The development of multicellular organisms requires the integration of signals controlling and coordinating cell fates. This process relies on numerous regulatory events that impact both chromatin structure and transcription. Chromatin undergoes global modifications at specific times and within specific cell subsets to dictate distinct cellular programs. However, the mechanisms by which chromatin is modulated during development remains highly elusive. Plants are ideal models for investigating cell-specific chromatin remodelling. Plant cells do not move, and their plastic development is the result of an exquisite interaction between environmental and intrinsic signals. How does this signal crosstalk guide chromatin orchestration? Our findings, derived from the study of flowering time in Arabidopsis may bring some answers. One key function of the plant hormone Brassinosteroids is to regulate the vegetative to reproductive fate transition of the cells in flower primordium. BR signalling acts through inactivation of GSK3 kinases responsible for the modulation of other protein’s activity. Interestingly, in contrast to other hormones, BR do not undergo long distant transport. We discovered that the BR dependent GSK3s bind and phosphorylate a central component of chromatin machinery involved in establishing and maintaining transcriptional programs. This finding may help explaining how chromatin is orchestrated in specific cells to guide cell fate transitions.