Transcriptome and volatile compounds profiling analyses provide insights into the molecular mechanism underlying the floral fragrance of tree peony

Tree peony (Paeonia suffruticosa Andr.) is a popular ornamental plant around the world, which is known for its distinctively large and fragrant flowers. However, the underlying molecular mechanism of floral fragrance synthesis in tree peony remains poorly understood. In this study, integrative volatile profiling and RNA sequencing were conducted in four wild tree peony species: Paeonia ostii, Paeonia rockii, Paeonia delavayi and Paeonia lutea. A total of 67 floral volatiles were identified through gas chromatography-mass spectrometry (GC-MS) analysis. Terpenes were most abundant volatiles in P. ostii and P. rockii, while benzenoids content were relatively higher in P. delavayi and P. lutea. Transcriptome data revealed 17,967 differential expression genes (DEGs), 116 and 147 of which were found be related to the accumulation of terpenes and benzenoids, respectively. Specifically, 1-deoxy-D-xylulose 5-phosphate synthase, geranyl pyrophosphate synthase, farnesyl pyrophosphate synthase and terpene synthase may be the major regulators of floral terpenes biosynthesis in P. ostii and P. rockii, whilst 3-deoxy-7-phosphoheptulonate synthase, phenylalanine ammonialyase, cinnamate: CoA ligase and short-chain dehydrogenases/reductases may control the production of benzenoids production in P. delavayi and P. lutea. Taken together, results from this study sheds light on the molecular mechanism of fragrance variation among different tree peony species and also provides a valuable resource to investigate floral fragrance formation in tree peony.