Mechanisms of Curled Branch Development in Gracilariopsis lemaneiformis Induced by Nutrient Limitation

In response to the abnormal branching of Gracilariopsis lemaneiformis observed in recent years in cultivation areas, this study investigated whether nutrient limitation could induce curly branch formation and preliminarily explored the mechanisms underlying this phenomenon. Thalli were cultured under different nitrogen and phosphorus levels, and changes in branch morphology were recorded.The induced curled branches were then characterized through morphological observation, physiological and biochemical measurements, and gene expression analysis. The results demonstrated that specific low-nitrogen and low-phosphorus conditions consistently induced curly branch formation.This curled phenotype was accompanied by disorganized cellular arrangement, reduced photosynthetic efficiency, and increased activities of oxidoreductase-related enzymes. Transcriptome analysis revealed significant down-regulation of photosynthesis-related pathways. Concurrently, up-regulation occurred in energy metabolism and oxidoreductase-related pathways. Taken together, these findings establish that nutrient limitation may affect branch development by altering photosynthesis, energy metabolism, oxidative status, and ROS-related signaling. These findings establish a mechanistic framework for elucidating branch development under nutrient limitation.