Chemistry, biosynthesis and biology of floral volatiles: roles in pollination and other functions

Revealing the key aromatic compounds in Malus 'Lollipop' flowers by transcriptome and metabolome

The ornamental crabapple Malus (M.) 'Lollipop' is renowned for its compact growth and fragrant flowers. This study aims to elucidate the biosynthesis molecular mechanism of volatile organic compounds (VOCs) across four developmental stages of the M. 'Lollipop' flowers using metabolomics and transcriptomics analyses. Gas chromatography-mass spectrometry (GC-MS) identified 29 VOCs (aliphatic derivatives, benzenes, and alkanes) in M. 'Lollipop' flowers. Orthogonal Partial Least Squares Discriminant Analysis (OPLS-DA) analysis highlights 14 key differential aromatic compounds (VIP ≥ 1), featuring (Z)-3-hexen-1-yl acetate in stage 1, methyl benzoate in stage 2, benzyl alcohol and linalool in stage 3, and camphene and (Z)-3-hexen-1-ol in stage 4. (Z)-3-hexen-1-yl acetate was identified as a co-primary constituent in the four flowering stages, designated as a key and floral contributing metabolite (variable importance in projection (VIP) ≥ 1& odor activity value (OAV) ≥ 1). RNA sequencing revealed key genes including CAT, DXS, MVD, HMGCR, FDPS, and TPSc in camphene and linalool synthesis, aroA, ADT, PDT, PAL, BEBT1, SDR, 4CL, CNL, and BALDH for benzyl alcohol, benzaldehyde, and methyl benzoate production. And PLA2G, SPLA2, TGL4, LOX2S and ADH1 in (Z)-3-hexen-1-yl acetate and (Z)-3-hexen-1-ol synthesis. 24 transcription factors (TFs) were predicted to be closely linked to genes involved in VOC synthesis. The findings above deepen our comprehension of the floral scent in crabapple, laying a foundation for further investigations into their functions and potential industrial applications.

Structure and release function of fragrance glands

Volatile compounds serve physiological, signaling, and defensive purposes in plants and have beneficial effects on the growth, reproduction, resistance, and yield of horticultural plants. They are released through fragrance glands and become gasses by passing through the plasma membrane, cell walls that contain water, and cuticle. Transporter proteins facilitate their transport and reduce the resistance of these barriers. They also regulate the rate of release and concentration of volatiles inside and outside of the membrane. However, there has been no summary of the structure and function of the fragrance glands of horticultural plants, as well as an introduction to the latest research progress on the mechanism of the transport of volatiles. This review focuses on the structure and function of the release of aromas in horticultural plants and explores the mechanism of the release of volatiles through a transporter model. Additionally, it considers the factors that affect their release and ecological functions and suggests directions for future research.

Floral scent emission of Epiphyllum oxypetalum: discovery of its cytosol-localized geraniol biosynthesis

Epiphyllum oxypetalum, a renowned ornamental species in Cactaceae, releases attractive fragrance during its infrequent, transient, and nocturnal blooms. However, the floral fragrance composition and biosynthesis remain largely unexplored. Employing volatilomics, transcriptomics, and biochemistry, we systematically characterized the composition, emission dynamics, and biosynthesis of the floral scent of E. oxypetalum. The floral scent composition of E. oxypetalum was highly dynamic. Starting after 8 p.m. local time, volatile emission increased 200-fold within 6 h. At full bloom, geraniol accounted for 72.54% of the total emission, followed by benzyl alcohol (12.96%) and methyl salicylate (3.75%). These scents predominantly originated from petals and sepals. Transcriptomic analysis and inhibition assays using pathway-specific inhibitors revealed that the mevalonate pathway was the precursor source for geraniol biosynthesis. Functionally characterized cytosol-localized geraniol synthase EoTPSa1 was the key enzyme responsible for geraniol biosynthesis. Together, these findings pinpoint a cytosolic biosynthetic route for the major scent volatile geraniol in E. oxypetalum. Our study provides new insights into the emission dynamics and biosynthesis of E. oxypetalum floral scents. In particular, we demonstrate a distinctive mevalonate pathway-based geraniol biosynthetic pathway, which may hold potential for the development of novel perfume products.

