Roles of the Putative Voltage-Gated Ca²⁺ Permeable Channels, the TPC1 Family, in Plant Stress Signaling

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　Ion fluxes including Ca²⁺ and production of reactive oxygen species (ROS) are induced at the early step of defense signaling triggered by both biotic and abiotic (environmental) stresses. To reveal the molecular mechanisms and physiological roles of the plasma membrane Ca²⁺ influx, a family of putative voltage-gated Ca²⁺ permeable channels, the TPC1 family, were identified from various plant species. The rice gene, OsTPC1, rescued the Ca²⁺ uptake activity and growth rate of a yeast mutant defective in Ca²⁺ uptake. OsTPC1 overexpressing cells showed hypersensitivity to excess Ca²⁺ but higher growth rate under Ca²⁺ limitation, while growth of the transposon-insertional mutant (Ostpc1) cells was less sensitive to extracellular free Ca²⁺ concentration, suggesting that OsTPC1 has Ca²⁺ transport activity across the plasma membrane. Knockdown/knockout of the TPC1 family resulted in inhibition of [Ca²⁺]_cyt rise in response to a pathogenic elicitor, as well as suppression of the elicitor-induced programmed cell death and defense-related gene expression. These results suggest that the TPC1 family is involved in elicitor-induced Ca²⁺ mobilization, and have crucial roles in stress-induced signal transduction pathways in plants.