ZMK1 Is Involved in K+ Uptake and Regulated by Protein Kinase ZmCIPK23 in Zea mays

Abstract

Potassium (K⁺) is one of essential mineral elements for plant growth and development. K⁺ channels, especially AKT1-like channels, play crucial roles in K⁺ uptake in plant roots. Maize is one of important crops; however, the K⁺ uptake mechanism in maize is little known. Here, we report the physiological functions of K⁺ channel ZMK1 in K⁺ uptake and homeostasis in maize. ZMK1 is a homolog of Arabidopsis AKT1 channel in maize, and mainly expressed in maize root. Yeast complementation experiments and electrophysiological characterization in Xenopus oocytes indicated that ZMK1 could mediate K⁺ uptake. ZMK1 rescued the low-K⁺-sensitive phenotype of akt1 mutant and enhanced K⁺ uptake in Arabidopsis. Overexpression of ZMK1 also significantly increased K⁺ uptake activity in maize, but led to an oversensitive phenotype. Similar to AKT1 regulation, the protein kinase ZmCIPK23 interacted with ZMK1 and phosphorylated the cytosolic region of ZMK1, activating ZMK1-mediated K⁺ uptake. ZmCIPK23 could also complement the low-K⁺-sensitive phenotype of Arabidopsis cipk23/lks1 mutant. These findings demonstrate that ZMK1 together with ZmCIPK23 plays important roles in K⁺ uptake and homeostasis in maize.

Keywords: K+ channel; K+ uptake; ZMK1; Zea mays; ZmCIPK23.