Integration of transcriptome, volatile and non-volatile metabolite profile reveals characteristic aroma formation in Toona sinensis

Toona sinensis is renowned for its unique aroma, but the formation mechanism remains unclear. In this study, volatile and non-volatile metabolites were combined with transcriptomes to investigate the potential mechanism of aroma formation in T. sinensis buds (TSB) and microgreens (TSM). Volatile sulfur compounds (VSCs) and terpenes were the main volatiles of TSM and TSB, respectively. 20 volatiles were identified as potential biomarkers, mainly VSCs and terpenes. In VSC biosynthesis pathways, cysteine was primarily synthesized from serine transformation in TSM. S-(trans-l-propenyl)-l-cysteine was likely to be the main precursor of VSC biosynthesis in T. sinensis. Higher expression of lachrymatory-factor synthase (LFS) consuming more precursor (1-propenyl sulfenic acid) in TSB led to reduced accumulation of VSCs. Isopentenyl diphosphate isomerase (IDI) and mevalonate diphosphate decarboxylase (MPDC) might play crucial roles in T. sinensis terpene biosynthesis. This study provided valuable insights into the formation of characteristic aromas in T. sinensis.