Volatile Biosynthesis Research Articles

Biochemical characterization of CsCXEs: Carboxylesterase enhances the biosynthesis of green odor volatiles during tea processing

Biochemical characterization of CsCXEs: Carboxylesterase enhances the biosynthesis of green odor volatiles during tea processing

Characterization of key aroma compounds in microgreens and mature plants of hydroponic fennel (Foeniculum vulgare Mill.)

Fennel is a popular culinary herb known for its unique flavor. In this study, we identified key aroma-active compounds in fresh fennel (Foeniculum vulgare Mill.) and its microgreens. Fennel was cultivated hydroponically with soilless substrates. Upon harvesting, samples were ground with liquid nitrogen, and headspace solid phase microextraction (SPME) gas chromatography-mass-spectrometry-olfactometry (GC-MS-O) was used for volatile analysis. Thirty-two and 28 key aroma-active compounds were identified in fennel microgreens and mature leaves, respectively. Phenylpropenes, especially (E)-anethole, were the predominant aroma-active compound in all samples (36.3–83.4 %). Quantitation results showed that fennel microgreens contained a significantly higher amount of monoterpenes, showing an 81.4–98.1 % increase when compared to mature fennel. Principal component analysis (PCA) of identified volatiles indicated a distinctive difference in the overall aroma profile between microgreens and mature leaf. The changes in aroma contents over different growth stages revealed the underlying volatile biosynthesis discrepancy. This study provided baseline information for understanding the aroma evolution from microgreen to mature fennel herbs

Identification and characterization of a key LcTPS in the biosynthesis of volatile monoterpenes and sesquiterpenes in Litchi fruit.

Litchi (Litchi chinensis Sonn.) has a desirable sweet taste and exotic aroma, making it popular in the markets. However, the biosynthesis of aroma volatiles in litchi fruit has rarely been investigated. In this study, the content and composition of volatile compounds were determined during litchi fruit ripening. In the mature green and mature red stages of litchi, 49 and 45 volatile compounds were detected, respectively. Monoterpenes were found to be the most abundant volatile compounds in mature red fruit, and their contents significantly increased compared to green fruit, mainly including citronellol, geraniol, myrcene, and D-limonene, which contributed to the aroma in litchi fruit. By comparing the expression profiles of the genes involved in the terpene synthesis pathway during fruit development, a terpene synthesis gene (LcTPS1-2) was identified and characterized as a major player in the synthesis of monoterpenes and sesquiterpenes. A subcellular localization analysis found LcTPS1-2 to be present in the plastid and cytoplasm. The recombinant LcTPS1-2 enzyme was able to catalyze the formation of three monoterpenes, myrcene, geraniol and citral, from geranyl pyrophosphate (GPP) and to convert farnesyl diphosphate (FPP) to a sesquiterpene, caryophyllene in vitro. Transgenic Arabidopsis thaliana plants overexpressing LcTPS1-2 exclusively released one monoterpene D-limonene, and three sesquiterpenes cis-thujopsene, (E)-β-famesene and trans-β-ionone. These results indicate that LcTPS1-2 plays an important role in the production of major volatile terpenes in litchi fruit and provides a basis for future investigations of terpenoid biosynthesis in litchi and other horticultural crops.

ABIOTIC STRESS GENE 1 mediates aroma volatiles accumulation by activating MdLOX1a in apple.

Fruit aroma is an important organoleptic quality, which influences consumer preference and market competitiveness. Aroma compound synthesis pathways in plants have been widely identified, among the lipoxygenase pathway is crucial for fatty acid catabolism to form esters in apple. However, the regulatory mechanism of this pathway remains elusive. In this study, linear regression analysis and transgene verification revealed that the lipoxygenase MdLOX1a is involved in ester biosynthesis. Yeast one-hybrid library screening indicated that a protein, MdASG1 (ABIOTIC STRESS GENE 1), was a positive regulator of MdLOX1a and ester production based on yeast one-hybrid and dual-luciferase assays, as well as correlation analysis among eight different apple cultivars. Overexpression of MdASG1 in apple and tomato stimulated the lipoxygenase pathway and increased the fatty acid-derived volatile content, whereas the latter was decreased by MdASG1 silencing and CRISPR/Cas9 knockout. Furthermore, MdASG1 overexpression enhanced the salt-stress tolerance of tomato and apple 'Orin' calli accompanied by a higher content of fatty acid-derived volatiles compared to that of non-stressed transgenic tomato fruit, while MdASG1-Cas9 knockdown calli do not respond to salt stress and promote the biosynthesis of fatty acid-derived volatiles. Collectively, these findings indicate that MdASG1 activates MdLOX1a expression and participates in the lipoxygenase pathway, subsequently increasing the accumulation of aroma compounds, especially under moderate salt stress treatment. The results also provide insight into the theory for improving fruit aroma quality in adversity.

