Role of a single aquaporin isoform in root water uptake.
Aquaporins are ubiquitous channel proteins that facilitate the transport of water across cell membranes. Aquaporins show a typically high isoform multiplicity in plants, with 35 homologs in Arabidopsis. The integrated function of plant aquaporins and the function of each individual isoform remain poorly understood. Matrix-assisted laser desorption/ionization time-of-flight analyses suggested that Plasma Membrane Intrinsic Protein2;2 (PIP2;2) is one of the abundantly expressed aquaporin isoforms in Arabidopsis root plasma membranes. Two independent Arabidopsis knockout mutants of PIP2;2 were isolated using a PCR-based strategy from a library of plant lines mutagenized by the insertion of Agrobacterium tumefaciens T-DNA. Expression in transgenic Arabidopsis of a PIP2;2 promoter-beta-glucuronidase gene fusion indicated that PIP2;2 is expressed predominantly in roots, with a strong expression in the cortex, endodermis, and stele. The hydraulic conductivity of root cortex cells, as measured with a cell pressure probe, was reduced by 25 to 30% in the two allelic PIP2;2 mutants compared with the wild type. In addition, free exudation measurements revealed a 14% decrease, with respect to wild-type values, in the osmotic hydraulic conductivity of roots excised from the two PIP2;2 mutants. Together, our data provide evidence for the contribution of a single aquaporin gene to root water uptake and identify PIP2;2 as an aquaporin specialized in osmotic fluid transport. PIP2;2 has a close homolog, PIP2;3, showing 96.8% amino acid identity. The phenotype of PIP2;2 mutants demonstrates that, despite their high homology and isoform multiplicity, plant aquaporins have evolved with nonredundant functions.
Javot
Hélène
H
Biochimie et Physiologie Moléculaire des Plantes, Agro-M/Centre National de la Recherche Scientifique/Institut National de la Recherche Agronomique/UM2 Unité Mixte de Recherche 5004, Place Viala, F-34060 Montpellier Cedex 1, France.
Lauvergeat
Virginie
V
Santoni
Véronique
V
Martin-Laurent
Fabrice
F
Güçlü
Josette
J
Vinh
Joëlle
J
Heyes
Julian
J
Franck
Katja I
KI
Schäffner
Anton R
AR
Bouchez
David
D
Maurel
Christophe
C
D000595:Amino Acid Sequence; D020346:Aquaporins / Q000235:genetics* / Q000502:physiology; D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D007473:Ion Channels / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D018526:Plant Transpiration; D020033:Protein Isoforms / Q000235:genetics / Q000502:physiology; D017386:Sequence Homology, Amino Acid; D014867:Water / Q000378:metabolism*
D020346:Aquaporins; D029681:Arabidopsis Proteins; D007473:Ion Channels; D010940:Plant Proteins; D020033:Protein Isoforms; C110065:major intrinsic protein, plant; C491680:plasma membrane intrinsic protein 2 Arabidopsis; D014867:Water