A new family of DNA binding proteins includes putative transcriptional regulators of the Antirrhinum majus floral meristem identity gene SQUAMOSA

Abstract

Several sites of nuclear protein interaction within the promoter region of the Antirrhinum majus floral meristem identity gene SQUAMOSA were detected using an electrophoretic mobility shift assay. One of these sites displayed a particularly clear interaction with nuclear protein extracted from inflorescences but not with nuclear protein extracted from young, nonflowering plants. This site could thus represent a binding motif for a transcriptional activator. A South-western screen of an inflorescence cDNA expression library resulted in the isolation of several cDNAs representing two different genes named SBP1 and SBP2 (for SQUAMOSA-pROMOTER BINDING PROTEIN gene 1 and 2). Both genes encode highly similar protein domains which were found to be necessary and sufficient for binding DNA in a sequence-specific manner. This DNA-binding domain showed no similarity to known proteins in the databases. However, it is characteristic for a small family of gene products in A. majus and other plant species. Expression of SBP1 and 2 is developmentally regulated and their transcriptional activation precedes that of SQUAMOSA. The data presented support the idea that members of the newly identified SBP gene family function as transcription factors involved in the control of early flower development.