ZmPEPCK2 enhances nutritional quality and yield potential by synchronizing carbon and nitrogen metabolism in maize kernels.

Based on meteorological data, agro-meteorological observations, and agricultural statistical data in Northeast China (NEC), by using the validated Agricultural Production System sIMulator (APSIM-maize), the potential, attainable, potential farmers' and actual farmers' yields of spring maize during the period 1961 to 2015 were analyzed, and the effects of climate variation on maize potential yield in NEC were quantified. Results indicated that the potential yield of spring maize was 12.2 t·hm-2 during the period 1961 to 2015, with those in northeast being lower than southwest within the study region. The attainable yield of spring maize was 11.3 t·hm-2, and showed a similar spatial distribution with potential yield. Under the current farmers' management practices, mean simulated potential and actual farmers' yields were 6.5 and 4.5 t·hm-2, respectively. Assuming there were no changes in cultivars and management practices in NEC, the mean potential, attainable, and potential farmers' yields of spring maize would decrease by 0.34, 0.25 and 0.10 t·hm-2 per decade in NEC. However, the actual farmers' yields increased with the value of 1.27 t·hm-2 per decade averaged over NEC. Due to climate variation, year-to-year variations of spring maize potential, attainable, and potential farmers' yields were significant, ranging from 10.0 to 14.4, 9.8 to 13.3, 4.4 to 8.5 t·hm-2, respectively.

Maize yield has undergone obvious spatial and temporal changes in recent decades in Northeast China. Understanding how maize potential yield has changed over the past few decades and how large the gaps between potential and actual maize yields are is essential for increasing maize yield to meet increased food demand in Northeast China. In this study, the spatial and temporal dynamics of maize potential yield in Northeast China from 1990 to 2015 were simulated using the Global Agro-ecological Zones (GAEZ) model at the pixel level firstly. Then, the yield gaps between actual and potential yields were analyzed at city scale. The results were the following. (1) The maize potential yield decreased by about 500 kg/ha and the potential production remained at around 260 million tonnes during 1990–2000. From 2000 to 2015, the maize potential yield and production increased by approximately 1000 kg/ha and 80 million tonnes, respectively. (2) The maize potential yield decreased in most regions of Northeast China in the first decade, such as the center area (CA), south area (SA), southwest area (SWA), and small regions in northeast area (NEA), due to lower temperature and insufficient rainfall. The maize potential yield increased elsewhere. (3) The maize potential yield increased by more than 1000 kg/ha in the center area (CA) in the latter 15 years, which may be because of the climate warming and sufficient precipitation. The maize potential yield decreased elsewhere and Harbin in the center area (CA). (4) In 40 cities of Northeast China, the rates of actual yield to potential yield in 17 cities were higher than 80%. The actual yields only attained 50–80% of the potential yields in 20 cities. The gaps between actual and potential yields in Hegang and Dandong were very large, which need to be shrunk urgently. The results highlight the importance of coping with climate change actively, arranging crop structure reasonably, improving farmland use efficiency and ensuring food security in Northeast China.

