Production of complementary defense metabolites reflects a co-evolutionary arms race between a host plant and a mutualistic bark beetle-fungal complex

Intra-specific variation in conifers has been extensively studied with respect to defense against herbivores and pathogens. While studies have shown the ability of individual or specific mixtures of compounds to influence insects and microbes, research testing biologically relevant mixtures of defense compounds reflecting intra-specific variation amongst tree populations to enemy complexes is needed. We characterized the variations in lodgepole pine monoterpenes from a progeny trial in western Canada and grouped trees in four clusters using their monoterpene profiles. We then selected 11 representative families across four clusters and amended their entire monoterpene profiles (with the exception of β-phellandrene) in media to determine how representative families affect the performance of the mountain pine beetle or its fungal symbiont. We placed adult beetles or inoculated fungus on the amended media and measured beetle performance and fungal growth as a proxy to host suitability. We found that different clusters or families differentially influenced beetle or fungal responses. However, monoterpene profiles of trees suitable to the beetle or the fungus were dissimilar. These outcomes reflect a co-evolutionary arms-race between the host and the bark beetle-fungus complex, which has resulted in the production of complementary defense metabolites among different pine populations to enhance tree survival.

Effects of methyl jasmonate on the monoterpenes of Muscat Hamburg grapes and wine

BACKGROUND

The importance of monoterpenes in grape and wine aroma has compelled researchers to focus on developing methods to increase their abundance. Recent research has revealed that exogenous elicitors can increase the contents of these compounds. This study determined the effects of methyl jasmonate (MeJA) preharvest treatments on the monoterpene profiles of Muscat Hamburg grapes and wine.

RESULTS

A total of 27 monoterpenes were identified for Muscat Hamburg grapes and wine. The contents of most of the monoterpenes (free and glycosylated forms) in the grapes and wine increased in response to MeJA. An analysis of the expression of the genes in the terpenoid biosynthesis pathway indicated that the related biosynthetic pathways were activated by MeJA. The transcript levels of some genes were consistent with monoterpene production, including VviCSLinNer, VviGwbOciF, VviPNRLin, VviGT14 and VviUGT85A1L1. The developmental expression patterns of the VviPP2B1 and VviMYB24 transcription factor genes were positively correlated with monoterpene accumulation in ripening grapes.

CONCLUSIONS

Our results suggest that MeJA may be useful for improving the aroma quality of grapes and wines.

α-Terpineol: An Aggregation Pheromone in Optatus palmaris (Coleoptera: Curculionidae) (Pascoe, 1889) Enhanced by Its Host-Plant Volatiles

The Annonaceae fruits weevil (Optatus palmaris) causes high losses to the soursop production in Mexico. Damage occurs when larvae and adults feed on the fruits; however, there is limited research about control strategies against this pest. However, pheromones provide a high potential management scheme for this curculio. Thus, this research characterized the behavior and volatile production of O. palmaris in response to their feeding habits. Olfactometry assays established preference by weevils to volatiles produced by feeding males and soursop. The behavior observed suggests the presence of an aggregation pheromone and a kairomone. Subsequently, insect volatiles sampled by solid-phase microextraction and dynamic headspace detected a unique compound on feeding males increased especially when feeding. Feeding-starvation experiments showed an averaged fifteen-fold increase in the concentration of a monoterpenoid on males feeding on soursop, and a decrease of the release of this compound males stop feeding. GC-MS analysis of volatiles identified this compound as α-terpineol. Further olfactometry assays using α-terpineol and soursop, demonstrated that this combination is double attractive to Annonaceae weevils than only soursop volatiles. The results showed a complementation effect between α-terpineol and soursop volatiles. Thus, α-terpineol is the aggregation pheromone of O. palmaris, and its concentration is enhanced by host-plant volatiles.

RNA-Seq used to identify ipsdienone reductase (IDONER): A novel monoterpene carbon-carbon double bond reductase central to Ips confusus pheromone production

