Metabolic engineering of the serine/glycine network as a means to improve the nitrogen content of crops.

In plants, L-serine (Ser) biosynthesis occurs through various pathways and is highly dependent on the atmospheric CO concentration, especially in C species, due to the association of the Glycolate Pathway of Ser Biosynthesis (GPSB) with photorespiration. Characterization of a second plant Ser pathway, the Phosphorylated Pathway of Ser Biosynthesis (PPSB), revealed that it is at the crossroads of carbon, nitrogen, and sulphur metabolism. The PPSB comprises three sequential reactions catalysed by 3-phosphoglycerate dehydrogenase (PGDH), 3-phosphoSer aminotransferase (PSAT) and 3-phosphoSer phosphatase (PSP).

The serine-glycine-one-carbon metabolic network orchestrates changes in nitrogen and sulfur metabolism and shapes plant development.

L-serine (Ser) and L-glycine (Gly) are critically important for the overall functioning of primary metabolism. We investigated the interaction of the phosphorylated pathway of Ser biosynthesis (PPSB) with the photorespiration-associated glycolate pathway of Ser biosynthesis (GPSB) using Arabidopsis thaliana PPSB-deficient lines, GPSB-deficient mutants, and crosses of PPSB with GPSB mutants. PPSB-deficient lines mainly showed retarded primary root growth.

The phosphorylated pathway of serine biosynthesis links plant growth with nitrogen metabolism.

Because it is the precursor for various essential cellular components, the amino acid serine is indispensable for every living organism. In plants, serine is synthesized by two major pathways: photorespiration and the phosphorylated pathway of serine biosynthesis (PPSB). However, the importance of these pathways in providing serine for plant development is not fully understood.

Phosphoglycerate dehydrogenase genes differentially affect Arabidopsis metabolism and development.

Unlike animals, plants possess diverse L-serine (Ser) biosynthetic pathways. One of them, the Phosphorylated Pathway of Serine Biosynthesis (PPSB) has been recently described as essential for embryo, pollen and root development, and required for ammonium and sulfur assimilation. The first and rate limiting step of PPSB is the reaction catalyzed by the enzyme phosphoglycerate dehydrogenase (PGDH).

PGDH family genes differentially affect Arabidopsis tolerance to salt stress.

The first step in the Phosphorylated Pathway of serine (Ser) Biosynthesis (PPSB) is catalyzed by the enzyme Phosphoglycerate Dehydrogenase (PGDH), coded in Arabidopsis thaliana by three genes. Gene expression analysis indicated that PGDH1 and PGDH2 were induced, while PGDH3 was repressed, by salt-stress. Accordingly, PGDH3 overexpressing plants (Oex PGDH3) were more sensitive to salinity than wild type plants (WT), while plants overexpressing PGDH1 (Oex PGDH1) performed better than WT under salinity conditions.

Deficiency in the Phosphorylated Pathway of Serine Biosynthesis Perturbs Sulfur Assimilation.

Although the plant Phosphorylated Pathway of l-Ser Biosynthesis (PPSB) is essential for embryo and pollen development, and for root growth, its metabolic implications have not been fully investigated. A transcriptomics analysis of Arabidopsis () PPSB-deficient mutants at night, when PPSB activity is thought to be more important, suggested interaction with the sulfate assimilation process. Because sulfate assimilation occurs mainly in the light, we also investigated it in PPSB-deficient lines in the day.

BvCOLD1: A novel aquaporin from sugar beet (Beta vulgaris L.) involved in boron homeostasis and abiotic stress.

Beta vulgaris (sugar beet) is one of the most important industrial crops. Screening of a cDNA library for sugar beet genes able to confer cold tolerance upon overexpression in yeast identified a novel aquaporin, which we named BvCOLD1. The amino acid sequence of BvCOLD1 indicated that an acidic protein (pI 5.

Phosphoglycerate Kinases Are Co-Regulated to Adjust Metabolism and to Optimize Growth.

In plants, phosphoglycerate kinase (PGK) converts 1,3-bisphosphoglycerate into 3-phosphoglycerate in glycolysis but also participates in the reverse reaction in gluconeogenesis and the Calvin-Benson cycle. In the databases, we found three genes that encode putative PGKs. Arabidopsis () PGK1 was localized exclusively in the chloroplasts of photosynthetic tissues, while PGK2 was expressed in the chloroplast/plastid of photosynthetic and nonphotosynthetic cells.

Studying the Function of the Phosphorylated Pathway of Serine Biosynthesis in Arabidopsis thaliana.

