The CBL-Interacting Protein Kinase CIPK23 Regulates HAK5-Mediated High-Affinity K+ Uptake in Arabidopsis Roots

Plant Physiol. 2015 Dec;169(4):2863-73. doi: 10.1104/pp.15.01401. Epub 2015 Oct 16.

Abstract

Plant growth and development requires efficient acquisition of essential elements. Potassium (K(+)) is an important macronutrient present in the soil solution at a wide range of concentrations. Regulation of the K(+) uptake systems in the roots is essential to secure K(+) supply. It has been shown in Arabidopsis (Arabidopsis thaliana) that when the external K(+) concentration is very low (<10 µm), K(+) nutrition depends exclusively on the high-affinity K(+) transporter5 (HAK5). Low-K(+)-induced transcriptional activation of the gene encoding HAK5 has been previously reported. Here, we show the posttranscriptional regulation of HAK5 transport activity by phosphorylation. Expression in a heterologous system showed that the Ca(2+) sensors calcineurin B-like (CBL1), CBL8, CBL9, and CBL10, together with CBL-interacting protein kinase23 (CIPK23), activated HAK5 in vivo. This activation produced an increase in the affinity and the Vmax of K(+) transport. In vitro experiments show that the N terminus of HAK5 is phosphorylated by CIPK23. This supports the idea that phosphorylation of HAK5 induces a conformational change that increases its affinity for K(+). Experiments of K(+) (Rb(+)) uptake and growth measurements in low-K(+) medium with Arabidopsis single mutants hak5, akt1, and cipk23, double mutants hak5 akt1, hak5 cipk23, and akt1 cipk23, and the triple mutant hak5 akt1 cipk23 confirmed the regulatory role of CIPK23 in planta.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis / genetics
  • Arabidopsis / metabolism*
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism*
  • Binding, Competitive
  • Calcium-Binding Proteins / genetics
  • Calcium-Binding Proteins / metabolism
  • Ion Transport
  • Kinetics
  • Mutation
  • Phosphorylation
  • Plant Roots / genetics
  • Plant Roots / metabolism*
  • Potassium / metabolism*
  • Potassium-Hydrogen Antiporters / genetics
  • Potassium-Hydrogen Antiporters / metabolism*
  • Protein Binding
  • Protein Serine-Threonine Kinases / genetics
  • Protein Serine-Threonine Kinases / metabolism*
  • Rubidium / metabolism
  • Two-Hybrid System Techniques

Substances

  • Arabidopsis Proteins
  • CBL10 protein, Arabidopsis
  • CBL9 protein, Arabidopsis
  • Calcium-Binding Proteins
  • Potassium-Hydrogen Antiporters
  • calcineurin B-like protein 1, Arabidopsis
  • potassium transporter, Arabidopsis
  • CIPK23 protein, Arabidopsis
  • Protein Serine-Threonine Kinases
  • Rubidium
  • Potassium