title: The small subunit 1 of the Arabidopsis isopropylmalate isomerase is required for normal growth and development and the early stages of glucosinolate formation.
abstract: In Arabidopsis thaliana the evolutionary and functional relationship between Leu biosynthesis and the Met chain elongation pathway, the first part of glucosinolate formation, is well documented. Nevertheless the exact functions of some pathway components are still unclear. Isopropylmalate isomerase (IPMI), an enzyme usually involved in Leu biosynthesis, is a heterodimer consisting of a large and a small subunit. While the large protein is encoded by a single gene (isopropylmalate isomerase large subunit1), three genes encode small subunits (isopropylmalate isomerase small subunit1 to 3). We have now analyzed small subunit 1 (isopropylmalate isomerase small subunit1) employing artificial microRNA for a targeted knockdown of the encoding gene. Strong reduction of corresponding mRNA levels to less than 5% of wild-type levels resulted in a severe phenotype with stunted growth, narrow pale leaf blades with green vasculature and abnormal adaxial-abaxial patterning as well as anomalous flower morphology. Supplementation of the knockdown plants with leucine could only partially compensate for the morphological and developmental abnormalities. Detailed metabolite profiling of the knockdown plants revealed changes in the steady state levels of isopropylmalate and glucosinolates as well as their intermediates demonstrating a function of IPMI SSU1 in both leucine biosynthesis and the first cycle of Met chain elongation. Surprisingly the levels of free leucine slightly increased suggesting an imbalanced distribution of leucine within cells and/or within plant tissues.
authors.affiliation: Institut Molekulare Botanik, Universität Ulm, Ulm, Germany.
authors.forename: Janet
authors.initials: J
authors.lastname: Imhof
authors.affiliation: Institut Molekulare Botanik, Universität Ulm, Ulm, Germany.
authors.forename: Florian
authors.initials: F
authors.lastname: Huber
authors.affiliation: Max Planck Institut für Chemische Ökologie, Abt. Biochemie, Beutenberg Campus, Jena, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Reichelt
authors.affiliation: Max Planck Institut für Chemische Ökologie, Abt. Biochemie, Beutenberg Campus, Jena, Germany.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Gershenzon
authors.affiliation: Institut für Molekulare und Zelluläre Anatomie, Universität Ulm, Ulm, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Wiegreffe
authors.affiliation: Institut Molekulare Botanik, Universität Ulm, Ulm, Germany.
authors.forename: Kurt
authors.initials: K
authors.lastname: Lächler
authors.affiliation: Institut Molekulare Botanik, Universität Ulm, Ulm, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Binder
mesh_terms: D000597:Amino Acids, Branched-Chain / Q000494:pharmacology; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development* / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002736:Chloroplasts / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D004926:Escherichia coli / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D055785:Gene Knockdown Techniques; D055786:Gene Knockout Techniques; D017343:Genes, Plant; D005816:Genetic Complementation Test; D005961:Glucosinolates / Q000378:metabolism*; D005966:Glucuronidase / Q000378:metabolism; D007535:Isomerases / Q000235:genetics / Q000378:metabolism*; D008293:Malates / Q000378:metabolism; D055432:Metabolomics; D009154:Mutation / Q000235:genetics; D009928:Organ Specificity / Q000187:drug effects / Q000235:genetics; D010641:Phenotype; D063245:Plant Development / Q000187:drug effects; D010937:Plant Growth Regulators / Q000378:metabolism; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D030821:Plants, Genetically Modified; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity / Q000187:drug effects
chemical_list: D000597:Amino Acids, Branched-Chain; D029681:Arabidopsis Proteins; D005961:Glucosinolates; D008293:Malates; D010937:Plant Growth Regulators; D021122:Protein Subunits; D012333:RNA, Messenger; D005966:Glucuronidase; C032241:isopropylmalate isomerase; D007535:Isomerases