Profiling of volatile and non-volatile metabolites in Polianthes tuberosa L. flowers reveals intraspecific variation among cultivars

Functional characterization of terpene synthases SmTPS1 involved in floral scent formation in Salvia miltiorrhiza

Plants attract beneficial insects and promote pollination by releasing floral scents. Salvia miltiorrhiza, as an insect-pollinated flowering plant, which has been less studied for its floral aroma substances. This study revealed that S. miltiorrhiza flowers produce various volatile terpenoids, including five monoterpenes and ten sesquiterpenes, with the sesquiterpene compound (E)-β-caryophyllene being the most abundant, accounting for 28.1% of the total volatile terpenoids. Y-tube olfactometer experiments were conducted on the primary pollinator of S. miltiorrhiza, the Apis ceranas. The results indicated that (E)-β-caryophyllene compound had an attractive effect on the Apis ceranas. By comparing the homologous sequences with the genes of (E)-β-caryophyllene terpene synthases in other plants, the SmTPS1 gene was selected for further experiment. Subcellular localization experiments showed SmTPS1 localized in the cytoplasm, and its in vitro enzyme assay revealed that it could catalyze FPP into β-Elemene, (E)-β-caryophyllene and α-Humulene. Overexpression of SmTPS1 in S. miltiorrhiza resulted in a 5.29-fold increase in gene expression. The GC-MS analysis revealed a significant increase in the concentration of (E)-β-caryophyllene in the transgenic plants, with levels 2.47-fold higher compared to the empty vector plants. Furthermore, Y-tube olfactometer experiments showed that the transgenic plants were significantly more attractive to Apis ceranas compared to the empty vector plants. Co-expression analysis suggested that four SmMYCs (SmMYC1, SmMYC5, SmMYC10, and SmMYC11) may be involved in the transcriptional regulation of SmTPS1. The yeast one-hybrid screen and the Dual luciferase assay indicated that SmMYC10 positively regulates the expression of SmTPS1. In conclusion, this study lays a foundation for the functional analysis and transcriptional regulation of terpene synthase genes in S. miltiorrhiza.

Exploring the Volatile Composition and Antibacterial Activity of Edible Flower Hydrosols with Insights into Their Spontaneous Emissions and Essential Oil Chemistry

In the circular economy framework, hydrosols, by-products of the essential oil industry, are gaining attention for their potential in waste reduction and resource reuse. This study analyzed hydrosols from six edible flowers, investigating their chemical composition (VOC-Hyd) and antibacterial properties alongside volatile organic compounds of fresh flowers (VOC-Fs) and essential oils (EOs). Antirrhinum majus exhibited ketones as major VOC-Fs (62.6%) and VOC-Hyd (41.4%), while apocarotenoids dominated its EOs (68.0%). Begonia cucullata showed alkanes (33.7%) and aldehydes (25.7%) as primary VOC-Fs, while alkanes were prevalent in both extracts (65.6% and 91.7% in VOC-Hyd and in EOs, respectively). Calandula officinalis had monoterpenoids in VOC-Fs and VOC-Hyd (89.3% and 49.7%, respectively), while its EOs were rich in sesquiterpenoids (59.7%). Dahlia hortensis displayed monoterpenoid richness in both VOC-Fs and extracts. Monocots species' VOC-Fs (Polianthes tuberosa, Tulbaghia cominsii) were esters-rich, replaced by monoterpenoids in VOC-Hyd. P. tuberosa EO maintained ester richness, while T. cominsii EOs contained a significant percentage of sulfur compounds (38.1%). Antibacterial assays indicated comparable minimum inhibitory concentration profiles across VOC-Hyd: B. calcullata and P. tuberosa against Staphylococcus aureus and Salmonella enterica ser. typhimurium, T. cominsii against Escherichia coli and S. enterica, A. majus and C. officinalis against S. aureus, and D. hortensis against S. enterica.

