IMMUNOLOCALIZATION OF A NOVEL ANNEXIN-LIKE PROTEIN ENCODED BY A STRESS AND ABSCISIC-ACID RESPONSIVE GENE IN ALFALFA

We report here on the isolation and characterization of a full-length cDNA clone from alfalfa termed AnnMs2 encoding a 333 amino acid long p olypeptide that shows 32-37% sequence identity with both mammalian and plant annexins, and has four tandem repeats. While other plant annexi ns exhibit a high level of sequence similarity to each other (up to 77 % identity at amino acid level),AnnMs2 appears to be a distinct type o f plant annexins. All the four endonexin folds contain the conserved e ukaryotic motif within this alfalfa protein, but this element is consi derably different in the second repeat. The AnnMs2 gene is expressed i n various tissues of alfalfa with elevated mRNA accumulation in root a nd flower. This gene is activated in cells or tissues exposed to osmot ic stress, abscisic acid (ABA) or water deficiency. The recombinant An nMs2 protein is able to bind to phospholipid in the presence of Ca2+. Indirect immunofluorescence studies using affinity purified rabbit ant i-AnnMs2 peptide antibody show mainly nucleolar localization, but the protein sequence lacks the usual nuclear localization signal. The pote ntial role of this novel annexin-like protein in the basic and stress- induced cellular functions is discussed.