RESUMO
Cofactors are fundamental to the catalytic activity of enzymes. Additionally, because plants are a critical source of several cofactors (i.e., including their vitamin precursors) within the context of human nutrition, there have been several studies aiming to understand the metabolism of coenzymes and vitamins in plants in detail. For example, compelling evidence has been brought forth regarding the role of cofactors in plants; specifically, it is becoming increasingly clear that an adequate supply of cofactors in plants directly affects their development, metabolism, and stress responses. Here, we review the state-of-the-art knowledge on the significance of coenzymes and their precursors with regard to general plant physiology and discuss the emerging functions attributed to them. Furthermore, we discuss how our understanding of the complex relationship between cofactors and plant metabolism can be used for crop improvement.
Assuntos
Coenzimas , Vitaminas , Humanos , Coenzimas/metabolismo , Vitaminas/metabolismo , Plantas/metabolismo , Fenômenos Fisiológicos VegetaisRESUMO
Nitrogen (N) nutrition and meiosis demand large amounts of energy and widely affect crop yield. Recently, Yang and colleagues connected both processes by demonstrating that meiosis initiation depends on the electron-transfer flavoprotein/electron-transfer flavoprotein:ubiquinone oxidoreductase (ETF/ETFQO) system, whereas meiotic defects of the etfß mutant can be rescued using N supplementation.
Assuntos
Aminoácidos , Ubiquinona , Aminoácidos/metabolismo , Meiose/genética , Nitrogênio , Sementes/genética , Sementes/metabolismoRESUMO
As sessile organisms, plants must adapt their physiology and developmental processes to cope with challenging environmental circumstances, such as the ongoing elevation in atmospheric carbon dioxide (CO2 ) levels. Nicotinamide adenine dinucleotide (NAD+ ) is a cornerstone of plant metabolism and plays an essential role in redox homeostasis. Given that plants impaired in NAD metabolism and transport often display growth defects, low seed production and disturbed stomatal development/movement, we hypothesized that subcellular NAD distribution could be a candidate for plants to exploit the effects of CO2 fertilization. We report that an efficient subcellular NAD+ distribution is required for the fecundity-promoting effects of elevated CO2 levels. Plants with reduced expression of either mitochondrial (NDT1 or NDT2) or peroxisomal (PXN) NAD+ transporter genes grown under elevated CO2 exhibited reduced total leaf area compared with the wild-type while PXN mutants also displayed reduced leaf number. NDT2 and PXN lines grown under elevated CO2 conditions displayed reduced rosette dry weight and lower photosynthetic rates coupled with reduced stomatal conductance. Interestingly, high CO2 doubled seed production and seed weight in the wild-type, whereas the mutants were less responsive to increases in CO2 levels during reproduction, producing far fewer seeds than the wild-type under both CO2 conditions. These data highlight the importance of mitochondrial and peroxisomal NAD+ uptake mediated by distinct NAD transporter proteins to modulate photosynthesis and seed production under high CO2 levels.
Assuntos
Dióxido de Carbono , NAD , Dióxido de Carbono/metabolismo , NAD/metabolismo , Fotossíntese/fisiologia , Folhas de Planta/metabolismo , Sementes/metabolismoRESUMO
The importance of the alternative donation of electrons to the ubiquinol pool via the electron-transfer flavoprotein/electron-transfer flavoprotein:ubiquinone oxidoreductase (ETF/ETFQO) complex has been demonstrated. However, the functional significance of this pathway during seed development and germination remains to be elucidated. To assess the function of this pathway, we performed a detailed metabolic and transcriptomic analysis of Arabidopsis mutants to test the molecular consequences of a dysfunctional ETF/ETFQO pathway. We demonstrate that the disruption of this pathway compromises seed germination in the absence of an external carbon source and also impacts seed size and yield. Total protein and storage protein content is reduced in dry seeds, whilst sucrose levels remain invariant. Seeds of ETFQO and related mutants were also characterized by an altered fatty acid composition. During seed development, lower levels of fatty acids and proteins accumulated in the etfqo-1 mutant as well as in mutants in the alternative electron donors isovaleryl-CoA dehydrogenase (ivdh-1) and d-2-hydroxyglutarate dehydrogenase (d2hgdh1-2). Furthermore, the content of several amino acids was increased in etfqo-1 mutants during seed development, indicating that these mutants are not using such amino acids as alternative energy source for respiration. Transcriptome analysis revealed alterations in the expression levels of several genes involved in energy and hormonal metabolism. Our findings demonstrated that the alternative pathway of respiration mediated by the ETF/ETFQO complex affects seed germination and development by directly adjusting carbon storage during seed filling. These results indicate a role for the pathway in the normal plant life cycle to complement its previously defined roles in the response to abiotic stress.
