A cytokinin-auxin antagonistic module regulates nitrogen-triggered tiller outgrowth in rice

Tillering is a key trait that shapes aboveground architecture and directly contributes to rice yield. While tiller bud formation is primarily under strong genetic control, bud outgrowth into functional tillers is strongly influenced by physiological and environmental cues. However, integration of environmental cues to genetic regulators for controlling tiller outgrowth remains poorly understood. Nitrogen availability is one of the most critical environmental factors regulating tiller outgrowth. Therefore, we investigated the effects of Nitrogen on the early stages of bud outgrowth and dissected the genetic module mediating nitrogen-mediated tiller outgrowth. Both nitrate (NO3-) and ammonium (NH4+) triggered tiller outgrowth and induced largely overlapping transcriptional responses, although nitrate acted with a temporal delay. Phytohormone signaling emerged as the central interface linking nitrogen supply to the early stages of bud outgrowth, with cytokinin - auxin antagonism playing a key role. Cytokinin promoted bud outgrowth by repressing the TCP transcription factor OsTB1, the key inhibitor of tillering, via Cytokinin Response Factors OsERF53/54. OsERF53/54 further reduced polar auxin transport by repressing OsPIN1a, which in turn, promoted bud activation. Conversely, auxin promoted bud dormancy by inducing OsTB1 and OsPIN1a via OsARF11/16. Adequate nitrogen supplies induced cytokinin signaling while inhibiting auxin signaling and transport in tiller buds, thereby triggering bud outgrowth. Together, we identify a key regulatory role of auxin cytokinin antagonistic module for integrating nitrogen signals to determine tiller bud fate.