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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

Diversity in Expression Patterns and Functional Properties in the Rice HKT Transporter Family^1,[W]

Biochimie et Physiologie Moléculaire des Plantes, UMR 5004 CNRS/INRA/SupAgro-M/UM2, Campus SupAgro-M/INRA, 34060 Montpellier cedex 1, France (M.J., S.E., D.M., C.F., G.C., H.S., A.-A.V.); Laboratoire d'Adaptation des Plantes aux Stress Abiotiques, Centre de Biotechnologie de Borj-Cédria, Hammam-Lif 2050, Tunisia (M.J., C.A.); UMR Développement et Amélioration des Plantes, Centre de Coopération Internationale en Recherche Agronomique pour le Développement/INRA/SupAgro-M/UM2, 34398 Montpellier cedex 5, France (S.E., D.M., J.-L.V., E.G.); and Departamento de Biotecnología, Universidad Politécnica de Madrid, 28040 Madrid, Spain (A.R.-N.)

Plant growth under low K⁺ availability or salt stress requires tight control of K⁺ and Na⁺ uptake, long-distance transport, and accumulation. The family of membrane transporters named HKT (for High-Affinity K⁺ Transporters), permeable either to K⁺ and Na⁺ or to Na⁺ only, is thought to play major roles in these functions. Whereas Arabidopsis (Arabidopsis thaliana) possesses a single HKT transporter, involved in Na⁺ transport in vascular tissues, a larger number of HKT transporters are present in rice (Oryza sativa) as well as in other monocots. Here, we report on the expression patterns and functional properties of three rice HKT transporters, OsHKT1;1, OsHKT1;3, and OsHKT2;1. In situ hybridization experiments revealed overlapping but distinctive and complex expression patterns, wider than expected for such a transporter type, including vascular tissues and root periphery but also new locations, such as osmocontractile leaf bulliform cells (involved in leaf folding). Functional analyses in Xenopus laevis oocytes revealed striking diversity. OsHKT1;1 and OsHKT1;3, shown to be permeable to Na⁺ only, are strongly different in terms of affinity for this cation and direction of transport (inward only or reversible). OsHKT2;1 displays diverse permeation modes, Na⁺-K⁺ symport, Na⁺ uniport, or inhibited states, depending on external Na⁺ and K⁺ concentrations within the physiological concentration range. The whole set of data indicates that HKT transporters fulfill distinctive roles at the whole plant level in rice, each system playing diverse roles in different cell types. Such a large diversity within the HKT transporter family might be central to the regulation of K⁺ and Na⁺ accumulation in monocots.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Anne-Aliénor Véry (very{at}supagro.inra.fr).

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.109.138008

^* Corresponding author; e-mail very{at}supagro.inra.fr.

Received March 3, 2009; accepted May 23, 2009; published May 29, 2009.