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ABSTRACT: Thioredoxins (TRXs) f and m are key components in the light regulation of photosynthetic metabolism via thiol-dithiol modulation in chloroplasts of leaves; however, little is known about the factors modulating the expression of these proteins. To investigate the effect of sugars as photosynthetic products on the expression of PsTRX f and m1 genes, sucrose and glucose were externally supplied to pea plants during the day. There was an increase in the mRNA levels of PsTRX f and m1 genes in response mainly to glucose. When leaf discs were incubated for up to 4h in the dark, glucose also led to an increase in both mRNA and protein levels of TRXs f and m, while sucrose had no substantial effect. Expression of PsDOF7, a carbon metabolism-related transcription factor gene, was also induced by glucose. Protein-DNA interaction showed that PsDOF7 binds specifically to the DOF core located in PsTRX f and m1 gene promoters. Transient expression in agroinfiltrated pea leaves demonstrated that PsDOF7 activated transcription of both promoters. The incubation of leaf discs in dithiotreitol (DTT) to increase the redox status led to a marked increase in the mRNA and protein levels of both TRXs within 4h. The increase in TRX protein levels occurred after 1h DTT feeding, implying a rapid effect of the thiol status on TRX f and m1 protein turnover rates, while transcriptional regulation took 3h to proceed. These results show that the protein levels of both TRXs are under short-term control of the sugar and thiol status in plants.
Journal of Experimental Botany 07/2012; 63(13):4887-900. · 5.36 Impact Factor
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ABSTRACT: Plastid thioredoxins (TRXs) f and m have long been considered to regulate almost exclusively photosynthesis-related processes. Nonetheless, some years ago, we found that type-f and m TRXs were also present in non-photosynthetic organs such as roots and flowers of adult pea plants. In the present work, using pea seedlings 2-5 days old, we have determined the mRNA expression profile of the plastid PsTRX f, m1, and m2, together with the ferredoxin NADP reductase (FNR). Our results show that these TRX isoforms are expressed in cotyledons, underlying similar expression levels in roots for PsTRX m2. We have also noted plastid TRX expression in cotyledons of etiolated seedlings of Arabidopsis thaliana lines carrying constructs corresponding to PsTRX f and m1 promoters fused to the reporter gene GUS, pointing to a role in reserve mobilization. Furthermore, the response of plastid TRXs to NaCl and their capacity in restoring the growth of a TRX-deficient yeast under saline conditions suggest a role in the tolerance to salinity. We propose that these redox enzymes take part of the reserve mobilization in seedling cotyledons and we suggest additional physiological functions of PsTRX m2 in roots and PsTRX m1 in the salinity-stress response during germination.
Plant Science 06/2012; 188-189:82-8. · 2.94 Impact Factor
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ABSTRACT: Thioredoxins (TRXs) are ubiquitous proteins involved in redox processes. About forty genes encode TRX or TRX-related proteins in plants, grouped in different families according to their subcellular localization. For instance, the h-type TRXs are located in cytoplasm or mitochondria, whereas f-type TRXs have a plastidial origin, although both types of proteins have an eukaryotic origin as opposed to other TRXs. Herein, we study the conformational and the biophysical features of TRXh1, TRXh2 and TRXf from Pisum sativum. The modelled structures of the three proteins show the well-known TRX fold. While sharing similar pH-denaturations features, the chemical and thermal stabilities are different, being PsTRXh1 (Pisum sativum thioredoxin h1) the most stable isoform; moreover, the three proteins follow a three-state denaturation model, during the chemical-denaturations. These differences in the thermal- and chemical-denaturations result from changes, in a broad sense, of the several ASAs (accessible surface areas) of the proteins. Thus, although a strong relationship can be found between the primary amino acid sequence and the structure among TRXs, that between the residue sequence and the conformational stability and biophysical properties is not. We discuss how these differences in the biophysical properties of TRXs determine their unique functions in pea, and we show how residues involved in the biophysical features described (pH-titrations, dimerizations and chemical-denaturations) belong to regions involved in interaction with other proteins. Our results suggest that the sequence demands of protein-protein function are relatively rigid, with different protein-binding pockets (some in common) for each of the three proteins, but the demands of structure and conformational stability per se (as long as there is a maintained core), are less so.