Agave amica a potential model for the study of agavins metabolism

Fructans found in agave are called agavins, highly branched neo-fructans. They are essential on the yield and quality of Tequila production. The need for agave specimens with higher accumulation of agavins became essential before the growing demand of such products. To get such specimens, understanding agavins metabolism is a quintessential requirement. For this, a more efficient biological model is required. The recently reclassified Agave amica possesses the potential to gather the requirements for becoming such a model. Therefore, this study dealt with the characterization of carbohydrates in the bulbs of A. amica focusing on fructans. Moreover, it tested and described its feasibility as model for the accelerated study of agavins. Infrared analysis unveiled potential content of fructans in the bulbs of A. amica. Furthermore, high performance thin layer chromatography detected fructooligosaccharides. High performance anion exchange chromatography confirmed a polydisperse mixture of branched fructans. Gas chromatography-mass spectrometry analysis demonstrated agavins like structures in the bulbs of A. amica. Moreover, total fructan content and multivariate data analysis through bulb's age demonstrated their correlation. Thus, the presence of agavins, their correlation with phenology, and their technical advantages highlighted the feasibility of this species as a potential new biological model for the study of agavins' metabolism.

A BAHD acyltransferase contributes to the biosynthesis of both ethyl benzoate and methyl benzoate in the flowers of Lilium oriental hybrid 'Siberia'

Lily is a popular flower worldwide due to its elegant appearance and pleasant fragrance. Floral volatiles of lily are predominated by monoterpenes and benzenoids. While a number of genes for monoterpene biosynthesis have been characterized, the molecular mechanism underlying floral benzenoid formation in lily remains unclear. Here, we report on the identification and characterization of a novel BAHD acyltransferase gene that contributes to the biosynthesis of two related floral scent benzoate esters, ethyl benzoate and methyl benzoate, in the scented Lilium oriental hybrid 'Siberia'. The emission of both methyl benzoate and ethyl benzoate in L. 'Siberia' was found to be tepal-specific, floral development-regulated and rhythmic. Through transcriptome profiling and bioinformatic analysis, a BAHD acyltransferase gene designated LoAAT1 was identified as the top candidate gene for the production of ethyl benzoate. In vitro enzyme assays and substrate feeding assays provide substantial evidence that LoAAT1 is responsible for the biosynthesis of ethyl benzoate. It was interesting to note that in in vitro enzyme assay, LoAAT1 can also catalyze the formation of methyl benzoate, which is typically formed by the action of benzoic acid methyltransferase (BAMT). The lack of an expressed putative BAMT gene in the flower transcriptome of L. 'Siberia', together with biochemical and expression evidence, led us to conclude that LoAAT1 is also responsible for, or at least contributes to, the biosynthesis of the floral scent compound methyl benzoate. This is the first report that a member of the plant BAHD acyltransferase family contributes to the production of both ethyl benzoate and methyl benzoate, presenting a new mechanism for the biosynthesis of benzoate esters.

Evaluation and Comparison of Pear Flower Aroma Characteristics of Seven Cultivars

Due to its ornamental and medicinal value, pear flower has been historically loved and used in China. However, the current understanding of their odor-active compounds and aroma profiles is rather limited. This work aimed to evaluate and compare the overall aroma profile of pear flowers; the volatiles in flowers of seven pear cultivars (Anli, Bayuesu, Golden, Brown peel, KorlaXiangli, Lyubaoshi, Xizilü) were analyzed using solid-phase microextraction–gas chromatography-mass spectrometry (SPME-GC-MS). A total of 93 volatile compounds were identified and quantified within the amount of volatiles in the range of 62.7–691.8 μg kg−1 (FW) and showed high and significant variability in different cultivars. Anli and Brown peel flowers showed a relatively higher volatile abundance, while KorlaXiangli flowers were significantly lower than other cultivars. Although the composition of volatiles depended on the existence of different chemical classes, the odor activity values (OAVs) and odor descriptions showed some aldehydes were part of their main peculiarities and were considered as the basic active odorants that presented strong intensity of citrus and floral odor. Moreover, multivariate analysis showed the pear flower of different cultivars could be arranged in different clusters by the identified odorants. This study provides first-hand knowledge regarding pear flower aroma profiles, and that the cultivar differences were critical for the overall pattern.

