The vacuolar Ca2+-activated channel TPC1 regulates germination and stomatal movement

Abstract

Cytosolic free calcium ([Ca²⁺]_cyt) is a ubiquitous signalling component in plant cells¹. Numerous stimuli trigger sustained or transient elevations of [Ca²⁺]_cyt that evoke downstream stimulus-specific responses. Generation of [Ca²⁺]_cyt signals is effected through stimulus-induced opening of Ca²⁺-permeable ion channels that catalyse a flux of Ca²⁺ into the cytosol from extracellular or intracellular stores. Many classes of Ca²⁺ current have been characterized electrophysiologically in plant membranes². However, the identity of the ion channels that underlie these currents has until now remained obscure. Here we show that the TPC1 (‘two-pore channel 1’) gene of Arabidopsis thaliana encodes a class of Ca²⁺-dependent Ca²⁺-release channel that is known from numerous electrophysiological studies as the slow vacuolar channel^3,4,5. Slow vacuolar channels are ubiquitous in plant vacuoles, where they form the dominant conductance at micromolar [Ca²⁺]_cyt. We show that a tpc1 knockout mutant lacks functional slow vacuolar channel activity and is defective in both abscisic acid-induced repression of germination and in the response of stomata to extracellular calcium. These studies unequivocally demonstrate a critical role of intracellular Ca²⁺-release channels in the physiological processes of plants.