As sessile organisms, plants are exposed to extreme variations in the environment over the course of their lives. Since plants initiate new organs continuously, they have to modulate the underlying developmental program to cope with this challenge. At the heart of this extraordinary developmental plasticity are pluripotent stem cells, which are maintained during the entire life-cycle and that are embedded within dynamic stem cell niches. Consequently, stem cell systems in plants respond strongly to variations in environmental conditions, in order to synchronize stem cell behavior with the overall growth status of the plant. In the proposed project we will study cell behavior in the apical stem cell niche and define the epigenetic and transcriptional states of stem cells and niche cells to elucidate how these cells are reprogrammed by environmental influences using advanced live imaging and cell type specific genomics, respectively. In addition, we will use these technologies to study how natural genetic variation impacts on stem cell behavior and the molecular signatures, which define these cells. Using comparative analysis we will identify loci that are responsive to specific environmental changes and study them functionally by advanced cell type specific genetics. To elucidate how environmental stimuli are sensed by the stem cell regulatory system, we will systematically test known regulators of light, temperature and metabolic signaling for their role in this process, both by traditional, as well as by advanced cell-type specific genetics. Together, these datasets will give an unprecedented insight into how plant stem cells perceive environmental signals and how their transcriptional and epigenetic programs respond under changing environments. In addition, our experiments will reveal whether the mechanisms of short-term environmental acclimatization of the regulatory system converge with the long-term evolutionary adaptation of organisms to their environment.