title: Mutations in the SLAC1 anion channel slow stomatal opening and severely reduce K+ uptake channel activity via enhanced cytosolic [Ca2+] and increased Ca2+ sensitivity of K+ uptake channels.
abstract: The Arabidopsis guard cell anion channel SLAC1 is essential for stomatal closure in response to various endogenous and environmental stimuli. Interestingly, here we reveal an unexpected impairment of slac1 alleles on stomatal opening. We report that mutations in SLAC1 unexpectedly slow stomatal opening induced by light, low CO(2) and elevated air humidity in intact plants and that this is caused by the severely reduced activity of inward K(+) (K(+)(in)) channels in slac1 guard cells. Expression of channels and transporters involved in stomatal opening showed small but significant reductions in transcript levels in slac1 guard cells; however, this was deemed insufficient to explain the severely impaired K(+)(in) channel activity in slac1. We further examined resting cytosolic Ca(2+) concentration ([Ca(2+)](cyt)) and K(+)(in) channel sensitivity to [Ca(2+)](cyt) in slac1. These experiments showed higher resting [Ca(2+)](cyt) in slac1 guard cells and that reducing [Ca(2+)](cyt) to < 10 nM rapidly restored the activity of K(+)(in) channels in slac1 closer to wild-type levels. These findings demonstrate an unanticipated compensatory feedback control in plant stomatal regulation, which counteracts the impaired stomatal closing response of slac1, by down-regulating stomatal opening mechanisms and implicates enhanced [Ca(2+)](cyt) sensitivity priming as a mechanistic basis for the down-regulated K(+)(in) channel activity.
authors.affiliation: Institute of Technology, University of Tartu, 50411, Tartu, Estonia.
authors.forename: Kristiina
authors.initials: K
authors.lastname: Laanemets
authors.affiliation: Division of Biological Sciences, Cell and Developmental Biology Section, University of California San Diego, La Jolla, CA, 92093-0116, USA.|National Key Laboratory of Plant Molecular Genetics, Institute of Plant Physiology and Ecology, Shanghai Institute for Biological Sciences, The Chinese Academy of Sciences, Shanghai, 200032, China.
authors.forename: Yong-Fei
authors.initials: YF
authors.lastname: Wang
authors.affiliation: Institute of Technology, University of Tartu, 50411, Tartu, Estonia.
authors.forename: Ove
authors.initials: O
authors.lastname: Lindgren
authors.affiliation: Division of Biological Sciences, Cell and Developmental Biology Section, University of California San Diego, La Jolla, CA, 92093-0116, USA.
authors.forename: Juyou
authors.initials: J
authors.lastname: Wu
authors.affiliation: Division of Biological Sciences, Cell and Developmental Biology Section, University of California San Diego, La Jolla, CA, 92093-0116, USA.
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Nishimura
authors.affiliation: Division of Biological Sciences, Cell and Developmental Biology Section, University of California San Diego, La Jolla, CA, 92093-0116, USA.
authors.forename: Stephen
authors.initials: S
authors.lastname: Lee
authors.affiliation: Division of Biological Sciences, Cell and Developmental Biology Section, University of California San Diego, La Jolla, CA, 92093-0116, USA.
authors.forename: Daniel
authors.initials: D
authors.lastname: Caddell
authors.affiliation: Institute of Technology, University of Tartu, 50411, Tartu, Estonia.
authors.forename: Ebe
authors.initials: E
authors.lastname: Merilo
authors.affiliation: Institute of Technology, University of Tartu, 50411, Tartu, Estonia.|Division of Plant Biology, Department of Biosciences, University of Helsinki, PO Box 65, FI-00014, Helsinki, Finland.
authors.forename: Mikael
authors.initials: M
authors.lastname: Brosche
authors.affiliation: Department of Biochemistry, University of Tartu, 50411, Tartu, Estonia.
authors.forename: Kalle
authors.initials: K
authors.lastname: Kilk
authors.affiliation: Department of Biochemistry, University of Tartu, 50411, Tartu, Estonia.
authors.forename: Ursel
authors.initials: U
authors.lastname: Soomets
authors.affiliation: Division of Plant Biology, Department of Biosciences, University of Helsinki, PO Box 65, FI-00014, Helsinki, Finland.
authors.forename: Jaakko
authors.initials: J
authors.lastname: Kangasjärvi
authors.affiliation: Division of Biological Sciences, Cell and Developmental Biology Section, University of California San Diego, La Jolla, CA, 92093-0116, USA.
authors.forename: Julian I
authors.initials: JI
authors.lastname: Schroeder
authors.affiliation: Institute of Technology, University of Tartu, 50411, Tartu, Estonia.
authors.forename: Hannes
authors.initials: H
authors.lastname: Kollist
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology; D000483:Alleles; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism; D002462:Cell Membrane / Q000201:enzymology; D003600:Cytosol / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D008027:Light; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D018408:Patch-Clamp Techniques; D059828:Plant Cells / Q000378:metabolism; D019441:Plant Epidermis / Q000187:drug effects / Q000378:metabolism; D054046:Plant Stomata / Q000187:drug effects / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying / Q000378:metabolism*; D011523:Protoplasts / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D008565:Membrane Proteins; D024661:Potassium Channels, Inwardly Rectifying; C528438:SLAC1 protein, Arabidopsis; D002245:Carbon Dioxide; D000040:Abscisic Acid; D002118:Calcium