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At least 343 records · Page 19Linked to original sources
PubMed1993

Differential expression of tomato (Lycopersicon esculentum L.) genes encoding shikimate pathway isoenzymes. II. Chorismate synthase.

In tomato (Lycopersicon esculentum L. cv. UC82b) two distinct genes (designated LeCS1 and LeCS2) code for chorismate synthase. The corresponding cDNAs have been isolated and characterized. The deduced amino acid sequences are 88% identical. Both genes encode chorismate synthases with putative plastid-specific N-terminal transit peptides. The two genes are predominantly expressed in flowers and roots and, to a lesser extent, in stems, leaves, and cotyledons, but the steady-state levels of LeCS1-specific transcripts are consistently higher than those of the LeCS2-specific transcripts.

Amino Acid Sequence↗
PubMed2003

(De)regulation of key enzyme steps in the shikimate pathway and phenylalanine-specific pathway of the actinomycete Amycolatopsis methanolica.

Prephenate dehydratase (PDT), chorismate mutase (CM) and 3-deoxy-D-arabino-7-heptulosonate 7-phosphate (DAHP) synthase are key regulatory enzymes in aromatic amino acid biosynthesis in the actinomycete Amycolatopsis methanolica. Deregulated, feedback-control-resistant mutants were isolated by incubation of A. methanolica on glucose mineral agar containing the toxic analogue p-fluoro-DL-phenylalanine (pFPhe). Several of these mutants had completely lost PDT sensitivity to Phe inhibition and Tyr activation. Mutant characterization yielded new information about PDT amino acid residues involved in Phe and Tyr effector binding sites. A. methanolica wild-type cells grown on glucose mineral medium normally possess a bifunctional CM/DAHP synthase protein complex (with DS1, a plant-type DAHP synthase). The CM activity of this protein complex is feedback-inhibited by Tyr and Phe, while DS1 activity is mainly inhibited by Trp. Isolation of pFPhe-resistant mutants yielded two feedback-inhibition-resistant CM mutants. These were characterized as regulatory mutants, derepressed in (a) synthesis of CM, now occurring as an abundant, feedback-inhibition-resistant, separate protein, and (b) synthesis of an alternative DAHP synthase (DS2, an E. coli-type DAHP synthase), only inhibited by Tyr and Trp. DS1 and DS2 thus are well integrated in A. methanolica primary metabolism: DS1 and CM form a protein complex, which stimulates CM activity and renders it sensitive to feedback inhibition by Phe and Tyr. Synthesis of CM and DS2 proteins appears to be controlled co-ordinately, sensitive to Phe-mediated feedback repression.

3-Deoxy-7-Phosphoheptulonate Synthase↗
PubMed1992

Purification and characterization of a dual function 3-dehydroquinate dehydratase from Amycolatopsis methanolica.

Studies on hydroaromatic metabolism in the actinomycete Amycolatopsis methanolica revealed that the organism grows rapidly on quinate (but not on shikimate) as sole carbon- and energy source. Quinate is initially converted into the shikimate pathway intermediate 3-dehydroquinate by an inducible NAD(+)-dependent quinate/shikimate dehydrogenase. 3-Dehydroquinate dehydratase subsequently converts 3-dehydroquinate into 3-dehydroshikimate, which is used partly for the biosynthesis of aromatic amino acids, and is partly catabolized via protocatechuate and the beta-ketoadipate pathway. Enzyme studies and analysis of mutants clearly showed that the single 3-dehydroquinate dehydratase present in A. methanolica has a dual function, the first example of a 3-dehydroquinate dehydratase enzyme involved in both the catabolism of quinate and the biosynthesis of aromatic amino acids. This enzyme was purified over 1700-fold to homogeneity. Its further characterization indicated that it is a Type II 3-dehydroquinate dehydratase, a thermostable enzyme with a large oligomeric structure (native M(r) 135 x 10(3)) and a subunit M(r) of 12 x 10(3). Characterization of aromatic amino acid auxotrophic mutants of A. methanolica suggested that genes encoding 3-dehydroquinate synthase and 3-dehydroquinate dehydratase are genetically linked but their transcription results in the synthesis of two separate proteins.

Actinomycetales↗
PubMed1994

The pca-pob supraoperonic cluster of Acinetobacter calcoaceticus contains quiA, the structural gene for quinate-shikimate dehydrogenase.