The pinyon ips beetle, Ips confusus (LeConte) is a highly destructive pest in pine forests in western North America. When colonizing a new host tree, I. confusus beetles coordinate a mass attack to overcome the tree's defenses using aggregation pheromones. Ips confusus, as with other Ips spp. beetles, biosynthesize ipsdienol and ipsenol in a specific enantiomeric blend and ratio as aggregation pheromones. While several of the initial steps in the pheromone biosynthetic pathway have been well defined, the final steps were unknown. We used comparative RNA-Seq analysis between fed and unfed male I. confusus midgut tissue to identify candidate genes involved in pheromone biosynthesis. The 12,995 potentially unique transcripts showed a clear separation based on feeding state. Differential expression analysis identified gene groups that were tightly connected. This analysis identified all known pheromone biosynthetic genes and suggested a novel monoterpene double bond reductase, ipsdienone reductase (IDONER), with pheromone biosynthetic gene expression patterns. IDONER cDNA was cloned, expressed, and functionally characterized. The coding DNA sequence has an ORF of 1101 nt with a predicted translation product of 336 amino acids. The enzyme has a molecular weight of 36.7 kDa with conserved motifs of the medium chain dehydrogenases/reductase (MDR) superfamily in the leukotriene B4 dehydrogenases/reductases (LTB₄R) family. Tagged recombinant protein was expressed and purified. Enzyme assays and GC/MS analysis showed IDONER catalyzed the reduction of ipsdienone to form ipsenone. This study shows that IDONER is a monoterpene double bond reductase involved in I. confusus pheromone biosynthesis.

Secondary Metabolic Profile as a Tool for Distinction and Characterization of Cultivars of Black Pepper (Piper nigrum L.) Cultivated in Pará State, Brazil

This study evaluated the chemical compositions of the leaves and fruits of eight black pepper cultivars cultivated in Pará State (Amazon, Brazil). Hydrodistillation and gas chromatography-mass spectrometry were employed to extract and analyze the volatile compounds, respectively. Sesquiterpene hydrocarbons were predominant (58.5-90.9%) in the cultivars "Cingapura", "Equador", "Guajarina", "Iaçará", and "Kottanadan", and "Bragantina", "Clonada", and "Uthirankota" displayed oxygenated sesquiterpenoids (50.6-75.0%). The multivariate statistical analysis applied using volatile composition grouped the samples into four groups: γ-Elemene, curzerene, and δ-elemene ("Equador"/"Guajarina", I); δ-elemene ("Iaçará"/"Kottanadan"/"Cingapura", II); elemol ("Clonada"/"Uthirankota", III) and α-muurolol, bicyclogermacrene, and cubebol ("Bragantina", IV). The major compounds in all fruit samples were monoterpene hydrocarbons such as α-pinene, β-pinene, and limonene. Among the cultivar leaves, phenolics content (44.75-140.53 mg GAE·g^-1 FW), the enzymatic activity of phenylalanine-ammonia lyase (20.19-57.22 µU·mL^-1), and carotenoids (0.21-2.31 µg·mL^-1) displayed significant variations. Due to black pepper's susceptibility to Fusarium infection, a molecular docking analysis was carried out on Fusarium protein targets using each cultivar's volatile components. F. oxysporum endoglucanase was identified as the preferential protein target of the compounds. These results can be used to identify chemical markers related to the susceptibility degree of black pepper cultivars to plant diseases prevalent in Pará State.

Physiological and biochemical responses of green and red perilla to LED-based light

BACKGROUND

Light-emitting diodes (LEDs) are widely used in closed-type plant production systems to improve biomass and accumulate bioactive compounds in plants. Perilla has been commonly used as herbal medicine because of its health-promoting effects. This study aimed to investigate the physiological and biochemical responses of green and red perilla under various visible-light spectra.

RESULTS

Results showed that red (R) LEDs improved fresh weights of shoots and roots, plant height, internode length, node number and leaf area, as well as photosynthetic rate of green and red perilla plants compared to blue (B) LEDs and RB combined LEDs. Meanwhile, B resulted in higher stomatal conductance, transpiration rate and Fv/Fm compared to R. Supplementation of green (G) and far-red (FR) did not enhance perilla growth. Reduction or absence of B decreased leaf thickness, adaxial and abaxial epidermis, and palisade and spongy mesophyll. Total phenolic content, antioxidant capacity, rosmarinic acid content and caffeic acid content of green perilla were higher under R, R8B2 and RGB + FR, while greater values were obtained in red perilla under R. Accumulation of perillaldehyde, luteolin and apigenin presented different trends from those of rosmarinic and caffeic acids in both cultivars.

CONCLUSIONS

Growth and accumulation of bioactive compounds in green perilla were greater than in red perilla under similar light quality, and R LEDs or a higher R ratio in combination treatments were suitable for cultivating high-quality green and red perilla plants in closed-type plant factories. © 2020 Society of Chemical Industry.

