An Extensive Survey of CK2 α and β Subunits in Arabidopsis: Multiple Isoforms Exhibit Differential Subcellular Localization

Abstract

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 alpha and beta subunits. We found four alpha subunit and four beta 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 alpha subunit harboring a putative chloroplastic destination peptide (alphacp), 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 alpha subunits are localized in the nucleus, with the exception of alphacp, which is only found in the chloroplasts. On the other hand, beta 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 CK2beta 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 CK2beta. 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.

The Rice CK2 Kinase Regulates Trafficking of Phosphate Transporters in Response to Phosphate Levels

“…To test this hypothesis, we examined the subcellular localization of CK2a3 and CK2b3. A z-stack image of confocal sections showed that both subunits localized in the ER (Supplemental Figure 1) as well as in the nucleus, which is consistent with a previously reported site of CK2 localization (Salinas et al, 2006).…”

“…The human genome has two genes encoding catalytic a-or a9-subunits and only one for the regulatory b-subunit (Wirkner et al, 1998;Ackermann et al, 2005), whereas plant genomes frequently have multigene families that encode each subunit (Espunya et al, 2005;Salinas et al, 2006). For example, four and two genes in rice encode CK2a and CK2b, respectively.…”

Phosphorylation by CK2 Enhances the Rapid Light-induced Degradation of Phytochrome Interacting Factor 1 in Arabidopsis

“…Relatively weak phosphorylation by the catalytic ␣ subunit and strong stimulation by the regulatory ␤ subunit might provide plants with enhanced regulatory power to modulate PIF1 activity in vivo. Moreover, CK2 subunit genes are differentially expressed in different tissues (39), suggesting that PIF1 might also be regulated in a tissue-specific manner.…”

“…The CK2 holoenzyme consists of two catalytic ␣ and two regulatory ␤ subunits. The Arabidopsis genome has four ␣ subunit and four ␤ subunit genes (39). Various members of both the ␣ and ␤ subunit families have been shown to be localized in the cytoplasm, nucleus, and also in chloroplasts (39).…”

“…The Arabidopsis genome has four ␣ subunit and four ␤ subunit genes (39). Various members of both the ␣ and ␤ subunit families have been shown to be localized in the cytoplasm, nucleus, and also in chloroplasts (39). A CK2-like activity has been shown to phosphorylate HY5, a positively acting component in a phy signaling pathway (34).…”