Epiallelic Variation of TILLER ANGLE CONTROL 5 (TAC5) Regulates Tiller Angle by Modulating Gravitropism in Rice.

Tiller angle is a major component of rice plant architecture and affects planting density, photosynthetic efficiency, and ventilation. An extremely narrow or wide tiller angle adversely affects rice yield. Thus, a suitable tiller angle is considered a major factor to achieve ideal plant architecture in rice. In this study, we identified a major quantitative trait locus (QTL) that controls tiller angle and cloned the gene, TILLER ANGLE CONTROL 5 (TAC5), which encodes a NAC domain-containing transcription factor. Epigenetic variants at the CG site in the TAC5 promoter were stably inherited and associated with TAC5 mRNA expression. The TAC5 epiallele with a hypermethylated cytosine in the promoter exhibited an immediate response to gravistimulation with a simultaneous elevation of H₂O₂ levels at the early stage of gravistimulation. Furthermore, TAC5 affected the expression patterns of transcripts involved in reactive oxygen species (ROS) generation and the response to excessive ROS. Population genetics and evolutionary analyses revealed that TAC5 alleles for the narrow tiller angle originated from a wild progenitor and were selected independently in temperate japonica and indica subspecies during domestication. Our results provide insight into the genetic mechanism of tiller angle control in rice and suggest potential applications of TAC5 in developing rice varieties with an ideal plant architecture.