MADS box genes encode transcription factors that play prominent roles in plant development. They are recruited for root formation, flowering, inflorescence architecture, organ identity specification, ovule formation and silique maturation. However, this is only a small portion of the potential of this large family of transcription factors. In Arabidopsis this family comprises at least 100 members divided over two distinct classes (see Pařenicová et al., 2003). 
MADS box proteins can be recognised by a conserved DNA binding domain of 56 amino acids located at the N-terminus. The K-box domain of the protein facilitates the dimerisation of two MADS box proteins by a hydrophobic interaction. We have determined all possible dimer combinations between the Arabidopsis MADS box proteins by a comprehensive yeast 2-hybrid screen (see De Folter et al., 2005).
Figure: Interactome of Arabidopsis MADS box proteins.
The ABCDE model is an extension on the well-known ABC model, which has been postulated by Coen and Meyerowitz in 1991. De ABCDE model describes 5 classes of genes that are responsible for the specification of floral organ identity in a combinatorial manner. The A function is required for sepal (S) specification, ABE together for petals (P), BCE for stamens (St), CE for carpels (C) and D, together with C and E for the determination of ovules (O). Experimental data in Arabidopsis and in petunia from our lab (see Ferrario et al., 2003) support this model in both dicot species.
Figure: Petunia FBP2 (E gene) cosuppression mutant (left) and Arabidopsis sepallata (E) mutant (right)
Selected references
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Ferrario, S.I.T., R.G.H. Immink, A. Shchennikova, J. Busscher-Lange & G.C. Angenent (2003). The MADS box gene FBP2 is required for the SEPALLATA function in petunia. The Plant Cell 15: 914-925.
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Pařenicová, L., S. de Folter, M. Kieffer, D.S. Horner, C. Favalli, J. Busscher, H.E. Cook, R.M. Ingram, M.M. Kater, B. Davies, G.C. Angenent & L. Colombo (2003). Molecular and phylogenetic analyses of the complete MADS-box transcription factor family in Arabidopsis: New openings to the MADS world. The Plant Cell 15: 1538-1551.
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De Folter, S., R.G.H. Immink, M. Kieffer, L. Pařenicová, S.R. Henz, D. Weigel, M. Busscher, M. Kooiker, L. Colombo, M.M. Kater, B. Davies & G.C. Angenent (2005). Comprehensive interaction map of the Arabidopsis MADS box transcription factors. The Plant Cell 17: 1424-1433.
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