ABSTRACT
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.
Subject(s)
Calcium-Transporting ATPases/physiology , Calcium/metabolism , Gene Expression Regulation, Plant , Plant Growth Regulators/chemistry , Plant Proteins/chemistry , Solanum lycopersicum/metabolism , Abscisic Acid/chemistry , Adenosine Triphosphatases/chemistry , Amino Acid Motifs , Base Sequence , Calcium/chemistry , Calcium-Transporting ATPases/metabolism , Cell Membrane/metabolism , Cell Proliferation , Indoleacetic Acids/metabolism , Solanum lycopersicum/enzymology , Molecular Sequence Data , Phosphorylation , Plant Growth Regulators/metabolism , Plant Proteins/metabolism , Plasmids/metabolism , Promoter Regions, Genetic , Protein Isoforms , Protein Structure, Tertiary , Protoplasts/chemistry , Protoplasts/metabolism , RNA/chemistry , RNA, Messenger/metabolism , Signal TransductionABSTRACT
Yeast lithium-sensitive inositol monophosphatase (IMPase) is encoded by a non-essential gene pair (IMP1 and IMP2). Inhibition of IMPase with either Li(+) or Na(+) or a double null mutation imp1 imp2 causes increased levels of inositol monophosphates and reduced level of inositol 1,4,5-trisphosphate. Overexpression of the IMP2 gene has the opposite effects and these results suggest that IMPase activity is limiting for the inositol cycle. Addition of ammonium to cells starved for this nutrient results in a decrease of inositol monophosphates and an increase of inositol 1,4,5-triphosphate, pointing to simultaneous regulation of both inositol 1,4,5-triphosphate production and IMPase activity.
