Floral volatiles: from biosynthesis to function

Multiple Attack to Inflorescences of an Annual Plant Does Not Interfere with the Attraction of Parasitoids and Pollinators

Plants in the flowering stage need to ensure reproduction by protecting themselves from attack and by preserving interactions with mutualist pollinators. When different plant mutualists are using the same type of cues, such as volatile compounds, attraction of parasitoids and pollinators may trade off. To explore this, we compared volatile emission of Brassica nigra plants in response to single or dual attack on their inflorescences. Additionally, we recorded flower visitation by pollinators and the attraction of parasitoids in the greenhouse and/or field. Brassica nigra were exposed in the flowering stage to one or two of the following three attackers: Brevicoryne brassicae aphids, Pieris brassicae caterpillars, and Xanthomonas campestris pv. raphani bacteria. We found that single attack by caterpillars, and dual attack by caterpillars plus aphids, induced the strongest changes in plant volatile emission. The caterpillars’ parasitoid C. glomerata did not exhibit preference for plants exposed to caterpillars only vs. plants exposed to caterpillars plus aphids or plus bacteria. However, the composition of the pollinator community associated with flowers of B. nigra was affected by plant exposure to the attackers, but the total number of pollinators visiting the plants did not change upon attack. We conclude that, when B. nigra were exposed to single or dual attack on their inflorescences, the plants maintained interactions with natural enemies of the insect attackers and with pollinators. We discuss how chemical diversity may contribute to plant resilience upon attack.

The Effect of Post-harvest Conditions in Narcissus sp. Cut Flowers Scent Profile

Narcissus flowers are used as cut flowers and to obtain high quality essential oils for the perfume industry. As a winter crop in the Mediterranean area, it flowers at temperatures ranging between 10 and 15°C during the day and 3-10°C during the night. Here we tested the impact of different light and temperature conditions on scent quality during post-harvest. These two types of thermoperiod and photoperiod. We also used constant darkness and constant temperatures. We found that under conditions of 12:12 Light Dark and 15-5°C, Narcissus emitted monoterpenes and phenylpropanoids. Increasing the temperature to 20°-10°C in a 12:12 LD cycle caused the loss of cinnamyl acetate and emission of indole. Under constant dark, there was a loss of scent complexity. Constant temperatures of 20°C caused a decrease of scent complexity that was more dramatic at 5°C, when the total number of compounds emitted decreased from thirteen to six. Distance analysis confirmed that 20°C constant temperature causes the most divergent scent profile. We found a set of four volatiles, benzyl acetate, eucalyptol, linalool, and ocimene that display a robust production under differing environmental conditions, while others were consistently dependent on light or thermoperiod. Scent emission changed significantly during the day and between different light and temperature treatments. Under a light:dark cycle and 15-5°C the maximum was detected during the light phase but this peak shifted toward night under 20-10°C. Moreover, under constant darkness the peak occurred at midnight and under constant temperature, at the end of night. Using Machine Learning we found that indole was the volatile with a highest ranking of discrimination followed by D-limonene. Our results indicate that light and temperature regimes play a critical role in scent quality. The richest scent profile is obtained by keeping flowers at 15°-5°C thermoperiod and a 12:12 Light Dark photoperiod.

Coordinated and High-Level Expression of Biosynthetic Pathway Genes Is Responsible for the Production of a Major Floral Scent Compound Methyl Benzoate in Hedychium coronarium

Methyl benzoate is a constituent of floral scent profile of many flowering plants. However, its biosynthesis, particularly in monocots, is scarcely reported. The monocot Hedychium coronarium is a popular ornamental plant in tropical and subtropical regions partly for its intense and inviting fragrance, which is mainly determined by methyl benzoate and monoterpenes. Interestingly, several related Hedychium species lack floral scent. Here, we studied the molecular mechanism of methyl benzoate biosynthesis in H. coronarium. The emission of methyl benzoate in H. coronarium was found to be flower-specific and developmentally regulated. As such, seven candidate genes associated with methyl benzoate biosynthesis were identified from flower transcriptome of H. coronarium and isolated. Among them, HcBSMT1 and HcBSMT2 were demonstrated to catalyze the methylation of benzoic acid and salicylic acid to form methyl benzoate and methyl salicylate, respectively. Methyl salicylate is a minor constituent of H. coronarium floral scent. Kinetic analysis revealed that HcBSMT2 exhibits a 16.6-fold lower Km value for benzoic acid than HcBSMT1, indicating its dominant role for floral methyl benzoate formation. The seven genes associated with methyl benzoate biosynthesis exhibited flower-specific or flower-preferential expression that was developmentally regulated. The gene expression and correlation analysis suggests that HcCNL and HcBSMT2 play critical roles in the regulation of methyl benzoate biosynthesis. Comparison of emission and gene expression among four Hedychium species suggested that coordinated and high-level expression of biosynthetic pathway genes is responsible for the massive emission of floral methyl benzoate in H. coronarium. Our results provide new insights into the molecular mechanism for methyl benzoate biosynthesis in monocots and identify useful molecular targets for genetic modification of scent-related traits in Hedychium.

Genome-Wide Analysis Reveals the Potential Role of MYB Transcription Factors in Floral Scent Formation in Hedychium coronarium

The MYB gene family is one of the largest groups of transcription factors (TFs) playing diverse roles in several biological processes. Hedychium coronarium (white ginger lily) is a renowned ornamental plant both in tropical and subtropical regions due to its flower shape and strong floral scent mainly composed of terpenes and benzenoids. However, there is no information available regarding the role of the MYB gene family in H. coronarium. In the current study, the MYB gene family was identified and extensively analyzed. The identified 253 HcMYB genes were unevenly mapped on 17 chromosomes at a different density. Promoter sequence analysis showed numerous phytohormones related to cis-regulatory elements. The majority of HcMYB genes contain two to three introns and motif composition analysis showed their functional conservation. Phylogenetic analysis revealed that HcMYBs could be classified into 15 distinct clades, and the segmental duplication events played an essential role in the expansion of the HcMYB gene family. Tissue-specific expression patterns of HcMYB genes displayed spatial and temporal expression. Furthermore, seven HcMYB (HcMYB7/8/75/79/145/238/248) were selected for further investigation. Through RT-qPCR, the response of candidates HcMYB genes toward jasmonic acid methyl ester (MeJA), abscisic acid (ABA), ethylene, and auxin was examined. Yeast one-hybrid (Y1H) assays revealed that candidate genes directly bind to the promoter of bottom structural volatile synthesis genes (HcTPS1, HcTPS3, HcTPS10, and HcBSMT2). Moreover, yeast two-hybrid (Y2H) assay showed that HcMYB7/8/75/145/248 interact with HcJAZ1 protein. In HcMYB7/8/79/145/248-silenced flowers, the floral volatile contents were decreased and downregulated the expression of key structural genes, suggesting that these genes might play crucial roles in floral scent formation in H. coronarium by regulating the expression of floral scent biosynthesis genes. Collectively, these findings indicate that HcMYB genes might be involved in the regulatory mechanism of terpenoids and benzenoid biosynthesis in H. coronarium.