Current Advances in the Bacterial Toolbox for the Biotechnological Production of Monoterpene-Based Aroma Compounds

Monoterpenes are plant secondary metabolites, widely used in industrial processes as precursors of important aroma compounds, such as vanillin and (-)-menthol. However, the physicochemical properties of monoterpenes make difficult their conventional conversion into value-added aromas. Biocatalysis, either by using whole cells or enzymes, may overcome such drawbacks in terms of purity of the final product, ecological and economic constraints of the current catalysis processes or extraction from plant material. In particular, the ability of oxidative enzymes (e.g., oxygenases) to modify the monoterpene backbone, with high regio- and stereo-selectivity, is attractive for the production of "natural" aromas for the flavor and fragrances industries. We review the research efforts carried out in the molecular analysis of bacterial monoterpene catabolic pathways and biochemical characterization of the respective key oxidative enzymes, with particular focus on the most relevant precursors, β-pinene, limonene and β-myrcene. The presented overview of the current state of art demonstrates that the specialized enzymatic repertoires of monoterpene-catabolizing bacteria are expanding the toolbox towards the tailored and sustainable biotechnological production of values-added aroma compounds (e.g., isonovalal, α-terpineol, and carvone isomers) whose implementation must be supported by the current advances in systems biology and metabolic engineering approaches.

New Hydroquinone Monoterpenoid and Cembranoid-Related Metabolites from the Soft Coral Sarcophyton tenuispiculatum

Chemical investigation of the marine soft coral Sarcophyton tenuispiculatum resulted in the isolation of a 1,4-dihydrobenzoquinone, sarcotenuhydroquinone (1), three new cembranoids, sarcotenusenes A‒C (2‒4), and ten previously reported metabolites 5–14. The chemical structures of all isolated metabolites were determined by detailed spectroscopic analyses. In biological assays, anti-inflammatory, cytotoxic, and peroxisome proliferator-activated receptor γ (PPAR-γ) transcription factor assays of all compounds were performed. None of the isolated compounds were found to exhibit activity in the PPAR-γ transcription factor assay. The anti-inflammatory assays showed that (+)-7α,8β-dihydroxydeepoxysarcophine (13) inhibited the production of IL-1β to 56 ± 1% at a concentration of 30 µM in lipopolysaccharide (LPS)-stimulated J774A.1 macrophage cells. In addition, 1 and 2 were found to exhibit cytotoxicity towards a panel of cancer cell lines.

Enhanced monoterpene emission in transgenic orange mint (Mentha × piperita f. citrata) overexpressing a tobacco lipid transfer protein (NtLTP1)

MAIN CONCLUSION

Overexpression of the tobacco lipid transfer protein (NtLTP1) gene in transgenic orange mint resulted in enhanced accumulation of monoterpenes in the cavity of head cells of glandular trichomes, which resulted in enhanced emission of monoterpenes from transgenic orange mints. Plants in the genus Mentha (Lamiaceae) produce volatile oils that accumulate in peltate glandular trichomes in the aerial parts of plants. A lipid transfer protein (NtLTP1) in tobacco showed glandular trichome-specific expression and supported the secretion of diterpenoid lipids from head cells of glandular trichomes (Choi et al., Plant J 70:480-491,2012). Here, we constructed transgenic orange mint (Mentha × piperita f. citrata) overexpressing the tobacco NtLTP1 gene via Agrobacterium-mediated transformation. Transgenic lines of orange mint overexpressing NtLTP1 were confirmed by genomic PCR and RT-PCR. Immunoblotting analysis using an NtLTP1 polyclonal antibody showed clear dark spots at the position of the lipid exudates from tobacco glandular trichomes and the squeezed out lipids from the glandular trichomes of transgenic orange mint. Heads of glandular trichomes in transgenic plants overexpressing the NtLTP1 gene showed a larger diameter than those of the wild-type control. The enhanced size of trichome heads in transgenic orange mint was confirmed by scanning electron microscopy. Volatile components were extracted from wild-type and transgenic orange mint by solid-phase microextraction (SPME) and analyzed by headspace-gas chromatography-mass spectrometry (HS/GC/MS). Linalyl acetate was the most abundant component among the eleven identified monoterpenes in the volatile compounds extracted from both the wild-type and transgenic lines of orange mint. Overexpression of NtLTP1 in transgenic orange mint plants resulted in enhanced emission of volatile monoterpenoids compared with that of volatile monoterpenoids in the wild-type control plants.

