AtKC1, a conditionally targeted Shaker-type subunit, regulates the activity of plant K+ channels

Authors

  • Geoffrey Duby,

    Search for more papers by this author
    • Contributed equally to this work.

    • Present address: Unité de Biochimie Physiologique, Institut des Sciences de la Vie, Catholic University of Louvain, Croix du Sud, 5-15, B-1348 Louvain-la-Neuve, Belgium.

  • Eric Hosy,

    Search for more papers by this author
    • Contributed equally to this work.

    • §

      Present address: Department of Neuroscience, Erasmus MC, PO Box 2040, 3000 CA, Rotterdam, The Netherlands.

  • Cécile Fizames,

    1. Biochimie et Physiologie Moléculaire des plantes, CNRS(UMR-5004)-INRA-SupAgro-UM2, 2 place Viala, F-34060 Montpellier cedex 1, France
    Search for more papers by this author
  • Carine Alcon,

    1. Biochimie et Physiologie Moléculaire des plantes, CNRS(UMR-5004)-INRA-SupAgro-UM2, 2 place Viala, F-34060 Montpellier cedex 1, France
    Search for more papers by this author
  • Alex Costa,

    Search for more papers by this author
    • Present address: Department of Biology, University of Padova, Viale G. Colombo 3, 35131 Padova, Italy.

  • Hervé Sentenac,

    1. Biochimie et Physiologie Moléculaire des plantes, CNRS(UMR-5004)-INRA-SupAgro-UM2, 2 place Viala, F-34060 Montpellier cedex 1, France
    Search for more papers by this author
  • Jean-Baptiste Thibaud

    Corresponding author
      (fax +33 499 612 930; e-mail thibaud@supagro.inra.fr).
    Search for more papers by this author

(fax +33 499 612 930; e-mail thibaud@supagro.inra.fr).

Summary

Amongst the nine voltage-gated K+ channel (Kv) subunits expressed in Arabidopsis, AtKC1 does not seem to form functional Kv channels on its own, and is therefore said to be silent. It has been proposed to be a regulatory subunit, and to significantly influence the functional properties of heteromeric channels in which it participates, along with other Kv channel subunits. The mechanisms underlying these properties of AtKC1 remain unknown. Here, the transient (co-)expression of AtKC1, AKT1 and/or KAT1 genes was obtained in tobacco mesophyll protoplasts, which lack endogenous inward Kv channel activity. Our experimental conditions allowed both localization of expressed polypeptides (GFP-tagging) and recording of heterologously expressed Kv channel activity (untagged polypeptides). It is shown that AtKC1 remains in the endoplasmic reticulum unless it is co-expressed with AKT1. In these conditions heteromeric AtKC1-AKT1 channels are obtained, and display functional properties different from those of homomeric AKT1 channels in the same context. In particular, the activation threshold voltage of the former channels is more negative than that of the latter ones. Also, it is proposed that AtKC1-AKT1 heterodimers are preferred to AKT1-AKT1 homodimers during the process of tetramer assembly. Similar results are obtained upon co-expression of AtKC1 with KAT1. The whole set of data provides evidence that AtKC1 is a conditionally-targeted Kv subunit, which probably downregulates the physiological activity of other Kv channel subunits in Arabidopsis.

Ancillary