Role of a Ca2+-ATPase induced by ABA and IAA in the generation of specific Ca2+ signals.

The control of the Ca(2+)-ATPase gene (LCA1) that encodes two different membrane-located isoforms by two antagonic phytohormones, ABA and IAA, has been investigated. Strikingly both the growth regulators induce the LCA1 expression. By using a protoplast transient system, the cis-acting DNA elements responding to both, abiotic stress (ABA) and normal development (IAA), are dissected. ABA triggered a 4-fold increase in the GUS-activity. A single ACGT motif responsible for most of the LCA1 mRNA induction was localized at an unexpectedly large distance (1577 bp) upstream of the translational start. In the case of IAA, although there is a TGTCTC sequence that is known to be an important cis-acting element, two TGA motifs play a more critical role. It is proposed that the Ca(2+)-ATPase isoforms might intervene in the generation of specific Ca(2+) signals by restoring steady-state Ca(2+) levels, modulating both frequency and amplitude of Ca(2+) waves via wave interference.