Transcriptome Analysis of Paeonia ostii ‘Fengdan’ Seeds Uncovers Starch and Sucrose Metabolism Conferring High Yield Under Brassinosteroid Treatment

<b>Background</b>: Tree peony (<i>Paeonia section Moutan</i> DC.) seeds, renowned for their rich content of unsaturated fatty acids, hold significant medicinal and nutritional value. Despite their potential, their yield is relatively low, which constrains economic gains and health benefits. Brassinosteroids (BRs), emerging as potent plant growth regulators, have demonstrated efficacy in boosting plant productivity. <b>Methods</b>: This study employed <i>Paeonia ostii</i> 'Fengdan' and administered either water (control group, CKs) or 0.05 mg/L BRs through foliar application during the seed enrichment and conversion phase to assess the effects of BR treatment on seed yield. <b>Results</b>: The BR treatment notably enhanced the protein, starch, and sugar content and yield of <i>P. ostii</i> 'Fengdan' seeds, surpassing those of the CKs. Transcriptome profiling identified a plethora of differentially expressed genes in <i>P. ostii</i> 'Fengdan' in response to BR treatment, which are implicated in biological processes associated with nutrient reservoir activity. KEGG analysis highlighted the pivotal role of starch and sucrose metabolism in the BR treatment response. WGCNA revealed key gene expression modules that correlate with physiological traits in <i>P. ostii</i> 'Fengdan'. Furthermore, the quantitative real-time PCR (qRT-PCR) validation of key genes in this pathway revealed that BR treatment enhances yield through a dual mechanism: accelerating the seed-filling process and optimizing developmental timing for earlier maturation. <b>Conclusions</b>: Collectively, these findings offer inaugural comprehensive genomic resources delineating the transcriptional regulatory mechanisms of BRs in <i>P. ostii</i> 'Fengdan' seeds.