Spatial partitioning of floral volatiles provides a "chemosensory roadmap" for bumblebee pollinators

How do plants with structurally complex flowers promote effective pollination? From the pollinator's perspective, complex flowers can be reimagined as mechanical puzzles that require the manipulation of a 3D object in search of a concealed reward.1 The spatial partitioning of volatile organic compounds (VOCs) within flowers may help flower-naive pollinators to successfully complete such puzzles, thereby increasing their foraging proficiency and, from the plant's perspective, promoting flower constancy and pollination efficiency.2,3 Here, we construct "chemosensory roadmaps" for Impatiens capensis and I. pallida, two North American plants pollinated by Bombus impatiens bumblebees. Although many VOCs are known to elicit olfactory responses,4 the presence of unique compounds in floral nectar,5 coupled with reports of inexperienced bees probing different flower parts as they learn how to manipulate flowers,6 suggest that VOCs might also elicit gustatory responses. Accordingly, we found that bumblebees showed no differential responses to VOCs when encountered as odorants but showed highly differential responses to the same VOCs when ingested with sugar rewards. VOCs present in nectar had agreeable flavors, whereas VOCs of other floral tissues such as nectar spurs were avoided. These findings suggest that VOC partitioning in Impatiens functions as a gustatory preference gradient that encourages legitimate pollination and potentially discourages nectar robbing by bumblebee visitors. Our findings highlight the non-olfactory functions of floral VOCs as flavors or contact chemical stimuli and their potential to structure plant-pollinator networks and filter their interactions with other organisms, including larcenists and other non-pollinating visitors.

Pollination chemistry: Roadmaps to reproduction or how to get lost

Chemical analyses of volatile organic compounds in flowers and nectar, combined with extensive behavioural bioassays, reveal complex roles for these compounds in olfaction and gustation, providing novel insights into plant pollination and nectar robbing.

Current insights into plant volatile organic compound biosynthesis

Plant-derived volatile organic compounds (VOCs) are essential for various ecological interactions, including plant communication, pollinator attraction, and defense against herbivores. Some VOCs are active ingredients with significant economic and medicinal value. For example, monoterpenoids such as linalool, geraniol, menthol, camphor, borneol, citral, and thymol are well-known for their flavor and aroma. Most monoterpenoids have a strong scent and physiological activity; some compounds, like thymoquinone, have excellent anti-cancer activities, making them important for pharmaceuticals and also beneficial in food and cosmetics. VOCs encompass a diverse range of chemical classes, such as terpenoids, benzenoids/phenylpropanoids, amino acid derivatives, and fatty acid-derived compounds. With the development of genomic, transcriptomic, and metabolomic techniques, significant progress has been made in the discovery of genes for the biosynthesis of VOCs. Herein, recent advances in the biosynthesis of plant-derived VOCs, focusing on two main classes: benzenoids/phenylpropanoids and monoterpenes, are discussed. It highlights the identification of a peroxisomal enzyme, benzaldehyde synthase, in petunia that elucidates the biosynthetic pathway of benzaldehyde, and a bifunctional enzyme, geranyl/farnesyl diphosphate synthase (RcG/FPPS1), in roses (Rosa chinensis "Old Blush") that contributes to the production of cytosolic geranyl diphosphate. Current understanding about canonical and non-canonical pathways for monoterpene formation and some approaches that are useful for gene discovery have been discussed. Open questions and future perspectives in this field have also been presented.

Chemical, morphological, and genetic characterization of the floral scent and scent-releasing structures of Gynandropsis gynandra (Cleomaceae, Brassicales)

Flowering plants showcase a remarkable diversity in floral fragrances, colours, and structures, which function harmoniously as signals to attract and guide pollinators. Like visual signals, the scents emitted by flowers can be associated with the attraction of specific pollinator classes. As such, divergence in floral scent composition can be a key isolation mechanism for speciation. Between continents, the leafy vegetable Gynandropsis gynandra possesses differences in morphology, phenology, foliar chemodiversity, and pollinators. Importantly, G. gynandra is pollinated by hawkmoths in Africa, and bees and butterflies in Asia. Here, we combined chemical, morphological, and transcriptome analyses to assess differences in the floral scent and scent-releasing structures between African and Asian G. gynandra accessions, and within flowers of the same accession. The prevalence of nitriles and benzenoids in the floral fragrance of the African and Asian accessions, respectively, corresponds to features typically associated with their differing pollinator classes. Further, we uncovered differences in floral epidermal cell morphology, with papillae present on the petal claws and nectary of the African accession and absent (or reduced) for the Asian accession. Through transcriptomic analyses, we showed that the stalk-like floral structures are putatively involved in terpenoid biosynthesis and emission. However, the epidermal cell morphology and staining suggests that the petals, stamens, and stigma may be involved in scent production of other floral volatile classes (e.g., nitrogen-containing compounds). These additional phytochemical and morphological distinctions between African and Asian accessions suggest that the divergent forms of G. gynandra may merit taxonomic recognition at subspecies level.