Auxin-Responsive R2R3-MYB Transcription Factors HcMYB1 and HcMYB2 Activate Volatile Biosynthesis in Hedychium coronarium Flowers

Auxin, an important plant hormone, induces the biosynthesis of various secondary metabolites by modulating the expression of auxin-responsive genes. In the ornamental plant Hedychium coronarium, linalool and methyl benzoate are biosynthesized by the terpene synthase (TPS) HcTPS5 and the benzoic/salicylic acid methyltransferase (BSMT) HcBSMT2, respectively. However, the transcriptional regulation of this process remains unclear. Here, we identified and functionally characterized the R2R3-MYB transcription factors HcMYB1 and HcMYB2 in regulating the biosynthesis of these floral aroma compounds. HcMYB1 and HcMYB2 are specifically expressed in flowers, their expression is correlated with the emission of volatile compounds in flowers, and is induced by auxin. Moreover, HcMYB1 and HcMYB2 interact with the HcBSMT2 promoter region. HcMYB2 activates the expression of the linalool synthase gene HcTPS5. In flowers with HcMYB1 or HcMYB2 silenced, the levels of floral scent compounds were significantly reduced, and HcBSMT2 and HcTPS5 were downregulated compared with the wild type. Moreover, HcMYB1 form protein-protein interaction with key scent-related HcIAA4 protein to regulate floral aroma production. Taken together, these results indicate that HcMYB1 and HcMYB2 play crucial roles in regulating the formation of scent compounds in Hedychium coronarium (H. coronarium) flowers in response to auxin signaling.

Metabolite and Transcriptome Profiling Analysis Revealed That Melatonin Positively Regulates Floral Scent Production in Hedychium coronarium

Melatonin is a pleiotropic molecule that regulates a variety of developmental processes. Floral volatiles are important features of flowers that facilitate flower-visitor interactions by attracting pollinators, structure flower-visitor communities, and play defensive roles against plant and flower antagonists. Aside from their role in plants, floral volatiles are an essential ingredient in cosmetics, perfumes, pharmaceuticals, and flavorings. Herein, integrated metabolomic and transcriptomic approaches were carried out to analyze the changes triggered by melatonin exposure during the Hedychium coronarium flower development stages. Quantitative analysis of the volatiles of H. coronarium flowers revealed that volatile organic compound emission was significantly enhanced after melatonin exposure during the half bloom (HS), full bloom (FB) and fade stage (FS). Under the melatonin treatment, the emission of volatile contents was highest during the full bloom stage of the flower. Variable importance in projection (VIP) analysis and partial least-squares discriminant analysis (PLS-DA) identified 15 volatile compounds with VIP > 1 that were prominently altered by the melatonin treatments. According to the transcriptome sequencing data of the HS, FB, and FS of the flowers, 1,372, 1,510, and 1,488 differentially expressed genes were identified between CK-HS and 100MT-HS, CK-FB and 100MT-FB, and CK-FS and 100MT-FS, respectively. Among the significant differentially expressed genes (DEGs), 76 were significantly upregulated and directly involved in the floral scent biosynthesis process. In addition, certain volatile organic compounds were substantially linked with various DEGs after combining the metabolome and transcriptome datasets. Moreover, some transcription factors, such as MYB and bHLH, were also significantly upregulated in the comparison, which might be related to the floral aroma mechanism. Our results suggested that melatonin increased floral aroma production in H. coronarium flowers by modifying the expression level of genes involved in the floral scent biosynthesis pathway. These findings serve as a foundation for future research into the molecular mechanisms underlying the dynamic changes in volatile contents induced by melatonin treatment in H. coronarium.

Climate change shapes the future evolution of plant metabolism

Planet Earth has experienced many dramatic atmospheric and climatic changes throughout its 4.5-billion-year history that have profoundly impacted the evolution of life as we know it. Photosynthetic organisms, and specifically plants, have played a paramount role in shaping the Earth's atmosphere through oxygen production and carbon sequestration. In turn, the diversity of plants has been shaped by historical atmospheric and climatic changes: plants rose to this challenge by evolving new developmental and metabolic traits. These adaptive traits help plants to thrive in diverse growth conditions, while benefiting humanity through the production of food, raw materials, and medicines. However, the current rapid rate of climate change caused by human activities presents unprecedented new challenges to the future of plants. Here, we discuss the potential effects of modern climate change on plants, with specific attention to plant specialized metabolism. We explore potential avenues of future scientific investigations, powered by cutting-edge methods such as synthetic biology and genome engineering, to better understand and mitigate the consequences of rapid climate change on plant fitness and plant usage by humans.

Plant Volatile Organic Compounds Evolution: Transcriptional Regulation, Epigenetics and Polyploidy

Volatile organic compounds (VOCs) are emitted by plants as a consequence of their interaction with biotic and abiotic factors, and have a very important role in plant evolution. Floral VOCs are often involved in defense and pollinator attraction. These interactions often change rapidly over time, so a quick response to those changes is required. Epigenetic factors, such as DNA methylation and histone modification, which regulate both genes and transcription factors, might trigger adaptive responses to these evolutionary pressures as well as regulating the rhythmic emission of VOCs through circadian clock regulation. In addition, transgenerational epigenetic effects and whole genome polyploidy could modify the generation of VOCs’ profiles of offspring, contributing to long-term evolutionary shifts. In this article, we review the available knowledge about the mechanisms that may act as epigenetic regulators of the main VOC biosynthetic pathways, and their importance in plant evolution.

Metabolic, Enzymatic Activity, and Transcriptomic Analysis Reveals the Mechanism Underlying the Lack of Characteristic Floral Scent in Apricot Mei Varieties

Apricot mei, a hybrid of Prunus mume and Prunus sibirica, usually has greater cold resistance than P. mume; however, most varieties of Apricot mei lack the characteristic floral scent of P. mume. The volatile and intracellular metabolites, activity levels of key enzymes, and transcriptomes of blooming flowers were comprehensively investigated in five varieties of P. mume. Benzyl acetate and eugenol were determined to be the main components of the P. mume floral scent. However, benzyl benzoate and benzyl alcohol benzoyltransferase activity was detected in only the low-fragrance varieties "Dan Fenghou" and "Yanxing." No benzyl alcohol or benzaldehyde reductase (BAR) activity was detected in the non-fragrant variety "Fenghou." PmBAR1 and PmBAR3 were identified as the key genes responsible for BAR activity. The lack of benzyl alcohol synthesis in the "Fenghou" variety was caused by low activity of PmBAR1-Fen and low expression of PmBAR3. The 60-aa segment at the N-terminus of PmBAR3 was found to play an important role in its enzymatic activity. Correlation tests between floral scent metabolites and the transcriptomes of the five different scented varieties showed that some transcripts associated with hormones, stresses, posttranslational modifications and transporters may also play important regulatory roles in floral scent metabolism in the different varieties.

Pollination in the Anthropocene: a Moth Can Learn Ozone-Altered Floral Blends

Insect pollination is essential to many unmanaged and agricultural systems and as such is a key element in food production. However, floral scents that pollinating insects rely on to locate host plants may be altered by atmospheric oxidants, such as ozone, potentially making these cues less attractive or unrecognizable to foraging insects and decreasing pollinator efficacy. We demonstrate that levels of tropospheric ozone commonly found in many rural areas are sufficient to disrupt the innate attraction of the tobacco hawkmoth Manduca sexta to the odor of one of its preferred flowers, Nicotiana alata. However, we further find that visual navigation together with associative learning can offset this disruption. Foraging moths that initially find an ozone-altered floral scent unattractive can target an artificial flower using visual cues and associate the ozone-altered floral blend with a nectar reward. The ability to learn ozone-altered floral odors may enable pollinators to maintain communication with their co-evolutionary partners and reduce the negative impacts that anthropogenically elevated oxidants may have on plant-pollinator systems.

