This project will investigate how small molecules produced in plant cells regulate gene activity. Plants produce a vast diversity of metabolites that are essential for growth, environmental responses, and the synthesis of valuable natural products, but their production must be tightly regulated in cells to avoid wasting energy or overaccumulation of harmful compounds. This research focuses on how small-molecule metabolites trigger feedback regulation of gene expression, a fundamental but poorly understood process in biology. Using petunia flowers as a model system, the project will examine how a metabolic enzyme may act as a sensor that links chemical changes in the cell to chromatin-based gene regulation. The findings will advance our understanding of how metabolism and gene expression are integrated, with broader relevance to plants and other biological systems. The project has potential biotechnology benefits for metabolic engineering and crop improvement by providing new strategies to optimize the production of beneficial natural products and improve plant health. In addition, the project will train postdoctoral researchers and students across multiple levels in interdisciplinary research spanning metabolism, gene regulation, bioinformatics, and biophysics, while engaging the public through outreach on plant chemical diversity. The research will test the hypothesis that a biosynthetic enzyme functions as a sensor that detects metabolite fluctuations and mediates the dynamic behavior of two chromatin modifiers with opposing roles, thereby altering histone acetylation and gene transcription. To address this hypothesis, the project will: (1) characterize the enzymatic activity of the enzyme sensor and determine its interactions with small-molecule metabolites and chromatin regulators; (2) define the spatiotemporal dynamics and nuclear-cytosolic partitioning of chromatin modifying proteins using single-molecule spectroscopy, subcellular fractionation, and phospho