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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 etfβ mutant can be rescued using N supplementation.

NAD is a ubiquitous metabolic coenzyme. Although the role of NAD as a central redox shuttle remains of critical interest in plant metabolism, recent evidence indicates that NAD serves additional functions in signaling and regulation. A link with the plant stress hormone abscisic acid (ABA) has emerged on the basis of similar plant phenotypes following interference with NAD or ABA, especially in stomatal development, stomatal movements, responses to pathogens and abiotic stress insults, and seed germination. The association between NAD and ABA regulation appears specific and cannot be accounted for by pleiotropic interference. Here, we review the current picture of the NAD - ABA relationship, discuss emerging candidate mechanisms, and assess avenues to dissect interaction mechanisms.

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.

Photosynthesis is responsible for the primary productivity and maintenance of life on Earth, boosting biological activity and contributing to the maintenance of the environment. In the past, traditional crop improvement was considered sufficient to meet food demands, but the growing demand for food coupled with climate change has modified this scenario over the past decades. However, advances in this area have not focused on photosynthesis per se but rather on fixed carbon partitioning. In short, other approaches must be used to meet an increasing agricultural demand. Thus, several paths may be followed, from modifications in leaf shape and canopy architecture, improving metabolic pathways related to CO

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.

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.

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 (CO

The Adenine Nucleotide Transporter 1 (ADNT1) carrier resides in the mitochondrial inner membrane of plants. Unlike other ADP/ATP carriers, ADNT1 mediates preferably an exchange of mitochondrial matrix ATP by cytosolic AMP, and, to a lesser extent, cytosolic ADP. Because we have previously demonstrated that ADNT1 expression is stronger in senescing tissues, we investigated here the role of ADNT1 carrier during natural and dark-induced senescence in Arabidopsis thaliana. ADNT1 deficient lines displayed an early onset of developmental senescence during both natural and dark-induced senescence. In agreement, moderate loss of chlorophyll content and a reduced PSII photochemical efficiency (Fv/Fm) was observed in the ADNT1 deficient lines at the end of an extended period of darkness. Despite these changes, minor alterations in the levels of sucrose and protein were observed in the ADNT1 deficient lines during dark treatment. However, the levels of a few amino acids as well as the tricarboxylic acid cycle intermediates correlated with ADNT1 expression mainly at the end of dark treatment. Altogether, these results demonstrate that the physiological influence of the AMP/ATP transporter ADNT1 increases during the natural aging and in the later stages of extended darkness treatment. Our data suggest that proper expression of the ADNT1 is important in plant senescence.

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.

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.

Phosphorus (P) deficiency affects agricultural systems by limiting crop quality and yield. Studies have suggested that silicon (Si) improves P uptake in plants grown under P deficiency. However, the effects of Si on photosynthesis and carbohydrate metabolism under P stress remain unclear. We performed a hydroponic study using two wheat cultivars with contrasting sensitivity to P deficiency (Purpura, sensitive; Fritz, semi-tolerant) that were exposed to P (0, 0.01, or 0.1 mM) and Si (0 or 2 mM), and we evaluated the photosynthetic performance and metabolic alterations. In plants from the sensitive cultivar undergoing P deficiency, Si application increased sucrose levels, starch breakdown and length of shoots, and also improved plant dry weight. In Fritz (the semi-tolerant cultivar), Si exposure reduced P concentration, and increased shoot length and P use efficiency (PUE) under P shortage. Interestingly, Si application altered cell wall composition, which was associated with higher mesophyll conductance and net CO2 assimilation in Fritz plants grown under P stress. Together, our results indicate that under P deficiency, Si nutrition positively affects photosynthesis and carbohydrate levels in a genotype-dependent manner. Furthermore, these results suggest that Si plays an important role in maintaining high photosynthetic rates in wheat plants undergoing P deficiency.

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., This review summarizes the progress in the emerging field of synthetic biology applied to photosynthesis. The authors also discuss recent strategies used for manipulating photosynthetic efficiency and their potential biotechnological applications.

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.

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 from altering the way carbon is partitioned within the plant. Given that the pathways of photosynthesis and respiration catalyze partially opposing processes, it follows that their relative activities must be carefully regulated within plant cells. Exciting recent developments in efforts to understanding the interaction between respiration and photosynthesis during the last decades and the potential mechanisms linking mitochondrial function and photosynthetic efficiency will be reviewed. We additionally emphasize the challenges and opportunities to further understand the complex interplay between photosynthesis and related metabolic processes that has limited success in the manipulation and improvement of photosynthesis. We will also summarize recent advances of alternative approaches for the manipulation and enhancement of photosynthesis and their possible application for crop improvement.

Thioredoxins (TRX) 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.

International audience; Thioredoxins (Trxs) modulate metabolic responses during stress conditions; however, the mechanisms governing the responses of plants subjected to multiple drought events and the role of Trxs under these conditions are not well understood. Here we explored the significance of the mito-chondrial Trx system in Arabidopsis following exposure to single and repeated drought events. We analyzed the previously characterized NADPH-dependent Trx reductase A and B double mutant (ntra ntrb) and two independent mito-chondrial thioredoxin o1 (trxo1) mutant lines. Following similar reductions in relative water content ($50%), Trx mutants subjected to two drought cycles displayed a significantly higher maximum quantum efficiency (F v /F m) and were less sensitive to drought than their wild-type counterparts and than all genotypes subjected to a single drought event. Trx mutant plants displayed a faster recovery after two cycles of drought, as observed by the higher accumulation of secondary metabolites and higher stomatal conduct-ance. Our results indicate that plants exposed to multiple drought cycles are able to modulate their subsequent metabolic and physiological response, suggesting the occurrence of an exquisite acclimation in stressed Arabidopsis plants. Moreover, this differential acclimation involves the participation of a set of metabolic changes as well as redox poise alteration following stress recovery.

