Transcriptome of Leaves in Blumea balsamifera Treated with Different Nitrogen Regimes

Nitrogen (N) plays key regulatory roles in both Blumea balsamifera growth and the synthesis of its medicinal component, (-)-borneol and total flavonoid, while the mechanism by which this nutrient regulates (-)-borneol and total flavonoid synthesis remains to be unclear. To address this question, a field experiment was conducted, in which B. balsamifera plants fertilized with 0 kg N hm-2 (control, CK), 150 kg N hm-2 (N1) and 300 kg N hm-2 (N2) treatments. Physiological and biochemical analyzes were carried out to determine the growth and metabolic response of plants to different N regimes. The results showed that CK treatment significantly inhibited plant growth and decreased leaf biomass, while elevated leaf (-)-borneol and total flavonoid contents in B. balsamifera; N1 treatment greatly promoted (-)-borneol accumulation. Then, transcriptome analysis was conducted to understand the underlying molecular mechanisms. A total of 6714 differentially expressed genes (DEGs) were identified. Many of these DEGs were significantly upregulated by CK treatment, including those involved in carbohydrate metabolism, terpenoid backbone biosynthesis, monoterpenoid biosynthesis and flavonoid biosynthesis. The potential transcription factors (TFs) linking N nutrition and medicinal component were also analyzed. CK treatment may promote (-)-borneol and total flavonoid synthesis by inducing terpenoids synthase gene (BbTPS) and MYB TFs, and using 150 kg N hm-2, a higher (-)-borneol accumulation in B. balsamifera leaves can be achieved. Our results provide deeper insight into the relationship between N nutrition and medicinal component synthesis in B. balsamifera.