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Ephraim Epstein - One of the best experts on this subject based on the ideXlab platform.
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Indole-3-Butyric Acid in Arabidopsis thaliana
Plant Growth Regulation, 1993Co-Authors: Jutta Ludwig-müller, Ephraim EpsteinAbstract:Indole-3-Butyric Acid (IBA) was metabolized by seedlings of Arabidopsis thaliana cultivated in liquid medium under sterile conditions to two major metabolites. One metabolite was hydrolyzed by 1 N NaOH and β-glucosidase and was tentatively identified as IBA-glucose and the other was hydrolyzed by 7 N NaOH and amidase and was identified as an amide-linked conjugate. IBA-glucose synthase activity was found in a soluble enzyme fraction after incubation of 3H-IBA, IBA and UDP-glucose. The labelled reaction product had an Rf value comparable to IBA glucose and stained positive with Ehmann reagent.
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Transport and metabolism of Indole-3-Butyric Acid in cuttings of Leucadendron discolor
Plant Growth Regulation, 1993Co-Authors: Ephraim Epstein, A. AckermanAbstract:Indole-3-Butyric Acid (IBA) greatly enhanced the rooting of an early-flowering variety of protea, Leucadendron discolor, but had very little effect on a late-flowering variety. IBA transport and metabolism were studied in both varieties after incubating the cuttings in 3H-IBA. More of the radio-label was transported to the leaves of the easy-to-root variety than the difficult-to-root (35–45% and 10%, respectively). IBA was metabolized rapidly by the cuttings of both varieties and after 24 h most of the label was in the new metabolite. However, free IBA (about 10%) was present in the cuttings during the whole period up to the time of root emergence (4 weeks). More free IBA was accumulated in the base of easy-to-root cuttings, while in the difficult-to-root variety most of the IBA was found in the leaves. The metabolite was identified tentatively as an ester conjugate with a glucose. It is possible that IBA-glucose serves as a source for free IBA, and the difference between the varieties is a consequence of the free IBA which is released, transported and accumulated in the site of a root formation.
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Uptake and metabolism of Indole-3-Butyric Acid and indole-3-acetic Acid by Petunia cell suspension culture
Plant Growth Regulation, 1993Co-Authors: Ephraim Epstein, O. Sagee, A. ZelcerAbstract:The uptake and metabolism of indole-3-acetic Acid (IAA) and Indole-3-Butyric Acid (IBA) were studied in suspension cell cultures of Petunia hybrida. The initial uptake of 3H-IBA was much higher than that of 3H-IAA, and after 10 min of incubation with labeled IBA and IAA, 4.6 pM vs 0.35 (39% vs 12% of total applied radioactivity) respectively, were found in the cell extracts. The uptake of IBA reached a plateau of 6.0 pM (62%) after 2 h while that of IAA increased continuously up to 1.5 pM (46%) after 24 h. Following the addition of 40 µM of unlabeled auxin more IBA was taken in initially than IAA (39% vs 12%), but the level almost equalized after 24 h of incubation when IBA uptake reached 890 nM (55%) and IAA 840 nM (46%).
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Indole-3-acetic Acid is converted to Indole-3-Butyric Acid by seedlings of Zea mays L.
Progress in Plant Growth Regulation, 1992Co-Authors: Jutta Ludwig-müller, Ephraim EpsteinAbstract:Indole-3-Butyric Acid (IBA) is the most widely used auxin for inducing rooting in agriculture (Hartmann and Kester, 1983). Several studies have provided evidence for IBA as a natural constituent of plants (Schneideret al.1985; Epsteinet al.1989; Falliket al.1989) but so far little attention has been paid to its metabolism and biosynthesis. Epstein and Lavee (1984) demonstrated that IBA may be converted to IAA in cuttings of grapevine and olives. Andreae and Good (1957) showed that IBA-treated tissues accumulated substances which were tentatively identified as indolebutyramide and indolebutyrylaspartic Acid (IBAsp). Wiesmanet al. (1988) demonstrated that IBA, as well as indole-3acetic Acid (IAA), were rapidly metabolized in mung bean and that conjugation is the major pathway of both substances in this tissue. The IBA conjugates were identified as IBAsp and two high molecular weight conjugates by GC-MS and gel filtration (Wiesmanet al.1989). Here we report about thein vivo andin vitro biosynthesis of IBA in maize seedlings.