Exogenous systemin peptide treatment in olive alters Bactrocera oleae oviposition preference

AbstractThe olive fruit fly, Bactrocera oleae (Rossi), is a key pest of the olive crop, whose control relies mostly on the use of insecticides. Plant peptides may represent a more environmentally-friendly tool to manage olive fly, due to their recognized role to activate and/or prime plant defence responses against pests. In this work, behavioural experiments (no-choice and two-choice) and analysis of volatile compounds were carried out to evaluate the impact of the exogenous application of the peptide systemin to olive tree on olive fly infestation, and to elucidate its mode of action to prime plant defence. The treatment of olive branches with 10 nM systemin showed to confer protection against olive fly, by reducing significantly the ovipositions (up to 3.0-fold) and the number of infested fruits (up to 2.9-fold) when compared to non-treated branches. This protective effect was even detected in neighbouring non-treated branches, suggesting the ability of systemin to trigger plant-to-plant communication. The deterrent activity of the primed olives was associated with the emission of the volatiles 2-ethyl-1-hexanol, 4-tert-butylcyclohexyl acetate and 1, 2, 3-trimethyl-benzene, which were negatively correlated with oviposition and fly infestation. Systemin has also showed to trigger the biosynthesis of specific volatiles (esters) in olives in response to fly attacks. Overall, the observed protection conferred by systemin against olive fly is likely due to the emission of specific volatiles that can act as a defence and/or as signalling molecules to upregulate the plant defence response. Thus, systemin represents a novel and useful tool to manage olive fruit fly.

Far-red light increases maize volatile emissions in response to volatile cues from neighbouring plants.

Plants perceive the presence and defence status of their neighbours through light and volatile cues, but how plants integrate both stimuli is poorly understood. We investigated if and how low Red to Far red light (R:FR) ratios, indicative of shading or canopy closure, affect maize (Zea mays) responses to herbivore-induced plant volatiles (HIPVs), including the green leaf volatile (Z)-3-hexenyl acetate. We modulated light signalling and perception by using FR supplementation and a phyB1phyB2 mutant, and we determined volatile release as a response readout. To gain mechanistic insights, we examined expression of volatile biosynthesis genes, hormone accumulation, and photosynthesis. Exposure to a full blend of HIPVs or (Z)-3-hexenyl acetate induced maize volatile release. Short-term FR supplementation increased this response. In contrast, prolonged FR supplementation or constitutive phytochrome B inactivation in phyB1phyB2 plants showed the opposite response. Short-term FR supplementation enhanced photosynthesis and stomatal conductance and (Z)-3-hexenyl acetate-induced JA-Ile levels. We conclude that a FR-enriched light environment can prompt maize plants to respond more strongly to HIPVs emitted by neighbours, which might be explained by changes in photosynthetic processes and phytochrome B signalling. Our findings reveal interactive responses to light and volatile cues with potentially important consequences for plant-plant and plant-herbivore interactions.

