A protein phosphatase 2C, AP2C1, interacts with and negatively regulates the function of CIPK9 under potassium-deficient conditions in Arabidopsis

J Exp Bot. 2018 Jul 18;69(16):4003-4015. doi: 10.1093/jxb/ery182.

Abstract

Potassium (K+) is a major macronutrient required for plant growth. An adaptive mechanism to low-K+ conditions involves activation of the Ca2+ signaling network that consists of calcineurin B-like proteins (CBLs) and CBL-interacting kinases (CIPKs). The CBL-interacting protein kinase 9 (CIPK9) has previously been implicated in low-K+ responses in Arabidopsis thaliana. Here, we report a protein phosphatase 2C (PP2C), AP2C1, that interacts with CIPK9. Fluorescence resonance energy transfer (FRET), bimolecular fluorescence complementation (BiFC), and co-localization analyses revealed that CIPK9 and AP2C1 interact in the cytoplasm. AP2C1 dephosphorylates the auto-phosphorylated form of CIPK9 in vitro, presenting a regulatory mechanism for CIPK9 function. Furthermore, genetic and molecular analyses revealed that ap2c1 null mutants (ap2c1-1 and ap2c1-2) are tolerant to low-K+ conditions, retain higher K+ content, and show higher expression of K+-deficiency related genes contrary to cipk9 mutants (cipk9-1 and cipk9-2). In contrast, transgenic plants overexpressing AP2C1 were sensitive to low-K+ conditions. Thus, this study shows that AP2C1 and CIPK9 interact to regulate K+-deficiency responses in Arabidopsis. CIPK9 functions as positive regulator whereas AP2C1 acts as a negative regulator of Arabidopsis root growth and seedling development under low-K+ conditions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis / genetics
  • Arabidopsis / metabolism*
  • Arabidopsis Proteins / metabolism*
  • Homeostasis
  • Mutation
  • Phosphoprotein Phosphatases / metabolism*
  • Phosphorylation
  • Potassium / metabolism*
  • Protein Binding
  • Protein Serine-Threonine Kinases / metabolism*
  • Signal Transduction

Substances

  • Arabidopsis Proteins
  • CIPK9 protein, Arabidopsis
  • Protein Serine-Threonine Kinases
  • AP2C1 protein, Arabidopsis
  • Phosphoprotein Phosphatases
  • Potassium