Floral scents and fruit aromas are crucial volatile organic compounds (VOCs) in plants. They are used in defense mechanisms, along with mechanisms to attract pollinators and seed dispersers. In addition, they are economically important for the quality of crops, as well as quality in the perfume, cosmetics, food, drink, and pharmaceutical industries. Floral scents and fruit aromas share many volatile organic compounds in flowers and fruits. Volatile compounds are classified as terpenoids, phenylpropanoids/benzenoids, fatty acid derivatives, and amino acid derivatives. Many genes and transcription factors regulating the synthesis of volatiles have been discovered. In this review, we summarize recent progress in volatile function, composition, biosynthetic pathway, and metabolism regulation. We also discuss unresolved issues and research perspectives, providing insight into improvements and applications of plant VOCs.

/pdf/floral-scents-and-fruit-aromas-functions-compositions-pprvvl8h.pdf

Floral Scents and Fruit Aromas: Functions, Compositions, Biosynthesis, and Regulation

Lilium is a world famous fragrant bulb flower with high ornamental and economic values, and significant differences in fragrance are found among different Lilium genotypes. In order to explore the mechanism underlying the different fragrances, the floral scents of Lilium 'Siberia', with a strong fragrance, and Lilium 'Novano', with very little fragrance, were collected in vivo using a dynamic headspace technique. These scents were identified using automated thermal desorption - gas chromatography / mass spectrometry (ATD-GC/MS) at different flowering periods. We used RNA-Seq technology to determine the petal transcriptome at the full-bloom stage and analyzed differentially expressed genes to investigate the molecular mechanism of floral scent biosynthesis. The results showed that a significantly higher amount of Lilium 'Siberia' floral scent was released compared with Lilium 'Novano'. Moreover, monoterpenes played a dominant role in the floral scent of Lilium 'Siberia'; therefore, it is believed that the different emissions of monoterpenes mainly contributed to the difference in the floral scent between the two Lilium genotypes. Transcriptome sequencing analysis indicated that approximately 29.24 Gb of raw data were generated and assembled into 124,233 unigenes, of which 35,749 unigenes were annotated. Through a comparison of gene expression between these two Lilium genotypes, 6,496 differentially expressed genes (DEGs) were identified. The genes in the terpenoid backbone biosynthesis pathway showed significantly different expression levels. The gene expressions of 1-deoxy-D-xylulose 5-phosphate synthase (DXS), 1-deoxy-D-xylulose-5-phosphate reductoisomerase (DXR), 4-hydroxy-3-methylbut-2-enyl diphosphate synthase (HDS), 4-hydroxy-3-methylbut-2-enyl diphosphate reductase (HDR), isopentenyl diphosphate isomerase (IDI), and geranyl diphosphate synthase (GPS/GGPS), were upregulated in Lilium 'Siberia' compared to Lilium 'Novano', and two monoterpene synthase genes, ocimene synthase gene (OCS) and myrcene synthase gene (MYS), were also expressed at higher levels in the tepals of Lilium 'Siberia', which is consistent with the monoterpene emissions. We demonstrated that the high activation levels of the pathways involved in monoterpene biosynthesis in Lilium 'Siberia' resulted in higher accumulations and emissions of monoterpenes, which led to the difference in fragrance between these two Lilium genotypes.

Transcriptome Sequencing Analysis Reveals a Difference in Monoterpene Biosynthesis between Scented Lilium ‘Siberia’ and Unscented Lilium ‘Novano’

Plants produce an incredible variety of volatile organic compounds (VOCs) that assist the interactions with their environment, such as attracting pollinating insects and seed dispersers and defense against herbivores, pathogens, and parasites. Furthermore, VOCs have a significant economic impact on crop quality, as well as the beverage, food, perfume, cosmetics and pharmaceuticals industries. These VOCs are mainly classified as terpenoids, benzenoids/phenylpropanes, and fatty acid derivates. Fruits and vegetables are rich in minerals, vitamins, antioxidants, and dietary fiber, while aroma compounds play a major role in flavor and quality management of these horticultural commodities. Subtle shifts in aroma compounds can dramatically alter the flavor and texture of fruits and vegetables, altering their consumer appeal. Rapid innovations in -omics techniques have led to the isolation of genes encoding enzymes involved in the biosynthesis of several volatiles, which has aided to our comprehension of the regulatory molecular pathways involved in VOC production. The present review focuses on the significance of aroma volatiles to the flavor and aroma profile of horticultural crops and addresses the industrial applications of plant-derived volatile terpenoids, particularly in food and beverages, pharmaceuticals, cosmetics, and biofuel industries. Additionally, the methodological constraints and complexities that limit the transition from gene selection to host organisms and from laboratories to practical implementation are discussed, along with metabolic engineering’s potential for enhancing terpenoids volatile production at the industrial level.

