Cytosine methylation is an epigenetic mark found in the genome of fungi, plants, and animals. DNA methylation is catalyzed by DNA methyltransferases. The function of DNA methyltransferases was shown to be highly conserved, but the biological role of these enzymes has not been clearly defined. We generated transgenic plants expressing METHYLTRANSFERASES::GUS reporter genes for three major DNA methyltransferases (MET1, DRM2 and CMT3) to gain insight into the potential physiological relevance of the individual members of the DNA methyltransferase family in Arabidopsis thaliana, and to investigate their expression patterns in detail. We found that METHYLTRANSFERASE::GUS genes display unique tissue, cell-type, and tem- poral patterns of expression throughout normal development, particularly in the flower. Our findings are supported by semi-quantitative reverse-transcription PCR, as well as by analyses of microarray databases. These data suggest that DNA methyltransferases may contribute to morphogenesis at every developmental stage and in every plant organ.