The Experts below are selected from a list of 339 Experts worldwide ranked by ideXlab platform
Suzanne R. Abrams - One of the best experts on this subject based on the ideXlab platform.
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abscisic Acid acts as a blocker of the bitter taste g protein coupled receptor t2r4
Biochemistry, 2015Co-Authors: Sai Prasad Pydi, Suzanne R. Abrams, Ken M. Nelson, Appalaraju Jaggupilli, Rajinder P Bhullar, Michele C Loewen, Prashen ChelikaniAbstract:Bitter taste receptors (T2Rs) belong to the G protein-coupled receptor superfamily. In humans, 25 T2Rs mediate bitter taste sensation. In addition to the oral cavity, T2Rs are expressed in many extraoral tissues, including the central nervous system, respiratory system, and reproductive system. To understand the mechanistic roles of the T2Rs in oral and extraoral tissues, novel blockers or antagonists are urgently needed. Recently, we elucidated the binding pocket of T2R4 for its agonist quinine, and an antagonist and inhibitory neurotransmitter, γ-aminobutyric Acid. This structure-function information about T2R4 led us to screen the plant hormone abscisic Acid (ABA), its precursor (xanthoxin), and catabolite Phaseic Acid for their ability to bind and activate or inhibit T2R4. Molecular docking studies followed by functional assays involving calcium imaging confirmed that ABA is an antagonist with an IC50 value of 34.4 ± 1.1 μM. However, ABA precursor xanthoxin acts as an agonist on T2R4. Interestingly, molecular model-guided site-directed mutagenesis suggests that the T2R4 residues involved in quinine binding are also predominantly involved in binding to the novel antagonist, ABA. The antagonist ability of ABA was tested using another T2R4 agonist, yohimbine. Our results suggest that ABA does not inhibit yohimbine-induced T2R4 activity. The discovery of natural bitter blockers has immense nutraceutical and physiological significance and will help in dissecting the T2R molecular pathways in various tissues.
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dynamic changes in concentrations of auxin cytokinin aba and selected metabolites in multiple genotypes of douglas fir pseudotsuga menziesii during a growing season
Tree Physiology, 2008Co-Authors: Lisheng Kong, Suzanne R. Abrams, Stacey J Owen, Annette Van Niejenhuis, Patrick Von AderkasAbstract:Changes in concentrations of several endogenous phytohormones and metabolites were analyzed in the long shoots of nine genotypes of coastal Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) at five developmental stages: (1) closed buds, (2) flushing buds, (3) rapidly elongating shoots, (4) growing shoots and (5) near full-length shoots during one growing season. When averaged across genotypes, indole-3-acetic Acid (IAA) concentration was high at stages 1 and 3. The only pattern that correlated with cone productivity was the one that was unique to IAA, in which high concentrations at stages 3 and 4 were found in all genotypes with high female cone productivity. Concentrations of isopentenyl adenosine (iPA) decreased and zeatin riboside (ZR) concentrations increased as the buds initiated and differentiated; ZR was 30 and 28 ng g(-1) dry weight (DW) at stages 1 and 4, respectively, before increasing to 166 ng g(-1) DW at stage 5. Isopentenyl adenosine peaked at 92 ng g(-1) DW at stage 2 and declined to low concentrations at stages 4 and 5. Zeatin-O-glucoside was 30 ng g(-1) DW at stage 1, declined at stages 2 and 3 and increased at stages 4 and 5. High abscisic Acid (ABA) concentrations were positively correlated with rapid shoot elongation (stages 1 and 2), but as growth slowed and terminated, ABA concentrations decreased. Abscisic Acid was 7 microg g(-1) DW at stage 1, increased to 13 microg g(-1) DW at stage 2 and then declined. The glucosyl ester (GE) of ABA decreased rapidly in early summer, and increased inversely with an increase in ABA. Between stages 1 and 2, ABA-GE decreased from 10 to 0.2 microg g(-1) DW and then increased. Of the ABA catabolites studied, 7'-hydroxy-ABA was about 2 microg g(-1) DW at stage 1, declined at stages 2 and 3 and increased at stages 4 and 5; Phaseic Acid concentrations were low at all stages, whereas dihydroPhaseic Acid was detected only at stages 4 and 5.
