We isolated a COP1 cDNA from rice and found that it could complement the Arabidopsis cop1-4 mutant. The putative rice COP1 protein has the Ring-finger, coiled-coil, and WD-40 repeat domains, which are also conserved in pea, tomato, and mammalian COP1 proteins. The degree of overall identity between rice COP1 and Arabidopsis COP1 is 73%, and the similarity value is 83%. Expression of rice COP1 was detected in almost all plant tissues, with the level being relatively higher in calli and very low in etiolated leaves. The expression level was positively controlled by light in etiolated and green leaves. At the end of the light period, expression of the gene in green leaves could be down-regulated by far-red light. This far-red light effect could be prevented by subsequent irradiation with red light. These results indicate that phytochrome regulates rice COP1 expression. © Springer-Verlag 2001.