Phosphoenolpyruvate Carboxylase Research Articles

Expression analysis of calcium-dependent protein kinases (CDPKs) superfamily genes in Medicago lupulina in response to high calcium, carbonate and drought

The aim of this study is to identify calcium dependent protein kinases (CDPKs) superfamily genes (including calcium dependent protein kinase (CDPK) genes, CDPK-related kinase (CRK) genes, and phosphoenolpyruvate carboxylase kinase-related kinase (PEPRK) genes) and to analyze their expression in response to high calcium, bicarbonate, and water deficit in Medicago lupulina. Transcriptome sequencing databases and bioinformatics were used to identify CDPK superfamily genes. qRT-PCR analyses were used to study the expression of CDPK superfamily genes in response to high calcium, bicarbonate, water deficit, and their combined treatments. Ten MlCDPKs, four MlCRKs, and two MlPEPRKs genes were identified from transcriptome sequencing databases. The identified MlCDPK superfamily genes could be divided into six subgroups including CDPK I, CDPK II, CDPK III, CDPK IV, CRK, and PEPRK according to evolutionary relationships. Analysis of protein structure indicated that MlCDPK proteins contained a protein kinase domain and EF-hand domain. However, PEPRKs contained only a protein kinase domain while CRKs contained also degenerative EF-hands. Most of the MlCDPK superfamily genes were differentially expressed in different organs. According to their expression levels, MlCDPK superfamily genes such as MlCDPK1, MlCDPK9, and MlCDPK10 were more sensitive in response to individual treatments of high calcium, carbonate or PEG rather than their combination of treatments. The results indicated that MlCDPK superfamily genes may play an important role in response to those stresses. These results provide important insight into the role of CDPKs in M. lupulina, especially in the tolerance to Karst habitats, where high calcium and carbonate and drought conditions are the dominant ecological limiting factors.

The differential carbon-fixing and nitrogen-assimilating enzyme activities of Oscillatorian marine cyanobacterium Phormidium valderianum BDU 20041

We have identified an efficient filamentous marine cyanobacterium, Phormidium valderianum BDU 20041, which was adaptive to different concentrations of CO2. In our study, P. valderianum BDU 20041 was grown under ambient (0.04) and elevated (2, 3, 4, 5, 10, and 15%) CO2 concentration. Its optimal growth occurred at 3% CO2 supply. P. valderianum displayed similar carbon fixation activities through Rubisco, phosphoenolpyruvate carboxylase (PEPC), carbonic anhydrase, and malate dehydrogenase. The activity of Rubisco, the primary carbon-fixing enzyme, was found to be approximately 80% higher in P. valderianum grown under 4% CO2 than under ambient air. This was substantiated by Western blot. The nitrogen-assimilating enzymes shared a similar trend at higher CO2 concentrations. Our study is one of the few reports that examined the activities of CO2-fixing and nitrogen-assimilating enzymes together. Due to the active PEPC, this cyanobacterium was found to have active C3 and C4 enzymes that promoted higher CO2 fixation and cellular growth. Thus, it may be an efficient organism for biotechnological exploitation.

Physiological and biochemical responses to aluminum-induced oxidative stress in two cyanobacterial species

