Phosphoenolpyruvate Carboxylase Research Articles

Nitrogen and Chemical Control Management Improve Yield and Quality in High-Density Planting of Maize by Promoting Root-Bleeding Sap and Nutrient Absorption.

High-density planting aggravates competition among plants and has a negative impact on plant growth and productivity. Nitrogen application and chemical control can improve plant growth and increase grain yield in high-density planting. Our experiment explored the effects of nitrogen fertilizer and plant growth regulators on maize root-bleeding sap, phosphorus (P) and potassium (K) accumulation and translocation, and grain yield and quality in high-density planting. We established a field study during the 2017 and 2018 growing seasons, with three nitrogen levels of N100 (100 kg ha−1), N200 (200 kg ha−1), and N300 (300 kg ha−1) at high-density planting (90,000 plants ha−1), and applied Yuhuangjin (a plant growth regulator mixture of 3% DTA-6 and 27% ethephon) at the 7th leaf. Our results showed that N200 application combined with chemical control could regulate amino acid and mineral nutrient concentration delivery rates in root-bleeding sap and improve its sap rate. Also, the treated plant exhibited higher P and K uptake and translocation ability. Furthermore, chemical control and N200 treatment maintained a high level of ribulose-1,5-bisphosphate carboxylase (RuBPCase), phosphoenolpyruvate carboxylase (PEPCase), nitrate reductase (NR), and glutamine synthetase (GS) enzymatic activities in leaves. In addition, plant growth regulator and nitrogen application improved the enzymatic activities of GS, glutamate dehydrogenase (GDH), and glutamic pyruvic transaminase (GPT) and the contents of crude protein, lysine, sucrose, and soluble sugar in grain and ultimately increased maize yield. This study suggests that N200 application in combination with chemical control promotes root vitality and nutrient accumulation and could improve grain yield and quality in high-density planting.

Effects of Nitrogen Fertilization on Physiological Response of Maize to Soil Salinity

Soil salinization is a global problem that causes huge losses in agricultural production. Salt can interfere with crop absorption and metabolism of nutrients and water, affect plant physiological responses and reduce plant biomass. Maize, a very important economic crop, can adapt to a certain degree of saline-alkali soil. It is essential to understand the physiological indexes of response to soil salinity concentrations and explore the effects of different nitrogen fertilizer treatments on maize growth. In this study, three soil salinity gradients (S1, S2 and S3 were with soil salt concentration, Ssc, of 0, 0.1% and 0.25%, respectively) and two nitrogen application rates (N0 and N1 were without and with nitrogen applied (13.2 g per pot), respectively) were set up. Plant growth and photosynthetic parameters were measured. Whether nitrogen was applied or not, with the increase in Ssc, leaf area, plant height, stem diameter, SPAD, leaf water potential, RuBP carboxylase, and PEP carboxylase activities, photosynthetic rate (A), stomatal conductance (gs), the maximum stomatal conductance (gsmax), and the stomatal morphological parameters such as stomatal width and maximum stomatal area (amax), all showed a downward trend. Under the S1 and S2 treatments, compared with the N0, the N1 treatment alleviated the stress effect of the Ssc on these indicators. However, under S3 treatment, the stress degrees of leaf water potential, gs, gsmax and amax, were aggravated after nitrogen application. This indicated that under the high Ssc of S3, the interaction between nitrogen application and soil salinity should be considered. WUEin increased with the increase in Ssc. Moreover, under N1 treatments, the increase in WUEin with Ssc was greater than that with N0. With the increase in Ssc, whether nitrogen was applied or not, the dry weight of maize declined by 44.2% and 73.0%, respectively, for the S2 and S3 treatments. Under S2 treatment, N1 significantly improved the dry matter mass of maize compared with the N0 treatment. The results showed that soil salt stress can inhibit crop growth, physiology and dry matter accumulation, and that nitrogen application can alleviate this within a specific salinity range. Such results indicate that in saline-alkali areas, whether nitrogen fertilizer is applied or not should depend on the level of Ssc to improve plant growth.

Differential timing of gene expression and recruitment in independent origins of CAM in the Agavoideae (Asparagaceae).

