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Tomato (Solanum lycopersicum) is one of the highest-value vegetable crops worldwide. Understanding the genetic regulation of primary metabolite levels can inform efforts aimed toward improving the nutrition of commercial tomato cultivars, while maintaining key traits such as yield and stress tolerance. We identified 388 suggestive association loci (including 126 significant loci) for 92 metabolic traits including nutrition and flavor-related loci by genome-wide association study from 302 accessions in two different environments. Among them, an ascorbate quantitative trait locus TFA9 (OMATO RUIT SCORBATEON CHROMOSOME ) co-localized with SlbHLH59, which promotes high ascorbate accumulation by directly binding to the promoter of structural genes involved in the D-mannose/L-galactose pathway. The causal mutation of TFA9 is an 8-bp InDel, named InDel_8, located in the promoter region of SlbHLH59 and spanned a 5’UTR Py-rich stretch motif affecting its expression. Phylogenetic analysis revealed that differentially expressed SlbHLH59 alleles were selected during tomato domestication. Our results provide a dramatic illustration of how ascorbate biosynthesis can be regulated and was selected during the domestication of tomato. Furthermore, the findings provide novel genetic insights into natural variation of metabolites in tomato fruit, and will promote efficient utilization of metabolite traits in tomato improvement. [ABSTRACT FROM AUTHOR]

Summary: Fenugreek microgreen and mint leaf displayed antidiabetic potential during in vitro assays including cell line‐based analysis. Aqueous fenugreek microgreen extract (FME) (2 mg mL−1) inhibited α‐amylase by 70%. It also enhanced glucose uptake in L6 cells by 25% at 10 mg mL−1 which further improved to 44% in the presence of insulin. On the other hand, fresh mint leaf extract (MLE) inhibited α‐glucosidase up to 90% and increased glucose uptake by 15% in HepG2 cells. Besides, both these extracts also inhibited nonenzymatic glycation of protein. FME and MLE were also found to have high levels of total phenolics, flavonoids and antioxidants which could play a possible role in the observed antidiabetic activity. As blood glucose levels in diabetes can be regulated by inhibition of enzymes regulating carbohydrate metabolism and improving glucose uptake in cells, the findings indicate a complimentary therapeutic role of these two dietary herbs in diabetes. [ABSTRACT FROM AUTHOR]

Rubisco activase (RCA) is essential for the activation of Rubisco, the carboxylating enzyme of photosynthesis. In Arabidopsis, RCA is composed of a large RCAα and small RCAβ isoform that are formed by alternative splicing of a single gene (At2g39730). The activity of Rubisco is controlled in response to changes in irradiance by regulation of RCA activity, which is known to involve a redox-sensitive disulfide bond located in the carboxy-terminal extension of the RCAα subunit. Additionally, phosphorylation of RCA threonine-78 (Thr-78) has been reported to occur in the dark suggesting that phosphorylation may also be associated with dark-inactivation of RCA and deactivation of Rubisco. In the present study, we developed site-specific antibodies to monitor phosphorylation of RCA at the Thr-78 site and used non-reducing SDS-PAGE to monitor the redox status of the RCAα subunit. By immunoblotting, phosphorylation of both RCA isoforms occurred at low light and in the dark and feeding peroxide or DTT to leaf segments indicated that redox status of the chloroplast stroma was a critical factor controlling RCA phosphorylation. Use of a knockout mutant identified the plastid-targeted casein kinase 2 (cpCK2α) as the major protein kinase involved in RCA phosphorylation. Studies with recombinant cpCK2α and synthetic peptide substrates identified acidic residues at the -1, +2, and +3 positions surrounding Thr-78 as strong positive recognition elements. The cpck2 knockout mutant had strongly reduced phosphorylation at the Thr-78 site but was similar to wild type plants in terms of induction kinetics of photosynthesis following transfer from darkness or low light to high light, suggesting that if phosphorylation of RCA Thr-78 plays a direct role it would be redundant to redox regulation for control of Rubisco activation state under normal conditions. [ABSTRACT FROM AUTHOR]

