Selenium enhances floral terpene emission in tree peony by upregulating MEP pathway genes and terpene synthase genes

Paeonia ostii ‘Fengdan’ is a multifunctional plant valued for its ornamental, medicinal, and edible properties. Its flowers emit a certain amount of volatile aromatic substances, showing potential applications in functional foods and natural fragrances. Selenium (Se) application can increase the Se content and nutrient quality of plant tissues. However, the impacts and mechanisms of Se application on the aroma substances of tree peony flowers remain largely elusive. In this study, 100 mg·L−1 Na2SeO3 was sprayed approximately one week prior to flowering, and floral volatiles were collected at full bloom. The composition and content of volatile organic compounds (VOCs) and the expression of related genes were comprehensively analyzed by GC-MS, GC-IMS, PLS-DA, and RT-qPCR in tree peony flowers. GC-MS and GC-IMS identified 24 and 54 VOCs in tree peony flowers respectively, including terpenoids, alcohols, aldehydes, esters, benzenes, and alkanes. Se altered the composition and content of VOCs, especially increasing the release of key terpenoids such as β-ocimene, 3,7-dimethyl-2,6-octadien-1-ol, γ-terpinene and linalool. PLS-DA analysis clearly distinguished the Se-treated samples from the control, with VIP scores identifying terpenoids as the major contributors. Moreover, the gene expression pattern revealed that Se upregulated the expression of five rate-limiting genes (PoDXR, PoMCT, PoCMK, PoHDS, and PoHDRS) in the MEP pathway and five downstream terpene synthase genes (PoTPS1, PoTPS2, PoTPS3, PoTPS4, and PoTPS8). These findings demonstrate that Se promotes floral terpene emission in tree peony by regulating the MEP pathway genes, offering new insights into enhancing floral quality in tree peony flowers.