GC-MS metabolite and transcriptome analyses reveal the differences of volatile synthesis and gene expression profiling between two Chinese rose cultivars

Floral fragrance is an important ornamental trait of horticultural crops. However, research on the physiological and molecular biology of the floral volatile compounds in Chinese rose is limited. This study conducted metabolomic and transcriptomic analyses on the floral volatile compounds of Rosa chinensis (R. chinensis) 'Old Blush' ('OB') and R. chinensis 'Chilong Hanzhu' ('CH'). A total of 22 major volatile organic compounds (VOCs) were detected in the blooming flowers of 'OB' and 'CH'. The main VOCs emitted from 'OB' petals was 1,3,5-trimethoxybenzene (TMB), while that from 'CH' petals was 2-phenylethanol (2-PE). The GO and KEGG enrichment on differentially expressed genes (DEGs) revealed the essential role of phenylpropanoid pathway in the difference of floral fragrance between two cultivars, and a total of 15 key genes involved in the biosynthesis of phenylpropanoid were identified in R. chinensis flowers. The overexpression of RcCH_AADC-1 in transgenic tobacco plants led to the accumulation of 2-PE. In contrast, no significant change in the level of 2-PE was observed after the transient transformation of RcCH_PAR1 or RcCH_PAR1_Like into tobacco plants. These findings provide valuable insight for enhancing the accumulation of 2-PE in R. chinensis.