Phycoremediation technologies significantly contribute to solving serious problems induced by heavy metals accumulation in the aquatic systems. Here we studied the mechanisms underlying Al stress tolerance in two diazotrophic cyanobacterial species, to identify suitable species for Al phycoremediation. Al uptake as well as the physiological and biochemical responses of Anabaena laxa and Nostoc muscorum to 7 days Al exposure at two different concentrations i.e., mild (100 μM) and high dose (200 μM), were investigated. Our results revealed that A. laxa accumulated more Al, and it could acclimatize to long-term exposure of Al stress. Al induced a dose-dependent decrease in photosynthesis and its related parameters e.g., chlorophyll content (Chl a), phosphoenolpyruvate carboxylase (PEPC) and Ribulose‒1,5‒bisphosphate carboxylase/oxygenase (RuBisCo) activities. The affect was less pronounced in A. laxa than N. muscorum. Moreover, Al stress significantly increased cellular membrane damage as indicated by induced H2O2, lipid peroxidation, protein oxidation, and NADPH oxidase activity. However, these increases were lower in A. laxa compared to N. muscorum. To mitigate the impact of Al stress, A. laxa induced its antioxidant defense system by increasing polyphenols, flavonoids, tocopherols and glutathione levels as well as peroxidase (POX), catalase (CAT), glutathione reductase (GR) and glutathione peroxidase (GPX) enzymes activities. On the other hand, the antioxidant increases in N. muscorum were only limited to ascorbate (ASC) cycle. Overall, high biosorption/uptake capacity and efficient antioxidant defense system of A. laxa recommend its feasibility in the treatment of Al contaminated waters/soils.

ZmbHLH80 and ZmbHLH90 transcription factors act antagonistically and contribute to regulatePEPC1cell‐specific gene expression in maize

Compartmentation of photosynthetic reactions between mesophyll and bundle sheath cells is a key feature of C4 photosynthesis and depends on the cell-specific accumulation of major C4 enzymes, such as phosphoenolpyruvate carboxylase 1. The ZmPEPC1 upstream region, which drives light-inducible and mesophyll-specific gene expression in maize, has been shown to keep the same properties when introduced into rice (C3 plant), indicating that rice has the transcription factors (TFs) needed to confer C4 -like gene expression. Using a yeast one-hybrid approach, we identified OsbHLH112, a rice basic Helix-Loop-Helix (bHLH) TF that interacts with the maize ZmPEPC1 upstream region. Moreover, we found that maize OsbHLH112 homologues, ZmbHLH80, and ZmbHLH90, also interact with the ZmPEPC1 upstream region, suggesting that these C4 regulators were co-opted from C3 plants. A transactivation assay in maize mesophyll protoplasts revealed that ZmbHLH80 represses, whereas ZmbHLH90 activates, ZmPEPC1 expression. In addition, ZmbHLH80 was shown to impair the ZmPEPC1 promoter activation caused by ZmbHLH90. We showed that ZmbHLH80 and ZmbHLH90 bind to the same cis-element within the ZmPEPC1 upstream region either as homodimers or heterodimers. The formation of homo- and heterodimers with higher oligomeric forms promoted by ZmbHLH80 may explain its negative effect on gene transcription. Gene expression analysis revealed that ZmbHLH80 is preferentially expressed in bundle sheath cells, whereas ZmbHLH90 does not show a clear cell-specific expression pattern. Altogether, our results led us to propose a model in which ZmbHLH80 contributes to mesophyll-specific ZmPEPC1 gene expression by impairing ZmbHLH90-mediated ZmPEPC1 activation in the bundle sheath cells.

2H and 13C metabolic flux analysis elucidates in vivo thermodynamics of the ED pathway in Zymomonas mobilis

Zymomonas mobilis is an industrially relevant bacterium notable for its ability to rapidly ferment simple sugars to ethanol using the Entner-Doudoroff (ED) glycolytic pathway, an alternative to the well-known Embden-Meyerhof-Parnas (EMP) pathway used by most organisms. Recent computational studies have predicted that the ED pathway is substantially more thermodynamically favorable than the EMP pathway, a potential factor explaining the high glycolytic rate in Z. mobilis. Here, to investigate the in vivo thermodynamics of the ED pathway and central carbon metabolism in Z. mobilis, we implemented a network-level approach that integrates quantitative metabolomics with 2H and 13C metabolic flux analysis to estimate reversibility and Gibbs free energy (ΔG) of metabolic reactions. This analysis revealed a strongly thermodynamically favorable ED pathway in Z. mobilis that is nearly twice as favorable as the EMP pathway in E. coli or S. cerevisiae. The in vivo step-by-step thermodynamic profile of the ED pathway was highly similar to previous in silico predictions, indicating that maximizing ΔG for each pathway step likely constitutes a cellular objective in Z. mobilis. Our analysis also revealed novel features of Z. mobilis metabolism, including phosphofructokinase-like enzyme activity, tricarboxylic acid cycle anaplerosis via PEP carboxylase, and a metabolic imbalance in the pentose phosphate pathway resulting in excretion of shikimate pathway intermediates. The integrated approach we present here for in vivo ΔG quantitation may be applied to the thermodynamic profiling of pathways and metabolic networks in other microorganisms and will contribute to the development of quantitative models of metabolism.