Genomic analysis based on chromosome-level genome assembly reveals Myrtaceae evolution and terpene biosynthesis of rose myrtle

BackgroundRose myrtle (Rhodomyrtus tomentosa (Ait.) Hassk), is an evergreen shrub species belonging to the family Myrtaceae, which is enriched with bioactive volatiles (α-pinene and β-caryophyllene) with medicinal and industrial applications. However, the mechanism underlying the volatile accumulation in the rose myrtle is still unclear.ResultsHere, we present a chromosome-level genomic assembly of rose myrtle (genome size = 466 Mb, scaffold N50 = 43.7 Mb) with 35,554 protein-coding genes predicted. Through comparative genomic analysis, we found that gene expansion and duplication had a potential contribution to the accumulation of volatile substances. We proposed that the action of positive selection was significantly involved in volatile accumulation. We identified 43 TPS genes in R. tomentosa. Further transcriptomic and TPS gene family analyses demonstrated that the distinct gene subgroups of TPS may contribute greatly to the biosynthesis and accumulation of different volatiles in the Myrtle family of shrubs and trees. The results suggested that the diversity of TPS-a subgroups led to the accumulation of special sesquiterpenes in different plants of the Myrtaceae family.ConclusionsThe high quality chromosome-level rose myrtle genome and the comparative analysis of TPS gene family open new avenues for obtaining a higher commercial value of essential oils in medical plants.

The Circadian Clock Gene PHYTOCLOCK1 Mediates the Diurnal Emission of the Anti-Insect Volatile Benzyl Nitrile from Damaged Tea (Camellia sinensis) Plants.

Benzyl nitrile from tea plants attacked by various pests displays a diurnal pattern, which may be closely regulated by the endogenous circadian clock. However, the molecular mechanism by the circadian clock of tea plants that regulates the biosynthesis and release of volatiles remains unclear. In this study, the circadian clock gene CsPCL1 can activate both the expression of the benzyl nitrile biosynthesis-related gene CsCYP79 and the jasmonic acid signaling-related transcription factor CsMYC2 involved in upregulating CsCYP79 gene, thereby resulting in the accumulation and release of benzyl nitrile. Therefore, the anti-insect function of benzyl nitrile was explored in the laboratory. The application of slow-release beads of benzyl nitrile in tea plantations significantly reduced the number of tea geometrids and had positive effects on the yield of fresh tea leaves. These findings reveal the potential utility of herbivore-induced plant volatiles for the green control of pests in tea plantations.

Transcriptome analysis revealed endophytic Beauveria bassiana triggered methyl jasmonate pathway associated with resistance against stem weevil (Apion corchori)

The fungal entomopathogen Beauveria bassiana could be established as an endophyte within jute (Corchorus capsularis) plant through seed inoculation. The highest colonization was observed in ITCC 6063 followed by ITCC 5562 and ITCC 5408 which are statistically at par (p < 0.05). The lowest apion infestation was observed in ITCC 5408, ITCC 6063, ITCC 4512 and ITCC 4563 which are statistically at par (p < 0.05). Highest apion infestation was observed in case of two non-endophytic isolates ITCC 4644 and ITCC 4925. Transcriptome study showed that a significant number of stem-weevil (Apion corchori) resistant genes involved in biosynthesis of plant volatiles viz., oxidative cleavage of fatty acids, LEGO-like building blocks, salicylic acid activation pathway, methyl jasmonic acid synthesis pathway were activated in ten B. bassiana isolate treated plants. RNA Sequencing was used to identify 1017 DEGs between ‘endophyte colonised plant’ and ‘untreated plant’. 1117 genes were up-regulated and 279 genes were down regulated in treated plant.

Effect of volatile compounds produced by Weissella cibaria BWL4 on Botrytis cinerea infection in fruit and complete genome sequence analysis of BWL4