Developmental Methylome of the Medicinal Plant Catharanthus roseus Unravels the Tissue-Specific Control of the Monoterpene Indole Alkaloid Pathway by DNA Methylation

Catharanthus roseus produces a wide spectrum of monoterpene indole alkaloids (MIAs). MIA biosynthesis requires a tightly coordinated pathway involving more than 30 enzymatic steps that are spatio-temporally and environmentally regulated so that some MIAs specifically accumulate in restricted plant parts. The first regulatory layer involves a complex network of transcription factors from the basic Helix Loop Helix (bHLH) or AP2 families. In the present manuscript, we investigated whether an additional epigenetic layer could control the organ-, developmental- and environmental-specificity of MIA accumulation. We used Whole-Genome Bisulfite Sequencing (WGBS) together with RNA-seq to identify differentially methylated and expressed genes among nine samples reflecting different plant organs and experimental conditions. Tissue specific gene expression was associated with specific methylation signatures depending on cytosine contexts and gene parts. Some genes encoding key enzymatic steps from the MIA pathway were found to be simultaneously differentially expressed and methylated in agreement with the corresponding MIA accumulation. In addition, we found that transcription factors were strikingly concerned by DNA methylation variations. Altogether, our integrative analysis supports an epigenetic regulation of specialized metabolisms in plants and more likely targeting transcription factors which in turn may control the expression of enzyme-encoding genes.

Molecular underpinnings of methyl jasmonate-induced resistance in Norway spruce

In response to various stimuli, plants acquire resistance against pests and/or pathogens. Such acquired or induced resistance allows plants to rapidly adapt to their environment. Spraying the bark of mature Norway spruce (Picea abies) trees with the phytohormone methyl jasmonate (MeJA) enhances resistance to tree-killing bark beetles and their associated phytopathogenic fungi. Analysis of spruce chemical defenses and beetle colonization success suggests that MeJA treatment both directly induces immune responses and primes inducible defenses for a faster and stronger response to subsequent beetle attack. We used metabolite and transcriptome profiling to explore the mechanisms underlying MeJA-induced resistance in Norway spruce. We demonstrated that MeJA treatment caused substantial changes in the bark transcriptional response to a triggering stress (mechanical wounding). Profiling of mRNA expression showed a suite of spruce inducible defenses are primed following MeJA treatment. Although monoterpenes and diterpene resin acids increased more rapidly after wounding in MeJA-treated than control bark, expression of their biosynthesis genes did not. We suggest that priming of inducible defenses is part of a complex mixture of defense responses that underpins the increased resistance against bark beetle colonization observed in Norway spruce. This study provides the most detailed insights yet into the mechanisms underlying induced resistance in a long-lived gymnosperm.

Transport properties of paeoniflorin and amygdalin across caco-2 cell monolayer model and their modulation of cytochrome p450 metabolism

Paeoniflorin and amygdalin are two major active saponins constituents in some Chinese herbal formulas used for cardio-cerebrovascular diseases. However, their intestinal absorption property and metabolic characteristics have not been clarified. The aim of this work was to study the absorption property of Paeoniflorin and Amygdalin across Caco-2 cell monolayer and their metabolic characteristics on the activity of cytochrome P450 (CYP450) enzyme. The results showed that the transport amount of Paeoniflorin and Amygdalin was positively correlated with the time and concentrations, and the transport amount from AP side to BL side was higher than that from BL to AP. The absorptions of Paeoniflorin and Amygdalin were reduced by P-glycoprotein, which provided the pharmacokinetic basis for their clinical application. Furthermore, we demonstrated that Paeoniflorin and Amygdalin had obvious inhibiting effects on CYP2C9 and CYP2E1. The transports of Paeoniflorin and Amygdalin across Caco-2 cell monolayer model were deduced as the passive transport, which indicated that the present bioassay system was appropriate and reliable for the evaluation of the transport characteristics and metabolic characteristics of active ingredient groups in Bu-yang-huan-wu decoction. Moreover, this research method may also be suitable for the appropriate bioactivity and metabolic characteristics analysis of other plant extracts.

Stem emissions of monoterpenes, acetaldehyde and methanol from Scots pine (Pinus sylvestris L.) affected by tree-water relations and cambial growth

Tree stems are an overlooked source of volatile organic compounds (VOCs). Their contribution to ecosystem processes and total VOC fluxes is not well studied, and assessing it requires better understanding of stem emission dynamics and their driving processes. To gain more mechanistic insight into stem emission patterns, we measured monoterpene, methanol and acetaldehyde emissions from the stems of mature Scots pines (Pinus sylvestris L.) in a boreal forest over three summers. We analysed the effects of temperature, soil water content, tree water status, transpiration and growth on the VOC emissions and used generalized linear models to test their relative importance in explaining the emissions. We show that Scots pine stems are considerable sources of monoterpenes, methanol and acetaldehyde, and their emissions are strongly regulated by temperature. However, even small changes in water availability affected the emission potentials: increased soil water content increased the monoterpene emissions within a day, whereas acetaldehyde and methanol emissions responded within 2-4 days. This lag corresponded to their transport time in the xylem sap from the roots to the stem. Moreover, the emissions of monoterpenes, methanol and acetaldehyde were influenced by the cambial growth rate of the stem with 6-10-day lags.

