Poster: Late and Moved Abstracts

Abs # 1028: Converting an external signal into cytosolic Ca²⁺ changes by a receptor CAS

Presenter:	Pei, Zhen-Ming , zpei@duke.edu
Authors	Han, Shengcheng  (A)   Tang, Ruhang  (A)   Lisa, Anderson K (A)   Todd, Woerner E (B)   Pei, Zhen-Ming  (A)
Affiliations:	(A): Department of Biology, Duke University (B): Department of Chemistry, Duke University

Living cells constantly receive signals from their environment, and continuously monitor and convert this external information into intracellular second messengers, which can be further decoded to give appropriate physiological and developmental responses. One of the most important and ubiquitous second messengers is cytosolic Ca²⁺, which is increased in response to various stimuli in animals and plants. In contrast to animal systems, the molecular nature of cell surface receptors that perceive stimuli remains largely unknown in plants. We have used a functional screening assay in mammalian cells to isolate an Arabidopsis cDNA clone encoding extracellular Ca²⁺ (Ca²⁺_o)-sensing receptor (CAS) (Han et al., Nature 425: 196, 2003). CAS is localized to the plasma membrane, exhibits low-affinity/high-capacity Ca²⁺-binding, and confers Ca²⁺_o-induced [Ca²⁺]_i increases reported previously (MacRobbie, 1992; McAinsh et al., 1995). CAS is predominantly expressed in the shoot, including guard cells. Repression of CAS disrupts guard cell Ca²⁺_o signalling, and impairs bolting in response to Ca²⁺ deficiency, highlighting that CAS may be a primary transducer of Ca²⁺_o in plants. In addition, we found that CAS is selective for Ca²⁺ over several other divalent cations and forms a dimmer, and that several amino acids are crucial for Ca²⁺ binding as well as CAS activity.