Composition and diurnal variation of floral scent emission in Rosa rugosa Thunb. and Tulipa gesneriana L

This study was aimed to explore the composition and diurnal variation analyses of floral scent emission from Rosa rugosa Thunb. and Tulipa gesneriana L. The floral scent from the fresh flower were collected at different time points (9:00, 12:00, 15:00, 18:00, and 21:00) using dynamic headspace collection and were analyzed using autothermal desorber-gas chromatography/mass spectrometry (ATD-GC/MS). The results showed that a total of 62 volatile flavor compounds were detected from Rosa rugosa Thunb and a total of 70 volatile flavor compounds were detected from Tulipa gesneriana L. They were identified with eight functional categories: alcohols, fatty hydrocarbons, terpenes, aldehydes, ketones, esters, and other substances. The total release amount first decreased, and then increased with time, and arrived at the lowest at 15:00. The release amounts of different categories present distinct change patterns. Among the components, phenylethyl alcohol, citronellol, methylene chloride, hexane, and acetone showed relatively higher release amounts and were thought as the main components in floral scent of Rosa rugosa Thunb. Alpha-Farnesene, ethanol, pentadecane, beta-ocimene, longifolene, caryophyllene, and acetone showed relatively higher release amounts and were thought as the main components in floral scent of Tulipa gesneriana L. Research of roses and tulips in aromatic in the garden provides a theoretical basis and research and improvement of the aroma components of aroma.

Diversification of petal monoterpene profiles during floral development and senescence in wild roses: relationships among geraniol content, petal colour, and floral lifespan

Wild roses store and emit a large array of fragrant monoterpenes from their petals. Maximisation of fragrance coincides with floral maturation in many angiosperms, which enhances pollination efficiency, reduces floral predation, and improves plant fitness. We hypothesized that petal monoterpenes serve additional lifelong functions such as limiting metabolic damage from reactive oxygen species (ROS), and altering isoprenoid hormonal abundance to increase floral lifespan. Petal monoterpenes were quantified at three floral life-stages (unopened bud, open mature, and senescent) in 57 rose species and 16 subspecies originating from Asia, America, and Europe, and relationships among monoterpene richness, petal colour, ROS, hormones, and floral lifespan were analysed within a phylogenetic context. Three distinct types of petal monoterpene profiles, revealing significant developmental and functional differences, were identified: Type A, species where monoterpene abundance peaked in open mature flowers depleting thereafter; Type B, where monoterpenes peaked in senescing flowers increasing from bud stage, and a rare Type C (8 species) where monoterpenes depleted from bud stage to senescence. Cyclic monoterpenes peaked during early floral development, whereas acyclic monoterpenes (dominated by geraniol and its derivatives, often 100-fold more abundant than other monoterpenes) peaked during floral maturation in Type A and B roses. Early-diverging roses were geraniol-poor (often Type C) and white-petalled. Lifetime changes in hydrogen peroxide (H₂O₂) revealed a significant negative regression with the levels of petal geraniol at all floral life-stages. Geraniol-poor Type C roses also showed higher cytokinins (in buds) and abscisic acid (in mature petals), and significantly shorter floral lifespan compared with geraniol-rich Type A and B roses. We conclude that geraniol enrichment, intensification of petal colour, and lower potential for H₂O₂-related oxidative damage characterise and likely contribute to longer floral lifespan in monoterpene-rich wild roses.

Terpenoids are transported in the xylem sap of Norway spruce

Norway spruce is a conifer storing large amounts of terpenoids in resin ducts of various tissues. Parts of the terpenoids stored in needles can be emitted together with de novo synthesized terpenoids. Since previous studies provided hints on xylem transported terpenoids as a third emission source, we tested if terpenoids are transported in xylem sap of Norway spruce. We further aimed at understanding if they might contribute to terpenoid emission from needles. We determined terpenoid content and composition in xylem sap, needles, bark, wood and roots of field grown trees, as well as terpenoid emissions from needles. We found considerable amounts of terpenoids-mainly oxygenated compounds-in xylem sap. The terpenoid concentration in xylem sap was relatively low compared with the content in other tissues, where terpenoids are stored in resin ducts. Importantly, the terpenoid composition in the xylem sap greatly differed from the composition in wood, bark or roots, suggesting that an internal transport of terpenoids takes place at the sites of xylem loading. Four terpenoids were identified in xylem sap and emissions, but not within needle tissue, suggesting that these compounds are likely derived from xylem sap. Our work gives hints that plant internal transport of terpenoids exists within conifers; studies on their functions should be a focus of future research.

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

Lilium 'Siberia' is a perennial herbaceous plant that is commercially significant because of its snowy white floral color and appealing scent which is mainly due to the presence of monoterpenes and benzoids compounds in floral volatile profile. In the current study, LoTPS5 was cloned and functionally characterized. Results revealed that LoTPS5 specifically generates squalene from FPP, whereas no product was produced when it was incubated with GPP or GGPP. The subcellular localization experiment showed that LoTPS5 was located in plastids. Furthermore, LoTPS5 showed its high expression in the leaf followed by petals and sepals of the flower. Moreover, the expression of LoTPS5 gradually increased from the bud stage and peak at the full-bloom stage. Besides, LoTPS5 showed a diurnal circadian rhythmic pattern with a peak in the afternoon (16:00) followed by deep night (24:00) and morning (8:00), respectively. LoTPS5 is highly responsive to mechanical wounding by rapidly elevating its mRNA transcript level. The current study will provide significant information for future studies of terpenoid and squalene biosynthesis in Lilium 'Siberia'.

Molecular Cloning and Functional Characterization of CpMYC2 and CpBHLH13 Transcription Factors from Wintersweet (Chimonanthus praecox L.)

Wintersweet (Chimonanthus praecox L.) is an ornamental and economically significant shrub known for its unique flowering characteristics, especially the emission of abundant floral volatile organic compounds. Thus, an understanding of the molecular mechanism of the production of these compounds is necessary to create new breeds with high volatile production. In this study, two bHLH transcription factors (CpMYC2 and CpbHLH13) of Wintersweet H29 were functionally characterized to illustrate their possible role in the production of volatile compounds. The qRT-PCR results showed that the expression of CpMYC2 and CpbHLH13 increased from the flower budding to full bloom stage, indicating that these two genes may play an essential role in blooming and aroma production in wintersweet. Gas chromatography-mass spectroscopy (GC-MS) analysis revealed that the overexpression of CpMYC2 in arabidopsis (Arabidopsis thaliana) AtMYC2-2 mutant (Salk_083483) and tobacco (Nicotiana tabaccum) genotype Petit Havana SR1 significantly increased floral volatile monoterpene, especially linalool, while the overexpression of CpbHLH13 in Arabidopsis thaliana ecotype Columbia-0 (Col-0) and tobacco genotype SR1 increased floral sesquiterpene β-caryophyllene production in both types of transgenic plants respectively. High expression of terpene synthase (TPS) genes in transgenic A. thaliana along with high expression of CpMYC2 and CpbHLH13 in transgenic plants was also observed. The application of a combination of methyl jasmonic acid (MeJA) and gibberellic acid (GA3) showed an increment in linalool production in CpMYC2-overexpressing arabidopsis plants, and the high transcript level of TPS genes also suggested the involvement of CpMYC2 in the jasmonic acid (JA) signaling pathway. These results indicate that both the CpMYC2 and CpbHLH13 transcription factors of wintersweet are possibly involved in the positive regulation and biosynthesis of monoterpene (linalool) and sesquiterpene (β-caryophyllene) in transgenic plants. This study also indicates the potential application of wintersweet as a valuable genomic material for the genetic modification of floral scent in other flowering plants that produce less volatile compounds.