Photorespiration is an essential pathway in photosynthetic organisms and is particularly important to detoxify and recycle 2-phosphoglycolate (2-PG), a by-product of oxygenic photosynthesis. The enzymes that catalyze the reactions in the photorespiratory core cycle and closely associated pathways have been identified; however, open questions remain concerning the metabolic network in which photorespiration is embedded. The amino acid serine represents one of the major intermediates in the photorespiratory pathway and photorespiration is thought to be the major source of serine in plants.

Overexpression of the triose phosphate translocator (TPT) complements the abnormal metabolism and development of plastidial glycolytic glyceraldehyde-3-phosphate dehydrogenase mutants.

The presence of two glycolytic pathways working in parallel in plastids and cytosol has complicated the understanding of this essential process in plant cells, especially the integration of the plastidial pathway into the metabolism of heterotrophic and autotrophic organs. It is assumed that this integration is achieved by transport systems, which exchange glycolytic intermediates across plastidial membranes. However, it is unknown whether plastidial and cytosolic pools of 3-phosphoglycerate (3-PGA) can equilibrate in non-photosynthetic tissues.

The specific role of plastidial glycolysis in photosynthetic and heterotrophic cells under scrutiny through the study of glyceraldehyde-3-phosphate dehydrogenase.

The cellular compartmentalization of metabolic processes is an important feature in plants where the same pathways could be simultaneously active in different compartments. Plant glycolysis occurs in the cytosol and plastids of green and non-green cells in which the requirements of energy and precursors may be completely different. Because of this, the relevance of plastidial glycolysis could be very different depending on the cell type.

Plastidial Glycolytic Glyceraldehyde-3-Phosphate Dehydrogenase Is an Important Determinant in the Carbon and Nitrogen Metabolism of Heterotrophic Cells in Arabidopsis.

This study functionally characterizes the Arabidopsis (Arabidopsis thaliana) plastidial glycolytic isoforms of glyceraldehyde-3-phosphate dehydrogenase (GAPCp) in photosynthetic and heterotrophic cells. We expressed the enzyme in gapcp double mutants (gapcp1gapcp2) under the control of photosynthetic (Rubisco small subunit RBCS2B [RBCS]) or heterotrophic (phosphate transporter PHT1.2 [PHT]) cell-specific promoters.

Serine in plants: biosynthesis, metabolism, and functions.

Serine (Ser) has a fundamental role in metabolism and signaling in living organisms. In plants, the existence of different pathways of Ser biosynthesis has complicated our understanding of this amino acid homeostasis. The photorespiratory glycolate pathway has been considered to be of major importance, whereas the nonphotorespiratory phosphorylated pathway has been relatively neglected.

Identification of the phosphoglycerate dehydrogenase isoform EDA9 as the essential gene for embryo and male gametophyte development in Arabidopsis.

Three different pathways of serine (Ser) biosynthesis have been described in plants: the Glycolate pathway, which is part of the Photorespiratory pathway, and 2 non-Photorespiratory pathways, the Glycerate and the Phosphorylated pathways. The Phosphorylated Pathway of Ser Biosynthesis (PPSB) has been known to exist since the 1950s, but its biological relevance was not revealed until quite recently when the last enzyme of the pathway, the Phosphoserine Phosphatase, was functionally characterized. In the associated study (1), we characterized a family of genes coding for putatite phosphoglycerate dehydrogenases (PGDH, 3-PGDH, and EDA9), the first enzyme of the PPSB.

The essential role of the phosphorylated pathway of serine biosynthesis in Arabidopsis.

In plants, 3 different pathways of serine biosynthesis have been described: the Glycolate pathway, which is associated with photorespiration, and 2 non-photorespiratory pathways, the Glycerate and the Phosphorylated pathways. The Phosphorylated Pathway of Serine Biosynthesis (PPSB) has been known since the 1950s, but has been studied relatively little, probably because it was considered of minor significance as compared with the Glycolate pathway. In the associated study (1), we described for the first time in plants the in vivo functional characterization of the PPSB, by targeting the phosphoserine phosphatase (PSP1), the last enzyme of the pathway.

Functional characterization of the plastidial 3-phosphoglycerate dehydrogenase family in Arabidopsis.

This work contributes to unraveling the role of the phosphorylated pathway of serine (Ser) biosynthesis in Arabidopsis (Arabidopsis thaliana) by functionally characterizing genes coding for the first enzyme of this pathway, 3-phosphoglycerate dehydrogenase (PGDH). We identified two Arabidopsis plastid-localized PGDH genes (3-PGDH and EMBRYO SAC DEVELOPMENT ARREST9 [EDA9]) with a high percentage of amino acid identity with a previously identified PGDH. All three genes displayed a different expression pattern indicating that they are not functionally redundant.

The phosphorylated pathway of serine biosynthesis is essential both for male gametophyte and embryo development and for root growth in Arabidopsis.