Integrative metabolome and transcriptome analyses reveal the molecular mechanism underlying variation in floral scent during flower development of Chrysanthemum indicum var. aromaticum

Chrysanthemum indicum var. aromaticum (CIA) is an endemic plant that occurs only in the high mountain areas of the Shennongjia Forest District in China. The whole plant, in particular the flowers of CIA, have intense fragrance, making it a novel resource plant for agricultural, medicinal, and industrial applications. However, the volatile metabolite emissions in relation to CIA flower development and the molecular mechanisms underlying the generation of floral scent remain poorly understood. Here, integrative metabolome and transcriptome analyses were performed to investigate floral scent-related volatile compounds and genes in CIA flowers at three different developmental stages. A total of 370 volatile metabolites, mainly terpenoids and esters, were identified, of which 89 key differential metabolites exhibited variable emitting profiles during flower development. Transcriptome analysis further identified 8,945 differentially expressed genes (DEGs) between these samples derived from different flower developmental stages and KEGG enrichment analyses showed that 45, 93, and 101 candidate DEGs associated with the biosynthesis of phenylpropanoids, esters, and terpenes, respectively. Interestingly, significant DEGs involved into the volatile terpenes are only present in the MEP and its downstream pathways, including those genes encoding ISPE, ISPG, FPPS, GPPS, GERD, ND and TPS14 enzymes. Further analysis showed that 20 transcription factors from MYB, bHLH, AP2/EFR, and WRKY families were potentially key regulators affecting the expressions of floral scent-related genes during the CIA flower development. These findings provide insights into the molecular basis of plant floral scent metabolite biosynthesis and serve as an important data resources for molecular breeding and utilization of CIA plants in the future.

Transcriptome sequencing reveals terpene biosynthesis pathway genes accounting for volatile terpene of tree peony

Transcriptomic and volatile component analyses showed that high expression levels of genes from the terpenoid backbone biosynthesis pathway and the monoterpene metabolic pathway can strengthen the floral fragrance of tree peony. Floral fragrance is a crucial ornamental trait whose improvement is one of the primary objectives of tree peony breeding. So far, exploration of the floral fragrance of tree peony has focused on the identification of its volatile components, but the molecular mechanisms responsible for their formation remain unclear. Here, we identified 128 volatile components from the petals of tree peony and found that they consisted primarily of terpenes, alcohols, and esters. Based on the distribution pattern of these major fragrance components, 24 tree peony cultivars were classified into 4 types: grassy scent (ocimene), woody scent (longifolene), lily of the valley scent (linalool), and fruity scent (2-ethyl hexanol). We used RNA-seq to explore the mechanistic basis of terpenoid metabolism in tree peony petals with various scents. The expression levels of AACT, HMGR, PMK, DXS, DXR, HDS, HDR, and GGPS, which encode key enzymes of terpenoid backbone biosynthesis, were upregulated in 'Huangguan' (strong fragrance) compared to 'Fengdan' (faint fragrance). Moreover, the transcript abundance of LIS and MYS, two monoterpene synthase genes, was also enhanced in petals of 'Huangguan' compared to those of 'Fengdan'. Together, these results demonstrate that differences in the expression of genes from the monoterpene synthesis and terpenoid backbone pathways are associated with differences in the fragrance of tree peony. This research provides crucial genetic resources for fragrance improvement and also lays a foundation for further clarification of the mechanisms that underlie tree peony fragrance.

Revealing floral metabolite network in tuberose that underpins scent volatiles synthesis, storage and emission

The role of central carbon metabolism in the synthesis and emission of scent volatiles in tuberose flowers was revealed through measurement of changes in transcripts and metabolites levels. Tuberose or Agave amica (Medikus) Thiede & Govaerts is a widely cultivated ornamental plant in several subtropical countries. Little is known about metabolite networking involved in biosynthesis of specialized metabolites utilizing primary metabolites. In this study, metabolite profiling and gene expression analyses were carried out from six stages of maturation throughout floral lifespan. Multivariate analysis indicated distinction between early and late maturation stages. Further, the roles of sugars viz. sucrose, glucose and fructose in synthesis, glycosylation and emission of floral scent volatiles were studied. Transcript levels of an ABC G family transporter (picked up from the floral transcriptome) was in synchronization with terpene volatiles emission during the anthesis stage. A diversion from phenylpropanoid/benzenoid to flavonoid metabolism was observed as flowers mature. Further, it was suggested that this metabolic shift could be mediated by isoforms of 4-Coumarate-CoA ligase along with Myb308 transcription factor. Maximum glycosylation of floral scent volatiles was shown to occur at the late mature stage when emission declined, facilitating both storage and export from the floral tissues. Thus, this study provides an insight into floral scent volatiles synthesis, storage and emission by measuring changes at transcripts and metabolites levels in tuberose throughout floral lifespan.

