Transcriptomic and proteomic approaches to explore the differences in monoterpene and benzenoid biosynthesis between scented and unscented genotypes of wintersweet

Abstract

Wintersweet (Chimonanthus praecox L.) is an important ornamental plant in China with a pleasant floral scent. To explore the potential mechanisms underlying differences in the fragrances among genotypes of this plant, we analyzed floral volatile organic compounds (VOCs) from two different genotypes: SW001, which has little to no fragrance, and the scented genotype H29. The major VOCs in H29 were linalool, trans-β-ocimene, benzyl acetate, methyl salicylate, benzyl alcohol (BAlc) and methyl benzoate. The most important aroma-active compound in H29, linalool, was emitted at a low concentration in SW001, which had markedly higher levels of trans-β-ocimene than H29. Next, to investigate scent biosynthesis, we analyzed the transcriptome and proteome of fully open flowers of the two genotypes. A total of 14 443 differentially expressed unigenes and 196 differentially expressed proteins were identified. Further analyses indicated that 56 differentially expressed genes involved in the terpenoid and benzenoid biosynthesis pathways might play critical roles in regulating floral fragrance difference. Disequilibrium expression of four terpene synthase genes resulted in diverse emission of linalool and trans-β-ocimene in both genotypes. In addition, the expressions of two CpMYC2 transcription factors were both upregulated in H29, implying that they may regulate linalool production. Notably, 16 of 20 genes in the benzenoid biosynthesis pathway were downregulated, corresponding to the relatively low level of benzenoid production in SW001. The lack of benzyl acetate might indicate that SW001 may lack substrate BAlc or functional acetyl-CoA:benzylalcohol acetyltransferase.

The chromosome-level wintersweet (Chimonanthus praecox) genome provides insights into floral scent biosynthesis and flowering in winter

“…Terpene synthases (TPSs) are the enzymes responsible for the last catalytic reaction in the MVA and MEP pathway to generate terpenoid compounds. With the aid of the assembly genome, a total of 52 complete CpTPSs were identified (Additional file 1: Table S19), the number of which is approximately double that detected by transcriptomics in our previous study [5]. Phylogenetic analysis of TPS from four species revealed that CpTPSs were clustered into five of six subfamilies described for land plants (Fig.…”

“…Monoterpenes are the major components of floral volatile organic compounds (VOCs) in wintersweet, especially the linalool, which accounts for more than half of the floral scent [5]. In plants, monoterpenes/diterpenes and sesquiterpenes are usually generated via the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway and the mevalonate (MVA) pathway, respectively [43].…”

“…Wintersweet flowers possess an intense fragrance that is endowed by a combination of volatile terpenoids (monoterpenes and sesquiterpenes) and benzenoids [5] which are emitted from nectaries distributed on the adaxial of inner petals [6]. These essential oils derived from its flower are widely used as components in perfume, cosmetics, and various flavor industries [7,8].…”

The role of volatiles in plant communication

“…() and Tian et al . () used RNA‐seq to try to pinpoint genes that are involved in flower volatile biosynthesis in Polianthes tuberosa , Freesia hybrida and wintersweet, respectively, that emit benzenoids and terpenoids, mostly terpenoids and terpenoids and benzenoids, respectively (Fan et al ., ; Huang et al ., ; Tian et al ., ). All three base their selection of gene candidates on homology and expression patterns.…”

Finding the fragrance genes of wintersweet

“…Tian et al () used an elegant combination of comparative transcriptomics and proteomics to explain the differences of VOC profiles between two genotypes of wintersweet, the fragrant H29 and the non‐fragrant SW001. The terpenoid and benzenoid profiles of the two genotypes differed widely.…”