Crassulacean acid metabolism (CAM) photosynthesis has evolved repeatedly across the plant tree of life, however our understanding of the genetic convergence across independent origins remains hampered by the lack of comparative studies. Here, we explore gene expression profiles in eight species from the Agavoideae (Asparagaceae) encompassing three independent origins of CAM. Using comparative physiology and transcriptomics, we examined the variable modes of CAM in this subfamily and the changes in gene expression across time of day and between well watered and drought-stressed treatments. We further assessed gene expression and the molecular evolution of genes encoding phosphoenolpyruvate carboxylase (PPC), an enzyme required for primary carbon fixation in CAM. Most time-of-day expression profiles are largely conserved across all eight species and suggest that large perturbations to the central clock are not required for CAM evolution. By contrast, transcriptional response to drought is highly lineage specific. Yucca and Beschorneria have CAM-like expression of PPC2, a copy of PPC that has never been shown to be recruited for CAM in angiosperms. Together the physiological and transcriptomic comparison of closely related C3 and CAM species reveals similar gene expression profiles, with the notable exception of differential recruitment of carboxylase enzymes for CAM function.

Overexpression of cytoplasmic C4 Flaveria bidentis carbonic anhydrase in C3 Arabidopsis thaliana increases amino acids, photosynthetic potential, and biomass.

SummaryAn important method to improve photosynthesis in C3 crops, such as rice and wheat, is to transfer efficient C4 characters to them. Here, cytosolic carbonic anhydrase (CA: βCA3) of the C4 Flaveria bidentis (Fb) was overexpressed under the control of 35S promoter in Arabidopsis thaliana, a C3 plant, to enhance its photosynthetic efficiency. Overexpression of CA resulted in a better supply of the substrate HCO3‐ for the endogenous phosphoenolpyruvate carboxylase in the cytosol of the overexpressers, and increased its activity for generating malate that feeds into the tricarboxylic acid cycle. This provided additional carbon skeleton for increased synthesis of amino acids aspartate, asparagine, glutamate, and glutamine. Increased amino acids contributed to higher protein content in the transgenics. Furthermore, expression of FbβCA3 in Arabidopsis led to a better growth due to expression of several genes leading to higher chlorophyll content, electron transport, and photosynthetic carbon assimilation in the transformants. Enhanced CO2 assimilation resulted in increased sugar and starch content, and plant dry weight. In addition, transgenic plants had lower stomatal conductance, reduced transpiration rate, and higher water‐use efficiency. These results, taken together, show that expression of C4 CA in the cytosol of a C3 plant can indeed improve its photosynthetic capacity with enhanced water‐use efficiency.

The Combined Application of Urea and Fulvic Acid Solution Improved Maize Carbon and Nitrogen Metabolism

It has been reported that fulvic acid (FA) application improves soil structure and nutrient availability. However, the effects of combined application of urea (U) and FA solution on the photosynthesis and nitrogen metabolism in maize (Zea mays L.) have rarely been reported. In this study, pot experiments were conducted in 2017 and 2018, and the effects of combined application of urea and FA solution (U+FA) on soil available nutrient contents, maize endogenous hormone concentrations, carbon and nitrogen metabolism-related enzyme concentrations, maize yield, and nitrogen use efficiency (NUE) were researched. Compared with the U treatment, the maize yield and NUE in the U+FA treatment were significantly increased by 8.31% and 17.09 percentage points in 2017 and by 16.90% and 24.31 percentage points in 2018. At the jointing and 12-leaf (V12) stages of maize, soil NH4+ content increased by 139.32% and 12.08%, separately, in the U+FA treatment. At the V12 stage, the auxin, nitrate reductase, nitrite reductase, and glutamine synthetase concentrations in maize root were increased by 42.31%, 74.17%, 16.61%, and 45.60%, respectively, and the concentrations of pyruvate phosphate dikinase and phosphoenolpyruvate carboxylase in maize leave were increased by 29.40% and 42.96%, respectively, in the U+FA treatment. The combined application of urea and FA solution significantly improved soil nutrient availability, increased the concentrations of endogenous hormones in maize, stimulated the activities of enzymes related to nitrogen metabolism, promoted the photosynthetic carbon assimilation efficiency, and ultimately improved crop yield and NUE.