Pyruvate, PI dikinase (EC 2.7.9.1) was present in crassulacean acid metabolism (CAM) plants that lack phosphoenolpyruvate (PEP) carboxykinase (EC 4.1.1.32) but was not detected in plants that contain PEP carboxykinase or in C3 plants. It is suggested that, during deacidification in CAM plants that contain NAD and NADP malic enzymes (EC 1.1.1.38 and EC 1.1.1.40) but not PEP carboxykinase, pyruvate, P*i dikinase reverses the glycolytic reaction catalysed by pyruvate kinase (EC 2.7.1.40) and converts pyruvate to PEP as the first step in the gluconeogenic conservation of pyruvate as storage carbohydrate. The enzyme is not required by CAM plants that contain PEP carboxykinase and produce mainly PEP during decarboxylation. Leaf slices from Kalanchoe daigremontiana and CAM Mesembryanthemum crystallinum, two species that possess pyruvate, PI dikinase, transfer label from exogenous [3-14C]pyruvate to carbohydrates more rapidly than either Stapelia gigantea, a PEP carboxykinase CAM plant, or C3 Mesembryanthemum crystallinum, which lack the dikinase. Label from [2-14C]- and [3-14C]pyruvate is converted to carbohydrate at the same rate in K. daigremontiana while in S. gigantea label from [2-14C]pyruvate accumulates in carbohydrates twice as rapidly as label from [3-14C]pyruvate. The patterns observed for K. daigremontiana and for CAM M. crystallinum are consistent with the gluconeogenic anabolism of pyruvate whereas the patterns observed for S. gigantea and for C.3 M. crystallinum suggest pyruvate is oxidized possibly via the tricarboxylic acid cycle in these species. Deacidification in Aloe arborescens, a PEP carboxykinase CAM plant that also possesses NAD and NADP malic enzyme activity, was inhibited 80% by 0.1 mM 3-mercaptopicolinic acid (3-MPA), an inhibitor of PEP carboxykinase. It is thus likely that, in this species and probably also in other CAM plants with high PEP carboxykinase activities, a small proportion of the malic acid may be decarboxylated by malic enzymes. However, as 0.5 mM 3-MPA inhibited deacidification in K. daigremontiana by 40%, the inhibitor is probably only specific at low concentrations. 14CO2 fixation in the light by mesophyll cells isolated from K. daigremontiana was stimulated by 20-50% in the presence of 10 mM pyruvate, but there was no increase in 14CO2 fixation by mesophyll cells isolated from S. gigantea.

Phosphoenolpyruvate carboxykinase revisited: Insights into its metabolic role

Phosphoenolpyruvate carboxykinase 1-mediated cataplerosis is required to maintain mitochondrial fitness and to avoid kidney disease progression.

ABSTRACTThis paper addresses the question of whether there has been an increase in yield potential of maize (Zea mays L.) hybrids released in the north‐central United States since the advent of the “Green Revolution” that began in the late 1960s. Because there are few published data about hybrid growth rates and yield‐determining plant traits when grown at yield potential levels, we attempt to address this issue indirectly by evaluation of maize breeding efforts, changes in plant traits of commercial hybrids, and by comparison of statewide average yield trends and yield trends in sanctioned yield contests. On the basis of these sources of information and a definition of yield potential as the yield that can be achieved with an adapted hybrid when grown without obvious stress of any kind, we found that there is conflicting evidence to support the hypothesis that maize yield potential has increased. We recommend experimental approaches to quantify and investigate the determinants of maize yield potential in the north‐central United States and for use in breeding hybrids with greater yield potential.

Lead (Pb(2+)) is one of the most abundant heavy-metal elements in the environment. Pb(2+) pollution has become increasingly serious in maize planting areas, especially in the southwest of China, which even threatens food security. In the present study, a RILpopulation derived from 178 (an inbred line with low accumulation of Pb(2+) in the kernels) and 9782 (a Pb(2+)-hyperaccumulator in the kernels) was used for QTL mapping. A molecular genetic map with the length of 1499.85 cM and an average inter-marker distance of 9.07 cM was constructed with 165 pairs of SSR markers. QTLs controlling Pb(2+) content in maize kernels were then analyzed to provide the basis for breeding elite maize varieties with low Pb(2+)in the kernels. Two QTLs, qPC1 and qPC4, related to Pb(2+) content in maize kernels were identified on chromosome 1 and 4, respectively. qPC1 was located between markers umc1661 and phi002, accounting for 11.13% of phenotypic variance with an additive effect value of 0.062. While qPC4 was located between markers umc1117 and nc005, explaining 5.55% of the phenotypic variance with an additive effect value of -0.044. However, there was no significant correlation observed between Pb(2+) content in the kernels and any of yield-related traits including ear length, ear diameter, kernel row number and weight of per-hundred kernels, indicating that yield-related traits would not be changed in the process of low-Pb(2+)maize breeding. This suggested that the Pb(2+)content in maize kernel under Pb(2+)stress was an independent genetic trait.