Botrytis cinerea, one of the most harmful pathogenic fungi, causes significant postharvest decay in fruit. In this study, the effects of Weissella cibaria BWL4 on B. cinerea and the gray mold in grape and kiwifruit were evaluated. Additionally, the genome of an antagonistic bacterium BWL4 was sequenced. Results showed that the application of BWL4 inhibited B. cinerea infection in grape and kiwifruit. BWL4 produced antifungal volatile substances against B. cinerea. A gas chromatography–mass spectrometry of solid phase microextraction samples (SPME-GC-MS) analysis showed that BWL4 produced 54 volatiles. Among these volatiles, furfural, 2,6-dimethyl-pyrazine, dimethyl trisulfide, 2-pentyl furan, 2-ethyl hexanol, hexamethyl-cyclotrisiloxane, dodecamethyl-cyclohexasiloxane, 2,4-di-tert-butylphenol, and butylated hydroxytoluene, exhibited antifungal activity against B. cinerea, with MICs of 0.8 g L−1, 0.2 g L−1, 0.9 g L−1, 5 g L−1, 0.4 g L−1, 8 g L−1, 8 g L−1, 80 mg L−1, and 2 g L−1, respectively. In vivo assay showed that these compounds inhibited the disease development in kiwifruit. These compounds except dimethyl trisulfide can also inhibit gray mold in grape. The genome of W. cibaria BWL4 consists of a circular chromosome of 2.42 Mb and 6 plasmids. The genome size is 2.53 Mb, encoding 2327 putative genes. Several genes involved in the biosynthesis of some antifungal volatiles and 17 genes associated with biocontrol were identified. These results suggested that W. cibaria BWL4 can be considered as an effective biological control agent for the postharvest management of B. cinerea infection.

Comprehensive analysis of silicon impact on defense and metabolic responses in rice exposed to herbivory stress.

Silicon (Si) uptake is generally beneficial for plants that need protection from insect herbivores. In pursue of mechanisms involved in Si-mediated defense, we comprehensively explored the impact of Si on several defensive and metabolic traits in rice exposed to simulated and real herbivory of Mythimna loreyi Duponchel larvae. Hydroponic experiments showed that Si-deprived rice supplemented with Si 72 h prior to insect infestation were similarly resistant to larvae as plants continuously grown in Si-containing media. Both Si and herbivory altered primary metabolism in rice, including the levels of several sugars, amino acids, and organic acids. While the accumulation of sugars was generally positively correlated with Si presence, multiple amino acids showed a negative correlation trend with Si supplementation. The levels of secondary metabolites, including isopentylamine, p-coumaroylputrescine and feruloylputrescine, were typically higher in the leaves of Si-supplemented plants exposed to herbivory stress compared to Si-deprived plants. In addition, simulated herbivory treatment in Si-supplemented plants induced more volatile emissions relative to Si-deprived plants, which was consistent with the increased transcripts of key genes involved in volatile biosynthesis. In ecological interactions, Si alone did not affect the oviposition choice of M. loreyi but gravid females showed a significant preference for simulated herbivory-treated/Si-deprived compared to Si-supplemented plants. Our data suggest that apart from mechanical defense, Si may affect rice metabolism in multiple ways that might enhance/modulate defense responses of rice under herbivory stress.

Effects of low-temperature storage on the aroma composition and quality of Golden Empress Hami melons: A transcriptomic and metabolomic analysis

Low-temperature storage is frequently employed to prolong the shelf life of Hami melons. Nevertheless, extended low-temperature storage can hamper the synthesis of aroma compounds in these fruits. This study investigated the effects of storage at 3 °C (LT) and 21 °C (RT) on the aroma quality of Golden Empress Hami melons (GEHMs) during a shelf life of 24 d. Further, the transcription levels of genes related to aroma metabolism were also examined during this period. After 12 d, the intensity of sweet aroma (LT: 2.3, RT: 8.2) and fruit aroma (LT: 2.1, RT: 8) was significantly lower in GEHMs stored at LT than in those stored at RT. Correspondingly, between-group differences in the content of esters with sweet and fruity aromas (RT: 782.76 ± 128.41 μg/kg, LT: 53.69 ± 24.32 μg/kg) and alcohols (RT: 2252.98 ± 297.65 μg/kg, LT: 448.80 ± 106.13 μg/kg) peaked at 12 d. Furthermore, the expression levels of 52 genes related to aroma volatile biosynthesis were significantly different between GEHMs stored at RT and LT. Specifically, the expression levels of genes encoding ethanol dehydrogenase (ADH), long-chain acyl-CoA synthetase (ACSL), and branched-chain amino acid aminotransferase (ilvE) which are involved in the production of alcohols and esters— were significantly lower in GEHMs stored at LT than in those stored at RT. This study provides a deeper understanding of aroma-related biosynthetic pathways of GEHMs during postharvest storage. Additionally, it offers valuable metabolomic and transcriptomic resources for the regulation of aroma compound metabolism in postharvest GEHMs.