N addition rebalances the carbon and nitrogen metabolisms of Leymus chinensis through leaf N investment

Intensifying nitrogen (N) deposition disturbs the growth of grassland plants due to an imbalance between their carbon (C) and N metabolism. However, it's unclear how plant physiological strategies restore balance. We investigated the effects of multiple N addition levels (0–25 g N m−2 yr−1) on the coordination of C and N metabolism in a dominant grass (Leymus chinensis) in a semiarid grassland in northern China. To do so, we evaluated photosynthetic parameters, leaf N allocation, C- and N-based metabolites, and metabolic enzymes. We found that a moderate N level (10 g N m−2 yr−1) promoted carboxylation and electron transport by allocating more N to the photosynthetic apparatus and increasing ribulose bisphosphate carboxylase/oxygenase activity, thereby increasing photosynthetic capacity. The highest N level (25 g N m−2 yr−1) promoted N investment in nonphotosynthetic pathways and increased the free amino acids in the leaves. N addition stimulated the accumulation of C and N compounds across organs by activating sucrose phosphate synthase, nitrate reductase, and glutamine synthetase. This enhancement triggered a transformation of primary metabolites (nonstructural carbohydrates, proteins, amino acids) to secondary metabolites (flavonoids, phenols, and alkaloids) for temporary storage or as defense compounds. Citric acid, as the C skeleton for enhanced N metabolism, decreased significantly, and malic acid increased by catalysis of phosphoenolpyruvate carboxylase. Our findings show the adaptability of L. chinensis to different N-addition levels by adjusting its allocations of C and N metabolic compounds and confirm the roles of C and N coordination by grassland plants in these adaptations.

Insight into Cistus salviifolius extract forpotential biostimulant effects in modulating cadmium-induced stress in sorghum plant.

The main aim of the current study was to investigate the role of Cistus salviifolius leaves extract (CSE) in alleviating the toxic effect of cadmium (Cd) in sorghum (Sorghum bicolor) plants. The plants exposed to Cd (200µM) exhibited limited growth, reduced biomass, and chlorophyll content compared to unstressed ones. Nevertheless, supplementation of CSE restored the negative effect of Cd and increased biomass and pigment content. CSE also increased the activities of antioxidant enzymes such as superoxide dismutase (SOD), isocitrate dehydrogenase (ICDH), glutathione peroxidase (GPx), glutathione reductase (GR), and Glutathione-S-Transferase (GST). Furthermore, supplementation of CSE decreased lipid peroxidation and further increased the content of soluble sugar and amino acid. We also found that CSE has a promising effect in modulating the perturbations of carbon and nitrogen metabolism in sorghum plants under Cd stress by examining several carbon-nitrogen enzyme activities: phosphoenolpyruvate carboxylase (PEPC), malate dehydrogenase (NAD-MDH), glutamine synthase (GS), glutamate dehydrogenase (GDH), and aspartate aminotransferase (AAT). Overall, our results confirm that the application of CSE can be a promising mechanism to overcome the negative effects of Cd stress in sorghum plants.

Conservation and Divergence of Phosphoenolpyruvate Carboxylase Gene Family in Cotton.

