title: Disruption of a guard cell-expressed protein phosphatase 2A regulatory subunit, RCN1, confers abscisic acid insensitivity in Arabidopsis.
abstract: Pharmacological studies have led to a model in which the phytohormone abscisic acid (ABA) may be positively transduced via protein phosphatases of the type 1 (PP1) or type 2A (PP2A) families. However, pharmacological evidence also exists that PP1s or PP2As may function as negative regulators of ABA signaling. Furthermore, recessive disruption mutants in protein phosphatases that function in ABA signal transduction have not yet been identified. A guard cell-expressed PP2A gene, RCN1, which had been characterized previously as a molecular component affecting auxin transport and gravity response, was isolated. A T-DNA disruption mutation in RCN1 confers recessive ABA insensitivity to Arabidopsis. The rcn1 mutation impairs ABA-induced stomatal closing and ABA activation of slow anion channels. Calcium imaging analyses show a reduced sensitivity of ABA-induced cytosolic calcium increases in rcn1, whereas mechanisms downstream of cytosolic calcium increases show wild-type responses, suggesting that RCN1 functions in ABA signal transduction upstream of cytosolic Ca(2+) increases. Furthermore, rcn1 shows ABA insensitivity in ABA inhibition of seed germination and ABA-induced gene expression. The PP1 and PP2A inhibitor okadaic acid phenocopies the rcn1 phenotype in wild-type plants both in ABA-induced cytosolic calcium increases and in seed germination, and the wild-type RCN1 genomic DNA complements rcn1 phenotypes. These data show that RCN1 functions as a general positive transducer of early ABA signaling.
authors.affiliation: Cell and Developmental Biology Section, Division of Biology and Center for Molecular Genetics, University of California, San Diego, La Jolla, California 92093-0116, USA.
authors.forename: June M
authors.initials: JM
authors.lastname: Kwak
authors.forename: Ji-Hye
authors.initials: JH
authors.lastname: Moon
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Murata
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Kuchitsu
authors.forename: Nathalie
authors.initials: N
authors.lastname: Leonhardt
authors.forename: Alison
authors.initials: A
authors.lastname: DeLong
authors.forename: Julian I
authors.initials: JI
authors.lastname: Schroeder
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology*; D017360:Arabidopsis / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D002118:Calcium / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic / Q000235:genetics; D018506:Gene Expression Regulation, Plant / Q000235:genetics; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007473:Ion Channels; D009154:Mutation; D019319:Okadaic Acid / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D019441:Plant Epidermis / Q000187:drug effects / Q000201:enzymology; D054648:Protein Phosphatase 2; D015398:Signal Transduction / Q000235:genetics
chemical_list: D007473:Ion Channels; D019319:Okadaic Acid; D000040:Abscisic Acid; D006861:Hydrogen Peroxide; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D002118:Calcium