PLoS ONE 01/2011; 6(2):e17068. · 4.09 Impact Factor
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ABSTRACT: Chloroplastic thioredoxins f and m (TRX f and TRX m) mediate light regulation of carbon metabolism through the activation of Calvin cycle enzymes. The role of TRX f and m in the activation of Calvin cycle enzymes is best known among the TRX family. However, the discoveries of new potential targets extend the functions of chloroplastic TRXs to other processes in non-photosynthetic tissues. As occurs with numerous chloroplast proteins, their expression comes under light regulation. Here, the focus is on the light regulation of TRX f and TRX m in pea and Arabidopsis during the day/night cycle that is maintained during the subjective night. In pea (Pisum sativum), TRX f and TRX m1 expression is shown to be governed by a circadian oscillation exerted at both the transcriptional and protein levels. Binding shift assays indicate that this control probably involves the interaction of the CCA1 transcription factor and an evening element (EE) located in the PsTRX f and PsTRX m1 promoters. In Arabidopsis, among the multigene family of TRX f and TRX m, AtTRX f2 and AtTRX m2 mRNA showed similar circadian oscillatory regulation, suggesting that such regulation is conserved in plants. However, this oscillation was disrupted in plants overexpressing CCA1 (cca1-ox) or repressing CCA1 and LHY (cca1-lhy). The physiological role of the oscillatory regulation of chloroplastic TRX f and TRX m in plants during the day/night cycle is discussed.
Journal of Experimental Botany 12/2010; 62(6):2039-51. · 5.36 Impact Factor
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ABSTRACT: The largest group of plant thioredoxins (TRXs) consists of the so-called h-type; their great number raises questions about their specific or redundant roles in plant cells. Pisum sativum thioredoxin h1 (PsTRXh1) and Pisum sativum thioredoxin h2 (PsTRXh2) are both h-type TRXs from pea (Pisum sativum) previously identified and biochemically characterized. While both are involved in redox regulation and show a high-sequence identity (60%), they display different behavior during in vitro and in vivo assays. In this work, we show that these two proteins display different specificity in the capturing of protein targets in vitro, by the use of a new stringent method. PsTRXh2 interacted with classical antioxidant proteins, whereas PsTRXh1 showed a completely different pattern of targeted proteins, and was able to capture a transcription factor. We also showed that the two proteins display very different thermal and chemical stabilities. We suggest that the differences in thermal and chemical stability point to a distinct and characteristic pattern of protein specificity.
Journal of plant physiology 12/2009; 167(6):423-9. · 2.50 Impact Factor
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ABSTRACT: This review offers an overview of the current state of our knowledge concerning the role of fructose-1,6-bisphosphatase (FBPase) in sugar partitioning and biosynthesis, through the analysis of genetically manipulated plants. The existence of two well-characterized isoforms is a consequence of the subcellular compartmentalization of photosynthetic eukaryotes, conditioning their respective regulatory mechanisms and their influence over plant metabolism and photosynthesis. Both isoforms are important, as has been deduced from previous work with different plant species, although there is still much to be done in order to gain a definitive vision of this issue. Despite that, alteration of the FBPase content follows a general pattern, there are some differences that could be considered species-specific. Modifications lead to profound changes in the carbohydrate content and carbon allocation, raising questions as to whether flux of some sugars or sugar precursors from one side to the other of the chloroplast envelope occurs to rebalance carbohydrate metabolism or whether other compensatory, though not fully efficient, enzymatic activities come into play. Due to the pleiotropic nature of modifying the core carbon metabolism, an answer to the above questions would require an exhaustive study involving diverse aspects of plant physiology.