Phosphoenolpyruvate carboxylase (PEPC) is an important enzyme in plants, which regulates carbon flow through the TCA cycle and controls protein and oil biosynthesis. Although it is important, there is little research on PEPC in cotton, the most important fiber crop in the world. In this study, a total of 125 PEPCs were identified in 15 Gossypium genomes. All PEPC genes in cotton are divided into six groups and each group generally contains one PEPC member in each diploid cotton and two in each tetraploid cotton. This suggests that PEPC genes already existed in cotton before their divergence. There are additional PEPC sub-groups in other plant species, suggesting the different evolution and natural selection during different plant evolution. PEPC genes were independently evolved in each cotton sub-genome. During cotton domestication and evolution, certain PEPC genes were lost and new ones were born to face the new environmental changes and human being needs. The comprehensive analysis of collinearity events and selection pressure shows that genome-wide duplication and fragment duplication are the main methods for the expansion of the PEPC family, and they continue to undergo purification selection during the evolutionary process. PEPC genes were widely expressed with temporal and spatial patterns. The expression patterns of PEPC genes were similar in G. hirsutum and G. barbadense with a slight difference. PEPC2A and 2D were highly expressed in cotton reproductive tissues, including ovule and fiber at all tested developmental stages in both cultivated cottons. However, PEPC1A and 1D were dominantly expressed in vegetative tissues. Abiotic stress also induced the aberrant expression of PEPC genes, in which PEPC1 was induced by both chilling and salinity stresses while PEPC5 was induced by chilling and drought stresses. Each pair (A and D) of PEPC genes showed the similar response to cotton development and different abiotic stress, suggesting the similar function of these PEPCs no matter their origination from A or D sub-genome. However, some divergence was also observed among their origination, such as PEPC5D was induced but PEPC5A was inhibited in G. barbadense during drought treatment, suggesting that a different organized PEPC gene may evolve different functions during cotton evolution. During cotton polyploidization, the homologues genes may refunction and play different roles in different situations.

Knock-down of phosphoenolpyruvate carboxylase 3 negatively impacts growth, productivity, and responses to salt stress in sorghum (Sorghum bicolor L.).

SUMMARYPhosphoenolpyruvate carboxylase (PEPC) is a carboxylating enzyme with important roles in plant metabolism. Most studies in C4 plants have focused on photosynthetic PEPC, but less is known about non‐photosynthetic PEPC isozymes, especially with respect to their physiological functions. In this work, we analyzed the precise roles of the sorghum (Sorghum bicolor) PPC3 isozyme by the use of knock‐down lines with the SbPPC3 gene silenced (Ppc3 lines). Ppc3 plants showed reduced stomatal conductance and plant size, a delay in flowering time, and reduced seed production. In addition, silenced plants accumulated stress indicators such as Asn, citrate, malate, and sucrose in roots and showed higher citrate synthase activity, even in control conditions. Salinity further affected stomatal conductance and yield and had a deeper impact on central metabolism in silenced plants compared to wild type, more notably in roots, with Ppc3 plants showing higher nitrate reductase and NADH‐glutamate synthase activity in roots and the accumulation of molecules with a higher N/C ratio. Taken together, our results show that although SbPPC3 is predominantly a root protein, its absence causes deep changes in plant physiology and metabolism in roots and leaves, negatively affecting maximal stomatal opening, growth, productivity, and stress responses in sorghum plants. The consequences of SbPPC3 silencing suggest that this protein, and maybe orthologs in other plants, could be an important target to improve plant growth, productivity, and resistance to salt stress and other stresses where non‐photosynthetic PEPCs may be implicated.

Metabolic pathway engineering for the non-growth-associated succinate production in Escherichia coli based on flux solution space

Non-growth-associated bio-production using microorganisms has the potential to achieve a higher target yield than growth-associated production since the latter approach does not waste the substrate for cell growth. We previously proposed a metabolic pathway engineering method (SSDesign) for non-growth-associated target production based on metabolic flux solution space using elementary mode analysis. SSDesign predicts gene knockout combinations for enforcing cells to produce a target compound under non-growing conditions. For succinate production from glucose in Escherichia coli, gene knockouts of pykA-pykF-sfcA-maeB-zwf and pykA-pykF-sfcA-pntAB-sthA were predicted as candidates. In the present study, to verify the predictions of SSDesign, succinate productivities of these multiple knockout strains were evaluated in the stationary phase under microaerobic conditions. Succinate yields of the BW25113ΔpykAΔpykFΔsfcAΔmaeBΔzwf and BW25113ΔpykAΔpykFΔsfcAΔpntABΔsthA strains were 0.48 and 0.52mol/mol, respectively, and were higher than that of wild type strain (0.20mol/mol). The succinate yield of BW25113ΔpykAΔpykFΔsfcAΔpntABΔsthA strain was further improved to 0.66mol/mol by overexpression of phosphoenolpyruvate carboxylase as a potential bottleneck step in the metabolic pathway.