Anionic Phospholipids Induce Conformational Changes in Phosphoenolpyruvate Carboxylase to Increase Sensitivity to Cathepsin Proteases.

Phosphoenolpyruvate carboxylase (PEPC) is a cytosolic, homotetrameric enzyme that serves a variety of functions in plants, acting as the primary form of CO2 fixation in the C4 photosynthesis pathway (C4-PEPC). In a previous work we have shown that C4-PEPC bind anionic phospholipids, resulting in PEPC inactivation. Also, we showed that PEPC can associate with membranes and to be partially proteolyzed. However, the mechanism controlling this remains unknown. Using semi purified-PEPC from sorghum leaf and a panel of PEPC-specific antibodies, we analyzed the conformational changes in PEPC induced by anionic phospholipids to cause the inactivation of the enzyme. Conformational changes observed involved the exposure of the C-terminus of PEPC from the native, active enzyme conformation. Investigation of the protease activity associated with PEPC demonstrated that cysteine proteases co-purify with the enzyme, with protease-specific substrates revealing cathepsin B and L as the major protease species present. The anionic phospholipid-induced C-terminal exposed conformation of PEPC appeared highly sensitive to the identified cathepsin protease activity and showed initial proteolysis of the enzyme beginning at the N-terminus. Taken together, these data provide the first evidence that anionic phospholipids promote not only the inactivation of the PEPC enzyme, but also its proteolysis.

The Stimulatory Effects of Nanochitin Whisker on Carbon and Nitrogen Metabolism and on the Enhancement of Grain Yield and Crude Protein of Winter Wheat.

Nanochitin whisker (NC) with a cationic nature could enhance plant photosynthesis, grain yield, and quality of wheat, but have not been systematically studied. This study was designed to investigate the stimulatory effects of NC on dry matter (DM) and nitrogen (N) accumulation and translocation, and on the metabolism of carbon (C) and N in later growth stages of winter wheat to reveal the enhancement mechanism of grain yield and crude protein concentration. Different parts of NC-treated plants from pot grown experiments were collected at the pre- and post-anthesis stages. The accumulation, translocation, and contributions of DM and N from pre-anthesis vegetation organs to grains, as well as key metabolic enzyme activities, including sucrose phosphate synthase (SPS) and phosphoenolpyruvate carboxylase (PEPC), were examined. The results showed that, at an application rate of 6 mg·kg−1 of NC in the soil, the accumulation of DM and N were significantly enhanced by 16.2% and 38.8% in pre-anthesis, and by 15.4% and 30.0% in post-anthesis, respectively. Translocation of N and DM in the post-anthesis periods were enhanced by 38.4% and 50.9%, respectively. NC could also stimulate enzyme activities, and increased 39.8% and 57.1% in flag leaves, and by 36.0% and 58.8% in spikes, respectively, at anthesis. SPS and PEPC increased by 28.2% and 45.1% in flag leaves, and by 42.2% and 56.5% in spikes, respectively, at 15 days after anthesis. The results indicated that the NC promoted N metabolism more than C metabolism, and resulted in the enhancement of grain yield by 27.56% and of crude protein concentration in grain by 13.26%, respectively.