A plastid-localized bona fide geranylgeranyl diphosphate synthase plays a necessary role in monoterpene indole alkaloid biosynthesis in Catharanthus roseus

In plants, geranylgeranyl diphosphate (GGPP, C₂₀ ) synthesized by GGPP synthase (GGPPS) serves as precursor for vital metabolic branches including specialized metabolites. Here, we report the characterization of a GGPPS (CrGGPPS2) from the Madagascar periwinkle (Catharanthus roseus) and demonstrate its role in monoterpene (C₁₀ )-indole alkaloids (MIA) biosynthesis. The expression of CrGGPPS2 was not induced in response to methyl jasmonate (MeJA), and was similar to the gene encoding type-I protein geranylgeranyltransferase_β subunit (CrPGGT-I_β), which modulates MIA formation in C. roseus cell cultures. Recombinant CrGGPPS2 exhibited a bona fide GGPPS activity by catalyzing the formation of GGPP as the sole product. Co-localization of fluorescent protein fusions clearly showed CrGGPPS2 was targeted to plastids. Downregulation of CrGGPPS2 by virus-induced gene silencing (VIGS) significantly decreased the expression of transcription factors and pathway genes related to MIA biosynthesis, resulting in reduced MIA. Chemical complementation of CrGGPPS2-vigs leaves with geranylgeraniol (GGol, alcoholic form of GGPP) restored the negative effects of CrGGPPS2 silencing on MIA biosynthesis. In contrast to VIGS, transient and stable overexpression of CrGGPPS2 enhanced the MIA biosynthesis. Interestingly, VIGS and transgenic-overexpression of CrGGPPS2 had no effect on the main GGPP-derived metabolites, cholorophylls and carotenoids in C. roseus leaves. Moreover, silencing of CrPGGT-I_β, similar to CrGGPPS2-vigs, negatively affected the genes related to MIA biosynthesis resulting in reduced MIA. Overall, this study demonstrated that plastidial CrGGPPS2 plays an indirect but necessary role in MIA biosynthesis. We propose that CrGGPPS2 might be involved in providing GGPP for modifying proteins of the signaling pathway involved in MIA biosynthesis.

Effect of Thidiazuron on Terpene Volatile Constituents and Terpenoid Biosynthesis Pathway Gene Expression of Shine Muscat (Vitis labrusca × V. vinifera) Grape Berries

Volatile compounds are considered to be essential for the flavor and aroma quality of grapes. Thidiazuron (TDZ) is a commonly used growth regulator in grape cultivation that stimulates larger berries and prevents fruit drop. This study was conducted to investigate the effect of TDZ on the production of aroma volatiles and to identify the key genes involved in the terpene biosynthesis pathways that are affected by this compound. Treatment with TDZ had a negative effect on the concentration of volatile compounds, especially on monoterpenes, which likely impacts the sensory characteristics of the fruit. The expression analysis of genes related to the monoterpenoid biosynthesis pathways confirmed that treatment with TDZ negatively regulated the key genes DXS1, DXS3, DXR, HDR, VvPNGer and VvPNlinNer1. Specifically, the expression levels of the aforementioned genes were down-regulated in almost all berry development stages in the TDZ-treated samples. The novel results from the present study can be used to aid in the development of food products which maintain the flavor quality and sensory characteristics of grape. Furthermore, these findings can provide the theoretical basis that can help to optimize the utilization of TDZ for the field production of grapes at a commercial scale.

