This review discusses the organization and regulation of the glycolytic pathway in plants and compares and contrasts plant and nonplant glycolysis. Plant glycolysis exists both in the cytosol and plastid, and the parallel reactions are catalyzed by distinct nuclear-encoded isozymes. Cytosolic glycolysis is a complex network containing alternative enzymatic reactions. Two alternate cytosolic reactions enhance the pathway's ATP yield through the use of pyrophosphate in place of ATP. The cytosolic glycolytic network may provide an essential metabolic flexibility that facilitates plant development and acclimation to environmental stress. The regulation of plant glycolytic flux is assessed, with a focus on the fine control of enzymes involved in the metabolism of fructose-6-phosphate and phosphoenolpyruvate. Plant and nonplant glycolysis are regulated from the "bottom up" and "top down," respectively. Research on tissue- and developmental-specific isozymes of plant glycolytic enzymes is summarized. Potential pitfalls associated with studies of glycolytic enzymes are considered. Some glycolytic enzymes may be multifunctional proteins involved in processes other than carbohydrate metabolism.

The organization and regulation of plant glycolysis

▪ Abstract Since plant phosphoenolpyruvate carboxylase (PEPC) was last reviewed in the Annual Review of Plant Physiology over a decade ago (O'Leary 1982), significant advances have been made in our knowledge of this oligomeric, cytosolic enzyme. This review highlights this exciting progress in plant PEPC research by focusing on the three major areas of recent investigation: the enzymology of the protein; its posttranslational regulation by reversible protein phosphorylation and opposing metabolite effectors; and the structure, expression, and molecular evolution of the nuclear PEPC genes. It is hoped that the next ten years will be equally enlightening, especially with respect to the three-dimensional structure of the plant enzyme, the molecular analysis of its highly regulated protein-Ser/Thr kinase, and the elucidation of its associated signal-transduction pathways in various plant cell types.

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PHOSPHOENOLPYRUVATE CARBOXYLASE: A Ubiquitous, Highly Regulated Enzyme in Plants.

A phylogenetic analysis of Chenopodiaceae and Amaranthaceae was carried out using sequence variation of the chloroplast gene rbcL. Our sampling included 108 species of these two families along with 29 species of Caryophyllales serving as outgroups. Phylogeny inferences with maximum parsimony and maximum likelihood indicate that the two families form a well‐supported monophyletic clade that is sister to Achatocarpaceae. Despite extensive sampling, we found that the relationship between Chenopodiaceae and Amaranthaceae remains unclear as a result of short and weakly supported basal branches. The clearly monophyletic Polycnemoideae (traditionally considered a subfamily of Chenopodiaceae) appear as sister to Amaranthaceae sensu stricto. Within Amaranthaceae, most major lineages inferred except Gomphrenoideae and Celosieae do not correspond to recognized subfamilies and tribes. Bosea and Charpentiera branch first in the Amaranthaceae. Within Chenopodiaceae, the genera of Betoideae occur in basal and largely un...

https://www.jstor.org/stable/pdf/10.1086/378649.pdf

Phylogeny of Amaranthaceae and Chenopodiaceae and the evolution of C4 photosynthesis.

Regulatory phosphorylation of C4 PEP carboxylase

The taxonomic distribution of C4 photosynthesis

Three to four families of nuclear genes encode different isoforms of phosphoenolpyruvate (PEP) carboxylase (PEPC): C4-specific, C3 or etiolated, CAM and root forms. C4 leaf PEPC is encoded by a single gene (ppc) in sorghum and maize, but multiple genes in the C4-dicot Flaveria trinervia. Selective expression of ppc in only C4-mesophyll cells is proposed to be due to nuclear factors, DNA methylation and a distinct gene promoter. Deduced amino acid sequences of C4-PEPC pinpoint the phosphorylatable serine near the N-terminus, C4-specific valine and serine residues near the C-terminus, conserved cysteine, lysine and histidine residues and PEP binding/catalytic sites. During the PEPC reaction, PEP and bicarbonate are first converted into carboxyphosphate and the enolate of pyruvate. Carboxyphosphate decomposes within the active site into Pi and CO2, the latter combining with the enolate to form oxalacetate. Besides carboxylation, PEPC catalyzes a HCO3--dependent hydrolysis of PEP to yield pyruvate and Pi. Post-translational regulation of PEPC occurs by a phosphorylation/dephosphorylation cascade in vivo and by reversible enzyme oligomerization in vitro. The interrelation between phosphorylation and oligomerization of the enzyme is not clear. PEPC-protein kinase (PEPC-PK), the enzyme responsible for phosphorylation of PEPC, has been studied extensively while only limited information is available on the protein phosphatase 2A capable of dephosphorylating PEPC. The C4ppc was cloned and expressed in Escherichia coli as well as tobacco. The transformed E. coli produced a functional/phosphorylatable C4 PEPC and the transgenic tobacco plants expressed both C3 and C4 isoforms. Site-directed mutagenesis of ppc indicates the importance of His138, His579 and Arg587 in catalysis and/or substrate-binding by the E. coli enzyme, Ser8 in the regulation of sorghum PEPC. Important areas for further research on C4 PEPC are: mechanism of transduction of light signal during photoactivation of PEPC-PK and PEPC in leaves, extensive use of site-directed mutagenesis to precisely identify other key amino acid residues, changes in quarternary structure of PEPC in vivo, a high-resolution crystal structure, and hormonal regulation of PEPC expression.

