Eugenol synthase genes in floral scent variation in Gymnadenia species

The Role of MbEGS1 and MbEGS2 in Methyleugenol Biosynthesis by Melaleuca bracteata

Many aromatic plant volatile compounds contain methyleugenol, which is an attractant for insect pollination and has antibacterial, antioxidant, and other properties. The essential oil of Melaleuca bracteata leaves contains 90.46% methyleugenol, which is an ideal material for studying the biosynthetic pathway of methyleugenol. Eugenol synthase (EGS) is one of the key enzymes involved in the synthesis of methyleugenol. We recently reported two eugenol synthase genes (MbEGS1 and MbEGS2) present in M. bracteata, where MbEGS1 and MbEGS2 were mainly expressed in flowers, followed by leaves, and had the lowest expression levels in stems. In this study, the functions of MbEGS1 and MbEGS2 in the biosynthesis of methyleugenol were investigated using transient gene expression technology and virus-induced gene silencing (VIGS) technology in M. bracteata. Here, in the MbEGSs genes overexpression group, the transcription levels of the MbEGS1 gene and MbEGS2 gene were increased 13.46 times and 12.47 times, respectively, while the methyleugenol levels increased 18.68% and 16.48%. We further verified the function of the MbEGSs genes by using VIGS, as the transcript levels of the MbEGS1 and MbEGS2 genes were downregulated by 79.48% and 90.35%, respectively, and the methyleugenol content in M. bracteata decreased by 28.04% and 19.45%, respectively. The results indicated that the MbEGS1 and MbEGS2 genes were involved in the biosynthesis of methyleugenol, and the transcript levels of the MbEGS1 and MbEGS2 genes correlated with the methyleugenol content in M. bracteata.

Transcriptomic and metabolomic data reveal key genes that are involved in the phenylpropanoid pathway and regulate the floral fragrance of Rhododendron fortunei

BACKGROUND

To reveal the key genes involved in the phenylpropanoid pathway, which ultimately governs the fragrance of Rhododendron fortunei, we performed a comprehensive transcriptome and metabolomic analysis of the petals of two different varieties of two alpine rhododendrons: the scented R. fortunei and the unscented Rhododendron 'Nova Zembla'.

RESULTS

Our transcriptomic and qRT-PCR data showed that nine candidate genes were highly expressed in R. fortunei but were downregulated in Rhododendron 'Nova Zembla'. Among these genes, EGS expression was significantly positively correlated with various volatile benzene/phenylpropanoid compounds and significantly negatively correlated with the contents of various nonvolatile compounds, whereas CCoAOMT, PAL, C4H, and BALDH expression was significantly negatively correlated with the contents of various volatile benzene/phenylpropanoid compounds and significantly positively correlated with the contents of various nonvolatile compounds. CCR, CAD, 4CL, and SAMT expression was significantly negatively correlated with the contents of various benzene/phenylpropanoid compounds. The validation of RfSAMT showed that the RfSAMT gene regulates the synthesis of aromatic metabolites in R. fortunei.

CONCLUSION

The findings of this study indicated that key candidate genes and metabolites involved in the phenylpropanoid biosynthesis pathway may govern the fragrance of R. fortunei. This lays a foundation for further research on the molecular mechanism underlying fragrance in the genus Rhododendron.

Comparative transcriptome analysis linked to key volatiles reveals molecular mechanisms of aroma compound biosynthesis in Prunus mume

BACKGROUND

Mei (Prunus mume) is the only woody plant in the genus Prunus with a floral fragrance, but the underlying mechanisms of aroma compound biosynthesis are unclear despite being a matter of considerable interest.