Transcriptome and Metabolite Conjoint Analysis Reveals that Exogenous Methyl Jasmonate Regulates Monoterpene Synthesis in Grape Berry Skin

Monoterpene is one of the important sources of varietal aroma, which provides a strong floral and fruity aroma in wines. Methyl jasmonate (MeJA) affects plant secondary metabolism. However, the regulatory mechanisms of monoterpene biosynthesis after MeJA application on grapes are not illuminated. In the present study, 10 mM MeJA was used as treatments in Italian Riesling grape at the preveraison stage in different ways, including grape cluster soaking, foliar spraying, and whole vine spraying, designated as T1, T2, and T3, respectively, while a blank group was used as the control (CK). HS-SPME/GC-MS and transcriptome sequencing analysis were performed to investigate the effect of exogenous MeJA on monoterpene synthesis in grape berry skin. The results of GC-MS showed that the application of MeJA induced the accumulation of volatile monoterpenes in grape berry skin, especially linalool, α-terpineol, and oxides. In addition, transcriptome analysis showed that differentially expressed genes were increased from T2 to T3 to T1 compared with CK, and significantly enriched in JA and monoterpene synthesis pathways. T1 application significantly upregulated the mRNA expression levels of LOX2S, AOS, OPR, and JMT involved in the JA biosynthesis pathway, as well as DXS, HMGCR, TPS14, and α-terpineol synthesis genes involved in the monoterpene synthesis pathway compared with T2, T3, and CK. Thus, grape cluster soaking treatment with MeJA could greatly activate volatile monoterpene synthesis. The results will deeply increase our understanding of the monoterpene biosynthesis of grape berry skin in response to MeJA.

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.

Influence of cluster thinning and girdling on aroma composition in 'Jumeigui' table grape

Cluster thinning and girdling are common and simple practices applied to improve berry quality in table grape cultivation. However, there is limited information about the accumulation and biosynthesis of the entire aromatic profile under cluster thinning and girdling, notably in table grapes. This research investigated the influences of cluster thinning and girdling (alone or in combination) on aroma profiles, particularly the changes in biosynthesis and accumulation of Muscat-flavored related compounds from véraison to harvest in 'Jumeigui' grape. Cluster thinning and girdling (alone or in combination) significantly increased the concentrations of total soluble solids (TSS) and key aromatic compounds at harvest, with higher concentrations of both under cluster thinning than girdling. Berry weight and titratable acidity (TA) were unaffected by cluster thinning, girdling, or in combination at harvest. Linalool, the most abundant and active odorant related to Muscat flavor, accumulated in 28.6% and 20.2% higher concentrations from cluster thinning than control and girdling at maturity, respectively. Furthermore, higher DXS3 transcript abundance in cluster thinning groups might contribute to the increased accumulation of terpenes and linalool in 'Jumeigui' grape. The results will contribute to further understand the mechanism of source/sink ratio modulation on aroma accumulation and better apply cluster thinning and girdling for grape production.

Surface plasmon resonance, fluorescence, and molecular docking studies of bovine serum albumin interactions with natural coumarin diversin

In the present study the binding of diversin (DIV), a prenylated coumarin isolated from Ferula diversivittata, to bovine serum albumin (BSA) was investigated using surface plasmon resonance (SPR), spectrofluorimetry, and molecular docking approaches. Following the activation of carboxylic groups, via NHS/EDC, BSA was immobilized on the carboxymethyl dextran (CMD) hydrogel coated Au sensor, and was used for real-time monitoring of the interactions between DIV and BSA. K_D value of DIV binding to BSA increased with increasing temperature, confirmed that the affinity between BSA and DIV decreases with rising temperature. In addition, the fluorescence and synchronous fluorescence spectroscopic data revealed that the intrinsic emission intensity of BSA was quenched via a dynamic mechanism. In addition, the micro-region around BSA tyrosine residue was changed upon interaction with DIV. The thermodynamic parameter findings suggested that the hydrophobic interactions were dominant in the binding and formation of the BSA and DIV complex. The molecular docking outputs indicated that there is only one binding site on BSA for DIV, in agreement with experimental data, and DIV bind BSA in subdomain IB.

Taming the Reactivity of Monoterpene Synthases To Guide Regioselective Product Hydroxylation

Monoterpenoids are industrially important natural products with applications in the flavours, fragrances, fuels and pharmaceutical industries. Most monoterpenoids are produced by plants, but recently two bacterial monoterpene synthases have been identified, including a cineole synthase (bCinS). Unlike plant cineole synthases, bCinS is capable of producing nearly pure cineole from geranyl diphosphate in a complex cyclisation cascade that is tightly controlled. Here we have used a multidisciplinary approach to show that Asn305 controls water attack on the α-terpinyl cation and subsequent cyclisation and deprotonation of the α-terpineol intermediate, key steps in the cyclisation cascade which direct product formation towards cineole. Mutation of Asn305 results in variants that no longer produce α-terpineol or cineole. Molecular dynamics simulations revealed that water coordination is disrupted in all variants tested. Quantum mechanics calculations indicate that Asn305 is most likely a (transient) proton acceptor for the final deprotonation step. Our synergistic approach gives unique insight into how a single residue, Asn305, tames the promiscuous chemistry of monoterpene synthase cyclisation cascades. It does this by tightly controlling the final steps in cineole formation catalysed by bCinS to form a single hydroxylated monoterpene product.