Journal of Experimental Botany 04/2009; 60(10):2923-31. · 5.36 Impact Factor
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ABSTRACT: A full-length FBPase cDNA has been isolated from Fragaria x ananassa (strawberry) corresponding to a novel putative chloroplastic FBPase but lacking the regulatory redox domain, a characteristic of the plastidial isoenzyme (cpFBPaseI). Another outstanding feature of this novel isoform, called cpFBPaseII, is the absence of the canonical active site. Enzymatic assays with cpFBPaseII evidenced clear Mg(2+)-dependent FBPase activity and a K(m) for fructose-1,6-bisphosphate (FBP) of 1.3 mM. Immunolocalization experiments and chloroplast isolation confirmed that the new isoenzyme is located in the stroma. Nevertheless, unlike cpFBPaseI, which is redox activated, cpFBPaseII did not increase its activity in the presence of either DTT or thioredoxin f (TRX f) and is resistant to H(2)O(2) inactivation. Additionally, the novel isoform was able to complement the growth deficiency of the yeast FBP1 deletion fed with a non-fermentable carbon source. Furthermore, orthologues are restricted to land plants, suggesting that cpFBPaseII is a novel and an intriguing chloroplastic FBPase that emerged late in the evolution of photosynthetic organisms, possibly because of a pressing need of land plants.
Plant Cell and Environment 03/2009; 32(7):811-27. · 5.22 Impact Factor
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ABSTRACT: Plants are the organisms containing the most complex multigenic family for thioredoxins (TRX). Several types of TRXs are targeted to chloroplasts, which have been classified into four subgroups: m, f, x, and y. Among them, TRXs f and m were the first plastidial TRXs characterized, and their function as redox modulators of enzymes involved in carbon assimilation in the chloroplast has been well-established. Both TRXs, f and m, were named according to their ability to reduce plastidial fructose-1,6-bisphosphatase (FBPase) and malate dehydrogenase (MDH), respectively. Evidence is presented here based on the immunocytochemistry of the localization of f and m-type TRXs from Pisum sativum in non-photosynthetic tissues. Both TRXs showed a different spatial pattern. Whilst PsTRXm was localized to vascular tissues of all the organs analysed (leaves, stems, and roots), PsTRXf was localized to more specific cells next to xylem vessels and vascular cambium. Heterologous complementation analysis of the yeast mutant EMY63, deficient in both yeast TRXs, by the pea plastidial TRXs suggests that PsTRXm, but not PsTRXf, is involved in the mechanism of reactive oxygen species (ROS) detoxification. In agreement with this function, the PsTRXm gene was induced in roots of pea plants in response to hydrogen peroxide.
Journal of Experimental Botany 02/2008; 59(6):1267-77. · 5.36 Impact Factor
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ABSTRACT: Plant thioredoxins (TRXs) are involved in redox regulation of a wide variety processes and usually exhibit organ specificity. We report strong evidence that chloroplastic TRXs are localized in heterotrophic tissues and suggest some ways in which they might participate in several metabolic and developmental processes. The promoter regions of the chloroplastic f and m1 TRX genes were isolated from a pea (Pisum sativum) plant genomic bank. Histochemical staining for beta-glucuronidase (GUS) in transgenic homozygous Arabidopsis (Arabidopsis thaliana) plants showed preferential expression of the 444-bp PsTRXf1 promoter in early seedlings, stems, leaves, and roots, as well as in flowers, stigma, pollen grains, and filaments. GUS activity under the control of the 1,874-bp PsTRXm1 promoter was restricted to the leaves, roots, seeds, and flowers. To gain insight into the translational regulation of these genes, a series of deletions of 5' elements in both TRX promoters were analyzed. The results revealed that a 126-bp construct of the PsTRXf2 promoter was unable to reproduce the expression pattern observed with the full promoter. The differences in expression and tissue specificity between PsTRXm1 and the deleted promoters PsTRXm2 and PsTRXm3 suggest the existence of upstream positive or negative regulatory regions that affect tissue specificity, sucrose metabolism, and light regulation. PsTRXm1 expression is finely regulated by light and possibly by other metabolic factors. In situ hybridization experiments confirmed new localizations of these chloroplastic TRX transcripts in vascular tissues and flowers, and therefore suggest possible new functions in heterotrophic tissues related to cell division, germination, and plant reproduction.