RESULTS

The volatile contents of the petals of two cultivars with significantly different aromas, Prunus mume 'Xiao Lve' and Prunus mume 'Xiangxue Gongfen', were characterised by GC-MS at different flowering periods, and a total of 44 volatile compounds were detected. Among these, the main substances forming the typical aroma of P. mume were identified as eugenol, cinnamyl acetate, hexyl acetate and benzyl acetate, with variations in their relative concentrations leading to sensory differences in the aroma of the two cultivars. We compiled a transcriptome database at key stages of floral fragrance formation in the two cultivars and used it in combination with differential analysis of floral volatiles to construct a regulatory network for the biosynthesis of key aroma compounds. The results indicated that PmPAL enzymes and PmMYB4 transcription factors play important roles in regulating the accumulation of key biosynthetic precursors to these compounds. Cytochrome P450s and short-chain dehydrogenases/reductases might also influence the biosynthesis of benzyl acetate by regulating production of key precursors such as benzaldehyde and benzyl alcohol. Furthermore, by analogy to genes with verified functions in Arabidopsis, we predicted that three PmCAD genes, two 4CL genes, three CCR genes and two IGS genes all make important contributions to the synthesis of cinnamyl acetate and eugenol in P. mume. This analysis also suggested that the downstream genes PmBGLU18-like, PmUGT71A16 and PmUGT73C6 participate in regulation of the matrix-bound and volatile states of P. mume aroma compounds.

CONCLUSIONS

These findings present potential new anchor points for further exploration of floral aroma compound biosynthesis pathways in P. mume, and provide new insights into aroma induction and regulation mechanisms in woody plants.

Fragrance components of Gymnadenia conopsea and Gymnadenia odoratissima collected at several sites in Italy and Germany

The SPME-GC-MS analysis of the aroma components of Gymnadenia conopsea subsp. conopsea, subsp. densiflora, var. alpina and Gymnadenia odoratissima var. odoratissima, var. idae were reported. The main components of in total 78 found in G. conopsea subsp. conopsea were elemicin, cis-9-hexadecenal, hexadecanal, isoelemicin and (Z)-11-hexadecen-1-ol acetate; in subsp. densiflora benzyl benzoate, eugenol and trans-isoeugenol; in var. alpina benzyl benzoate, methyleugenol and elemicin. In the scent of G. odoratissima var. odoratissima were found 2-phenylethyl acetate, eugenol and pentadecane, in var. idae mainly C15-C21 alkanes and C16, C18 carbonic acids and some isoprenoid-derivatives. As all tested Gymnadenia-taxa are allogamous, the differences in scent composition may play a role in pollinator attraction.

Why does an obligate autogamous orchid produce insect attractants in nectar? - a case study on Epipactis albensis (Orchidaceae)

BACKGROUND

The flowers of some species of orchids produce nectar as a reward for pollination, the process of transferring pollen from flower to flower. Epipactis albensis is an obligatory autogamous species, does not require the presence of insects for pollination, nevertheless, it has not lost the ability to produce nectar, the chemical composition of which we examined by gas chromatography-mass spectrometry (GC-MS) method for identification of potential insect attractants.

RESULTS

During five years of field research, we did not observe any true pollinating insects visiting the flowers of this species, only accidental insects as ants and aphids. As a result of our studies, we find that this self-pollinating orchid produces in nectar inter alia aliphatic saturated and unsaturated aldehydes such as nonanal (pelargonal) and 2-pentenal as well as aromatic ones (i.e., syringaldehyde, hyacinthin). The nectar is low in alkenes, which may explain the absence of pollinating insects. Moreover, vanillin and eugenol derivatives, well-known as important scent compounds were also identified, but the list of chemical compounds is much poorer compared with a closely related species, insect-pollinating E. helleborine.

CONCLUSION

Autogamy is a reproductive mechanism employed by many flowering plants, including the orchid genus Epipactis, as an adaptation to growing in habitats where pollinating insects are rarely observed due to the lack of nectar-producing plants they feed on. The production of numerous chemical attractants by self-pollinated E. albensis confirms the evolutionary secondary process, i.e., transition from ancestral insect-pollinating species to obligatory autogamous.