Molecular cloning, characterization and expression analysis of LoTPS2 and LoTPS4 involved in floral scent formation in oriental hybrid Lilium variety 'Siberia'

Lilies are a commercially significant cut flower worldwide due not only to their elegant shape but also to their appealing scent. Among Lilium varieties, Lilium 'Siberia' is a cultivar that is prominent and highly favored by consumers due to its snowy white color and strong floral scent. Here, two terpene synthase genes (LoTPS2 and LoTPS4) that are responsible for floral scent production in Lilium 'Siberia' were cloned and functionally characterized. Recombinant LoTPS2 specifically catalyzed the formation of (E, E)-α-farnesene from FPP. Recombinant LoTPS4 is a multiproduct enzyme that produces D-limonene and β-myrcene as major volatile compounds and β-phellandrene, (+)-4-carene and 3-carene as minor products from GPP. Furthermore, LoTPS4 generates trans-α-bergamotene as a major product and di-epi-α-cedrene, α-cubebene and (E)-β-farnesene as minor compounds from FPP. Subcellular localization analysis using GFP fusion constructs revealed that LoTPS2 was localized in the cytosol, whereas LoTPS4 was localized in plastids. Real-time PCR analysis showed that LoTPS2 was highly expressed in the petals and sepals of the flower, while LoTPS4 was highly expressed in the filament of the flower. Moreover, mechanical wounding of flowers revealed that LoTPS2 showed a strong response to wounding via a rapid increase in its mRNA transcript level. Our results will assist scientists in exploring the molecular mechanisms of terpene biosynthesis in this species and will provide new insight into the biotechnological modification of the floral bouquet in Lilium.

VviWRKY40, a WRKY Transcription Factor, Regulates Glycosylated Monoterpenoid Production by VviGT14 in Grape Berry

Glycosylated volatile precursors are important, particularly in wine grape berries, as they contribute to the final aroma in wines by releasing volatile aglycones during yeast fermentation and wine storage. Previous study demonstrated that VviGT14 was functioned as a critical monoterpene glucosyltransferase in grape berry, while the transcriptional regulation mechanism of VviGT14 was still unknown. Here we identified VviWRKY40 as a binding factor of VviGT14 promoter by both DNA pull-down and yeast one-hybrid screening, followed by a series of in vitro verification. VviWRKY40 expression pattern negatively correlated with that of VviGT14 in grape berries. And the suppressor role of VviWRKY40 was further confirmed by using the dual luciferase assay with Arabidopsis protoplast and grape cell suspension system. Furthermore, the grape suspension cell ABA treatment study showed that ABA downregulated VviWRKY40 transcript level but promoted that of VviGT14, indicating that VviWRKY40 was at the downstream of ABA signal transduction network to regulate monoterpenoid glycosylation. These data extend our knowledge of transcriptional regulation of VviGT14, and provide new targets for grape breeding to alter monoterpenoid composition.

Molecular Mechanisms of Pollination Biology

Pollination is the transfer of pollen grains from the stamens to the stigma, an essential requirement of sexual reproduction in flowering plants. Cross-pollination increases genetic diversity and is favored by selection in the majority of situations. Flowering plants have evolved a wide variety of traits that influence pollination success, including those involved in optimization of self-pollination, attraction of animal pollinators, and the effective use of wind pollination. In this review we discuss our current understanding of the molecular basis of the development and production of these various traits. We conclude that recent integration of molecular developmental studies with population genetic approaches is improving our understanding of how selection acts on key floral traits in taxonomically diverse species, and that further work in nonmodel systems promises to provide exciting insights in the years to come.

Composition and Biosynthesis of Scent Compounds from Sterile Flowers of an Ornamental Plant Clematis florida cv. 'Kaiser'

Clematisflorida is a popular ornamental vine species known for diverse colors and shapes of its flowers but not for scent. Here we investigated the composition and biosynthesis of floral scent in ‘Kaiser’, a fragrant cultivar of C. florida that has sterile flowers. Volatile profiling revealed that flowers of ‘Kaiser’ emit more than 20 compounds, with monoterpenes being most abundant. Among the three floral organs, namely sepals, transformed-petals, and ovaries, ovaries had the highest rates of total volatile emission. To determine the molecular mechanism underlying floral scent biosynthesis in ‘Kaiser’, we sequenced a flower transcriptome and searched the transcriptome for terpene synthase genes (TPSs), which are key genes for terpene biosynthesis. Among the TPS genes identified, three were putative intact full-length genes and were designated CfTPS1, CfTPS2, and CfTPS3. Phylogenetic analysis placed CfTPS1, CfTPS2, and CfTPS3 to the TPS-g, TPS-b, and TPS-a subfamily, respectively. Through in vitro enzyme assays with Escherichia coli-expressed recombinant proteins, both CfTPS1 and CfTPS2 were demonstrated to catalyze the conversion of geranyl diphosphate to linalool, the most abundant constituent of C. florida floral scent. In addition, CfTPS1 and CfTPS2 produced the sesquiterpene nerolidol from (E,E)-farnesyl diphosphate. CfTPS3 showed sesquiterpene synthase activity and produced multiple products in vitro. All three CfTPS genes showed higher levels of expression in sepals than those in transformed-petals and ovaries. Our results show that despite being sterile, the flowers of ‘Kaiser’ have normal mechanisms for floral scent biosynthesis that make the flowers fragrant.

Evolution of a Novel and Adaptive Floral Scent in Wild Tobacco

Many plants emit diverse floral scents that mediate plant-environment interactions and attain reproductive success. However, how plants evolve novel and adaptive biosynthetic pathways for floral volatiles remains unclear. Here, we show that in the wild tobacco, Nicotiana attenuata, a dominant species-specific floral volatile (benzyl acetone, BA) that attracts pollinators and deters florivore is synthesized by phenylalanine ammonia-lyase 4 (NaPAL4), isoflavone reductase 3 (NaIFR3), and chalcone synthase 3 (NaCHAL3). Transient expression of NaFIR3 alone in N. attenuata leaves is sufficient and necessary for ectopic foliar BA emissions, and coexpressing NaIFR3 with NaPAL4 and NaCHAL3 increased the BA emission levels. Independent changes in transcription of NaPAL4 and NaCHAL3 contributed to intraspecific variations of floral BA emission. However, among species, the gain of expression of NaIFR3 resulted in the biosynthesis of BA, which was only found in N. attenuata. This study suggests that novel metabolic pathways associated with adaptation can arise via reconfigurations of gene expression.

Characterization of Guaiene Synthases from Stellera chamaejasme L. Flowers and Their Application in De novo Production of (-)-Rotundone in Yeast

Four terpene synthases for the biosynthesis of volatile terpenoids were identified from the transcriptome of Stellera chamaejasme L. flowers, including SchTPS1, SchTPS2, SchTPS3, and SchTPS4. Their functions were characterized by synthetic biology approaches in Escherichia coli and in vitro enzymatic assays. SchTPS1, SchTPS2, and SchTPS3 are guaiene synthases, while SchTPS4 is an (E,E)-geranyl linalool synthase. Next, SchTPS1 and α-guaiene 2-oxidase VvSTO2 were co-expressed in Saccharomyces cerevisiae to reconstruct the biosynthetic pathway of (-)-rotundone, which is a unique aroma compound in fruits, vegetables, and wines. This is the first report for the construction of a (-)-rotundone-producing microbial platform.

