title: The oxylipin signal jasmonic acid is activated by an enzyme that conjugates it to isoleucine in Arabidopsis.
abstract: Despite its importance in a variety of plant defense responses, our understanding of how jasmonic acid (JA) functions at the biochemical level is limited. Several amino acid conjugates of JA were tested for their ability to complement the JA-insensitive Arabidopsis thaliana mutant jar1-1. Unlike free JA, JA-Ile inhibited root growth in jar1-1 to the same extent as in the wild type, whereas JA-Val, JA-Leu, and JA-Phe were ineffective inhibitors in both genotypes. Thin-layer chromatography and gas chromatography-mass spectrometry (GC-MS) analysis of products produced in vitro by recombinant JAR1 demonstrated that this enzyme forms JA-amido conjugates with several amino acids, including JA-Ile. JA-Val, -Leu, -Ile, and -Phe were each quantified in Arabidopsis seedlings by GC-MS. JA-Ile was found at 29.6 pmole g(-1) fresh weight (FW) in the wild type but was more than sevenfold lower in two jar1 alleles. JA-Leu, -Val, and -Phe were present at only low levels in both genotypes. Expression of wild-type JAR1 in transgenic jar1-1 plants restored sensitivity to JA and elevated JA-Ile to the same level as in the wild type. The ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) conjugated to JA was also found in plant tissue at 18.4 pmole g(-1) FW. JA-ACC was determined not be an effective jasmonate root inhibitor, and surprisingly, was twofold higher in the mutants than in the wild type. This suggests that another JA-conjugating enzyme(s) is present in Arabidopsis. Synthesis of JA-ACC might provide a mechanism to coregulate the availability of JA and ACC for conversion to the active hormones JA-Ile and ethylene, respectively. We conclude that JAR1 is a JA-amino synthetase that is required to activate JA for optimal signaling in Arabidopsis. Plant hormone activation by conjugation to amino acids and the enzymes involved in their formation were previously unknown.
authors.affiliation: Department of Agronomy and Horticulture, University of Nebraska, Lincoln, Nebraska 68583, USA. pstaswick1@unl.edu
authors.forename: Paul E
authors.initials: PE
authors.lastname: Staswick
authors.forename: Iskender
authors.initials: I
authors.lastname: Tiryaki
mesh_terms: D020816:Amino Acid Motifs; D000596:Amino Acids / Q000737:chemistry; D000598:Amino Acids, Cyclic / Q000378:metabolism; D017360:Arabidopsis / Q000033:anatomy & histology / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D003517:Cyclopentanes / Q000737:chemistry / Q000378:metabolism*; D007192:Indenes / Q000737:chemistry; D007532:Isoleucine / Q000737:chemistry / Q000378:metabolism*; D007554:Isotopes / Q000378:metabolism; D009154:Mutation; D009713:Nucleotidyltransferases / Q000235:genetics / Q000378:metabolism; D054883:Oxylipins; D010937:Plant Growth Regulators / Q000737:chemistry / Q000378:metabolism*; D018515:Plant Leaves / Q000737:chemistry / Q000378:metabolism; D018517:Plant Roots / Q000254:growth & development / Q000378:metabolism; D030821:Plants, Genetically Modified; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D036226:Seedlings / Q000737:chemistry / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D010453:Peptide Synthases
chemical_list: D000596:Amino Acids; D000598:Amino Acids, Cyclic; D029681:Arabidopsis Proteins; D003517:Cyclopentanes; D007192:Indenes; D007532:Isoleucine; D007554:Isotopes; D009713:Nucleotidyltransferases; D054883:Oxylipins; D010937:Plant Growth Regulators; D011993:Recombinant Fusion Proteins; C023863:1-aminocyclopropane-1-carboxylic acid; C058487:coronatine; C011006:jasmonic acid; C412831:AT2G46370 protein, Arabidopsis; D010453:Peptide Synthases