Navegando por Autor "Araújo, Wagner L."

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2-Oxoglutarate: linking TCA cycle function with amino acid, glucosinolate, flavonoid, alkaloid, and gibberellin biosynthesis
(Frontiers in Plant Science, 2014-10-05) Araújo, Wagner L.; Martins, Auxiliadora O.; Fernie, Alisdair R.; Tohge, Takayuki
The tricarboxylic acid (TCA) cycle intermediate 2-oxoglutarate (2-OG) is used as an obligatory substrate in a range of oxidative reactions catalyzed by 2-OG-dependent dioxygenases. These enzymes are widespread in nature being involved in several important biochemical processes. We have recently demonstrated that tomato plants in which the TCA cycle enzyme 2-OG dehydrogenase (2-ODD) was antisense inhibited were characterized by early senescence and modified fruit ripening associated with differences in the levels of bioactive gibberellin (GA). Accordingly, there is now compelling evidence that the TCA cycle plays an important role in modulating the rate of flux from 2-OG to amino acid metabolism. Here we discuss recent advances in the biochemistry and molecular biology of 2-OG metabolism occurring in different biological systems indicating the importance of 2-OG and 2-OG dependent dioxygenases not only in glucosinolate, flavonoid and alkaloid metabolism but also in GA and amino acid metabolism. We additionally summarize recent findings regarding the impact of modification of 2-OG metabolism on biosynthetic pathways involving 2-ODDs.
Alternative carbon sources for isoprene Emission
(Trends in Plant Science, 2018-12-01) Araújo, Wagner L.; Souza, Vinícius Fernandes de; Niinemets, Ülo; Rasulov, Bahtijor; Vickers, Claudia E.; Duvoisin Júnior, Sergio; Gonçalves, José Francisco de Carvalho
Isoprene and other plastidial isoprenoids are produced primarily from recently assimilated photosynthates via the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway. However, when environmental conditions limit photosynthesis, a fraction of carbon for MEP pathway can come from extrachloroplastic sources. The flow of extrachloroplastic carbon depends on the species and on leaf developmental and environmental conditions. The exchange of common phosphorylated intermediates between the MEP pathway and other metabolic pathways can occur via plastidic phosphate translocators. C1 and C2 carbon intermediates can contribute to chloroplastic metabolism, including photosynthesis and isoprenoid synthesis. Integration of these metabolic processes provide an example of metabolic flexibility, and results in the synthesis of primary metabolites for plant growth and secondary metabolites for plant defense, allowing effective use of environmental resources under multiple stresses.
Amino acid catabolism in plants
(Molecular Plant, 2015-09-15) Hildebrandt, Tatjana M.; Nesi, Adriano Nunes; Araújo, Wagner L.; Braun, Hans-Peter
Amino acids have various prominent functions in plants. Besides their usage during protein biosynthesis, they also represent building blocks for several other biosynthesis pathways and play pivotal roles during signaling processes as well as in plant stress response. In general, pool sizes of the 20 amino acids differ strongly and change dynamically depending on the developmental and physiological state of the plant cell. Besides amino acid biosynthesis, which has already been investigated in great detail, the catabolism of amino acids is of central importance for adjusting their pool sizes but so far has drawn much less attention. The degradation of amino acids can also contribute substantially to the energy state of plant cells under certain physiological conditions, e.g. carbon starvation. In this review, we discuss the biological role of amino acid catabolism and summarize current knowledge on amino acid degradation pathways and their regulation in the context of plant cell physiology.
Analysis of knockout mutants reveals non-redundant functions of poly(ADP-ribose)polymerase isoforms in Arabidopsis
(Plant Molecular Biology, 2015-10-01) Pham, Phuong Anh; Wahl, Vanessa; Tohge, Takayuki; Souza, Laise Rosado de; Zhang, Youjun; Do, Phuc Thi; Olas, Justyna J.; Stitt, Mark; Araújo, Wagner L.; Fernie, Alisdair R.
