A Protein Kinase, Interacting with Two Calcineurin B-like Proteins, Regulates K+ Transporter AKT1 in Arabidopsis

Abstract

Potassium is an essential mineral element for plant growth and development. Although it is known that plants absorb and transport K+ through membrane transporters, it remains unclear how these transporters are regulated. Here we show that the protein kinase CIPK23, encoded by the LKS1 gene, regulates K+ uptake under low-K+ conditions. Lesion of LKS1 significantly reduced K+ uptake and caused leaf chlorosis and growth inhibition, whereas overexpression of LKS1 significantly enhanced K+ uptake and tolerance to low K+. We demonstrate that CIPK23 directly phosphorylates the K+ transporter AKT1 and further find that CIPK23 is activated by the binding of two calcineurin B-like proteins, CBL1 and CBL9. We propose a model in which the CBL1/9-CIPK23 pathway ensures activation of AKT1 and enhanced K+ uptake under low-K+ conditions.

NRT1.5/NPF7.3 Functions as a Proton-Coupled H+/K+ Antiporter for K+ Loading into the Xylem in Arabidopsis

“…The lks2 mutant shows a similar low-K + -sensitive phenotype to the lks1/cipk23 mutant reported previously (Xu et al, 2006;Supplemental Figure 3A). However, they are different in K + content.…”

“…In lks2, K + was accumulated in the root but reduced in the shoot ( Figure 1B). In lks1, K + content was reduced in both root and shoot (Xu et al, 2006). In addition, CIPK23 transcript was not significantly altered in the lks2 mutant (Supplemental Figure 3B).…”

“…Possibly, NRT1.5 requires some special partner components or regulators for functional NO 3 2 transport in oocytes. For example, the K + transport activity of the AKT1 channel requires coexpression of protein kinase CIPK23 and calcium binding proteins CBL1/9 in oocytes (Xu et al, 2006). Nonetheless, NRT1.5 plays an essential role in coordinating K + /NO 3 2 transport in xylem under K + -limited conditions.…”

“…The lks2 mutant was isolated from EMS-mutagenized M2 seeds of wildtype Arabidopsis thaliana (Columbia ecotype, Col-0) as described previously (Xu et al, 2006). Arabidopsis T-DNA insertion lines, including nrt1.5 K + efflux activities of the yeast mutant strain ANT5 (ena1-4D and nha1D) expressing NRT1.5 or NRT1.5 G209E .…”

The role of calcium sensor-interacting protein kinases in plant adaptation to potassium-deficiency: new answers to old questions

“…Wu and colleagues [4] and Luan and colleagues [5] identified a calcineurin B-like protein (CBL)-interacting protein kinase CIPK23 and two upstream elements, CBL1 and CBL9, as regulators of AKT1. AKT1 is a Shaker-type voltage-gated ion channel that mediates the uptake of K + at hyperpolarized membrane voltages [2].…”