Cold-Shock Regulation of the Arabidopsis TCH Genes and the Effects of Modulating lntracellular Calcium Levels'

The Arabidopsis TCH genes, which encode calmodulin-related proteins and a xyloglucan endotransglycosylase, are shown to be up-regulated in expression following cold shock. We investigated a possible role of fluctuations in intracellular calcium ion concentrations ([CaZ+I) in the cold-shock-induced TCH gene expression. Transgenic plants harboring the apoaequorin gene were generated to monitor [CaZ+] and to test the necessity of cold-induced [CaZ+] increases for TCH expression. Cold-shock-induced [Ca2+l increases can be blocked by La3+ and Cd3+, putative plasma membrane Ca2+ channel blockers, and 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'tetraacetic acid, an extracellular Caz+ chelator. Cold-shockinduced expression of the TCH genes is inhibited by levels of La3+, Cd3+, and 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, that have been shown to block [Ca2+] increases. These data support the hypotheses that (a) intracellular [CaZ+] increases following cold shock require extracellular CaZ+ and may derive from a Ca" influx mediated by piasmalemma CaZ+ channels, and (b) cold up-regulation of expression of at least a subset of the TCH genes requires an intracellular [CaZ+l increase. The inhibitors are also shown to have stimulus-independent effects on gene expression, providing strong evidence that these commonly used chemicais have more complex effects than generally reported.