A rapid induction by elicitors of the mRNA encoding CCD-1, a 14kDa Ca2+ -binding protein in wheat cultured cells.

Intracellular Ca(2+) has been implicated in the signal transduction processes during the development of the plant defense system against fungal pathogens. From wheat cultured cells that had been treated with the elicitor derived from Typhula ishikariensis, the ccd-1 gene encoding a 14 kDa Ca(2+)-binding protein with an acidic amphiphilic feature was isolated. The ccd-1-encoded protein (CCD-1) shares homology to the C-terminal half domain of centrin, a Ca(2+)-binding protein conserved in eukaryotes. Unlike typical eukaryotic centrins, CCD-1 contains only one Ca(2+)-binding loop, which corresponds to the one in the fourth EF-hand from the N-terminus of centrin. The recombinant CCD protein expressed in Escherichia coli bound to a phenyl-Sepharose column in the presence of Ca(2+) and was eluted out by EGTA. It also showed a Ca(2+)-dependent electrophoretic mobility shift on the non-denaturing polyacrylamide gel. The ccd-1 mRNA expression was rapidly induced by treatment with fungal and chitosan oligosaccharide elicitors, implying that it might have a role in transducing Ca(2+) signals provoked by the elicitors. The expression of the ccd-1 mRNA was induced by treatment with A23187, and the induction was suppressed by La(3+) or 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA). This study suggests the involvement of intracellular Ca(2+) in the elicitor-induced mRNA expression of a novel class of Ca(2+)-binding proteins conserved in higher plants.