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J. Biol. Chem., Vol. 282, Issue 1, 486-494, January 5, 2007

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Increased Functional Diversity of Plant K⁺ Channels by Preferential Heteromerization of the Shaker-like Subunits AKT2 and KAT2^*

From the Laboratoire de Biochimie et Physiologie Moléculaire des Plantes, UMR 5004 Agro-Montpellier/Centre National de la Recherche Scientifique/Institut National de la Recherche Agronomique/Université Montpellier II, Place Viala, 34060 Montpellier Cedex 1, France

Assembly of plant Shaker subunits as heterotetramers, increasing channel functional diversity, has been reported. Here we focus on a new interaction, between AKT2 and KAT2 subunits. The assembly as AKT2/KAT2 heterotetramers is demonstrated by (i) a strong signal in two-hybrid tests with intracytoplasmic C-terminal regions, (ii) the effect of KAT2 on AKT2 subunit targeting in tobacco cells, (iii) the complete inhibition of AKT2 currents by co-expression with a dominant-negative KAT2 subunit in Xenopus oocytes, and reciprocally, and (iv) the appearance, upon co-expression of wild-type AKT2 and KAT2 subunits, of new channel functional properties that cannot be explained by the co-existence of two kinds of homotetrameric channels. In particular, the instantaneous current, characteristic of AKT2, displayed new functional features when compared with those of AKT2 homotetramers: activation by external acidification (instead of inhibition) and weak inhibition by calcium. Single channel current measurements in oocytes co-expressing AKT2 and KAT2 revealed a strong preference for incorporation of subunits into heteromultimers and a diversity of individual channels. In planta, these new channels, which may undergo specific regulations, are likely to be formed in guard cells and in the phloem, where they could participate in the control of membrane potential and potassium fluxes.

Received for publication, August 9, 2006 , and in revised form, October 13, 2006.

^* This work was supported by grants from the programs "Toxicologie Nucléaire Environnementale - Transporters" and GABI-Génoplante "Functional genomics of membrane transporters." The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ Present address: Universität Potsdam, Institut für Biochemie und Biologie, Karl-Liebknecht-Str. 24/25, Haus 20, D-14476 Potsdam-Golm, Germany.

² To whom correspondence should be addressed: Biochimie et Physiologie Moléculaire des Plantes, INRA, Place Viala, F-34060 Montpellier cedex 1, France. Tel.: 33-499-612-565; Fax: 33-467-525-737; E-mail: cherel{at}ensam.inra.fr.

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