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use of the glucosyltransferase ugt71b6 to disturb abscisic Acid homeostasis in arabidopsis thaliana
Plant Journal, 2006Co-Authors: David M Priest, Suzanne R. Abrams, Stephen J Ambrose, Andrew R S Ross, Fabian E Vaistij, Luisa Elias, Gillian S Higgins, Dianna J BowlesAbstract:A glucosyltransferase (GT) of Arabidopsis, UGT71B6, recognizing the naturally occurring enantiomer of abscisic Acid (ABA) in vitro, has been used to disturb ABA homeostasis in planta. Transgenic plants constitutively overexpressing UGT71B6 (71B6-OE) have been analysed for changes in ABA and the related ABA metabolites abscisic Acid glucose ester (ABA-GE), Phaseic Acid (PA), dihydroPhaseic Acid (DPA), 7'-hydroxyABA and neo-Phaseic Acid. Overexpression of the GT led to massive accumulation of ABA-GE and reduced levels of the oxidative metabolites PA and DPA, but had marginal effect on levels of free ABA. The control of ABA homeostasis, as reflected in levels of the different metabolites, differed in the 71B6-OEs whether the plants were grown under standard conditions or subjected to wilt stress. The impact of increased glucosylation of ABA on ABA-related phenotypes has also been assessed. Increased glucosylation of ABA led to phenotypic changes in post-germinative growth. The use of two structural analogues of ABA, known to have biological activity but to differ in their capacity to act as substrates for 71B6 in vitro, confirmed that the phenotypic changes arose specifically from the increased glucosylation caused by overexpression of 71B6. The phenotype and profile of ABA and related metabolites in a knockout line of 71B6, relative to wild type, has been assessed during Arabidopsis development and following stress treatments. The lack of major changes in these parameters is discussed in the context of functional redundancy of the multigene family of GTs in Arabidopsis.
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purification and characterization of a barley aleurone abscisic Acid binding protein
Journal of Biological Chemistry, 2004Co-Authors: Fawzi A Razem, Suzanne R. Abrams, Ma Luo, Jinhao Liu, Robert D HillAbstract:Abstract A protein designated ABAP1 and encoded by a novel gene (GenBank™ accession number AF127388) was purified and shown to specifically bind abscisic Acid (ABA). ABAP1 protein is a 472-amino Acid polypeptide containing a WW protein interaction domain and is induced by ABA in barley aleurone layers. Polyclonal antiidiotypic antibodies (AB2) cross-reacted with purified ABAP1 and with a corresponding 52-kDa protein associated with membrane fractions of ABA-treated barley aleurones. ABAP1 genes were detected in diverse monocot and dicot species, including wheat, tobacco, alfalfa, garden pea, and oilseed rape. The recombinant ABAP1 protein optimally bound 3H-(+)-ABA at neutral pH. Denatured ABAP1 protein did not bind 3H-(+)-ABA, nor did bovine serum albumin. The maximum specific binding as shown by Scatchard plot analysis was 0.8 mol of ABA mol–1 protein with a linear function of r2 = 0.94, an indication of one ABA-binding site with a dissociation constant (Kd) of 28 × 10–9 m. ABA binding in aleurone plasma membranes showed a maximum binding capacity of 330 nmol of ABA g–1 protein with a Kd of 26.5 × 10–9 m. The similarities in the dissociation constants for ABA binding of the recombinant protein and that of the plasma membranes suggest that the protein within the plasma membrane fraction is the native form of ABAP1. The stereospecificity of ABAP1 was established by the incapability of ABA analogs and metabolites, including (–)-ABA, trans-ABA, Phaseic Acid, dihydroPhaseic Acid, and (+)-abscisic Acid-glucose ester, to displace 3H-(+)-ABA bound to ABAP1. However, two ABA precursors, (+)-ABA aldehyde and (+)-ABA alcohol, were able to displace 3H-(+)-ABA, an indication that the structural requirement of ABAP1 at the C-1 position is not strict. Our data show that ABAP1 exerts high binding affinity for ABA. The interaction is reversible, follows saturation kinetics, and has stereospecificity, thus meeting the criteria for an ABA-binding protein.