Plant physiology 12/2007; 145(3):946-60. · 6.53 Impact Factor
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ABSTRACT: During the last decade, plant thioredoxins (TRX) h-type have been shown to be implicated in several new roles like the protection against the oxidative stress by their ability to reduce some antioxidant proteins as peroxiredoxins (PRX) or methionine-sulphoxide-reductases (MSR). However, the concept of the oxidative stress is changing and this fact raises the question of the TRX roles in this new context. In the January issue of Plant Physiology, we have presented two TRXsh from Pisum sativum differently involved in the control of the redox status. PsTRXh1 is an h-type TRX that acts by reducing classical antioxidant proteins. PsTRXh2 seems to be also involved in redox control, however it could act contrary to its counterpart h1. Both proteins may play antagonistic roles in pea in order to lead a better control of the redox status.
Plant signaling & behavior 10/2007; 2(5):426-7.
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ABSTRACT: Thioredoxins (TRXs) are small ubiquitous oxidoreductases involved in disulfide bond reduction of a large panel of target proteins. The most complex cluster in the family of plant TRXs is formed by h-type TRXs. In Arabidopsis (Arabidopsis thaliana), nine members of this subgroup were described, which are less well known than their plastidial counterparts. The functional study of type-h TRXs is difficult because of the high number of isoforms and their similar biochemical characteristics, thus raising the question whether they have specific or redundant functions. Type-h TRXs are involved in seed germination and self incompatibility in pollen-pistil interaction. Their function as antioxidants has recently been proposed, but further work is needed to clarify this function in plants. In this study, we describe two new h-type TRXs from pea (Pisum sativum; stated PsTRXh1 and PsTRXh2). By functional complementation of a yeast (Saccharomyces cerevisiae) trx1Delta trx2Delta double mutant, we demonstrate that PsTRXh1 is involved in the redox-imbalance control, possibly through its interaction with peroxiredoxins. In contrast, PsTRXh2 provokes a phenotype of hypersensitivity to hydrogen peroxide in the yeast mutant. Furthermore, we show differential gene expression and protein accumulation of the two isoforms, PsTRXh1 protein being abundantly detected in vascular tissue and flowers, whereas PsTRXh2 gene expression was hardly detectable. By comparison with previous data of additional PsTRXh isoforms, our results indicate specific functions for the pea h-type TRXs so far described.
Plant physiology 02/2007; 143(1):300-11. · 6.53 Impact Factor
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ABSTRACT: Fructose-1,6-bisphosphatase (FBPase; EC 3.1.3.11) binds its putative physiological activator thioredoxin f (Trxf) at pH 7.9, the pH in the stroma of the illuminated chloroplast. Since Trx m, described as specific in NADP+-malate dehydrogenase (NADPMDH) activation, appears in pea (Pisum sativum L.) also to be functional in FBPase modulation, we have here analyzed the effect of pH and the redox status of the chloroplast stroma in the pea FBPase binding of homologous Trx f and m. Both pea Trx were strongly bound by purified FBPase when they were preincubated at pH 7.9 with 2.5 mM dithiothreitol (DTT), but not when the reductant was omitted. As occurs with Trx f the Trx m/FBPase ratio of the complex was 4, but this was only observed with a Trx m/FBPase concentration ratio > 10 in the preincubation mixture. The FBPase-Trx m binding disappeared in the presence of 100 mM NaCl, even with 2.5 mM DTT at pH 7.9, with a concomitant appearance of different aggregation states of the FBPase subunit. A similar FBPase-Trx m complex was detected in the stromal solution when pea chloroplasts were lysed at pH 7.9 in the presence of DTT. No interaction was observed between NADP-MDH and Trx f or m, either in the presence or in the absence of DTT. Pea FBPase showed sigmoidal activation kinetics with pea Trx m, and an S0.5 of 133 nM versus 6.6 nM with pea Trx f. About 10-fold higher concentration of the former than that of the latter was required for obtaining maximum activity; however, the Vmax with Trx f was only 2-fold higher than that with Trx m. We conclude that pea FBPase binds and is activated by the homologous Trx m, even though to a lesser extent than with Trx f. We also deduce that in the light the conditions in the chloroplast stroma are optimal for forming an FBPase-Trx complex.
