Functional analysis of AtHKT1 in Arabidopsis shows that Na(+) recirculation by the phloem is crucial for salt tolerance.
Two allelic recessive mutations of Arabidopsis, sas2-1 and sas2-2, were identified as inducing sodium overaccumulation in shoots. The sas2 locus was found (by positional cloning) to correspond to the AtHKT1 gene. Expression in Xenopus oocytes revealed that the sas2-1 mutation did not affect the ionic selectivity of the transporter but strongly reduced the macro scopic (whole oocyte current) transport activity. In Arabidopsis, expression of AtHKT1 was shown to be restricted to the phloem tissues in all organs. The sas2-1 mutation strongly decreased Na(+) concentration in the phloem sap. It led to Na(+) overaccumulation in every aerial organ (except the stem), but to Na(+) underaccumulation in roots. The sas2 plants displayed increased sensitivity to NaCl, with reduced growth and even death under moderate salinity. The whole set of data indicates that AtHKT1 is involved in Na(+) recirculation from shoots to roots, probably by mediating Na(+) loading into the phloem sap in shoots and unloading in roots, this recirculation removing large amounts of Na(+) from the shoot and playing a crucial role in plant tolerance to salt.
Biochimie et Physiologie Moléculaire des Plantes, UMR 5004, ENSA M INRA CNRS UMII and UMR Agronomie Ecophysiologie des Plantes sous Stress Environnementaux, INRA ENSA.M, 34060 Montpellier Cedex 2, France. berthom@ensam.inra.fr
Pierre
P
Berthomieu
Geneviève
G
Conéjéro
Aurélie
A
Nublat
William J
WJ
Brackenbury
Cécile
C
Lambert
Cristina
C
Savio
Nobuyuki
N
Uozumi
Shigetoshi
S
Oiki
Katsuyuki
K
Yamada
Françoise
F
Cellier
Françoise
F
Gosti
Thierry
T
Simonneau
Pauline A
PA
Essah
Mark
M
Tester
Anne-Aliénor
AA
Véry
Hervé
H
Sentenac
Francine
F
Casse
D000222:Adaptation, Physiological / Q000235:genetics*; D000595:Amino Acid Sequence; D000818:Animals; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D029681:Arabidopsis Proteins / Q000235:genetics*; D001483:Base Sequence; D027682:Cation Transport Proteins / Q000235:genetics*; D017931:DNA Primers; D018076:DNA, Complementary; D008969:Molecular Sequence Data; D009154:Mutation; D010940:Plant Proteins; D030821:Plants, Genetically Modified; D017386:Sequence Homology, Amino Acid; D012964:Sodium / Q000378:metabolism*; D012965:Sodium Chloride / Q000378:metabolism*; D027981:Symporters; D014981:Xenopus
D029681:Arabidopsis Proteins; D027682:Cation Transport Proteins; D017931:DNA Primers; D018076:DNA, Complementary; C490286:HKT1 protein, Arabidopsis; C088864:HKT1 protein, plant; D010940:Plant Proteins; D027981:Symporters; D012965:Sodium Chloride; D012964:Sodium