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A cell surface receptor mediates extracellular Ca2+ sensing in guard cells


Extracellular Ca2+ (Ca2+o) is required for various physiological and developmental processes in animals and plants1,2,3. In response to varied Ca2+o levels, plants maintain relatively constant internal Ca2+ content, suggesting a precise regulatory mechanism for Ca2+ homeostasis4. However, little is known about how plants monitor Ca2+o status and whether Ca2+o-sensing receptors exist. The effects of Ca2+o on guard cells in promoting stomatal closure by inducing increases in the concentration of cytosolic Ca2+ ([Ca2+]i)5,6,7,8 provide a clue to Ca2+o sensing. Here we have used a functional screening assay in mammalian cells9 to isolate an Arabidopsis complementary DNA clone encoding a Ca2+-sensing receptor, CAS. CAS is localized to the plasma membrane, exhibits low-affinity/high-capacity Ca2+ binding, and mediates Ca2+o-induced [Ca2+]i increases. CAS is expressed predominantly in the shoot, including guard cells. Repression of CAS disrupts Ca2+o signalling in guard cells, and impairs bolting (swift upward growth at the transition to seed production) in response to Ca2+ deficiency, so we conclude that CAS may be a primary transducer of Ca2+o in plants.

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Figure 1: Calcium-imaging-based expression cloning of a Ca2+o-sensing receptor from an Arabidopsis cDNA library.
Figure 2: CAS encodes a low-affinity/high-capacity Ca2+-binding protein.
Figure 3: Expression pattern and subcellular location of CAS.
Figure 4: CAS is required for guard-cell Ca2+o signalling and plant development.


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We thank L. Jing, Y. Hao and Y. He for assistance; W. Zhang for HEK293 cells and discussions on expression cloning; D. McClay and R. Fehon for use of cell culture and imaging facilities; J. Schroeder, J. Kwak, J. Harper and A. VanDogen for vectors; J. Schroeder, T. Sun and R. Venters for discussions; and J. Siedow, X. Dong, W. Durrant, P. Benfey, W. Zhang and R. Fehon for comments on the manuscript. R.T. was supported in part by a Hargitt Fellowship. This work was supported by start-up funds from Duke University and by a grant from the NSF to Z.-M.P.

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Han, S., Tang, R., Anderson, L. et al. A cell surface receptor mediates extracellular Ca2+ sensing in guard cells. Nature 425, 196–200 (2003).

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