Hundreds of proteins involved in signaling pathways contain a Ca(2+)-dependent membrane-binding motif called the C2-domain. However, no small C2-domain proteins consisting of a single C2-domain have been reported in animal cells. We have isolated two cDNA clones, OsERG1a and OsERG1b, that encode two small C2-domain proteins of 156 and 159 amino acids, respectively, from a fungal elicitor-treated rice cDNA library. The clones are believed to have originated from a single gene by alternative splicing. Transcript levels of the OsERG1 gene are dramatically elevated by a fungal elicitor prepared from Magnaporthe grisea or by Ca(2+) ions. The OsERG1 protein produced in Escherichia coli binds to phospholipid vesicles in a Ca(2+)-dependent manner and is translocated to the plasma membrane of plant cells by treatment with either a fungal elicitor or a Ca(2+) ionophore. These results suggest that OsERG1 proteins containing a single C2-domain are involved in plant defense signaling systems.