There is much evidence that C4-dicarboxylic acids, such as malate and succinate, are the principle energy sources utilized by N2-fixing bacteroids within root nodules. These acids are taken into the bacteroids via a C4-dicarboxylate transport (Dct) system which has been extensively studied in a number of Rhizobium species (Ronson et al. 1981; Finan et al. 1983; Dilworth, Glenn 1984; Vance, Heichel 1991). In addition to the C4-dicarboxylates malate and succinate, the possibility that aspartate may also be supplied to bacteroids is supported by the finding that R. meliloti mutants lacking a particular aspartate aminotransferase are unable to fix N2 (Rastogi, Watson 1991). Following transport of the C4-dicarboxylates into the bacteroids, we believe that they are metabolized via the tricarboxylic acid (TCA) cycle. To our knowledge, all results of enzymatic assays are consistent with the operation of an intact TCA cycle in bacteroids. We are studying the pathway by which the C4-dicarboxylates malate and succinate are metabolized in bacteroids. Without an efficient pathway for the synthesis of acetyl-CoA, the metabolism of these and other C4-dicarboxylates via the TCA cycle would lead to a rapid accumulation of oxaloacetate. We have focused on the role of malic enzymes in the generation of acetyl-CoA. Malic enzyme catalyzes the oxidative decarboxylation of malate to pyruvate and CO2 with the simultaneous reduction of NAD(P) to NAD(P)H. The pyruvate thus formed would then be converted to acetyl- CoA by pyruvate dehydrogenase. An additional pathway for the synthesis of acetyl- CoA from oxaloacetate could be mediated by the combined activities of phosphoenolpyruvate carboxykinase (PCK), pyruvate kinase and pyruvate dehydrogenase. The very low PCK activities detected in bacteroids from alfalfa and pea root nodules, together with the symbiotic phenotypes of Pck- mutants, clearly shows that the PCK pathway is not operative in N2-fixing bacteroids (McKay et al. 1985; Finan et al. 1991). We note however that Pck- mutants of R. meliloti have a reduced N2-fixation phenotype. In addition, Pck− mutants of Rhizobium sp. NGR234 have a pronounced plant-host-dependent symbiotic phenotype. We attribute the latter two results to a requirement for the PCK enzyme during the infection process, for example growth of the bacteria in the infection thread, rather than a role for PCK during N2-fixation in the bacteroid (Finan et al. 1991; Osteras et al, 1991).

Maize (Zea mays L.) yield potential has not undergone genetic improvement during the hybrid era, yet substantial genetic improvement has occurred for tolerance to high plant population densities. As many crops including maize are approaching yield plateaus, it may be necessary to exploit other means of increasing grain yields. In this study, we examine potential reasons for why this occurred. Using a four‐way breeding cross representing the commercial germplasm pool, we demonstrate that the lack of genetic improvement in yield potential is not due to the two attributes being antagonistic. We then demonstrate that the lack of genetic improvement in yield potential is not due to density‐tolerant genotypes being higher yielding at modern conventional plant densities. We show that physiological differences in partitioning dry matter to the grain (i.e., harvest index [HI]) are present in a set of genotypes with contrasting yield potential and density tolerance genotypes. However, a higher or a lower HI is not associated with yield potential either. Finally, we show that the density‐tolerant genotypes exhibit a static kernel set efficiency (KSE), meaning that regardless of the plant growth rate at silking (pGRS), the number of kernels formed per unit dry matter fixed is constant. Surprisingly, the hybrids with high yield potential possess a dynamic KSE and are capable of sustaining kernel set at higher levels when pGRS is low. Given our findings, there is no apparent biological or genetic explanation for genetic improvement in only density tolerance during the hybrid era.