Assuntos
Aminoácidos/metabolismo , Arabidopsis/genética , Carbono/metabolismo , Flavoproteínas Transferidoras de Elétrons/metabolismo , Proteínas Ferro-Enxofre/metabolismo , Oxirredutases atuantes sobre Doadores de Grupo CH-NH/metabolismo , Arabidopsis/enzimologia , Arabidopsis/crescimento & desenvolvimento , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Flavoproteínas Transferidoras de Elétrons/genética , Germinação , Proteínas Ferro-Enxofre/genética , Mutação , Oxirredutases atuantes sobre Doadores de Grupo CH-NH/genética , Sementes/enzimologia , Sementes/genética , Sementes/crescimento & desenvolvimento , Ubiquinona/análogos & derivados , Ubiquinona/metabolismoRESUMO
Thioredoxins (TRXs) are ubiquitous proteins engaged in the redox regulation of plant metabolism. Whilst the light-dependent TRX-mediated activation of Calvin-Benson cycle enzymes is well documented, the role of extraplastidial TRXs in the control of the mitochondrial (photo)respiratory metabolism has been revealed relatively recently. Mitochondrially located TRX o1 has been identified as a regulator of alternative oxidase, enzymes of, or associated with, the tricarboxylic acid (TCA) cycle, and the mitochondrial dihydrolipoamide dehydrogenase (mtLPD) involved in photorespiration, the TCA cycle, and the degradation of branched chain amino acids. TRXs are seemingly a major point of metabolic regulation responsible for activating photosynthesis and adjusting mitochondrial photorespiratory metabolism according to the prevailing cellular redox status. Furthermore, TRX-mediated (de)activation of TCA cycle enzymes contributes to explain the non-cyclic flux mode of operation of this cycle in illuminated leaves. Here we provide an overview on the decisive role of TRXs in the coordination of mitochondrial metabolism in the light and provide in silico evidence for other redox-regulated photorespiratory enzymes. We further discuss the consequences of mtLPD regulation beyond photorespiration and provide outstanding questions that should be addressed in future studies to improve our understanding of the role of TRXs in the regulation of central metabolism.
Assuntos
Arabidopsis , Arabidopsis/metabolismo , Oxirredução , Fotossíntese , Respiração , Tiorredoxinas/metabolismoRESUMO
Much attention has been given to the enhancement of photosynthesis as a strategy for the optimization of crop productivity. As traditional plant breeding is most likely reaching a plateau, there is a timely need to accelerate improvements in photosynthetic efficiency by means of novel tools and biotechnological solutions. The emerging field of synthetic biology offers the potential for building completely novel pathways in predictable directions and, thus, addresses the global requirements for higher yields expected to occur in the 21st century. Here, we discuss recent advances and current challenges of engineering improved photosynthesis in the era of synthetic biology toward optimized utilization of solar energy and carbon sources to optimize the production of food, fiber, and fuel.
Assuntos
Produtos Agrícolas/fisiologia , Fotossíntese , Melhoramento Vegetal/métodos , Biologia Sintética/métodos , Dióxido de Carbono/metabolismo , Produtos Agrícolas/genética , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Plantas Geneticamente Modificadas , Ribulose-Bifosfato Carboxilase/genética , Ribulose-Bifosfato Carboxilase/metabolismoRESUMO
Nicotinamide adenine dinucleotide (NAD) plays a central role in redox metabolism in all domains of life. Additional roles in regulating posttranslational protein modifications and cell signaling implicate NAD as a potential integrator of central metabolism and programs regulating stress responses and development. Here we found that NAD negatively impacts stomatal development in cotyledons of Arabidopsis thaliana. Plants with reduced capacity for NAD+ transport from the cytosol into the mitochondria or the peroxisomes exhibited reduced numbers of stomatal lineage cells and reduced stomatal density. Cotyledons of plants with reduced NAD+ breakdown capacity and NAD+ -treated cotyledons also presented reduced stomatal number. Expression of stomatal lineage-related genes was repressed in plants with reduced expression of NAD+ transporters as well as in plants treated with NAD+ . Impaired NAD+ transport was further associated with an induction of abscisic acid (ABA)-responsive genes. Inhibition of ABA synthesis rescued the stomatal phenotype in mutants deficient in intracellular NAD+ transport, whereas exogenous NAD+ feeding of aba-2 and ost1 seedlings, impaired in ABA synthesis and ABA signaling, respectively, did not impact stomatal number, placing NAD upstream of ABA. Additionally, in vivo measurement of ABA dynamics in seedlings of an ABA-specific optogenetic reporter - ABAleon2.1 - treated with NAD+ showed increases in ABA content suggesting that NAD+ impacts on stomatal development through ABA synthesis and signaling. Our results demonstrate that intracellular NAD+ homeostasis as set by synthesis, breakdown and transport is essential for normal stomatal development, and provide a link between central metabolism, hormone signaling and developmental plasticity.
