High-resolution transcriptome and volatile assays provide insights into flower development and aroma formation in single- and double-petal jasmines (Jasminum sambac)

Jasmine (Jasminum sambac) is one of the most popular ornamental plant species in the world, with diverse floral morphology, including single-petal (SP), double-petal (DP) and multi-petal (MP). Here, based on our recently published chromosome-level genome assemblies of SP and DP Jasmines, we generated high-resolution transcriptional profiles of SP and DP jasmine flowers at six developmental stages and identified key events and regulators contributing to the differences between the two jasmines. The upregulated genes of DP jasmine in early flower development were mainly related to photosynthesis and light reactions, which may contribute to its stronger energy metabolism and environmental adaptability compared with SP jasmine. AGL63 (GOA) and PLETHORA3 (PLT3) motifs involved in floral organogenesis in Arabidopsis were overrepresented at the initial stages in SP and DP, respectively, and may be involved in the development of different petal layers in jasmines. The specific high expression of volatile terpene and benzene/phenylpropane synthesis genes during flowering is an important factor why jasmines during bud development and other tissues are scentless. This factor is also responsible for the typical floral volatiles of jasmine, including terpenes (α-farnesene, linalool, and (E)-β-ocimene), and benzenoid lipids (benzyl acetate, methyl salicylate, and methyl benzoate). The high content of α-farnesene and the low content of other core volatiles may constitute the fresh and elegant fragrance of SP compared to DP jasmine. Only DP jasmine had high expression of benzoic acid/salicylic acid carboxyl methyltransferase (BMST), which resulted in its higher content of volatile methyl salicylate and methyl benzoate. Our findings lay the foundation for understanding the flower development and aroma formation mechanisms of different jasmine petal morphologies.