Arabidopsis transcriptional response to extracellular Ca2+ depletion involves a transient rise in cytosolic Ca2+

Ecological evidence indicates a worldwide trend of dramatically decreased soil Ca2 tlevels caused by increased acid deposition and massive timber harvesting. Little is known about the genetic and cellular mechanism of plants’ responses to Ca2 t depletion. In this study, transcriptional profiling analysis helped identify multiple extracellular Ca([Ca]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([Ca]cyt)sensors were significantly upregulated, implying that [Ca]cyt has a role in sensing [Ca]extdepletion. Consistent with this observation, [Ca]extdepletion stimulated a transient rise in[Ca]cytthat was negatively influenced by [Kt]ext, suggesting the involvement of a membrane potential-sensitive component.The [Ca]cytresponse to [Ca]extdepletion was significantly desensitized after the initial treatment, which is typical of a receptor-mediated signaling event. The response was insensiResearch Ative to an animal Ca2 tsensor antagonist, but was suppressed by neomycin, an inhibitor of phospholipase C. Gd3 t, an inhibitor of Ca2 tchannels, suppressed the [Ca]ext-triggered rise in[Ca]cytand downstream changes in gene expression. Taken together, this study demonstrates that [Ca]cytplays an important role in the putative receptor-mediated cellular and transcriptional response to [Ca]extdepletion of plant cells.