Genes and genome editing tools for breeding desirable phenotypes in ornamentals

We review the main genes underlying commercial traits in cut flower species and critically discuss the possibility to apply genome editing approaches to produce novel variation and phenotypes. Promoting flowering and flower longevity as well as creating novelty in flower structure, colour range and fragrances are major objectives of ornamental plant breeding. The novel genome editing techniques add new possibilities to study gene function and breed new varieties. The implementation of such techniques, however, relies on detailed information about structure and function of genomes and genes. Moreover, improved protocols for efficient delivery of editing reagents are required. Recent results of the application of genome editing techniques to elite ornamental crops are discussed in this review. Enabling technologies and genomic resources are reviewed in relation to the implementation of such approaches. Availability of the main gene sequences, underlying commercial traits and in vitro transformation protocols are provided for the world's best-selling cut flowers, namely rose, lily, chrysanthemum, lisianthus, tulip, gerbera, freesia, alstroemeria, carnation and hydrangea. Results obtained so far are described and their implications for the improvement of flowering, flower architecture, colour, scent and shelf-life are discussed.

Sweet Basil Has Distinct Synthases for Eugenol Biosynthesis in Glandular Trichomes and Roots with Different Regulatory Mechanisms

Production of a volatile phenylpropene; eugenol in sweet basil is mostly associated with peltate glandular trichomes (PGTs) found aerially. Currently only one eugenol synthase (EGS), ObEGS1 which belongs to PIP family is identified from sweet basil PGTs. Reports of the presence of eugenol in roots led us to analyse other EGSs in roots. We screened for all the PIP family reductase transcripts from the RNA-Seq data. In vivo functional characterization of all the genes in E. coli showed their ability to produce eugenol and were termed as ObEGS2-8. Among all, ObEGS1 displayed highest expression in PGTs and ObEGS4 in roots. Further, eugenol was produced only in the roots of soil-grown plants, but not in roots of aseptically-grown plants. Interestingly, eugenol production could be induced in roots of aseptically-grown plants under elicitation suggesting that eugenol production might occur as a result of environmental cues in roots. The presence of ObEGS4 transcript and protein in aseptically-grown plants indicated towards post-translational modifications (PTMs) of ObEGS4. Bioinformatics analysis showed possibility of phosphorylation in ObEGS4 which was further confirmed by in vitro experiment. Our study reveals the presence of multiple eugenol synthases in sweet basil and provides new insights into their diversity and tissue specific regulation.

Transcriptional response of Asarum heterotropoides Fr. Schmidt var. mandshuricum (Maxim.) Kitag. leaves grown under full and partial daylight conditions

BACKGROUND

Asarum heterotropides Fr. Schmidt var. mandshuricum (Maxim.) Kitag. is an important medicinal and industrial plant, which is used in the treatment of various diseases. The main bioactive ingredient is the volatile oil having more than 82 identified components of which methyleugenol, safrole, myristicin, and toluene account for about 70% of the total volume. As a sciophyte plant, the amount of light it absorbs through leaves is an important factor for growth and metabolism.

RESULTS

We grew Asarum plants under full, 50, 28, and 12% sunlight conditions to investigate the effect of different light irradiances on the four major volatile oil components. We employed de novo transcriptome sequencing to understand the transcriptional behavior of Asarum leaves regarding the biosynthetic pathways of the four volatile oil components, photosynthesis and biomass accumulation, and hormone signaling. Our results demonstrated that the increasing light conditions promoted higher percent of the four components. Under full sunlight conditions, cinnamyl alcohol dehydrogenase and cytochrome p450719As were upregulated and led the increased methyleugenol, safrole, and myristicin. The transcriptomic data also showed that Asarum leaves, under full sunlight conditions, adjust their photosynthesis-antenna proteins as a photoprotective response with the help of carotenoids. Plant hormone-signaling related genes were also differentially expressed between full sunlight and low light conditions.

CONCLUSIONS

High light induces accumulation of major bioactive ingredients A. heterotropides volatile oil and this is ascribed to upregulation of key genes such as cinnamyl alcohol dehydrogenase and cytochrome p450719As. The transcriptome data presented here lays the foundation of further understanding of light responses in sciophytes and provides guidance for increasing bioactive molecules in Asarum.

