Phosphoenolpyruvate Carboxylase Research Articles

The C4 Ppc promoters of many C4 grass species share a common regulatory mechanism for gene expression in the mesophyll cell.

C4 photosynthetic plants have evolved from C3 ancestors and are characterized by differential expression of several hundred genes. Strict compartmentalization of key C4 enzymes either to mesophyll (M) or bundle sheath cells is considered a crucial step towards the evolution of C4 photosynthesis. In this study, we demonstrate that the 5'-flanking sequences of the C4 type phosphoenolpyruvate carboxylase (Ppc) gene from three C4 grass species could drive M-cell-specific expression of a reporter gene in rice. In addition to that, we identified about 450bp (upstream of their transcription start site) of the analyzed C4 Ppc promoters contain all the essential regulatory elements for driving M-cell-specific expression in rice leaves. Importantly, four motifs of conserved nucleotide sequences (CNSs) were also determined, which are essential for the activity of the promoter. A putative interaction between the CNSs and an unknown upstream element(s) is required for driving M-cell-specific expression. This work identifies the evolutionary conservation of C4 Ppc regulatory mechanisms of multiple closely related C4 grass species.

Activities of key enzymes in the C4 pathway and anatomy of sugarcane infected by Leifsonia xyli subsp. xyli.

Ratoon stunting disease caused by Leifsonia xyli subsp. xyli (Lxx) is a bacterial disease that has plagued sugarcane-planting countries for a long time. This study mainly analysed Lxx localization and its effects on sugarcane leaf. Badila were inocultated by bacteria of Lxx. It was noted that the number of Lxx cells were rapidly enriched in sugarcane leaves from the 150th to the 210th days of post inoculation (dpi). Lxx infection disrupted the integrity of vascular bundle sheath cells (BSC) in the 'Kranz anatomy' of leaves, resulting in irregular accumulation of starch in vascular BSC of leaves. In situ PCR showed that the Lxx localized in the xylem vessels, mesophyll cell (MC) and BSC as described before in sugarcane leaf, a new niche within the host tissues in the phloem of sugarcane stem. The gene expression and activities of phosphoenolpyruvate carboxylase (PEPC), pyruvate, orthophosphate dikinase (PPDK) and NADP-malic enzyme (NADP-ME) enzymes were lower in Lxx-inoculated sugarcane plants as compared to the MI group. Lxx infection not only disrupted the structure of vascular BSC in the C4 'Kranz anatomy' of sugarcane leaves, but also affected the activities and gene expression of the key enzymes PEPC, PPDK and NADP-ME in the C4 cycle of sugarcane suggesting a reduction in CO2 fixation. The effect of Leifsonia xyli subsp. xyli (Lxx) infection on the photosynthetic physiology of sugarcane is currently limited to the evaluation of photosynthetic parameters. This study assessed the impact of Lxx infection on the mechanism of C4 cycle CO2 fixation and to accompanying plant anatomy.

Overexpression of PtPEPCK1 gene promotes nitrogen metabolism in poplar

To understand the function of phosphoenolpyruvate carboxylase kinase, we introduced PtPEPCK1 gene under the control of 35S promoter into 84K poplar (Populus alba × P. glandulosa). PtPEPCK1 gene is well-known for its role in gluconeogenesis. However, our data confirmed that it has significant effects on amino acid biosynthesis and nitrogen metabolism. Immunohistochemistry and fluorescence microscopy indicate that PtPEPCK1 is specifically expressed in the cytoplasm of the spongy and palisade tissues. Overexpression of PtPEPCK1 was characterized through transcriptomics and metabolomics. The metabolites concentration of the ornithine cycle and its precursors also increased, of which N-acetylornithine was up-regulated almost 50-fold and ornithine 33.7-fold. These were accompanied by a massive increase in levels of several amino acids. Therefore, overexpression of PtPEPCK1 increases amino acid levels with urea cycle disorder.

Whole Grain Brown Rice Extrudate Ameliorates the Symptoms of Diabetes by Activating the IRS1/PI3K/AKT Insulin Pathway in db/db Mice.