ROS Scavenging and $${\text{NH}}_{4}^{ + }$$ Nitrogen Fertilizer Roles in Alleviation of Cd-Induced Oxidative Stress in Arabidopsis thaliana

Arabidopsis thaliana (L.) Heynh. receiving ammonium, were transferred on modified Hoagland nutrient solution containing Cd (25 µM) alone or supplemented with buthionine sulfoximine (BSO, an inhibitor of glutathione synthesis). In ammonium-fed A. thaliana treated with Cd alone, leaf and root growth was not negatively affected. Carbon metabolism was stimulated through activation of Rubisco and maintain of phosphoenol pyruvate carboxylase (PEP) and NADP(+)-isocitrate dehydrogenase (NADP(+)-ICDH). In another way, superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and peroxidase (GPX), and ascorbate-glutathione-regenerating enzymes (glutathione reductase (GR), dehydroascorbate reductase(DHAR) and monodehydroascorbate reductase (MDHAR) activities were stimulated by Cd. Ascorbate (AsA) and dehydroascorbate (DHA) contents were significantly raised. More that, the high NAD/NADH ratio in Cd-treated A. thaliana fed with ammonium proved the capacity of leaf cells to maintain NAD homeostasis under stressful conditions. The dramatic effect of BSO when added currently with Cd was reflected by the imbalance of all the patterns shown and described previously. Growth was inhibited in parallel to MDA and H2O2 accumulation. Carbon metabolism, ascorbate-glutathione-regenerating and antioxidative enzymes were all reduced. Revealing that alleviation of Cd toxicity by ammonium nitrogen is due to a beneficial relationship between carbon metabolism activation and ROS production minimization also than there may be scavenging enhancement.

Transcriptional and post-translational upregulation of phosphoenolpyruvate carboxylase in Arabidopsis thaliana (L. Heynh) under cadmium stress

Phosphoenolpyruvate carboxylase (PEPC) is a tightly controlled anaplerotic enzyme that replenishes organic acids that have been withdrawn from the tricarboxylic acid cycle. Organic acid anions are important chelators of toxic metals, including cadmium (Cd). To determine the Cd-stress responses of two isozymes of PEPC in Arabidopsis (AtPPC1 and AtPPC3), we compared wild type (Col-0) with two T-DNA insertional mutant lines (atppc1 and atppc3). Plant mass decreased in response to Cd in all lines, but atppc3 was the most sensitive to Cd even though its roots contained 30% lower concentrations of Cd. Treatment with 1 or 5 μM CdCl2 resulted in up to 400% higher expression of genes encoding three isozymes of plant-type PEPCs and up to 200% higher expression of genes encoding two isozymes of PEPC kinase, especially in roots. The amount of PEPC and its phosphorylation status also increased by up to 40% with Cd treatment, as did enzyme activity (up to 200%). AtPPC1 and AtPPC3 transcript levels in the mutant lines were as much as 50% lower than in wild type plants, even in control (no Cd) plants. AtPPC2 expression was unaffected in both mutant lines. In general, concentrations of organic acid anions increased or remained unchanged in response to Cd treatment in each plant line, although roots of atppc1 and atppc3 mutants under control conditions had 25–50% less malate and citrate. Our results confirm the importance of root-specific (i) AtPPC3 expression for the normal development of Arabidopsis, as well as (ii) AtPPC1 and AtPPC3 upregulation for acclimation to Cd stress.

Mechanistic understanding towards the effective lipid production of a microalgal mutant strain Scenedesmus sp. Z-4 by the whole genome bioinformation.

Currently, the complex mechanism of lipid production in microalgal cells is still unclear, and the platform suitable for microalgal genetic transformation is urgent to be established. In this study, the whole genome of a lipid-rich microalgal mutant strain Scenedesmus sp. Z-4 and a lipid-poor wild strain Scenedesmus sp. MC-1 were sequenced, and results revealed that the sequences of 1,256 genes were changed and 148 differential genes related to glucose and lipid metabolism were identified. Especially, gene differentiation of acetyl-CoA carboxylase (ACCase) and phosphoenolpyruvate carboxylase (PEPC) in mutant strain Z-4 and wild strain MC-1, which played key roles in lipid synthesis, were evaluated. Furthermore, to investigate whether mutated ACCase and PEPC genes affect the lipid production, two genes from mutant strain Z-4 were transformed into the expression system of wild strain MC-1. Nine transformants with higher lipid content were successfully obtained, in which the optimal transformant with 28.6% more intracellular lipid than wild strain MC-1 was isolated by overexpression of mutated ACCase gene, demonstrating the important role of ACCase in lipid accumulation of microalgal cells. These results could provide a better understanding of the superior lipid production of mutant strain Scenedesmus sp. Z-4.

