Abstract
Root growth is a fundamental process in plants and assures nutrient and water uptake required for efficient photosynthesis and metabolism. Postembryonic development of roots is controlled by the functionality of the meristem. Several hormones and signaling molecules regulate the size of the meristem, and among them, auxins play a major role. Protein kinase CK2, along with the chaperone protein HSP90, has been found to be involved in the regulation of auxin transport. Here, we show that p23-1, a cochaperone of HSP90, is phosphorylated by CK2 in Arabidopsis. We identified Ser201 as the major CK2 target site in p23-1 and demonstrated that phosphorylation of this site is necessary for normal root development. Moreover, we shed light on the nature of CK2 in Arabidopsis, showing that the three catalytic isoforms, CK2 αA, αB and αC, are proteins of approximately 40 kDa. Our results increase knowledge of the connection among HSP90, p23-1 and CK2 in Arabidopsis, suggesting the existence of a possible common root development mechanism controlled by these signaling molecules.
Highlights
The protein kinase CK2 is a Ser/Thr protein kinase that is usually organized as a tetrameric complex composed of two catalytic (α) and two regulatory (β) subunits[5,6]
These results suggest a model of root growth regulation that involves HSP90 in controlling auxin transport through the interaction of both PIN and HSP90 with TWD1 (Twisted Dwarf 1)[21,27]
In an in-gel kinase assay (Fig. 2B), we found that Arabidopsis total protein extract contains only a single band that is able to phosphorylate p23-1
Summary
The protein kinase CK2 is a Ser/Thr protein kinase that is usually organized as a tetrameric complex composed of two catalytic (α) and two regulatory (β) subunits[5,6]. We tested the in vitro phosphorylation of the recombinant p23-1 and compared it with the already characterized p23-2 in a radioactive phosphorylation assay, using Arabidopsis total protein extract as the source of kinases.
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