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Indole-3-acetic Acid and Indole-3-Butyric Acid in tissues of carrot inoculated with Agrobacterium rhizogenes
Journal of Plant Growth Regulation, 1991Co-Authors: Ephraim Epstein, Scott J. Nissen, Ellen G. SutterAbstract:The role of auxins in induction of roots byAgrobacterium rhizogenes was studied in carrot root disks. Transformed roots were produced on root disks by inoculation withA. rhizogenes, A4. Measurement of indole-3-acetic Acid (IAA) by gas chromatography-mass spectrometry (GC-MS) indicated that there was a significant increase in the concentration of IAA in transformed callus and induced roots compared with initial IAA concentrations in carrot disks. Indole-3-Butyric Acid (IBA) was found to occur naturally in carrot roots. The presence of IBA, a potent root inducer, must be taken into account when assessing the role of auxin during transformation and induction of roots byA. rhizogenes.
Jutta Ludwig-müller - One of the best experts on this subject based on the ideXlab platform.
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ABCG36/PEN3/PDR8 Is an Exporter of the Auxin Precursor, Indole-3-Butyric Acid, and Involved in Auxin-Controlled Development.
Frontiers in plant science, 2019Co-Authors: Bibek Aryal, Jutta Ludwig-müller, John Huynh, Jerôme Schneuwly, Alexandra Siffert, Jie Liu, Santiago Alejandro, Enrico Martinoia, Markus GeislerAbstract:The PDR-type ABCG transporter, ABCG36/PDR8/PEN3, is thought to be implicated in the export of a few structurally unrelated substrates, including the auxin precursor, Indole-3-Butyric Acid (IBA), although a clear-cut proof of transport is lacking. An outward facing, lateral root (LR) location for ABCG36 fuelled speculations that it might secrete IBA into the rhizosphere. Here, we provide strong evidence that ABCG36 catalyzes the export of IBA - but not of indole-3-acetic Acid - through the plasma membrane. ABCG36 seems to function redundantly with the closely related isoform ABCG37/PDR9/PIS1 in a negative control of rootward IBA transport in roots, which might be dampened by concerted, lateral IBA export. Analyses of single and double mutant phenotypes suggest that both ABCG36 and ABCG37 function cooperatively in auxin-controlled plant development. Both seem to possess a dual function in the control of auxin homeostasis in the root tip and long-range transport in the mature root correlating with non-polar and polar expression profiles in the LR cap and epidermis, respectively.
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Analysis of Indole-3-Butyric Acid-induced adventitious root formation on Arabidopsis stem segments.
Journal of experimental botany, 2005Co-Authors: Jutta Ludwig-müller, Amy Vertocnik, Christopher D. TownAbstract:Root induction by auxins is still not well understood at the molecular level. In this study a system has been devised which distinguishes between the two active auxins Indole-3-Butyric Acid (IBA) and indole-3-acetic Acid (IAA). IBA, but not IAA, efficiently induced adventitious rooting in Arabidopsis stem segments at a concentration of 10 microM. In wild-type plants, roots formed exclusively out of calli at the basal end of the segments. Root formation was inhibited by 10 microM 3,4,5-triiodobenzoic Acid (TIBA), an inhibitor of polar auxin transport. At intermediate IBA concentrations (3-10 microM), root induction was less efficient in trp1, a tryptophan auxotroph of Arabidopsis with a bushy phenotype but no demonstrable reduction in IAA levels. By contrast, two mutants of Arabidopsis with measurably higher levels of IAA (trp2, amt1) show root induction characteristics very similar to the wild type. Using differential display, transcripts specific to the rooting process were identified by devising a protocol that distinguished between callus production only and callus production followed by root initiation. One fragment was identical to the sequence of a putative regulatory subunit B of protein phosphatase 2A. It is suggested that adventitious rooting in Arabidopsis stem segments is due to an interaction between endogenous IAA and exogenous IBA. In stem explants, residual endogenous IAA is transported to the basal end of each segment, thereby inducing root formation. In stem segments in which the polar auxin transport is inhibited by TIBA, root formation does not occur.