Complex Floral Scent Profile of Neottia ovata (Orchidaceae): General Attractants and Beyond

Understanding the complexity of flower scent-a crucial attractant for pollinators and a key factor in ensuring plant reproduction-is an essential ecological task for highly endangered orchids. To address this issue, we studied the flower volatiles profile of Neottia ovata, a nectar-rewarding orchid known for its generalist pollination strategy. We then compared the chemical composition of N. ovata floral scent with scent data of other orchid species to place our findings in the context of general volatile attractants emitted by nectar-rewarding or food-deceptive species. Our results contribute to understanding the complexity of the N. ovata floral scent profile and provide valuable methodological insights. The scented bouquet of N. ovata comprises 100 compounds with a relatively consistent composition across the analyzed samples. It is rich in terpenes, including linalool and trans-/cis-sabinene hydrate, compounds commonly associated with generalized rewarding or food-deceptive pollination systems. Other terpenes identified include α- and β-pinene, limonene, and β-phellandrene, whose presence underscores the generalized nature of the floral scent. Interestingly, in the studied N. ovata populations, the dominance among terpenes is shifting markedly towards γ-terpinene, α-terpinene, and terpinene-4-ol, commonly found in essential oils and the floral scents of some supergeneralist-pollination plants. Aromatic compounds were less represented in the N. ovata scent profile and those of other orchids studied, though benzyl alcohol and benzaldehyde were noticeably more abundant. Aliphatic compounds composed the least prevalent fraction, showing a marked decreasing trend among nectar-rewarding species with generalized or specialized pollination systems. It is worth emphasizing that the applied methodology revealed an extensive group of low-frequency compounds in the N. ovata floral scent. This finding raises new ecological questions about the intraspecific diversity of floral scent profiles and sheds new light on the factors determining effective reproduction in this species of orchid.

Accumulation differences of high-value ingredients in different phenotype Lonicera macranthoides: insights from integrative metabolome and transcriptome analyses

Background

Lonicera macranthoides Hand.-Mazz., the primary sources of Lonicerae Flos(Shanyinhua), brings great medicinal and economic value as an invaluable source of natural bioactive compounds. Nutrient and metabolites accumulation generally changed accompany with its floral development and opening. While the specific accumulation pattern and the underlying molecular regulatory networks remain unclear.

Methods

The present study intergrated a comparative analysis upon UPLC-MS/MS-based metabolomics and RNA-seq-based transcriptomics to revealed the differences in accumulation of flavonoids, phenolic acids, and terpenoids between the xianglei-type (corolla-closed) and wild-type (corolla-unfolded) of L. macranthoides flowers.

Results and conclusion

674 differentially accumulated metabolites(DAMs) were identified in WT and XL, with 5,776 common differentially expressed genes(DEGs), revealing a significant differences in accumulation of flavonoids, phenolic acids, and terpenoids during the late stage of flower development between the xianglei-type and wild-type of L. macranthoides flowers. Combined analysis further identified 36 hub genes, major transcription factors and hormone-related genes, which play key roles in the differential accumulation of the abovementioned metabolites. These lines of evidences provide a molecular basis for the metabolic changes occurring during growth and can be significantly implicated in further research on the biosynthetic pathways associated with high-value potent active components in woody plants.

Pollinator, pollen, and cultivar identity drive crop quality

Animal pollination enhances a third of global food production, yet the roles of pollinator, pollen, and cultivar identity in shaping crop quality, such as nutritional, sensory, and marketing value, are underexplored. Crop quality often depends on pollinator movement patterns, which vary with cultivar selection and spatial arrangement, pollen donor identity, and landscape context. Transfer of the right pollen between cultivars may fail, as pollen is often not transported far, even by highly dispersive pollinators, reducing cross-pollination and crop quality. Both pollinator identity and complementary spatiotemporal activity of diverse pollinators can shape crop quality. Here, we argue that promoting crop quality needs better understanding of species-specific pollinator behaviour and cultivar distribution patterns, rather than only focusing on enhancing pollinator densities.

Untargeted flower volatilome profiling highlights differential pollinator attraction strategies in muscadine

Floral aromas are a mixture of volatile organic compounds, essential attributes associated with the attraction of different pollinators. This investigation is the first in-depth exploration of the volatile profiles of sixteen muscadine grape genotypes, producing female and perfect flowers using the headspace solid-phase microextraction (HS-SPME)-GC-MS-based untargeted volatilomics approach. A total of one hundred fifty volatile metabolites were identified in the muscadine flower genotypes, including the functional groups of hydrocarbons, esters, alcohols, ketones, aldehydes, miscellaneous, and acids. Multivariate statistical analysis for volatile terpenes revealed eleven bio-marker terpene volatiles that primarily distinguish between female and perfect flowers. The β-elemene, β-bisabolene, and α-muurolene were the marker volatiles characterizing perfect flowers; however, α-selinene, (Z,E)-α-farnesene, and (E,E)-geranyl linalool were the typical marker terpene in the female flowers. Perfect flowers exhibited better pollinator attraction capacity associated with a higher number of flowers per inflorescence, enhanced pollinator rewards, and higher numbers and quantities of terpene volatiles than female flowers, resulting in superior pollinator attraction capacity and fruit set efficiency. The pollinator attraction mechanism of female flowers exhibited several morphological and biochemical floral defects, causing random pollinator visits and low fruit set efficiency. The controlled pollination assay could express female flowers' full fruit set capabilities by avoiding casual insect pollination. This comprehensive study suggests that these marker terpenes might contribute to pollinator attraction in muscadine flower genotypes and should be considered an excellent reference for agroecosystem ecologists and entomologists.

