title: The grapevine root-specific aquaporin VvPIP2;4N controls root hydraulic conductance and leaf gas exchange under well-watered conditions but not under water stress.
abstract: We functionally characterized the grape (Vitis vinifera) VvPIP2;4N (for Plasma membrane Intrinsic Protein) aquaporin gene. Expression of VvPIP2;4N in Xenopus laevis oocytes increased their swelling rate 54-fold. Northern blot and quantitative reverse transcription-polymerase chain reaction analyses showed that VvPIP2;4N is the most expressed PIP2 gene in root. In situ hybridization confirmed root localization in the cortical parenchyma and close to the endodermis. We then constitutively overexpressed VvPIP2;4N in grape 'Brachetto', and in the resulting transgenic plants we analyzed (1) the expression of endogenous and transgenic VvPIP2;4N and of four other aquaporins, (2) whole-plant, root, and leaf ecophysiological parameters, and (3) leaf abscisic acid content. Expression of transgenic VvPIP2;4N inhibited neither the expression of the endogenous gene nor that of other PIP aquaporins in both root and leaf. Under well-watered conditions, transgenic plants showed higher stomatal conductance, gas exchange, and shoot growth. The expression level of VvPIP2;4N (endogenous + transgene) was inversely correlated to root hydraulic resistance. The leaf component of total plant hydraulic resistance was low and unaffected by overexpression of VvPIP2;4N. Upon water stress, the overexpression of VvPIP2;4N induced a surge in leaf abscisic acid content and a decrease in stomatal conductance and leaf gas exchange. Our results show that aquaporin-mediated modifications of root hydraulics play a substantial role in the regulation of water flow in well-watered grapevine plants, while they have a minor role upon drought, probably because other signals, such as abscisic acid, take over the control of water flow.
authors.affiliation: Department of Agricultural, Forestry, and Food Sciences, University of Turin, 10095 Grugliasco, Italy.
authors.forename: Irene
authors.initials: I
authors.lastname: Perrone
authors.forename: Giorgio
authors.initials: G
authors.lastname: Gambino
authors.forename: Walter
authors.initials: W
authors.lastname: Chitarra
authors.forename: Marco
authors.initials: M
authors.lastname: Vitali
authors.forename: Chiara
authors.initials: C
authors.lastname: Pagliarani
authors.forename: Nadia
authors.initials: N
authors.lastname: Riccomagno
authors.forename: Raffaella
authors.initials: R
authors.lastname: Balestrini
authors.forename: Ralf
authors.initials: R
authors.lastname: Kaldenhoff
authors.forename: Norbert
authors.initials: N
authors.lastname: Uehlein
authors.forename: Ivana
authors.initials: I
authors.lastname: Gribaudo
authors.forename: Andrea
authors.initials: A
authors.lastname: Schubert
authors.forename: Claudio
authors.initials: C
authors.lastname: Lovisolo
mesh_terms: D000818:Animals; D020346:Aquaporins / Q000235:genetics / Q000502:physiology*; D001692:Biological Transport; D002462:Cell Membrane / Q000502:physiology; D003001:Cloning, Molecular; D003681:Dehydration; D055864:Droughts; D005740:Gases / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D009865:Oocytes; D018515:Plant Leaves / Q000235:genetics / Q000502:physiology*; D010940:Plant Proteins / Q000235:genetics / Q000502:physiology; D018517:Plant Roots / Q000502:physiology*; D054046:Plant Stomata / Q000502:physiology; D018526:Plant Transpiration; D030821:Plants, Genetically Modified / Q000235:genetics / Q000502:physiology; D013312:Stress, Physiological; D019076:Transgenes; D027843:Vitis / Q000235:genetics / Q000502:physiology*; D014867:Water / Q000502:physiology*; D014981:Xenopus
chemical_list: D020346:Aquaporins; D005740:Gases; D010940:Plant Proteins; D014867:Water