In annual plants, which include most crops species, onset of flower formation triggers a transition from biomass and resource production in the leaves and branches to allocation of these resources to the next generation in the seeds formed in the flowers. Both timing of the onset of flower formation and proper flower development are important for plant survival and for agriculture. Understanding the regulation of these processes will allow optimization of the duration of the vegetative phase for biofuel production or food production and optimal elaboration of the reproductive structures for food production. Despite much recent progress in the understanding of the regulation of both of these processes, much remains unknown. The plant specific transcription factor LEAFY (LFY) is a master regulator of the switch to flower formation and of early flower development. This project uses LFY as an entry point and Arabidopsis thaliana as the plant model species to address two key questions that represent major gaps in the understanding of flower development: (1) What are regulators that act downstream of LFY to trigger the switch to flower formation? LFY sets in motion the series of events that result in formation of the first flower. Despite the importance of this developmental switch for plant reproductive fitness and human sustenance, key regulators of this transition that are induced by LFY remain unidentified. We will take a novel genetic approach to address this question. (2) How do LFY and another important regulator of flower development, the MADS box transcription factor APETALA1 together direct the cell fate changes required to form a floral meristem? It is now widely accepted that LFY and AP1 together orchestrate early flower development. In this AIM insight gained from recent genomic datasets will be harnessed to identify candidate regulators important for early events in flower morphogenesis followed by elucidation of their role in plants. These early events in flower morphogenesis are poorly understood in all plant systems so this investigation should generate novel insight of broad significance.