Volatile Organic Compounds from Orchids: From Synthesis and Function to Gene Regulation

Orchids are one of the most significant plants that have ecologically adapted to every habitat on earth. Orchids show a high level of variation in their floral morphologies, which makes them popular as ornamental plants in the global market. Floral scent and color are key traits for many floricultural crops. Volatile organic compounds (VOCs) play vital roles in pollinator attraction, defense, and interaction with the environment. Recent progress in omics technology has led to the isolation of genes encoding candidate enzymes responsible for the biosynthesis and regulatory circuits of plant VOCs. Uncovering the biosynthetic pathways and regulatory mechanisms underlying the production of floral scents is necessary not only for a better understanding of the function of relevant genes but also for the generation of new cultivars with desirable traits through molecular breeding approaches. However, little is known about the pathways responsible for floral scents in orchids because of their long life cycle as well as the complex and large genome; only partial terpenoid pathways have been reported in orchids. Here, we review the biosynthesis and regulation of floral volatile compounds in orchids. In particular, we focused on the genes responsible for volatile compounds in various tissues and developmental stages in Cymbidium orchids. We also described the emission of orchid floral volatiles and their function in pollination ecology. Taken together, this review will provide a broad scope for the study of orchid floral scents.

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.

Duplication and selection in β-ketoacyl-ACP synthase gene lineages in the sexually deceptive Chiloglottis (Orchidaceace)

BACKGROUND AND AIMS

The processes of gene duplication, followed by divergence and selection, probably underpin the evolution of floral volatiles crucial to plant-insect interactions. The Australian sexually deceptive Chiloglottis orchids use a class of 2,5-dialkylcyclohexan-1,3-dione volatiles or 'chiloglottones' to attract specific male wasp pollinators. Here, we explore the expression and evolution of fatty acid pathway genes implicated in chiloglottone biosynthesis.

METHODS

Both Chiloglottis seminuda and C. trapeziformis produce chiloglottone 1, but only the phylogenetically distinct C. seminuda produces this volatile from both the labellum callus and glandular sepal tips. Transcriptome sequencing and tissue-specific contrasts of the active and non-active floral tissues was performed. The effects of the fatty acid synthase inhibitor cerulenin on chiloglottone production were tested. Patterns of selection and gene evolution were investigated for fatty acid pathway genes.

KEY RESULTS

Tissue-specific differential expression of fatty acid pathway transcripts was evident between active and non-active floral tissues. Cerulenin significantly inhibits chiloglottone 1 production in the active tissues of C. seminuda. Phylogenetic analysis of plant β-ketoacyl synthase I (KASI), a protein involved in fatty acid biosynthesis, revealed two distinct clades, one of which is unique to the Orchidaceae (KASI-2B). Selection analysis indicated a strong signal of positive selection at the split of KASI-2B followed by relaxed purifying selection in the Chiloglottis clade.

CONCLUSIONS

By capitalizing on a phylogenetically distinct Chiloglottis from earlier studies, we show that the transcriptional and biochemical dynamics linked to chiloglottone biosynthesis in active tissues are conserved across Chiloglottis. A combination of tissue-specific expression and relaxed purifying selection operating at specific fatty acid pathway genes may hold the key to the evolution of chiloglottones.

Biosynthesis of methyleugenol and methylisoeugenol in Daucus carota leaves: Characterization of eugenol/isoeugenol synthase and O-Methyltransferase

Carrot (Daucus carota subsp. sativus) is a widely cultivated root vegetable of high economic importance. The aroma of carrot roots and aboveground organs is mainly defined by terpenes. We found that leaves of orange carrot cultivar also produce considerable amounts of the phenylpropenes methyleugenol and methylisoeugenol. Notably, methyleugenol is most abundant in young leaves, while methylisoeugenol is the dominant phenylpropene in mature leaf tissue. The goal of the present study was to shed light on the biochemistry and molecular biology of these compounds' biosynthesis and accumulation. Using the available genomic and transcriptomic data, we isolated a cDNA encoding eugenol/isoeugenol synthase (DcE(I)GS1), an NADPH-dependent enzyme that converts coniferyl acetate to eugenol. This enzyme exhibits dual product specificity and yields propenylphenol isoeugenol alongside allylphenol eugenol. Furthermore, we identified a cDNA encoding S-adenosyl-L-methionine:eugenol/isoeugenol O-methyltransferase 1 (DcE(I)OMT1) that produces methyleugenol and methylisoeugenol via methylation of the para-OH-group of their respective precursors. Both DcE(I)GS1 and DcE(I)OMT1 were expressed in seeds, roots, young and mature leaves, and the DcE(I)OMT1 transcript levels were the highest in leaves. The DcE(I)GS1 protein is 67% identical to anise t-anol/isoeugenol synthase and displays an apparent K_m of 247 μM for coniferyl acetate. The catalytic efficiency of DcEOMT1 with eugenol is more than five-fold higher than that with isoeugenol, with K_m values of 40 μM for eugenol, and of 115 μM for isoeugenol. This work expands the current knowledge of the enzymes involved in phenylpropene biosynthesis and would enable studies into structural elements defining the regioselectivity of phenylpropene synthases.

