title: Stomatal Function Requires Pectin De-methyl-esterification of the Guard Cell Wall.
abstract: Stomatal opening and closure depends on changes in turgor pressure acting within guard cells to alter cell shape [1]. The extent of these shape changes is limited by the mechanical properties of the cells, which will be largely dependent on the structure of the cell walls. Although it has long been observed that guard cells are anisotropic due to differential thickening and the orientation of cellulose microfibrils [2], our understanding of the composition of the cell wall that allows them to undergo repeated swelling and deflation remains surprisingly poor. Here, we show that the walls of guard cells are rich in un-esterified pectins. We identify a pectin methylesterase gene, PME6, which is highly expressed in guard cells and required for stomatal function. pme6-1 mutant guard cells have walls enriched in methyl-esterified pectin and show a decreased dynamic range in response to triggers of stomatal opening/closure, including elevated osmoticum, suggesting that abrogation of stomatal function reflects a mechanical change in the guard cell wall. Altered stomatal function leads to increased conductance and evaporative cooling, as well as decreased plant growth. The growth defect of the pme6-1 mutant is rescued by maintaining the plants in elevated CO2, substantiating gas exchange analyses, indicating that the mutant stomata can bestow an improved assimilation rate. Restoration of PME6 rescues guard cell wall pectin methyl-esterification status, stomatal function, and plant growth. Our results establish a link between gene expression in guard cells and their cell wall properties, with a corresponding effect on stomatal function and plant physiology.
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK.
authors.forename: Sam
authors.initials: S
authors.lastname: Amsbury
authors.affiliation: Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, UK.
authors.forename: Lee
authors.initials: L
authors.lastname: Hunt
authors.affiliation: Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, UK; Department of Botany, University of Omar Al-Mukhtar, Al-Baida, Libya.
authors.forename: Nagat
authors.initials: N
authors.lastname: Elhaddad
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK.
authors.forename: Alice
authors.initials: A
authors.lastname: Baillie
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK.
authors.forename: Marjorie
authors.initials: M
authors.lastname: Lundgren
authors.affiliation: Biological Systems and Engineering Division and Joint BioEnergy Institute, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Yves
authors.initials: Y
authors.lastname: Verhertbruggen
authors.affiliation: Biological Systems and Engineering Division and Joint BioEnergy Institute, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Henrik V
authors.initials: HV
authors.lastname: Scheller
authors.affiliation: Centre for Plant Sciences, Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, UK.
authors.forename: J Paul
authors.initials: JP
authors.lastname: Knox
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK. Electronic address: a.fleming@sheffield.ac.uk.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Fleming
authors.affiliation: Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, UK. Electronic address: j.e.gray@sheffield.ac.uk.
authors.forename: Julie E
authors.initials: JE
authors.lastname: Gray
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D002473:Cell Wall / Q000378:metabolism; D000073398:Demethylation; D004951:Esterification; D018506:Gene Expression Regulation, Plant; D010368:Pectins / Q000378:metabolism*; D054046:Plant Stomata / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; C583986:PME6 protein, Arabidopsis; D010368:Pectins
keywords: Arabidopsis; cell wall; guard cell; pectin; stomata