Plant growth and organogenesis are coordinated by stem cells located in specialized tissues known as meristems. Virtually all the aerial parts of the plant derive from stem cells located in niches at the shoot apical meristem (SAM), where they process internal and external cues to sustain their function. As cells are continuously produced at SAM, it is essential for plants to precisely regulate the timing of proliferation as development and plant organogenesis occurs over time throughout the life cycle. The circadian clock is the primary timing device that enables an organism to measure the pass of the time to precisely coordinate biological activities with the internal cues and its surrounding environment. Despite the importance of stem cell function, the mechanisms controlling the timing of SAM activity in synchronization with the environment remain essentially unknown. we propose to investigate the role of the circadian clock as a flexible biological metronome orchestrating the SAM activity in plants. The Clock-SAM proposal aims to generate a road-map of clock function, defining circadian similarities and divergences among the different functional states at the SAM and establishing the correlation between the circadian pace of the clock and cell fate and specification. We will follow an ambitious integrative approach combining epigenetic and transcriptional regulatory mechanisms to understand stem cell function. Our studies will thus answer a fundamental question in plant cell biology by determining how the plant is temporally constructed in our rotating world. The results from this proposal will provide a framework that can be tested for regulating plant productivity and survival in different environmental conditions. Hence, in the long term our findings could be applied to crops of agronomical interest.