A protein phosphorylation/dephosphorylation network regulates a plant potassium channel

Abstract

Potassium (K ؉ ) is an essential nutrient for plant growth and development. Plants often adapt to low K ؉ conditions by increasing their K ؉ uptake capability. Recent studies have led to the identification of a calcium signaling pathway that enables plants to act in this capacity. Calcium is linked to two calcineurin B-like calcium sensors (CBLs) and a target kinase (CBL-interacting protein kinase 23 or CIPK23) that, in turn, appears to phosphorylate and activate the potassium channel, Arabidopsis K ؉ transporter 1 (AKT1), responsible for K ؉ uptake in roots. Here, we report evidence that this regulatory mechanism is more elaborate than earlier envisaged. The recently described pathway is part of an extensive network whereby several CBLs interact with multiple CIPKs in the activation of the potassium channel, AKT1. The physical interactions among the CBL, CIPK, and AKT1 components provide a mechanism for specifying the members of the CBL and CIPK families functional in AKT1 regulation. The interaction between the CIPKs and AKT1 was found to involve the kinase domain of the CIPK component and the ankyrin repeat domain of the channel. Furthermore, we identified a 2C-type protein phosphatase that physically interacts and inactivates the AKT1 channel.

AtKC1 and CIPK23 Synergistically Modulate AKT1-Mediated Low-Potassium Stress Responses in Arabidopsis

“…A similar mechanism was also identified in other plant species (for review, see Véry et al, 2014), such as rice (Oryza sativa; Li et al, 2014). Subsequently, a 2C-type protein phosphatase, AIP1, was identified that interacts with and inactivates the AKT1 channel (Lee et al, 2007). Therefore, a phosphorylation/ dephosphorylation regulatory mechanism for the AKT1 channel was proposed (Lee et al, 2007).…”

“…Subsequently, a 2C-type protein phosphatase, AIP1, was identified that interacts with and inactivates the AKT1 channel (Lee et al, 2007). Therefore, a phosphorylation/ dephosphorylation regulatory mechanism for the AKT1 channel was proposed (Lee et al, 2007). In addition, the Ca 2+ -binding protein CBL10 interacts directly with AKT1 and negatively modulates AKT1 activity by competing with CIPK23 to bind AKT1 .…”

Structural basis of the regulatory mechanism of the plant CIPK family of protein kinases controlling ion homeostasis and abiotic stress

“…CIPKs include an N-terminal kinase catalytic domain followed by a characteristic self-inhibitory motif known as FISL or NAF motif (hereinafter NAF, Pfam no. PF03822) (1, 6) and a protein phosphatase 2C binding domain designated as PPI (11,18,19). The NAF motif directly interacts with the catalytic domain and inhibits the kinase activity.…”

Identification of regions responsible for the function of the plant K+ channels KAT1 and AKT2 in Saccharomyces cerevisiae and Xenopus laevis oocytes

“…The ankyrin domain, which is present in AKT2 but not in KAT1, is proposed to be important for the interaction of the channel with kinases. 29 Insertion of this domain possibly resulted in a distortion of the proper interaction between cNBD and K HA /K T and in the aberration of functional channel assembly in S. cerevisiae and oocytes.…”