Physiologia Plantarum 04/2006; 101(3):463 - 470. · 3.11 Impact Factor
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ABSTRACT: Upon continuous illumination of dark-grown spinach (Spinacia oleracea L. cv. Winter Giant) seedlings, the thioredoxin f (Td f) content (ELISA) showed a steep rise, which can be evaluated after 3 and 36 h illumination as 3 times and 10 times the dark value, respectively. These figures correspond to 0.03% and 0.1% of total soluble protein, which means a higher biosynthetic rate for Td f compared to the average of total proteins in the earlier steps of plant development. After 40-50 h light the Td f level reached its highest value which remained stable for an additional 40 h and then decreased. Pulse-chase in vivo experiments with [35S]-methionine also showed this sharp increase of Td f in the dark-light transition. From the pattern of decay of [35S]-labelled Td f, a half-life of 7 h was determined for this chloroplast protein. In vitro translation experiments with poly(A)-mRNA isolated from illuminated young spinach seedlings, coupled to a wheat-germ synthesizing system, showed the appearance of a labelled fraction of ca 19 kDa molecular mass, recognizable by a specific Td f antiserum. When intact spinach chloroplasts were added to the translation assay medium, and then illuminated, the 19 kDa band disappeared, with a parallel increase of an internalized 13 kDa labelled polypeptide, also recognized by the Td f antiserum. These results are good evidence for a nuclear-coded synthesis of a Td f precursor, which travels through the chloroplast envelope, leaving the functional protein inside the organelle after the loss of a 6 kDa transit peptide.
Physiologia Plantarum 04/2006; 84(2):236 - 242. · 3.11 Impact Factor
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ABSTRACT: The pea chloroplastic fructose-1,6-bisphosphatase (FBPase) antisense construct reduced the endogenous level of expression of the corresponding Arabidopsis thaliana gene. The reduction of foliar FBPase activity in the transformants T(2) and T(3) generation ranged from 20% to 42%, and correlated with lower levels of FBPase protein. FBPase antisense plants displayed different phenotypes with a clear increase in leaf fresh weight. Measurements of photosynthesis revealed a higher carbon-assimilation rate. Decreased FBPase activity boosted the foliar carbohydrate contents, with a shift in the sucrose:starch ratio, which reached a maximum of 0.99 when the activity loss was 41%. Nitrate reductase activity decreased simultaneously with an increase in glutamine synthetase activity, which could be explained in terms of ammonium assimilation regulation by sugar content. These results suggest the role of FBPase as a key enzyme in CO(2) assimilation, and also in co-ordinating carbon and nitrogen metabolism.
Journal of Experimental Botany 01/2005; 55(408):2495-503. · 5.36 Impact Factor
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ABSTRACT: Redox regulation of photosynthetic enzymes has been a preferred research topic in recent years. In this area chloroplast fructose-1,6-bisphosphatase is probably the most extensively studied target enzyme of the CO(2) assimilation pathway. This review analyzes the structure, biosynthesis, phylogeny, action mechanism, regulation and kinetics of fructose-1,6-bisphosphatase in the light of recent findings on structure-function relationship, and from a molecular biology viewpoint.