The enzyme poly(ADP-ribose)polymerase (PARP) has a dual function being involved both in the poly(ADP-ribosyl)ation and being a constituent of the NAD+ salvage pathway. To date most studies, both in plant and non-plant systems, have focused on the signaling role of PARP in poly(ADP-ribosyl)ation rather than any role that can be ascribed to its metabolic function. In order to address this question we here used a combination of expression, transcript and protein localization studies of all three PARP isoforms of Arabidopsis alongside physiological analysis of the corresponding mutants. Our analyses indicated that whilst all isoforms of PARP were localized to the nucleus they are also present in non-nuclear locations with parp1 and parp3 also localised in the cytosol, and parp2 also present in the mitochondria. We next isolated and characterized insertional knockout mutants of all three isoforms confirming a complete knockout in the full length transcript levels of the target genes as well as a reduced total leaf NAD hydrolase activity in the two isoforms (PARP1, PARP2) that are highly expressed in leaves. Physiological evaluation of the mutant lines revealed that they displayed distinctive metabolic and root growth characteristics albeit unaltered leaf morphology under optimal growth conditions. We therefore conclude that the PARP isoforms play non-redundant non-nuclear metabolic roles and that their function is highly important in rapidly growing tissues such as the shoot apical meristem, roots and seeds.
Antisense inhibition of the 2-oxoglutarate dehydrogenase complex in tomato demonstrates its importance for plant respiration and during leaf senescence and fruit maturation
(The Plant Cell, 2012-06) Araújo, Wagner L.; Nunes-Nesi, Adriano; Tohge, Takayuki; Osorio, Sonia; Lohse, Marc; Balbo, Ilse; Krahnert, Ina; Sienkiewicz-Porzucek, Agata; Usadel, Björn; Fernie, Alisdair R.
Transgenic tomato (Solanum lycopersicum) plants expressing a fragment of the gene encoding the E1 subunit of the 2-oxoglutarate dehydrogenase complex in the antisense orientation and exhibiting substantial reductions in the activity of this enzyme exhibit a considerably reduced rate of respiration. They were, however, characterized by largely unaltered photosynthetic rates and fruit yields but restricted leaf, stem, and root growth. These lines displayed markedly altered metabolic profiles, including changes in tricarboxylic acid cycle intermediates and in the majority of the amino acids but unaltered pyridine nucleotide content both in leaves and during the progression of fruit ripening. Moreover, they displayed a generally accelerated development exhibiting early flowering, accelerated fruit ripening, and a markedly earlier onset of leaf senescence. In addition, transcript and selective hormone profiling of gibberellins and abscisic acid revealed changes only in the former coupled to changes in transcripts encoding enzymes of gibberellin biosynthesis. The data obtained are discussed in the context of the importance of this enzyme in both photosynthetic and respiratory metabolism as well as in programs of plant development connected to carbon–nitrogen interactions.
Autophagy deficiency compromises alternative pathways of respiration following energy deprivation in Arabidopsis thaliana
(Plant Physiology, 2017-09-22) Barros, Jessica A.S.; Cavalcanti, João Henrique F.; Medeiros, David B.; Nunes-Nesi, Adriano; Avin-Wittenberg, Tamar; Fernie, Alisdair R.; Araújo, Wagner L.
Under heterotrophic conditions, carbohydrate oxidation inside the mitochondrion is the primary energy source for cellular metabolism. However, during energy-limited conditions, alternative substrates are required to support respiration. Amino acid oxidation in plant cells plays a key role in this by generating electrons that can be transferred to the mitochondrial electron transport chain via the electron transfer flavoprotein/ubiquinone oxidoreductase system. Autophagy, a catabolic mechanism for macromolecule and protein recycling, allows the maintenance of amino acid pools and nutrient remobilization. Although the association between autophagy and alternative respiratory substrates has been suggested, the extent to which autophagy and primary metabolism interact to support plant respiration remains unclear. To investigate the metabolic importance of autophagy during development and under extended darkness, Arabidopsis (Arabidopsis thaliana) mutants with disruption of autophagy (atg mutants) were used. Under normal growth conditions, atg mutants showed lower growth and seed production with no impact on photosynthesis. Following extended darkness, atg mutants were characterized by signatures of early senescence, including decreased chlorophyll content and maximum photochemical efficiency of photosystem II coupled with increases in dark respiration. Transcript levels of genes involved in alternative pathways of respiration and amino acid catabolism were up-regulated in atg mutants. The metabolite profiles of dark-treated leaves revealed an extensive metabolic reprogramming in which increases in amino acid levels were partially compromised in atg mutants. Although an enhanced respiration in atg mutants was observed during extended darkness, autophagy deficiency compromises protein degradation and the generation of amino acids used as alternative substrates to the respiration.
