Rice OsERG3 encodes an unusual small C2-domain protein containing a Ca(2+)-binding module but lacking phospholipid-binding properties.

The C2 domain is a Ca(2+)/phospholipid-binding motif found in many proteins involved in signal transduction or membrane trafficking. OsERG3 is a homolog of OsERG1, a gene encoding a small C2-domain protein in rice.OsERG3 Ca(2+)-binding and phospholipid-binding assays were carried out using (3)H-labeled phospholipid liposomes and a (45)Ca(2+) overlay assay, respectively. Cytosolic expression of OsERG3 was investigated by Western blot analysis and the OsERG3::smGFP transient expression assay.OsERG3 transcript levels were greatly enhanced by treatment with a fungal elicitor and Ca(2+)-ionophore. OsERG3 protein proved unable to interact with phospholipids regardless of the presence or absence of Ca(2+) ions. Nonetheless, OsERG3 displayed calcium-binding activity in an in vitro(45)Ca(2+)-binding assay, a property not observed with OsERG1. The cytosolic location of OsERG3 was not altered by the presence of fungal elicitor or Ca(2+)-ionophore.OsERG3 encodes a small C2-domain protein consisting of a single C2 domain. OsERG3 binds Ca(2+) ions but not phospholipids. OsERG3 is a cytosolic soluble protein. The OsERG3 gene may play a role in signaling pathway involving Ca(2+) ions.The data demonstrate that OsERG3 is an unusual small C2-domain protein containing a Ca(2+)-binding module but lacking phospholipid-binding properties.