Photosynthesis Research 02/2002; 74(3):235-49. · 3.24 Impact Factor
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ABSTRACT: The interaction between chloroplast fructose-1,6-bisphosphatase (FBPase) and thioredoxin (Trx) f, two plant proteins involved in the Benson-Calvin cycle, is mainly of an electrostatic nature [Hermoso et al. (1996) Plant Mol Biol 30: 455–465; Reche et al. (1997) Physiol Plant 101: 463–470; Sahrawy et al. (1997) J Mol Biol 269: 623–630; Hermoso et al. (1999) Physiol Plant 105: 756–762], possibly involving carboxyl groups of the enzyme and amino groups of Trx f. We carried out the covalent stabilization of that ionic complex, for the purpose of studying the interaction between both proteins and the factors that influence it. We have used 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide, a reagent able to cross-link carboxyl and amino groups, which allows the formation of covalent bonds between the groups that, in solution, form ionic bonds. A stable functional complex between both proteins was formed. The efficiency in the formation of that complex depends on the redox state of Trx f, ionic strength and pH, showing a strong correlation with the Trx f-dependent enzyme activity. The complex also retains enzyme activity. This suggests that the formation of the covalent complex requires the previous stabilization of a specific functional ionic complex between both proteins, and that in this functional complex carboxyl groups of the enzyme and primary amines of Trx f are involved. This complex is not stable in a tetrameric structure of the enzyme. We could also detect covalent aggregates of FBPase subunits, which indicates the implication of ionic interactions in the stabilization of the tetrameric structure of the enzyme; besides, as molecular filtration experiments and electrophoresis suggest, hydrophobic forces would also be implicated in the enzyme structure.
Physiologia Plantarum 01/2002; 113(4):452 - 460. · 3.11 Impact Factor
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ABSTRACT: Two hybrid thioredoxins (Trx) have been constructed from cDNA clones coding for pea chloroplast Trxs m and f. The splitting point was the AvaII site situated between the two cysteines of the regulatory cluster. One hybrid, Trx m/f, was purified from Escherichia coli-expressed cell lysates as a high yielding 12 kDa protein. Western blot analysis showed a positive reaction with antibodies against pea Trxs m and f and, like the parenteral pea Trx m, displayed an acidic pI (5.0) and a high thermal stability. In contrast, the opposite hybrid Trx f/m appeared in E. coli lysates as inclusion bodies, where it was detected by Western blot against pea Trx f antibodies as a 40 kDa protein. Trx f/m was very unstable, sensitive to heat denaturation, and could not be purified. Trx m/f showed a higher affinity for pea chloroplast fructose-1,6-bisphosphatase (FBPase) and a smaller Trx/FBPase saturation ratio than both parenterals; however, the FBPase catalytic rate was lower than that with Trxs m and f. Surprisingly, the hybrid Trx m/f appeared to be incompetent in the activation of pea NADP-malate dehydrogenase. Computer-assisted models of pea Trxs m and f, and of the chimeric Trx m/f, showed a change in the orientation of the α4-helix in the hybrid, which could explain the kinetic modifications with respect to Trxs m and f. We conclude that the stability of Trxs lies on the N-side of the regulatory cluster, and is associated with the acidic character of this fragment and, as a consequence, with the acidic pI of the whole molecule. In contrast, the ability of FBPase binding and enzyme catalysis depends on the structure on the C-side of the regulatory cysteines.
The Plant Journal 01/2002; 15(2):155 - 163. · 6.16 Impact Factor
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ABSTRACT: We previously demonstrated that a cluster in the available Asn-170Glu region of pea chloroplast fructose-1,6-bisphosphatase (FBPase) could be involved in its interaction with the physiological modulator thioredoxin (Trx). Using as template a cDNA coding for pea chloroplast FBPase, a DNA insert coding for a 19 amino acid fragment ( Pro-167Gly) was amplified by PCR. After insertion in the pGEX-4T vector-1, it was expressed in Escherichia coli as a fusion protein (GST-19) with the vector-coded glutathione transferase (GST). This protein appears in the supernatant of cell lysates, and was purified to homogeneity. After thrombin digestion, the 19 amino acid insert was isolated as a polypeptide which displayed a positive reaction against pea chloroplast FBPase antibodies. GST-19 linked to glutathione-Sepharose beads, but not the GST, strongly interacts with pea Trx f, suggesting that this binding depends on the 19 amino acid insert. ELISA and Western blot experiments also demonstrate the existence of a GST-19-Trx f interaction, as well as a negligible quantity of Trx f bound by the vector-coded GST. Putative competitive inhibition assays of FBPase activity carried out in the presence of increasing concentrations of the 19 amino acid insert do not demonstrate any enzyme inhibition. On the contrary, this protein fragment enhances the enzyme activity proportionally to its concentration in the assay mixture. This indicates that the FBPase-Trx f binding promotes some type of structural modification of the Trx molecule, or of the FBPase-Trx docking site, thus facilitating the reductive modulation of FBPase.
