Integrated metabolome and transcriptome of champak identifies biosynthetic pathways for floral VOCs. Magnolia champaca

Magnolia champaca, commonly known as champak is a well-known tree due to its highly fragrant flowers. Champak floral scent is attributed to a complex mix of volatile organic compounds (VOCs). These aromatic flowers are widely used in flavors and fragrances industry. Despite its commercial importance, the VOC biosynthesis pathways in these flowers are largely unknown. Here, we combine metabolite and RNA sequencing (RNA-seq) analyses of mature champak flowers to discover the active VOC biosynthesis pathways as well as floral scent-related genes. A total of 43 VOCs were identified from champak flowers of which 46.9% were terpenoids, 38.9% were volatile esters and 5.2% belonged to phenylpropanoids/benzenoids. The detailed profiles of VOCs led to the discovery of pathways genes involved in floral scent biosynthesis from RNA-seq data. Moreover, our metabolite-guided transcriptomics, in vitro and in vivo enzyme assays and transgenic studies identified (R)-linalool synthase that is essential for the production of major VOCs of champak flowers, (R)-linalool and linalool oxides. Taken together, our findings will not only facilitate better understanding of ecological functions of champak floral VOCs, but also provide biotechnological targets for sustainable production of champak floral scent.