Effects of Phosphorus Application Rate on Lipid Synthesis and Eating Quality of Two Rice Grains

Lipids are an important nutritional component of rice, and lipid content has an important effect on rice eating quality. However, the effects of the fertilizer application rate on lipid synthesis and eating quality of rice are poorly understood. To investigate the effects of phosphorus (P) fertilizer on lipid synthesis and eating quality of rice, we used Nanjing (NJ) 9108 (japonica) and IR72 (indica) rice as experimental materials, and four P levels, P0 (0 kg ha−1), P1 (45 kg ha−1), P2 (67.5 kg ha−1) and P3 (135 kg ha−1). The results showed that the lipid, free fatty acid (FFA) content, unsaturated fatty acid (UFA) content, malonyl-CoA (MCA) content, phosphatidic acid (PA) content, lipid synthesis-related enzyme activities and eating quality of both cultivars increased with increasing P. However, the saturated fatty acid (SFA) content showed the opposite trend. No significant differences were found in pyruvate (PYR) content between P treatments. Protein and oxaloacetic acid (OAA) contents and phosphoenolpyruvate carboxylase (PEPCase) activity first increased and then decreased with increasing P, which indicated that high P levels could stimulate lipid synthesis more than protein synthesis. Overall, increasing P optimized fatty acid components and increased the lipid content and eating quality of rice by enhancing lipid synthesis-related enzyme activities and regulating substrate competition for lipid and protein synthesis. The optimal P application rate for lipid synthesis and eating quality of both cultivars was 135 kg ha−1.

Bacillus velezensis SX13 promoted cucumber growth and production by accelerating the absorption of nutrients and increasing plant photosynthetic metabolism

Rhizosphere colonization by plant growth-promoting rhizobacteria (PGPR) facilitates the ability of PGPR to promotes plant growth and health. Among the rhizosphere microbial communities, the dominant PGPR strains should be tapped to analyze their growth-promoting mechanism, and then promote the development and utilization of related agricultural products. In the current study, Bacillus velezensis SX13, Bacillus paralicheniformis SX21, and Bacillus tequilensis SX31, which can dissolve inorganic and organic phosphorus and produce auxin (IAA; except B. tequilensis SX31), were isolated from cucumber rhizosphere. Three weeks after the strains were separately inoculated into the rhizosphere of cucumber plants, the plants treated with the three strains showed improved root structures, photosynthetic parameters, increased growth rate, and high degree of biomass accumulation, compared with the control plants. Plants inoculated with B. velezensis SX13 had the highest seedling growth rate. Experiment using different inoculation doses was conducted. Results showed that B. velezensis SX13 promoted the absorption of elements by the roots and the transport of these elements to the shoots by improving the root structures and up-regulating the expression of CsNRT1 subfamily genes in the roots. Increases in element absorption and transport rates promoted photosynthesis and the activities of enzymes related to carbon metabolism (including ribulose-1,5-bisphosphate carboxylase/oxygenase, sucrose phosphate synthase, phosphoenolpyruvate carboxylase, ribulose-1,5-bisphosphate carboxylase/oxygenase activase, and fructose-l.6-bisphosphate aldolase) and nitrogen metabolism (including nitrate reductase, glutamine synthase, glutamine-2-oxoglutarate aminotransferase, and glutamate dehydrogenase) in the leaves. In addition, the levels of glucose, sucrose, fructose, soluble proteins, and amino acids increased in the leaves. Induced by B. velezensis SX13, increase in photosynthetic metabolism promoted biomass and element accumulation in the roots and shoots and significantly improved fruit quality and yield. However, a dose effect was observed in the case of B. velenzensis SX13 at the doses assayed in this work.

Comparative transcriptomic analysis and antioxidant defense mechanisms in clusterbean (Cyamopsis tetragonoloba (L.) Taub.) genotypes with contrasting drought tolerance.