Bundle sheath extensions affect leaf structural and physiological plasticity in response to irradiance
(Plant, Cell & Environment, 2018) Barbosa, Maria Antonia M.; Chitwood, Daniel H.; Azevedo, Aristéa A.; Araújo, Wagner L.; Ribeiro, Dimas M.; Peres, Lázaro E. P.; Martins, Samuel C. V.; Zsögön, Agustin
Coordination between structural and physiological traits is key to plants' responses to environmental fluctuations. In heterobaric leaves, bundle sheath extensions (BSEs) increase photosynthetic performance (light‐saturated rates of photosynthesis, Amax) and water transport capacity (leaf hydraulic conductance, Kleaf). However, it is not clear how BSEs affect these and other leaf developmental and physiological parameters in response to environmental conditions. The obscuravenosa (obv) mutation, found in many commercial tomato varieties, leads to absence of BSEs. We examined structural and physiological traits of tomato heterobaric and homobaric (obv) near‐isogenic lines grown at two different irradiance levels. Kleaf, minor vein density, and stomatal pore area index decreased with shading in heterobaric but not in homobaric leaves, which show similarly lower values in both conditions. Homobaric plants, on the other hand, showed increased Amax, leaf intercellular air spaces, and mesophyll surface area exposed to intercellular airspace (Smes) in comparison with heterobaric plants when both were grown in the shade. BSEs further affected carbon isotope discrimination, a proxy for long‐term water‐use efficiency. BSEs confer plasticity in traits related to leaf structure and function in response to irradiance levels and might act as a hub integrating leaf structure, photosynthetic function, and water supply and demand.
Can stable isotope mass spectrometry replace ‎radiolabelled approaches in metabolic studies?
(Plant Science, 2016-05-14) Silva, Willian Batista; Daloso, Danilo M.; Fernie, Alisdair R.; Nunes-Nesi, Adriano; Araújo, Wagner L.
Metabolic pathways and the key regulatory points thereof can be deduced using isotopically labelled substrates. One prerequisite is the accurate measurement of the labeling pattern of targeted metabolites. The subsequent estimation of metabolic fluxes following incubation in radiolabelled substrates has been extensively used. Radiolabelling is a sensitive approach and allows determination of total label uptake since the total radiolabel content is easy to detect. However, the incubation of cells, tissues or the whole plant in a stable isotope enriched environment and the use of either mass spectrometry or nuclear magnetic resonance techniques to determine label incorporation within specific metabolites offers the possibility to readily obtain metabolic information with higher resolution. It additionally also offers an important complement to other post-genomic strategies such as metabolite profiling providing insights into the regulation of the metabolic network and thus allowing a more thorough description of plant cellular function. Thus, although safety concerns mean that stable isotope feeding is generally preferred, the techniques are in truth highly complementary and application of both approaches in tandem currently probably provides the best route towards a comprehensive understanding of plant cellular metabolism.
Comparative evaluation of different preservation methods for cyanobacterial strains
(Journal of Applied Phycology, 2013-08) Esteves-Ferreira, Alberto A.; Corrêa, Débora M.; Carneiro, Antônio P. S.; Rosa, Rinamara M.; Loterio, Robson; Araújo, Wagner L.
Maintaining pure cultures using preservation methods is of high importance for biotechnological purposes. However, preservation does not necessarily guarantee the genetic stability of these cultures. Therefore, preservation methods are currently needed to assure viability as well as genetic, physiological, and morphological integrity across storage periods. In this study, preservation of five isolates from the microalgae and cyanobacteria collection of the Plant Biology Department, Federal University of Viçosa, Minas Gerais, Brazil was investigated via monthly analyses of cell viability, biomass recovery, and contaminant concentrations over a period of 120 days. Lyophilization was adequate for both heterocystous cyanobacteria and other strains that were able to differentiate hormogones or to synthesize thick layers of exopolysaccharides. Lyophilization was also able to maintain cultures with low levels of contaminants. Dimethyl sulfoxide was relatively efficient, though some of the strains were susceptible to its cytotoxic effects. Our results demonstrated that cryopreservation with glycerol was the most efficient method. The ability to routinely preserve cyanobacterial strains reduces costs associated with maintaining large culture collections and reduces the risks of losing particular strains or species through contamination and genetic drift. The results obtained in this study are therefore discussed in the context of the efficiency of the methods and the current need to develop suitable methods for maintenance of cyanobacterial collections.