Phytochemical analysis of UV active and inactive bioactive compounds present in Polianthes tuberosa (Linn.) flower

Polianthes tuberosa (Linn.) is traditionally considered an ornamental and medicinal plant worldwide. However, extensive studies on its phytochemical composition are very limited. Hence the present work aims to identify the total phytochemical ingredients present in different crude extracts of tuberosa. Phytochemical analysis has been carried out for differential cold solvent extracts of various parts of tuberosa such as petals, stamens, and ovary by gas chromatography coupled with mass spectrometry, ultra-performance liquid chromatography to quadrupole time-of-flight mass spectrometry, and evaporative light scattering detector analyzers for the identification of bioactive components. Among the various solvents used for the extraction, diethyl ether is found to be the most suitable and efficient solvent, as its total differential recovery from the crude extract is about 0.24% as compared to 0.04% obtained by using n-hexane or petroleum ether. Numerous phytochemicals have been identified by the chromatography and MS techniques, which demonstrate the presence of essential fatty acids along with other pharmacological importance phytoconstituents. Identification of additional phytochemicals present in the crude extract of tuberosa flower further enhances its biological and pharmacological significance. The present work lays a foundation for further research and development of phytoconstituents of the tuberosa flower.

Profiling of Volatile Compounds and Associated Gene Expression in Two Anthurium Cultivars and Their F1 Hybrid Progenies

Anthurium is an important ornamental crop in the world market and its floral scent can enhance its ornamental value. To date, studies of the components and formation mechanism of the floral scent of Anthurium are relatively few. In this study, the scent profiles of two Anthurium varieties were measured by gas chromatograph-mass spectrometer (GC-MS). There were 32 volatile organic compounds (VOCs) identified in Anthurium ‘Mystral’, and the most abundant compound was eucalyptol (57.5%). Extremely small amounts of VOCs were detected in Anthurium ‘Alabama’. Compared with A. ‘Alabama’, most genes related to floral scent synthesis exhibited a higher expression in A.‘Mystral’, including AaDXS, AaDXR, AaMDS, AaHDS, AaTPS, AaDAHPS, AaADT2, AaPAL1, and AaPAL2. In order to produce new varieties of Anthurium with fragrance, 454 progenies of two crossbred combinations of A. ‘Mystral’ and A. ‘Alabama’ were obtained. Four F1 generation plants with different floral scent intensities were selected for further study. The major components of floral scent in the progenies were similar to that of the parental A.‘Mystral’ plant. The expression patterns of genes related to floral scent synthesis were consistent with the relative contents of different types of VOCs. This study revealed the profiles of volatile compounds and associated gene expression in two Anthurium cultivars and their F1 hybrids, which provided a basis for the floral scent inheritance of Anthurium andraeanum.

A Comparative Analysis of Floral Scent Compounds in Intraspecific Cultivars of Prunus mume with Different Corolla Colours

Prunus mume is the only fragrant flowering species of Prunus. According to the previous studies, benzyl acetate and eugenol dominate its floral scent. However, the diversity of its floral scents remains to be elucidated. In this work, the floral volatiles emitted from eight intraspecific cultivars of P. mume with white, pink and red flowers, were collected and analyzed using headspace solid-phase microextraction combined with gas chromatograms-mass spectrometry (HS-SPME-GC-MS). In total, 31 volatile compounds were identified, in which phenylpropanoids/benzenoids accounted for over 95% of the total emission amounts. Surprisingly, except for benzyl acetate and eugenol, several novel components, such as benzyl alcohol, cinnamyl acohol, cinnamy acetate, and benzyl benzoate were found in some cultivars. The composition of floral volatiles in cultivars with white flowers was similar, in which benzyl acetate was dominant, while within pink flowers, there were differences of floral volatile compositions. Principal component analysis (PCA) showed that the emissions of benzyl alcohol, cinnamyl alcohol, benzyl acetate, eugenol, cinnamyl acetate, and benzyl benzoate could make these intraspecific cultivars distinguishable from each other. Further, hierarchical cluster analysis indicated that cultivars with similar a category and amount of floral compounds were grouped together. Our findings lay a theoretical basis for fragrant plant breeding in P. mume.

