Volatile Composition and Classification of Paeonia lactiflora Flower Aroma Types and Identification of the Fragrance-Related Genes

Abstract

Flower scent is one of the main ornamental characteristics of herbaceous peony, and the improvement of flower fragrance is a vital objective of herbaceous peony breeding. In this study, 87 herbaceous peony cultivars were divided into three groups (no/light fragrance, medium fragrance, and strong fragrance) based on their sensory evaluation scores, and 16 strong fragrance cultivars and one no fragrance cultivar were selected for subsequent analysis. Sixty-eight volatile components were detected in these 17 cultivars based on solid-phase microextraction (SPME) and gas chromatography/mass spectrometry (GC/MS), and 26 types were identified as important scent components. They were composed of terpenoids, benzenoids/phenylpropanoids, and fatty acid derivatives. According to the content and odor threshold of these main aroma components, the characteristic aroma substances of herbaceous peony were identified, including linalool, geraniol, citronellol, and phenylethyl alcohol (2-PE). The cultivars of strong scented herbaceous peony were divided into three types: rose scent, lily scent, and mixed scent. We explored the possible key genes of characteristic aroma substances in herbaceous peony petals with different odors through the qRT-PCR. The key genes encoding monoterpene biosynthesis were found to be PlDXS2, PlDXR1, PlMDS1, PlHDR1, PlGPPS3, and PlGPPS4. In addition, the linalool synthase (LIS) gene and the geraniol synthase (GES) gene were also found. PlAADC1, PlPAR1, and PlMAO1, related to the biosynthesis of 2-PE were detected, and the synthetic pathway of 2-PE was speculated. In conclusion, these findings revealed that the difference in gene expression of monoterpene and 2-PE synthesis pathway was related to the difference in the fragrance of herbaceous peony. This study explored the releasing pathway of herbaceous peony characteristic aroma substances and provided key genetic resources for fragrance improvement.

Integration of RNA-Seq and Metabolite Analysis Reveals the Key Floral Scent Biosynthetic Genes in Herbaceous Peony

“…In detail, 2-PE, 1,4-dimethedoxybenzene, citronellol, geraniol, β-caryophyllene, and 1,8-cineole were identified as the most dominant floral VOCs conferring the aroma diversity to herbaceous peony (Figure 2A). As noted in previous studies [40], terpenoids appear as leading compounds, followed by volatile phenylpropanoid-related (C6-C2) compounds, fatty acid derivatives, and other compounds in peony plants (Figure 2B). For instance, terpenoids were highly observed in P. lactiflora cv.…”

“…Scent is an incredibly complex element of floral phenotype, a chemical masterpiece with dynamic patterns of emission. Previous studies categorized floral scent as no/light fragrance, medium fragrance, and strong fragrance based on the sensory evaluation in herbaceous peony cultivars [40]. Similarly, based on the composition and contribution of main aroma chemicals, the scent can also be classified in various ways [43][44][45].…”

“…RNA sequencing technologies have evolved into reliable and commonly used, massively parallel sequencing means for the study of molecular insights linked to various phenotypic traits without a reference genome [35,36]. RNA-Seq has been used to screen genes related to scent biosynthesis in plant such as Clivia miniata [37], Freesia hybrida [31,38], Aquilegia [33] and Paeonia species [39,40]. Similarly, our study aimed to understand the biochemical and molecular networks that may contribute to the biosynthesis of the main VOCs in peony by integrating metabolome analysis and transcriptome sequencing.…”

Transcriptome and volatile compounds analyses of floral development provide insight into floral scent formation in Paeonia lactiflora ‘Wu Hua Long Yu’

“…sensory perception of fragrance, peaking in S3 and subsequently declining, establishing them as the principal aromatic components of 'Wu Hua Long Yu' (Figure 1E). Significantly, linalool, citronellol, and geraniol were identified as monoterpenoids, confirming their role as the primary contributors to the fragrance of herbaceous peony (Zhao et al, 2023).…”

“…The formula is as follows. Each component content (ng•g -¹) = (peak area of each component/peak area of internal standard) × internal standard content (ng•μL -¹) ×internal standard volume (μL)/sample weight (g) (Zhao et al, 2023).…”