Transcript and metabolite changes during the early phase of abscisic acid-mediated induction of crassulacean acid metabolism in Talinum triangulare.

Crassulacean acid metabolism (CAM) has evolved as a water-saving strategy, and its engineering into crops offers an opportunity to improve their water use efficiency. This requires a comprehensive understanding of the regulation of the CAM pathway. Here, we use the facultative CAM species Talinum triangulare as a model in which CAM can be induced rapidly by exogenous abscisic acid. RNA sequencing and metabolite measurements were employed to analyse the changes underlying CAM induction and identify potential CAM regulators. Non-negative matrix factorization followed by k-means clustering identified an early CAM-specific cluster and a late one, which was specific for the early light phase. Enrichment analysis revealed abscisic acid metabolism, WRKY-regulated transcription, sugar and nutrient transport, and protein degradation in these clusters. Activation of the CAM pathway was supported by up-regulation of phosphoenolpyruvate carboxylase, cytosolic and chloroplastic malic enzymes, and several transport proteins, as well as by increased end-of-night titratable acidity and malate accumulation. The transcription factors HSFA2, NF-YA9, and JMJ27 were identified as candidate regulators of CAM induction. With this study we promote the model species T. triangulare, in which CAM can be induced in a controlled way, enabling further deciphering of CAM regulation.

Evaluation of cobalt hyperaccumulation and tolerance potential of the duckweed (Lemna minor L.)

Lemna minor could tolerate and accumulate more than 5,000 μg g-1 DW of cobalt (Co) without foliar symptoms, indicating it is a Co hyperaccumulator. However, the physiological and metabolomics mechanisms that are responsible for Co accumulation and tolerance are largely unknown. In the present study, Fourier transform infrared spectroscopy suggested that CO, CH, and OH groups are involved in Co biosorption. The activation of antioxidant enzymes, such as superoxide dismutase, guiacol peroxidase, catalase, and glutathione reductase, as well as ascorbic acid and glutathione might be involved in capturing reactive oxygen species as evidenced by decreased malondialdehyde in fronds treated with Co. Metabolomics analysis revealed that Co stress significantly increased the production of several amino acids (except aspartic acid and cysteine at 200 μM) and organic acids (with the exception of succinic acid). In particular, an approximate 15-fold increase was noted in the citric acid concentration. Upon exposure to Co, increases were observed in citrate synthase, malate dehydrogenase, and phosphoenolpyruvate carboxylase activities, and a decrease was observed in isocitrate dehydrogenase related to the metabolism of organic acids. Overall, the increase in concentration of organic and amino acids and antioxidants support their effective involvement in improving Co tolerance and accumulation in L. minor.

Development of a compartmentalized model for insight into the structured metabolic pathway of carbon metabolism in cassava leaves