A pivotal switch in β-domain determines the substrate selectivity of terpene synthases involved in Gardenia jasminoides floral scent synthesis

Plants have evolved a diverse array of secondary metabolites to enhance their adaptability to environmental stresses, with volatile terpenoids being a notable example. Gardenia (Gardenia jasminoides), celebrated for its unique fragrance, is a key natural source of volatile terpenoids. Using our chromosome-level genome and transcriptome data of G. jasminoides, we previously identified six terpene synthases (TPSs) involved in the production of its floral scent. Here, we functionally characterized these six key TPS enzymes, aligning their product profiles with volatile organic compound (VOC) analysis. Notably, we identified two highly similar TPSs, GjTPS1 and GjTPS2, which share high sequence homology but differ in substrate selectivity. Through AI-based predictions and site-directed mutagenesis, we pinpointed a single amino acid in the β-domain that acts as a "switch," modulating substrate selectivity-an unusual finding, as this residue is outside the active site region. Comparative genomic analyses with Coffea canephora and other eudicots revealed that G. jasminoides TPS genes primarily expanded through dispersed duplications (DSD) and tandem duplications (TD). Our study is the first to reveal a "switch" in a previously deemed "non-functional" region, regulating substrate selectivity in TPS proteins. These insights could facilitate breeding elite Gardenia varieties and support the rational engineering of terpene synthases.

Decoding the aroma of Rosa canina L.: Chemical composition and gene expression

OBJECTIVE

The aromatic profile of Rosa canina L. petals hold immense potential for the fragrance and pharmaceutical industries. This study aims to investigate the chemical composition and gene expression patterns across different floral development stages to uncover the biosynthetic pathways of floral scent.

METHODS

Essential oils (EOs) were extracted from petals at five developmental stages (S1-S5) and analyzed using Gas Chromatography-Mass Spectrometry (GC-MS), identifying 20 distinct compounds. RNA isolation and quantitative real-time PCR (qRT-PCR) analysis were performed to assess gene expression.

RESULTS

Stage S3, notable for its enhanced aromatic profile, was dominated by terpenoid compounds such as β-Citronellol (1.18%), Caryophyllene (8.59%), β-Selinene (1.50%), and Caryophyllene oxide (0.50%), indicating significant upregulation of terpenoid biosynthesis genes. qRT-PCR analysis revealed that CCD1 had the highest expression in S4 (9.51-fold), while DXR and DXS peaked at S3 with fold changes of 29058.38 and 73.35, respectively. Other genes like AAT1, LIS, and GPS also showed peak expressions at S3 with fold changes of 1.33, 10.70, and 1.18, respectively. PAR exhibited the highest expression in S1, while GGPPS peaked in S4 (2.01-fold). Clustering analysis indicated distinct groupings of developmental stages and gene expression patterns, with strong correlations between specific genes and compounds, such as CCD1 with GGPPS (0.78) and β-Citronellol with Caryophyllene (0.92). Principal Component Analysis (PCA) highlighted significant contributions of AAT1, GPS, and nonadecane compounds to the overall variance.

CONCLUSION

These findings provide a comprehensive understanding of the chemical and genetic factors shaping the aromatic profile of R. canina, with promising applications for both the fragrance and pharmaceutical sectors. The study's innovation lies in the detailed correlation between EO composition and gene expression, presenting new insights into the biosynthetic pathways of floral scent.

Natural selection on floral volatiles and other traits can change with snowmelt timing and summer precipitation

Climate change is disrupting floral traits that mediate mutualistic and antagonistic species interactions. Plastic responses of these traits to multiple shifting conditions may be adaptive, depending on natural selection in new environments. We manipulated snowmelt date over three seasons (3-11 d earlier) in factorial combination with growing-season precipitation (normal, halved, or doubled) to measure plastic responses of volatile emissions and other floral traits in Ipomopsis aggregata. We quantified how precipitation and early snowmelt affected selection on traits by seed predators and pollinators. Within years, floral emissions did not respond to precipitation treatments but shifted with snowmelt treatment depending on the year. Across 3 yr, emissions correlated with both precipitation and snowmelt date. These effects were driven by changes in soil moisture. Selection on several traits changed with earlier snowmelt or reduced precipitation, in some cases driven by predispersal seed predation. Floral trait plasticity was not generally adaptive. Floral volatile emissions shifted in the face of two effects of climate change, and the new environments modulated selection imposed by interacting species. The complexity of the responses underscores the need for more studies of how climate change will affect floral volatiles and other floral traits.

Molecular background of the diverse metabolic profiles in leaves and inflorescences of naked catmint (Nepeta nuda L.)