The therapeutic benefits of whole grains on diabetes mellitus have been continuously confirmed by in-depth research. To date, limited studies have investigated the effect of extruded products of whole grains on the insulin signaling pathway in vivo. This study investigated the effects of oral consumption of whole grain extrudate, including 97% brown rice and 3% defatted rice bran (w/w, BRD), on glucose metabolism and the hepatic insulin signaling pathway in C57BL/KsJ-db/db mice. BRD treatment induced a remarkable reduction in blood glucose. Moreover, glucose intolerance and insulin resistance were ameliorated in the BRD-treated group compared with those in the db/db control group. BRD also increased the hepatic glycogen content by reducing the expression and increasing the phosphorylation of glycogen synthase kinase 3β (GSK3β). The activities of glucose-6-phosphatase and phosphoenolpyruvate carboxylase and their respective mRNA expression levels in the liver were simultaneously decreased in the BRD-treated group. BRD also significantly upregulated the expression of phosphatidylinositol 3-kinase (PI3K) and increased the phosphorylation of insulin receptor substrate 1 (IRS1) and protein kinase B (AKT). These results indicate that BRD exhibits antidiabetic potential by activating the IRS1/PI3K/AKT signaling pathway, further regulating the expression of the FOXO1 gene and p-GSK3β protein, thus inhibiting hepatic gluconeogenesis, increasing hepatic glycogen storage, and improving insulin resistance. Therefore, BRD could be used as a functional ingredient to alleviate the symptoms of hyperglycemia.

In Vivo Phosphorylation: Development of Specific Antibodies to Detect the Phosphorylated PEPC Isoform for the C4 Photosynthesis in Zea mays.

Phosphoenolpyruvate carboxylases (PEPCs), mostly known as the enzymes responsible for the initial CO2 fixation during C4 photosynthesis, are regulated by reversible phosphorylation in vascular plants. The phosphorylation site on a PEPC molecule is conserved not only among isoforms but also across plant species. An anti-phosphopeptide antibody is a common and powerful tool for detecting phosphorylated target proteins with high specificity. We generated two antibodies, one against a peptide containing a phosphoserine (phosphopeptide) and the other against a peptide containing a phosphoserine mimetic, (S)-2-amino-4-phosphonobutyric acid (phosphonopeptide). The amino acid sequence of the peptide was taken from the site around the phosphorylation site near the N-terminal region of the maize C4-isoform of PEPC. The former antibodies detected almost specifically the phosphorylated C4-isoform of PEPC, whereas the latter antibodies had a broader specificity for the phosphorylated PEPC in various plant species. The following procedures are described herein: (1) preparation of the phosphopeptide and phosphonopeptide; (2) preparation and purification of rabbit antibodies; (3) preparation of cell extracts from leaves for analyses of PEPC phosphorylation with antibodies; and (4) characterization of the obtained antibodies. Finally, (5) two cases involving the application of these antibodies are presented.

Physiological and Molecular Osmotic Stress Responses in Three Durum Wheat (Triticum Turgidum ssp Durum) Genotypes

This study aims to investigate the activities and expression of enzymes of primary metabolism and relate these data with the growth performance of three different durum wheat genotypes (Maali; YT13; and ON66) under osmotic stress. Growth traits—including plant height, dry weight (DW) and relative water content (RWC)—were measured to classify genotypes depending on their tolerance to stress. Several enzymes were investigated: Ascorbate peroxidase (APX), Glutamine Synthetase (GS), Glutamine dehydrogenase (GDH), Glutamate synthase (GOGAT), Glucose 6-phosphate dehydrogenase (G6PDH), and Phosphoenolpyruvate Carboxylase (PEPC). The expression of the cytosolic and plastidic glutamine synthetase (TaGS1 and TaGS2), high affinity nitrate transporters (TaNRT2.3) and Glutamate dehydrogenase (TaGDH) were also detected by qRT-PCR. The results indicated different growth performances among genotypes, indicating Maali and YT13 as tolerant genotypes and ON66 as a drought-susceptible variety. Data showed a decrease in PEPC and increase in APX activities under osmotic stress; a slight decrease in GS activity was observed, together with an increase in G6PDH in all genotypes; GS and NRT2 expressions changed in a similar pattern in the different genotypes. Interestingly, Maali and YT13 showed higher transcript abundance for GDH under stress compared to ON66, suggesting the implication of GDH in protective phenomena upon osmotic stress.