NADPH is a key reductant carrier that maintains internal redox and antioxidant status, and that links biosynthetic, catabolic and signalling pathways. Plants have a mitochondrial external NADPH oxidation pathway, which depends on Ca2+ and pH in vitro, but concentrations of Ca2+ needed are not known. We have determined the K0.5(Ca2+) of the external NADPH dehydrogenase from Solanum tuberosum mitochondria and membranes of E. coli expressing Arabidopsis thaliana NDB1 over the physiological pH range using O2 and decylubiquinone as electron acceptors. The K0.5(Ca2+) of NADPH oxidation was generally higher than for NADH oxidation, and unlike the latter, it depended on pH. At pH 7.5, K0.5(Ca2+) for NADPH oxidation was high (≈100 μM), yet 20-fold lower K0.5(Ca2+) values were determined at pH 6.8. Lower K0.5(Ca2+) values were observed with decylubiquinone than with O2 as terminal electron acceptor. NADPH oxidation responded to changes in Ca2+ concentrations more rapidly than NADH oxidation did. Thus, cytosolic acidification is an important activator of external NADPH oxidation, by decreasing the Ca2+-requirements for NDB1. The results are discussed in relation to the present knowledge on how whole cell NADPH redox homeostasis is affected in plants modified for the NDB1 gene. [ABSTRACT FROM AUTHOR]

The plant cell wall (PCW) represents the most abundant renewable biomass resource for lignocellulosic ethanol production. Economical and efficient degradation of PCW to fermentable sugars is an essential subprocess during lignocellulosic ethanol production. At present, the recalcitrance of PCW to various pretreatments and enzymatic hydrolysis makes the PCW degradation unacceptably expensive. Engineering cell wall-degrading enzymes into growing plants provides a promising solution to lower the PCW degradation cost and increase its degradation efficiency for lignocellulosic ethanol production. Avoiding damage by the expressed biomass-degrading enzymes to growing plants is the key to successful use of this method. Two modern biological technologies can be used to solve this problem. One is to engineer a thermoregulated intein-modified cell wall-degrading enzyme into growing plants. The other is to use the genetimed expression technique. This editorial will give a brief discussion of opportunities and challenges of engineering cell wall-degrading enzymes into growing plants for improvement of lignocellulosic ethanol production. [ABSTRACT FROM AUTHOR]

The RubisCO enzyme activity was studied in wheat cultivars exposed to salinity. Four Cuban varieties of wheat species T. aestivum and T. durum were selected and mounted two experimental variants in hydroponic conditions. He saline the first treatment with NaCl to a conductivity of 8 dS.m-1 in the nutrient solution, while in the control treatment (no applied NaCl for all cases) the pH of the solution was adjusted to 6.0. Treatments were applied from the time of planting to 35 days after seed germination when the determinations were made. As a result a significant decrease in RubisCO enzyme activity was obtained in all varieties in saline, where there were highly significant differences compared to the control treatment. Affectations than 10 % due to salinity were found. Wheat varieties of the species T. durum always occurred in the control treatment increased enzyme activity of RubisCO but the intensity of stress was higher in this species so it showed increased sensitivity to salinity compared to T. aestivum. [ABSTRACT FROM AUTHOR]

The article focuses on a study regarding the need of metabolic requirements for photo respiratory enzyme activities in heterotrophic tissues. Topics discussed are the role of photorespiration in avoiding the accumulation of 2-phosphoglycolate (2PG), analysis of expression of genes encoding photo respiratory enzymes and the presence of high transcripts levels of glycolate oxidase, alanine:glyoxylate aminotransferase 2 and glyoxylate reductase 1 in tissues.

