Phytochrome-interacting factor-like protein OsPIL15 integrates light and gravitropism to regulate tiller angle in rice

Main conclusion Rice phytochrome-interacting factor-like protein OsPIL15 regulates tiller angle through light and gravity signals in rice. Tiller angle of cereal crops is a key agronomic trait that contributes to grain production. An understanding of how tiller angle is controlled is helpful for achieving ideal plant architecture to improve grain yield. Phytochrome-interacting factors (PIFs) are known to regulate seed germination, seedling skotomorphogenesis, shade avoidance, and flowering in Arabidopsis thaliana . Here, we report that OsPIL15 is, indeed, a rice PIF that negatively regulates tiller angle. Dominant-negative OsPIL15 plants displayed a larger tiller angle, which was associated with reduced shoot gravitropism. Phytochrome B (phyB) is the main photoreceptor perceiving the low red:far-red ratio of shade light. Compared with wild-type rice plants, loss-of-function phyB plants and OsPIL15 -overexpressing plants showed smaller tiller angles and enhanced shoot gravitropism. In addition, more OsPIL15 protein accumulated in phyB plants than in wild-type plants. Light regulates the level of the OsPIL15 protein negatively, depending on phyB partially. We propose that OsPIL15 integrates light and gravity signals to regulate tiller angle in rice.