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

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 (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. 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(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. 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.

Pathogen- and NaCl-induced expression of the SCaM-4 promoter is mediated in part by a GT-1 box that interacts with a GT-1-like transcription factor.

The Ca(2+)-binding protein calmodulin mediates cellular Ca(2+) signals in response to a wide array of stimuli in higher eukaryotes. Plants express numerous CaM isoforms. Transcription of one soybean (Glycine max) CaM isoform, SCaM-4, is dramatically induced within 30 min of pathogen or NaCl stresses. To characterize the cis-acting element(s) of this gene, we isolated an approximately 2-kb promoter sequence of the gene. Deletion analysis of the promoter revealed that a 130-bp region located between nucleotide positions -858 and -728 is required for the stressors to induce expression of SCaM-4. A hexameric DNA sequence within this region, GAAAAA (GT-1 cis-element), was identified as a core cis-acting element for the induction of the SCaM-4 gene. The GT-1 cis-element interacts with an Arabidopsis GT-1-like transcription factor, AtGT-3b, in vitro and in a yeast selection system. Transcription of AtGT-3b is also rapidly induced within 30 min after pathogen and NaCl treatment. These results suggest that an interaction between a GT-1 cis-element and a GT-1-like transcription factor plays a role in pathogen- and salt-induced SCaM-4 gene expression in both soybean and Arabidopsis.