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

Abstract

In Arabidopsis (Arabidopsis thaliana), the Shaker K + channel AKT1 conducts K + uptake in root cells, and its activity is regulated by CBL1/9-CIPK23 complexes as well as by the AtKC1 channel subunit. CIPK23 and AtKC1 are both involved in the AKT1-mediated low-K + (LK) response; however, the relationship between them remains unclear. In this study, we screened suppressors of low-K + sensitive [lks1 (cipk23)] and isolated the suppressor of lks1 (sls1) mutant, which suppressed the leaf chlorosis phenotype of lks1 under LK conditions. Map-based cloning revealed a point mutation in AtKC1 of sls1 that led to an amino acid substitution (G322D) in the S6 region of AtKC1. The G322D substitution generated a gain-of-function mutation, AtKC1 D , that enhanced K + uptake capacity and LK tolerance in Arabidopsis. Structural prediction suggested that glycine-322 is highly conserved in K + channels and may function as the gating hinge of plant Shaker K + channels. Electrophysiological analyses revealed that, compared with wild-type AtKC1, AtKC1 D showed enhanced inhibition of AKT1 activity and strongly reduced K + leakage through AKT1 under LK conditions. In addition, phenotype analysis revealed distinct phenotypes of lks1 and atkc1 mutants in different LK assays, but the lks1 atkc1 double mutant always showed a LK-sensitive phenotype similar to that of akt1. This study revealed a link between CIPK-mediated activation and AtKC1-mediated modification in AKT1 regulation. CIPK23 and AtKC1 exhibit distinct effects; however, they act synergistically and balance K + uptake/leakage to modulate AKT1-mediated LK responses in Arabidopsis.

Advances and current challenges in calcium signaling

“…An interesting emerging case of a multifunctional CIPK is provided by CIPK23, which appears to represent a key master regulator of plant nutrient sensing and acquisition. This kinase has been reported to function in potassium and nitrate as well as iron, magnesium and ammonium homeostasis (Geiger et al ., ; Ho et al ., ; Maierhofer et al ., ; Scherzer et al ., ; Wang et al ., ; Behera et al ., ; Straub et al ., ) (Fig. ).…”

The K+ channel KZM2 is involved in stomatal movement by modulating inward K+ currents in maize guard cells

“…In addition, a silent Shaker channel α‐subunit AtKC1 is also expressed in guard cells, and can assemble with these four channels forming heteromeric K + channels (Duby et al ., ; Wang et al ., ; Jeanguenin et al ., ). AtKC1 behaves as a general modulator of Shaker K in channels, reducing channel conductance and negatively shifting the activation threshold of these K in channels (Duby et al ., ; Wang et al ., , ; Jeanguenin et al ., ). In rice, the Shaker channel genes OsKAT2 and OsKAT3 are expressed in guard cells, and the silent OsKAT3 could interact with and negatively regulate OsKAT2 channel activity (Hwang et al ., ; Moon et al ., ).…”

Transcriptome Changes Induced by Different Potassium Levels in Banana Roots

“…In this study, it was predicted that KC1 interacted with CIPK23, TPK1 and KUP3 respectively, and CIPK23 also interacted with SOS1 and CBL4(SOS3) respectively ( Figure 6C). Given that the interaction between SOS1 and SOS3 [56], KC1 and CIPK23 [51,52], CBL4(SOS3) and CIPK6 [53] has been proved, thus the consistent expression and their interaction of SOS1, KC1, CIPK23, CBL4, CIPK6, KUP3, TPK1 in the network, provide new possible mechanisms for banana roots to response to potassium stress. In a word, the genes in profile 7 were mainly related to ion transport of potassium.…”

“…The results suggested that the CBL1/CBL9-CIPK23-AKT1 pathway was not involved in banana root system in response to potassium stress. AtKC1 is a K + channel regulatory subunit, which together with AtCIPK23, has been reported to coordinate the regulation of AtAKT1-mediated K + short stress response in Arabidopsis [51,52]. In addition, the CBL4/CIPK6 complex was revealed to modulating AKT2 activity in Arabidopsis [53].…”