To understand drought tolerance mechanism(s) in clusterbean (Cyamopsis tetragonoloba), we conducted physiological, biochemical, and de novo comparative transcriptome analysis of drought-tolerant (RGC-1002) and drought-sensitive (RGC-1066) genotypes subjected to 30days of drought stress. Relative water content (RWC) was maintained in tolerant genotype but was reduced in sensitive genotype. Leaf pigment concentrations were higher in tolerant genotype. Net photosynthesis was significantly decreased in sensitive genotype but insignificant reduction was found in tolerant genotype. Enzymatic antioxidant (GR, APX, DHAR) activities were enhanced in tolerant genotype, while there were insignificant changes in these enzymes in sensitive genotype. The ratios of antioxidant molecules (ASC/DHA and GSH/GSSG) were higher in tolerant genotype as compared to sensitive genotype. In sensitive genotype, 6625 differentially expressed genes (DEGs) were upregulated and 5365 genes were downregulated. In tolerant genotype, 5206 genes were upregulated and 2793 genes were downregulated. In tolerant genotype, transketolase family protein, phosphoenolpyruvate carboxylase 3, temperature-induced lipocalin, and cytochrome oxidase were highly upregulated. Moreover, according to Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, the drought tolerance may be attributed to upregulated starch and sucrose metabolism-related genes in tolerant genotype. Finally, quantitative real-time PCR confirmed the reproducibility of the RNA-seq data.

Salt stress induces Kranz anatomy and expression of C4 photosynthetic enzymes in the amphibious sedge Eleocharis vivipara

Eleocharis vivipara Link is a unique amphibious leafless plant of the Cyperaceae. The terrestrial form develops culms with Kranz anatomy and C4-like traits, while the submerged form does culms with non-Kranz anatomy and C3 traits. The submerged form develops new culms with C4-like mode when exposed to air or exogenous abscisic acid. In this study, we investigated whether salt stress (0.05-0.3M NaCl) has a similar effect. When the submerged form was grown for one month in solutions of 0.1M NaCl and more, culm growth was strongly suppressed. However, these plants slowly developed new culms that had Kranz anatomy with chloroplast-abundant Kranz bundle sheath cells. Although the culms of the submerged form had only few stomata, culms grown in the NaCl solution had many stomata. The NaCl-grown culms also accumulated large amounts of C4 photosynthetic enzymes (phosphoenolpyruvate carboxylase and pyruvate Pi dikinase), and the cellular localization patterns of these enzymes and ribulose 1,5-bisphosphate carboxylase/oxygenase were similar to those in terrestrial culms. Accumulation of C4 enzymes increased in mature culms of the submerged form (with non-Kranz anatomy) when exposed to 0.2M NaCl solution for one week. These results suggest that salt stress induces development of Kranz anatomy and expression of C4 photosynthetic enzymes in the submerged C3 form of E. vivipara, whereas the anatomical and biochemical traits of C4 photosynthesis appear to be regulated independently.

Gene co-expression reveals the modularity and integration of C4 and CAM in Portulaca.

C4 photosynthesis and Crassulacean acid metabolism (CAM) have been considered as largely independent adaptations despite sharing key biochemical modules. Portulaca is a geographically widespread clade of over 100 annual and perennial angiosperm species that primarily use C4 but facultatively exhibit CAM when drought stressed, a photosynthetic system known as C4 + CAM. It has been hypothesized that C4 + CAM is rare because of pleiotropic constraints, but these have not been deeply explored. We generated a chromosome-level genome assembly of Portulaca amilis and sampled mRNA from P. amilis and Portulaca oleracea during CAM induction. Gene co-expression network analyses identified C4 and CAM gene modules shared and unique to both Portulaca species. A conserved CAM module linked phosphoenolpyruvate carboxylase to starch turnover during the day-night transition and was enriched in circadian clock regulatory motifs in the P. amilis genome. Preservation of this co-expression module regardless of water status suggests that Portulaca constitutively operate a weak CAM cycle that is transcriptionally and posttranscriptionally upregulated during drought. C4 and CAM mostly used mutually exclusive genes for primary carbon fixation, and it is likely that nocturnal CAM malate stores are shuttled into diurnal C4 decarboxylation pathways, but we found evidence that metabolite cycling may occur at low levels. C4 likely evolved in Portulaca through co-option of redundant genes and integration of the diurnal portion of CAM. Thus, the ancestral CAM system did not strongly constrain C4 evolution because photosynthetic gene networks are not co-regulated for both daytime and nighttime functions.

