A Survey of Chloroplast Protein Kinases and Phosphatases in Arabidopsis thaliana

I Schliebner,J Zuhlke,A Dietzmann,D Leister,M Pribil

doi:10.2174/138920208784340740

Abstract

Protein phosphorylation is a major mode of regulation of metabolism, gene expression and cell architecture. In chloroplasts, reversible phosphorylation of proteins is known to regulate a number of prominent processes, for instance photosynthesis, gene expression and starch metabolism. The complements of the involved chloroplast protein kinases (cpPKs) and phosphatases (cpPPs) are largely unknown, except 6 proteins (4 cpPKs and 2 cpPPs) which have been experimentally identified so far. We employed combinations of programs predicting N-terminal chloroplast transit peptides (cTPs) to identify 45 tentative cpPKs and 21 tentative cpPPs. However, test sets of 9 tentative cpPKs and 13 tentative cpPPs contain only 2 and 7 genuine cpPKs and cpPPs, respectively, based on experimental subcellular localization of their N-termini fused to the reporter protein RFP. Taken together, the set of enzymes known to be involved in the reversible phosphorylation of chloroplast proteins in A. thaliana comprises altogether now 6 cpPKs and 9 cpPPs, the function of which needs to be determined in future by functional genomics approaches. This includes the calcium-regulated PK CIPK13 which we found to be located in the chloroplast, indicating that calcium-dependent signal transduction pathways also operate in this organelle.

Highlights

Phosphorylation of amino acid side chains can modulate the conformation, activity, localization and stability of proteins, and around one-third of all eukaryotic proteins are thought to be reversibly phosphorylated [1]
Test sets of 9 tentative chloroplast protein kinases (cpPKs) and 13 tentative cpPPs contain only 2 and 7 genuine cpPKs and cpPPs, respectively, based on experimental subcellular localization of their N-termini fused to the reporter protein redfluorescent protein (RFP)
The set of enzymes known to be involved in the reversible phosphorylation of chloroplast proteins in A. thaliana comprises altogether 6 cpPKs and 9 cpPPs, the function of which needs to be determined in future by functional genomics approaches

Summary

Introduction

Phosphorylation of amino acid side chains can modulate the conformation, activity, localization and stability of proteins, and around one-third of all eukaryotic proteins are thought to be reversibly phosphorylated [1]. The complements of the involved chloroplast protein kinases (cpPKs) and phosphatases (cpPPs) are largely unknown, except 6 proteins (4 cpPKs and 2 cpPPs) which have been experimentally identified so far. The set of enzymes known to be involved in the reversible phosphorylation of chloroplast proteins in A. thaliana comprises altogether 6 cpPKs and 9 cpPPs, the function of which needs to be determined in future by functional genomics approaches.

Results

Conclusion