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Dormancy termination of western white pine (Pinus monticola Dougl. Ex D. Don) seeds is associated with changes in abscisic Acid metabolism
Planta, 2004Co-Authors: J. Allan Feurtado, Adrian J. Cutler, Suzanne R. Abrams, Stephen J Ambrose, Andrew R S Ross, Allison R KermodeAbstract:Western white pine ( Pinus monticola ) seeds exhibit deep dormancy at maturity and seed populations require several months of moist chilling to reach their uppermost germination capacities. Abscisic Acid (ABA) and its metabolites, Phaseic Acid (PA), dihydroPhaseic Acid (DPA), 7′-hydroxy ABA (7′OH ABA) and ABA-glucose ester (ABA-GE), were quantified in western white pine seeds during dormancy breakage (moist chilling) and germination using an HPLC–tandem mass spectrometry method with multiple reaction monitoring and internal standards incorporating deuterium-labeled analogs. In the seed coat, ABA and metabolite levels were high in dry seeds, but declined precipitously during the pre-moist-chilling water soak to relatively low levels thereafter. In the embryo and megagametophyte, ABA levels decreased significantly during moist chilling, coincident with an increase in the germination capacity of seeds. ABA catabolism occurred via several routes, depending on the stage and the seed tissue. Moist chilling of seeds led to increases in PA and DPA levels in both the embryo and megagametophyte. Within the embryo, 7′OH ABA and ABA-GE also accumulated during moist chilling; however, 7′OH ABA peaked early in germination. Changes in ABA flux, i.e. shifts in the ratio between biosynthesis and catabolism, occurred at three distinct stages during the transition from dormant seed to seedling. During moist chilling, the relative rate of ABA catabolism exceeded ABA biosynthesis. This trend became even more pronounced during germination, and germination was also accompanied by a decrease in the ABA catabolites DPA and PA, presumably as a result of their further metabolism and/or leaching/transport. The transition from germination to post-germinative growth was accompanied by a shift toward ABA biosynthesis. Dormant imbibed seeds, kept in warm moist conditions for 30 days (after an initial 13 days of soaking), maintained high ABA levels, while the amounts of PA, 7′OH ABA, and DPA decreased or remained at steady-state levels. Thus, in the absence of conditions required to break dormancy there were no net changes in ABA biosynthesis and catabolism.
Adrian J. Cutler - One of the best experts on this subject based on the ideXlab platform.
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Dormancy termination of western white pine (Pinus monticola Dougl. Ex D. Don) seeds is associated with changes in abscisic Acid metabolism
Planta, 2004Co-Authors: J. Allan Feurtado, Adrian J. Cutler, Suzanne R. Abrams, Stephen J Ambrose, Andrew R S Ross, Allison R KermodeAbstract:Western white pine ( Pinus monticola ) seeds exhibit deep dormancy at maturity and seed populations require several months of moist chilling to reach their uppermost germination capacities. Abscisic Acid (ABA) and its metabolites, Phaseic Acid (PA), dihydroPhaseic Acid (DPA), 7′-hydroxy ABA (7′OH ABA) and ABA-glucose ester (ABA-GE), were quantified in western white pine seeds during dormancy breakage (moist chilling) and germination using an HPLC–tandem mass spectrometry method with multiple reaction monitoring and internal standards incorporating deuterium-labeled analogs. In the seed coat, ABA and metabolite levels were high in dry seeds, but declined precipitously during the pre-moist-chilling water soak to relatively low levels thereafter. In the embryo and megagametophyte, ABA levels decreased significantly during moist chilling, coincident with an increase in the germination capacity of seeds. ABA catabolism occurred via several routes, depending on the stage and the seed tissue. Moist chilling of seeds led to increases in PA and DPA levels in both the embryo and megagametophyte. Within the embryo, 7′OH ABA and ABA-GE also accumulated during moist chilling; however, 7′OH ABA peaked early in germination. Changes in ABA flux, i.e. shifts in the ratio between biosynthesis and catabolism, occurred at three distinct stages during the transition from dormant seed to seedling. During moist chilling, the relative rate of ABA catabolism exceeded ABA biosynthesis. This trend became even more pronounced during germination, and germination was also accompanied by a decrease in the ABA catabolites DPA and PA, presumably as a result of their further metabolism and/or leaching/transport. The transition from germination to post-germinative growth was accompanied by a shift toward ABA biosynthesis. Dormant imbibed seeds, kept in warm moist conditions for 30 days (after an initial 13 days of soaking), maintained high ABA levels, while the amounts of PA, 7′OH ABA, and DPA decreased or remained at steady-state levels. Thus, in the absence of conditions required to break dormancy there were no net changes in ABA biosynthesis and catabolism.
