title: Sugar and hexokinase suppress expression of PIP aquaporins and reduce leaf hydraulics that preserves leaf water potential.
abstract: Sugars affect central aspects of plant physiology, including photosynthesis, stomatal behavior and the loss of water through the stomata. Yet, the potential effects of sugars on plant aquaporins (AQPs) and water conductance have not been examined. We used database and transcriptional analyses, as well as cellular and whole-plant functional techniques to examine the link between sugar-related genes and AQPs. Database analyses revealed a high level of correlation between the expression of AQPs and that of sugar-related genes, including the Arabidopsis hexokinases 1 (AtHXK1). Increased expression of AtHXK1, as well as the addition of its primary substrate, glucose (Glc), repressed the expression of 10 AQPs from the plasma membrane-intrinsic proteins (PIP) subfamily (PIP-AQPs) and induced the expression of two stress-related PIP-AQPs. The osmotic water permeability of mesophyll protoplasts of AtHXK1-expressing plants and the leaf hydraulic conductance of those plants were significantly reduced, in line with the decreased expression of PIP-AQPs. Conversely, hxk1 mutants demonstrated a higher level of hydraulic conductance, with increased water potential in their leaves. In addition, the presence of Glc reduced leaf water potential, as compared with an osmotic control, indicating that Glc reduces the movement of water from the xylem into the mesophyll. The production of sugars entails a significant loss of water and these results suggest that sugars and AtHXK1 affect the expression of AQP genes and reduce leaf water conductance, to coordinate sugar levels with the loss of water through transpiration.
authors.affiliation: Institute of Plant Sciences, Agricultural Research Organization, The Volcani Center, Rishon LeZion, 7505101, Israel.
authors.forename: Gilor
authors.initials: G
authors.lastname: Kelly
authors.affiliation: The Institute of Plant Sciences and Genetics in Agriculture, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, 76100, Israel.
authors.forename: Nir
authors.initials: N
authors.lastname: Sade
authors.affiliation: Institute of Plant Sciences, Agricultural Research Organization, The Volcani Center, Rishon LeZion, 7505101, Israel.
authors.forename: Adi
authors.initials: A
authors.lastname: Doron-Faigenboim
authors.affiliation: The Institute of Plant Sciences and Genetics in Agriculture, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, 76100, Israel.
authors.forename: Stephen
authors.initials: S
authors.lastname: Lerner
authors.affiliation: The Institute of Plant Sciences and Genetics in Agriculture, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, 76100, Israel.
authors.forename: Arava
authors.initials: A
authors.lastname: Shatil-Cohen
authors.affiliation: Institute of Plant Sciences, Agricultural Research Organization, The Volcani Center, Rishon LeZion, 7505101, Israel.
authors.forename: Yelena
authors.initials: Y
authors.lastname: Yeselson
authors.affiliation: Institute of Plant Sciences, Agricultural Research Organization, The Volcani Center, Rishon LeZion, 7505101, Israel.
authors.forename: Aiman
authors.initials: A
authors.lastname: Egbaria
authors.affiliation: Institute of Plant Sciences, Agricultural Research Organization, The Volcani Center, Rishon LeZion, 7505101, Israel.
authors.forename: Jayaram
authors.initials: J
authors.lastname: Kottapalli
authors.affiliation: Institute of Plant Sciences, Agricultural Research Organization, The Volcani Center, Rishon LeZion, 7505101, Israel.
authors.forename: Arthur A
authors.initials: AA
authors.lastname: Schaffer
authors.affiliation: The Institute of Plant Sciences and Genetics in Agriculture, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, 76100, Israel.
authors.forename: Menachem
authors.initials: M
authors.lastname: Moshelion
authors.affiliation: Institute of Plant Sciences, Agricultural Research Organization, The Volcani Center, Rishon LeZion, 7505101, Israel.
authors.forename: David
authors.initials: D
authors.lastname: Granot
mesh_terms: D020346:Aquaporins / Q000235:genetics* / Q000378:metabolism; D017360:Arabidopsis / Q000187:drug effects / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology; D006593:Hexokinase / Q000235:genetics* / Q000378:metabolism; D058503:Mesophyll Cells / Q000378:metabolism; D018515:Plant Leaves / Q000502:physiology*; D018526:Plant Transpiration; D030821:Plants, Genetically Modified; D000073893:Sugars / Q000378:metabolism*
chemical_list: D020346:Aquaporins; D029681:Arabidopsis Proteins; C000611205:PIP1;4 protein, Arabidopsis; D000073893:Sugars; D006593:Hexokinase; C473630:ATHXK1 protein, Arabidopsis; D005947:Glucose
keywords: 
  Arabidopsis thaliana
  ; Hexokinase; aquaporins; glucose; leaf hydraulic conductivity (Kleaf); plasma membrane-intrinsic proteins (PIPs); sugar