The E3 ubiquitin ligase RHB1A and GRF1 transcript factor forms a regulatory module to orchestrate the trade-off between photosynthetic growth and salt tolerance in poplar

Salt stress imposes a major constraint on plant growth and prompts plants to actively suppress developmental programs, including the downregulation of photosynthesis-related genes, to prioritize stress defense and survival. However, the dynamic transcriptional regulation underlying this growth-to-stress transition remains poorly understood. Here, we identified the bifunctional transcription factor (TF) GROWTH REGULATORY FACTOR 1 (GRF1) and its interacting partner, the RING-H2 E3 ubiquitin ligase RHB1A, in poplar, and delineated the GRF1 regulatory network by demonstrating RHB1A-mediated ubiquitination and proteasomal degradation of GRF1 using transgenic poplar lines and an integrated multi-omics approach. Under favorable conditions, GRF1 acts as a transcriptional activator of photosynthesis-related genes and a repressor of stress-responsive genes, thereby enhancing photosynthetic growth. However, salt stress induces RHB1A, which promotes GRF1 degradation, attenuating growth-promoting pathways and derepressing stress response genes, ultimately conferring salt tolerance. These findings uncover a GRF1-RHB1A regulatory module that dynamically coordinates the trade-off between photosynthetic growth and salt responses in poplar, providing key mechanistic insights into the transcriptional control of environmental responses in woody plants.