Integrated transcriptomic and metabolomic analysis reveals the changes in monoterpene compounds during the development of Muscat Hamburg (Vitis vinifera L.) grape berries

Monoterpenes are important compounds that influence the aromas of grapes and wines. The molecular mechanisms underlying the changes in monoterpenes during the grape ripening period have not been thoroughly characterized. In this study, the free and bound monoterpene profiles in Muscat Hamburg grape berries at different phenological stages were investigated at the transcriptomic and metabolomic levels. Principal component analyses indicated that the free and bound monoterpene profiles were affected by the developmental stages. Most monoterpenes were produced slowly before veraison, but they accumulated rapidly during the veraison period, after which their contents decreased slightly in mature berries. The transcriptomic analysis revealed 35 differentially expressed genes involved in the monoterpene synthesis pathway. The VIT_04s0008g04970, VIT_03s0063g02030 and VIT_15s0024g00850 expression levels were consistent with the changes in the accumulation of monoterpene compounds. The quantitative real-time polymerase chain reaction analysis of eight key differentially expressed genes in the monoterpenoid pathway confirmed the RNA-seq data were reliable. Our findings provide new insights into Muscat Hamburg grape aroma development. Further research on the period with the highest aroma potential may lead to enhanced grape berry aroma qualities.