title: SLAC1 is required for plant guard cell S-type anion channel function in stomatal signalling.
abstract: Stomatal pores, formed by two surrounding guard cells in the epidermis of plant leaves, allow influx of atmospheric carbon dioxide in exchange for transpirational water loss. Stomata also restrict the entry of ozone--an important air pollutant that has an increasingly negative impact on crop yields, and thus global carbon fixation and climate change. The aperture of stomatal pores is regulated by the transport of osmotically active ions and metabolites across guard cell membranes. Despite the vital role of guard cells in controlling plant water loss, ozone sensitivity and CO2 supply, the genes encoding some of the main regulators of stomatal movements remain unknown. It has been proposed that guard cell anion channels function as important regulators of stomatal closure and are essential in mediating stomatal responses to physiological and stress stimuli. However, the genes encoding membrane proteins that mediate guard cell anion efflux have not yet been identified. Here we report the mapping and characterization of an ozone-sensitive Arabidopsis thaliana mutant, slac1. We show that SLAC1 (SLOW ANION CHANNEL-ASSOCIATED 1) is preferentially expressed in guard cells and encodes a distant homologue of fungal and bacterial dicarboxylate/malic acid transport proteins. The plasma membrane protein SLAC1 is essential for stomatal closure in response to CO2, abscisic acid, ozone, light/dark transitions, humidity change, calcium ions, hydrogen peroxide and nitric oxide. Mutations in SLAC1 impair slow (S-type) anion channel currents that are activated by cytosolic Ca2+ and abscisic acid, but do not affect rapid (R-type) anion channel currents or Ca2+ channel function. A low homology of SLAC1 to bacterial and fungal organic acid transport proteins, and the permeability of S-type anion channels to malate suggest a vital role for SLAC1 in the function of S-type anion channels.
authors.affiliation: Plant Biology, Department of Biological and Environmental Sciences, University of Helsinki, FI-00014 Helsinki, Finland.
authors.forename: Triin
authors.initials: T
authors.lastname: Vahisalu
authors.forename: Hannes
authors.initials: H
authors.lastname: Kollist
authors.forename: Yong-Fei
authors.initials: YF
authors.lastname: Wang
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Nishimura
authors.forename: Wai-Yin
authors.initials: WY
authors.lastname: Chan
authors.forename: Gabriel
authors.initials: G
authors.lastname: Valerio
authors.forename: Airi
authors.initials: A
authors.lastname: Lamminmäki
authors.forename: Mikael
authors.initials: M
authors.lastname: Brosché
authors.forename: Heino
authors.initials: H
authors.lastname: Moldau
authors.forename: Radhika
authors.initials: R
authors.lastname: Desikan
authors.forename: Julian I
authors.initials: JI
authors.lastname: Schroeder
authors.forename: Jaakko
authors.initials: J
authors.lastname: Kangasjärvi
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D000838:Anions / Q000378:metabolism*; D017360:Arabidopsis / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D003624:Darkness; D004777:Environment; D006813:Humidity; D006861:Hydrogen Peroxide / Q000378:metabolism / Q000494:pharmacology; D015640:Ion Channel Gating / Q000187:drug effects / Q000528:radiation effects; D007473:Ion Channels / Q000378:metabolism*; D017136:Ion Transport / Q000187:drug effects / Q000528:radiation effects; D008027:Light; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism; D019697:Onions / Q000378:metabolism; D009865:Oocytes; D010126:Ozone / Q000378:metabolism / Q000494:pharmacology; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism; D054046:Plant Stomata / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects; D015398:Signal Transduction / Q000187:drug effects / Q000528:radiation effects; D014026:Nicotiana / Q000166:cytology / Q000378:metabolism; D014867:Water / Q000378:metabolism; D014981:Xenopus
chemical_list: D000838:Anions; D029681:Arabidopsis Proteins; D007473:Ion Channels; D008565:Membrane Proteins; C528438:SLAC1 protein, Arabidopsis; D014867:Water; D009569:Nitric Oxide; D010126:Ozone; D000040:Abscisic Acid; D006861:Hydrogen Peroxide; D002118:Calcium