Integrated physiological, transcriptomic, and metabolomic analyses reveal that low-nitrogen conditions improve the accumulation of flavonoids in snow chrysanthemum

Nitrogen (N) levels have significant effects on plant growth and chemical composition. Previous studies found that low-N treatment maintained the number of inflorescences and promoted flavonoid accumulation in snow chrysanthemum, but the underlying mechanism was not clear. To investigate the complex flavonoid biosynthesis pathway of snow chrysanthemum under low-N conditions, we compared low-N and normal-N groups across the four harvest stages. Low-N treatment caused early flowering in snow chrysanthemum and maintained the production of flowers. Low-N stress increased the carbon (C)/N ratio in flowers, thus significantly increasing the total flavonoid content in the flower bud stage, early flowering stage and full flowering stage. Moreover, analysis of the flavonoid metabolome showed that low-N treatment resulted in increased levels of kaempferol-3-O-(6''-p-coumaroyl)galactoside, quercetin-3-O-(2''-acetyl)glucuronide, 3,7-dimethylquercetagetin-(3′,4′,5,6-tetrahydroxy-3,7-dime-thoxyflavone), isotamarixin, apigenin-8-C-arabinoside, quercetin-5-O-glucuronide, and cyanidin-3-O-(6''-O-p-coumaroyl)glucoside, which further enhanced antioxidant activity. Combined flavonoid metabolism and transcriptomic data analysis indicated that PAL, 4CL, HCT, C3'H, CHS, DFR and ANR are key genes leading to the accumulation of flavonoids in snow chrysanthemum under low-N conditions. In addition, 6 transcription factors (especially MYB26c, Cluster-16181.96870) and 17 other regulators (mainly including transporter proteins) under low-N conditions are also involved in the regulation of flavonoid accumulation. This research provides a new perspective for studying the regulatory effect of N levels on the growth and flavonoid biosynthesis in snow chrysanthemum. The data presented in this study are available in the article and supplementary materials.