Calcineurin B‐like protein CBL 10 directly interacts with AKT 1 and modulates K + homeostasis in Arabidopsis

Potassium transporters and channels play crucial roles in K + uptake and translocation in plant cells. These roles are essential for plant growth and development. AKT 1 is an important K + channel in Arabidopsis roots that is involved in K + uptake. It is known that AKT 1 is activated by a protein kinase CIPK 23 interacting with two calcineurin B‐like proteins CBL 1/ CBL 9. The present study showed that another calcineurin B‐like protein ( CBL 10) may also regulate AKT 1 activity. The CBL 10 ‐over‐expressing lines showed a phenotype as sensitive as that of the akt1 mutant under low‐K + conditions. In addition, the K + content of both CBL 10 ‐over‐expressing lines and akt1 mutant plants were significantly reduced compared with wild‐type plants. Moreover, CBL 10 directly interacted with AKT 1, as verified in yeast two‐hybrid , Bi FC and co‐immunoprecipitation experiments. The results of electrophysiological analysis in both Xenopus oocytes and Arabidopsis root cell protoplasts demonstrated that CBL 10 impairs AKT 1‐mediated inward K + currents. Furthermore, the results from the yeast two‐hybrid competition assay indicated that CBL 10 may compete with CIPK 23 for binding to AKT 1 and negatively modulate AKT 1 activity. The present study revealed a CBL ‐interacting protein kinase‐independent regulatory mechanism of calcineurin B‐like proteins in which CBL 10 directly regulates AKT 1 activity and affects ion homeostasis in plant cells.