Two Ca2+-dependent protein kinases (cpks) oppositely regulate a ubiquitous k+ channel in arabidopsis thaliana

In plant cells, as regards both the electrical polarization of the plasma-membrane and the osmotic homeostasis, voltage-gated K + channels participate in transduction chains, often downstream Ca 2+ signals. Thus, worth considering is, among the range of post-translational modifications, that potentially regulate their activity, the phosphorylation of these so-called Shaker channels by Ca 2+ -dependent protein kinases (CPKs). We investigated the interactions between these two families of proteins by a combination of techniques: heterologous expression in Xenopus oocytes followed by electrophysiology recordings, in planta interaction by FRET-FLIM imaging, in vitro phosphorylation study using channel-derived peptide arrays, looking for overlap of expression patterns and characterization of gain- or loss-of-function mutants. Here we have identified several CPKs targeting and regulating the Shaker channel activities. Interestingly, we found that CPK13, a Ca 2+ -insensitive CPK, and CPK6, a Ca 2+ -strictly dependent CPK, respectively inhibits and activates the same Shaker channel, KAT2. In the context of (i) the large expression pattern of KAT2 (e.g. in leaf vasculature and in guard cells) and (ii) the documented ability of KAT2 to form heteromeric channels with the Shaker sub‐units AKT2 and KAT1, we shall discuss the potential implication of KAT2 regulation by CPKs in phloem and stomata physiology.