Phase separation of Rht8 -derived RNHL1 integrates ethylene and gibberellin signaling to regulate wheat internode elongation

Abstract Semi-dwarf varieties of wheat (Triticum aestivum L.) carrying Reduced height (Rht) genes revolutionized wheat production. Rht8, a widely deployed semi-dwarfing allele, encodes RNHL1 (Ribonuclease H-Like 1), yet the molecular mechanisms underlying its growth regulation remain unclear. Here, we uncover a liquid-liquid phase separation (LLPS)-mediated transcriptional pathway by which RNHL1 controls plant height. We show that RNHL1 forms nuclear biomolecular condensates via its intrinsically disordered regions (IDR1 and IDR3) and physically interacts with the ethylene signaling transcription factor TaEIL1 (Ethylene insensitive3-like 1) to establish functional transcriptional hubs. These RNHL1–TaEIL1 condensates directly bind and repress the ethylene response factor gene TaERF1 (Ethylene response factor 1), and TaERF1 suppresses the gibberellin (GA) biosynthetic gene TaGA3ox2 (Gibberellin 3-beta dioxygenase 2). Genetic analyses demonstrate that both RNHL1 and TaEIL1 positively regulate plant height, with loss-of-function mutants exhibiting similar dwarf phenotypes and convergent transcriptomic profiles. Importantly, we establish TaERF1 as a direct repressor of TaGA3ox2, completing a regulatory cascade in which RNHL1–TaEIL1 condensates modulate GA-mediated internode elongation. Our findings reveal an integration point between ethylene and GA signaling orchestrated by RNHL1–TaEIL1 phase separation and highlight RNHL1’s roles in nucleic acid metabolism and transcriptional regulation. This study provides fundamental insights into LLPS-mediated growth control in crops and identifies specific protein domains as potential targets for wheat improvement.