Identification of key gene networks controlling monoterpene biosynthesis during grape ripening by integrating transcriptome and metabolite profiling

Monoterpenes are typical aroma components of muscat grape cultivars, providing pleasant floral and fruity aromas to grapes and wines. However, the molecular mechanism of monoterpene biosynthesis between muscat and non-muscat grape remains unclear. Here, the muscat grape cultivar ‘Jumeigui’ and the non-muscat grape cultivar ‘Kyoho’ were chosen as plant materials for a comprehensive transcriptome and metabolite analysis. The gas chromatography–mass spectrometry (GC–MS) analysis demonstrated that a total of 27 and 23 monoterpene compounds were identified and quantified in the ‘Jumeigui’ and ‘Kyoho’ grape, respectively. ‘Jumeigui’ grape accumulated significantly higher concentrations of monoterpenes than ‘Kyoho’ grape. Furthermore, geraniol, linalool, geranic acid, and β-citronellol might be important odorants contributing to the floral character of the ‘Jumeigui’ grape due to the high levels odor activity values (OAVs). Transcriptome analysis demonstrated that the expression profiles of VvDXS, VvGGPPS.SSU1, VvTPS-b/g showed a positive correlation with monoterpene accumulation in grapes. In addition, the expression patterns of the genes involved in jasmonic acid (JA) synthesis and signal were also positively correlated with monoterpene accumulation. All these results will help guide the functional verification of candidate genes related to monoterpene biosynthesis, as well as identify the master transcriptional and hormonal regulators of this pathway in grapes.