Regulation of Symbiotic Nitrogen Fixation in Legume Root Nodules.

In most legume nodules, the di-nitrogen (N2)-fixing rhizobia are present as organelle-like structures inside their root host cells. Many processes operate and interact within the symbiotic relationship between plants and nodules, including nitrogen (N)/carbon (C) metabolisms, oxygen flow through nodules, oxidative stress, and phosphorous (P) levels. These processes, which influence the regulation of N2 fixation and are finely tuned on a whole-plant basis, are extensively reviewed in this paper. The carbonic anhydrase (CA)-phosphoenolpyruvate carboxylase (PEPC)-malate dehydrogenase (MDH) is a key pathway inside nodules involved in this regulation, and malate seems to play a crucial role in many aspects of symbiotic N2 fixation control. How legumes specifically sense N-status and how this stimulates all of the regulatory factors are key issues for understanding N2 fixation regulation on a whole-plant basis. This must be thoroughly studied in the future since there is no unifying theory that explains all of the aspects involved in regulating N2 fixation rates to date. Finally, high-throughput functional genomics and molecular tools (i.e., miRNAs) are currently very valuable for the identification of many regulatory elements that are good candidates for accurately dissecting the particular N2 fixation control mechanisms associated with physiological responses to abiotic stresses. In combination with existing information, utilizing these abundant genetic molecular tools will enable us to identify the specific mechanisms underlying the regulation of N2 fixation.

Transcriptomic and phosphoproteomic profiling and metabolite analyses reveal the mechanism of NaHCO3-induced organic acid secretion in grapevine roots

BackgroundOrganic acid secretion is a widespread physiological response of plants to alkalinity. However, the characteristics and underlying mechanism of the alkali-induced secretion of organic acids are poorly understood.ResultsOxalate was the main organic acid synthesized and secreted in grapevine (a hybrid of Vitis amurensis, V. berlandieri and V. riparia) roots, while acetate synthesis and malate secretion were also promoted under NaHCO3 stress. NaHCO3 stress enhanced the H+ efflux rate of grapevine roots, which is related to the plasma membrane H+-ATPase activity. Transcriptomic profiling revealed that carbohydrate metabolism was the most significantly altered biological process under NaHCO3 stress; a total of seven genes related to organic acid metabolism were significantly altered, including two phosphoenolpyruvate carboxylases and phosphoenolpyruvate carboxylase kinases. Additionally, the expression levels of five ATP-binding cassette transporters, particularly ATP-binding cassette B19, and two Al-activated malate transporter 2 s were substantially upregulated by NaHCO3 stress. Phosphoproteomic profiling demonstrated that the altered phosphoproteins were primarily related to binding, catalytic activity and transporter activity in the context of their molecular functions. The phosphorylation levels of phosphoenolpyruvate carboxylase 3, two plasma membrane H+-ATPases 4 and ATP-binding cassette B19 and pleiotropic drug resistance 12 were significantly increased. Additionally, the inhibition of ethylene synthesis and perception completely blocked NaHCO3-induced organic acid secretion, while the inhibition of indoleacetic acid synthesis reduced NaHCO3-induced organic acid secretion.ConclusionsOur results demonstrated that oxalate was the main organic acid produced under alkali stress and revealed the necessity of ethylene in mediating organic acid secretion. Additionally, we further identified several candidate genes and phosphoproteins responsible for organic acid metabolism and secretion.

Drought survival strategies of juvenile bromeliads of Alcantarea imperialis (Carrière) Harms