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Indole‐3‐butyric Acid biosynthesis in maize is enhanced by cyclohexanedione herbicides
Physiologia Plantarum, 2000Co-Authors: Jutta Ludwig-müller, Birgit Schubert, Wilhelm Rademacher, Willy HilgenbergAbstract:It has recently been shown that Indole-3-Butyric Acid (IBA) is formed in maize, via acetylation of indoleacetic Acid, by a microsomal membrane fraction, ATP and acetyl-CoA. A similarity of this reaction to the carboxylation of acetyl-CoA is proposed and therefore the effects of herbicides specific for the inhibition of acetyl-CoA carboxylase were tested on IBA synthesis. Aryloxyphenoxypropionates and cyclohexanediones inhibited the growth of the maize seedlings as predicted, whereas IBA biosynthesis was promoted after the application of cyclohexanediones. Herbicides with different targets, however, did not increase IBA synthesis. IBA synthetase was not influenced in sethoxydim-tolerant maize seedlings as compared to susceptible plants. It was shown that IBA synthetase from dicotyledonous plants was not affected by sethoxydim application, whereas IBA synthesis in wheat was modulated in the same way as in maize.
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Indole-3-Butyric Acid in Arabidopsis thaliana
Plant Growth Regulation, 1993Co-Authors: Jutta Ludwig-müller, Ephraim EpsteinAbstract:Indole-3-Butyric Acid (IBA) was metabolized by seedlings of Arabidopsis thaliana cultivated in liquid medium under sterile conditions to two major metabolites. One metabolite was hydrolyzed by 1 N NaOH and β-glucosidase and was tentatively identified as IBA-glucose and the other was hydrolyzed by 7 N NaOH and amidase and was identified as an amide-linked conjugate. IBA-glucose synthase activity was found in a soluble enzyme fraction after incubation of 3H-IBA, IBA and UDP-glucose. The labelled reaction product had an Rf value comparable to IBA glucose and stained positive with Ehmann reagent.
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Indole-3-acetic Acid is converted to Indole-3-Butyric Acid by seedlings of Zea mays L.
Progress in Plant Growth Regulation, 1992Co-Authors: Jutta Ludwig-müller, Ephraim EpsteinAbstract:Indole-3-Butyric Acid (IBA) is the most widely used auxin for inducing rooting in agriculture (Hartmann and Kester, 1983). Several studies have provided evidence for IBA as a natural constituent of plants (Schneideret al.1985; Epsteinet al.1989; Falliket al.1989) but so far little attention has been paid to its metabolism and biosynthesis. Epstein and Lavee (1984) demonstrated that IBA may be converted to IAA in cuttings of grapevine and olives. Andreae and Good (1957) showed that IBA-treated tissues accumulated substances which were tentatively identified as indolebutyramide and indolebutyrylaspartic Acid (IBAsp). Wiesmanet al. (1988) demonstrated that IBA, as well as indole-3acetic Acid (IAA), were rapidly metabolized in mung bean and that conjugation is the major pathway of both substances in this tissue. The IBA conjugates were identified as IBAsp and two high molecular weight conjugates by GC-MS and gel filtration (Wiesmanet al.1989). Here we report about thein vivo andin vitro biosynthesis of IBA in maize seedlings.
Bonnie Bartel - One of the best experts on this subject based on the ideXlab platform.
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Multiple Facets of Arabidopsis Seedling Development Require Indole-3-Butyric Acid–Derived Auxin
The Plant cell, 2011Co-Authors: Lucia C. Strader, Jerry D. Cohen, Dorthea L. Wheeler, Sarah E. Christensen, John C. Berens, Rebekah A. Rampey, Bonnie BartelAbstract:Levels of auxin, which regulates both cell division and cell elongation in plant development, are controlled by synthesis, inactivation, transport, and the use of storage forms. However, the specific contributions of various inputs to the active auxin pool are not well understood. One auxin precursor is Indole-3-Butyric Acid (IBA), which undergoes peroxisomal β-oxidation to release free indole-3-acetic Acid (IAA). We identified ENOYL-COA HYDRATASE2 (ECH2) as an enzyme required for IBA response. Combining the ech2 mutant with previously identified iba response mutants resulted in enhanced IBA resistance, diverse auxin-related developmental defects, decreased auxin-responsive reporter activity in both untreated and auxin-treated seedlings, and decreased free IAA levels. The decreased auxin levels and responsiveness, along with the associated developmental defects, uncover previously unappreciated roles for IBA-derived IAA during seedling development, establish IBA as an important auxin precursor, and suggest that IBA-to-IAA conversion contributes to the positive feedback that maintains root auxin levels.
