Sclareol and linalyl acetate are produced by glandular trichomes through the MEP pathway.

Sclareol, an antifungal specialized metabolite produced by clary sage, Salvia sclarea, is the starting plant natural molecule used for the hemisynthesis of the perfume ingredient ambroxide. Sclareol is mainly produced in clary sage flower calyces; however, the cellular localization of the sclareol biosynthesis remains unknown. To elucidate the site of sclareol biosynthesis, we analyzed its spatial distribution in the clary sage calyx epidermis using laser desorption/ionization mass spectrometry imaging (LDI-FTICR-MSI) and investigated the expression profile of sclareol biosynthesis genes in isolated glandular trichomes (GTs). We showed that sclareol specifically accumulates in GTs' gland cells in which sclareol biosynthesis genes are strongly expressed. We next isolated a glabrous beardless mutant and demonstrate that more than 90% of the sclareol is produced by the large capitate GTs. Feeding experiments, using 1-13C-glucose, and specific enzyme inhibitors further revealed that the methylerythritol-phosphate (MEP) biosynthetic pathway is the main source of isopentenyl diphosphate (IPP) precursor used for the biosynthesis of sclareol. Our findings demonstrate that sclareol is an MEP-derived diterpene produced by large capitate GTs in clary sage emphasing the role of GTs as biofactories dedicated to the production of specialized metabolites.

Study of the genetic and phenotypic variation among wild and cultivated clary sages provides interesting avenues for breeding programs of a perfume, medicinal and aromatic plant.

A road-map of the genetic and phenotypic diversities in both crops and their wild related species can help identifying valuable genetic resources for further crop breeding. The clary sage (Salvia sclarea L.), a perfume, medicinal and aromatic plant, is used for sclareol production and ornamental purposes. Despite its wide use in the field of cosmetics, the phenotypic and genetic diversity of wild and cultivated clary sages remains to be explored. We characterized the genetic and phenotypic variation of a collection of six wild S. sclarea populations from Croatia, sampled along an altitudinal gradient, and, of populations of three S. sclarea cultivars. We showed low level of genetic diversity for the two S. sclarea traditional cultivars used for essential oil production and for ornamental purposes, respectively. In contrast, a recent cultivar resulting from new breeding methods, which involve hybridizations among several genotypes rather than traditional recurrent selection and self-crosses over time, showed high genetic diversity. We also observed a marked phenotypic differentiation for the ornamental clary sage compared with other cultivated and wild clary sages. Instead, the two cultivars used for essential oil production, a traditional and a recent one, respectively, were not phenotypically differentiated from the wild Croatian populations. Our results also featured some wild populations with high sclareol content and early-flowering phenotypes as good candidates for future breeding programs. This study opens up perspectives for basic research aiming at understanding the impact of breeding methods on clary sage evolution, and highlights interesting avenues for clary breeding programs.

Photo-pollution stress in skin: Traces of pollutants (PAH and particulate matter) impair redox homeostasis in keratinocytes exposed to UVA1.

BACKGROUND: It is likely that skin is exposed to low concentrations of pollutants such as Polycyclic Aromatic Hydrocarbons (PAH) either through topical penetration by ultrafine particles or by systemic distribution. No precise estimation of pollutants in living skin is available, but literature has reported contamination of blood by PAH at concentrations in the nanomolar range. Some pollutants (PAH for example) are photo-reactive and phototoxic: sunlight and pollution might thus synergistically compromise skin health. OBJECTIVE: Here, the biological effects of particulate matter, PM extract and various PAH were compared in normal human epidermal keratinocytes (NHEK) and reconstructed skin model exposed to either daily UV (d-UV 300-400nm) or UVA1 (350-400nm). Impact of pollutants (PM, PAH or PM extract) combined to UV was studied on NHEK by measuring toxicity, redox homeostasis and GSH metabolism in NHEK. METHODS: NHEK were exposed to UV from solar simulator (either d-UV or UVA1) combined with pollutants. Viability, clonogenic efficiency, redox homeostasis and GSH metabolism were assessed. RESULTS: Pollutants (PAH, PM or PM extract) ±UVA1 irradiation was associated with a significant phototoxic effect that was equal to or greater than that produced by d-UV. This result is interesting considering that UVA1 represents around 80% of daily UV and reaches the dermal-epidermal junction with ease. Moreover, among PAH studied, benzo[a]pyrene and indeno[1,2,3-cd]pyrene were phototoxic at very low concentrations (nanomolar range) on cultured cells or in reconstructed epidermis and also impaired keratinocyte clonogenic potential at sub-toxic doses. ROS generation within cells and in the inner mitochondrial compartment, mitochondrial membrane depolarization and/or reduced ATP production were also noted. Meanwhile, intracellular glutathione concentrations transiently decreased several hours post-treatment and reduction of its synthesis by buthionine sulfoximine potentiated PAH phototoxicity. Consequently, expression of GSH neo-synthesis genes such as SLC7A11 or GCLc was upregulated several hours post-treatment. CONCLUSION: These results obtained using PAH concentrations in the range of those reported in blood of pollution-exposed people suggest that exposure to such a photo-pollution stress, particularly if chronic, may impair cutaneous homeostasis and aggravate sunlight-induced skin damage.