Biosynthèse du sclaréol et sa régulation chez la sauge sclarée

Sclareol is a diterpene produced by floral organs of clary sage (Salvia sclarea, Lamiaceae). It is used in perfume industry for the hemisynthesis of ambroxide, a high-valued perfume component characterized by an amber scent and a high perfume fixation capacity. The global demand for sclareol currently rises, prompting attempts at increasing the yield of sclareol production from clary sage. The purpose of the work presented in this manuscript was to improve knowledge on sclareol biosynthesis and its regulation in clary sage, in order to highlight strategies aiming at enhancing clary sage sclareol content. The analysis of the surface of clary sage calyces by mass spectrometry imaging suggests that sclareol is mainly secreted by specialized epidermal structures called glandular trichomes. Moreover, we have highlighted the respective contributions of the two terpenoid biosynthesis pathways present in plants, MVA and MEP pathways, to the biosynthesis of three terpenoids of clary sage. ¹³C-labeling experiments indicate that sclareol and linalyl acetate both originate from the MEP pathway, whereas β-caryophyllene seems to be of mixed origin. We have also investigated the potential role of a phytohormone, methyljasmonate, in the regulation of sclareol production in clary sage. Finally, we have explored the genetic and phenotypic diversity of Croatian wild clary sage populations and show that these populations represent a distinct genetic resource compared to reference populations. Taken together, these results highlight promising avenues for targeted genetic enhancement of clary sage performances.Le sclaréol est un diterpène produit par les organes floraux de la sauge sclarée (Salvia sclarea, Lamiaceae). Il est utilisé en parfumerie pour l’hémisynthèse de l’ambroxide, une substance caractérisée par une odeur ambrée et une grande capacité de fixation des parfums. L’augmentation de la demande mondiale en sclaréol stimule actuellement les tentatives d’accroître le rendement de la production de sclaréol à partir de la sauge sclarée. L’objectif du travail présenté dans ce manuscrit était d’améliorer notre compréhension de la biosynthèse du sclaréol et de sa régulation chez la sauge sclarée, afin de mettre en évidence des stratégies d’augmentation du contenu en sclaréol de la sauge sclarée. L'analyse de la surface des calices de sauge sclarée par imagerie par spectrométrie de masse suggère que le sclaréol est principalement sécrété par des structures épidermiques spécialisées appelées trichomes glandulaires. De plus, nous avons mis en évidence les contributions respectives des deux voies de biosynthèse des terpènes présentes chez les plantes, les voies MVA et MEP, à la biosynthèse de trois terpènes de la sauge sclarée. Des expériences de marquage au ¹³C indiquent que le sclaréol et l’acétate de linalyle sont tous deux issus de la voie MEP, alors que le β-caryophyllène semble être d’origine mixte. Nous avons également étudié le rôle potentiel d’une phytohormone, le méthyljasmonate, dans la régulation de la production de sclaréol chez la sauge sclarée. Enfin, nous avons exploré la diversité génétique et phénotypique de populations croates de sauge sclarée sauvage, et montrons que ces populations représentent une ressource génétique distincte par rapport aux populations de référence. L’ensemble de ces résultats met en évidence des pistes prometteuses pour l'amélioration génétique ciblée des performances de la sauge sclarée

Genetic Control of Glandular Trichome Development

International audiencePlant glandular trichomes are epidermal secretory structures producing various specialized metabolites. These metabolites are involved in plant adaptation to its environment and many of them have remarkable properties exploited by fragrance, flavor, and pharmaceutical industries. The identification of genes controlling glandular trichome development is of high interest to understand how plants produce specialized metabolites. Our knowledge about this developmental process is still limited, but genes controlling glandular trichome initiation and morphogenesis have recently been identified. In particular, R2R3-MYB and HD-ZIP IV transcription factors appear to play essential roles in glandular trichome initiation in Artemisia annua and tomato. In this review, we focus on the results obtained in these two species and we propose genetic regulation models integrating these data

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

International audienceA 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

Gene stacking of multiple traits for high yield of fermentable sugars in plant biomass.

BackgroundSecond-generation biofuels produced from biomass can help to decrease dependency on fossil fuels, bringing about many economic and environmental benefits. To make biomass more suitable for biorefinery use, we need a better understanding of plant cell wall biosynthesis. Increasing the ratio of C6 to C5 sugars in the cell wall and decreasing the lignin content are two important targets in engineering of plants that are more suitable for downstream processing for second-generation biofuel production.ResultsWe have studied the basic mechanisms of cell wall biosynthesis and identified genes involved in biosynthesis of pectic galactan, including the GALS1 galactan synthase and the UDP-galactose/UDP-rhamnose transporter URGT1. We have engineered plants with a more suitable biomass composition by applying these findings, in conjunction with synthetic biology and gene stacking tools. Plants were engineered to have up to fourfold more pectic galactan in stems by overexpressing GALS1, URGT1, and UGE2, a UDP-glucose epimerase. Furthermore, the increased galactan trait was engineered into plants that were already engineered to have low xylan content by restricting xylan biosynthesis to vessels where this polysaccharide is essential. Finally, the high galactan and low xylan traits were stacked with the low lignin trait obtained by expressing the QsuB gene encoding dehydroshikimate dehydratase in lignifying cells.ConclusionThe results show that approaches to increasing C6 sugar content, decreasing xylan, and reducing lignin content can be combined in an additive manner. Thus, the engineered lines obtained by this trait-stacking approach have substantially improved properties from the perspective of biofuel production, and they do not show any obvious negative growth effects. The approach used in this study can be readily transferred to bioenergy crop plants

Bulletin de la Société pour la protection des paysages de France

novembre 19111911/11 (N48,A10)-1911/11

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

International audienceAbstract 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

Increased drought tolerance in plants engineered for low lignin and low xylan content

Abstract Background We previously developed several strategies to engineer plants to produce cost-efficient biofuels from plant biomass. Engineered Arabidopsis plants with low xylan and lignin content showed normal growth and improved saccharification efficiency under standard growth conditions. However, it remains to be determined whether these engineered plants perform well under drought stress, which is the primary source of abiotic stress in the field. Results Upon exposing engineered Arabidopsis plants to severe drought, we observed better survival rates in those with a low degree of xylan acetylation, low lignin, and low xylan content compared to those in wild-type plants. Increased pectic galactan content had no effect on drought tolerance. The drought-tolerant plants exhibited low water loss from leaves, and drought-responsive genes (RD29A, RD29B, DREB2A) were generally up-regulated under drought stress, which did not occur in the well-watered state. When compared with the wild type, plants with low lignin due to expression of QsuB, a 3-dehydroshikimate dehydratase, showed a stronger response to abscisic acid (ABA) in assays for seed germination and stomatal closure. The low-lignin plants also accumulated more ABA in response to drought than the wild-type plants. On the contrary, the drought tolerance in the engineered plants with low xylan content and low xylan acetylation was not associated with differences in ABA content or response compared to the wild type. Surprisingly, we found a significant increase in galactose levels and sugar released from the low xylan-engineered plants under drought stress. Conclusions This study shows that plants engineered to accumulate less lignin or xylan are more tolerant to drought and activate drought responses faster than control plants. This is an important finding because it demonstrates that modification of secondary cell walls does not necessarily render the plants less robust in the environment, and it shows that substantial changes in biomass composition can be achieved without compromising plant resilience