The 'ABC' of MADS domain protein behaviour and interactions

Development of eudicot flowers is under tight developmental control by genes belonging to the MADS box transcription factor family, as is nicely represented by the well-known ABC model of floral organ development. During the last two decades enormous progress has been made in our understanding of the molecular mechanisms underlying the combinatorial activity of the encoded MADS domain proteins. Here, we review how various state-of-the-art technologies were implemented in order to unravel the protein-protein interaction network for the plant MADS domain transcription factor family. In addition, results from in planta studies of MADS domain protein behaviour and interactions will be discussed. Dimerisation and higher-order complex formation of MADS domain proteins appear to be instrumental and essential for floral organ identity determination and the precise regulation of specific target gene sets. According to the current molecular model, the floral MADS proteins assemble into quaternary complexes consisting of two dimers, which is mediated by the E class proteins. Furthermore, evidence has been provided that MADS protein-protein interactions specify DNA binding capacity, inter- and intracellular localisations of the proteins and the biological function of the constituted transcription complexes.