Characterisation of plant MADS box transcription factor protein-protein interactions : use of Petunia hybrida as a model system

Homeotic genes specify the identity of different plant tissues and organs. Mutations in of these genes results in replacement of a specific organ or tissue by another plant body part or tissue, which is normally formed at a different position. An important group of homeotic genes in plants is represented by members of the MADS box family of transcription factors. The first members isolated from this large family were involved in specifying the identity of floral organs. Based on the genetic and molecular analysis of these genes the "ABC(DE)" model of floral development was established. Meanwhile, MADS box transcription factors with other kind of functions were identified, like the regulation of flowering time.To gain insight in the molecular mechanisms underlying MADS box transcription factor functioning, the MADS box family of the model species Petunia hybrida has been analysed. MADS box proteins are active as homo- or heterodimers and even higher-order ternary and quaternary complex formation have been shown recently. Therefore, this study focuses mainly on the characterisation of protein-protein interactions. Initially, some new members of the petunia MADS box family were isolated from inflorescence and ovary cDNA-libraries, bringing the total number of identified petunia MADS box genes up-to 23. Members of this family are either named FLORAL BINDING PROTEINs ( FBPs ) or PETUNIA MADS ( pMADS ). The 23 members were all characterised by expression pattern analysis, phylogenetic comparison and yeast two-hybrid screenings for the identification of protein-protein interactions. The obtained results were compared with data from MADS box transcription factor families of other species, like Antirrhinum majus and Arabidopsis thaliana . This comparison demonstrated that MADS box genes and their functions are largely conserved among flowering plants and therefore, functions could be predicted for some unknown petunia and Arabidopsis MADS box proteins. Furthermore, some of t