Significance: As the largest class of natural products found in all living organisms, terpenoids play essential roles in plant growth, development, respiration, photosynthesis, and environmental interactions. Geranylgeranyl diphosphate (GGPP), a precursor for several terpenoid metabolic branches including chlorophyll, carotenoid, and gibberellin biosynthesis, is produced by GGPP synthase (GGPPS) in plastids. We discovered that rice GGPPS recruiting protein (GRP), which forms a heterodimer with the only plastidic GGPPS, controls GGPPS dimerization state and enhances its catalytic properties. By interacting with GGPPS, GRP determines its allocation from stroma to thylakoid membranes, where the heterodimer exists in a complex with chlorophyll biosynthetic proteins. GGPPS recruitment to thylakoids by GRP represents a mechanism directing metabolic flux toward a specific product in the terpenoid metabolic network.