A Cytosol-Localized Geranyl Diphosphate Synthase from Lithospermum erythrorhizon and Its Molecular Evolution

Geranyl diphosphate (GPP) is the direct precursor of all monoterpenoids and is the prenyl source of many meroterpenoids, such as geranylated coumarins. GPP synthase (GPPS) localized in plastids is responsible for providing the substrate for monoterpene synthases and prenyltransferases for synthesis of aromatic substances that are also present in plastids, but GPPS activity in Lithospermum erythrorhizon localizes to the cytosol, in which GPP is utilized for the biosynthesis of naphthoquinone pigments, which are shikonin derivatives. This study describes the identification of the cytosol-localized GPPS gene, LeGPPS, through EST- and homology-based approaches followed by functional analyses. The deduced amino acid sequence of the unique LeGPPS showed greater similarity to that of farnesyl diphosphate synthase (FPPS), which generally localizes to the cytosol, than to plastid-localized conventional GPPS. Biochemical characterization revealed that recombinant LeGPPS predominantly produces GPP along with a trace amount of FPP. LeGPPS expression was mainly detected in root bark, in which shikonin derivatives are produced, and in shikonin-producing cultured cells. The GFP fusion protein in onion (Allium cepa) cells localized to the cytosol. Site-directed mutagenesis of LeGPPS and another FPPS homolog identified in this study, LeFPPS1, showed that the His residue at position 100 of LeGPPS, adjacent to the first Asp-rich motif, contributes to substrate preference and product specificity, leading to GPP formation. These results suggest that LeGPPS, which is involved in shikonin biosynthesis, is recruited from cytosolic FPPS and that point mutation(s) result in the acquisition of GPPS activity.

Genome-Wide Identification, Classification, and Expression Profiling Reveals R2R3-MYB Transcription Factors Related to Monoterpenoid Biosynthesis in Osmanthus fragrans

Osmanthus fragrans is widely grown for the purpose of urban greening and the pleasant aroma emitted from its flowers. The floral scent is determined by several monoterpenoid volatiles, such as linalool and its oxides, which are a few of the most common volatiles and the main components of the essential oils in most sweet osmanthus cultivars. In addition, the relative contents of cis- and trans-linalool oxide (furan) may affect the aromas and quality of the essential oils. MYB proteins represent the largest family of transcription factors in plants and participate in regulating secondary metabolites. Several cis-elements, especially AC-rich regions, are known to be bound by 2R-MYBs and could be found in the promoter of the enzyme genes in the terpenoid metabolic pathway. However, there has to date been no investigation into the 2R-MYB family genes involved in regulating terpenoid biosynthesis in O. fragrans. Here, 243 non-redundant 2R-MYB proteins were grouped into 33 clusters based on the phylogeny and exon-intron distribution. These genes were unevenly distributed on 23 chromosomes. Ka/Ks analysis showed that the major mode of 2R-MYB gene evolution was purifying selection. Expression analysis indicated that 2R-MYB genes in O. fragrans exhibited varied expression patterns. A total of 35 OfMYBs representing the highest per kilobase per million mapped reads in the flower were selected for quantitative real-time PCR analysis. The correlation analysis between the expression level and the contents of fragrant compounds at different flowering stages suggested that OfMYB19/20 exhibited remarkably positive correlation with the accumulation of cis-linalool oxides. OfMYB51/65/88/121/137/144 showed significantly negative correlations with one or more linalool oxides. Characterization of these proteins revealed that OfMYB19 and OfMYB137 were localized in the nuclei, but did not show transcriptional activation in the yeast system, which suggested that they may be bound to other transcription factors to exert regulatory functions. These findings provide useful information for further functional investigation of the 2R-MYBs and offer a foundation for clarifying the 2R-MYB transcription factors involved in the molecular mechanism of the regulation of monoterpenoid biosynthesis in Osmanthus fragrans.

