Calcium-dependent modulation and plasma membrane targeting of the AKT2 potassium channel by the CBL4/CIPK6 calcium sensor/protein kinase complex

Abstract

Potassium (K +)channel function is fundamental to many physiological processes. However, components and mechanisms regulating the activity of plant K + channels remain poorly understood. Here, we show that the calcium (Ca 2+ ) sensor CBL4 together with the interacting protein kinase CIPK6 modulates the activity and plasma membrane (PM) targeting of the K + channel AKT2 from Arabidopsis thaliana by mediating translocation of AKT2 to the PM in plant cells and enhancing AKT2 activity in oocytes. Accordingly, akt2, cbl4 and cipk6 mutants share similar developmental and delayed flowering phenotypes. Moreover, the isolated regulatory C-terminal domain of CIPK6 is sufficient for mediating CBL4-and Ca 2+-dependent channel translocation from the endoplasmic reticulum membrane to the PM by a novel targeting pathway that is dependent on dual lipid modifications of CBL4 by myristoylation and palmitoylation. Thus, we describe a critical mechanism of ion-channel regulation where a Ca 2+ sensor modulates K + channel activity by promoting a kinase interaction-dependent but phosphorylation-independent translocation of the channel to the PM.

The Tomato Calcium Sensor Cbl10 and Its Interacting Protein Kinase Cipk6 Define a Signaling Pathway in Plant Immunity

“…Arabidopsis CIPK6, CBL10, and orthologs have been shown to participate in different processes like salt stress tolerance, development, regulation of potassium channel AKT2 activity or modulation, or abscisic acid signaling Quan et al, 2007;Tripathi et al, 2009;Held et al, 2011;Chen et al, 2012;Ren et al, 2013). We did not observe any abnormal growth or development in N. benthamiana or tomato plants silenced for either Cbl10, Cipk6, or both, growing under standard greenhouse conditions.…”

Lighting the Way to Protein-Protein Interactions: Recommendations on Best Practices for Bimolecular Fluorescence Complementation Analyses

“…If the subcellular localization of the BiFC complexes is to be reliably determined, coexpression of a well characterized marker protein fused to a different, compatible FP should be performed to assess colocalization with the BiFC signal. Colocalization and fluorescence intensities can be determined by fluorescence intensity line-scan or scatterplot analyses (Held et al, 2011;Offenborn et al, 2015).…”

Ca2+-Dependent Protein Kinase11 and 24 Modulate the Activity of the Inward Rectifying K+ Channels inArabidopsisPollen Tubes

“…Based on the observation that Ca 2+ is known to regulate the activity of ion channels in many other physiological processes, Ca 2+ and its downstream components are assumed to play crucial roles in modulating ion channel activity during pollen tube growth. The activity or membrane localization of Shaker K + channel is modulated by calcineurin B-like proteins (CBLs) and CBL-interacting protein kinases (CIPKs), which plays important roles in K + uptake and distribution (Xu et al, 2006;Held et al, 2011). In guard cells, Ca 2+ signals can be transduced from some CDPKs or other Ca 2+ sensor proteins to various types of ion channels, such as K + in channels, nonselective Ca 2+ -permeable channels, and S-type anion channels, to regulate stomatal movements (Schroeder and Hagiwara, 1989;Li et al, 1998;Berkowitz et al, 2000;Mori et al, 2006;Geiger et al, 2010;Zou et al, 2010).…”