Microstructure of floral nectaries in Robinia viscosa var. hartwigii (Papilionoideae, Fabaceae)-a valuable but little-known melliferous plant

Floral nectaries are important components of floral architecture and significant taxonomic traits facilitating assessment of relationships between taxa and can contribute substantially to studies on the ecology and evolution of a particular genus. Knowledge of nectary structure and functioning allows better understanding of the mutualistic interactions between the pollinator and the plant. Robinia viscosa var. hartwigii (Hartweg's locust), planted in many European countries as an ornamental plant and used for recovery of degraded areas and urban arborisation, is a valuable melliferous species often visited by honeybees and bumblebees. The aim of this study was to investigate the microstructure of the floral nectaries of R. viscosa var. hartwigii with the use of light, fluorescence, scanning, and transmission electron microscopes. The photosynthetic nectaries were located on the inner surface of the cup-like receptacle. The components of pre-nectar were synthesised in the chloroplasts of the glandular parenchyma and transported via the conducting elements of the phloem. Nectar was released through modified nectarostomata. Nectar secretion presumably proceeded in the eccrine mode, whereas nectar transport represented the symplastic and apoplastic types. The cuticle on the nectary epidermis surface contained lipids, essentials oils, and flavonoids, while proteins and flavonoids were present in the glandular parenchyma cells. Idioblasts containing phenolic compounds, tannins, and polysaccharides were observed between the glandular parenchyma cells. The location of the nectaries and the mode of nectar production in the flowers of the Hartweg's locust follow the common location and structure pattern characteristic for the nectaries in some members of the subfamily Papilionoideae and can be a significant taxonomic trait for the genus Robinia and the tribe Robinieae.

Effect of cluster zone leaf removal on monoterpene profiles of Sauvignon Blanc grapes and wines

Monoterpenes contribute to the varietal aromas of grapes and wines. We determined the effects of cluster zone leaf removal on the monoterpene profiles of Sauvignon Blanc grape berries and wines, and on the expression of key genes in the terpenoid pathway. Leaf removal at two intensities (half basic, 50%; full basic, 100%) was conducted at two weeks before veraison, veraison, and two weeks after veraison. Half basic leaf removal increased the pH and decreased the tartaric acid content in grapes and wines. The concentrations of most free- and bound-form monoterpenes in grapes were increased by early leaf removal. The total monoterpene contents were increased in wines in the defoliation treatments, but were significantly lower in wines from the full basic leaf removal treatments than in wines from the half basic leaf removal treatments. The defoliation treatments resulted in increased transcript levels of some key genes in terpene biosynthesis (VvPNLinNer1, VvPNLinNer2, VvPNLNGl1, VvPNLNGl2, and VvUGT88A1L1).

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.

The effect of elevated ozone on floral chemistry of Brassicaceae species

Tropospheric ozone is a major atmospheric pollutant; it is phytotoxic and has a strong effect on phytochemicals, which are constitutively present in plant tissues, but also produced de novo in response to stress. It has been shown that ozone exposure can modify volatile phytochemical emissions from leaves, which could disturb interactions between plants and other organisms. However, there is a lack of knowledge on the effects of ozone on floral chemistry. The aim of this study was to determine the effects of two elevated ozone exposure scenarios (80 and 120 ppb during daylight hours for 5 consecutive days) on the floral volatile emissions and floral chemical (molecular size range C₆-C₂₀) content of four Brassicaceae species: Sinapis alba, Sinapis arvensis, Brassica napus and Brassica nigra. The results showed that the emissions of individual compounds and their relative contributions to volatile blends are both affected by ozone exposure. In addition, for all four species studied, three diterpenes (neophytadiene, cis-phytol and trans-phytol) were present in significantly lower amounts and a fourth diterpene (hexahydrofarnesyl acetone) in significantly greater amounts in ozone-exposed plants. Consistent effects of ozone exposure on volatile emissions and terpene content were observed for each of the four species studied with no significant effect of exposure level. It appeared that B. napus is the most ozone-sensitive species, whereas B. nigra is the most ozone-tolerant. Since earlier studies have indicated that ratios of phytochemicals can have substantial effects on the efficacy of chemical use by pollinators, these changes may have ecological and biological relevance that should be the focus of further elucidation.

Flowering-mediated root-fungus symbiosis loss is related to jasmonate-dependent root soluble sugar deprivation

The role of flowering in root-fungal symbiosis is not well understood. Because flowering and fungal symbionts are supported by carbohydrates, we hypothesized that flowering modulates root-beneficial fungal associations through alterations in carbohydrate metabolism and transport. We monitored fungal colonization and soluble sugars in the roots of Arabidopsis thaliana following inoculation with a mutualistic fungus Phomopsis liquidambari across different plant developmental stages. Jasmonate signalling of wild-type plants, sugar transport, and root invertase of wild-type and jasmonate-insensitive plants were exploited to assess whether and how jasmonate-dependent sugar dynamics are involved in flowering-mediated fungal colonization alterations. We found that flowering restricts root-fungal colonization and activates root jasmonate signalling upon fungal inoculation. Jasmonates reduce the constitutive and fungus-induced accumulation of root glucose and fructose at the flowering stage. Further experiments with sugar transport and metabolism mutant lines revealed that root glucose and fructose positively influence fungal colonization. Diurnal, jasmonate-dependent inhibitions of sugar transport and soluble invertase activity were identified as likely mechanisms for flowering-mediated root sugar depletion upon fungal inoculation. Collectively, our results reveal that flowering drives root-fungus cooperation loss, which is related to jasmonate-dependent root soluble sugar depletion. Limiting the spread of root-fungal colonization may direct more resources to flower development.

Male flowers of Aconitum compensate for toxic pollen with increased floral signals and rewards for pollinators

Many plants require animal pollinators for successful reproduction; these plants provide pollinator resources in pollen and nectar (rewards) and attract pollinators by specific cues (signals). In a seeming contradiction, some plants produce toxins such as alkaloids in their pollen and nectar, protecting their resources from ineffective pollinators. We investigated signals and rewards in the toxic, protandrous bee-pollinated plant Aconitum napellus, hypothesizing that male-phase flower reproductive success is pollinator-limited, which should favour higher levels of signals (odours) and rewards (nectar and pollen) compared with female-phase flowers. Furthermore, we expected insect visitors to forage only for nectar, due to the toxicity of pollen. We demonstrated that male-phase flowers emitted more volatile molecules and produced higher volumes of nectar than female-phase flowers. Alkaloids in pollen functioned as chemical defences, and were more diverse and more concentrated compared to the alkaloids in nectar. Visitors actively collected little pollen for larval food but consumed more of the less-toxic nectar. Toxic pollen remaining on the bee bodies promoted pollen transfer efficiency, facilitating pollination.