The establishment of bromeliad populations in rupicolous environments depends on the efficient survival strategy of juvenile individuals under adverse conditions, such as drought. Juvenile plants of Alcantarea imperialis do not form water reservoir (phytotelm) as adult individuals and then they require metabolic mechanisms to cope with water deficit during the initial stages of plant growth. It has been reported that sugar accumulation and crassulacean acid metabolism (CAM) photosynthesis are related to plant responses to water deficit. This study investigated whether these physiological adjustments could be dual strategies to drought survive of juvenile A. imperialis plants. Plants were cultivated in vitro with polyethylene glycol 6000 (PEG 6000) to simulate different degrees of water deficit (moderate stress, − 1.9 mega Pascal (MPa) and severe stress, − 8.5 MPa) and a control treatment without PEG (− 0.5 MPa) for 7, 15 and 30 days. Plant growth, biochemical and anatomical parameters were analyzed. Under 15 days in moderate stress condition, the plants initially accumulated soluble sugars and at 30 days, their leaves presented a thicker aquiferous parenchyma, which might facilitate the accumulation of high concentrations of carbohydrates and polyalcohols (sorbitol and mannitol) and perform CAM pathway due to the increase of phosphoenolpyruvate carboxylase (PEPC) activity and accumulate organic acids during the night. Under severe stress CAM was intensified and their leaves were less thick. The results showed that juvenile A. imperialis plants are able to make metabolic adjustments in response to water shortage, and these responses are dependent on the intensity and/or duration of the drought conditions. Overall, this work provides a better understanding of how rupicolous plants survive under different drought conditions. Rupicolous juvenile bromeliads of Alcantarea imperialis subjected to drought are able to survive by increasing the production of sugars under conditions of moderate stress or performing CAM under severe stress.

Expression Profiles and Post-Translational Modifications of Phosphoenolpyruvate Carboxylase Isozymes of Bienertia sinuspersici during Leaf Development

Phosphoenolpyruvate carboxylase (PEPC) is the primary acceptor of carbon dioxide in C4 photosynthesis. Three isozymes of PEPC: PEPC1, PEPC2, and PEPC3, in the single cell, C4 plant Bienertiasinuspersici Akhani were determined in this study. Differential expressions of these isoforms were observed at different stages of leaf development. Amino acid sequence alignment revealed that PEPC1, PEPC2, and PEPC3 had characteristics of C3-C4 PEPC type, C4 PEPC, and C3 PEPC, respectively. Gene expression profiles showed that PEPC3 was highly expressed in young leaves while PEPC1 and PEPC2 were more expressed in intermediate and mature leaves, respectively. Using immunoblotting, we also assessed tissue-specific expression and post-translational modifications (PTMs) of PEPC in B. sinuspersici. During leaf maturation, phosphorylation at Ser 11 and monoubiquitination at Lys 629 were highly increased. The phosphorylation pattern on PEPC was diurnally regulated but monoubiquitination was not. Moreover, dimorphic chloroplasts from B. sinuspersici chlorenchyma cell of mature leaf were isolated to study spatial localization of PEPC by PTM. Monoubiquitinated PEPC were specifically interacting with peripheral chloroplasts. These results indicated that phosphorylation and monoubiquitination on PEPC were mutually exclusive as well as affecting spatial localization in single cell C4 plants.

Transgenic maize phosphoenolpyruvate carboxylase alters leaf\u2013atmosphere CO2 and 13CO2 exchanges in Oryza sativa

The engineering process of C4 photosynthesis into C3 plants requires an increased activity of phosphoenolpyruvate carboxylase (PEPC) in the cytosol of leaf mesophyll cells. The literature varies on the physiological effect of transgenic maize (Zea mays) PEPC (ZmPEPC) leaf expression in Oryza sativa (rice). Therefore, to address this issue, leaf–atmosphere CO2 and 13CO2 exchanges were measured, both in the light (at atmospheric O2 partial pressure of 1.84 kPa and at different CO2 levels) and in the dark, in transgenic rice expressing ZmPEPC and wild-type (WT) plants. The in vitro PEPC activity was 25 times higher in the PEPC overexpressing (PEPC-OE) plants (~20% of maize) compared to the negligible activity in WT. In the PEPC-OE plants, the estimated fraction of carboxylation by PEPC (β) was ~6% and leaf net biochemical discrimination against 13CO2left( {Delta_{text{bio}} } right) was ~ 2‰ lower than in WT. However, there were no differences in leaf net CO2 assimilation rates (A) between genotypes, while the leaf dark respiration rates (Rd) over three hours after light–dark transition were enhanced (~ 30%) and with a higher 13C composition left( {delta^{ 1 3} {text{C}}_{text{Rd}} } right) in the PEPC-OE plants compared to WT. These data indicate that ZmPEPC in the PEPC-OE rice plants contributes to leaf carbon metabolism in both the light and in the dark. However, there are some factors, potentially posttranslational regulation and PEP availability, which reduce ZmPEPC activity in vivo.