Unraveling the terpene synthase family and characterization of BsTPS2 contributing to (S)-( +)-linalool biosynthesis in Boswellia.

Boswellia tree bark exudes oleo-gum resin in response to wounding, which is rich in terpene volatiles. But, the molecular and biochemical basis of wound-induced formation of resin volatiles remains poorly understood. Here, we combined RNA-sequencing (RNA-seq) and metabolite analysis to unravel the terpene synthase (TPS) family contributing to wound-induced biosynthesis of resin volatiles in B. serrata, an economically-important Boswellia species. The analysis of large-scale RNA-seq data of bark and leaf samples representing more than 600 million sequencing reads led to the identification of 32 TPSs, which were classified based on phylogenetic relationship into various TPSs families found in angiosperm species such as TPS-a, b, c, e/f, and g. Moreover, RNA-seq analysis of bark samples collected at 0-24h post-wounding shortlisted 14 BsTPSs that showed wound-induced transcriptional upregulation in bark, suggesting their important role in wound-induced biosynthesis of resin volatiles. Biochemical characterization of a bark preferentially-expressed and wound-inducible TPS (BsTPS2) in vitro and in planta assays revealed its involvement in resin terpene biosynthesis. Bacterially-expressed recombinant BsTPS2 catalyzed the conversion of GPP and FPP into (S)-( +)-linalool and (E)-(-)-nerolidol, respectively, in vitro assays. However, BsTPS2 expression in Nicotiana benthamiana found that BsTPS2 is a plastidial linalool synthase. In contrast, cytosolic expression of BsTPS2 did not form any product. Overall, the present work unraveled a suite of TPSs that potentially contributed to the biosynthesis of resin volatiles in Boswellia and biochemically characterized BsTPS2, which is involved in wound-induced biosynthesis of (S)-( +)-linalool, a monoterpene resin volatile with a known role in plant defense.

BZIP transcription factor PubZIP914 enhances production of fatty acid-derived volatiles in pear

‘Nanguo’ pear emitted a rich aroma when entirely ripe. The six-carbon (C6) volatiles, including the aldehydes, 2-hexenal, and hexanal, as well as their corresponding alcohols and esters which are derived from lipoxygenase pathway are the important volatile components in ‘Nanguo’ pears. However, the transcriptional regulation mechanism of aroma synthesis of ‘Nanguo’ pears remains largely unknown. bZIP transcription factors (TFs) mediate different developmental processes in plants. In this study, we identified and characterized a bZIP TF that is highly expressed and induced in ‘Nanguo’ pear fruits at the mature stage. The content of fatty acid-derived volatiles increased significantly in transgenic pears and tomatoes of PubZIP914 overexpression. Meanwhile, PubZIP914 could regulate PuLOX3.1 by binding directly to PuLOX3.1 promoter. The results of this study provide evidence demonstrating how bZIP transcription factors regulate fatty acid-derived volatiles biosynthesis during pear fruit ripening.

Jasmonate-induced MdMYC2 improves fruit aroma during storage of ‘Ruixue’ apple based on transcriptomic, metabolic and functional analyses

Abundant volatile compounds are predominant contributors to fruit aroma in various species. Plant hormones and transcription factors are pivotal for volatile compound production in fruit. Jasmonate (JA) regulates the biosynthesis of volatiles such as aldehydes and alcohols, but a possible mechanism by which JA-induced MdMYC2 regulates aldehyde and alcohol biosynthesis in apple fruit has not been described. To study the effects of JA on the critical volatiles of ‘Ruixue’ fruit, gas chromatography‒mass spectrometry (GC‒MS) was used to determine the content of volatiles in fruits treated with JA. Our results showed that JA treatment effectively improved fruit quality during storage of ‘Ruixue’ fruit; for instance, sweetness increased and aroma volatiles accumulated. Furthermore, we identified the transcription factor (TF) MdMYC2 (MD16G1274200), whose expression increased 1.5- to 2.0-fold in JA-treated fruits. Subsequently, MdMYC2 overexpression dramatically increased volatile biosynthesis in apple calli (1.6-fold) and tomato calli (2.1-fold). Furthermore, MdMYC2 upregulated MdLOX5a transcription (3-fold) by binding to its promoter according to dual-luciferase and yeast one-hybrid (Y1H) assays. Collectively, these findings provide beneficial information to illustrate the mechanisms by which JA regulates volatile biosynthesis in fruit.

