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Plant architecture is dynamic as plants develop. Although many genes associated with specific plant architecture components have been identified in rice, genes related to underlying dynamic changes in plant architecture remain largely unknown. Here, we identified two highly similar recombinant inbred lines (RILs) with different plant architecture: RIL-Dynamic (D) and RIL-Compact (C). The dynamic plant architecture of RIL-D is characterized by ‘loose^{tiller angle} (tillering stage)–compact (heading stage)–loose^{curved stem} (maturing stage)’ under natural long-day (NLD) conditions, and ‘loose^{tiller angle} (tillering and heading stages)–loose^{tiller angle and curved stem} (maturing stage)’ under natural short-day (NSD) conditions, while RIL-C exhibits a compact plant architecture both under NLD and NSD conditions throughout growth. The candidate locus was mapped to the chromosome 9 tail via the rice 8K chip assay and map-based cloning. Sequencing, complementary tests, and gene knockout tests demonstrated that <i>Tiller Angle Control 1</i> (<i>TAC1</i>) is responsible for dynamic plant architecture in RIL-D. Moreover, <i>TAC1</i> positively regulates loose plant architecture, and high <i>TAC1</i> expression cannot influence the expression of tested tiller-angle-related genes. Our results reveal that <i>TAC1</i> is necessary for the dynamic changes in plant architecture, which can guide improvements in plant architecture during the modern super rice breeding.