title: PHO1 expression in guard cells mediates the stomatal response to abscisic acid in Arabidopsis.
abstract: Stomatal opening and closing are driven by ion fluxes that cause changes in guard cell turgor and volume. This process is, in turn, regulated by environmental and hormonal signals, including light and the phytohormone abscisic acid (ABA). Here, we present genetic evidence that expression of PHO1 in guard cells of Arabidopsis thaliana is required for full stomatal responses to ABA. PHO1 is involved in the export of phosphate into the root xylem vessels and, as a result, the pho1 mutant is characterized by low shoot phosphate levels. In leaves, PHO1 was found expressed in guard cells and up-regulated following treatment with ABA. The pho1 mutant was unaffected in production of reactive oxygen species following ABA treatment, and in stomatal movements in response to light cues, high extracellular calcium, auxin, and fusicoccin. However, stomatal movements in response to ABA treatment were severely impaired, both in terms of induction of closure and inhibition of opening. Micro-grafting a pho1 shoot scion onto wild-type rootstock resulted in plants with normal shoot growth and phosphate content, but failed to restore normal stomatal response to ABA treatment. PHO1 knockdown using RNA interference specifically in guard cells of wild-type plants caused a reduced stomatal response to ABA. In agreement, specific expression of PHO1 in guard cells of pho1 plants complemented the mutant guard cell phenotype and re-established ABA sensitivity, although full functional complementation was dependent on shoot phosphate sufficiency. Together, these data reveal an important role for phosphate and the action of PHO1 in the stomatal response to ABA.
authors.affiliation: Département de Biologie Moléculaire Végétale, Biophore, Université de Lausanne, CH-1015 Lausanne, Switzerland.
authors.forename: Céline
authors.initials: C
authors.lastname: Zimmerli
authors.forename: Cécile
authors.initials: C
authors.lastname: Ribot
authors.forename: Alain
authors.initials: A
authors.lastname: Vavasseur
authors.forename: Hubert
authors.initials: H
authors.lastname: Bauer
authors.forename: Rainer
authors.initials: R
authors.lastname: Hedrich
authors.forename: Yves
authors.initials: Y
authors.lastname: Poirier
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology*; D017360:Arabidopsis / Q000187:drug effects* / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D001692:Biological Transport; D018506:Gene Expression Regulation, Plant; D055785:Gene Knockdown Techniques; D005816:Genetic Complementation Test; D008027:Light; D009154:Mutation; D009928:Organ Specificity; D010641:Phenotype; D010710:Phosphates / Q000032:analysis / Q000378:metabolism*; D019441:Plant Epidermis / Q000187:drug effects / Q000235:genetics / Q000502:physiology / Q000528:radiation effects; D010937:Plant Growth Regulators / Q000494:pharmacology*; D018515:Plant Leaves / Q000187:drug effects / Q000235:genetics / Q000502:physiology / Q000528:radiation effects; D018517:Plant Roots / Q000187:drug effects / Q000235:genetics / Q000502:physiology / Q000528:radiation effects; D054046:Plant Stomata / Q000187:drug effects / Q000235:genetics / Q000502:physiology / Q000528:radiation effects; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D015854:Up-Regulation; D052584:Xylem / Q000187:drug effects / Q000235:genetics / Q000502:physiology / Q000528:radiation effects
chemical_list: D029681:Arabidopsis Proteins; C460111:PHO1 protein, Arabidopsis; D010710:Phosphates; D010937:Plant Growth Regulators; D017382:Reactive Oxygen Species; D000040:Abscisic Acid