Nepeta nuda L. shares a typical secondary chemistry with other Nepeta species (fam. Lamiaceae), characterized by the tendency to intensively produce monoterpenoid iridoids, whereas the phenylpropanoid chemistry is steered towards the production of a caffeic acid ester, rosmarinic acid. Combining complementary state-of-the-art analytical techniques, N. nuda metabolome was here comprehensively characterized in the quest for the organ-specific composition of phenolics and terpenoids that possess well-defined functions in plant-biotic interactions as well as therapeutic potential. N. nuda inflorescences showed generally higher constitutive levels of specialized metabolites, as compared to leaves, and the composition of major iridoids and phenolics in reproductive organs was found to be more conserved than in leaves across 13 populations from the Central Balkans. The results suggest that N. nuda plants most likely invest more in constitutive than inducible biosynthesis of functional metabolites in flowers, since they are of essential importance for both pollination and defense against herbivores and pathogens. Conversely, specialized metabolism of leaves is found to be more susceptible to reprograming in response to differential growth conditions. The defense strategy of leaves, primarily functioning in CO2 fixation during photosynthesis, more likely relies on the induction of metabolite levels following plant-environment interplay. Organ-specific biosynthesis of iridoids in N. nuda is found to be tightly regulated at the transcriptional level, and high constitutive levels of these compounds in inflorescences most likely result from the up-regulated expression of several key genes (NnG8H, NnNEPS1, NnNEPS2, and NnNEPS3) determining the metabolic flux through the pathway. The organ-specific content of rosmarinic acid and co-expression patterns of the corresponding biosynthetic genes were much less correlated, which suggests independent organ-specific transcriptional regulation of the iridoid and phenolic pathways. Knowledge gathered within the present study can assist growers to select productive genotypes and manipulate phenology of N. nuda towards maximizing yields and facilitating its integration into pest management systems and other applications related to human health.

Exploring geography and evolutionary history as drivers of variation in floral scent chemistry in western sessile-flowered Trillium using parsimony-constrained phylogenetics

BACKGROUND AND AIMS

The sessile-flowered Trillium species from western North America have been challenging to distinguish morphologically owing to overlapping characters and intraspecific variation. Molecular phylogenetic analyses, currently inconclusive for this group, have not sampled multiple populations of the different species to account for this. Here, we query the diversity of floral volatile composition to understand its bearings on the taxonomy, distribution and evolution of this group.

METHODS

We explored taxonomic and geographical patterns in average floral volatile composition (105 different compounds) among 42 wild populations of four sessile-flowered Trillium species and the outgroup, Pseudotrillium, in California, Oregon and Washington, by means of parsimony-constrained phylogenetic analyses. To assess the influence of character construction, we coded compound abundance in three different ways for the phylogenetic analyses and compared the results with those of statistical analyses using the same dataset and previously published statistical analyses.

KEY RESULTS

Different codings of floral volatile composition generated different phylogenetic topologies with different levels of resolution. The different phylogenies provide similar answers to taxonomic questions but support different evolutionary histories. Monophyly of most populations of each taxon suggests that floral scent composition bears phylogenetic signal in the western sessile-flowered Trillium. Lack of correlation between the distribution of populations and their position in scent-based phylogenies does not support a geographical signal in floral scent composition.

CONCLUSIONS

Floral scent composition is a valuable data source for generating phylogenetic hypotheses. The way in which scent composition is coded into characters is important. The phylogenetic patterns supported by floral volatile compounds are incongruent with previously reported phylogenies of the western sessile-flowered Trillium obtained using molecular or morphological data. Combination of floral scent data with gene sequence data and detailed morphological data from multiple populations of each species in future studies is needed for understanding the evolutionary history of western sessile-flowered Trillium.

Negative and sex-specific effects of drought on flower production, resources and pollinator visitation, but not on floral scent in monoecious Cucurbita pepo

The globally changing climatic condition is increasing the incidences of drought in several parts of the world. This is predicted and already shown to not only impact plant growth and flower development, but also plant-pollinator interactions and the pollination success of entomophilous plants. However, there is a large gap in our understanding of how drought affects the different flowers and pollen transfer among flowers in sexually polymorphic species. Here, we evaluated in monoecious Styrian oil pumpkin, and separately for female and male flowers, the responses of drought stress on flower production, petal size, nectar, floral scent and visitation by bumblebee pollinators. Drought stress adversely affected all floral traits studied, except floral scent. Although both flower sexes were adversely affected by drought stress, the effects were more severe on female flowers, with most of the female flowers even aborted before opening. The drought had negative effects on floral visitation by the pollinators, which generally preferred female flowers. Overall, our study highlights that the two flower sexes of a monoecious plant species are differently affected by drought stress and calls for further investigations to better understand the cues used by the pollinators to discriminate against male flowers and against flowers of drought-stressed plants.