In silico metabolic modeling has enabled systematic study of complicated metabolic processes underlying phenotypes of organisms. Modeling of plant metabolism is often hampered by the network complexity and lack of adequate knowledge. The existing metabolic networks of cassava only cover broad metabolism and are not compartmentalized to truly represent metabolism in photosynthetic tissues. To address the aforementioned limitations and develop a robust metabolic network, physiological and genomic data derived from cassava and leaf models of Arabidopsis and rice were to extend the scope of the existing model. The proposed compartmentalized network of metabolism in photosynthetic tissues of cassava, ph-MeRecon (photosynthetic-Manihot esculenta Metabolic Pathway Reconstruction) was developed based on the information resulting of the comparative study of multiple model plants and cassava genome. The ph-MeRecon covers primary carbon metabolism and comprises 461 metabolites, 550 reactions, and 1,037 metabolic genes. Enzymatic genes on the network were validated using RNA-expression data, and the reactions and pathways were compartmentalized into cytoplasm, chloroplast, mitochondria, and peroxisome. To ensure network connectivity, metabolic gaps were filled using gap reactions obtained from literature and metabolic pathway omnibus. In addition, information on plant physiology, including photosynthetic light-dependent reactions, carboxylase and oxygenase activity of RuBisCO enzyme, and phosphoenolpyruvate carboxylase enzyme activity was incorporated into ph-MeRecon to mimic cellular metabolism in cassava leaves. Thus, ph-MeRecon offers a multi-level platform for system analysis of cellular mechanisms underlying phenotypes of interest in cassava. The ph-MeRecon metabolic model is available at http://bml.sbi.kmutt.ac.th/ph-MeRecon/.

Phosphoproteomic Analysis of Two Contrasting Maize Inbred Lines Provides Insights into the Mechanism of Salt-Stress Tolerance.

Salinity is a major abiotic stress that limits maize yield and quality throughout the world. We investigated phosphoproteomics differences between a salt-tolerant inbred line (Zheng58) and a salt-sensitive inbred line (Chang7-2) in response to short-term salt stress using label-free quantitation. A total of 9448 unique phosphorylation sites from 4116 phosphoproteins in roots and shoots of Zheng58 and Chang7-2 were identified. A total of 209 and 243 differentially regulated phosphoproteins (DRPPs) in response to NaCl treatment were detected in roots and shoots, respectively. Functional analysis of these DRPPs showed that they were involved in carbon metabolism, glutathione metabolism, transport, and signal transduction. Among these phosphoproteins, the expression of 6-phosphogluconate dehydrogenase 2, pyruvate dehydrogenase, phosphoenolpyruvate carboxykinase, glutamate decarboxylase, glutamate synthase, l-gulonolactone oxidase-like, potassium channel AKT1, high-affinity potassium transporter, sodium/hydrogen exchanger, and calcium/proton exchanger CAX1-like protein were significantly regulated in roots, while phosphoenolpyruvate carboxylase 1, phosphoenolpyruvate carboxykinase, sodium/hydrogen exchanger, plasma membrane intrinsic protein 2, glutathione transferases, and abscisic acid-insensitive 5-like protein were significantly regulated in shoots. Zheng58 may activate carbon metabolism, glutathione and ascorbic acid metabolism, potassium and sodium transportation, and the accumulation of glutamate to enhance its salt tolerance. Our results help to elucidate the mechanisms of salt response in maize seedlings. They also provide a basis for further study of the mechanism underlying salt response and tolerance in maize and other crops.

UV-C treatment promotes quality of early ripening apple fruit by regulating malate metabolizing genes during postharvest storage.

Early ripening apples are usually used for fresh marketing because of short storage life, although they are with high acid and low sugar contents. Understanding the malate metabolism in fleshy fruit and underpinning process during ripening is crucial for particular crop improvement where acidity is a concern for direct consumption or further processing. In this research, a traditional Chinese apple cultivar ‘Hongyu’, which belongs to early ripening apple cultivar, were freshly harvested at commercial maturity stage (120 Days after full bloom) and used for different storage temperature (4°C, 20°C) and UV-C treatment (following storage at 20°C after treatment). Simple sugars (glucose, sucrose, and fructose) and organic acids (malic, and oxalic) were assessed after 14 d of storage. Compared to fruits stored at 20°C, the malate content in fruits stored at 4°C significantly higher, while it was decreased significantly in UV-C treated fruits stored at 20°C after 14 d of storage. The sugar content was almost similar throughout the UV-C-treated fruits and fruits stored at different temperature. The higher ratios of total sugars to total organic acids in UV-C treated fruits after 14 d suggest that UV-C treatment has the potential to improve the taste of early ripening apple cultivars. Considering the significant difference in malate the samples at 14 d of storage were subjected for RNA-seq analysis. Transcriptome analysis revealed that the phenomena underlying this change were governed by metabolism of malate by the regulation of NADP-malic enzyme (NADP-ME) and phosphoenolpyruvate carboxylase kinase (PEPCK) in apple during postharvest storage. This transcriptome profiling results have specified the transcript regulation of malate metabolism and lead to possible taste improvement without affecting the other fruit quality attributes.