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a method for profiling classes of plant hormones and their metabolites using liquid chromatography electrospray ionization tandem mass spectrometry an analysis of hormone regulation of thermodormancy of lettuce lactuca sativa l seeds
Plant Journal, 2003Co-Authors: Sheila Chiwocha, Adrian J. Cutler, Suzanne R. Abrams, Stephen J Ambrose, Mary K Loewen, Andrew R S Ross, Allison R KermodeAbstract:A highly selective and sensitive method for the simultaneous analysis of several plant hormones and their metabolites is described. The method combines high-performance liquid chromatography (HPLC) with positive and negative electrospray ionization-tandem mass spectrometry (ESI-MS/MS) to quantify a broad range of chemically and structurally diverse compounds. The addition of deuterium-labeled analogs for these compounds prior to sample extraction permits accurate quantification by multiple reaction monitoring (MRM). Endogenous levels of abscisic Acid (ABA), abscisic Acid glucose ester (ABA-GE), 7'-hydroxy-abscisic Acid (7'-OH-ABA), Phaseic Acid (PA), dihydroPhaseic Acid (DPA), indole-3-acetic Acid (IAA), indole-3-aspartate (IAAsp), zeatin (Z), zeatin riboside (ZR), isopentenyladenine (2iP), isopentenyladenosine (IPA), and gibberellins (GA)1, GA3, GA4, and GA7 were determined simultaneously in a single run. Detection limits ranged from 0.682 fmol for Z to 1.53 pmol for ABA. The method was applied to the analysis of plant hormones and hormonal metabolites associated with seed dormancy and germination in lettuce (Lactuca sativa L. cv. Grand Rapids), using extracts from only 50 to 100 mg DW of seed. Thermodormancy was induced by incubating seeds at 33 degrees C instead of 23 degrees C. Germinating seeds transiently accumulated high levels of ABA-GE. In contrast, thermodormant seeds transiently accumulated high levels of DPA after 7 days at 33 degrees C. GA1 and GA3 were detected during germination, and levels of GA1 increased during early post-germinative growth. After several days of incubation, thermodormant seeds exhibited a striking transient accumulation of IAA, which did not occur in seeds germinating at 23 degrees C. We conclude that hormone metabolism in thermodormant seeds is surprisingly active and is significantly different from that of germinating seeds.
