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ABA-induced stomatal closure involves ALMT4, a phosphorylation-dependent vacuolar anion channel of arabidopsis


Eisenach, Cornelia; Baetz, Ulrike; Huck, Nicola V; Zhang, Jingbo; De Angeli, Alexis; Beckers, Gerold J M; Martinoia, Enrico (2017). ABA-induced stomatal closure involves ALMT4, a phosphorylation-dependent vacuolar anion channel of arabidopsis. Plant Cell, 29(10):2552-2569.

Abstract

Stomatal pores are formed between a pair of guard cells and allow plant uptake of CO2 and water evaporation. Their aperture depends on changes in osmolyte concentration of guard cell vacuoles, specifically of K+ and Mal2- Efflux of Mal2- from the vacuole is required for stomatal closure; however, it is not clear how the anion is released. Here, we report the identification of ALMT4 (ALUMINUM ACTIVATED MALATE TRANSPORTER4) as an Arabidopsis thaliana ion channel that can mediate Mal2- release from the vacuole and is required for stomatal closure in response to abscisic acid (ABA). Knockout mutants showed impaired stomatal closure in response to the drought stress hormone ABA and increased whole-plant wilting in response to drought and ABA. Electrophysiological data show that ALMT4 can mediate Mal2- efflux and that the channel activity is dependent on a phosphorylatable C-terminal serine. Dephosphomimetic mutants of ALMT4 S382 showed increased channel activity and Mal2- efflux. Reconstituting the active channel in almt4 mutants impaired growth and stomatal opening. Phosphomimetic mutants were electrically inactive and phenocopied the almt4 mutants. Surprisingly, S382 can be phosphorylated by mitogen-activated protein kinases in vitro. In brief, ALMT4 likely mediates Mal2- efflux during ABA-induced stomatal closure and its activity depends on phosphorylation.

Abstract

Stomatal pores are formed between a pair of guard cells and allow plant uptake of CO2 and water evaporation. Their aperture depends on changes in osmolyte concentration of guard cell vacuoles, specifically of K+ and Mal2- Efflux of Mal2- from the vacuole is required for stomatal closure; however, it is not clear how the anion is released. Here, we report the identification of ALMT4 (ALUMINUM ACTIVATED MALATE TRANSPORTER4) as an Arabidopsis thaliana ion channel that can mediate Mal2- release from the vacuole and is required for stomatal closure in response to abscisic acid (ABA). Knockout mutants showed impaired stomatal closure in response to the drought stress hormone ABA and increased whole-plant wilting in response to drought and ABA. Electrophysiological data show that ALMT4 can mediate Mal2- efflux and that the channel activity is dependent on a phosphorylatable C-terminal serine. Dephosphomimetic mutants of ALMT4 S382 showed increased channel activity and Mal2- efflux. Reconstituting the active channel in almt4 mutants impaired growth and stomatal opening. Phosphomimetic mutants were electrically inactive and phenocopied the almt4 mutants. Surprisingly, S382 can be phosphorylated by mitogen-activated protein kinases in vitro. In brief, ALMT4 likely mediates Mal2- efflux during ABA-induced stomatal closure and its activity depends on phosphorylation.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Plant and Microbial Biology
07 Faculty of Science > Zurich-Basel Plant Science Center
Dewey Decimal Classification:580 Plants (Botany)
Language:English
Date:October 2017
Deposited On:26 Feb 2018 16:09
Last Modified:14 Mar 2018 17:55
Publisher:American Society of Plant Biologists
ISSN:1040-4651
OA Status:Closed
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.1105/tpc.17.00452
PubMed ID:28874508

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