Abstract

According to the ‘floral quartet model’ the identities of the different floral organs are specified during development by specific tetrameric complexes of transcription factors; these tetramers bind to two cis-regulatory elements (CArG-boxes), thereby looping the DNA in between them. Intriguingly, the protein constituents of floral quartets are all encoded by paralogous, seed plant-specific MIKC -type MADS -domain proteins. The floral quartet model thus provides an excellent starting point for investigations on the molecular mechanisms underlying the evolution of the angiosperm flower in the framework of evo-devo. We use methods ranging from molecular biophysics to phylogenomics to better understand the origin and functionality of floral quartets and their contributions to the evolution of flowers. Our data suggest that the capacity to constitute floral quartet-like complexes is an ancestral feature of homologues of floral homeotic proteins that had already been established in the most recent common ancestor of extant angiosperms and gymnosperms 300 million years ago. I’ll discuss data suggesting that by changes in the protein-protein and protein-DNA interactions of floral homeotic proteins, target gene specificity and developmental robustness have been improved. This way more efficient ‘developmental switches’ may have originated that facilitated the origin and diversification of the angiosperm flower during evolution.