Physiologia Plantarum 01/2002; 105(4):756 - 762. · 3.11 Impact Factor
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ABSTRACT: The transcript (mRNA) level and the protein content (as determined by enzyme-linked immunosorbent assay) of thioredoxins (Trx) f and m, and of their targets, chloroplast fructose-1,6-bisphosphatase (FBPase) and NAD(P)- malate dehydrogenase (NADP-MDH), increase over the ontogeny of pea plants grown under normal conditions, showing their highest values before flowering (40 d growth). The clearest results appear in apical, but also in middle leaves. Enzyme activites of FBPase and NADP-MDH were lowest just before flowering. In the case of FBPase this was probably a mechanism to facilitate triose-phosphate export to the cytosol for sucrose synthesis. The likely function of NADP-MDH is to supply the cytosol, via the malate translocator, with the NAD(P)H necessary for UTP regeneration in the sucrose biosynthetic pathway. Both the Fv/Fm ratio and the net photosynthetic rate (IRGA) decreased at saturating irradiance (16 h photoperiod) and under sub-saturating continuous light. However, the Fv/Fm quotient recovered to normal values after several days adaptation to high light. A similar recovery was also observed in net photosynthesis, although normal levels were never obtained. Under light-stress conditions the concentration of Trxs f and m, and of the targets FBPase and NADP-MDH, were somewhat lower than those of unstressed plants. Even though the levels of the corresponding transcripts (mRNAs) are similar in upper leaves from control and light-stressed plants, those of the middle and basal leaves from plants grown under high light were substantially higher than those of the control plants. In addition to the well-documented transcriptional regulation of nuclear-coded chloroplast proteins, these results seem to indicate the existence of an additional post-transcriptional control.
New Phytologist 12/1999; 145(1):21 - 28. · 6.64 Impact Factor
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ABSTRACT: In contrast to prokaryotes, which typically possess one thioredoxin gene per genome, three different thioredoxin types have
been described in higher plants. All are encoded by nuclear genes, but thioredoxins m and f are chloroplastic while thioredoxins
h have no transit peptide and are probably cytoplasmic. We have cloned and sequencedArabidopsis thaliana genomic fragments encoding the five previously described thioredoxins h, as well as a sixth gene encoding a new thioredoxin
h. In spite of the high divergence of the sequences, five of them possess two introns at positions identical to the previously
sequenced tobacco thioredoxin h gene, while a single one has only the first intron. The recently published sequence ofChlamydomonas thioredoxin h shows three introns, two at the same positions as in higher plants. This strongly suggests a common origin
for all cytoplasmic thioredoxins of plants and green algae. In addition, we have cloned and sequenced pea DNA genomic fragments
encoding thioredoxins m and f. The thioredoxin m sequence shows only one intron between the regions encoding the transit peptide
and the mature protein, supporting the prokaryotic origin of this sequence and suggesting that its association with the transit
peptide has been facilitated by exon shuffling. In contrast, the thioredoxin f sequence shows two introns, one at the same
position as an intron in various plant and animal thioredoxins and the second at the same position as an intron in thioredoxin
domains of disulfide isomerases. This strongly supports the hypothesis of a eukaryotic origin for chloroplastic thioredoxin
f.
Journal of Molecular Evolution 04/1996; 42(4):422-431. · 2.27 Impact Factor
