We are studying the mechanisms that control flower development and analyzes the changes undergone by these regulators during evolution. The LEAFY protein (LFY) is a key regulator of floral development and according to evolutionary theories, would also be the major player behind the rise of flowering plants. We have just obtained the first 3-D structure of the binding domain of LEAFY to the DNA in the model plant Arabidopsis thaliana. By the mean of a biochemical approach confirmed by the structure, we showed that the cooperative DNA/protein interaction could partly explain the ability of LEAFY to initiate the floral transition.