The complex role of mitochondrial metabolism in plant aluminum resistance
(Trends in Plant Science, 2014-01-24) Nunes-Nesi, Adriano; Brito, Danielle Santos; Inostroza-Blancheteau, Claudio; Fernie, Alisdair R.; Araújo, Wagner L.
The majority of soils in tropical and subtropical regions are acidic, rendering the soil a major limitation to plant growth and food production in many developing countries. High concentrations of soluble aluminum cations,particularly Al 3+ , are largely responsible for reducing root elongation and disrupting nutrient and water uptake.Two mechanisms, namely, the exclusion mechanism and tolerance mechanism, have been proposed to govern Al 3+ resistance in plants. Both mechanisms are related to mitochondrial activity as well as to mitochondrial metabolism and organic acid transport. Here, we review the considerable progress that has been made towards developing an understanding of the physiological role of mitochondria in the aluminum response and discuss the potential for using this knowledge in next-generation engineering.
Comprehensive metabolic reprograming in freshwater Nitzschia palea strains undergoing nitrogen starvation is likely associated with its ecological origin
(Algal Research, 2016-09) Machado, Mariana; Bromke, Mariusz; Domingues Júnior, Adilson Pereira; Vaz, Marcelo Gomes Marçal Vieira; Rosa, Rinamara Martins; Vinson, Christina C.; Sabir, Jamal S.; Rocha, Diego Ismael; Martins, Marcio Arêdes; Araújo, Wagner L.; Willmitzer, Lothar; Szymanski, Jedrzej; Nunes-Nesi, Adriano
Nitrogen deficiency can increase the lipid content in certain microalgae species, including diatoms. However, the molecular and metabolic basis of such changes remains rather unclear. We analyzed strains of freshwater Nitzschia palea collected from a eutrophic pond and from an artificial rock. The habitats, differing in light and nutrient availability, lead to two metabolically distinct strains, BR006 and BR022. Differential accumulation of primary compounds, membrane lipid composition and fatty acid saturation were observed. Metabolic and biophysical analysis demonstrated differential sensitivity to N regimes: depleted, replete and saturated. Whereas N depletion leads to typical stress-related responses in both strains, including reduction of protein and photosynthesis, the response observed in BR006 is far more severe. Our results demonstrated that these strains developed distinct metabolic responses to N conditions. BR022 is able to maintain cellular homeostasis and slows down growth according to N availability. In contrast, BR006 maximizes growth rate even under N limitation, by triggering stress response, relocating carbon pool to lipid compounds and quickly reaching growth arrest after N exhaustion. We identified a relationship between habitat characteristics and metabolic responses, providing a metabolic perspective on ecological plasticity of N. palea, which helps it to survive a wide range of habitats.
Cyanobacterial nitrogenases: phylogenetic diversity, regulation and functional predictions
(Genetics and Molecular Biology, 2016-12-21) Esteves-Ferreira, Alberto A.; Cavalcanti, João Henrique Frota; Vaz, Marcelo Gomes Marçal Vieira; Alvarenga, Luna V.; Nunes-Nesi, Adriano; Araújo, Wagner L.
