Transcriptomics and metabolomics reveal the molecular mechanisms of synergistic effects between green nanosilica and arbuscular mycorrhizal fungi in alleviating drought stress in blueberry seedlings

Blueberry ( Vaccinium corymbosum ) possesses a shallow root system lacking root hairs, rendering it highly sensitive to drought stress. This study is the first to elucidate the molecular mechanisms by which green nanosilica (GNS) and arbuscular mycorrhizal fungi (AMF, Rhizophagus irregularis ) synergistically alleviate drought stress in blueberry seedlings through integrated transcriptomic and metabolomic analyses. A pot experiment was conducted with five treatments: well-watered control (CK), drought control (DR), AMF alone, GNS alone, and the GNS + AMF combination. After 30 days of drought stress, phenotypic, physiological, transcriptomic, and metabolomic analyses were performed. The GNS + AMF treatment was significantly more effective than either single application and performed comparably to the well-watered control. Seedlings maintained green leaves and robust root systems, exhibiting the highest root length and leaf biomass. They also displayed the highest maximum quantum yield of PSII (Fv/Fm) and effective quantum yield [Y(II)], indicating strong photosynthetic protection. In addition, soluble sugar, soluble protein, superoxide dismutase (SOD), and catalase (CAT) levels were highest, whereas malondialdehyde (MDA) content was lowest, demonstrating superior antioxidant capacity and osmotic regulation. Transcriptomic analysis revealed strong activation of the phenylpropanoid biosynthesis pathway, particularly in the GNS + AMF group, together with significant enrichment of the MAPK signaling pathway. Weighted gene co-expression network analysis (WGCNA) identified key gene modules positively correlated with antioxidant enzymes, chlorophyll content, root growth, and biomass. Metabolomics detected nine differential metabolites, with anthocyanins (malvidin, delphinidin, and cyanidin derivatives, among others) markedly upregulated in the GNS + AMF treatment. Joint analysis identified MYB, bHLH, and ERF transcription factors as core regulators of anthocyanin accumulation. In conclusion, GNS and AMF synergistically enhance drought tolerance through a “root–microbe–nano” system by activating phenylpropanoid metabolism, MAPK signaling, and anthocyanin biosynthesis. This approach provides a green and sustainable strategy for drought-resistant blueberry cultivation.