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

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Background 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. Methods OsERG3 Ca 2+-binding and phospholipid-binding assays were carried out using 3H-labeled phospholipid liposomes and a 45Ca 2+ overlay assay, respectively. Cytosolic expression of OsERG3 was investigated by Western blot analysis and the OsERG3::smGFP transient expression assay. Results 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 45Ca 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. Conclusions 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. General significance The data demonstrate that OsERG3 is an unusual small C2-domain protein containing a Ca 2+-binding module but lacking phospholipid-binding properties.