N-Butylamine production from glucose using a transaminase-mediated synthetic pathway in Escherichia coli

Bioamination methods using microorganisms have attracted much attention because of the increasing demand for environmentally friendly bioprocesses. n-Butylamine production from glucose in Escherichia coli was demonstrated in this study, which has never been reported because of the absence of n-butylamine-producing pathway in nature. We focused on a transaminase-mediated cascade for bioamination from an alcohol or aldehyde. The cascade can convert an alcohol or an aldehyde to the corresponding amine with l-alanine as an amine donor. Here, n-butyraldehyde, which is a metabolic intermediate in the n-butanol producing pathway, is a potential intermediate for producing n-butylamine using this cascade. Hence, the n-butanol-producing pathway and the transaminase-mediated cascade were combined into a synthetic metabolic pathway for producing n-butylamine from glucose. Firstly, we demonstrated the conversion of n-butanol to n-butylamine using a three enzyme-mediated cascade. n-Butanol was successfully converted to n-butylamine in 92% yield in the presence of l-alanine and ammonium chloride. Then, the n-butanol-producing pathway and transaminase-mediated cascade were introduced into E. coli. Using this system, n-butylamine was successfully produced from glucose as a carbon source at a concentration of 53.2mgL-1 after 96h cultivation using a ppc (phosphoenolpyruvate carboxylase)-deficient strain. To the best of our knowledge, this is the first report of the direct production of n-butylamine from glucose, and may provide a starting point for the development of microbial methods to produce other bioamines.

Prediction of Rate-Limiting Reactions for Growth-Associated Production Using a Constraint-Based Approach.

Identification of a rate-limiting step in pathways is a key challenge in metabolic engineering. Although the prediction of rate-limiting steps using a kinetic model is a powerful approach, there are several technical hurdles for developing a kinetic model. In this study, an in silico screening algorithm of key enzyme for metabolic engineering is developed to identify the possible rate-limiting reactions for the growth-coupled target production using a stoichiometric model without any experimental data and kinetic parameters. In this method, for each reaction, an upper-bound flux constraint is imposed and the target production is predicted by linear programming. When the constraint decreases the target production at the optimal growth state, the reaction is thought to be a possible rate-limiting step. For validation, this method is applied to the production of succinate or 1,4-butanediol (1,4-BDO) in Escherichia coli, in which the experimental engineering for eliminating rate-limiting steps has been previously reported. In succinate production from glycerol, nine reactions including phosphoenolpyruvate carboxylase are predicted as the rate-limiting steps. In 1,4-BDO production from glucose, eight reactions including pyruvate dehydrogenase are predicted as the rate-limiting steps. These predictions include experimentally identified rate-limiting steps, which would contribute to metabolic engineering as a practical tool for screening candidates of rate-limiting reactions.

Co-cultivation of cyanobacteria for raising nursery of chrysanthemum using a hydroponic system

The present investigation aimed to utilize plant growth–promoting diazotrophic cyanobacteria as an option to raise the chrysanthemum varieties Pusa Aditya and Jaya in a nursery by co-culturing hydroponically. Fresh stem cuttings of chrysanthemum were planted in BG 11 medium (−N) which was inoculated to log-phase cultures of Anabaena torulosa (BF1), Anabaena doliolum (BF4), and Anabaena laxa (RPAN8) individually. Analyses of chrysanthemum growth and biometric/biochemical parameters after 30 days of co-cultivation revealed that co-culturing treatments performed significantly better, as compared with BG11 medium alone. Anabaena laxa brought about an increment of 27–40% in IAA production in the root tissues of both varieties grown in hydroponics. Quantification of biofilm formation on roots (measured as OD550) illustrated a two- to four-fold increment in the co-culture treatments. PEP carboxylase activity was significantly enhanced in root and shoot tissues of cuttings in Jaya, and the medium chlorophyll enhanced by several folds in both varieties. Significant increases in root dry biomass were recorded, which positively correlated with root protein (r = 0.992) in Pusa Aditya, illustrating the superiority of co-culturing as a promising option for nursery propagation. The economic benefits of BG 11 medium (without combined N) as a novel growth medium for growing the cyanobacterium and raising chrysanthemum nursery, in co-culturing mode, were also highlighted. Anabaena torulosa (BF1) performed well in both Pusa Aditya and Jaya, while Anabaena laxa (RPAN8) was significantly superior in Jaya. Future research is focused towards integration of such novel and cheap organic inputs in maintaining disease-free and nutrient-enriched plants in long-term experiments up to flowering stage.