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Journal of Experimental Botany Induction of (H-)-abscisic Acid 8 hydroxylase by
1997Co-Authors: Adrian J. Cutler, Mary K Loewen, Timothy M. Squires, John J. BalsevichAbstract:In vivo measurements of the enzymatic hydroxylation of the phytohormone (+)-abscisic Acid to hormonally inactive (—)-Phaseic Acid in corn cell cultures revealed that ( +)-abscisic Acid 8 ' hydroxylase activity was induced by (+)-abscisic Acid treatment. This induction was blocked by the protein synthesis inhibitor cyclo-heximide and by the transcription inhibitor cordycepin. Following an induction treatment with abscisic Acid, the amount of induced enzyme was measured by addi-tion of both cycloheximide, to prevent further induc-tion, and fresh abscisic Acid as substrate for the induced enzyme. Phaseic Acid production was related to the amount of enzyme induced. The experimental system was optimized for studying enzyme induction and the substrate specificity of the induced enzyme. The induced 8 ' hydroxylase was specific for (+)-abscisic Acid, whereas the low basal activity also hydroxylated (—)-abscisic Acid at the 7 ' position to form 7-hydroxy abscisic Acid. After induction, the 8' hydroxylase was rapidly degraded with a half-life of approximately 2 h. Phaseic and (—(-abscisic Acid were weak inducers; however, the unstable oxidation prod-uct 8-hydroxy abscisic Acid exhibited 42 % of the activ-ity of (+)-abscisic Acid. When corn cells were placed under water stress by increasing concentrations of mannitol in the culture medium, 8 ' hydroxylase induc-tion was suppressed. The experimental system described will be useful for further studies of the physiological and hormonal factors that modulate abscisic Acid metabolism and for testing potential enzyme inhibitors and hormone analogues. Key words: ABA-induced gene, 8 ' hydroxy ABA, Phaseic Acid, water stress, ABA homeostasis
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Response of Cultured Maize Cells to (+)-Abscisic Acid, (-)-Abscisic Acid, and Their Metabolites.
Plant physiology, 1994Co-Authors: J. J. Balsevich, L. J. Friesen, E. U. Kurz, M. R. Perras, N Lamb, Adrian J. Cutler, Suzanne R. AbramsAbstract:The metabolism and effects of (+)-S- and (-)-R-abscisic Acid (ABA) and some metabolites were studied in maize (Zea mays L. cv Black Mexican Sweet) suspension-cultured cells. Time-course studies of metabolite formation were performed in both cells and medium via analytical high-performance liquid chromatography. Metabolites were isolated and identified using physical and chemical methods. At 10 [mu]M concentration and 28[deg] C, (+)-ABA was metabolized within 24 h, yielding natural (-)-Phaseic Acid [(-)-PA] as the major product. The unnatural enantiomer (-)-ABA was less than 50% metabolized within 24 h and gave primarily (-)-7[prime]-hydroxyABA [(-)-7[prime]-HOABA], together with (+)-PA and ABA glucose ester. The distribution of metabolites in cells and medium was different, reflecting different sites of metabolism and membrane permeabilities of conjugated and nonconjugated metabolites. The results imply that (+)-ABA was oxidized to (-)-PA inside the cell, whereas (-)-ABA was converted to (-)-7[prime]-HOABA at the cell surface. Growth of maize cells was inhibited by both (+)- and (-)-ABA, with only weak contributions from their metabolites. The concentration of (+)-ABA that caused a 50% inhibition of growth of maize cells was approximately 1 [mu]M, whereas that for its metabolite (-)-PA was approximately 50 [mu]M. (-)-ABA was less active than (+)-ABA, with 50% growth inhibition observed at about 10 [mu]M. (-)-7[prime]-HOABA was only weakly active, with 50% inhibition caused by approximately 500 [mu]M. Time-course studies of medium pH indicated that (+)-ABA caused a transient pH increase (+0.3 units) at 6 h after addition that was not observed in controls or in samples treated with (-)-PA. The effect of (-)-ABA on medium Ph was marginal. No racemization at C-1[prime] of (+)-ABA, (-)-ABA, or metabolites was observed during the studies.
Prashen Chelikani - One of the best experts on this subject based on the ideXlab platform.