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Transport and metabolism of the endogenous auxin precursor Indole-3-Butyric Acid.
Molecular plant, 2011Co-Authors: Lucia C. Strader, Bonnie BartelAbstract:Plant growth and morphogenesis depend on the levels and distribution of the plant hormone auxin. Plants tightly regulate cellular levels of the active auxin indole-3-acetic Acid (IAA) through synthesis, inactivation, and transport. Although the transporters that move IAA into and out of cells are well characterized and play important roles in development, little is known about the transport of IAA precursors. In this review, we discuss the accumulating evidence suggesting that the IAA precursor Indole-3-Butyric Acid (IBA) is transported independently of the characterized IAA transport machinery along with the recent identification of specific IBA efflux carriers and enzymes suggested to metabolize IBA. These studies have revealed important roles for IBA in maintaining IAA levels and distribution within the plant to support normal development.
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Conversion of Endogenous Indole-3-Butyric Acid to Indole-3-Acetic Acid Drives Cell Expansion in Arabidopsis Seedlings
Plant physiology, 2010Co-Authors: Lucia C. Strader, Angela Hendrickson Culler, Jerry D. Cohen, Bonnie BartelAbstract:Genetic evidence in Arabidopsis (Arabidopsis thaliana) suggests that the auxin precursor Indole-3-Butyric Acid (IBA) is converted into active indole-3-acetic Acid (IAA) by peroxisomal beta-oxidation; however, direct evidence that Arabidopsis converts IBA to IAA is lacking, and the role of IBA-derived IAA is not well understood. In this work, we directly demonstrated that Arabidopsis seedlings convert IBA to IAA. Moreover, we found that several IBA-resistant, IAA-sensitive mutants were deficient in IBA-to-IAA conversion, including the Indole-3-Butyric Acid response1 (ibr1) ibr3 ibr10 triple mutant, which is defective in three enzymes likely to be directly involved in peroxisomal IBA beta-oxidation. In addition to IBA-to-IAA conversion defects, the ibr1 ibr3 ibr10 triple mutant displayed shorter root hairs and smaller cotyledons than wild type; these cell expansion defects are suggestive of low IAA levels in certain tissues. Consistent with this possibility, we could rescue the ibr1 ibr3 ibr10 short-root-hair phenotype with exogenous auxin. A triple mutant defective in hydrolysis of IAA-amino Acid conjugates, a second class of IAA precursor, displayed reduced hypocotyl elongation but normal cotyledon size and only slightly reduced root hair lengths. Our data suggest that IBA beta-oxidation and IAA-amino Acid conjugate hydrolysis provide auxin for partially distinct developmental processes and that IBA-derived IAA plays a major role in driving root hair and cotyledon cell expansion during seedling development.