https://www.mdpi.com/2223-7747/12/9/1748/pdf?version=1682340382

Aroma Components in Horticultural Crops: Chemical Diversity and Usage of Metabolic Engineering for Industrial Applications

Flower fragrance is an important character for economic and ecological reasons. Lilies (Lilium spp.), important ornamental crops, mainly emit benzenoids/phenylpropanoids and terpenoids. Oriental hybrid lilies emit a strong fragrance, while Asiatic hybrid lilies often emit a weak fragrance. To delineate the genetic backgrounds that regulate volatile benzenoid/phenylpropanoid production in lilies, we isolated an R2R3-MYB transcription factor similar to Petunia × hybrida ODORANT1 (ODO1) from Oriental and Asiatic hybrid lilies. An identified gene, named Lilium hybrid ODO1 (LhODO1), could upregulate the expression of shikimate pathway genes and phenylalanine ammonia lyase (PAL) genes in transgenic petunia plants. The expression of LhODO1 in the Oriental hybrid lily ‘Casa Blanca’ exhibited a diurnal rhythm, which was highest at 16:00 and lowest at 4:00, and was attuned to the expressional rhythms of shikimate pathway and PAL genes. These diurnal changes in gene expression preceded changes in the production of endogenous volatile compounds. Expression of LhODO1 was specific to tepals, which are major sources of floral scent, and began at anthesis. These results indicate that LhODO1 plays a key role in the regulation of volatile benzenoid/phenylpropanoid production in lilies. In addition, LhODO1 may be responsible for the different fragrance intensities observed between the Oriental and Asiatic hybrid lilies, because LhODO1 expression was high in the Oriental hybrid lily cultivars but very low in wild lilies in sections Sinomartagon and Daurolirion, which are parental species of Asiatic hybrid lilies.

An R2R3-MYB transcription factor ODORANT1 regulates fragrance biosynthesis in lilies (Lilium spp.).

Cloning, functional characterization and expression analysis of LoTPS5 from Lilium ‘Siberia’

Terpenoids are economically and ecologically important compounds, and they are vital constituents in rose flower fragrance and rose essential oil. The terpene synthase genes (TPSs), trans-prenyltransferases genes (TPTs), NUDX1 are involved in middle and downstream pathway of volatile terpene biosynthesis in rose flowers. We identified 7 complete RcTPTs, 49 complete RcTPSs, and 9 RcNUDX1 genes in the genome of Rosa chinensis. During the flower opening process of butterfly rose (Rosa chinensis ‘Mutabilis’, MU), nine RcTPSs expressed in the petals of opening MU flowers exhibited two main expression trends, namely high and low, in old and fresh petals. Five short-chain petal-expressed RcTPTs showed expression patterns corresponding to RcTPSs. Analysis of differential volatile terpenes and differential expressed genes indicated that higher emission of geraniol from old MU petals might be related to the RcGPPS expression. Comprehensive analysis of volatile emission, sequence structure, micro-synteny and gene expression suggested that RcTPS18 may encode (E,E)-α-farnesene synthase. These findings may be useful for elucidating the molecular mechanism of terpenoid metabolism in rose and are vital for future studies on terpene regulation.