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abscisic Acid acts as a blocker of the bitter taste g protein coupled receptor t2r4
Biochemistry, 2015Co-Authors: Sai Prasad Pydi, Suzanne R. Abrams, Ken M. Nelson, Appalaraju Jaggupilli, Rajinder P Bhullar, Michele C Loewen, Prashen ChelikaniAbstract:Bitter taste receptors (T2Rs) belong to the G protein-coupled receptor superfamily. In humans, 25 T2Rs mediate bitter taste sensation. In addition to the oral cavity, T2Rs are expressed in many extraoral tissues, including the central nervous system, respiratory system, and reproductive system. To understand the mechanistic roles of the T2Rs in oral and extraoral tissues, novel blockers or antagonists are urgently needed. Recently, we elucidated the binding pocket of T2R4 for its agonist quinine, and an antagonist and inhibitory neurotransmitter, γ-aminobutyric Acid. This structure-function information about T2R4 led us to screen the plant hormone abscisic Acid (ABA), its precursor (xanthoxin), and catabolite Phaseic Acid for their ability to bind and activate or inhibit T2R4. Molecular docking studies followed by functional assays involving calcium imaging confirmed that ABA is an antagonist with an IC50 value of 34.4 ± 1.1 μM. However, ABA precursor xanthoxin acts as an agonist on T2R4. Interestingly, molecular model-guided site-directed mutagenesis suggests that the T2R4 residues involved in quinine binding are also predominantly involved in binding to the novel antagonist, ABA. The antagonist ability of ABA was tested using another T2R4 agonist, yohimbine. Our results suggest that ABA does not inhibit yohimbine-induced T2R4 activity. The discovery of natural bitter blockers has immense nutraceutical and physiological significance and will help in dissecting the T2R molecular pathways in various tissues.
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Abscisic Acid Acts as a Blocker of the Bitter Taste G Protein-Coupled Receptor T2R4
2015Co-Authors: Sai Prasad Pydi, Ken M. Nelson, Appalaraju Jaggupilli, Rajinder P Bhullar, Michele C Loewen, Suzanne R. Abrams, Prashen ChelikaniAbstract:Bitter taste receptors (T2Rs) belong to the G protein-coupled receptor superfamily. In humans, 25 T2Rs mediate bitter taste sensation. In addition to the oral cavity, T2Rs are expressed in many extraoral tissues, including the central nervous system, respiratory system, and reproductive system. To understand the mechanistic roles of the T2Rs in oral and extraoral tissues, novel blockers or antagonists are urgently needed. Recently, we elucidated the binding pocket of T2R4 for its agonist quinine, and an antagonist and inhibitory neurotransmitter, γ-aminobutyric Acid. This structure–function information about T2R4 led us to screen the plant hormone abscisic Acid (ABA), its precursor (xanthoxin), and catabolite Phaseic Acid for their ability to bind and activate or inhibit T2R4. Molecular docking studies followed by functional assays involving calcium imaging confirmed that ABA is an antagonist with an IC50 value of 34.4 ± 1.1 μM. However, ABA precursor xanthoxin acts as an agonist on T2R4. Interestingly, molecular model-guided site-directed mutagenesis suggests that the T2R4 residues involved in quinine binding are also predominantly involved in binding to the novel antagonist, ABA. The antagonist ability of ABA was tested using another T2R4 agonist, yohimbine. Our results suggest that ABA does not inhibit yohimbine-induced T2R4 activity. The discovery of natural bitter blockers has immense nutraceutical and physiological significance and will help in dissecting the T2R molecular pathways in various tissues
Michele C Loewen - One of the best experts on this subject based on the ideXlab platform.
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abscisic Acid acts as a blocker of the bitter taste g protein coupled receptor t2r4
Biochemistry, 2015Co-Authors: Sai Prasad Pydi, Suzanne R. Abrams, Ken M. Nelson, Appalaraju Jaggupilli, Rajinder P Bhullar, Michele C Loewen, Prashen ChelikaniAbstract:Bitter taste receptors (T2Rs) belong to the G protein-coupled receptor superfamily. In humans, 25 T2Rs mediate bitter taste sensation. In addition to the oral cavity, T2Rs are expressed in many extraoral tissues, including the central nervous system, respiratory system, and reproductive system. To understand the mechanistic roles of the T2Rs in oral and extraoral tissues, novel blockers or antagonists are urgently needed. Recently, we elucidated the binding pocket of T2R4 for its agonist quinine, and an antagonist and inhibitory neurotransmitter, γ-aminobutyric Acid. This structure-function information about T2R4 led us to screen the plant hormone abscisic Acid (ABA), its precursor (xanthoxin), and catabolite Phaseic Acid for their ability to bind and activate or inhibit T2R4. Molecular docking studies followed by functional assays involving calcium imaging confirmed that ABA is an antagonist with an IC50 value of 34.4 ± 1.1 μM. However, ABA precursor xanthoxin acts as an agonist on T2R4. Interestingly, molecular model-guided site-directed mutagenesis suggests that the T2R4 residues involved in quinine binding are also predominantly involved in binding to the novel antagonist, ABA. The antagonist ability of ABA was tested using another T2R4 agonist, yohimbine. Our results suggest that ABA does not inhibit yohimbine-induced T2R4 activity. The discovery of natural bitter blockers has immense nutraceutical and physiological significance and will help in dissecting the T2R molecular pathways in various tissues.