Liver-specific phosphoenolpyruvate carboxykinase (PEPCK) null mice, when fasted, maintain normal whole body glucose kinetics but develop dramatic hepatic steatosis. To identify the abnormalities of hepatic energy generation that lead to steatosis during fasting, we studied metabolic fluxes in livers lacking hepatic cytosolic PEPCK by NMR using 2H and 13C tracers. After a 4-h fast, glucose production from glycogenolysis and conversion of glycerol to glucose remains normal, whereas gluconeogenesis from tricarboxylic acid (TCA) cycle intermediates was nearly absent. Upon an extended 24-h fast, livers that lack PEPCK exhibit both 2-fold lower glucose production and oxygen consumption, compared with the controls, with all glucose production being derived only from glycerol. The mitochondrial reduction-oxidation (red-ox) state, as indicated by the NADH/NAD+ ratio, is 5-fold higher, and hepatic TCA cycle intermediate concentrations are dramatically increased in the PEPCK null livers. Consistent with this, flux through the TCA cycle and pyruvate cycling pathways is 10- and 40-fold lower, respectively. Disruption of hepatic cataplerosis due to loss of PEPCK leads to the accumulation of TCA cycle intermediates and a nearly complete blockage of gluconeogenesis from amino acids and lactate (an energy demanding process) but intact gluconeogenesis from glycerol (which contributes to net NADH production). Inhibition of the TCA cycle and fatty acid oxidation due to increased TCA cycle intermediate concentrations and reduced mitochondrial red-ox state lead to the development of steatosis.

Examination of the effects of dry storage stress on mitochondrial energy synthesis in the scallop Mizuhopecten yessoensis

Twelve major QTL in five optimal clusters and several epistatic QTL are identified for maize kernel size and weight, some with pleiotropic will be promising for fine-mapping and yield improvement. Kernel size and weight are important target traits in maize (Zea mays L.) breeding programs. Here, we report a set of quantitative trait loci (QTL) scattered through the genome and significantly controlled the performance of four kernel traits including length, width, thickness and weight. From the cross V671 (large kernel) × Mc (small kernel), 270 derived F2:3 families were used to identify QTL of maize kernel-size traits and kernel weight in five environments, using composite interval mapping (CIM) for single-environment analysis along with mixed linear model-based CIM for joint analysis. These two mapping strategies identified 55 and 28 QTL, respectively. Among them, 6 of 23 coincident were detected as interacting with environment. Single-environment analysis showed that 8 genetic regions on chromosomes 1, 2, 4, 5 and 9 clustered more than 60 % of the identified QTL. Twelve stable major QTLs accounting for over 10 % of phenotypic variation were included in five optimal clusters on the genetic region of bins 1.02-1.03, 1.04-1.06, 2.05-2.07, 4.07-4.08 and 9.03-9.04; the addition and partial dominance effects of significant QTL play an important role in controlling the development of maize kernel. These putative QTL may have great promising for further fine-mapping with more markers, and genetic improvement of maize kernel size and weight through marker-assisted breeding.

BackgroundThe light environment significantly influences crop growth, development, quality, and yield, particularly in controlled-environment agriculture. Recent advances in artificial lighting technology have allowed growers to precisely control the light environment in terms of duration, spectrum, and intensity. Starch and protein are the most significant nutritional constituents of maize kernels. However, little is known about the effects of the light environment on starch and protein content in maize kernels. Therefore, we investigated the effects of natural light and supplemental exposure to blue (B), far-red (FR), and red (R) light on starch and protein content in kernels of the inbred maize line B73.ResultsExposure to supplemental B, FR, or R light resulted in significant increases in starch content but decreases in protein content. Notably, protein content was lowest under B light. Substantial proportions of genes (5.03–75.23%) and metabolites (46.89–85.64%) were regulated by different wavelengths of light. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses, as well as weighted gene co-expression network analysis (WGCNA), revealed that differentially expressed genes (DEGs) under B, FR, and R light were involved in pathways related to starch and protein synthesis. KEGG metabolomic analysis showed that differentially abundant metabolites (DAMs) were primarily associated with histidine, D-amino acid, cysteine, and methionine metabolism. Nine DEGs related to starch synthesis were identified as potential candidates for investigating the effects of light quality on starch synthesis, and 14 DEGs related to protein synthesis provided evidence for the influence of light quality on protein synthesis in maize.ConclusionsThis study identified the regulatory network governing starch and protein content in B73 maize kernels under different light conditions, contributing to a deeper understanding of how light quality affects the nutritional components of maize kernels.

