Toward an understanding of selenium accumulation in rice: a preliminary transcriptomic inquiry of selenium fertilizer forms

Selenium (Se) biofortification in rice addresses dietary Se deficiencies. While Se fertilization is key, the efficiency and molecular mechanisms differ among Se forms (selenate, nano-Se (SeNPs)) and application methods (soil vs. foliar). This study aimed to compare the effects of selenate and biosynthesized SeNPs, applied via soil and foliar methods, on rice growth, Se accumulation, speciation, and the associated transcriptional responses. Rice plants were treated with selenate or biosynthesized SeNPs via soil application or foliar spraying. Biomass, yield, grain Se concentration and speciation were analyzed. Transcriptomic profiling of roots (soil-applied Se) and leaves (foliar-applied Se) was performed, with validation by qPCR and WGCNA. Both application methods enhanced biomass and yield. Foliar spraying was more efficient for grain Se enrichment, increasing Se concentration by 28.13-fold (selenate) and 89.87-fold (SeNPs), versus 7.83–9.87-fold for soil application. Selenomethionine was the predominant Se species in grains. Transcriptomics revealed selenate upregulated sulfate transporter and xylem-related genes in roots, whereas SeNPs enhanced aquaporin and sulfur assimilation gene expression. Foliar SeNPs triggered stomatal and aquaporin-related gene expression. Both forms influenced sulfur/nitrogen metabolism, with SeNPs additionally modulating organic acid and amino acid pathways. WGCNA identified co-expression modules correlated with grain Se content and selenomethionine proportion, enriched in transcription factors (MYB, WRKY, bHLH) and ABC transporters. Foliar application, particularly of SeNPs, is highly effective for Se biofortification in rice, associated with distinct molecular uptake and assimilation pathways. These findings provide insights for optimizing Se fertilization strategies to enhance dietary Se supply.