Genome-wide identification, characterization, expression and enzyme activity analysis of coniferyl alcohol acetyltransferase genes involved in eugenol biosynthesis in Prunus mume

Prunus mume, a traditional Chinese flower, is the only species of Prunus known to produce a strong floral fragrance, of which eugenol is one of the principal components. To explore the molecular mechanism of eugenol biosynthesis in P. mume, patterns of dynamic, spatial and temporal variation in eugenol were analysed using GC-MS. Coniferyl alcohol acetyltransferase (CFAT), a member of the BAHD acyltransferase family, catalyses the substrate of coniferyl alcohol to coniferyl acetate, which is an important substrate for synthesizing eugenol. In a genome-wide analysis, we found 90 PmBAHD genes that were phylogenetically clustered into five major groups with motif compositions relatively conserved in each cluster. The phylogenetic tree showed that the PmBAHD67-70 proteins were close to the functional CFATs identified in other species, indicating that these four proteins might function as CFATs. In this work, 2 PmCFAT genes, named PmCFAT1 and PmCFAT2, were cloned from P. mume ‘Sanlunyudie’, which has a strong fragrance. Multiple sequences indicated that PmCFAT1 contained two conserved domains, HxxxD and DFGWG, whereas DFGWG in PmCFAT2 was changed to DFGFG. The expression levels of PmCFAT1 and PmCFAT2 were examined in different flower organs and during the flowering stages of P. mume ‘Sanlunyudie’. The results showed that PmCFAT1 was highly expressed in petals and stamens, and this expression increased from the budding stage to the full bloom stage and decreased in the withering stage, consistent with the patterns of eugenol synthesis and emission. However, the peak of gene expression appeared earlier than those of eugenol synthesis and emission. In addition, the expression level of PmCFAT2 was higher in pistils and sepals than in other organs and decreased from the budding stage to the blooming stage and then increased in the withering stage, which was not consistent with eugenol synthesis. Subcellular localization analysis indicated that PmCFAT1 and PmCFAT2 were located in the cytoplasm and nucleus, while enzyme activity assays showed that PmCFAT1 is involved in eugenol biosynthesis in vitro. Overall, the results suggested that PmCFAT1, but not PmCFAT2, contributed to eugenol synthesis in P. mume.

Anti-aphrodisiac pheromone, a renewable signal in adult butterflies

The male butterfly Pieris napi produces the anti-aphrodisiac pheromone methyl salicylate (MeS) and transfers it to the female during mating. After mating she releases MeS, when courted by conspecific males, which decreases her attractiveness and the duration of male harassment, thus increasing her time available for egg-laying. In previous studies we have shown that males produced MeS from the amino acid L-phenylalanine (L-Phe) acquired during larval stage. In this study we show that adult males of P. napi can utilize L-Phe and aromatic flower volatiles as building blocks for production of anti-aphrodisiac pheromone and transfer it to females during mating. We demonstrate this by feeding butterflies with stable isotope labelled molecules mixed in sugar solutions, and, to mimic the natural conditions, we fed male butterflies with floral nectar of Bunias orientalis plants treated with labelled L-Phe. The volatiles from butterflies and plants were collected and identified by solid phase micro extraction, gas chromatography and mass spectrometry techniques. Since P. napi is polygamous, males would gain from restoring the titre of MeS after mating and the use of aromatic precursors for production of MeS could be considered as an advantageous trait which could enable butterflies to relocate L-Phe for other needs.

Roles of plant volatiles in defence against microbial pathogens and microbial exploitation of volatiles

Plants emit a large variety of volatile organic compounds during infection by pathogenic microbes, including terpenes, aromatics, nitrogen-containing compounds, and fatty acid derivatives, as well as the volatile plant hormones, methyl jasmonate, and methyl salicylate. Given the general antimicrobial activity of plant volatiles and the timing of emission following infection, these compounds have often been assumed to function in defence against pathogens without much solid evidence. In this review, we critically evaluate current knowledge on the toxicity of volatiles to fungi, bacteria, and viruses and their role in plant resistance as well as how they act to induce systemic resistance in uninfected parts of the plant and in neighbouring plants. We also discuss how microbes can detoxify plant volatiles and exploit them as nutrients, attractants for insect vectors, and inducers of volatile emissions, which stimulate immune responses that make plants more susceptible to infection. Although much more is known about plant volatile-herbivore interactions, knowledge of volatile-microbe interactions is growing and it may eventually be possible to harness plant volatiles to reduce disease in agriculture and forestry. Future research in this field can be facilitated by making use of the analytical and molecular tools generated by the prolific research on plant-herbivore interactions.

Developmental mechanisms involved in the diversification of flowers

We all appreciate the fantastic diversity of flowers. How flowers diversified, however, remains largely enigmatic. The mechanisms underlying the diversification of flowers are complex because the overall appearance of a flower is determined by many factors, such as the shape and size of its receptacle, and the arrangement, number, type, shape and colour of floral organs. Modifications of the developmental trajectories of a flower and its components, therefore, can lead to the generation of new floral types. In this Review, by summarizing the recent progress in studying the initiation, identity determination, morphogenesis and maturation of floral organs, we present our current understanding of the mechanisms underlying the diversification of flowers.

No evidence of flowering synchronization upon floral volatiles for a short lived annual plant species: revisiting an appealing hypothesis

BACKGROUND

Self-incompatible plants require simultaneous flowering mates for crosspollination and reproduction. Though the presence of flowering conspecifics and pollination agents are important for reproductive success, so far no cues that signal the flowering state of potential mates have been identified. Here, we empirically tested the hypothesis that plant floral volatiles induce flowering synchrony among self-incompatible conspecifics by acceleration of flowering and flower opening rate of non-flowering conspecifics. We exposed Brassica rapa Maarssen, a self-incompatible, in rather dense patches growing annual, to (1) flowering or non-flowering conspecifics or to (2) floral volatiles of conspecifics by isolating plants in separate containers with a directional airflow. In the latter, odors emitted by non-flowering conspecifics were used as control.

RESULTS

Date of first bud, duration of first flower bud, date of first flower, maximum number of open flowers and flower opening rate were not affected by the presence of conspecific flowering neighbors nor by floral volatiles directly.

CONCLUSIONS

This study presents a compelling approach to empirically test the role of flower synchronization by floral volatiles and challenges the premises that are underlying this hypothesis. We argue that the life history of the plant as well as its interaction with pollinators and insect herbivores, as well as the distance over which volatiles may serve as synchronization cue, set constraints on the fitness benefits of synchronized flowering which needs to be taken into account when testing the role of floral volatiles in synchronized flowering.

RNA sequencing analysis of Cymbidium goeringii identifies floral scent biosynthesis related genes

BACKGROUND

Cymbidium goeringii belongs to the Orchidaceae, which is one of the most abundant angiosperm families. Cymbidium goeringii consist with high economic value and characteristics include fragrance and multiple flower colors. Floral scent is one of the important strategies for ensuring fertilization. However, limited genetic data is available in this non-model plant, and little known about the molecular mechanism responsible for floral scent in this orchid. Transcriptome and expression profiling data are needed to identify genes and better understand the biological mechanisms of floral scents in this species. Present transcriptomic data provides basic information on the genes and enzymes related to and pathways involved in flower secondary metabolism in this plant.

RESULTS

In this study, RNA sequencing analyses were performed to identify changes in gene expression and biological pathways related scent metabolism. Three cDNA libraries were obtained from three developmental floral stages: closed bud, half flowering stage and full flowering stage. Using Illumina technique 159,616,374 clean reads were obtained and were assembled into 85,868 final unigenes (average length 1194 nt), 33.85% of which were annotated in the NCBI non redundant protein database. Among this unigenes 36,082 were assigned to gene ontology and 23,164 were combined with COG groups. Total 33,417 unigenes were assigned in 127 pathways according to the Kyoto Encyclopedia of Genes and Genomes pathway database. According these transcriptomic data we identified number of candidates genes which differentially expressed in different developmental stages of flower related to fragrance biosynthesis. In q-RT-PCR most of the fragrance related genes highly expressed in half flowering stage.

