Cytosolic and plastidic chorismate mutase isozymes from Arabidopsis thaliana: molecular characterization and enzymatic properties

Abstract

The three aromatic amino acids phenylalanine, tyrosine, and tryptophan are synthesized in the plastids of higher plants. There is, however, biochemical evidence that a cytosolic isoform exists of the enzyme catalysing the first step of that branch of the pathway which is specific for the synthesis of phenylalanine and tyrosine, i.e. chorismate mutase (CM). We now report on the isolation of a cDNA clone encoding a cytosolic CM isozyme from Arabidopsis thaliana that was identified by complementing a CM-deficient Escherichia coli strain. The deduced amino acid sequence of this isozyme was 50% identical to that of a previously isolated plastidic CM, and 41% identical to that of yeast CM. The organ-specific expression patterns of the two CM genes were rather similar, but only the gene encoding the plastidic isozyme was elicitor- and pathogen-inducible. The plastidic CM expressed in E. coli was activated by tryptophan and inhibited by phenylalanine and tyrosine, whereas the cytosolic isozyme was insensitive. The existence of a cytosolic CM isozyme implies that either a cytosolic pathway (partial or complete) for the biosynthesis of phenylalanine and tyrosine exists, or that prephenate, originating from chorismate in the cytosol, is utilized for the synthesis of metabolites other than these two aromatic amino acids.

A Root-Expressed l-Phenylalanine:4-Hydroxyphenylpyruvate Aminotransferase Is Required for Tropane Alkaloid Biosynthesis in Atropa belladonna

“…Feedback inhibition of L-Phe biosynthesis and/or diversion of L-Phe to other metabolites also represent potential mechanisms that could suppress free L-Phe accumulation in ArAT4-silenced lines. For example, L-Phe biosynthesis is subject to feedback inhibition of chorismate mutase and arogenate dehydratase (Jung et al, 1986;Eberhard et al, 1996). In addition, attempts to overproduce L-Phe in transgenic lines and the characterization of mutations in regulatory domains of L-Phe biosynthesis genes result in diversion of L-Phe toward additional aromatic amino acid-derived specialized metabolites (Tzin et al, 2009;Huang et al, 2010).…”

G-Protein-Coupled Receptor 1, G-Protein Gα-Subunit 1, and Prephenate Dehydratase 1 Are Required for Blue Light-Induced Production of Phenylalanine in Etiolated Arabidopsis

“…In contrast, the Arabidopsis genome contains three genes coding for chorismate mutase, two chloroplastic and one cytosolic (Eberhard et al, 1996;Mobley et al, 1999). Six PD genes are described for Arabidopsis, where sequence analysis predicts four have signal peptides, suggesting they are chloroplastic, and two less likely to have signal peptides (including PD1), suggesting they are cytosolic (K.M.…”

“…Two of the encoded proteins locate to the plastid (CM1 and CM3) and one is cytosolic (CM2; Eberhard et al, 1996;Mobley et al, 1999). The Arabidopsis genome is not known to encode for an arogenate dehydratase or a cyclohexadienyl dehydratase, the enzymatic activities necessary to convert arogenate to Phe.…”

The sink-specific and stress-regulated Arabidopsis STP4 gene: enhanced expression of a gene encoding a monosaccharide transporter by wounding, elicitors, and pathogen challenge.

“…chorismate mutase, or 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase (Eberhard et al, 1996). STP4 induction is rapid and depends on the concentration of the P. s. tabaci elicitor preparation.…”

“…The identical RNA preparations from f? s. tabaci elicitor-treated suspension-cultured cells that were used in this study were used previously to investigate the effect of elicitation on'the transcript levels of the Arabidopsis PAL7 and PALP genes, encoding phenylalanine ammonium-lyases (Eberhard et al, 1996). Treatment with 5 pg/mL/?…”