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DEVELOPMENT AND HORMONE ACTION

Arabidopsis Calcium-Dependent Protein Kinase AtCPK32 Interacts with ABF4, a Transcriptional Regulator of Abscisic Acid-Responsive Gene Expression, and Modulates Its Activity¹

Kumho Life and Environmental Science Laboratory, Gwangju 500–712, South Korea (H.C., H.-J.P., J.H.P., S.K., M.-Y.I., H.-H.S., S.Y.K.); and Department of Life Science, Pohang University of Science and Technology, Pohang, Kyungbuk 790–784, South Korea (Y.-W.K., I.H.)

The phytohormone abscisic acid (ABA) regulates stress-responsive gene expression during vegetative growth. The ABA regulation of many genes is mediated by a subfamily of basic leucine zipper class transcription factors referred to as ABFs (i.e. ABF1–ABF4), whose transcriptional activity is induced by ABA. Here we show that a calcium-dependent protein kinase is involved in the ABA-dependent activation process. We carried out yeast two-hybrid screens to identify regulatory components of ABF4 function and isolated AtCPK32 as an ABF4-interacting protein. AtCPK32 has autophosphorylation activity and can phosphorylate ABF4 in vitro. Mutational analysis indicated that serine-110 of ABF4, which is highly conserved among ABF family members, may be phosphorylated by AtCPK32. The serine-110 residue is essential for ABF4-AtCPK32 interaction, and transient expression assay revealed that it is also required for the normal transcriptional function of ABF4. The expression patterns and subcellular localization of AtCPK32 are similar to those of ABF4. Furthermore, its overexpression affects both ABA sensitivity and the expression of a number of ABF4-regulated genes. Together, our data demonstrate that AtCPK32 is an ABA signaling component that regulates the ABA-responsive gene expression via ABF4.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Soo Young Kim (sooykim{at}kkpc.com).

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.069757.

^* Corresponding author; e-mail sooykim{at}kkpc.com; fax 82–62–972–5085.

Received August 9, 2005; returned for revision September 30, 2005; accepted October 9, 2005.

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