Autophosphorylation Inhibits RcCDPK1, a Dual-Specificity Kinase that Phosphorylates Bacterial-Type Phosphoenolpyruvate Carboxylase in Castor Oil Seeds.

Phosphoenolpyruvate carboxylase (PEPC) is a tightly regulated enzyme that plays a crucial anaplerotic role in central plant metabolism. Bacterial-type PEPC (BTPC) of developing castor oil seeds (COS) is highly expressed as a catalytic and regulatory subunit of a novel Class-2 PEPC heteromeric complex. Ricinus communis Ca2+-dependent protein kinase-1 (RcCDPK1) catalyzes in vivo inhibitory phosphorylation of COS BTPC at Ser451. Autokinase activity of recombinant RcCDPK1 was detected and 42 autophosphorylated Ser, Thr or Tyr residues were mapped via liquid chromatography-tandem mass spectrometry. Prior autophosphorylation markedly attenuated the ability of RcCDPK1 to transphosphorylate its BTPC substrate at Ser451. However, fully dephosphorylated RcCDPK1 rapidly autophosphorylated during the initial stages of a BTPC transphosphorylation assay. This suggests that Ca2+-dependent binding of dephospho-RcCDPK1 to BTPC may trigger a structural change that leads to rapid autophosphorylation and subsequent substrate transphosphorylation. Tyr30 was identified as an autophosphorylation site via LC-MS/MS and immunoblotting with a phosphosite-specific antibody. Tyr30 occurs at the junction of RcCDPK1's N-terminal variable (NTVD) and catalytic domains and is widely conserved in plant and protist CDPKs. Interestingly, a reduced rate and extent of BTPC transphosphorylation occurred with a RcCDPK1Y30F mutant. Prior research demonstrated that RcCDPK1's NTVD is essential for its Ca2+-dependent autophosphorylation or BTPC transphosphorylation activities but plays no role in target recognition. We propose that Tyr30 autophosphorylation facilitates a Ca2+-dependent interaction between the NTVD and Ca2+-activation domain that primes RcCDPK1 for transphosphorylating BTPC at Ser451. Our results provide insights into links between the post-translational control of COS anaplerosis, Ca2+-dependent signaling and the biological significance of RcCDPK1 autophosphorylation.

Bicarbonate uptake experiment show potential karst carbon sinks transformation into carbon sequestration by terrestrial higher plants

ABSTRACT Karstification forms tremendous karst carbon sinks in the Earth. Whether terrestrial higher plants can absorb and utilize bicarbonate, there is a key testimony that karst carbon sinks can be transformed into carbon sequestrations by terrestrial higher plants. The uptake and use of root-derived bicarbonate, photosynthesis, phosphoenolpyruvate carboxylase and ribulose-1,5-bisphosphate carboxylase contents of Broussonetia papyrifera (Bp) and Morus alba L. (Ma) were measured. This study provides the most direct and primary evidence for the transformation using the bidirectional isotope tracer technique. The transformation may result from the synergism in the absorption and utilization of photosynthetic and nonphotosynthetic pathway, and simultaneously strengthen karst carbon sink and carbon sequestrations of plants, while it had no effect on photosynthetic CO2 assimilation in leaves. Differences in the transformation result in the discrepancies of Bp and Ma in the adaptation to karst environments. Karst-adaptable plants can more regulate the entire carbon cycle.

Lack of leaf carbonic anhydrase activity eliminates the C4 carbon-concentrating mechanism requiring direct diffusion of CO2 into bundle sheath cells.

