Significance Many phytopathogenic fungi need specialized structures, called appressoria, to penetrate the plant before infection starts. For these structures, the fungus must carefully control when and where its cells divide, and it has been reported in different fungal phytopathogens that appressorium formation is subordinated to the cell cycle control. However, the molecular details about how this control operates were unknown. We described in the corn smut fungus U. maydis that Biz1, a regulator for the formation of appressorium, is phosphorylated by the kinase responsible for cell cycle progression. Biz1 is part of a negative feedback loop responsible for the final decision to invade or not the plant tissue. Targeting this process will lead to the development of antipenetrant fungicides.