CONCLUSIONS

RNA-seq and DEG data provided comprehensive gene expression information at the transcriptional level that could be facilitate the molecular mechanisms of floral biosynthesis pathways in three developmental phase's flowers in Cymbidium goeringii, moreover providing useful information for further analysis on C. goeringii, and other plants of genus Cymbidium.

The MYB transcription factor Emission of Methyl Anthranilate 1 stimulates emission of methyl anthranilate from Medicago truncatula hairy roots

Plants respond to herbivore or pathogen attacks by activating specific defense programs that include the production of bioactive specialized metabolites to eliminate or deter the attackers. Volatiles play an important role in the interaction of a plant with its environment. Through transcript profiling of jasmonate-elicited Medicago truncatula cells, we identified Emission of Methyl Anthranilate (EMA) 1, a MYB transcription factor that is involved in the emission of the volatile compound methyl anthranilate when expressed in M. truncatula hairy roots, giving them a fruity scent. RNA sequencing (RNA-Seq) analysis of the fragrant roots revealed the upregulation of a methyltransferase that was subsequently characterized to catalyze the O-methylation of anthranilic acid and was hence named M. truncatula anthranilic acid methyl transferase (MtAAMT) 1. Given that direct activation of the MtAAMT1 promoter by EMA1 could not be unambiguously demonstrated, we further probed the RNA-Seq data and identified the repressor protein M. truncatula plant AT-rich sequence and zinc-binding (MtPLATZ) 1. Emission of Methyl Anthranilate 1 binds a tandem repeat of the ACCTAAC motif in the MtPLATZ1 promoter to transactivate gene expression. Overexpression of MtPLATZ1 in transgenic M. truncatula hairy roots led to transcriptional silencing of EMA1, indicating that MtPLATZ1 may be part of a negative feedback loop to control the expression of EMA1. Finally, application of exogenous methyl anthranilate boosted EMA1 and MtAAMT1 expression dramatically, thus also revealing a positive amplification loop. Such positive and negative feedback loops seem to be the norm rather than the exception in the regulation of plant specialized metabolism.

Differences in flavonoid pathway metabolites and transcripts affect yellow petal colouration in the aquatic plant Nelumbo nucifera

BACKGROUND

The Asia lotus (Nelumbo nucifera Gaertn.) is an ornamental aquatic plant with high economic value. Flower colour is an important ornamental trait, with much of N. nucifera breeding focusing on its yellow flowers. To explore the yellow flower colouration mechanism in N. nucifera, we analysed its pigment constituents and content, as well as gene expression in the flavonoid pathway, in two N. nucifera cultivars.

RESULTS

We performed metabolomic and gene expression analyses in two N. nucifera cultivars with yellow and white flowers, Molinqiuse (MLQS) and Yeguangbei (YGB), respectively, at five stages of flower colouration. Based on phenotypic observation and metabolite analyses, the later stages of flower colouration (S3-S5) were determined to be key periods for differences between MLQS and YGB, with dihydroflavonols and flavonols differing significantly between cultivars. Dihydroquercetin, dihydrokaempferol, and isorhamnetin were significantly higher in MLQS than in YGB, whereas kaempferol was significantly higher in YGB. Most of the key homologous structural genes in the flavonoid pathway were significantly more active in MLQS than in YGB at stages S1-S4.

CONCLUSION

In this study, we performed the first analyses of primary and secondary N. nucifera metabolites during flower colouration, and found that isorhamnetin and kaempferol shunting resulted in petal colour differences between MLQS and YGB. Based on our data integration analyses of key enzyme expression in the putative flavonoid pathways of the two N. nucifera cultivars, NnFLS gene substrate specificity and differential expression of NnOMTs may be related to petal colour differences between MLQS and YGB. These results will contribute to determining the mechanism of yellow flower colouration in N. nucifera, and will improve yellow petal colour breeding in lotus species.

Down regulation of p-coumarate 3-hydroxylase in petunia uniquely alters the profile of emitted floral volatiles

Petunia × hybrida cv ‘Mitchell Diploid’ floral volatile benzenoid/phenylpropanoid (FVBP) biosynthesis ultimately produces floral volatiles derived sequentially from phenylalanine, cinnamic acid, and p-coumaric acid. In an attempt to better understand biochemical steps after p-coumaric acid production, we cloned and characterized three petunia transcripts with high similarity to p-coumarate 3-hydroxylase (C3H), hydroxycinnamoyl-CoA:shikimate/quinate hydroxycinnamoyl transferase (HCT), and caffeoyl shikimate esterase (CSE). Transcript accumulation of PhC3H and PhHCT was highest in flower limb tissue during open flower stages. PhCSE transcript accumulation was also highest in flower limb tissue, but it was detected earlier at initial flower opening with a bell-shaped distribution pattern. Down regulation of endogenous PhC3H transcript resulted in altered transcript accumulation of many other FVBP network transcripts, a reduction in floral volatiles, and the emission of a novel floral volatile. Down regulation of PhHCT transcript did not have as large of an effect on floral volatiles as was observed for PhC3H down regulation, but eugenol and isoeugenol emissions were significantly reduced on the downstream floral volatiles. Together these results indicate that PhC3H is involved in FVBP biosynthesis and the reduction of PhC3H transcript influences FVBP metabolism at the network level. Additional research is required to illustrate PhHCT and PhCSE functions of petunia.

Finding the fragrance genes of wintersweet

Fragrant flowers emit a complex mixture of volatile organic compounds (VOCs) that we perceive as pleasant. While we know the chemical nature of these volatiles, the molecular traits that regulate their biosynthesis are poorly understood. In this issue, Tian et al. (2019) compare the transcriptomic and proteomic profiles of a scented genotype of wintersweet (Chimonanthus praecox) with a non-scented one. By correlating the differential gene expression profile with the observed differences in VOC profiles, they attempt to identify the genes that regulate the fragrance of wintersweet.

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

Polianthes tuberosa L. (tuberose) is a widely cultivated ornamental crop in Asian countries. Different cultivars of tuberose have been developed through breeding programs in India. However, no reports on floral fragrance and metabolite contents of these cultivars are available. In this study, an attempt has been made to evaluate the levels of both volatile and non-volatile metabolites from seven different cultivars of P. tuberosa. Presence of benzenoids, phenylpropanoids, terpenoids, and few fatty acid derivatives as emitted, endogenous and glycosylated forms were revealed from the studied cultivars. Further, chemometric analyses in both supervised and unsupervised manner led to identification of patterns among the cultivars. Among the seven cultivars, four distinct clusters were obtained linking to their volatiles, flavonoids and primary metabolite levels. Metabolic variations obtained from the cultivars also suggest cross-talks between phenylpropanoid, benzenoid, and flavonoid pathways. Thus metabolite profiling reported here may help in characterization of tuberose cultivars for perfumery utility and future breeding programme.