Short-chain isoprenyl diphosphate synthases of lavender (Lavandula)

KEY MESSAGE

We reported the functional characterization of cDNAs encoding short-chain isoprenyl diphosphate synthases that control the partitioning of precursors for lavender terpenoids. Lavender essential oil is composed of regular and irregular monoterpenes, which are derived from linear precursors geranyl diphosphate (GPP) and lavandulyl diphosphate (LPP), respectively. Although this plant strongly expresses genes responsible for the biosynthesis of both monoterpene classes, it is unclear why regular monoterpenes dominate the oil. Here, we cloned and characterized Lavandula x intermedia cDNAs encoding geranyl diphosphate synthase (LiGPPS), geranylgeranyl diphosphate synthase (LiGGPPS) and farnesyl diphosphate synthase (LiFPPS). LiGPPS was heteromeric protein, consisting of a large subunit (LiGPPS.LSU) and a small subunit for which two different cDNAs (LiGPPS.SSU1 and LiGPPS.SSU2) were detected. Neither recombinant LiGPPS subunits was active by itself. However, when co-expressed in E. coli LiGPPS.LSU and LiGPPS.SSU1 formed an active heteromeric GPPS, while LiGPPS.LSU and LiGPPS.SSU2 did not form an active protein. Recombinant LiGGPPS, LiFPPS and LPP synthase (LPPS) proteins were active individually. Further, LiGPPS.SSU1 modified the activity of LiGGPPS (to produce GPP) in bacterial cells co-expressing both proteins. Given this, and previous evidence indicating that GPPS.SSU can modify the activity of GGPPS to GPPS in vitro and in plants, we hypothesized that LiGPPS.SSU1 modifies the activity of L. x intermedia LPP synthase (LiLPPS), thus accounting for the relatively low abundance of LPP-derived irregular monoterpenes in this plant. However, LiGPPS.SSU1 did not affect the activity of LiLPPS. These results, coupled to the observation that LiLPPS transcripts are more abundant than those of GPPS subunits in L. x intermedia flowers, suggest that regulatory mechanisms other than transcriptional control of LPPS regulate precursor partitioning in lavender flowers.

The Molecular Mechanism of Perillaldehyde Inducing Cell Death in Aspergillus flavus by Inhibiting Energy Metabolism Revealed by Transcriptome Sequencing

Perillaldehyde (PAE), an essential oil in Perilla plants, serves as a safe flavor ingredient in foods, and shows an effectively antifungal activity. Reactive oxygen species (ROS) accumulation in Aspergillus flavus plays a critical role in initiating a metacaspase-dependent apoptosis. However, the reason for ROS accumulation in A. flavus is not yet clear. Using transcriptome sequencing of A. flavus treated with different concentrations of PAE, our data showed that the ROS accumulation might have been as a result of an inhibition of energy metabolism with less production of reducing power. By means of GO and KEGG enrichment analysis, we screened four key pathways, which were divided into two distinct groups: a downregulated group that was made up of the glycolysis and pentose phosphate pathway, and an upregulated group that consisted of MAPK signaling pathway and GSH metabolism pathway. The inhibition of dehydrogenase gene expression in two glycometabolism pathways might play a crucial role in antifungal mechanism of PAE. Also, in our present study, we systematically showed a gene interaction network of how genes of four subsets are effected by PAE stress on glycometabolism, oxidant damage repair, and cell cycle control. This research may contribute to explaining an intrinsic antifungal mechanism of PAE against A. flavus.

Distinct metabolic pathways drive monoterpenoid biosynthesis in a natural population of Pelargonium graveolens

Pelargonium graveolens is a wild predecessor to rose-scented geranium hybrids prized for their essential oils used as fragrances and flavorings. However, little is known about their biosynthesis. Here we present metabolic evidence that at least two distinct monoterpene biosynthetic pathways contribute to their volatile profiles, namely, cyclic p-menthanes such as (-)-isomenthone and acyclic monoterpene alcohols such as geraniol and (-)-citronellol and their derivatives (referred to here as citronelloid monoterpenes). We established their common origin via the 2C-methyl-d-erythritol-4-phosphate pathway but found no indication these pathways share common intermediates beyond geranyl diphosphate. Untargeted volatile profiling of 22 seed-grown P. graveolens lines demonstrated distinct chemotypes that preferentially accumulate (-)-isomenthone, geraniol, or (-)-citronellol along with approximately 85 minor volatile products. Whole plant 13CO2 isotopic labeling performed under physiological conditions permitted us to measure the in vivo rates of monoterpenoid accumulation in these lines and quantify differences in metabolic modes between chemotypes. We further determined that p-menthane monoterpenoids in Pelargonium are likely synthesized from (+)-limonene via (+)-piperitone rather than (+)-pulegone. Exploitation of this natural population enabled a detailed dissection of the relative rates of competing p-menthane and citronelloid pathways in this species, providing real time rates of monoterpene accumulation in glandular trichomes.