Evolution of regulatory networks controlling flower development: MADS get physical

 Flower development is controlled by hierarchically organized networks of genes, many of which encode MIKC-type MADS-domain transcription factors. Changes in these regulatory networks are underlying the morphological evolution of flowers and hence the generation of floral biodiversity. The interactions between floral developmental control genes have so far mainly been defined genetically. However, to better understand the molecular evolutionary dynamics of the gene regulatory networks, their 'hard-wiring' has to be determined, i.e. the physico-chemical interactions on which network topology is based. Especially important are the protein-protein interactions that generate trans-acting transcription factor complexes, and the specific binding of theses complexes to cis-regulatory DNA sequences of target genes. Of central interest are the floral homeotic proteins, which form multimeric complexes ('floral quartets') specifying floral organ identity by activating and repressing appropriate target genes during the development of floral organs. Almost all of them are MIKC-type proteins. We have developed a hypothesis that links the evolutionary importance of MIKC-type proteins via their unprecedented capacity to form different heteromultimers of homologous proteins and hence to achieve target gene specificity to their unique domain structure (Kaufmann et al., 2005). We are testing this hypothesis by studying protein-protein interactions of MIKC-type proteins from phylogenetically informative seed plants. Techniques used are yeast-n-hybrid-analyses, gel retardation assays, and coimmunoprecipitation assays.

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