The calcineurin ß-like interacting protein kinase CIPK25 regulates potassium homeostasis under low oxygen in Arabidopsis.

Hypoxic conditions often arise from waterlogging and flooding, affecting several aspects of plant metabolism, including the uptake of nutrients. We identified a member of the CALCINEURIN ß-LIKE INTERACTING PROTEIN KINASE (CIPK) family in Arabidopsis, CIPK25, which is induced in the root endodermis under low-oxygen conditions. A cipk25 mutant exhibited higher sensitivity to anoxia in conditions of potassium limitation, suggesting that this kinase is involved in the regulation of potassium uptake. Interestingly, we found that CIPK25 interacts with AKT1, the major inward rectifying potassium channel in Arabidopsis. Under anoxic conditions, cipk25 mutant seedlings were unable to maintain potassium concentrations at wild-type levels, suggesting that CIPK25 likely plays a role in modulating potassium homeostasis under low-oxygen conditions. In addition, cipk25 and akt1 mutants share similar developmental defects under waterlogging, further supporting an interplay between CIPK25 and AKT1.

A calcineurin B-like protein participates in low oxygen signalling in rice.

Following the identification of the calcineurin B-like interacting protein kinase 15 (CIPK15), which is a regulator of starch degradation, the low O2 signal elicited during rice germination under submergence has been linked to the sugar sensing cascade and calcium (Ca2+) signalling. CIPK proteins are downstream effectors of calcineurin B-like proteins (CBLs), which act as Ca2+ sensors, whose role under low O2 has yet to be established. In the present study we describe CBL4 as a putative CIPK15 partner, transcriptionally activated under low O2 in rice coleoptiles. The transactivation of the rice embryo CBL4 transcript and CBL4 promoter was influenced by the Ca2+ blocker ruthenium red (RR). The bimolecular fluorescence complementation (BiFC) assay associated to fluorescence recovery after photobleaching (FRAP) analysis confirmed that CBL4 interacts with CIPK15. The CBL4-CIPK15 complex is localised in the cytoplasm and the plasma-membrane. Experiments in protoplasts showed a dampening of α-amylase 3 (RAMY3D) expression after CBL4 silencing by artificial miRNA. Our results suggest that under low O2, the Ca2+ sensor CBL4 interacts with CIPK15 to regulate RAMY3D expression in a Ca2+-dependent manner.