A modified protocol for differential display of mRNA was used to identify and clone genes expressed in developing Arabidopsis thaliana seeds. Two novel embryo-specific genes designated ATS1 and ATS3 (Arabidopsis thaliana seed gene) were identified. In situ hybridization showed that, spatially, ATS1 is expressed in a pattern similar to the Arabidopsis GEA1 gene and that ATS3 is expressed in a pattern similar to the Arabidopsis seed storage protein genes. Southern analysis of Arabidopsis genomic DNA indicated that ATS1 is a member of a small gene family and that ATS3 is present as a single copy in the diploid genome. Sequence analysis of both genes showed that ATS1 is similar to the rice EFA27 gene and that ATS3 is unique. Western analysis and light level immunocytochemistry using antisera raised against the putative ATS1 and ATS3 translation products verified that ATS1 and ATS3 proteins are seed-specific and accumulate in a spatial pattern similar to their respective transcripts. Taken together, these data show that ATS1 and ATS3 are novel embryo-specific genes in Arabidopsis.