Sci. STKE, 22 March 2005
PLANT BIOLOGY Vacuolar Calcium Channel Revealed
In plant cells, the vacuole serves as an intracellular calcium store and buffer. Peiter et al. have identified the TPC1 gene as encoding the cation channel responsible for Ca2+-dependent Ca2+ release in response to micromolar concentrations of intracellular calcium. TPC stands for two-pore channel, and TPC1 has two fused Shaker-like segments, each with six transmembrane domains and two EF hands, which are domains associated with calcium binding. Expression of a TPC1-green fluorescent protein (GFP) fusion protein in Arabidopsis protoplasts showed that TPC1 is localized to the vacuolar membrane. Electrophysiology experiments with vacuolar membrane patches showed that membranes from wild-type Arabidopsis or cells engineered to overexpress TPC1, but not those from a mutant plant that does not express TPC1, had a cationic current with a steep calcium dependence. The functional importance of TPC1 was demonstrated by the lack of responsiveness of seeds lacking the protein to the hormone abscisic acid (ABA). In contrast, cells engineered to overexpress TPC1 were hyperresponsive to ABA and showed decreased seed germination type compared with wild-type. In guard cells, TPC1 was not directly responsible for ABA regulation of stomatal aperture, but TPC1-deficient cells did not exhibit a decrease in stomatal aperture in response to elevated calcium concentration.
E. Peiter, F. J. M. Maathuis, L. N. Mills, H. Knight, J. Pelloux, A. M. Hetherington, D. Sanders, The vacuolar Ca2+-activated channel TPC1 regulates germination and stomatal movement. Nature 434, 404-408 (2005). [PubMed]
Citation: Vacuolar Calcium Channel Revealed. Sci. STKE 2005, tw110 (2005).
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