Arabidopsis transcriptional response to extracellular Ca 2+ depletion involves a transient rise in cytosolic Ca 2+

Ecological evidence indicates a worldwide trend of dramatically decreased soil Ca 2+ levels caused by increased acid deposition and massive timber harvesting. Little is known about the genetic and cellular mechanism of plants' responses to Ca 2+ depletion. In this study, transcriptional profiling analysis helped identify multiple extracellular Ca 2+ ([Ca 2+ ] ext ) depletion‐responsive genes in Arabidopsis thaliana L., many of which are involved in response to other environmental stresses. Interestingly, a group of genes encoding putative cytosolic Ca 2+ ([Ca 2+ ] cyt ) sensors were significantly upregulated, implying that [Ca 2+ ] cyt has a role in sensing [Ca 2+ ] ext depletion. Consistent with this observation, [Ca 2+ ] ext depletion stimulated a transient rise in [Ca 2+ ] cyt that was negatively influenced by [K + ] ext , suggesting the involvement of a membrane potential‐sensitive component. The [Ca 2+ ] cyt response to [Ca 2+ ] ext depletion was significantly desensitized after the initial treatment, which is typical of a receptor‐mediated signaling event. The response was insensitive to an animal Ca 2+ sensor antagonist, but was suppressed by neomycin, an inhibitor of phospholipase C. Gd 3+ , an inhibitor of Ca 2+ channels, suppressed the [Ca 2+ ] ext ‐triggered rise in [Ca 2+ ] cyt and downstream changes in gene expression. Taken together, this study demonstrates that [Ca 2+ ] cyt plays an important role in the putative receptor‐mediated cellular and transcriptional response to [Ca 2+ ] ext depletion of plant cells.