title: A redox-active isopropylmalate dehydrogenase functions in the biosynthesis of glucosinolates and leucine in Arabidopsis.
abstract: We report a detailed functional characterization of an Arabidopsis isopropylmalate dehydrogenase (AtIPMDH1) that is involved in both glucosinolate biosynthesis and leucine biosynthesis. AtIPMDH1 shares high homology with enzymes from bacteria and yeast that are known to function in leucine biosynthesis. In plants, AtIPMDH1 is co-expressed with nearly all the genes known to be involved in aliphatic glucosinolate biosynthesis. Mutation of AtIPMDH1 leads to a significant reduction in the levels of free leucine and of glucosinolates with side chains of four or more carbons. Complementation of the mutant phenotype by ectopic expression of AtIPMDH1, together with the enzyme's substrate specificity, implicates AtIPMDH1 in both glucosinolate and leucine biosynthesis. This functional assignment is substantiated by subcellular localization of the protein in the chloroplast stroma, and the gene expression patterns in various tissues. Interestingly, AtIPMDH1 activity is regulated by a thiol-based redox modification. This work characterized an enzyme in plants that catalyzes the oxidative decarboxylation step in both leucine biosynthesis (primary metabolism) and methionine chain elongation of glucosinolates (specialized metabolism). It provides evidence for the hypothesis that the two pathways share a common origin, and suggests a role for redox regulation of glucosinolate and leucine synthesis in plants.
authors.affiliation: Department of Biology, Genetics Institute, Plant Molecular and Cellular Biology Program, University of Florida, Gainesville, FL 32610, USA.
authors.forename: Yan
authors.initials: Y
authors.lastname: He
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Mawhinney
authors.forename: Mary L
authors.initials: ML
authors.lastname: Preuss
authors.forename: Amy C
authors.initials: AC
authors.lastname: Schroeder
authors.forename: Bing
authors.initials: B
authors.lastname: Chen
authors.forename: Linda
authors.initials: L
authors.lastname: Abraham
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Jez
authors.forename: Sixue
authors.initials: S
authors.lastname: Chen
mesh_terms: D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002736:Chloroplasts / Q000201:enzymology / Q000235:genetics; D019295:Computational Biology; D004269:DNA, Bacterial / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D005961:Glucosinolates / Q000096:biosynthesis*; D007930:Leucine / Q000096:biosynthesis*; D008291:Malate Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D016254:Mutagenesis, Insertional; D009154:Mutation; D010084:Oxidation-Reduction; D030821:Plants, Genetically Modified / Q000201:enzymology / Q000235:genetics; D013379:Substrate Specificity
chemical_list: D029681:Arabidopsis Proteins; D004269:DNA, Bacterial; D018744:DNA, Plant; D005961:Glucosinolates; C036483:T-DNA; D008291:Malate Dehydrogenase; C521419:PMDH1 protein, Arabidopsis; D007930:Leucine