Cyanobacteria is a remarkable group of prokaryotic photosynthetic microorganisms, with several genera capable of fixing atmospheric nitrogen (N2) and presenting a wide range of morphologies. Although the nitrogenase complex is not present in all cyanobacterial taxa, it is spread across several cyanobacterial strains. The nitrogenase complex has also a high theoretical potential for biofuel production, since H2 is a by-product produced during N2 fixation. In this review we discuss the significance of a relatively wide variety of cell morphologies and metabolic strategies that allow spatial and temporal separation of N2 fixation from photosynthesis in cyanobacteria. Phylogenetic reconstructions based on 16S rRNA and nifD gene sequences shed light on the evolutionary history of the two genes. Our results demonstrated that (i) sequences of genes involved in nitrogen fixation (nifD) from several morphologically distinct strains of cyanobacteria are grouped in similarity with their morphology classification and phylogeny, and (ii) nifD genes from heterocytous strains share a common ancestor. By using this data we also discuss the evolutionary importance of processes such as horizontal gene transfer and genetic duplication for nitrogenase evolution and diversification. Finally, we discuss the importance of H2 synthesis in cyanobacteria, as well as strategies and challenges to improve cyanobacterial H2 production.
Data-mining bioinformatics: connecting adenylate transport and metabolic responses to stress
(Trends in Plant Science, 2018-11) Fonseca-Pereira, Paula da; Neri-Silva, Roberto; Cavalcanti, João Henrique F.; Brito, Danielle S.; Weber, Andreas P. M.; Araújo, Wagner L.; Nunes-Nesi, Adriano
Adenine nucleotides are essential in countless processes within the cellular metabolism. In plants, ATP is mainly produced in chloroplasts and mitochondria through photophosphorylation and oxidative phosphorylation, respectively. Thus, efficient adenylate transport systems are required for intracellular energy partitioning between the cell organelles. Adenylate carriers present in different subcellular compartments have been previously identified and biochemically characterized in plants. Here, by using data-mining bioinformatics tools, we propose how, and to what extent, these carriers integrate energy metabolism within a plant cell under different environmental conditions. We demonstrate that the expression pattern of the corresponding genes is variable under different environmental conditions, suggesting that specific adenylate carriers have distinct and nonredundant functions in plants.
Differential impact of amino acids on OXPHOS system activity following carbohydrate starvation in Arabidopsis cell suspensions
(Physiologia Plantarum, 2017-07-20) Cavalcanti, João Henrique F.; Quinhones, Carla G. S.; Schertl, Peter; Brito, Danielle S.; Eubel, Holger; Hildebrandt, Tatjana; Nunes-Nesi, Adriano; Braun, Hans-Peter; Araújo, Wagner L.
Plant respiration mostly depends on the activity of glycolysis and the oxidation of organic acids in the tricarboxylic acid cycle to synthesize ATP. However, during stress situations plant cells also use amino acids as alternative substrates to donate electrons through the electron-transfer flavoprotein (ETF)/ETF:ubiquinone oxidoreductase (ETF/ETFQO) complex to the mitochondrial electron transport chain (mETC). Given this, we investigated changes of the oxidative phosphorylation (OXPHOS) system in Arabidopsis thaliana cell culture under carbohydrate starvation supplied with a range of amino acids. Induction of isovaleryl-CoA dehydrogenase (IVDH) activity was observed under carbohydrate starvation which was associated with increased amounts of IVDH protein detected by immunoblotting. Furthermore, activities of the protein complexes of the mETC were reduced under carbohydrate starvation. We also observed that OXPHOS system activity behavior is differently affected by different amino acids and that proteins associated with amino acids catabolism are upregulated in cells following carbohydrate starvation. Collectively, our results support the contention that ETF/ETFQO is an essential pathway to donate electrons to the mETC and that amino acids are alternative substrates to maintain respiration under carbohydrate starvation.
Differential root and shoot responses in the metabolism of tomato plants exhibiting reduced levels of gibberellin
(Environmental and Experimental Botany, 2019-01) Martins, Auxiliadora O.; Omena-Garcia, Rebeca P.; Oliveira, Franciele S.; Silva, Welder A.; Hajirezaei, Mohammad-Reza; Vallarino, José G.; Ribeiro, Dimas Mendes; Fernie, Alisdair R.; Nunes-Nesi, Adriano; Araújo, Wagner L.