Comparative Transcriptomics Analysis for Gene Mining and Identification of a Cinnamyl Alcohol Dehydrogenase Involved in Methyleugenol Biosynthesis from Asarum sieboldii Miq

Asarum sieboldii Miq., one of the three original plants of TCM ASARI RADIX ET RHIZOMA, is a perennial herb distributed in central and eastern China, the Korean Peninsula, and Japan. Methyleugenol has been considered as the most important constituent of Asarum volatile oil, meanwhile asarinin is also employed as the quality control standard of ASARI RADIX ET RHIZOMA in Chinese Pharmacopeia. They both have shown wide range of biological activities. However, little was known about genes involved in biosynthesis pathways of either methyleugenol or asarinin in Asarum plants. In the present study, we performed de novo transcriptome analysis of plant tissues (e.g., roots, rhizomes, and leaves) at different developmental stages. The sequence assembly resulted in 311,597 transcripts from these plant materials, among which 925 transcripts participated in 'secondary metabolism' with particularly up to 20.22% of them falling into phenylpropanoid biosynthesis pathway. The corresponding enzymes belong to seven families potentially encoding phenylalanine ammonia-lyase (PAL), trans-cinnamate 4-monooxygenase (C4H), p-coumarate 3-hydroxylase (C3H), caffeoyl-CoA O-methyltransferase (CCoAOMT), cinnamoyl-CoA reductase (CCR), cinnamyl alcohol dehydrogenase (CAD), and eugenol synthase (EGS). Moreover, 5 unigenes of DIR (dirigent protein) and 11 unigenes of CYP719A (719A subfamily of cytochrome P450 oxygenases) were speculated to be involved in asarinin pathway. Of the 15 candidate CADs, four unigenes that possessed high FPKM (fragments per transcript kilobase per million fragments mapped) value in roots were cloned and characterized. Only the recombinant AsCAD5 protein efficiently converted p-coumaryl, coniferyl, and sinapyl aldehydes to their corresponding alcohols, which are key intermediates employed not only in biosynthesis of lignin but also in that of methyleugenol and asarinin. qRT-PCR revealed that AsCAD5 had a high expression level in roots at three developmental stages. Our study will provide insight into the potential application of molecular breeding and metabolic engineering for improving the quality of TCM ASARI RADIX ET RHIZOMA.

Functional evolution of biosynthetic enzymes that produce plant volatiles

Plants synthesize volatile compounds to attract pollinators. The volatiles emitted by flowers are often complex mixtures of organic compounds; pollinators are capable of distinctly recognizing different volatile compounds. Plants also produce volatile compounds to protect themselves against herbivores and pathogens. Some of the volatile compounds produced in floral and vegetative tissues are toxic to insects and microbes. To adapt changes in the environment, plants have evolved the ability to synthesize a unique set of volatiles. Intensive studies have identified and characterized the enzymes responsible for the formation of plant volatiles. In particular, many biosynthetic genes have been isolated and their enzymatic functions have been proposed. This review describes how plants have evolved the biosynthetic pathways leading to the formation of green leaf volatiles and phenylpropene volatiles.