An 18-kbp Acinetobacter calcoaceticus chromosomal segment contains the pcaIJFBDKCHG operon, which is required for catabolism of protocatechuate, and pobSRA, genes associated with conversion of p-hydroxybenzoate to protocatechuate. The genetic function of the 6.5 kbp of DNA between pcaG and pobS was unknown. Deletions in this DNA were designed by removal of fragments between restriction sites, and the deletion mutations were introduced into A. calcoaceticus by natural transformation. The mutations prevented growth with either quinate or shikimate, growth substrates that depend upon qui gene function for their catabolism to protocatechuate. The location of quiA, a gene encoding quinate-shikimate dehydrogenase, was indicated by its expression in one of the deletion mutants, and the position of the gene was confirmed by determination of its 2,427-bp nucleotide sequence. The deduced amino acid sequence of QuiA confirmed that it is a member of a family of membrane-associated, pyrrolo-quinoline quinone-dependent dehydrogenases, as had been suggested by earlier biochemical investigations. Catabolism of quinate and skikimate is initiated by NAD(+)-dependent dehydrogenases in other microorganisms, so it is evident that different gene pools were called upon to provide the ancestral enzyme for this metabolic step.

Acinetobacter calcoaceticus↗
PubMed1992

Differential flux through the quinate and shikimate pathways. Implications for the channelling hypothesis.

The qutC gene encoding dehydroshikimate dehydratase has been constitutively overexpressed in Aspergillus nidulans from a range of 1-30-fold over the normal wild-type level. This overexpression leads to impaired growth in minimal medium which can be alleviated by the addition of aromatic amino acids to the medium. Overexpression of the qutC gene in mutant strains lacking protocatechuic acid (PCA) oxygenase leads to the build up of PCA in the medium, which can be measured by a simple assay. Measuring the rate of production of PCA in strains overproducing dehydroshikimate dehydratase and correlating this with the level of overproduction and impaired ability to grow in minimal medium lacking aromatic amino acids leads to the conclusion that (a) the metabolites 3-dehydroquinate and dehydroshikimate leak from the AROM protein at a rate comparable with the extent of flux catalysed by the AROM protein, (b) the AROM protein has a low-level channelling function probably as a result of the close juxtaposition of five active sites and (c) this channelling function is only physiologically significant under non-optimal conditions of nutrient supply and oxygenation, when the organism is in situ in its natural environment.

Alcohol Oxidoreductases↗
PubMed1993

Differential expression of tomato (Lycopersicon esculentum L.) genes encoding shikimate pathway isoenzymes. I. 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase.

Tomato (Lycopersicon esculentum L. cv. UC82b) was found to contain two distinct 3-deoxy-D-arabino-heptulosonate 7-phosphate (DAHP) synthase genes that are differentially expressed. The corresponding cDNAs were isolated and characterized. Both genes code for putative plastidic DAHP synthase isoforms. The deduced amino acid sequences are 79% identical. A comparison of the known Solanaceae DAHP synthases indicates two distinct conserved isoforms. The steady-state levels of transcripts of the two tomato genes differ in all organs analysed.

3-Deoxy-7-Phosphoheptulonate Synthase↗
PubMed2005

ODORANT1 regulates fragrance biosynthesis in petunia flowers.

Floral scent is important to plant reproduction because it attracts pollinators to the sexual organs. Therefore, volatile emission is usually tuned to the foraging activity of the pollinators. In Petunia hybrida, volatile benzenoids determine the floral aroma. Although the pathways for benzenoid biosynthesis have been characterized, the enzymes involved are less well understood. How production and emission are regulated is unknown. By targeted transcriptome analyses, we identified ODORANT1 (ODO1), a member of the R2R3-type MYB family, as a candidate for the regulation of volatile benzenoids in Petunia hybrida cv W115 (Mitchell) flowers. These flowers are only fragrant in the evening and at night. Transcript levels of ODO1 increased before the onset of volatile emission and decreased when volatile emission declined. Downregulation of ODO1 in transgenic P. hybrida Mitchell plants strongly reduced volatile benzenoid levels through decreased synthesis of precursors from the shikimate pathway. The transcript levels of several genes in this pathway were reduced by suppression of ODO1 expression. Moreover, ODO1 could activate the promoter of the 5-enol-pyruvylshikimate-3-phosphate synthase gene. Flower pigmentation, which is furnished from the same shikimate precursors, was not influenced because color and scent biosynthesis occur at different developmental stages. Our studies identify ODO1 as a key regulator of floral scent biosynthesis.

Amino Acid Sequence↗