Assuntos
Ácido Abscísico/metabolismo , Arabidopsis/metabolismo , NAD/metabolismo , Estômatos de Plantas/crescimento & desenvolvimento , Arabidopsis/efeitos dos fármacos , Arabidopsis/genética , Arabidopsis/crescimento & desenvolvimento , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Cotilédone/efeitos dos fármacos , Cotilédone/metabolismo , Regulação da Expressão Gênica de Plantas , Mitocôndrias/metabolismo , Mutação , NAD/farmacologia , Estômatos de Plantas/metabolismoRESUMO
Despite the fundamental importance of nicotinamide adenine dinucleotide (NAD+) for metabolism, the physiological roles of NAD+ carriers in plants remain unclear. We previously characterized the Arabidopsis thaliana gene (At1g25380), named AtNDT2, encoding a protein located in the mitochondrial inner membrane, which imports NAD+ from the cytosol using ADP and AMP as counter-exchange substrates for NAD+. Here, we further investigated the physiological roles of NDT2, by isolating a T-DNA insertion line, generating an antisense line and characterizing these genotypes in detail. Reduced NDT2 expression affected reproductive phase by reducing total seed yield. In addition, reduced seed germination and retardation in seedling establishment were observed in the mutant lines. Moreover, remarkable changes in primary metabolism were observed in dry and germinated seeds and an increase in fatty acid levels was verified during seedling establishment. Furthermore, flowers and seedlings of NDT2 mutants displayed upregulation of de novo and salvage pathway genes encoding NAD+ biosynthesis enzymes, demonstrating the transcriptional control mediated by NDT2 activity over these genes. Taken together, our results suggest that NDT2 expression is fundamental for maintaining NAD+ balance amongst organelles that modulate metabolism, physiology and developmental processes of heterotrophic tissues.
Assuntos
Proteínas de Arabidopsis/genética , Regulação para Baixo/genética , Regulação da Expressão Gênica de Plantas , Germinação/genética , Mitocôndrias/metabolismo , Proteínas Mitocondriais/genética , NAD/metabolismo , Proteínas de Transporte de Nucleotídeos/genética , Sementes/crescimento & desenvolvimento , Sementes/genética , Proteínas de Arabidopsis/metabolismo , Transporte Biológico , Flores/fisiologia , Genótipo , Processos Heterotróficos , Proteínas Mitocondriais/metabolismo , Proteínas de Transporte de Nucleotídeos/metabolismo , Nucleotídeos/metabolismo , Piridinas/metabolismo , Reprodução/fisiologiaRESUMO
Thioredoxins (TRXs) are important proteins involved in redox regulation of metabolism. In plants, it has been shown that the mitochondrial metabolism is regulated by the mitochondrial TRX system. However, the functional significance of TRX h2, which is found at both cytosol and mitochondria, remains unclear. Arabidopsis plants lacking TRX h2 showed delayed seed germination and reduced respiration alongside impaired stomatal and mesophyll conductance, without impacting photosynthesis under ambient O2 conditions. However, an increase in the stoichiometry of photorespiratory CO2 release was found during O2 -dependent gas exchange measurements in trxh2 mutants. Metabolite profiling of trxh2 leaves revealed alterations in key metabolites of photorespiration and in several metabolites involved in respiration and amino acid metabolism. Decreased abundance of serine hydroxymethyltransferase and glycine decarboxylase (GDC) H and L subunits as well as reduced NADH/NAD+ ratios were also observed in trxh2 mutants. We further demonstrated that the redox status of GDC-L is altered in trxh2 mutants in vivo and that recombinant TRX h2 can deactivate GDC-L in vitro, indicating that this protein is redox regulated by the TRX system. Collectively, our results demonstrate that TRX h2 plays an important role in the redox regulation of mitochondrial photorespiratory metabolism.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Mitocôndrias/metabolismo , Tiorredoxina h/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Dióxido de Carbono/metabolismo , Respiração Celular/fisiologia , Clorofila A , Regulação da Expressão Gênica de Plantas , Glicina Desidrogenase (Descarboxilante)/metabolismo , Glicina Hidroximetiltransferase , Oxirredução , Fotossíntese/fisiologia , Folhas de Planta/metabolismo , Tiorredoxina h/genética , TranscriptomaRESUMO