Synergistic effects of floral phytochemicals against a bumble bee parasite

Floral landscapes comprise diverse phytochemical combinations. Individual phytochemicals in floral nectar and pollen can reduce infection in bees and directly inhibit trypanosome parasites. However, gut parasites of generalist pollinators, which consume nectar and pollen from many plant species, are exposed to phytochemical combinations. Interactions between phytochemicals could augment or decrease effects of single compounds on parasites. Using a matrix of 36 phytochemical treatment combinations, we assessed the combined effects of two floral phytochemicals, eugenol and thymol, against four strains of the bumblebee gut trypanosome Crithidia bombi. Eugenol and thymol had synergistic effects against C. bombi growth across seven independent experiments, showing that the phytochemical combination can disproportionately inhibit parasites. The strength of synergistic effects varied across strains and experiments. Thus, the antiparasitic effects of individual compounds will depend on both the presence of other phytochemicals and parasite strain identity. The presence of synergistic phytochemical combinations could augment the antiparasitic activity of individual compounds for pollinators in diverse floral landscapes.

Evolution of resistance to single and combined floral phytochemicals by a bumble bee parasite

Repeated exposure to inhibitory compounds can drive the evolution of resistance, which weakens chemical defence against antagonists. Floral phytochemicals in nectar and pollen have antimicrobial properties that can ameliorate infection in pollinators, but evolved resistance among parasites could diminish the medicinal efficacy of phytochemicals. However, multicompound blends, which occur in nectar and pollen, present simultaneous chemical challenges that may slow resistance evolution. We assessed evolution of resistance by the common bumble bee gut parasite Crithidia bombi to two floral phytochemicals, singly and combined, over 6 weeks (~100 generations) of chronic exposure. Resistance of C. bombi increased under single and combined phytochemical exposure, without any associated costs of reduced growth under phytochemical-free conditions. After 6 weeks' exposure, phytochemical concentrations that initially inhibited growth by > 50%, and exceeded concentrations in floral nectar, had minimal effects on evolved parasite lines. Unexpectedly, the phytochemical combination did not impede resistance evolution compared to single compounds. These results demonstrate that repeated phytochemical exposure, which could occur in homogeneous floral landscapes or with therapeutic phytochemical treatment of managed hives, can cause rapid evolution of resistance in pollinator parasites. We discuss possible explanations for submaximal phytochemical resistance in natural populations. Evolved resistance could diminish the antiparasitic value of phytochemical ingestion, weakening an important natural defence against infection.

The molecular bases of floral scent evolution under artificial selection: insights from a transcriptome analysis in Brassica rapa

In an artificial selection experiment using fast-cycling Brassica rapa plants it was recently shown that floral VOCs respond rapidly to selection for increased amounts. Here we carried out transcriptome analysis in these plants to explore the molecular bases of the augmentation in the artificially selected scent compound, phenylacetaldehyde (PAA), as well as other compounds that increased through pleiotropy. In the transcriptome data, we found up-regulation of genes likely underlying PAA synthesis, but also several genes of the shikimate pathway and the related phenylalanine metabolism. As phenylalanine is the precursor of many aromatic volatiles that showed increased emission, this result could explain some of the pleiotropic evolutionary responses. In addition, we found that ribosomal protein genes were up-regulated in “high” (high PAA amount) selection line plants, a mechanism that might further augment the effect of elevated gene expression at the proteomic level. Our study shows that selection on an individual trait can impose changes in the expression of several different genes, which could explain pleiotropic responses in the biosynthetic network of floral volatiles.

The chemical ecology of plant-pollinator interactions: recent advances and future directions

Floral chemistry mediates plant-pollinator interactions through floral scents and reward components. Although improved techniques have increased interest in studying floral volatiles and nectar chemistry, these two foci have generally been studied in isolation. The ecological functions of floral chemistry have been relatively well studied and focused on pollinator behaviour. While studies comparing chemistry between plant parts and across phylogenies are increasing, work on the evolution of floral chemistry and the importance of community context in mediating pollinator responses is lacking. Future research should concentrate on more holistic studies that include both signal and reward chemistry to understand the relative contribution of these complex and dynamic floral traits to the ecology and evolution of plants and their pollinators.