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

Abstract

The involvement of calcium and different calmodulin isoforms (Ca 2+-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 β-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-amhiohexyl)-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°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. © 2005 Blackwell Publishing Ltd.