Floral Scent Components Research Articles

Molecular cloning and expression analysis of a monoterpene synthase gene involved in floral scent production in lily (Lilium ‘Siberia’)

Lilium ‘Siberia’ flowers produce a strong scent, with monoterpenes serving as the main volatile component. Using a homology-based PCR strategy, we cloned a monoterpene synthase gene (LiTPS) from Lilium ‘Siberia’ petals. The gene consisted of a 1761-bp open reading frame, and encoded a 587-amino acid protein. The deduced amino acid sequence contained a highly conserved DDxxD domain at the C-terminus and RRx8W motifs at the N-terminus, which are both characteristic features of terpene synthase genes. Additionally, LiTPS was 40–50% similar to already known monoterpene synthases from other plants. Phylogenetic analysis of LiTPS revealed that it belonged to the TPS-b terpene synthase subfamily. LiTPS was predicted to contain an organelle-targeting peptide and function as a monoterpene synthase in plastids. Analyses of the structure of LiTPS suggested that it is a Class III terpene synthase gene. Furthermore, LiTPS was highly expressed in petals, but almost undetectable in stamens, styles, and leaves. During floral development in Lilium ‘Siberia’ plants, LiTPS was expressed in mature flower buds, with the highest expression levels registered on day 4 after anthesis (i.e., with fully open flowers), followed by a gradual decrease in expression levels. To the best of our knowledge, this is the first report describing cloning a Lilium terpene synthase gene. We report a positive correlation between the LiTPS expression level and floral scent component emission rate. This study provides potentially useful information for future research into the possible roles of LiTPS in the monoterpene metabolic pathway.

The Emission of the Floral Scent of Four Osmanthus fragrans Cultivars in Response to Different Temperatures.

Floral scent is an important part of volatile organic compounds (VOCs) emitted from plants, and is influenced by many environmental and endogenous factors. To investigate the influence of temperature on the emission of the floral scent of Osmanthus fragrans, the number of chemical compounds and their relative release amounts from four cultivars of O. fragrans under different temperature treatments, were identified using the solid-phase microextraction (SPME) technique and gas chromatography-mass spectrometry (GC-MS) in this study. Results revealed that the numbers and release amounts of floral scent components were significantly influenced by different temperatures, and depend on different cultivars and different types of compounds. Overall, most cultivars had the largest number of chemical compounds in 19 °C and the numbers of chemical compounds decreased with the increase or decrease in the temperature. Alcohols and ketones were the two main kinds of compounds responding to temperature change. The response of a specific chemical compound to temperature change was different in four cultivars. Generally, linalool, α-ionone, β-ionone, and γ-decalactone accounted for the highest proportion in the nine main compounds, and changes of these four chemical compounds to different temperatures had obvious contributions to the floral scent of O. fragrans. The results obtained provide evidence that temperatures can greatly influence the emission of floral scent.

Modeling the two-locus architecture of divergent pollinator adaptation: how variation in SAD paralogs affects fitness and evolutionary divergence in sexually deceptive orchids.

Divergent selection by pollinators can bring about strong reproductive isolation via changes at few genes of large effect. This has recently been demonstrated in sexually deceptive orchids, where studies (1) quantified the strength of reproductive isolation in the field; (2) identified genes that appear to be causal for reproductive isolation; and (3) demonstrated selection by analysis of natural variation in gene sequence and expression. In a group of closely related Ophrys orchids, specific floral scent components, namely n-alkenes, are the key floral traits that control specific pollinator attraction by chemical mimicry of insect sex pheromones. The genetic basis of species-specific differences in alkene production mainly lies in two biosynthetic genes encoding stearoyl–acyl carrier protein desaturases (SAD) that are associated with floral scent variation and reproductive isolation between closely related species, and evolve under pollinator-mediated selection. However, the implications of this genetic architecture of key floral traits on the evolutionary processes of pollinator adaptation and speciation in this plant group remain unclear. Here, we expand on these recent findings to model scenarios of adaptive evolutionary change at SAD2 and SAD5, their effects on plant fitness (i.e., offspring number), and the dynamics of speciation. Our model suggests that the two-locus architecture of reproductive isolation allows for rapid sympatric speciation by pollinator shift; however, the likelihood of such pollinator-mediated speciation is asymmetric between the two orchid species O. sphegodes and O. exaltata due to different fitness effects of their predominant SAD2 and SAD5 alleles. Our study not only provides insight into pollinator adaptation and speciation mechanisms of sexually deceptive orchids but also demonstrates the power of applying a modeling approach to the study of pollinator-driven ecological speciation.