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Conversion of Endogenous Indole-3-Butyric Acid to Indole-3-Acetic Acid Drives Cell Expansion in
2010Co-Authors: Lucia C. Strader, Angela Hendrickson Culler, D. Cohen, Bonnie BartelAbstract:Genetic evidence in Arabidopsis (Arabidopsis thaliana) suggests that the auxin precursor Indole-3-Butyric Acid (IBA) is converted into active indole-3-acetic Acid (IAA) by peroxisomal b-oxidation; however, direct evidence that Arabidopsis converts IBA to IAA is lacking, and the role of IBA-derived IAA is not well understood. In this work, we directly demonstrated that Arabidopsis seedlings convert IBA to IAA. Moreover, we found that several IBA-resistant, IAA-sensitive mutants were deficient in IBA-to-IAA conversion, including the Indole-3-Butyric Acid response1 (ibr1) ibr3 ibr10 triple mutant, which is defective in three enzymes likely to be directly involved in peroxisomal IBA b-oxidation. In addition to IBA-to-IAA conversion defects, the ibr1 ibr3 ibr10 triple mutant displayed shorter root hairs and smaller cotyledons than wild type; these cell expansion defects are suggestive of low IAA levels in certain tissues. Consistent with this possibility, we could rescue the ibr1 ibr3 ibr10 shortroot-hair phenotype with exogenous auxin. A triple mutant defective in hydrolysis of IAA-amino Acid conjugates, a second class of IAA precursor, displayed reduced hypocotyl elongation but normal cotyledon size and only slightly reduced root hair lengths. Our data suggest that IBA b-oxidation and IAA-amino Acid conjugate hydrolysis provide auxin for partially distinct developmental processes and that IBA-derived IAA plays a major role in driving root hair and cotyledon cell expansion during seedling development. The auxin indole-3-acetic Acid (IAA) controls both cell division and cell expansion and thereby orchestrates many developmental events and environmental responses. For example, auxin regulates lateral root initiation, root and stem elongation, and leaf expansion (for review, see Davies, 2004). Normal plant morphogenesis and environmental responses require modulation of auxin levels by controlling biosynthesis, regulating transport, and managing storage forms (for review, see Woodward and Bartel, 2005a). In some storage forms, the carboxyl group of IAA is conjugated to amino Acids or peptides or to sugars, and free IAA
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The Arabidopsis PLEIOTROPIC DRUG RESISTANCE8/ABCG36 ATP Binding Cassette Transporter Modulates Sensitivity to the Auxin Precursor Indole-3-Butyric Acid
The Plant cell, 2009Co-Authors: Lucia C. Strader, Bonnie BartelAbstract:Plants have developed numerous mechanisms to store hormones in inactive but readily available states, enabling rapid responses to environmental changes. The phytohormone auxin has a number of storage precursors, including Indole-3-Butyric Acid (IBA), which is apparently shortened to active indole-3-acetic Acid (IAA) in peroxisomes by a process similar to fatty Acid beta-oxidation. Whereas metabolism of auxin precursors is beginning to be understood, the biological significance of the various precursors is virtually unknown. We identified an Arabidopsis thaliana mutant that specifically restores IBA, but not IAA, responsiveness to auxin signaling mutants. This mutant is defective in PLEIOTROPIC DRUG RESISTANCE8 (PDR8)/PENETRATION3/ABCG36, a plasma membrane-localized ATP binding cassette transporter that has established roles in pathogen responses and cadmium transport. We found that pdr8 mutants display defects in efflux of the auxin precursor IBA and developmental defects in root hair and cotyledon expansion that reveal previously unknown roles for IBA-derived IAA in plant growth and development. Our results are consistent with the possibility that limiting accumulation of the IAA precursor IBA via PDR8-promoted efflux contributes to auxin homeostasis.
Ismail Celik - One of the best experts on this subject based on the ideXlab platform.
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Influence of Indole-3-Butyric Acid on antioxidant defense systems in various tissues of rats at subacute and subchronic exposure.
Food and chemical toxicology : an international journal published for the British Industrial Biological Research Association, 2009Co-Authors: Nuray Topalca, Esref Yegin, Ismail CelikAbstract:This study was carried out to investigate the effects of Indole-3-Butyric Acid (IBA), a plant growth regulator (PGR), on antioxidant defense systems (ADS) such as reduced glutathione (GSH) level and Glutathione-S-transferase (GST), glutathione peroxidase (GSH-Px) superoxide dismutase (SOD) enzymes activity in various tissues of rats exposed to 25 and 50 ppm dosages of IBA for 20 and 45 days. Results showed that the administrations of IBA fluctuated GSH levels in some tissues of rats treated with both dosages and periods. With regard to the ADS enzymes, SOD and GST activities increased significantly in the most of the tissues in rats treated with both dosages and periods of IBA. Also, GSH-Px activity fluctuated after subacute and subchronic exposure with both dosages in some of the tissues in rats compared to that the control rats. The observations presented led us to conclude that the administrations of IBA at subacute and subchronic affected the ADS system in various tissues of rats. This may reflect the potential role of these parameters as useful biomarkers for toxicity of IBA.