Metabolome and Transcriptome Combined Reveal the Main Floral Volatile Compounds and Key Regulatory Genes of Castanea mollissima

Chestnut (Castanea mollissima) is an economically important forest tree species, and its flowers possess functions such as repelling mosquitoes, killing bacteria, and clearing heat. However, the regulatory mechanisms of floral volatile organic compounds (VOCs) in chestnut are still unclear. This study analyzed the contents of major volatile compounds and related gene expression levels in chestnut flowers during the initial flowering stage (IFS) and full-flowering stage (FFS) using metabolomics and transcription techniques. In total, 926 volatile compounds were detected, mainly terpenes, heterocyclic compounds, and esters. Acetylenone, styrene, and β-pinene had contents that exceeded 5% in FFS chestnut flowers. In total, 325 differential metabolites between the IFS and FFS were significantly (p < 0.05) enriched in the biosynthetic pathways of sesquiterpenes and triterpenes, as well as the ethylbenzene metabolic pathway. In total, 31 differentially expressed genes (DEGs) were related to terpenoid biosynthesis. There were only two DEGs related to the ethylbenzene metabolic pathway. In summary, we identified the volatile components of chestnut flowers and analyzed the changes in the contents of major volatile compounds in the flowers and the expression patterns of the related genes. The research results are helpful for understanding the regulation of VOCs in chestnut flowers.

Integration of attractive and defensive phytochemicals is unlikely to constrain chemical diversification in a perennial herb

Diversification of plant chemical phenotypes is typically associated with spatially and temporally variable plant-insect interactions. Floral scent is often assumed to be the target of pollinator-mediated selection, whereas foliar compounds are considered targets of antagonist-mediated selection. However, floral and vegetative phytochemicals can be biosynthetically linked and may thus evolve as integrated phenotypes. Utilizing a common garden of 28 populations of the perennial herb Arabis alpina (Brassicaceae), we investigated integration within and among floral scent compounds and foliar defense compounds (both volatile compounds and tissue-bound glucosinolates). Within floral scent volatiles, foliar volatile compounds, and glucosinolates, phytochemicals were often positively correlated, and correlations were stronger within these groups than between them. Thus, we found no evidence of integration between compound groups indicating that these are free to evolve independently. Relative to self-compatible populations, self-incompatible populations experienced stronger correlations between floral scent compounds, and a trend toward lower integration between floral scent and foliar volatiles. Our study serves as a rare test of integration of multiple, physiologically related plant traits that each are potential targets of insect-mediated selection. Our results suggest that independent evolutionary forces are likely to diversify different axes of plant chemistry without major constraints.

Chemical imitation of yeast fermentation by the drosophilid-pollinated deceptive trap-flower Aristolochia baetica (Aristolochiaceae)

Deceptive flowers, unlike in mutualistic pollination systems, mislead their pollinators by advertising rewards which ultimately are not provided. Although our understanding of deceptive pollination systems increased in recent years, the attractive signals and deceptive strategies in the majority of species remain unknown. This is also true for the genus Aristolochia, famous for its deceptive and fly-pollinated trap flowers. Representatives of this genus were generally assumed to be oviposition-site mimics, imitating vertebrate carrion or mushrooms. However, recent studies found a broader spectrum of strategies, including kleptomyiophily and imitation of invertebrate carrion. A different deceptive strategy is presented here for the western Mediterranean Aristolochia baetica L. We found that this species is mostly pollinated by drosophilid flies (Drosophilidae, mostly Drosophila spp.), which typically feed on fermenting fruit infested by yeasts. The flowers of A. baetica emitted mostly typical yeast volatiles, predominantly the aliphatic compounds acetoin and 2,3-butandiol, and derived acetates, as well as the aromatic compound 2-phenylethanol. Analyses of the absolute configurations of the chiral volatiles revealed weakly (acetoin, 2,3-butanediol) to strongly (mono- and diacetates) biased stereoisomer-ratios. Electrophysiological (GC-EAD) experiments and lab bioassays demonstrated that most of the floral volatiles, although not all stereoisomers of chiral compounds, were physiologically active and attractive in drosophilid pollinators; a synthetic mixture thereof successfully attracted them in field and lab bioassays. We conclude that A. baetica chemically mimics yeast fermentation to deceive its pollinators. This deceptive strategy (scent chemistry, pollinators, trapping function) is also known from more distantly related plants, such as Arum palaestinum Boiss. (Araceae) and Ceropegia spp. (Apocynaceae), suggesting convergent evolution. In contrast to other studies working on floral scents in plants imitating breeding sites, the present study considered the absolute configuration of chiral compounds.

The heat is on: reduced detection of floral scents after heatwaves in bumblebees

Global climate change disrupts key ecological processes and biotic interactions. The recent increase in heatwave frequency and severity prompts the evaluation of physiological processes that ensure the maintenance of vital ecosystem services such as pollination. We used experimental heatwaves to determine how high temperatures affect the bumblebees' ability to detect floral scents. Heatwaves induced strong reductions in antennal responses to floral scents in both tested bumblebee species (Bombus terrestris and Bombus pascuorum). These reductions were generally stronger in workers than in males. Bumblebees showed no consistent pattern of recovery 24 h after heat events. Our results suggest that the projected increased frequency and severity of heatwaves may jeopardize bumblebee-mediated pollination services by disrupting the chemical communication between plants and pollinators. The reduced chemosensitivity can decrease the bumblebees' abilities to locate food sources and lead to declines in colonies and populations.