Exploration of Floral Volatile Organic Compounds in Six Typical Lycoris taxa by GC-MS

Lycoris, which is known as the ‘Chinese tulip,’ has diverse flower colors and shapes, and some species have a delicate fragrance. However, limited studies have reported the volatile organic compounds (VOCs) of Lycoris. In this study, headspace solid-phase microextraction combined with gas chromatography-mass spectrometry was used to analyze the floral VOCs of six typical Lycoris taxa. Thirty-two VOCs were identified, including terpenoids, alcohols, esters, aldehydes, ketones, and phenols. The aldehyde and terpenoid contents in Lycoris aurea were higher than in the other taxa, and the ester and alcohol contents in L. sprengeri were the highest compared to all taxa tested. Compared with other species and cultivars, L. longituba and L. longituba var. flava were the two most scented taxa and the VOCs were dominated by terpenoids and esters. L. radiate and L. chinensis were two unscented taxa and, accordingly, the VOC content was weak. A partial least squares discriminate analysis of the floral VOCs among the six Lycoris taxa showed that the six taxa could be successfully separated. Moreover, the VOCs of L. longituba and L. longituba var. flava clustered together. β-Ocimene was verified as the most important aroma compound, as determined via the calculation of the variable importance in projection values and significance analysis. β-Ocimene and its trans isomer, trans-β-ocimene, had a high relative content in L. longituba, L. longituba var. flava, L. aurea, and L. chinensis but were not detected in L. sprengeri and L. radiata. These results indicate that floral VOCs might be selected during the evolutional processes of Lycoris, and β-ocimene could be the most typical VOC among the different Lycoris taxa.

Dynamic trajectories of volatile and non-volatile specialised metabolites in 'overnight' fragrant flowers of Murraya paniculata

Ephemeral flowers, especially nocturnal ones, usually emit characteristic scent profiles within their post-anthesis lifespans of a few hours. Whether these flowers exhibit temporal variability in the composition and profile of volatile and non-volatile specialised metabolites has received little attention. Flowers of Murraya paniculata bloom in the evenings during the summer and monsoon, and their sweet, intense fragrance enhances the plant's value as an ornamental. We aimed to investigate profiles of both volatile and non-volatile endogenous specialised metabolites (ESM) in nocturnal ephemeral flowers of M. paniculata to examine whether any biochemically diverse groups of ESM follow distinct patterns of accumulation while maintaining synchrony with defensive physiological functions. Targeted ESM contents of M. paniculata flowers were profiled at ten time points at 2-h intervals, starting from late bud stage (afternoon) up to the start of petal senescence (mid-morning). Emitted volatiles were monitored continuously within the whole 20-h period using headspace sampling. The ESM contents were mapped by time point to obtain a highly dynamic and biochemically diverse profile. Relative temporal patterns of ESM accumulation indicated that the active fragrance-emitting period might be divided into 'early bloom', 'mid-bloom' and 'late bloom' phases. Early and late bloom phases were characterised by high free radical generation, with immediate enhancement of antioxidant enzymes and phenolic compounds. The mid-bloom phase was relatively stable and dedicated to maximum fragrance emission, with provision for strong terpenoid-mediated defence against herbivores. The late bloom phase merged into senescence with the start of daylight; however, even the senescent petals continued to emit fragrance to attract diurnal pollinators. Our study suggests that dynamic relations between the different ESM groups regulate the short-term requirements of floral advertisement and phytochemical defence in this ephemeral flower. This study also provided fundamental information on the temporal occurrence of emitted volatiles and internal pools of specialised metabolites in M. paniculata flowers, which could serve as an important model for pollination biology of Rutaceae, which includes many important fruit crops.