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Abscisic Acid Acts as a Blocker of the Bitter Taste G Protein-Coupled Receptor T2R4
2015Co-Authors: Sai Prasad Pydi, Ken M. Nelson, Appalaraju Jaggupilli, Rajinder P Bhullar, Michele C Loewen, Suzanne R. Abrams, Prashen ChelikaniAbstract:Bitter taste receptors (T2Rs) belong to the G protein-coupled receptor superfamily. In humans, 25 T2Rs mediate bitter taste sensation. In addition to the oral cavity, T2Rs are expressed in many extraoral tissues, including the central nervous system, respiratory system, and reproductive system. To understand the mechanistic roles of the T2Rs in oral and extraoral tissues, novel blockers or antagonists are urgently needed. Recently, we elucidated the binding pocket of T2R4 for its agonist quinine, and an antagonist and inhibitory neurotransmitter, γ-aminobutyric Acid. This structure–function information about T2R4 led us to screen the plant hormone abscisic Acid (ABA), its precursor (xanthoxin), and catabolite Phaseic Acid for their ability to bind and activate or inhibit T2R4. Molecular docking studies followed by functional assays involving calcium imaging confirmed that ABA is an antagonist with an IC50 value of 34.4 ± 1.1 μM. However, ABA precursor xanthoxin acts as an agonist on T2R4. Interestingly, molecular model-guided site-directed mutagenesis suggests that the T2R4 residues involved in quinine binding are also predominantly involved in binding to the novel antagonist, ABA. The antagonist ability of ABA was tested using another T2R4 agonist, yohimbine. Our results suggest that ABA does not inhibit yohimbine-induced T2R4 activity. The discovery of natural bitter blockers has immense nutraceutical and physiological significance and will help in dissecting the T2R molecular pathways in various tissues
Jan A D Zeevaart - One of the best experts on this subject based on the ideXlab platform.
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Overexpression of a 9-cis-epoxycarotenoid dioxygenase gene in Nicotiana plumbaginifolia increases abscisic Acid and Phaseic Acid levels and enhances drought tolerance.
Plant Physiology, 2002Co-Authors: Xiaoqiong Qin, Jan A D ZeevaartAbstract:The plant hormone abscisic Acid (ABA) plays important roles in seed maturation and dormancy and in adaptation to a variety of environmental stresses. An effort to engineer plants with elevated ABA levels and subsequent stress tolerance is focused on the genetic manipulation of the cleavage reaction. It has been shown in bean (Phaseolus vulgaris) that the gene encoding the cleavage enzyme (PvNCED1) is up-regulated by water stress, preceding accumulation of ABA. Transgenic wild tobacco (Nicotiana plumbaginifolia Viv.) plants were produced that overexpress the PvNCED1 gene either constitutively or in an inducible manner. The constitutive expression of PvNCED1 resulted in an increase in ABA and its catabolite, Phaseic Acid (PA). When the PvNCED1 gene was driven by the dexamethasone (DEX)-inducible promoter, a transient induction of PvNCED1 message and accumulation of ABA and PA were observed in different lines after application of DEX. Accumulation of ABA started to level off after 6 h, whereas the PA level continued to increase. In the presence of DEX, seeds from homozygous transgenic line TN1 showed a 4-d delay in germination. After spraying with DEX, the detached leaves from line TN1 had a drastic decrease in their water loss relative to control leaves. These plants also showed a marked increase in their tolerance to drought stress. These results indicate that it is possible to manipulate ABA levels in plants by overexpressing the key regulatory gene in ABA biosynthesis and that stress tolerance can be improved by increasing ABA levels.