Mercury-induced genes in Arabidopsis thaliana: identification of induced genes upon long-term mercuric ion exposure

Mercuric-ion-induced gene expression was studied in Arabidopsis thaliana Co lumbia wild type. Rosettes of plants grown for 21 d on agar medium suppleme nted with 20, 30 and 40 muM HgCl2 were pooled and used to isolate cDNAs of induced genes by suppression subtractive hybridization. Of the 576 clones i solated initially, 31 turned out to be mercury-induced by Northern hybridiz ation. However, kinetic studies using cDNA arrays clearly showed that seven genes were exclusively mercuric-ion-induced, 14 were induced by mercury bu t also affected by a diurnal rhythm, and 10 clones were only modulated by t he day-night cycle. The expression levels of the metal-induced genes increa sed from 1-5-fold to 10-fold. Functional classification resulted in genes e ncoding proteins for the photosynthetic apparatus and for the antioxidative system. In addition, unexpected genes, whose connection to mercury ion str ess is not evident, were identified.