Ca2+ and AtCaM3 are involved in the expression of heat shock protein gene in Arabidopsis

The involvement of calcium and different calmodulin isoforms (Ca2+-CaM) in heat shock (HS) signal transduction in Arabidopsis (Arabidopsis thaliana) was investigated. Using transgenic Arabidopsis plants which have the AtHsp18.2 promoter/GUS fusion gene, it was found that the level of beta-glucuronidase (GUS) activity was up-regulated by the addition of CaCl2 and down-regulated by the calcium ion chelator EGTA, the calcium ion channel blockers LaCl3 and verapamil, or the CaM antagonists N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W7), chlorpromazine (CPZ) and trifluoperazine (TFP). CaCl2 not only increased the GUS activity after HS, but also up-regulated the GUS activity under non-HS conditions. These results provide additional support for the involvement of the Ca2+-CaM signalling system in HSP gene expression. The expression of nine CaM genes (AtCaM1-9) from Arabidopsis was differentially regulated by HS at 37 degrees C. The expression of AtCaM3 and AtCaM7 genes increased during HS. The temporal expression of the AtCaM3, AtCaM7 and hsp18.2 genes demonstrated that up-regulation of AtCaM3 expression occurred earlier than that of AtCaM7 or hsp18.2.