Physiological and Transcriptomic Insights into Salicylic Acid-Mediated Alleviation of Low Phosphorus Stress in Rapeseed (Brassica napus L.)

Phosphorus (P) deficiency is a major constraint on crop productivity, and rapeseed (Brassica napus L.) is particularly sensitive to low phosphorus (LP) stress, yet the role of salicylic acid (SA) in alleviating LP stress in this crop remains poorly understood. Here, we investigated how exogenous SA alleviates LP stress in rapeseed seedlings. SA was applied at 0.1 mM and 0.2 mM under LP conditions, and its effects on plant growth, physiological traits, and transcriptomic responses were evaluated. SA treatment significantly ameliorated LP-induced growth inhibition, increased chlorophyll content and peroxidase activity, and reduced superoxide anion accumulation. RNA-seq analysis revealed that SA up-regulated the expression of phosphate transporter (PHT) family genes and activated genes involved in nitric oxide biosynthesis, flavonoid biosynthesis, glutathione metabolism, and nitrogen metabolism. These findings indicate that SA enhances LP tolerance in rapeseed through coordinated regulation of phosphorus acquisition, antioxidant defense, and key metabolic pathways, highlighting the potential of exogenous SA as an approach that could be further explored to improve phosphorus use efficiency under phosphorus-limited conditions in controlled environments, with field validation still needed.