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A full‐length cDNA clone encoding a phosphoprotein (pp56) involved in the regeneration of rice (Oryza sativa L.)‐cultured suspension cells was isolated by screening a rice cultured suspension cell cDNA library. The 1558‐bp cDNA sequence contains an ORF encoding an acidic (pI 4.38) protein of 424 amino acids (47.9 kDa), sharing 70–93% and 50–53% homology with other plant and mammalian calreticulins, respectively. Sequence analysis of the cDNA clone revealed several significant conserved motifs, including a calreticulin family repeat motif in the central domain and two calreticulin family motifs in the N‐domain, indicating that this gene is a rice calreticulin (CRO1). The CRO1 gene in long‐term rice cultured suspension cells shows constitutive expression in both suspension culture and regeneration media. In contrast, expression of the CRO1 gene in short‐term rice cultured suspension cells, which …