Comparison of Five Endogenous Reference Genes for Specific PCR Detection and Quantification of Rice

Endogenous reference genes (ERGs) provide vital information regarding genetically modified organisms (GMOs). The successful detection of ERGs can identity GMOs and the source of genes, verify stability and reliability of the detection system, and calculate the level of genetically modified (GM) ingredients in mixtures. The reported ERGs in rice include sucrose-phosphate synthase (SPS), phospholipase D (PLD), RBE4 and rice root-specific GOS9 genes. Based on the characteristics of ERGs, a new ERG gene, phosphoenolpyruvate carboxylase (PEPC), was selected, and further compared with the four existing genes. A total of 18 rice varieties and 29 non-rice crops were used to verify the interspecies specificity, intraspecies consistency, sensitivity, stability and reliability of these five ERGs using qualitative and quantitative PCR. Qualitative detection indicated that SPS and PEPC displayed sufficient specificity, and the detection sensitivity was 0.05% and 0.005%, respectively. Although the specificity of both RBE4 and GOS9 were adequate, the amplicons were small and easily confused with primer dimers. Non-specific amplification of the PLD gene was present in maize and potato. Real-time quantitative PCR detection indicated that PLD, SPS and PEPC displayed good specificity, with R2 of the standard curve greater than 0.98, while the amplification efficiency ranged between 90% and 110%. Both the detection sensitivities of PLD and PEPC were five copies and that of SPS was ten copies. RBE4 showed typical amplification in maize, beet and Arabidopsis, while GOS9 was found in maize, tobacco and oats. PEPC exhibited excellent detection sensitivity and species specificity, which made it a potentially useful application in GM-rice supervision and administration. Additionally, SPS and PLD are also suitable for GM-rice detection. This study effectively established a foundation for GMO detection, which not only provides vital technical support for GMO identification, but also is of great significance for enhancing the comparability of detection results, and the standardization of ERG testing in GM-rice.

English

A glasshouse experiment was conducted to compare the performance of a stay-green QTL introgression line (RSG 03123) and its parental lines (B35, a stay-green and R16, a high yielding cultivar with rapid senescence) after flowering, when water-limited (WL) or well-watered (WW). Flowering time and plant height were similar in RSG 03123 and the recurrent parent, R16. Under WW conditions, retention of green leaf area (GLA) and chlorophyll was similar in RSG 03123 and R16, whereas under WL conditions RSG 03123 retained significantly (P<0.05) more GLA. The rate of senescence was also lower in RSG 03123 as compared to R16 under WL conditions. B35 displayed a delayed onset of senescence under both WW and WL conditions while both R16 and RSG 01323 displayed an earlier onset of senescence under WL conditions. Photochemical efficiency of photosystem II (ΦPSII), gas exchange characteristics, and total soluble carbohydrates contents, in both leaf and stem, were higher in RSG 03123 than in R16 under WL conditions. These parameters were enhanced in RSG 03123 due to higher retention of chloroplast proteins, such as light-harvesting chlorophyll binding protein complex of PSII (LHCPII), oxygen-evolving complex 33 kDa (OEC33), phosphoenolpyruvate carboxylase (PEPC) and the large subunit of ribulose bisphosphate carboxylase-oxygenase (Rubisco). The stay-green characteristics of RSG 03123 were intermediate between R16 and B35; nonetheless, the results show that stay-green QTL are functional during senescence and improve tolerance to water limitation after flowering. Key words: Stay-green QTL, introgression, drought, photosynthesis.

Increasing Agmatine Production in Escherichia coli through Metabolic Engineering.

