Identification of putative voltage-dependent Ca2+-permeable channels involved in cryptogein-induced Ca2+ transients and defense responses in tobacco BY-2 cells

Ca2+ is the pivotal second messenger for induction of defense responses induced by treatment of pathogen-derived elicitor or microbial infection in plants. However, molecular bases for elicitor-induced generation of Ca2+ signals (Ca2+ transients) are largely unknown. We here identified cDNAs for Putative voltage-dependent Ca2+-permeable channels, NtTPC1A and NtTPC1B, that are homologous to TPC1 (two pore channel) front suspension-cultured tobacco BY-2 cells. NtTPC1s complemented the growth of a Saccharomyces cerevisiae mutant defective in CCH1, a putative Ca2+ channel, in a low Ca2+ medium, suggesting that both products permeate Ca2+ through the plasma membrane. Cosuppression of NtTPC1s in apoaequorin-expressing BY-2 cells resulted in inhibition of rise in cytosolic free Ca2+ concentration ([Ca2+](cyt)) in response to sucrose and a fungal elicitor cryptogein, while it did not affect hypoosmotic shock-induced [Ca2+](cyt) increase. Cosuppression of NtTPC1s also caused suppression of cryptogein-induced programmed cell death and defense-related gene expression. These results suggest that NtTPC1s are involved in Ca2+ mobilization induced by the cryptogein and sucrose, and have crucial roles in cryptogein-induced signal transduction pathway. (C) 2004 Elsevier Inc. All rights reserved.