In vivo imaging of MADS-box transcription factor interactions

MADS-box transcription factors are major regulators of development in flowering plants. The factors act in a combinatorial manner, either as homo- or heterodimers, and they control floral organ formation and identity and many other developmental processes through a complex network of protein¿protein and protein¿DNA interactions. Despite the fact that many studies have been carried out to elucidate MADS-box protein dimerization by yeast systems, very little information is available on the behaviour of these molecules in planta. Here, evidence for specific interactions between the petunia MADS-box proteins FBP2, FBP11, and FBP24 is provided in vivo. The dimers identified in yeast for the ovule-specific FBP24 protein have been confirmed in living plant cells by means of fluorescence resonance energy transfer¿fluorescence lifetime imaging microscopy and, in addition, some of the most likely, less stable homo- and heterodimers were identified. This in vivo approach revealed that particular dimers could only be detected in specific sub-nuclear domains. In addition, evidence for the in planta assembly of these ovule-specific MADS-box transcription factors into higher-order complexes is provided.