The ability to adapt to the environment is crucial for plant survival and thus a refined communication system capable of integrating endogenous and exogenous signals and further relaying this information to different parts of the plant is a key component of such adaptability. Given that they grow in highly distinct environments it is arguably unsurprising that roots and shoots display different responses to a given environmental condition. Accordingly, a higher sensitivity of roots to gibberellins (GAs) allows rapid adjustments in growth and development possibly triggering (a) stress tolerance mechanism(s). Here we investigated the differential metabolic responses between root and shoot following reductions of the endogenous GA content using tomato (Solanum lycopersicum L.) plants deficient in GA biosynthesis (gib3, moderately deficient, gib2, intermediate deficiency and gib1, extremely deficient in GAs). GA depletion impedes shoot growth to a greater extent than root growth in all mutants. Moreover, the greater the reduction in GA content the greater the extent of a disturbance at the metabolic level. Low leaf carbohydrate contents were observed in plants displaying higher root growth, suggesting an enhanced flow of photoassimilate to support root growth. Large increases in amino acids contents of either roots or shoot were observed. The increased amino acid content was coupled to reduced levels of TCA cycle intermediates suggesting that these changes are directly linked to early reactions of nitrogen assimilation. The combined data are discussed in terms of our current understanding of the interaction between GA and primary metabolism and their crosstalk in environmental responses.
Downregulation of the δ-subunit reduces mitochondrial ATP synthase levels, alters respiration, and restricts growth and gametophyte development in Arabidopsis
(The Plant Cell, 2012-07) Nunes-Nesi, Adriano; Geisler, Daniela A.; Päpke, Carola; Obata, Toshihiro; Matthes, Annemarie; Schneitz, Kay; Maximova, Eugenia; Araújo, Wagner L.; Fernie, Alisdair R.; Persson, Staffan
The mitochondrial ATP synthase (F1Fo complex) is an evolutionary conserved multimeric protein complex that synthesizes the main bulk of cytosolic ATP, but the regulatory mechanisms of the subunits are only poorly understood in plants. In yeast, the δ-subunit links the membrane-embedded Fo part to the matrix-facing central stalk of F1. We used genetic interference and an inhibitor to investigate the molecular function and physiological impact of the δ-subunit in Arabidopsis thaliana. Delta mutants displayed both male and female gametophyte defects. RNA interference of delta resulted in growth retardation, reduced ATP synthase amounts, and increased alternative oxidase capacity and led to specific long-term increases in Ala and Gly levels. By contrast, inhibition of the complex using oligomycin triggered broad metabolic changes, affecting glycolysis and the tricarboxylic acid cycle, and led to a successive induction of transcripts for alternative respiratory pathways and for redox and biotic stress-related transcription factors. We conclude that (1) the δ-subunit is essential for male gametophyte development in Arabidopsis, (2) a disturbance of the ATP synthase appears to lead to an early transition phase and a long-term metabolic steady state, and (3) the observed long-term adjustments in mitochondrial metabolism are linked to reduced growth and deficiencies in gametophyte development.
Engineering photosynthesis: progress and perspectives
(F1000Research, 2017-10-26) Orr, Douglas J.; Pereira, Auderlan M.; Pereira, Paula da Fonseca; Pereira-Lima, Ítalo A.; Zsögön, Agustin; Araújo, Wagner L.
Photosynthesis is the basis of primary productivity on the planet. Crop breeding has sustained steady improvements in yield to keep pace with population growth increases. Yet these advances have not resulted from improving the photosynthetic process per se but rather of altering the way carbon is partitioned within the plant. Mounting evidence suggests that the rate at which crop yields can be boosted by traditional plant breeding approaches is wavering, and they may reach a “yield ceiling” in the foreseeable future. Further increases in yield will likely depend on the targeted manipulation of plant metabolism. Improving photosynthesis poses one such route, with simulations indicating it could have a significant transformative influence on enhancing crop productivity. Here, we summarize recent advances of alternative approaches for the manipulation and enhancement of photosynthesis and their possible application for crop improvement.
Enhanced photosynthesis and growth in atquac1 knockout mutants are due to altered organic acid accumulation and an increase in both stomatal and mesophyll conductance
(Plant Physiology, 2015-11-05) Medeiros, David B.; Martins, Samuel C.V.; Cavalcanti, João Henrique F.; Daloso, Danilo M.; Martinoia, Enrico; Nunes-Nesi, Adriano; DaMatta, Fábio M.; Fernie, Alisdair R.; Araújo, Wagner L.
