Minisymposium 12:

Abs # 24003: A calcium sensor and its interacting protein kinase are global regulators of abscisic acid signaling in Arabidopsis

Presenter:	Zhu, Jian-Kang , jkzhu@ag.arizona.edu
Authors	Zhu, Jian-Kang  (A)   Guo, Yan  (A)   Stevenson, Rebecca  (A)
Affiliations:	(A): Department of Plant Sciences, University of Arizona
Web Site:	http://ag.arizona.edu/pls/zhulab

The phytohormone abscisic acid (ABA) triggers an osicillation in the cytosolic Ca²⁺ concentration, which is then perceived by unknown Ca²⁺ binding proteins to initiate a series of signaling cascades that control many physiological processes, including adaptation to environmental stress. We report here that a Ca²⁺ binding protein, SCaBP5, and its interacting protein kinase, PKS3, function as global regulators of ABA responses. Arabidopsis mutants with silenced SCaBP5 or PKS3 are hypersensitive to ABA in seed germination, seedling growth, stomatal closing, and gene expression. PKS3 physically interacts with the 2C-type protein phosphatase ABI2 (ABA-insensitive 2) and to a lesser extent with the homologous ABI1 (ABA-insensitive 1) protein. Thus, SCaBP5 and PKS3 are a part of a calcium-responsive negative regulatory loop controlling ABA sensitivity.