title: Action of natural abscisic acid precursors and catabolites on abscisic acid receptor complexes.
abstract: The phytohormone abscisic acid (ABA) regulates stress responses and controls numerous aspects of plant growth and development. Biosynthetic precursors and catabolites of ABA have been shown to trigger ABA responses in physiological assays, but it is not clear whether these are intrinsically active or whether they are converted into ABA in planta. In this study, we analyzed the effect of ABA precursors, conjugates, and catabolites on hormone signaling in Arabidopsis (Arabidopsis thaliana). The compounds were also tested in vitro for their ability to regulate the phosphatase moiety of ABA receptor complexes consisting of the protein phosphatase 2C ABI2 and the coreceptors RCAR1/PYL9, RCAR3/PYL8, and RCAR11/PYR1. Using mutants defective in ABA biosynthesis, we show that the physiological activity associated with ABA precursors derives predominantly from their bioconversion to ABA. The ABA glucose ester conjugate, which is the most widespread storage form of ABA, showed weak ABA-like activity in germination assays and in triggering ABA signaling in protoplasts. The ABA conjugate and precursors showed negligible activity as a regulatory ligand of the ABI2/RCAR receptor complexes. The majority of ABA catabolites were inactive in our assays. To analyze the chemically unstable 8'- and 9'-hydroxylated ABA catabolites, we used stable tetralone derivatives of these compounds, which did trigger selective ABA responses. ABA synthetic analogs exhibited differential activity as regulatory ligands of different ABA receptor complexes in vitro. The data show that ABA precursors, catabolites, and conjugates have limited intrinsic bioactivity and that both natural and synthetic ABA-related compounds can be used to probe the structural requirements of ABA ligand-receptor interactions.
authors: Plant Biotechnology Institute, National Research Council of Canada, Saskatoon, Saskatchewan, Canada.
authors: Michal
authors: M
authors: Kepka
authors: Chantel L
authors: CL
authors: Benson
authors: Vijay K
authors: VK
authors: Gonugunta
authors: Ken M
authors: KM
authors: Nelson
authors: Alexander
authors: A
authors: Christmann
authors: Erwin
authors: E
authors: Grill
authors: Suzanne R
authors: SR
authors: Abrams
mesh_terms: D000040:Abscisic Acid / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D017360:Arabidopsis / Q000187:drug effects* / Q000235:genetics / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017930:Genes, Reporter; D018525:Germination / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D047908:Intracellular Signaling Peptides and Proteins; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D010749:Phosphoprotein Phosphatases / Q000235:genetics / Q000378:metabolism; D010937:Plant Growth Regulators / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D018515:Plant Leaves / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D018517:Plant Roots / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D054046:Plant Stomata / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D030821:Plants, Genetically Modified; D011523:Protoplasts; D011993:Recombinant Fusion Proteins; D036226:Seedlings / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D012639:Seeds / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects; D044024:Tetralones / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology
chemical_list: D029681:Arabidopsis Proteins; D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D026901:Membrane Transport Proteins; D010937:Plant Growth Regulators; C540976:AT4G17870 protein, Arabidopsis; C540972:RCAR1 protein, Arabidopsis; D011993:Recombinant Fusion Proteins; D044024:Tetralones; D000040:Abscisic Acid; C106443:ABI2 protein, Arabidopsis; D010749:Phosphoprotein Phosphatases