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

Abstract

Tillering is a key trait that shapes aboveground architecture and directly contributes to rice yield. However, integration of environmental cues to genetic regulators for controlling tiller outgrowth remains poorly understood. We investigated the effects of nitrogen, one of the critical environmental factors, on the early stages of tiller bud outgrowth. Comprehensive temporal transcriptomic analyses in response to two nitrogen forms, nitrate (NO -) and ammonium (NH +), identified gene-regulatory networks for nitrogen-triggered tiller outgrowth, with phytohormone signaling as the central interface. Pharmacological, molecular, and genetic experiments established cytokinin-auxin antagonism as a central regulator of the nitrogen-mediated tillering. 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 to promote bud activation. Conversely, auxin promoted bud dormancy by inducing OsTB1 and OsPIN1a via OsARF11/16. Both NO - and NH + triggered tiller outgrowth and induced largely overlapping transcriptional responses, with a temporal delay for NO -. 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.