Stomata control the exchange of CO2 and water vapor in land plants. Thus, whereas a constant supply of CO2 is required to maintain adequate rates of photosynthesis, the accompanying water losses must be tightly regulated to prevent dehydration and undesired metabolic changes. Accordingly, the uptake or release of ions and metabolites from guard cells is necessary to achieve normal stomatal function. The AtQUAC1, an R-type anion channel responsible for the release of malate from guard cells, is essential for efficient stomatal closure. Here, we demonstrate that mutant plants lacking AtQUAC1 accumulated higher levels of malate and fumarate. These mutant plants not only display slower stomatal closure in response to increased CO2 concentration and dark but are also characterized by improved mesophyll conductance. These responses were accompanied by increases in both photosynthesis and respiration rates, without affecting the activity of photosynthetic and respiratory enzymes and the expression of other transporter genes in guard cells, which ultimately led to improved growth. Collectively, our results highlight that the transport of organic acids plays a key role in plant cell metabolism and demonstrate that AtQUAC1 reduce diffusive limitations to photosynthesis, which, at least partially, explain the observed increments in growth under well-watered conditions.
Ethylene coordinates seed germination behavior in response to low soil pH in Stylosanthes humilis
(Plant and Soil, 2018-04) Ribeiro, Ricardo P.; Costa, Lucas C.; Medina, Eduardo F.; Araújo, Wagner L.; Zsögön, Agustín; Ribeiro, Dimas M.
Stylosanthes humilis is known to exhibit high persistence in acid soils, however, how low soil pH controls seed germination as well as root and hypocotyl growth remains unknown. This study was carried out to evaluate the hormonal and metabolic alterations induced by low soil pH on seed germination behavior of S. humilis.Seeds of S. humilis were sown in acid soil samples or sand soaked in buffer solution with pH ranging from 4.0 to 7.0. Concentrations of indole-3-acetic acid, ethylene, 1-aminocyclopropane-1-carboxylic acid (ACC), primary metabolite profile and final seed germination were evaluated after four days.Low soil pH led to increased final seed germination, concomitantly with higher root penetration into the soil as well as higher ACC and ethylene production by seedlings. Treatment with the ethylene biosynthesis inhibitor L-α-(2-aminoethoxyvinyl)-glycine (AVG) greatly reduced final seed germination under acidic conditions. Final seed germination of seeds treated with AVG was increased by exogenous ethylene application in a dose-dependent manner. Furthermore, low soil pH promoted distinct changes in IAA concentrations, and in carbon and nitrogen metabolism in hypocotyl and roots.Low soil pH increases the final germination of S. humilis seeds through alterations in ethylene metabolism, allowing root penetration into the soil.
Evolution and functional implications of the tricarboxylic acid cycle as revealed by phylogenetic analysis
(Genome Biology and Evolution, 2014-09-25) Cavalcanti, João Henrique Frota; Esteves-Ferreira, Alberto A.; Quinhones, Carla G.S.; Pereira-Lima, Italo A.; Nunes-Nesi, Adriano; Fernie, Alisdair R.; Araújo, Wagner L.
The tricarboxylic acid (TCA) cycle, a crucial component of respiratory metabolism, is composed of a set of eight enzymes present in the mitochondrial matrix. However, most of the TCA cycle enzymes are encoded in the nucleus in higher eukaryotes. In addition, evidence has accumulated demonstrating that nuclear genes were acquired from the mitochondrial genome during the course of evolution. For this reason, we here analyzed the evolutionary history of all TCA cycle enzymes in attempt to better understand the origin of these nuclear-encoded proteins. Our results indicate that prior to endosymbiotic events the TCA cycle seemed to operate only as isolated steps in both the host (eubacterial cell) and mitochondria (alphaproteobacteria). The origin of isoforms present in different cell compartments might be associated either with gene-transfer events which did not result in proper targeting of the protein to mitochondrion or with duplication events. Further in silico analyses allow us to suggest new insights into the possible roles of TCA cycle enzymes in different tissues. Finally, we performed coexpression analysis using mitochondrial TCA cycle genes revealing close connections among these genes most likely related to the higher efficiency of oxidative phosphorylation in this specialized organelle. Moreover, these analyses allowed us to identify further candidate genes which might be used for metabolic engineering purposes given the importance of the TCA cycle during development and/or stress situations.