The E3 ubiquitin ligase RHB1A and the transcription factor GRF1 form a regulatory module that orchestrates the trade-off between photosynthetic growth and salt tolerance in poplar

Salt stress imposes a major constraint on plant growth and prompts plants to suppress growth-related processes, including photosynthesis, to prioritize stress defense and survival. However, the dynamic transcriptional regulation underlying this transition from growth to stress responses remains poorly understood. Here, we identify the bifunctional transcription factor GROWTH REGULATORY FACTOR 1 (GRF1) and its interacting partner, the RING-H2 E3 ubiquitin ligase RHB1A, in poplar. We define the GRF1 regulatory network by demonstrating that RHB1A mediates the 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 promoting photosynthetic growth. However, salt stress induces RHB1A, which promotes GRF1 degradation, thereby 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 response in poplar, providing key mechanistic insights into the transcriptional control of environmental responses in woody plants.