This study characterizes the phosphorylated pathway of Ser biosynthesis (PPSB) in Arabidopsis thaliana by targeting phosphoserine phosphatase (PSP1), the last enzyme of the pathway. Lack of PSP1 activity delayed embryo development, leading to aborted embryos that could be classified as early curled cotyledons. The embryo-lethal phenotype of psp1 mutants could be complemented with PSP1 cDNA under the control of Pro35S (Pro35S:PSP1).

Interactions between abscisic acid and plastidial glycolysis in Arabidopsis.

The phytohormone abscisic acid (ABA) controls the development of plants and plays a crucial role in their response to adverse environmental conditions like salt and water stress. Complex interactions between ABA and sugar signal transduction pathways have been shown. However, the role played by glycolysis in these interactions is not known.

Arabidopsis plants deficient in plastidial glyceraldehyde-3-phosphate dehydrogenase show alterations in abscisic acid (ABA) signal transduction: interaction between ABA and primary metabolism.

Abscisic acid (ABA) controls plant development and regulates plant responses to environmental stresses. A role for ABA in sugar regulation of plant development has also been well documented although the molecular mechanisms connecting the hormone with sugar signal transduction pathways are not well understood. In this work it is shown that Arabidopsis thaliana mutants deficient in plastidial glycolytic glyceraldehyde-3-phosphate dehydrogenase (gapcp1gapcp2) are ABA insensitive in growth, stomatal closure, and germination assays.

A critical role of plastidial glycolytic glyceraldehyde-3-phosphate dehydrogenase in the control of plant metabolism and development.

Glycolysis is a central metabolic pathway that provides energy and generates precursors for the synthesis of primary metabolites such as amino acids and fatty acids. In plants, glycolysis occurs in the cytosol and plastids, which complicates the understanding of this essential process. As a result, the contribution of each glycolytic pathway to the specific primary metabolite production and the degree of integration of both pathways is still unresolved.

The plastidial glyceraldehyde-3-phosphate dehydrogenase is critical for viable pollen development in Arabidopsis.

Plant metabolism is highly coordinated with development. However, an understanding of the whole picture of metabolism and its interactions with plant development is scarce. In this work, we show that the deficiency in the plastidial glycolytic glyceraldehyde-3-phosphate dehydrogenase (GAPCp) leads to male sterility in Arabidopsis (Arabidopsis thaliana).

Plastidial glyceraldehyde-3-phosphate dehydrogenase deficiency leads to altered root development and affects the sugar and amino acid balance in Arabidopsis.

Glycolysis is a central metabolic pathway that, in plants, occurs in both the cytosol and the plastids. The glycolytic glyceraldehyde-3-phosphate dehydrogenase (GAPDH) catalyzes the conversion of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate with concomitant reduction of NAD(+) to NADH. Both cytosolic (GAPCs) and plastidial (GAPCps) GAPDH activities have been described.

Expression of spearmint limonene synthase in transgenic spike lavender results in an altered monoterpene composition in developing leaves.

We generated transgenic spike lavender (Lavandula latifolia) plants constitutively expressing the limonene synthase (LS) gene from spearmint (Mentha spicata), encoding the LS enzyme that catalyzes the synthesis of limonene from geranyl diphosphate. Overexpression of the LS transgene did not consistently affect monoterpene profile in pooled leaves or flowers from transgenic T(0) plants. Analyses from cohorts of leaves sampled at different developmental stages showed that essential oil accumulation in transgenic and control plants was higher in developing than in mature leaves.

Up-regulation of an N-terminal truncated 3-hydroxy-3-methylglutaryl CoA reductase enhances production of essential oils and sterols in transgenic Lavandula latifolia.

Spike lavender (Lavandula latifolia) essential oil is widely used in the perfume, cosmetic, flavouring and pharmaceutical industries. Thus, modifications of yield and composition of this essential oil by genetic engineering should have important scientific and commercial applications. We generated transgenic spike lavender plants expressing the Arabidopsis thaliana HMG1 cDNA, encoding the catalytic domain of 3-hydroxy-3-methylglutaryl CoA reductase (HMGR1S), a key enzyme of the mevalonic acid (MVA) pathway.

Up-regulation of 1-deoxy-D-xylulose-5-phosphate synthase enhances production of essential oils in transgenic spike lavender.

Spike lavender (Lavandula latifolia) is an aromatic shrub cultivated worldwide for the production of essential oils. The major constituents of these oils are monoterpenes, which are obtained from isopentenyl diphosphate and dimethylallyl diphosphate precursors through the plastidial methylerythritol phosphate (MEP) pathway and/or the cytosolic mevalonate pathway. 1-Deoxy-D-xylulose-5-P synthase (DXS) catalyzes the first step of the MEP pathway.