Integrated transcriptomic and volatilomic profiles to explore the potential mechanism of aroma formation in Toona sinensis.

As an important quality determinant of Toona sinensis, the unique aroma largely impacts the purchasing behavior of consumers. However, the underlying formation mechanism of the characteristic aroma of T. sinensis remains poorly understood. In this work, integrative volatile/nonvolatile compounds profiling and RNA sequencing were used to characterize six T. sinensis cultivars. Volatile sulfur compounds (VSCs) and terpenoids were the main volatile organic compounds (VOCs) in T. sinensis, accounting for 36.95-67.27% and 17.75-31.36% of the total VOC content, respectively. Notably, the VOCs originated from terpenoid biosynthesis, and the degradation of unsaturated fatty acids (UFAs) played important roles in reconciling the irritating odor of VSCs. The above differential metabolic profiles are the main sources of the specific aroma of different T. sinensis cultivars. Furthermore, 13 volatile organic compounds were identified as potential biomarkers to distinguish these T. sinensis cultivars by chemometric analysis. Based on the analysis of transcriptomic datasets, the potential biosynthetic pathways of the key VSCs were firstly confirmed in T. sinensis. It was found that 1-propenylsulfenic acid is a crucial precursor in the formation of characteristic VSCs in T. sinensis. Additionally, two potential mechanisms were proposed to explain the differences of the key VSCs among six T. sinensis cultivars. These results provide theoretical guidance for improving the aroma quality of T. sinensis.

Integrated volatilomic profiles and chemometrics provide new insights into the spatial distribution and aroma differences of volatile compounds in seven Toona sinensis cultivars.

As a popular vegetable, the unique and pleasant aroma is the key quality characteristic of Toona sinensis. To explore the sources and differences of aroma, the volatilomic profiling in the leaves and shoots of seven T. sinensis cultivars were investigated by chemometric analysis. The results indicated that aroma differences of each cultivar can be distinguished by W5S, W1S, W1W and W2S sensors during E-nose analysis. More than two thirds of all volatile organic compounds (VOCs) were derived from the leaves of most cultivars, except for Ximu toon. Notably, 2-mercapto-3,4-dimethyl-2,3-dihydrothiophene, 3,4-dimethyl thiophene, methyl thiirane, isocaryophyllene and hexanal were the major VOCs in both the leaves and shoots of T. sinensis. By constructing a weighted correlation network model, 5 modules and 11 hub VOCs were identified in the leaf samples of all cultivars. The data indicate that differential intracellular metabolic responses are responsible for the aroma formation of seven T. sinensis cultivars.