Green-synthesized silver nanoparticles (AgNPs) elicit phenolic and flavonoid enrichment and promote the expression of phenylpropanoid biosynthesis genes in callus cultures of ramie (Boehmeria nivea L.)

Ramie ( Boehmeria nivea L.), one of the oldest bast fiber crops, is increasingly recognized worldwide for its rich phenolic and flavonoid content in leaves and non-fibrous tissues. In this study, B. nivea leaf extract was used as both reducing and capping agent to produce silver nanoparticles (AgNPs) with a 24 ± 7 diameter and -26.1 mV zeta potential (ζ). Dynamic light scattering (DLS) analysis revealed a mean hydrodynamic Z-average of 146.7 ± 6.8 nm with a 0.168 polydispersity index, compatible with the phytochemical capping layer encircling the metallic core. The crystallinity of elemental Ag₂ was analyzed using X-ray diffraction to confirm the face-centered cubic (fcc) form. These self-derived AgNPs were used as abiotic elicitors in the callus cultures of ramie. At 20 mg L⁻¹, AgNPs increased fresh biomass 1.61-fold with a significant increase in specialized metabolite production, including total phenolics by +45% (2.62 vs. 1.81 mg GAE g⁻¹ FW), flavonoids by +74% (23.94 vs. 13.73 mg QE g⁻¹ FW), and tannins by +8%. Moreover, phenylpropanoid and flavonoid biosynthesis pathways were enriched. Transcriptomic analysis revealed the most significant upregulation (log₂FC = 7.89) of a nin-like transcription factor (gene_Bni09263), potentially coordinating metabolite accumulation and persistent defense against high-dose nanoparticle application. This work provides the first report of a nano-enabled platform that transforms a well-known industrial fiber crop into a high-value biofactory for consistent synthesis of antioxidant phytochemicals.