Hierarchical clustering reveals unique features in the diel dynamics of metabolites in the CAM orchid Phalaenopsis.

Crassulacean acid metabolism (CAM) is a major adaptation of photosynthesis that involves temporally separated phases of CO2 fixation and accumulation of organic acids at night, followed by decarboxylation and refixation of CO2 by the classical C3 pathway during the day. Transitory reserves such as soluble sugars or starch are degraded at night to provide the phosphoenolpyruvate (PEP) and energy needed for initial carboxylation by PEP carboxylase. The primary photosynthetic pathways in CAM species are well known, but their integration with other pathways of central C metabolism during different phases of the diel light-dark cycle is poorly understood. Gas exchange was measured in leaves of the CAM orchid Phalaenopsis 'Edessa' and leaves were sampled every 2 h during a complete 12-h light-12-h dark cycle for metabolite analysis. A hierarchical agglomerative clustering approach was employed to explore the diel dynamics and relationships of metabolites in this CAM species, and compare these with those in model C3 species. High levels of 3-phosphoglycerate (3PGA) in the light activated ADP-glucose pyrophosphorylase, thereby enhancing production of ADP-glucose, the substrate for starch synthesis. Trehalose 6-phosphate (T6P), a sugar signalling metabolite, was also correlated with ADP-glucose, 3PGA and PEP, but not sucrose, over the diel cycle. Whether or not this indicates a different function of T6P in CAM plants is discussed. T6P levels were low at night, suggesting that starch degradation is regulated primarily by circadian clock-dependent mechanisms. During the lag in starch degradation at dusk, carbon and energy could be supplied by rapid consumption of a large pool of aconitate that accumulates in the light. Our study showed similarities in the diel dynamics and relationships between many photosynthetic metabolites in CAM and C3 plants, but also revealed some major differences reflecting the specialized metabolic fluxes in CAM plants, especially during light-dark transitions and at night.

Key changes in gene expression identified for different stages of C4 evolution in Alloteropsis semialata.

C4 photosynthesis is a complex trait that boosts productivity in tropical conditions. Compared with C3 species, the C4 state seems to require numerous novelties, but species comparisons can be confounded by long divergence times. Here, we exploit the photosynthetic diversity that exists within a single species, the grass Alloteropsis semialata, to detect changes in gene expression associated with different photosynthetic phenotypes. Phylogenetically informed comparative transcriptomics show that intermediates with a weak C4 cycle are separated from the C3 phenotype by increases in the expression of 58 genes (0.22% of genes expressed in the leaves), including those encoding just three core C4 enzymes: aspartate aminotransferase, phosphoenolpyruvate carboxykinase, and phosphoenolpyruvate carboxylase. The subsequent transition to full C4 physiology was accompanied by increases in another 15 genes (0.06%), including only the core C4 enzyme pyruvate orthophosphate dikinase. These changes probably created a rudimentary C4 physiology, and isolated populations subsequently improved this emerging C4 physiology, resulting in a patchwork of expression for some C4 accessory genes. Our work shows how C4 assembly in A. semialata happened in incremental steps, each requiring few alterations over the previous step. These create short bridges across adaptive landscapes that probably facilitated the recurrent origins of C4 photosynthesis through a gradual process of evolution.

