An isolated polypeptide containing an amino acid sequence at least 70% identical to a Tubby-like protein (SEQ ID NO: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or 11), and an isolated nucleic acid encoding the polypeptide. Disclosed is an isolated nucleic acid that, under stringent conditions, hybridizes to a probe containing one of SEQ ID NOs:1-11; or its complementary sequence. Also disclosed are (1) a transformed cell or a transgenic plant containing such a nucleic acid and (2) a transformed cell or a transgenic plant having a reduced level(s) of one or more of the Tubby-like proteins. Also within the scope of the invention are methods for making the transformed cells or transgenic plants.