Functional analysis of AtHKT1 in Arabidopsis shows that Na+ recirculation by the phloem is crucial for salt tolerance

• Published in: The EMBO journal Vol. 22; no. 9; pp. 2004 - 2014
• Main Authors: Berthomieu, Pierre, Conéjéro, Geneviève, Nublat, Aurélie, Brackenbury, William J, Lambert, Cécile, Savio, Cristina, Uozumi, Nobuyuki, Oiki, Shigetoshi, Yamada, Katsuyuki, Cellier, Françoise, Gosti, Françoise, Simonneau, Thierry, Essah, Pauline A, Tester, Mark, Véry, Anne-Aliénor, Sentenac, Hervé, Casse, Francine
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01-05-2003; Blackwell Publishing Ltd; EMBO Press; Oxford University Press
• Subjects: Adaptation, Physiological - genetics; Amino Acid Sequence; Animals; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis - physiology; Arabidopsis Proteins - genetics; Base Sequence; Cation Transport Proteins - genetics; Cloning; DNA Primers; DNA, Complementary; Life Sciences; Molecular Sequence Data; Mutation; Na+ exclusion; Na+ transport; phloem; Plant Proteins; Plants, Genetically Modified; positional cloning; Roots; Salt tolerance; Sequence Homology, Amino Acid; Shoots; Sodium - metabolism; Sodium chloride; Sodium Chloride - metabolism; Symporters; Vegetal Biology; Xenopus; BETA GLUCURONIDASE; TOLERANCE AU SOL; SALINITE DU SOL
• ISSN: 0261-4189; 1460-2075; 1460-2075
• DOI: 10.1093/emboj/cdg207

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.