Floral scent of eastern skunk cabbage (Symplocarpus foetidus: Araceae)

Symplocarpus foetidus (L.) Salisb. (eastern skunk cabbage) occurs across a broad geographic range of northeastern North America, blooming in winter between December and March. The inflorescences are well-known for their thermogenic and thermoregulatory metabolic capabilities. The perceptual qualities of their fetid floral aroma have been described widely in the literature, but to date the floral volatile composition remained largely unknown. Here we present a detailed study of the floral scent produced by S. foetidus collected from intact female- and male-stage inflorescences and from dissected floral parts. Our results show a large range of biosynthetically diverse volatiles including nitrogen- and sulfur-containing compounds, monoterpenes, benzenoids, and aliphatic esters and alcohols. We document high inter-individual variation with some organ-specific volatile trends but no clear strong variation based on sexual stage. Multivariate data analysis revealed two distinct chemotypes from our study populations that are not defined by sexual stage or population origin. The chemotype differences may explain the bimodal perceptual descriptions in earlier work which vary between highly unpleasant/fetid and pleasant/apple-like. We discuss the results in ecological contexts including potential for floral mimicry, taking into account existing pollination studies for the species. We also discuss the results in evolutionary contexts, comparing our scent data to published scent data from the close sister species Symplocarpus renifolius. Future work should more closely examine the chemotype occurrence and frequency within these and other populations, and the impact these chemotypes may have on pollinator attraction and reproductive success.

Floral Trait Preferences of Three Common wild Bee Species

The interaction between bees and flowering plants is mediated by floral cues that enable bees to find foraging plants. We tested floral cue preferences among three common wild bee species: Lasioglossum villosulum, Osmia bicornis, and Bombus terrestris. Preferences are well studied in eusocial bees but almost unknown in solitary or non-eusocial generalist bee species. Using standardized artificial flowers altered in single cues, we tested preferences for color hue, achromatic contrast, scent complexity, corolla size, and flower depth. We found common attractive cues among all tested bees. Intensively colored flowers and large floral displays were highly attractive. No preferences were observed in scent complexity experiments, and the number of volatiles did not influence the behavior of bees. Differing preferences were found for color hue. The specific behaviors were probably influenced by foraging experience and depended on the flower choice preferences of the tested bee species. In experiments testing different flower depths of reward presentation, the bees chose flat flowers that afforded low energy costs. The results reveal that generalist wild bee species other than well-studied honeybees and bumblebees show strong preferences for distinct floral cues to find potential host plants. The diverse preferences of wild bees ensure the pollination of various flowering plants.

Transcriptome Analysis of Stigmas of Vicia faba L. Flowers

Pollination in angiosperms depends on complex communication between pollen grains and stigmas, classified as wet or dry, depending on the presence or absence of secretions at the stigma surface, respectively. In species with wet stigma, the cuticle is disrupted and the presence of exudates is indicative of their receptivity. Most stigma studies are focused on a few species and families, many of them with self-incompatibility systems. However, there is scarce knowledge about the stigma composition in Fabaceae, the third angiosperm family, whose stigmas have been classified as semidry. Here we report the first transcriptome profiling and DEGs of Vicia faba L. styles and stigmas from autofertile (flowers able to self-fertilize in the absence of manipulation, whose exudate is released spontaneously) and autosterile (flowers that need to be manipulated to break the cuticle and release the exudates to be receptive) inbred lines. From the 76,269 contigs obtained from the de novo assembly, only 45.1% of the sequences were annotated with at least one GO term. A total of 115,920, 75,489, and 70,801 annotations were assigned to Biological Process (BP), Cellular Component (CC), and Molecular Function (MF) categories, respectively, and 5918 differentially expressed genes (DEGs) were identified between the autofertile and the autosterile lines. Among the most enriched metabolic pathways in the DEGs subset were those related with amino acid biosynthesis, terpenoid metabolism, or signal transduction. Some DEGs have been related with previous QTLs identified for autofertility traits, and their putative functions are discussed. The results derived from this work provide an important transcriptomic reference for style-stigma processes to aid our understanding of the molecular mechanisms involved in faba bean fertilization.

A novel O-methyltransferase Cp4MP-OMT catalyses the final step in the biosynthesis of the volatile 1,4-dimethoxybenzene in pumpkin (Cucurbita pepo) flowers

BACKGROUND

Floral scents play a crucial role in attracting insect pollinators. Among the compounds attractive to pollinators is 1,4-dimethoxybenzene (1,4-DMB). It is a significant contributor to the scent profile of plants from various genera, including economically important Cucurbita species. Despite its importance, the biosynthetic pathway for the formation of 1,4-DMB was not elucidated so far.