Effects of waterlogging stress at different growth stages on the photosynthetic characteristics and grain yield of spring maize (Zea mays L.) Under field conditions

A field experiment was conducted to investigate the effects of waterlogging stress on the photosynthetic characteristics, dry matter accumulation (including stem, leaf, and ear), and grain yield of spring maize (Zea mays L.) hybrids Demeiya1 (DMY1) and Keyu16 (KY16). The waterlogging and subsurface waterlogging treatments were implemented for different durations (3, 6, and 9 days and 5, 10, and 15 days, respectively) at the seedling (V3), jointing (V6), and tasseling (VT) stages. The results showed that the adverse effects of waterlogging on spring maize growth varied with the duration of waterlogging and the growth stage. The most obvious effect of waterlogging stress occurred at the V3 stage, followed by the V6 and VT stages. Ribulose-1,5-bisphosphate (RuBP) carboxylase and phosphoenolpyruvate (PEP) carboxylase activities, as well as the photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs) and intercellular CO2 concentration (Ci) decreased with an increase in the duration of waterlogging, which caused a decrease in the total dry matter weight and ultimately resulted in a significant reduction in spring maize grain yield. The grain yield of DMY1 and KY16 significantly (P < 0.05) decreased by 64.8% and 80.2% in the V3-9 treatment and decreased by 61.5% and 71.9%, respectively, in the V3-s15 treatment.

Enhancement of lipid production and nutrient removal of Monoraphidium sp. FXY-10 by combined melatonin and molasses wastewater treatment

Abstract Molasses wastewater can be utilized for microalgae cultivation, and the harvested algal biomass is suitable for biofuel production. In this study, the effects of melatonin on the metabolism and activities of three key lipid biosynthetic enzymes of Monoraphidium sp. FXY-10 cultured in molasses wastewater were evaluated. The maximal biomass (1.21 g L−1) and lipid content (68.69%) were obtained during melatonin treatment and were approximately 1.42- and 1.15-fold, respectively, of the group not treated with melatonin. The carbohydrate and protein contents of melatonin-treated cells were also increased. MT treatment upregulated the activities of malic enzyme and acetyl-CoA carboxylase but downregulated phosphoenolpyruvate carboxylase activity, which was correlated with lipid accumulation in FXY-10. MT-treated samples showed greater potentials for removing organic carbon (92.33% chemical oxygen demand removal) and nutrients (90.07% nitrogen removal, 86.04% phosphorus removal) than the non-treated samples. Additionally, the economic feasibility of melatonin treatment demonstrated that a combined strategy is ideal for molasses wastewater treatment and biofuel production.

Tissue-specific organic acid metabolism in reproductive and non-reproductive parts of the fig fruit is partially induced by pollination.

Organic acids are important components of overall fruit quality through flavor, taste, nutritional and medicinal values. Pollinated fig (Ficus carica L.) fruit quality is enhanced by increased acidity. We quantified the major organic acids and characterized the expression pattern of organic acid metabolic pathway-related genes in the reproductive part-inflorescence and non-reproductive part-receptacle of parthenocarpic and pollinated fig fruit during ripening. Essentially, pollinated fruit contains seeds in the inflorescence, as opposed to no seeds in the parthenocarpic inflorescence. The major organic acids-citrate and malate-were found in relatively high quantities in the inflorescence compared to the receptacle of both parthenocarpic and pollinated fig fruit. Notably, pollination increased citric acid content significantly in both inflorescence and receptacle. Genes related to the phosphoenolpyruvate carboxylase (PEPC) cycle, tricarboxylic acid cycle, citrate catabolism and glyoxylate cycle were identified in fig fruit. Expression levels of most of these genes were higher in inflorescences than in receptacles. In particular, FcPEPC and FcFUM (encoding fumarase) had significantly higher expression in the inflorescence of pollinated fruit. Most importantly, expression of the glyoxylate cycle genes FcMLS and FcICL (encoding malate synthase and isocitrate lyase, respectively) was induced to strikingly high levels in the inflorescence by pollination, and their expression level was highly positively correlated with the contents of all organic acids. Therefore, the glyoxylate cycle may be responsible for altering the accumulation of organic acids to upgrade the fruit taste during ripening, especially in the pollinated, seeded inflorescence.