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Neurotoxic and immunotoxic effects of Indole-3-Butyric Acid on rats at subacute and subchronic exposure.
Neurotoxicology, 2009Co-Authors: Zeycan Yilmaz, Ismail CelikAbstract:This study was carried out to investigate the neurotoxic and immunotoxic effects of Indole-3-Butyric Acid (IBA), a plant growth regulator (PGR), on rats at subacute and subchronic exposure. The neurotoxic effects of IBA were evaluated by measuring the activities of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Biomarkers selected for immunotoxic monitoring were the activities of adenosine deaminase (ADA) and myeloperoxidase (MPO) in various tissues of rats exposed to 25 and 50 ppm dosages of IBA for 20 and 45 days. Results showed that the administrations of IBA decreased AChE and BChE activities in some tissues of the rats treated with both dosages and periods of IBA. With regard to the immunotoxic effects, ADA activity significantly decreased whereas MPO activity increased after subacute and subchronic exposure with both dosages in most of the tissues of rats compared with controls. The observations presented led us to conclude that the administrations of IBA at subacute and subchronic exposure decreased AChE, BChE and ADA activities whereas increased MPO activity in various tissues of rats. This may reflect the potential role of these parameters as useful biomarkers for toxicity of IBA.
Lucia C. Strader - One of the best experts on this subject based on the ideXlab platform.
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Indole 3-Butyric Acid Metabolism and Transport in Arabidopsis thaliana
Frontiers in plant science, 2019Co-Authors: Suresh Damodaran, Lucia C. StraderAbstract:Auxin is a crucial phytohormone involved in multiple plant developmental processes. Spatiotemporal regulation of auxin levels is necessary to achieve development of organs in the proper place and at the proper time. These levels can be regulated by conversion of auxin [indole 3-acetic Acid (IAA)] from its conjugated forms and its precursors. Indole 3-butyric Acid (IBA) is an auxin precursor that is converted to IAA in a peroxisomal β-oxidation process. In Arabidopsis, altered IBA-to-IAA conversion leads to multiple plant defects, indicating that IBA contributes to auxin homeostasis in critical ways. Like IAA, IBA and its conjugates can be transported in plants, yet many IBA carriers still need to be identified. In this review, we discuss IBA transporters identified in Arabidopsis thus far, including the pleiotropic drug resistance (PDR) members of the G subfamily of ATP-binding cassette transporter (ABCG) family, the TRANSPORTER OF IBA1 (TOB1) member of the major facilitator superfamily (MFS) family and hypothesize other potential IBA carriers involved in plant development.
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Multiple Facets of Arabidopsis Seedling Development Require Indole-3-Butyric Acid–Derived Auxin
The Plant cell, 2011Co-Authors: Lucia C. Strader, Jerry D. Cohen, Dorthea L. Wheeler, Sarah E. Christensen, John C. Berens, Rebekah A. Rampey, Bonnie BartelAbstract:Levels of auxin, which regulates both cell division and cell elongation in plant development, are controlled by synthesis, inactivation, transport, and the use of storage forms. However, the specific contributions of various inputs to the active auxin pool are not well understood. One auxin precursor is Indole-3-Butyric Acid (IBA), which undergoes peroxisomal β-oxidation to release free indole-3-acetic Acid (IAA). We identified ENOYL-COA HYDRATASE2 (ECH2) as an enzyme required for IBA response. Combining the ech2 mutant with previously identified iba response mutants resulted in enhanced IBA resistance, diverse auxin-related developmental defects, decreased auxin-responsive reporter activity in both untreated and auxin-treated seedlings, and decreased free IAA levels. The decreased auxin levels and responsiveness, along with the associated developmental defects, uncover previously unappreciated roles for IBA-derived IAA during seedling development, establish IBA as an important auxin precursor, and suggest that IBA-to-IAA conversion contributes to the positive feedback that maintains root auxin levels.
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Transport and metabolism of the endogenous auxin precursor Indole-3-Butyric Acid.