Background: The mountain pine beetle (MPB, Dendroctonus ponderosae) epidemic has affected lodgepole pine (Pinus contorta) across an area of more than 18 million hectares of pine forests in western Canada, and is a threat to the boreal jack pine (Pinus banksiana) forest. Defence of pines against MPB and associated fungal pathogens, as well as other pests, involves oleoresin monoterpenes, which are biosynthesized by families of terpene synthases (TPSs). Volatile monoterpenes also serve as host recognition cues for MPB and as precursors for MPB pheromones. The genes responsible for terpene biosynthesis in jack pine and lodgepole pine were previously unknown. Results: We report the generation and quality assessment of assembled transcriptome resources for lodgepole pine and jack pine using Sanger, Roche 454, and Illumina sequencing technologies. Assemblies revealed transcripts for approximately 20,000 - 30,000 genes from each species and assembly analyses led to the identification of candidate full-length prenyl transferase, TPS, and P450 genes of oleoresin biosynthesis. We cloned and functionally characterized, via expression of recombinant proteins in E. coli, nine different jack pine and eight different lodgepole pine mono-TPSs. The newly identified lodgepole pine and jack pine mono-TPSs include (+)-α-pinene synthases, (-)-α-pinene synthases, (-)-β-pinene synthases, (+)-3-carene synthases, and (-)-β-phellandrene synthases from each of the two species. Conclusion: In the absence of genome sequences, transcriptome assemblies are important for defence gene discovery in lodgepole pine and jack pine, as demonstrated here for the terpenoid pathway genes. The product profiles of the functionally annotated mono-TPSs described here can account for the major monoterpene metabolites identified in lodgepole pine and jack pine. [ABSTRACT FROM AUTHOR]

A new hypothesis is proposed to explain the metabolic regulation of intracellular pH (especially of the cytoplasm) in plants and replace the classic biochemical pH-stat [Davies (1973) Symp. Soc. Exp. Biol. 27: 513]. Alternative route glycolysis [Plaxton (1996) Annu. Rev. Plant Physiol. Plant Mol. Biol. 47: 185], alternative pathway respiration [Day et al. (1996) Plant Physiol. 110: 1], and malate-de-rived lactic and alcoholic fermentation (alternative pathway fermentation), all unique to plants, are organized into a novel mechanism that functions in toto as biochemical pH-stat. Its uniqueness to plants is examined from the evolutionary viewpoint that plants adopted the proton as the ion with which to create the electrochemical potential difference across the plasma membrane to energize uphill transports (“proton system”). The biochemical pH-stat is assumed to have evolved as a security mechanism for the “proton system” so that it could cope with the potential acidification of the cytoplasm under environmental stress. [ABSTRACT FROM AUTHOR]

In a recent paper (Ohana et al. 1998), we described the purification and structural characterization of a novel glycosidic triterpenoid saponin (GTS), a specific inhibitor of diguanylate cyclase (dgc), the key regulatory enzyme of the cellulose synthesizing apparatus of the bacterium Acetobacter xylinum. This compound and an identical or very similar one were isolated from pea (Pisum sativum), and A. xylinum respectively. We now present the effects of GTS on the kinetic properties of dgc. The observed inhibition is non-competitive with respect to the substrate GTP, is decreased by 50% in the presence of 20 μM c-di-GMP, and is not observed in the presence of various detergents. Photo-affinity labeling studies using [32P]c-di-GMP and purified enzyme showed that the inhibitor affects binding of c-di-GMP to dgc. It was ascertained that GTS, or at least a very similar compound, is present in other plant systems. The antibiotic Papulacandin B also inhibits dgc, although less efficiently than GTS (Ki = 70 μM vs. 5 μM). In in situ assays, highly purified GTS inhibits bacterial cellulose synthesis and dgc activity. Similary, digitonin permeabilized tobacco cell cultures display inhibition of glucan synthesis in the presence of GTS. [ABSTRACT FROM AUTHOR]