Nicotinamide adenine dinucleotide (NAD+ ) is an essential coenzyme required for all living organisms. In eukaryotic cells, the final step of NAD+ biosynthesis is exclusively cytosolic. Hence, NAD+ must be imported into organelles to support their metabolic functions. Three NAD+ transporters belonging to the mitochondrial carrier family (MCF) have been biochemically characterized in plants. AtNDT1 (At2g47490), focus of the current study, AtNDT2 (At1g25380), targeted to the inner mitochondrial membrane, and AtPXN (At2g39970), located in the peroxisomal membrane. Although AtNDT1 was presumed to reside in the chloroplast membrane, subcellular localization experiments with green fluorescent protein (GFP) fusions revealed that AtNDT1 locates exclusively in the mitochondrial membrane in stably transformed Arabidopsis plants. To understand the biological function of AtNDT1 in Arabidopsis, three transgenic lines containing an antisense construct of AtNDT1 under the control of the 35S promoter alongside a T-DNA insertional line were evaluated. Plants with reduced AtNDT1 expression displayed lower pollen viability, silique length, and higher rate of seed abortion. Furthermore, these plants also exhibited an increased leaf number and leaf area concomitant with higher photosynthetic rates and higher levels of sucrose and starch. Therefore, lower expression of AtNDT1 was associated with enhanced vegetative growth but severe impairment of the reproductive stage. These results are discussed in the context of the mitochondrial localization of AtNDT1 and its important role in the cellular NAD+ homeostasis for both metabolic and developmental processes in plants.
Assuntos
Antiporters/metabolismo , Proteínas de Arabidopsis/metabolismo , Arabidopsis/genética , Regulação da Expressão Gênica de Plantas , NAD/metabolismo , Antiporters/genética , Arabidopsis/crescimento & desenvolvimento , Arabidopsis/fisiologia , Proteínas de Arabidopsis/genética , Transporte Biológico , Proteínas de Transporte/genética , Proteínas de Transporte/metabolismo , Cloroplastos/metabolismo , Citosol/metabolismo , Proteínas de Fluorescência Verde , Homeostase , Mitocôndrias/metabolismo , Proteínas Mitocondriais/genética , Proteínas Mitocondriais/metabolismo , Mutagênese Insercional , Proteínas de Transporte de Nucleotídeos , Peroxissomos/metabolismo , Folhas de Planta/genética , Folhas de Planta/crescimento & desenvolvimento , Folhas de Planta/fisiologia , Pólen/genética , Pólen/crescimento & desenvolvimento , Pólen/fisiologia , Amido/metabolismoRESUMO
Thiol-disulfide redox exchanges are widely distributed modifications of great importance for metabolic regulation in living cells. In general, the formation of disulfide bonds is controlled by thioredoxins (TRXs), ubiquitous proteins with two redox-active cysteine residues separated by a pair of amino acids. While the function of plastidial TRXs has been extensively studied, the role of the mitochondrial TRX system is much less well understood. Recent studies have demonstrated that the mitochondrial TRXs are required for the proper functioning of the major metabolic pathways, including stomatal function and antioxidant metabolism under sub-optimal conditions including drought and salinity. Furthermore, inactivation of mitochondrial TRX system leads to metabolite adjustments of both primary and secondary metabolism following drought episodes in arabidopsis, and makes the plants more resistant to salt stress. Here we discuss the implications of these findings, which clearly open up several research avenues to achieve a full understanding of the redox control of metabolism under environmental constraining conditions.
Assuntos
Arabidopsis/fisiologia , Mitocôndrias/metabolismo , Estresse Fisiológico , Tiorredoxinas/metabolismo , Arabidopsis/enzimologia , Transporte de Elétrons , Modelos Biológicos , Oxirredução , Fotossíntese , Estômatos de Plantas/fisiologia , Superóxido Dismutase/metabolismoRESUMO
Two independent but complementary studies recently provided the first biochemical proof of the complete absence of mitochondrial Complex I in a multicellular eukaryote. The mitochondrial electron transport chain (mETC) of the hemiparasitic European mistletoe (Viscum album) displays dramatic rearrangements of its components, most likely reflecting its parasitic lifestyle.