Regulation of Arabidopsis thaliana Calcineurin B-like Interacting Protein Kinases (CIPKs) by the Ubiquitin-Proteasome System

Abstract

Ubiquitin Proteasome System (UPS) regulates the abundance of proteins by first attaching ubiquitin molecules and then targeting the modified protein for degradation by the 26S proteasome. E3 ubiquitin ligases are the central enzymes of the UPS that is responsible for selecting substrates for ubiquitination. The Arabidopsis thaliana E3 Keep on Going (KEG) was shown to negatively regulate the activity of the stress hormone abscisic acid (ABA) by ubiquitinating components of the hormone signaling network, including Calcineurin B-Like Interacting Protein Kinase 26 (CIPK26). This work investigates the role of the UPS in regulating CIPK proteins, specifically CIPK3, CIPK8, CIPK20, and CIPK24. We examine ubiquitination and the proteasome-dependent degradation of the selected CIPKs in the plant cell by using transient protein expression systems. All the examined CIPKs were found to be ubiquitinated in plant cells. Interestingly, we found that all but CIPK24, which is stable, are targeted for degradation by 26S proteasome.