Transcriptomic and proteomic approaches to explore the differences in monoterpene and benzenoid biosynthesis between scented and unscented genotypes of wintersweet

Wintersweet (Chimonanthus praecox L.) is an important ornamental plant in China with a pleasant floral scent. To explore the potential mechanisms underlying differences in the fragrances among genotypes of this plant, we analyzed floral volatile organic compounds (VOCs) from two different genotypes: SW001, which has little to no fragrance, and the scented genotype H29. The major VOCs in H29 were linalool, trans-β-ocimene, benzyl acetate, methyl salicylate, benzyl alcohol (BAlc) and methyl benzoate. The most important aroma-active compound in H29, linalool, was emitted at a low concentration in SW001, which had markedly higher levels of trans-β-ocimene than H29. Next, to investigate scent biosynthesis, we analyzed the transcriptome and proteome of fully open flowers of the two genotypes. A total of 14 443 differentially expressed unigenes and 196 differentially expressed proteins were identified. Further analyses indicated that 56 differentially expressed genes involved in the terpenoid and benzenoid biosynthesis pathways might play critical roles in regulating floral fragrance difference. Disequilibrium expression of four terpene synthase genes resulted in diverse emission of linalool and trans-β-ocimene in both genotypes. In addition, the expressions of two CpMYC2 transcription factors were both upregulated in H29, implying that they may regulate linalool production. Notably, 16 of 20 genes in the benzenoid biosynthesis pathway were downregulated, corresponding to the relatively low level of benzenoid production in SW001. The lack of benzyl acetate might indicate that SW001 may lack substrate BAlc or functional acetyl-CoA:benzylalcohol acetyltransferase.

Floral plasticity: Herbivore-species-specific-induced changes in flower traits with contrasting effects on pollinator visitation

Plant phenotypic plasticity in response to antagonists can affect other community members such as mutualists, conferring potential ecological costs associated with inducible plant defence. For flowering plants, induction of defences to deal with herbivores can lead to disruption of plant-pollinator interactions. Current knowledge on the full extent of herbivore-induced changes in flower traits is limited, and we know little about specificity of induction of flower traits and specificity of effect on flower visitors. We exposed flowering Brassica nigra plants to six insect herbivore species and recorded changes in flower traits (flower abundance, morphology, colour, volatile emission, nectar quantity, and pollen quantity and size) and the behaviour of two pollinating insects. Our results show that herbivory can affect multiple flower traits and pollinator behaviour. Most plastic floral traits were flower morphology, colour, the composition of the volatile blend, and nectar production. Herbivore-induced changes in flower traits resulted in positive, negative, or neutral effects on pollinator behaviour. Effects on flower traits and pollinator behaviour were herbivore species-specific. Flowers show extensive plasticity in response to antagonist herbivores, with contrasting effects on mutualist pollinators. Antagonists can potentially act as agents of selection on flower traits and plant reproduction via plant-mediated interactions with mutualists.

Natural fumigation as a mechanism for volatile transport between flower organs

Plants synthesize volatile organic compounds (VOCs) to attract pollinators and beneficial microorganisms, to defend themselves against herbivores and pathogens, and for plant-plant communication. In general, VOCs accumulate in and are emitted from the tissue of their biosynthesis. However, using biochemical and reverse genetic approaches, we demonstrate a new physiological phenomenon: inter-organ aerial transport of VOCs via natural fumigation. Before petunia flowers open, a tube-specific terpene synthase produces sesquiterpenes, which are released inside the buds and then accumulate in the stigma, potentially defending the developing stigma from pathogens. These VOCs also affect reproductive organ development and seed yield, which are previously unknown functions of terpenoid compounds.

Identification of Floral Scent Profiles in Bearded Irises

Bearded irises are ornamental plants with distinctive floral fragrance grown worldwide. To identify the floral scent profiles, twenty-seven accessions derived from three bearded iris, including Iris. germanica, I. pumila and I. pallida were used to investigate the composition and relative contents of floral scent components by headspace solid-phase microextraction (HS-SPME) and gas chromatography–mass spectrometry (GC-MS). A total of 219 floral scent components were detected in blooming flowers. The scent profile varied significantly among and within the three investigated species. Principal component analysis (PCA) indicated that terpenes, alcohols and esters contributed the most to the floral scent components and 1-caryophyllene, linalool, citronellol, methyl cinnamate, β-cedrene, thujopsene, methyl myristate, linalyl acetate, isosafrole, nerol, geraniol were identified as the major components. In a hierarchical cluster analysis, twenty-seven accessions could be clustered into six different groups, most of which had representative scent components such as linalool, citronellyl acetate, thujopsene, citronellol, methyl cinnamate and 1-caryophyllene. Our findings provide a theoretical reference for floral scent evaluation and breeding of bearded irises.

Association of Pollinators of Different Species of Oil Palm with the Metabolic Profiling of Volatile Organic Compounds

The development of studies on emissions of volatile organic compounds (VOCs) by inflorescence of oil palms deserves a special attention regarding the importance to reproduction success and for increase of production. This study aimed to evaluate metabolic profiling of VOCs expelled by male and female inflorescences of different oil palm species (African oil palm, Amazonian Caiaué and the interspecific hybrid BRS-Manicoré), associating the composition variability with main pollinators to improve the comprehension of the plant-insect relationship. The phenylpropanoids, terpenoids and the aliphatic hydrocarbons were predominant classes detected in inflorescences of oil palms and the major compound was estragole. This result may be correlated with attraction of Elaidobius pollinators, since these insects were not attracted by Caiaué, which emitted estragole only in trace amounts. However, Caiaué and the hybrid species were visited by other native species whose frequencies were low and their success as pollinators could not be expected.

Photosynthesis in Ranunculus asiaticus L.: The Influence of the Hybrid and the Preparation Procedure of Tuberous Roots

Ranunculus asiaticus L. is a quantitative long-day geophyte, grown in a cold greenhouse for cut flowers and potted plants. Flowering in ranunculus is a complex process, strongly steered by temperature and photoperiodism. Vernalization of rehydrated tuberous roots anticipate sprouting and leaf rosette formation and flowering. It is known that the time for flowering and the sensitivity to cold treatment, in terms of flowering anticipation, varies in numerous hybrids, while no information seems to be available on the influence of hybrids and on the vernalization on the photosynthetic process and primary metabolite profiling. We investigated the influence of two ranunculus hybrids, MDR and MBO, and two preparation procedures of tuberous roots, only rehydration (Control, C) and rehydration followed by vernalization (V), on the photosynthesis and photochemistry of plants grown in a climatic chamber, under a controlled environment. In addition, in MBO plants, in which the vernalization showed the main effects, carbohydrate, amino acid and protein levels were also investigated. In control plants, the response of leaf photosynthesis, to increasing white light, revealed higher photosynthetic activity in MDR than in MBO. The quantum yield of PSII (ϕPSII), electron transport rate (ETR) and non-photochemical quenching (NPQ) did not differ between the two hybrids. The maximal photochemical efficiency (Fv/Fm) was higher in MBO than in MDR and showed a decrease in both hybrids after vernalization. The preparation treatment of propagation material affected the light response of photosynthesis in the two hybrids differently, which increased in plants from vernalized tuberous roots, compared to those from only rehydrated in MBO and decreased in MDR, in accordance to the effects of vernalization observed in leaf photosynthetic pigments. In MBO vernalized tuberous roots, starch was rapidly degraded, and the carbon skeletons used to synthesize amino acids. Control plants of MBO, developed more leaves than those of MDR and a consequent larger plant leaf area. Compared to only rehydration, vernalization of rehydrated tuberous roots increased the plant leaf area in both the hybrids. Compared to the control, vernalized tuberous roots of MBO showed higher concentrations of sucrose and free amino acids, which could act as a long-distance signal promoting floral transition in young leaf primordia.