Plant architecture strongly influences rice grain yield. We report the cloning and characterization of the LTA1 gene, which simultaneously controls tiller angle and yield of rice. LTA1 encodes a chloroplast-localized protein with a conserved YbaB DNA-binding domain, and is highly expressed in photosynthetic tissues including leaves and leaf sheaths. Disrupting the function of LTA1 leads to large tiller angle and yield reduction of rice. LTA1 affects the gravity response by mediating the distribution of endogenous auxin, thereby regulating the tiller angle. An lta1 mutant showed abnormal chloroplast development and decreased chlorophyll content and photosynthetic rate, in turn leading to reduction of rice yield. Our findings shed light on the genetic basis of tiller angle and provide a potential gene resource for the improvement of plant architecture and rice yield.