title: The grape aquaporin VvSIP1 transports water across the ER membrane.
abstract: Water diffusion through biological membranes is facilitated by aquaporins, members of the widespread major intrinsic proteins (MIPs). In the present study, the localization, expression, and functional characterization of a small basic intrinsic protein (SIP) from the grapevine were assessed. VvSIP1 was expressed in leaves and berries from field-grown vines, and in leaves and stems from in vitro plantlets, but not in roots. When expressed in tobacco mesophyll cells and in Saccharomyces cerevisiae, fluorescent-tagged VvSIP1 was localized at the endoplasmic reticulum (ER). Stopped-flow spectroscopy showed that VvSIP1-enriched ER membrane vesicles from yeast exhibited higher water permeability and lower activation energy for water transport than control vesicles, indicating the involvement of protein-mediated water diffusion. This aquaporin was able to transport water but not glycerol, urea, sorbitol, glucose, or inositol. VvSIP1 expression in Xenopus oocytes failed to increase the water permeability of the plasma membrane. VvSIP1-His-tag was solubilized and purified to homogeneity from yeast ER membranes and the reconstitution of the purified protein in phosphatidylethanolamine liposomes confirmed its water channel activity. To provide further insights into gene function, the expression of VvSIP1 in mature grapes was studied when vines were cultivated in different field conditions, but its transcript levels did not increase significantly in water-stressed plants and western-exposed berries. However, the expression of the aquaporin genes VvSIP1, VvPIP2;2, and VvTIP1;1 was up-regulated by heat in cultured cells.
authors.affiliation: Centro de Investigação e de Tecnologias Agro-ambientais e Biológicas CITAB, Portugal.
authors.forename: Henrique
authors.initials: H
authors.lastname: Noronha
authors.forename: Alice
authors.initials: A
authors.lastname: Agasse
authors.forename: Ana Paula
authors.initials: AP
authors.lastname: Martins
authors.forename: Marie C
authors.initials: MC
authors.lastname: Berny
authors.forename: Dulceneia
authors.initials: D
authors.lastname: Gomes
authors.forename: Olfa
authors.initials: O
authors.lastname: Zarrouk
authors.forename: Pierre
authors.initials: P
authors.lastname: Thiebaud
authors.forename: Serge
authors.initials: S
authors.lastname: Delrot
authors.forename: Graça
authors.initials: G
authors.lastname: Soveral
authors.forename: François
authors.initials: F
authors.lastname: Chaumont
authors.forename: Hernâni
authors.initials: H
authors.lastname: Gerós
mesh_terms: D000818:Animals; D020346:Aquaporins / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D015870:Gene Expression; D018506:Gene Expression Regulation, Plant; D017930:Genes, Reporter; D006358:Hot Temperature; D009865:Oocytes; D010539:Permeability; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018547:Plant Stems / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation; D027843:Vitis / Q000235:genetics / Q000378:metabolism*; D014867:Water / Q000378:metabolism*; D014981:Xenopus
chemical_list: D020346:Aquaporins; D010940:Plant Proteins; D014867:Water
keywords: Aquaporin; Vitis vinifera; VvSIP1; protein purification; proteoliposomes; water transport.