Carbonic anhydrase (CA) performs the first enzymatic step of C4 photosynthesis by catalysing the reversible hydration of dissolved CO2 that diffuses into mesophyll cells from intercellular airspaces. This CA-catalysed reaction provides the bicarbonate used by phosphoenolpyruvate carboxylase to generate products that flow into the C4 carbon-concentratingmechanism (CCM). It was previously demonstrated that the Zea mays ca1ca2 double mutant lost 97% of leaf CA activity, but there was little difference in the growth phenotype under ambient CO2 partial pressures (pCO2 ). We hypothesise that since CAs are among the fastest enzymes, minimal activity from a third CA, CA8, can provide the inorganic carbon needed to drive C4 photosynthesis. We observed that removing CA8 from the maize ca1ca2 background resulted in plants that had 0.2% of wild-type leaf CA activity. These ca1ca2ca8 plants had reduced photosynthetic parameters and could only survive at elevated pCO2 . Photosynthetic and carbon isotope analysis combined with modelling of photosynthesis and carbon isotope discrimination was used to determine if ca1ca2ca8 plants had a functional C4 cycle or were relying on direct CO2 diffusion to ribulose 1,5-bisphosphate carboxylase/oxygenase within bundle sheath cells. The results suggest that leaf CA activity in ca1ca2ca8 plants was not sufficient to sustain the C4 CCM.

Exogenous trehalose differently improves photosynthetic carbon assimilation capacities in maize and wheat under heat stress

ABSTRACT High temperature inhibits the growth and development of maize (Zea mays L.) and wheat (Triticum aestivum L.) seedlings. The current study attempts to elucidate the underlying mechanisms of exogenous trehalose for the improvement of maize and wheat responses to heat stress. Results show that, in maize seedlings, exogenously-supplied trehalose was able to effectively elevate the capacity of photosynthetic carbon assimilation and improve the carbohydrate content via up-regulating the transcript levels of key enzymes including phosphoenol pyruvate carboxylase (PEPC), NADP-malate dehydrogenase (NADP-MDH), NADP-malic enzyme (NADP-ME), pyruvate phosphate dikinase (PPDK) and Ribulose-1,5-bisphosphate carboxylase/oxygenase small subunit. Besides, it was also able to improve C4 pathway enzyme activities, including PEPC, NADP-MDH, NADP-ME and Ribulose-1,5-bisphosphate carboxylase (RUBPCase). In wheat seedlings, exogenously-supplied trehalose promoted photosynthetic carbon assimilation by elevating the activity of RUBPCase. These results show that exogenous trehalose improved photosynthetic carbon assimilation capacities in maize and wheat seedlings under heat stress through different mechanisms.

Polyphenol from Rosaroxburghii Tratt Fruit Ameliorates the Symptoms of Diabetes by Activating the P13K/AKT Insulin Pathway in db/db Mice.

About 4% of the world’s population has type 2 diabetes mellitus (T2DM), and the available hypoglycemic drugs for treating diabetes have some side effects. Therefore, research on the extraction of hypoglycemic components from plants has gradually become popular. This study aimed to investigate the hypoglycemic effects of polyphenol-rich Rosa roxburghii Tratt extract (RP) isolated from Rosa roxburghii Tratt fruit and of four constituents (IRP 1–4 ) isolated from RP on db/db mice. The results indicated that the oral administration of RP and IRP 1–4 could markedly decrease the food intake, water intake, fasting blood glucose (FBG), and serum insulin levels in the db/db mice. Glucose intolerance, insulin resistance, and oxidative stress were ameliorated in the RP and IRP 1–4 groups. Histopathological observation revealed that RP and IRP 1–4 could effectively protect the liver fat against damage and dysfunction. RP and IRP 1–4 also increased the hepatic and muscle glycogen contents by increasing the phosphorylation and reducing the expression of glycogen synthase kinase 3β (GSK3β). The activities of glucokinase (GCK), phosphoenolpyruvate carboxylase (PEPCK), and glucose-6-phosphatase (G6PC) and their respective mRNA expression levels in the liver of db/db mice were simultaneously increased and decreased in the intervention groups. RP and IRP 1–4 significantly increased the expression of phosphatidylinositol 3-kinase (P13K) and the phosphorylation of protein kinase B (AKT). These results indicate that RP and IRP 1–4 exhibit good hypoglycemic effects by activating the P13K/AKT signaling pathway and regulating the expression of FOXO1 and p-GSK3β proteins, controlling hepatic gluconeogenesis and improving hepatic glycogen storage insulin resistance. Therefore, RP and IRP 1–4 could be utilized as the hypoglycemic functional component to alleviate the symptoms of T2DM.