Foliar application of biological nano-selenium reduces cadmium accumulation in peppers with concentration-associated regulation under controlled conditions

Guizhou karst soils exhibit elevated cadmium background levels, increasing cadmium accumulation risk in chili peppers. Research regarding foliar bio-selenium nanoparticle (Bio-SeNP) regulation of cadmium stress remains limited. This study examined Bio-SeNP effects through germination, hydroponic, soil experiments, and transcriptomics. Bio-SeNP (2–20 mg/L) enhanced germination (100% at 5 mg/L), while concentrations>50 mg/L inhibited growth. Foliar application of 5 mg/L Bio-SeNP improved growth, photosynthesis, and antioxidant defense under cadmium stress: SOD, POD, CAT activities increased 2.51%–54.90%, malondialdehyde decreased 173.40 nmol/g, root cadmium decreased 23.20%. Soil experiments demonstrated 5 mg/L Bio-SeNP increased plant height 10.78%, fruit fresh weight 27.78%, yield 27.86%, and decreased fruit cadmium 30.00%. Transcriptomic analysis identified 1,762 differentially expressed genes enriched in detoxification pathways. Bio-SeNP treatment modified the expression of cadmium-responsive transcription factors, with WRKY53 upregulated 2.46-fold and CRF1 downregulated 5.09-fold. In auxin signaling, AUX1 downregulation (5.64-fold) and TIR1 upregulation (7.34-fold) indicated Bio-SeNP modulates hormone perception for growth-defense balance. This establishes 5 mg/L as optimal for cadmium mitigation, informing safe chili production in contaminated soil. • 5 mg/L Bio-SeNP optimally alleviates cadmium stress in chili peppers; • Foliar Bio-SeNP treatment reduces fruit cadmium content by 30.00%; • Bio-SeNP enhances antioxidant enzyme activities and photosynthetic capacity; • WRKY53 and auxin signaling pathways respond to Bio-SeNP treatment; • AUX 1 downregulation and TIR1 upregulation modulate auxin perception.