Cinnamon essential oil vapor alleviates the reduction of aroma-related volatiles in cold-stored "Feicheng" peach using HS-GC-IMS.

"Feicheng" peach is popular for its unique aroma, but its defect of being highly sensitive to chilling injury (CI) often leads to aroma loss and internal browning. Essential oils (EOs) are often used to enhance the antioxidant capacity of plants and fruits, as well as to trigger their defense against biotic/abiotic stresses. This study aimed to examine the effect of cinnamon essential oil (CEO) vapor treatment on the aroma quality of peach fruit during cold storage using HS-GC-IMS. The results showed that 50 μL/L CEO vapor reduced the severity of internal browning (IB) in peaches at the stage of 7 ~ 21 d during refrigeration (Significantly, the L* value was higher and the IB index was lower than that of control, p < 0.05). Meanwhile, the evident reduction or loss of aroma content caused by CI was restored to a higher level than the control (p < 0.05). Furthermore, CEO treatment promoted the release of aroma-related volatiles as evidenced by more propyl acetate, and the dimer of amyl acetate, isoamyl acetate, butyl acetate detected than that on harvest day and no-treated group after 21 d of cold storage plus 2 d of shelf life. Genes of PpLOX1, PpLOX2, PpHPL1 and PpADH1 associated with aroma-related volatile biosynthesis revealed higher transcript abundance in peach fruits treated with CEO than the control (p < 0.05). Overall, our study demonstrated that CEO in vapor phase may be beneficial to alleviate the quality deterioration in aroma and flesh color of "Feicheng" peaches caused by CI, which lays a theoretical reference for maintaining postharvest quality of peach fruits.

Strawberry breeding for improved flavor

AbstractStrawberry (Fragaria ×ananassa Duchesne ex Rozier) is cultivated and enjoyed globally for its health properties and flavor. Improvements in agronomic performance and fruit quality attributes highlight the successes of strawberry breeding in recent decades. Nevertheless, sweetness and flavor continue to fall below the ideal for the average consumer. While flavor is an important trait of focus, it is one of many critical traits necessary for the success of a strawberry variety. In addition, the chemical complexity of flavor and the genetic complexity of octoploid strawberry have slowed the development of genomics tools for flavor improvement. Recent efforts to understand consumer preference and the chemical drivers of strawberry flavor have revealed the strong impact of sugar content and specific volatile compounds. These large‐scale sensory studies combined with multi‐omics resources have set the stage for new levels of flavor improvement. Marker‐assisted selection for volatile biosynthesis genes has begun to take place in breeding programs, along with genomic selection for increased sugar content. Enhancing levels of existing volatile compounds and targeted introgression of rare compounds using genomics tools will continue to improve flavor intensity and complexity.

Expression patterns of volatile compounds during ‘FL 47′ tomato ripening and their response to exogenous methyl salicylate (MeSA) fumigation

Aroma, a complex mixture of volatiles, is essential for tomato flavor; however, the expression patterns of most volatile compounds and their response to exogenous methyl salicylate (MeSA) treatment are still unclarified. In this study, in association with the alteration in ethylene evolution and its biosynthetic genes (SlACO1 and SlACS2/4), 31 volatiles fluctuated or accumulated during ‘FL 47′ tomato ripening with a burst at pink or red stage, resulting in the alteration in aroma quality. Meanwhile, the alternation of 29 volatiles, lycopene and β-carotenoid content as well as SlPSY1 and SlCCD1A/B mRNAs demonstrated a strong correlation with ethylene evolution. Further study validated the role of ethylene in apocarotenoid volatile biosynthesis. The formation of 24 volatiles were greatly suppressed in MeSA-treated fruit at red stage along with lower ethylene. In addition, the reduction of apocarotenoid volatiles was associated with downregulated SlPSY1 and SlCCD1A/B mRNAs and carotenoid accumulation when compared with control. In combination with the alternation of ethylene evolution and apocarotenoid volatile formation in SlACS2-overexpressing fruit after MeSA treatment, our results implied that ethylene played a critical role in MeSA-induced reduction of apocarotenoid volatiles via its influence on carotenoid biosynthesis and SlCCD1A/B expression. Although the formation of over 60% of the tomato volatiles was altered by MeSA fumigation, no difference in total volatile abundance or aroma quality could be detected between samples. On the other hand, the taste quality was substantiality altered by MeSA treatment in association with the reduction of TSS and TSS/TA ratio as well as TA increment. Taken together, our results illustrated that MeSA application for fruit quality control was at the expense of flavor alternation.