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.

The objective of this work was to establish an efficient protocol for in vitro multiplication and rooting, as well as ex vitroacclimatization of Aegiphila verticillata, a woody species found in Brazilian rocky fields. Aseptic cultures were established by seeds and two multiplication analyses were performed. In the first, we employed 6-benzylaminopurine (BAP – 0, 2.5, 5 and 7.5 μM) + α-naphthalene acetic acid (NAA – 0, 0.2, 0.4 and 0.6 μM) and, in the second, were studied adenine sulfate, kinetin and thidiazuron (0, 5, 7.5, 10 and 12.5 μM). After 90 days, we assessed the quantitative and qualitative shoot propagation. There were more than 90% seed germination and low contamination (2%). In multiplication phase, the culture medium that promoted the best quantitative and qualitative culture development was supplemented with 7.5 μM BAP + 0.4 μM NAA. In the rooting assay, were used NAA, indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA) (0, 0.1, 0.2, 0.3 or 0.4 μM). After 90 days, the root number and rooting quality were evaluated. In this analysis, differences were not found between the control and the other treatments. Rooted plantlets were acclimatized in styrofoam trays for 30 days, after which they were transferred to pots in the greenhouse. Only 3% of the plants subjected to initial acclimatization died and 70% of the plants transferred to the field conditions survived and showed normal development. The results founded in this work are the first involving in vitro propagation and ex vitroacclimatization of Aegiphila verticillata and provide a continuous supply of this medicinal native species, endangered due anthropogenic activities. Os objetivos deste trabalho foram estabelecer protocolos eficientes para a multiplicação e enraizamento in vitro, bem como para a aclimatização ex vitro de Aegiphila verticillata, uma espécie arbórea típica dos campos rupestres brasileiros. Culturas assépticas foram estabelecidas a partir de sementes, e dois experimentos de multiplicação foram realizados. No primeiro experimento, foram utilizados 6-benzilaminopurina (BAP – 0; 2,5; 5; e 7,5 μM) + ácido α-naftaleno acético (ANA – 0; 0,2; 0,4; e 0,6 μM) e, no segundo, sulfato de adenina, cinetina ou thidiazuron (0; 5; 7,5; 10; e 12,5 μM). Após 90 dias, foram avaliados o número e a qualidade das brotações. Houve mais de 90% de germinação das sementes e reduzida taxa de contaminação (2%). Na etapa de multiplicação, o meio que promoveu o melhor desenvolvimento qualitativo e quantitativo das culturas foi o suplementado com 7,5 μM de BAP + 0,4 μM de ANA. No experimento de enraizamento, foram utilizados ANA, ácido indol acético (AIA) ou ácido indol butírico (AIB) (0; 0,1; 0,2; 0,3; e 0,4 μM). Após 90 dias, foram avaliados o número de raízes e a qualidade do sistema radicular. Nessa análise, não foram encontradas diferenças entre o controle e os demais tratamentos. Plântulas enraizadas foram aclimatizadas inicialmente por 30 dias em bandejas de isopor, período após o qual foram transferidas para vasos, em casa de vegetação. Apenas 3% das plantas submetidas à aclimatização inicial morreram, e 70% daquelas transferidas para a casa de vegetação sobreviveram e apresentaram desenvolvimento normal. Os resultados encontrados neste trabalho são os primeiros relatos envolvendo a propagação in vitro e a aclimatização ex vitro de Aegiphila verticillata e possibilitam o fornecimento de um suprimento contínuo dessa espécie medicinal nativa, ameaçada de extinção devido às atividades antrópicas.

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.

This study aimed to establish and propagate in vitro plants of Bouchea fluminensis, a medicinal species known in Brazil as gervão-falso ("false verbena"), evaluating the influences of different growth regulators on in vitro multiplication and rooting stages, as well as examining ex vitro acclimatization of rooted plants. Explants were established on Murashige and Skoog medium at half strength of salts and vitamins without growth regulators. For multiplication, the explants were subjected to combinations of 6-benzyladenine (BA; 0, 2.5, 5.0 and 7.5 µM) and α-naphthalene-acetic acid (NAA; 0, 0.2, 0.4 and 0.6 µM). The medium found to induce the greatest number of shoot was that containing 5 µM of BA (NAA-free). For rooting, we evaluated three auxins (NAA, indole-3-acetic acid and indole-3-butyric acid; 0.1, 0.2, 0.3 and 0.4 µM), as well as a control. No differences were observed between the control and the other treatments. The auxin-free medium was deemed the most suitable, because it ensures the lowest cost in the micropropagation procedures. We obtained 100% survival of the acclimatized seedlings, and the plants showed normal vegetative and reproductive development, suggesting that the micropropagation did not alter the biological cycle of this species. The results show the importance and potential of micropropagation for biodiversity conservation of Bouchea fluminensis.