RESULTS

In this study we showed the catalysis of 1,4-DMB in the presence of 4-methoxyphenol (4-MP) by protein extract from Styrian oil pumpkin (Cucurbita pepo) flowers. Based on this finding, we identified a novel O-methyltransferase gene, Cp4MP-OMT, whose expression is highly upregulated in the volatile-producing tissue of pumpkin flowers when compared to vegetative tissues. OMT activity was verified by purified recombinant Cp4MP-OMT, illustrating its ability to catalyse the methylation of 4-MP to 1,4-DMB in the presence of cofactor SAM (S-(5'-adenosyl)-L-methionine).

CONCLUSIONS

Cp4MP-OMT is a novel O-methyltransferase from C. pepo, responsible for the final step in the biosynthesis of the floral scent compound 1,4-DMB. Considering the significance of 1,4-DMB in attracting insects for pollination and in the further course fruit formation, enhanced understanding of its biosynthetic pathways holds great promise for both ecological insights and advancements in plant breeding initiatives.

Physiological and Biochemical Analysis Revealing the Key Factors Influencing 2-Phenylethanol and Benzyl Alcohol Production in Crabapple Flowers

Floral scent (FS) plays a crucial role in the ecological functions and industrial applications of plants. However, the physiological and metabolic mechanisms underlying FS formation remain inadequately explored. Our investigation focused on elucidating the differential formation mechanisms of 2-phenylethanol (2-PE) and benzyl alcohol (BA) by examining seven related enzyme concentrations and the content of soluble sugar, soluble proteins, carbon (C) and nitrogen (N), as well as the C/N ratio. The findings revealed that the peak content of 2-PE in M. 'Praire Rose' and BA in M. 'Lollipop' occurred during the end flowering stage (S4) and flowering stage (S3) periods, respectively. The enzyme concentration change trends of phenylpyruvate decarboxylase (PDL), phenylacetaldehyde reductase (PAR), soluble protein, C, N, and C/N ratio changes during the S3-S4 period in M. 'Praire Rose' and M. 'Lollipop' were entirely opposite. Correlation and PCA analysis demonstrated that the content of CYP79D73 (a P450) and N, and the C/N ratio were key factors in 2-PE production in M. 'Praire Rose'. The production of BA in M. 'Lollipop' was more influenced by the content of phenylacetaldehyde synthase (PAAS), CYP79D73, and soluble sugar. As CYP79D73 exits oppositely in correlation to 2-PE (M. 'Praire Rose') and BA (M. 'Lollipop'), it is hypothesized that CYP79D73 was postulated as the primary factor contributing to the observed differences of 2-PE (M. 'Praire Rose') and BA (M. 'Lollipop') formation. These results carry significant implications for crabapple aromatic flower breeding and the essential oil industry etc.

To be or not to be fragrant: floral scent of some bat-pollinated cacti

Floral scent is a key olfactory cue in both diurnal and nocturnal pollination systems. In the case of nocturnal systems, such as bat-pollinated flowers, odour seems to play a more important role than visual cues. Cactaceae include many bat-pollinated species; however, few studies have investigated the olfactory cues in this family. We analysed and compared the chemical composition of the floral bouquet of three chiropterophilous cactus species, among which are a pair of congeners that differ considerably in scent intensity. Our research presents novel findings regarding the floral scent chemistry of chiropterophilous cactus species. We documented the first case of a bat-pollinated cactus whose flowers lack perceptible floral scent and in which no volatile compounds were detected in our chemical analyses. Additionally, we provide a comprehensive analysis of the chemical composition of the floral bouquet of the other two bat-pollinated species, revealing a resemblance among closely related species within the same genus. We highlight the need for further studies using biotests to investigate the mechanisms through which bats find flowers lacking scent.

Multi-integrated genomic data for Passiflora foetida provides insights into genome size evolution and floral development in Passiflora

Passiflora is a plant genus known for its extremely distinctive and colorful flowers and a wide range of genome size variation. However, how genome characteristics are related to flower traits among Passiflora species remains poorly understood. Here, we assembled a chromosome-scale genome of P. foetida, which belongs to the same subgenus as the commercial passionfruit P. edulis. The genome of P. foetida is smaller (424.16 Mb) and contains fewer copies of long terminal repeat retrotransposons (LTR-RTs). The disparity in LTR-RTs is one of the main contributors to the differences in genome sizes between these two species and possibly in floral traits. Additionally, we observed variation in insertion times and copy numbers of LTR-RTs across different transposable element (TE) lineages. Then, by integrating transcriptomic data from 33 samples (eight floral organs and flower buds at three developmental stages) with phylogenomic and metabolomic data, we conducted an in-depth analysis of the expression, phylogeny, and copy number of MIKC-type MADS-box genes and identified essential biosynthetic genes responsible for flower color and scent from glandular bracts and other floral organs. Our study pinpoints LRT-RTs as an important player in genome size variation in Passiflora species and provides insights into future genetic improvement.