Potassium nutrient status drives posttranslational regulation of a low-K response network in Arabidopsis

Potassium is essential for plant growth and development. Here the authors present evidence that plants respond to low potassium availability by modulating the abundance and phosphorylation status of proteins in CBL-CIPK-channel modules. Under low-potassium (K+) stress, a Ca2+ signaling network consisting of calcineurin B-like proteins (CBLs) and CBL-interacting kinases (CIPKs) play essential roles. Specifically, the plasma membrane CBL1/9-CIPK pathway and the tonoplast CBL2/3-CIPK pathway promotes K+ uptake and remobilization, respectively, by activating a series of K+ channels. While the dual CBL-CIPK pathways enable plants to cope with low-K+ stress, little is known about the early events that link external K+ levels to the CBL-CIPK proteins. Here we show that K+ status regulates the protein abundance and phosphorylation of the CBL-CIPK-channel modules. Further analysis revealed low K+-induced activation of VM-CBL2/3 happened earlier and was required for full activation of PM-CBL1/9 pathway. Moreover, we identified CIPK9/23 kinases to be responsible for phosphorylation of CBL1/9/2/3 in plant response to low-K+ stress and the HAB1/ABI1/ABI2/PP2CA phosphatases to be responsible for CBL2/3-CIPK9 dephosphorylation upon K+-repletion. Further genetic analysis showed that HAB1/ABI1/ABI2/PP2CA phosphatases are negative regulators for plant growth under low-K+, countering the CBL-CIPK network in plant response and adaptation to low-K+ stress.

Automated summary

Plants respond to low potassium levels by modulating the abundance and phosphorylation of proteins in CBL-CIPK-channel modules, with the CBL1/9-CIPK pathway promoting potassium uptake and the CBL2/3-CIPK pathway facilitating potassium remobilization. The phosphatases HAB1/ABI1/ABI2/PP2CA act as negative regulators of plant growth under low potassium conditions.