(33):14174-9. Epub 2009 Aug 7.

Department of Plant Sciences, University of California, One Shields Avenue, Davis, CA 95616, USA.

Inadequate availability of inorganic phosphate (Pi) in the rhizosphere is a common challenge to plants, which activate metabolic and developmental responses to maximize Pi acquisition. The sensory mechanisms that monitor environmental Pi status and regulate root growth via altered meristem activity are unknown. Here, we show that PHOSPHATE DEFICIENCY RESPONSE 2 (PDR2) encodes the single P(5)-type ATPase of Arabidopsis thaliana. PDR2 functions in the endoplasmic reticulum (ER) and is required for proper expression of SCARECROW (SCR), a key regulator of root patterning, and for stem-cell maintenance in Pi-deprived roots. We further show that the multicopper oxidase encoded by LOW PHOSPHATE ROOT 1 (LPR1) is targeted to the ER and that LPR1 and PDR2 interact genetically. Because the expression domains of both genes overlap in the stem-cell niche and distal root meristem, we propose that PDR2 and LPR1 function together in an ER-resident pathway that adjusts root meristem activity to external Pi. Our data indicate that the Pi-conditional root phenotype of pdr2 is not caused by increased Fe availability in low Pi; however, Fe homeostasis modifies the developmental response of root meristems to Pi availability.
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http://dx.doi.org/10.1073/pnas.0901778106DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2723163PMC
August 2009

Auxin is surfacing.

Authors:
Steffen Abel

ACS Chem Biol 2007 Jun;2(6):380-4

Department of Plant Sciences, University of California-Davis, Davis, California 95616, USA.

Indole-3-acetic acid (IAA or auxin) is essential throughout the life cycle of a plant. It controls diverse cellular processes, including gene expression. The hormone is perceived by a ubiquitin protein ligase (E3) and triggers the rapid destruction of repressors, called Aux/IAA proteins. The first structural model of a plant hormone receptor illustrates how auxin promotes Aux/IAA substrate recruitment by extending the hydrophobic protein-interaction surface. This work establishes a novel mechanism of E3 regulation by small molecules and promises a novel strategy for the treatment of human disorders associated with defective ubiquitin-dependent proteolysis.
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http://dx.doi.org/10.1021/cb7001158DOI Listing
June 2007
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