The present invention provides a non-naturally occurring seed plant that is characterized by producing seeds of increased size due to ectopic expression of a nucleic acid molecule encoding an AGL8-related gene product. The AGL8-related gene product can have, for example, substantially the amino acid sequence of an AGL8 ortholog such as Arabidopsis AGL8 (SEQ ID NO:2). The present invention further provides a non-naturally occurring seed plant that is characterized by producing fruit of increased size due to ectopic expression of a nucleic acid molecule encoding an AGL8-family gene product. The AGL8-family gene product can have substantially the amino acid sequence of an AGL8 ortholog, for example, the amino acid sequence of Arabidopsis AGL8 (SEQ ID NO:2). Related methods and kits also are provided.