The Arabidopsis bZIP Gene AtbZIP63 Is a Sensitive Integrator of Transient Abscisic Acid and Glucose Signals
Cleverson C. MatiolliJuarez Pires TomazGustavo Turqueto DuarteFernanda M. PradoLuiz‐Eduardo Del‐BemAmanda Bortolini SilveiraLuciane GauerLuiz Gustavo Guedes CorrêaRodrigo Duarte DrumondAmérico José Carvalho VianaPaolo Di MascioChristian MeyerMichel Vincentz
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Abstract Glucose modulates plant metabolism, growth, and development. In Arabidopsis (Arabidopsis thaliana), Hexokinase1 (HXK1) is a glucose sensor that may trigger abscisic acid (ABA) synthesis and sensitivity to mediate glucose-induced inhibition of seedling development. Here, we show that the intensity of short-term responses to glucose can vary with ABA activity. We report that the transient (2 h/4 h) repression by 2% glucose of AtbZIP63, a gene encoding a basic-leucine zipper (bZIP) transcription factor partially involved in the Snf1-related kinase KIN10-induced responses to energy limitation, is independent of HXK1 and is not mediated by changes in ABA levels. However, high-concentration (6%) glucose-mediated repression appears to be modulated by ABA, since full repression of AtbZIP63 requires a functional ABA biosynthetic pathway. Furthermore, the combination of glucose and ABA was able to trigger a synergistic repression of AtbZIP63 and its homologue AtbZIP3, revealing a shared regulatory feature consisting of the modulation of glucose sensitivity by ABA. The synergistic regulation of AtbZIP63 was not reproduced by an AtbZIP63 promoter-5′-untranslated region::β-glucuronidase fusion, thus suggesting possible posttranscriptional control. A transcriptional inhibition assay with cordycepin provided further evidence for the regulation of mRNA decay in response to glucose plus ABA. Overall, these results indicate that AtbZIP63 is an important node of the glucose-ABA interaction network. The mechanisms by which AtbZIP63 may participate in the fine-tuning of ABA-mediated abiotic stress responses according to sugar availability (i.e., energy status) are discussed.HD2 proteins are plant-specific histone deacetylases. Little is known about the function of HD2 proteins in plants. In this paper, we report that an Arabidopsis HD2 protein, AtHD2C, is involved in abscisic acid and abiotic stress responses. Analysis of Arabidopsis plants containing the AtHD2C:beta-glucuronidase fusion gene revealed that AtHD2C was constitutive expressed in plants. Furthermore, expression of AtHD2C was repressed by abscisic acid. Over-expression of 35S:AtHD2C-GFP in transgenic Arabidopsis plants conferred an abscisic acid-insensitive phenotype. In addition, 35S:AtHD2C-GFP transgenic plants displayed reduced transpiration and enhanced tolerance to salt and drought stresses when compared with wild-type plants. The expression of several abscisic acid-responsive genes was affected in the 35S:AtHD2C-GFP plants. Our study provides evidence indicating that AtHD2C can modulate abscisic acid and stress responses. PMID: 16553900
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Two Arabidopsis mutants atmyb123 and atkor1 were identified from the T-DNA insertion knockout mutant lines SAIL_005260 and SAIL_2_G11,respectively,and then a double mutant atmyb123/atkor1 was established by crossing method.The two mutants are lacking expression for ATMYB123 and ATKOR1 genes,respectively,which two were found to be tightly related to root development in Arabidopsis thaliana.The results obtained here showed that lack of ATMYB123 gene in expression led to a slow growth of plant rosettes and a yellow skin of seeds in Arabidopsis,while lack of ATKOR1 gene in expression had no marked effects on these two factors.Any one of the two genes ATMYB123 and ATKOR1 knockout extremely repressed the root development in Arabidopsis,especially the knockout of ATKOR1 gene,the mutant atkor1 showed only one third of length of roots as compared to wild type(WT).Interestingly,the double mutant atmyb123/atkor1 exhibited the characteristics of the single mutant atmyb123 has in plant rosette morphology and seed skins but presented intermediated root length between the two single mutants.In addition,the growth trend of roots among the three mutants had no fundamental changes when the plants were cultivated under different pH,NaCl treatments and GA concentration conditions,which imply that these three factors were not concerned in the root shortening event induced by lack of any one of ATMYB123 or/and ATKOR1 proteins in A.thaliana.These results suggest that both ATMYB123 and ATKOR1 genes participate in the root development of Arabidopsis and a specific relationship in functions exist between the two proteins,ATMYB123 and ATKOR1.The transcription factor ATMYB123 might act as a major regulator of ATKOR1 protein for participating the control of root development in Arabidopsis.
