Plant and Cell Physiology Advance Access originally published online on August 21, 2006
Plant and Cell Physiology 2006 47(9):1295-1308; doi:10.1093/pcp/pcj100
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An Extensive Survey of CK2 
and ß Subunits in Arabidopsis: Multiple Isoforms Exhibit Differential Subcellular Localization
1 Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, PO Box 114-D, Santiago, Chile
2 UMR CNRS 5096, Génome et Développement des Plantes, Université de Perpignan, France
* Corresponding author: E-mail, lholuigue{at}bio.puc.cl; Fax, +56-2-222 5515.
Casein kinase 2 (CK2) is a ubiquitous enzyme essential for the viability of eukaryotic cells. In the present work we analyzed the Arabidopsis thaliana genome in a search for the genes coding for all CK2 
and ß subunits. We found four subunit and four ß subunit genes. Expression analysis showed that all CK2 subunit genes are expressed in inflorescences, stems, leaves and roots. The level of expression of these genes is very similar, except for the one that codes for an subunit harboring a putative chloroplastic destination peptide (cp), which shows a slightly higher expression level in all tissues. Using transgenic plants and agroinfiltration, we have also characterized the subcellular localization of all proteins encoded by CK2 genes. Our results show that all subunits are localized in the nucleus, with the exception of cp, which is only found in the chloroplasts. On the other hand, ß subunits have a more diverse distribution, with some of them localizing both to the nucleus and to the cytosol, while others are exclusively located in one of these compartments. Remarkably, no CK2ß subunit was found in the chloroplasts. Finally, by directly measuring its activity, we have demonstrated that purified Arabidopsis chloroplasts have active CK2 that can be regulated by external addition of CK2ß. This study represents a complete survey of the CK2 gene family in Arabidopsis and the first step for future studies on CK2 cellular function in this species.
3 These authors contributed equally to this work.
(Received May 29, 2006; Accepted July 31, 2006)
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