Natural Variations at TIG1 Encoding a TCP Transcription Factor Contribute to Plant Architecture Domestication in Rice

The modification of plant architecture is a crucial target in rice domestication and modern genetic improvement. Although several genes regulating rice plant architecture have been characterized, the molecular mechanisms underlying rice plant architecture domestication remain largely unclear. Here we show that the inclined tiller growth in wild rice is controlled by a single dominant gene, TILLER INCLINED GROWTH 1 (TIG1), which is located on chromosome 8 and encodes a TCP transcriptional activator. TIG1 is primarily expressed in the adaxial side of the tiller base, promotes cell elongation, and enlarges the tiller angle in wild rice. Variations in the TIG1 promoter of indica cultivars (tig1 allele) resulted in decreased expression of TIG1 in the adaxial side of tiller base and reduced cell length and tiller angle, leading to the transition from inclined tiller growth in wild rice to erect tiller growth during rice domestication. TIG1 positively regulates the expression of EXPA3, EXPB5, and SAUR39 to promote cell elongation and increase the tiller angle. Selective sweep analysis revealed that the tig1 allele was selected in indica cultivars by human beings. The cloning and characterization of TIG1 supports a new scenario of plant architecture evolution in rice. This study identified TILLER INCLINED GROWTH 1 (TIG1), which encodes a TCP transcriptional activator controlling the tiller angle in rice. TIG1 is primarily expressed in the adaxial side of the tiller base, promotes cell elongation, and enlarges the tiller angle in wild rice. Variations in the TIG1 promoter of cultivated rice inactivated the tissue-specific expression of TIG1, and led to the transition from the inclined tiller growth of wild rice to the erect tiller growth of cultivated rice during rice domestication.