Two cDNA clones, MdCOL1 and MdCOL2, encoding CONSTANS (CO)-like proteins were isolated from an apple (Malus domestica cv. Fuji) fruit cDNA library. Both proteins contain two zinc finger motifs at the amino terminal end and a putative nuclear localization domain at the carboxyl terminal end. Genomic DNA blot analysis suggests that the CO-like genes are members of a small multigene family. RNA blot and RT-PCR anaylses revealed that these genes are expressed in every organ that was examined. However, the expression levels were higher in floral buds and fruits at their early devfelopmental stages compared to late reproductive stages or vegetative organs. Such expression patterns are quite different from those of the CO-like genes from Arabidopsis, which show strong organ specificity in either roots, cauline leaves, or flowers. These results indicate that the apple CO-like genes are significantly different from the Arabidopsis genes and that they appear to play important roles in reproductive organ development.