Relearning our ABCs: new twists on an old model

Over the past decade, the ABC model of flower development has been widely p romulgated. However, correct flower-organ development requires not only the ABC genes but also the SEPALLATA genes. When the SEPALLATA genes are expre ssed together with the ABC genes, both vegetative and cauline leaves are co nverted to floral organs. Most of the ABC genes and all three SEPALLATA gen es encode MADS transcription factors, which bind to DNA as dimers. Here, am endments to the ABC model are considered that incorporate both the SEPALLAT A genes and the ability of MADS proteins to form higher-order complexes.