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

Abstract

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.

Transcriptomic Analysis Reveals Calcium Regulation of Specific Promoter Motifs inArabidopsis

“…These transcription factors may therefore be regulated by [Ca 2+ ] c on a posttranslational level. In some cases, potential pathways for posttranslational regulation are already evident; for example, the Ca 2+ -binding protein CaM regulates CAMTAs, and ABF4 has been shown to interact with CPK32, one of the calciumdependant kinases (Choi et al, 2005). Future research effort should therefore be directed toward revealing the precise molecular pathways by which calcium regulates these transcription factors and their interaction with these motifs in target gene promoters.…”

DREB2C Interacts with ABF2, a bZIP Protein Regulating Abscisic Acid-Responsive Gene Expression, and Its Overexpression Affects Abscisic Acid Sensitivity

“…Overexpression of ABF3 or ABF4 in Arabidopsis (Arabidopsis thaliana), for instance, confers ABA hypersensitivity and drought tolerance (Kang et al, 2002;Kim et al, 2004aKim et al, , 2004c, whereas their knockout mutants are partially insensitive to ABA and susceptible to drought (Kim et al, 2004c;Finkelstein et al, 2005). Several studies indicate that the in vivo functions of ABFs/AREBs are modulated by various kinases (Choi et al, 2005;Furihata et al, 2006;Chae et al, 2007). ABFs/AREBs are highly homologous to ABI5 (Finkelstein and Lynch, 2000;Lopez-Molina and Chua, 2000), sunflower (Helianthus annuus) and Arabidopsis DPBFs (Kim et al, 1997;Kim and Thomas, 1998;Kim et al, 2002), and rice (Oryza sativa) TRAB1 (Hobo et al, 1999b).…”

Seasonal Abscisic Acid Signal and a Basic Leucine Zipper Transcription Factor, DkbZIP5, Regulate Proanthocyanidin Biosynthesis in Persimmon Fruit

“…Among them, one of the major TFs involved in ABA signaling is the basic leucine zipper (bZIP) class TF (Jakoby et al, 2002). bZIP TFs binding ACGTG-containing motifs, which are known as ABA-responsive elements (ABREs), constitute the ABF/AREB/ABI5 subfamily (Choi et al, 2000(Choi et al, , 2005Uno et al, 2000;Wasilewska et al, 2008). bZIP TFs have a regulatory function in ABA and/or stress responses.…”