Carbohydrates and lipids are primary energy sources in mammals; thus, their oxidation and synthesis are carefully controlled. The tricarboxylic acid (TCA) cycle is necessary to oxidize these substrates, and in liver it also supports their synthesis. However, its role in regulating these processes, particularly de novo lipogenesis (DNL) is underappreciated. We report that activation of hepatic gluconeogenesis (GNG) is required to trigger the canonical lipid and carbohydrate response to fasting in mice. Phosphoenolpyruvate carboxykinase (PEPCK) catalyzes cataplerotic flux from the TCA cycle and is required for GNG from lactate, pyruvate and amino acids. Knockdown (KD) or knockout (KO) of PEPCK caused the massive accumulation of TCA cycle intermediates and KO mice developed fatty liver after an overnight fast. Lipidomic profiling of liver suggested increased lipid desaturation and elongation with loss of PEPCK. 2H NMR analysis of liver lipids following 2H2O administration demonstrated elevated fasting DNL in KO mice, which was similar to fed WT mice. In addition, fasting ketogenesis, estimated by infusions of [U-13C]BHB and [3,4-13C]AcAc, was decreased in KO mice. Despite an impaired fasting response, the expression of genes related to control of fat oxidation and DNL were not decreased, suggesting that loss of regulation was mediated by a metabolic mechanism. Inhibition of GNG produced a reduced mitochondrial redox state which limited oxidative pathways and decreased acetyl-CoA concentration. Inhibition of GNG also decreased fasting ATP requirements, resulting in a high energy charge which suppressed activation of AMPK, its canonical suppression of acetyl-CoA carboxylase and caused increased malonyl-CoA during fasting. Hence, PEPCK mediated cataplerosis and GNG during fasting is not only an important source of glucose, it is also necessary to shift cellular redox and energetics to states necessary to suppress lipogenesis and maintain ketogenesis during fasting. Disclosure S. Deja: None. J. Duarte: None. J.A. Fletcher: None. B. Kucejova: None. X. Fu: None. G. Vale: None. J. Young: Board Member; Self; Metalytics. Consultant; Self; Pfizer Inc. J. Browning: None. S.C. Burgess: None. Funding National Institutes of Health (R01DK078184, P41EB015908); Robert A. Welch Foundation (I-1804)

The ability of insulin to suppress gluconeogenesis in type II diabetes mellitus is impaired; however, the cellular mechanisms for this insulin resistance remain poorly understood. To address this question, we generated transgenic (TG) mice overexpressing the phosphoenolpyruvate carboxykinase (PEPCK) gene under control of its own promoter. TG mice had increased basal hepatic glucose production (HGP), but normal levels of plasma free fatty acids (FFAs) and whole-body glucose disposal during a hyperinsulinemic-euglycemic clamp compared with wild-type controls. The steady-state levels of PEPCK and glucose-6-phosphatase mRNAs were elevated in livers of TG mice and were resistant to down-regulation by insulin. Conversely, GLUT2 and glucokinase mRNA levels were appropriately regulated by insulin, suggesting that insulin resistance is selective to gluconeogenic gene expression. Insulin-stimulated phosphorylation of the insulin receptor, insulin receptor substrate (IRS)-1, and associated phosphatidylinositol 3-kinase were normal in TG mice, whereas IRS-2 protein and phosphorylation were down-regulated compared with control mice. These results establish that a modest (2-fold) increase in PEPCK gene expression in vivo is sufficient to increase HGP without affecting FFA concentrations. Furthermore, these results demonstrate that PEPCK overexpression results in a metabolic pattern that increases glucose-6-phosphatase mRNA and results in a selective decrease in IRS-2 protein, decreased phosphatidylinositol 3-kinase activity, and reduced ability of insulin to suppress gluconeogenic gene expression. However, acute suppression of HGP and glycolytic gene expression remained intact, suggesting that FFA and/or IRS-1 signaling, in addition to reduced IRS-2, plays an important role in downstream insulin signal transduction pathways involved in control of gluconeogenesis and progression to type II diabetes mellitus.