Molecular biology of C4 phosphoenolpyruvate carboxylase: Structure, regulation and genetic engineering.

The rate and extent of light activation of PEPC may be used as another criterion to distinguish C3 and C4 plants. Light stimulated phosphoenolypyruvate carboxylase (PEPC) in leaf discs of C4 plants, the activity being three times greater than that in the dark but stimulation of PEPC was limited about 30% over the dark-control in C3 species. The light activation of PEPC in leaves of C3 plants was complete within 10 min, while maximum activation in C4 plants required illumination for more than 20 min, indicating that the relative pace of PEPC activation was slower in C4 plants than in C3 plants. Similarly, the dark-deactivation of the enzyme was also slower in leaves of C4 than in C3 species. The extent of PEPC stimulation in the alkaline pH range indicated that the dark-adapted form of the C4 enzyme is very sensitive to changes in pH. The pH of cytosol-enriched cell sap extracted from illuminated leaves of C4 plants was more alkaline than that of dark-adapted leaves. The extent of such light-dependent alkalization of cell sap was three times higher in C4 leaves than in C3 plants. The course of light-induced alkalization and dark-acidification of cytosol-enriched cell sap was markedly similar to the pattern of light activation and dark-deactivation of PEPC in Alternanthera pungens, a C4 plant. Our report provides preliminary evidence that the photoactivation of PEPC in C4 plants may be mediated at least partially by the modulation of cytosolic pH.

Patterns of phosphoenolpyruvate carboxylase activity and cytosolic pH during light activation and dark deactivation in C3 and C4 plants

Glycolate oxidase (GO; EC 1131) was purified from the leaves of three plant species:Amaranthus hypochondriacus L(NAD-ME type C4 dicot),Pisum sativum L (C3 species) andParthenium hysterophorus L (C3–C4 intermediate) A flavin moiety was present in the enzyme from all the three species The enzyme from the C4 plant had a low specific activity, exhibited lower KM for glycolate, and required a lower pH for maximal activity, compared to the C3 enzyme The enzyme from the C4 species oxidized glyoxylate at <10% of the rate with glycolate, while the GO from the C3 plant oxidized glyoxylate at a rate of about 35 to 40% of that with glycolate The sensitivity of GO from C4 plant to α-hydroxypyridinemethane sulfonate, 2-hydroxy-3-butynoate and other inhibitors was less than that of the enzyme from C3 source The properties of GO fromParthenium hysterophorus, were similar to those of the enzyme fromPisum sativum The characteristics of glycolate oxidase from leaves of a C4 plant,Amaranthus hypochondriacus are different from those of the C3 species or the C3–C4 intermediate

Purification and properties of glycolate oxidase from plants with different photosynthetic pathways: Distinctness of C 4 enzyme from that of a C 3 species and a C 3 –C 4 intermediate

The maximum catalytic activities of several photorespiratory and photosynthetic enzymes were determined in leaf extracts of three C 3 -C 4 intermediates (Alternanthera ficoides, A. tenella and Parthenium hysterophorus) and were compared to those of C 3 (A. sessiles, Pisum sativum) and C 4 (A. pungens, Zea mays and Amaranthus hypochondriacus) species. The activity levels of key photorespiratory enzymes, glycolate oxidase, catalase, NADH-hydroxypyruvate reductase and glycerate kinase were less (28 to 35% reduced) in intermediates than those of typical C 3 species. Similarly, the activities of photorespiratory aminotransferases in the C 3 -C 4 intermediates were also partially reduced (23 to 37% reduction). The activities of phosphoenolpyruvate carboxylase (PEPC), pyruvate, orthophosphate dikinase and NAD-malic enzyme were higher (2 to 7 times) in leaf extracts of the intermediates than those of C 3 species. But the ratios of PEPC/rubisco in the C 3 -C 4 intermediates were more like C 3 than C 4 species. We draw attention to the partial reduction in enzyme activity of photorespiratory metabolism, which could be an important factor for restriction of photorespiration in the C 3 -C 4 intermediate species, in addition to enzyme compartmentation and/or operation of a 'C 4 -like' cycle

M. Tirumala Devi

Papers

Molecular biology of C4 phosphoenolpyruvate carboxylase: Structure, regulation and genetic engineering.

Patterns of phosphoenolpyruvate carboxylase activity and cytosolic pH during light activation and dark deactivation in C3 and C4 plants

Purification and properties of glycolate oxidase from plants with different photosynthetic pathways: Distinctness of C 4 enzyme from that of a C 3 species and a C 3 –C 4 intermediate

Partial reduction in activities of photorespiratory enzymes in C3-C4 intermediates of Alternanthera and Parthenium

Light Activation of Phosphoenolpyruvate Carboxylase in Maize Mesophyll Protoplasts