/pdf/effect-of-developmental-stages-on-genes-involved-in-middle-2vi1mhfx.pdf

Effect of Developmental Stages on Genes Involved in Middle and Downstream Pathway of Volatile Terpene Biosynthesis in Rose Petals

: Petal blotch is a specific flower color pattern commonly found in angiosperm families. In particular, Rosa persica is characterized by dark red blotches at the base of yellow petals. Modern rose cultivars with blotches inherited the blotch trait from R. persica. Therefore, understanding the mechanism for blotch formation is crucial for breeding rose cultivars with various color patterns. In this study, the metabolites and genes responsible for the blotch formation in R. persica were identified for the first time through metabolomic and transcriptomic analyses using LC-MS/MS and RNA-seq. A total of 157 flavonoids were identified, with 7 anthocyanins as the major flavonoids, namely, cyanidin 3-O-(6″-O-malonyl) glucoside 5-O-glucoside, cyanidin-3-O-glucoside, cyanidin 3-O-galactoside, cyanidin O-rutinoside-O-malonylglucoside, pelargonidin 3-O-glucoside, pelargonidin 3,5-O-diglucoside, and peonidin O-rutinoside-O-malonylglucoside, contributing to pigmentation and color darkening in the blotch parts of R. persica, whereas carotenoids predominantly influenced the color formation of non-blotch parts. Zeaxanthin and antheraxanthin mainly contributed to the yellow color formation of petals at the semi-open and full bloom stages. The expression levels of two 4-coumarate: CoA ligase genes (Rbe014123 and Rbe028518), the dihydroflavonol 4-reductase gene (Rbe013916), the anthocyanidin synthase gene (Rbe016466), and UDP-flavonoid glucosyltransferase gene (Rbe026328) indicated that they might be the key structural genes affecting the formation and color of petal blotch. Correlation analysis combined with weighted gene co-expression network analysis (WGCNA) further characterized 10 transcription factors (TFs). These TFs might participate in the regulation of anthocyanin accumulation in the blotch parts of petals by modulating one or more structural genes. Our results elucidate the compounds and molecular mechanisms underlying petal blotch formation in R. persica and provide valuable candidate genes for the future genetic improvement of rose cultivars with novel flower color patterns.

Integrative Metabolomic and Transcriptomic Analyses Reveal the Mechanism of Petal Blotch Formation in Rosa persica

The invention discloses a lily-derived LhWDR protein as well as an encoding gene and application thereof. The LhWDR protein provided by the invention is particularly any one of the following proteins: 1) a protein with an amino acid sequence represented by a sequence 1; 2) a protein which is prepared from the amino acid sequence represented by a sequence 1 through substitution and/or deletion and/or addition of one or several amino acid residues and has the same functions with the protein with the amino acid sequence represented by a sequence 1; and 3) a protein which has over 99%, 95%, 90%, 85% or 80% of homology with the amino acid sequence limited by 1) or 2) and has the same functions with amino acid sequence limited by 1) or 2); and 4) a fusion protein obtained by connecting a label to a terminal N and/or a terminal C of the protein limited by any of 1)-3). Experiments prove that WDR is capable of promoting the expression of a downstream gene DFR in a cyanin synthetic route after the overexpression in arabidopsis. The lily-derived LhWDR protein has very important significances to the further understanding and synthesis of lily cyanin and the formation of flower colors.

Lily-derived LhWDR protein as well as encoding gene and application thereof

/pdf/variation-in-floral-scent-compositions-of-different-lily-4uepo7q3t1.pdf

Variation in Floral Scent Compositions of Different Lily Hybrid Groups

The bulbs of several Lilium species are considered to be both functional foods and traditional medicine in northern and eastern Asia. Considering the limited information regarding the specific bioactive compounds contributing to the functional properties of these bulbs, we compared the secondary metabolites of ten Lilium bulb samples belonging to five different species, using an ultrahigh-performance liquid chromatography-electrospray ionization-tandem mass spectrometry (UPLC-ESI-MS/MS)-based secondary metabolomics approach. In total, 245 secondary metabolites were detected; further, more metabolites were detected from purple Lilium bulbs (217 compounds) than from white bulbs (123–171 compounds). Similar metabolite profiles were detected in samples within the same species irrespective of where they were collected. By combining herbal analysis and screening differential metabolites, steroid saponins were considered the key bioactive compounds in medicinal lilies. Of the 14 saponins detected, none were accumulated in the bulbs of L. davidii var. willmottiae, also called sweet lily. The purple bulbs of L. regale accumulated more secondary metabolites, and, notably, more phenolic acid compounds and flavonoids. Overall, this study elucidates the differential metabolites in lily bulbs with varying functions and colors and provides a reference for further research on functional foods and the medicinal efficacy of Lilium species.

Metabolome-Based Discrimination Analysis of Five Lilium Bulbs Associated with Differences in Secondary Metabolites

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