The evolution of plants is characterized by several rounds of ancient whole genome duplication, sometimes closely associated with the origin of large groups of species. A good example is the γ triplication at the origin of core eudicots. Core eudicots comprise about 75% of flowering plants and are characterized by the canalization of reproductive development. To better understand the impact of this genomic event, we studied the protein interaction network of MADS-domain transcription factors, which are key regulators of reproductive development. We accurately inferred, resurrected and tested the interactions of ancestral proteins before and after the γ triplication and directly compared these ancestral networks to the networks of Arabidopsis and tomato. We find that the γ triplication generated a dramatically innovated network that strongly rewired through the addition of many new interactions. Many of these interactions were established between paralogous proteins and a new interaction partner, establishing new redundancy. Simulations show that both node and edge addition through the γ triplication were important to maintain modularity in the network. In addition to generating insights into the impact of whole genome duplication and elementary processes involved in network evolution, our data provide a resource for comparative developmental biology in flowering plants.