An Aromatic Volatile Attracts Oligolectic bee Pollinators in an Interdependent bee-Plant Relationship

Chemical signals emitted by the plant frequently mediate host-plant localization in specialized animal - plant associations. Studying the interdependent highly specialized association of the narrowly oligolectic bee pollinator Protodiscelis palpalis (Colletidae, Neopasiphaeinae) with Hydrocleys martii (Alismataceae) in ephemeral aquatic water bodies in semi-arid Caatinga of Brazil, we asked if specific volatile compounds produced by the flowers mediate pollinator attraction. The yellow Hydrocleys flowers are the sole pollen and nectar resources, and mating sites for the bees. We analyzed the floral scents of this species and of the closely related H. nymphoides, which is not visited by P. palpalis, and tested the main volatile compounds of both species under field conditions to evaluate their attractiveness to bees of P. palpalis. Methoxylated aromatics were the dominant floral scent components in both species, but each species exhibited a characteristic scent profile. Dual choice bioassays using artificial flowers made of yellow and blue adhesive paper clearly revealed that ρ-methylanisole alone, the dominant volatile of H. martii, attracted significantly more bees than unbaited flowers. This compound represents an olfactory communication channel used by the plant that lures its effective oligolectic pollinators to its flowers. Yellow artificial flowers baited significantly more bees than blue ones. Our study reinforces the recent findings that specific compounds in complex floral scent bouquets are crucial for host-plant location in oligolectic bees.

The emission of floral scent from Lilium ‘siberia’ in response to light intensity and temperature

Floral scent is an important part of volatile compounds emitted from plants, and is influenced by many environmental factors. In this study, the floral scent emitted from Lilium ‘siberia’, a common breed of lily, was collected by dynamic headspace at different levels of light intensity (0, 100, 300, 600, 1,000, and 1,500 μmol m−2 s−1) and temperature (10, 20, 30, and 40 °C). Using the automated thermal desorption-gas chromatography/mass spectrometry (ATD-GC/MS) technique, the components and release amounts were subsequently identified to investigate the influence of light and temperature on the emission of floral scent. The results revealed that the numbers and release amounts of floral scent components were significantly influenced by light intensity and temperature, showing the similar pattern: first increasing and then decreasing. After light intensity treatment, the maximum numbers and release amounts mainly appeared at 600 and 1,000 μmol m−2 s−1. For temperature treatment, 30 °C resulted in the highest numbers and release amounts of the floral scent components. At different levels of light intensity and temperature, terpenoid compounds showed the highest numbers and release amounts among the component categories. α-Ocimene and linalool were the two terpenoid compounds with the highest release amounts, and accounted for the highest proportion. The results obtained provide evidence that both light intensity and temperature trigger the emission of floral scent. The particular response mechanisms must be investigated in future research.

DISTRIBUTION AND ACCUMULATION OF FLORAL SCENT COMPOUNDS IN ROSE FLOWERS, AND THE CHANGE IN THE GENE EXPRESSION INVOLVED IN THE BIOSYNTHESIS OF THESE COMPOUNDS DURING THE UNFURLING PROCESS

The concentrations of the aroma components 2-phenylethanol (2PE) and 3,5-dimethoxytoluene (DMT) emitted from the flower of Rosa 'Yves Piaget' change remarkably during the unfurling process. At each unfurling stage, flowers were separated into the following parts: outer petals, middle petals, and inner petals. The floral scent components were extracted from each sample and subjected to GC-MS analysis. 2PE accumulated mostly at the initial unfurling stage in outer petals, and DMT in inner petals. In addition we examined the gene expression levels corresponding to the enzymes involved in the biosyntheses of DMT by real time RT-PCR.

ペチュニア野生種Petunia axillaris subspecies parodiiにおける香気成分イソオイゲノールの欠失はイソオイゲノール合成酵素の変異に因る

ペチュニア野生種Petunia axillaris subspecies parodiiにおける香気成分イソオイゲノールの欠失はイソオイゲノール合成酵素の変異に因る

(E)-beta-ocimene and myrcene synthase genes of floral scent biosynthesis in snapdragon: function and expression of three terpene synthase genes of a new terpene synthase subfamily.

Snapdragon flowers emit two monoterpene olefins, myrcene and (E)-beta-ocimene, derived from geranyl diphosphate, in addition to a major phenylpropanoid floral scent component, methylbenzoate. Emission of these monoterpenes is regulated developmentally and follows diurnal rhythms controlled by a circadian clock. Using a functional genomics approach, we have isolated and characterized three closely related cDNAs from a snapdragon petal-specific library that encode two myrcene synthases (ama1e20 and ama0c15) and an (E)-beta-ocimene synthase (ama0a23). Although the two myrcene synthases are almost identical (98%), except for the N-terminal 13 amino acids, and are catalytically active, yielding a single monoterpene product, myrcene, only ama0c15 is expressed at a high level in flowers and contributes to floral myrcene emission. (E)-beta-Ocimene synthase is highly similar to snapdragon myrcene synthases (92% amino acid identity) and produces predominantly (E)-beta-ocimene (97% of total monoterpene olefin product) with small amounts of (Z)-beta-ocimene and myrcene. These newly isolated snapdragon monoterpene synthases, together with Arabidopsis AtTPS14 (At1g61680), define a new subfamily of the terpene synthase (TPS) family designated the Tps-g group. Members of this new Tps-g group lack the RRx(8)W motif, which is a characteristic feature of the Tps-d and Tps-b monoterpene synthases, suggesting that the reaction mechanism of Tps-g monoterpene synthase product formation does not proceed via an RR-dependent isomerization of geranyl diphosphate to 3S-linalyl diphosphate, as shown previously for limonene cyclase. Analyses of tissue-specific, developmental, and rhythmic expression of these monoterpene synthase genes in snapdragon flowers revealed coordinated regulation of phenylpropanoid and isoprenoid scent production.