Molecular plant, 2011Co-Authors: Lucia C. Strader, Bonnie BartelAbstract:Plant growth and morphogenesis depend on the levels and distribution of the plant hormone auxin. Plants tightly regulate cellular levels of the active auxin indole-3-acetic Acid (IAA) through synthesis, inactivation, and transport. Although the transporters that move IAA into and out of cells are well characterized and play important roles in development, little is known about the transport of IAA precursors. In this review, we discuss the accumulating evidence suggesting that the IAA precursor Indole-3-Butyric Acid (IBA) is transported independently of the characterized IAA transport machinery along with the recent identification of specific IBA efflux carriers and enzymes suggested to metabolize IBA. These studies have revealed important roles for IBA in maintaining IAA levels and distribution within the plant to support normal development.
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Conversion of Endogenous Indole-3-Butyric Acid to Indole-3-Acetic Acid Drives Cell Expansion in Arabidopsis Seedlings
Plant physiology, 2010Co-Authors: Lucia C. Strader, Angela Hendrickson Culler, Jerry D. Cohen, Bonnie BartelAbstract:Genetic evidence in Arabidopsis (Arabidopsis thaliana) suggests that the auxin precursor Indole-3-Butyric Acid (IBA) is converted into active indole-3-acetic Acid (IAA) by peroxisomal beta-oxidation; however, direct evidence that Arabidopsis converts IBA to IAA is lacking, and the role of IBA-derived IAA is not well understood. In this work, we directly demonstrated that Arabidopsis seedlings convert IBA to IAA. Moreover, we found that several IBA-resistant, IAA-sensitive mutants were deficient in IBA-to-IAA conversion, including the Indole-3-Butyric Acid response1 (ibr1) ibr3 ibr10 triple mutant, which is defective in three enzymes likely to be directly involved in peroxisomal IBA beta-oxidation. In addition to IBA-to-IAA conversion defects, the ibr1 ibr3 ibr10 triple mutant displayed shorter root hairs and smaller cotyledons than wild type; these cell expansion defects are suggestive of low IAA levels in certain tissues. Consistent with this possibility, we could rescue the ibr1 ibr3 ibr10 short-root-hair phenotype with exogenous auxin. A triple mutant defective in hydrolysis of IAA-amino Acid conjugates, a second class of IAA precursor, displayed reduced hypocotyl elongation but normal cotyledon size and only slightly reduced root hair lengths. Our data suggest that IBA beta-oxidation and IAA-amino Acid conjugate hydrolysis provide auxin for partially distinct developmental processes and that IBA-derived IAA plays a major role in driving root hair and cotyledon cell expansion during seedling development.
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Arabidopsis PIS1 encodes the ABCG37 transporter of auxinic compounds including the auxin precursor Indole-3-Butyric Acid
Proceedings of the National Academy of Sciences of the United States of America, 2010Co-Authors: Kamil Ruzicka, Lucia C. Strader, Aurélien Bailly, Haibing Yang, Joshua J. Blakeslee, Ltukasz Langowski, Eliška Nejedlá, Hironori Fujita, Hironori Itoh, Kunihiko SyonoAbstract:Differential distribution of the plant hormone auxin within tissues mediates a variety of developmental processes. Cellular auxin levels are determined by metabolic processes including synthesis, degradation, and (de)conjugation, as well as by auxin transport across the plasma membrane. Whereas transport of free auxins such as naturally occurring indole-3-acetic Acid (IAA) is well characterized, little is known about the transport of auxin precursors and metabolites. Here, we identify a mutation in the ABCG37 gene of Arabidopsis that causes the polar auxin transport inhibitor sensitive1 (pis1) phenotype manifested by hypersensitivity to auxinic compounds. ABCG37 encodes the pleiotropic drug resistance transporter that transports a range of synthetic auxinic compounds as well as the endogenous auxin precursor Indole-3-Butyric Acid (IBA), but not free IAA. ABCG37 and its homolog ABCG36 act redundantly at outermost root plasma membranes and, unlike established IAA transporters from the PIN and ABCB families, transport IBA out of the cells. Our findings explore possible novel modes of regulating auxin homeostasis and plant development by means of directional transport of the auxin precursor IBA and presumably also other auxin metabolites.