Aroma Components in Horticultural Crops: Chemical Diversity and Usage of Metabolic Engineering for Industrial Applications.

Plants produce an incredible variety of volatile organic compounds (VOCs) that assist the interactions with their environment, such as attracting pollinating insects and seed dispersers and defense against herbivores, pathogens, and parasites. Furthermore, VOCs have a significant economic impact on crop quality, as well as the beverage, food, perfume, cosmetics and pharmaceuticals industries. These VOCs are mainly classified as terpenoids, benzenoids/phenylpropanes, and fatty acid derivates. Fruits and vegetables are rich in minerals, vitamins, antioxidants, and dietary fiber, while aroma compounds play a major role in flavor and quality management of these horticultural commodities. Subtle shifts in aroma compounds can dramatically alter the flavor and texture of fruits and vegetables, altering their consumer appeal. Rapid innovations in -omics techniques have led to the isolation of genes encoding enzymes involved in the biosynthesis of several volatiles, which has aided to our comprehension of the regulatory molecular pathways involved in VOC production. The present review focuses on the significance of aroma volatiles to the flavor and aroma profile of horticultural crops and addresses the industrial applications of plant-derived volatile terpenoids, particularly in food and beverages, pharmaceuticals, cosmetics, and biofuel industries. Additionally, the methodological constraints and complexities that limit the transition from gene selection to host organisms and from laboratories to practical implementation are discussed, along with metabolic engineering's potential for enhancing terpenoids volatile production at the industrial level.

Biochemical basis for the formation of organ-specific volatile blends in mint.

Above-ground material of members of the mint family is commercially distilled to extract essential oils, which are then formulated into a myriad of consumer products. Most of the research aimed at characterizing the processes involved in the formation of terpenoid oil constituents has focused on leaves. We now demonstrate, by investigating three mint species, peppermint (Mentha ˣ piperita L.), spearmint (Mentha spicata L.) and horsemint (Mentha longifolia (L.) Huds.; accessions CMEN 585 and CMEN 584), that other organs - namely stems, rhizomes and roots - also emit volatiles and that the terpenoid volatile composition of these organs can vary substantially from that of leaves, supporting the notion that substantial, currently underappreciated, chemical diversity exists. Differences in volatile quantities released by plants whose roots had been dipped in a Verticillium dahliae-spore suspension (experimental) or dipped in water (controls) were evident: increases of some volatiles in the root headspace of mint species that are susceptible to Verticillium wilt disease (peppermint and M. longifolia CMEN 584) were detected, while the quantities of certain volatiles decreased in rhizomes of species that show resistance to the disease (spearmint and M. longifolia CMEN 585). To address the genetic and biochemical basis underlying chemical diversity, we took advantage of the newly sequenced M. longifolia CMEN 585 genome to identify candidate genes putatively coding for monoterpene synthases (MTSs), the enzymes that catalyze the first committed step in the biosynthesis of monoterpenoid volatiles. The functions of these genes were established by heterologous expression in Escherichia coli, purification of the corresponding recombinant proteins, and enzyme assays, thereby establishing the existence of MTSs with activities to convert a common substrate, geranyl diphosphate, to (+)-α-terpineol, 1,8-cineole, γ-terpinene, and (-)-bornyl diphosphate, but were not active with other potential substrates. In conjunction with previously described MTSs that catalyze the formation of (-)-β-pinene and (-)-limonene, the product profiles of the MTSs identified here can explain the generation of all major monoterpene skeletons represented in the volatiles released by different mint organs.