In this study, to obtain higher agmatine yields using the previously developed E. coli strain AUX4 (JM109 ΔspeC ΔspeF ΔspeB ΔargR), the genes encoding glutamate dehydrogenase (gdhA), glutamine synthetase (glnA), phosphoenolpyruvate carboxylase (ppc), aspartate aminotransferase (aspC), transhydrogenase (pntAB), and biosynthetic arginine decarboxylase (speA) were sequentially overexpressed by replacing their native promoters with the heterologous strong trp, core-trc, or 5Ptacs promoters to generate the plasmid-free E. coli strain AUX11. The fermentation results obtained using a 3-L bioreactor showed that AUX11 produced 2.93 g L-1 agmatine with the yield of 0.29 g agmatine g-1 glucose in the batch fermentation, and the fed-batch fermentation of AUX11 allowed the production of 40.43 g L-1 agmatine with the productivity of 1.26 g L-1 h-1 agmatine. The results showed that the engineered E. coli strain AUX11 can be used for the industrial fermentative production of agmatine.

C4 photosynthetic enzymes play a key role in wheat spike bracts primary carbon metabolism response under water deficit

C4 photosynthetic enzymes are present in C3 plants and participate in non-photosynthetic metabolism. Wheat spike bracts had a higher drought tolerance, photosynthesis and senesced later compared to the flag leaves under water deficit. This research was conducted to investigate the different response of primary carbon metabolism induced by C4 photosynthetic enzymes in wheat flag leaves and spike bracts including glumes and lemmas under water deficit. The activities of C4 photosynthetic enzymes and Ribulose bisphosphate carboxylase oxygenase (Rubisco), the expression of related genes and primary carbon metabolism contents were demonstrated in wheat flag leaves and spike bracts exposed to water deficit. Results showed that drought stress strongly inhibited wheat photosynthetic metabolism by decreasing Rubisco activity in flag leaves. The activities of phosphoenolpyruvate carboxylase (PEPC), NADP-malic enzyme (NADP-ME), phosphate dikinase (PPDK) and NADP- malic dehydrogenase (NADP-MDH) increased in wheat spike bracts under water deficit. Transcript levels of C4 photosynthetic genes in wheat spike bracts were higher under water deficit than that of control. Furthermore, the results indicated that drought stress induced changes in the contents of primary carbon metabolism including malate, oxaloacetic acid (OAA), citric, fumaric acid were organ-specific. In conclusion, the functions of C4 photosynthetic enzymes appear to be important for wheat spike bracts primary carbon metabolism and defence response under drought stress.

Nitrogen drives plant growth to the detriment of leaf sugar and steviol glycosides metabolisms in Stevia (Stevia rebaudiana Bertoni)

Steviol glycosides (SGs) in Stevia (Stevia rebaudiana Bertoni) leaves are important due to their high sweetness and low calorific value. The yield of SGs is dependent on fertilization regimes, but the relationship between nitrogen (N) administration and SGs synthesis is still unclear. In this study, we investigate the effects of N rates on SGs production through hydroponic and plot experiments. The SGs yield was not significantly changed by N fertilization, but leaf SGs concentrations were significantly reduced due to the “dilution effect”. Additionally, N addition decreased leaf carbon (C)/N ratio and soluble sugar concentration, accompanied with the inhibited phosphoenolpyruvate carboxylase and L-phenylalanine ammonia_lyase activities. A significant positive correlation between leaf SGs concentrations, C/N ratio and soluble sugar concentration was observed. Overall, we suggest that N-driven Stevia growth negatively affects SGs concentrations. The leaf C/N ratio and soluble sugar changes indicated the occurrence of metabolic reprogramming.

Expression of autotrophic genes under CO2 environment and genome mining of desert bacterium Cupriavidus sp. HPC(L)

Increasing levels of atmospheric CO2 and plastic pollution are major environmental threats that need serious attention. The invisible microbial world has the key to solve this issue by sinking CO2 to PHB, biofuels and other bio-based products. Cupriavidus is one of them, that synthesis PHB from CO2. The study demonstrate autotrophic growth of Cupriavidus sp. HPC(L), gene expression of rubisco (cbbLR), carbonic anhydrase (ca) and phosphoenolpyruvate (ppc) carboxylase and genome mining. Under autotrophic condition, there was 104 folds increase in CFU/ml after three months. The genome was sequenced to track CO2 fixation routes available through molecular and bioinformatics tools. The relative gene expression of cbbLR, ca and ppc increased by 2.5 to 3.0 fold under CO2. The bacterium uses Calvin cycle for CO2 fixation. Genome shows presence of carboxylases, polyhydroxybutyrate synthesis gene cluster and sox pathway gene, that makes it apt for sinking CO2 to PHB for sustainable environment.