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Abscisic acid (ABA) plays a key role in plant growth and development. The effect of ABA in plants mainly depends on its concentration, which is determined by a balance between biosynthesis and catabolism of ABA. In this study, we characterize a unique UDP-glucosyltransferase (UGT), UGT71C5, which plays an important role in ABA homeostasis by glucosylating ABA to abscisic acid -: glucose ester (GE) in Arabidopsis (Arabidopsis thaliana). Biochemical analyses show that UGT71C5 glucosylates ABA in vitro and in vivo. Mutation of UGT71C5 and down-expression of UGT71C5 in Arabidopsis cause delay in seed germination and enhanced drought tolerance. In contrast, overexpression of UGT71C5 accelerates seed germination and reduces drought tolerance. Determination of the content of ABA and ABA-GE in Arabidopsis revealed that mutation in UGT71C5 and down-expression of UGT71C5 resulted in increased level of ABA and reduced level of ABA-GE, whereas overexpression of UGT71C5 resulted in reduced level of ABA and increased level of ABA-GE. Furthermore, altered levels of ABA in plants lead to changes in transcript abundance of ABA-responsive genes, correlating with the concentration of ABA regulated by UGT71C5 in Arabidopsis. Our work shows that UGT71C5 plays a major role in ABA glucosylation for ABA homeostasis.
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Excised embryonic bean axes (Phaseolus vulgaris, var. White Marrowfat) rapidly metabolize 2-(14)C-(+/-)-abscisic acid to two compounds, M-1 and M-2, which have very low growth-inhibitory activity. Chemical tests indicate the M-1 and M-2 are not previously described abscisic acid metabolites. M-2 accumulates in the axes and evidence is presented for the hypothesis that abscisic acid --> M-1 --> M-2. Zeatin, which partially reverses the abscisic acid-mediated growth inhibition of axes, neither decreases abscisic acid uptake nor causes any major changes in its metabolism. It was observed that axes transferred from abscisic acid-containing solutions to buffer resume control rates of fresh weight increase while still containing considerable quantities of abscisic acid.
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Tomato shoots that had been (a) fed (�)-[2H9]abscisic aldehyde via the xylem or (b) fed H218O together with (�)-[2H9]abscisic aldehyde via the xylem or (c) exposed to 18O2 and fed (�)-[2H9]abscisic aldehyde, were then wilted. The abscisic acid present was isolated, methylated and resolved into (+)- and (-)- methyl abscisate. These methyl abscisate samples were then examined by negative ion chemical ionisation (methane) gas chromatography/mass spectrometry. The undeuteriated (+)-abscisic acid contained no 180 from H218O but did contain one 18O from 18O2. No 18O from either of these sources was present in the undeuteriated (-)-abscisic acid. It was not possible to discount the xanthophyll hypothesis for the origin of stress-induced abscisic acid on the basis of these experiments. Both (+)- and (-)- multiply deuteriated abscisic acid contained one and two 18O atoms from H218O but none from 18O2. It is postulated that this multiply deuteriated (�)-abscisic acid is formed by a separate enzyme system from that which forms endogenous stress-induced (+)-abscisic acid. On the basis of the low incor- poration of abscisic aldehyde into abscisic acid, it is suggested that the endogenous precursor of stress- induced abscisic acid is an as yet unidentified structure and that abscisic aldehyde competes with it.
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The main activities of abscisic acid in seeds are abscisic acid synthesis,catabolism,transport and response.Abscisic acid levels,the specific enzyme and the transcription factor in signal transduction pathway of abscisic acid,the relation between abscisic acid and dormancy of seeds are reviewed in this paper.
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Summary HD2 proteins are plant‐specific histone deacetylases. Little is known about the function of HD2 proteins in plants. In this paper, we report that an Arabidopsis HD2 protein, AtHD2C, is involved in abscisic acid and abiotic stress responses. Analysis of Arabidopsis plants containing the AtHD2C : β ‐ glucuronidase fusion gene revealed that AtHD2C was constitutive expressed in plants. Furthermore, expression of AtHD2C was repressed by abscisic acid. Over‐expression of 35S: AtHD2C‐GFP in transgenic Arabidopsis plants conferred an abscisic acid‐insensitive phenotype. In addition, 35S: AtHD2C‐GFP transgenic plants displayed reduced transpiration and enhanced tolerance to salt and drought stresses when compared with wild‐type plants. The expression of several abscisic acid‐responsive genes was affected in the 35S: AtHD2C‐GFP plants. Our study provides evidence indicating that AtHD2C can modulate abscisic acid and stress responses.
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The closure of stomata by abscisic acid was examined in several species of plants through measurements of CO(2) and H(2)O exchange by the leaf. The onset of closure was very rapid, beginning at 3 minutes from the time of abscisic acid application to the cut base of the leaf of corn, or at 8 or 9 minutes for bean, Rumex and sugarbeet; rose leaves were relatively slow at 32 minutes. The timing and the concentration of abscisic acid needed to cause closure were related to the amounts of endogenous abscisic acid in the leaf. Closure was obtained in bean leaves with 8.9 picomoles/cm(2). (+)-Abscisic acid had approximately twice the activity of the racemic material. The methyl ester of abscisic acid was inactive, and trans-abscisic acid was likewise inactive. The effects of stress on levels of endogenous abscisic acid, and the ability of very small amounts of abscisic acid to cause rapid closure suggests that stomatal control is a regulatory function of this hormone.
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