Biochemistry and genetics of floral scent: a historical perspective

Identification and functional analysis of terpene synthases revealing the secrets of aroma formation in Chrysanthemum aromaticum

C. aromaticum is widely cultivated for its aromatic, medicinal, and tea-applicable properties, earning the nickname 'lavender in composite'. Terpenoids are the major compounds of C. aromaticum fragrance. To reveal the molecular mechanisms of terpenoid biosynthesis in C. aromaticum, NGS and SMRT sequencing were employed to identify the key terpene synthase genes. A total of 59,903 non-redundant transcripts were obtained by the transcriptome analysis. Twenty-nine terpene synthase genes (TPSs) were identified, and phylogenetic analysis showed that they belong to four subfamilies of terpene synthases. Five CaTPSs were successfully cloned. Subcellular localization showed they were present in the nucleus and cytosol. Structure models of five terpene synthases were predicted, and molecular docking results showed good binding affinities with FPP/GPP. In vitro enzymatic tests showed that CaTPS7, CaTPS8, CaTPS10 and CaTPS20 could catalyze substrates to produce terpenoids. CaTPS7 and CaTPS20 were both able to effectively convert the precursor FPP into caryophyllene. CaTPS8 could convert FPP to trans-nerolidol and nerolidyl acetate, while CaTPS10 could convert FPP to elemene and aristolochene. This study lays the groundwork for further research to depict the metabolism network of terpenoid in C. aromaticum. These identical terpene synthase genes could be introduced into the cultivated chrysanthemums to enhance their fragrance.

Sniffing Out the Sustainable Future: The Renewability Revolution in Fragrance Chemistry

In this review, the impact of the transition from today's resource-wasting petrochemical economy towards a 100/100 renewable and biodegradable future is discussed with respect to the fragrance families: "citrus", "green", "fruity", "floral", "floriental", "oriental", "woody", "chypre" and "fougère". After benchmark data on ingredients usage, definitions on biodegradation and sustainability are given. Celebrating the 150th anniversary of synthetic vanillin, its historic synthesis from renewable starting materials serves as introduction. In the grand scheme of things, citrus scents upcycled from the beverages industry, are already an ideal case for 100/100 with new opportunities for artificial essential oils. In the fruity domain, transparent and lactonic ingredients are available in a sustainable manner. However, in the domain of green odorants, there is a lack of green chemistry for important key materials. In the floral family, renewability is more critical than biodegradability, but cost is an issue. Thanks to Ambrox and maltol, florientals and orientals will persist, while woody notes severely lack an Iso E Super replacer. In the chypre genre, patchouli became the new moss, but more musks are increasingly in demand. With their high percentage of linalool and dihydromyrcenol, the construction of fougères could well become a precedent for other families, despite challenges in vetiver and salicylates. Still, the challenges exemplified here create immense opportunities for new perfumery materials.

The scent of roses, a bouquet of fragrance diversity

Roses have been domesticated since antiquity for their therapeutic, cosmetic, and ornamental properties. Their floral fragrance has great economic value, which has influenced the production of rose varieties. The production of rose water and essential oil is one of the most lucrative activities, supplying bioactive molecules to the cosmetic, pharmaceutical, and therapeutic industries. In recent years, major advances in molecular genetics, genomic, and biochemical tools have paved the way for the identification of molecules that make up the specific fragrance of various rose cultivars. The aim of this review is to highlight current knowledge on metabolite profiles, and more specifically on fragrance compounds, as well as the specificities and differences between rose species and cultivars belonging to different rose sections and how they contribute to modern roses fragrance.

Characterization of a partially saturated and glycosylated apocarotenoid from wheat that is depleted upon leaf rust infection

Recent semi-targeted metabolomics studies have highlighted a number of metabolites in wheat that associate with leaf rust resistance genes and/or rust infection. Here, we report the structural characterization of a novel glycosylated and partially saturated apocarotenoid, reminiscent of a reduced form of mycorradicin, (6E,8E,10E)-4,9-dimethyl-12-oxo-12-((3,4,5-trihydroxy-6-(2-hydroxyethoxy)tetrahydro-2H-pyran-2-yl)methoxy)-3-((3,4,5-trihydroxy-6-(hydroxymethyl)tetrahydro-2H-pyran-2-yl)oxy)dodeca-6,8,10-trienoic acid, isolated from Triticum aestivum L. (Poaceae) variety 'Thatcher' (Tc) flag leaves. While its accumulation was not associated with any of Lr34, Lr67 or Lr22a resistance genes, infection of Tc with leaf rust was found to deplete it, consistent with the idea of this metabolite being a glycosylated-storage form of an apocarotenoid of possible relevance to plant defense. A comparative analysis of wheat transcriptomic changes shows modulation of terpenoid, carotenoid, UDP-glycosyltransferase and glycosylase -related gene expression profiles, consistent with anticipated biosynthesis and degradation mechanisms. However, details of the exact nature of the relevant pathways remain to be validated in the future. Together these findings highlight another example of the breadth of unique metabolites underlying plant host-fungal pathogen interactions.