title: The protein phosphatase AtPP2CA negatively regulates abscisic acid signal transduction in Arabidopsis, and effects of abh1 on AtPP2CA mRNA.
abstract: To identify new loci in abscisic acid (ABA) signaling, we screened a library of 35ScDNA Arabidopsis (Arabidopsis thaliana)-expressing lines for ABA-insensitive mutants in seed germination assays. One of the identified mutants germinated on 2.5 microm ABA, a concentration that completely inhibits wild-type seed germination. Backcrosses and F2 analyses indicated that the mutant exhibits a dominant phenotype and that the ABA insensitivity was linked to a single T-DNA insertion containing a 35ScDNA fusion. The inserted cDNA corresponds to a full-length cDNA of the AtPP2CA gene, encoding a protein phosphatase type 2C (PP2C). Northern-blot analyses demonstrated that the AtPP2CA transcript is indeed overexpressed in the mutant (named PP2CAox). Two independent homozygous T-DNA insertion lines, pp2ca-1 and pp2ca-2, were recovered from the Arabidopsis Biological Resource Center and shown to lack full-length AtPP2CA expression. A detailed characterization of PP2CAox and the T-DNA disruption mutants demonstrated that, whereas ectopic expression of a 35SAtPP2CA fusion caused ABA insensitivity in seed germination and ABA-induced stomatal closure responses, disruption mutants displayed the opposite phenotype, namely, strong ABA hypersensitivity. Thus our data demonstrate that the PP2CA protein phosphatase is a strong negative regulator of ABA signal transduction. Furthermore, it has been previously shown that the AtPP2CA transcript is down-regulated in the ABA-hypersensitive nuclear mRNA cap-binding protein mutant abh1. We show here that down-regulation of AtPP2CA in abh1 is not due to impaired RNA splicing of AtPP2CA pre-mRNA. Moreover, expression of a 35SAtPP2CA cDNA fusion in abh1 partially suppresses abh1 hypersensitivity, and the data further suggest that additional mechanisms contribute to ABA hypersensitivity of abh1.
authors.affiliation: Division of Biological Sciences, Cell and Developmental Biology Section, and Center for Molecular Genetics, University of California, La Jolla, California 92093-0116, USA.
authors.forename: Josef M
authors.initials: JM
authors.lastname: Kuhn
authors.forename: Aurélien
authors.initials: A
authors.lastname: Boisson-Dernier
authors.forename: Marie B
authors.initials: MB
authors.lastname: Dizon
authors.forename: Mohammad H
authors.initials: MH
authors.lastname: Maktabi
authors.forename: Julian I
authors.initials: JI
authors.lastname: Schroeder
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism* / Q000494:pharmacology; D017360:Arabidopsis / Q000196:embryology* / Q000201:enzymology / Q000235:genetics; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics* / Q000502:physiology*; D018076:DNA, Complementary / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D018525:Germination; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D010641:Phenotype; D010749:Phosphoprotein Phosphatases / Q000737:chemistry / Q000235:genetics* / Q000502:physiology*; D018517:Plant Roots / Q000033:anatomy & histology / Q000254:growth & development / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D039381:RNA Cap-Binding Proteins / Q000235:genetics; D012326:RNA Splicing; D012333:RNA, Messenger / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism / Q000502:physiology; D036226:Seedlings / Q000033:anatomy & histology / Q000201:enzymology; D012639:Seeds / Q000254:growth & development / Q000378:metabolism; D015398:Signal Transduction; D040681:Structural Homology, Protein; D015854:Up-Regulation
chemical_list: D000040:Abscisic Acid; D029681:Arabidopsis Proteins; D018076:DNA, Complementary; D010749:Phosphoprotein Phosphatases; D039381:RNA Cap-Binding Proteins; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; C435105:At2g13540 protein, Arabidopsis; C463465:AHG3 protein, Arabidopsis