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The terpenoids are a major class of natural products with a range of functions in plants. In the grape, monoterpenes, sesquiterpenes and C₁₃‐norisoprenoids are present either in a free volatile form, or bound to sugars and rendered non‐volatile. Of the many terpenoids in grapes, only a relatively small number makes an important contribution to wine aroma. This review summarises new developments in understanding terpenoids, including the monoterpenes linalool, cis‐rose oxide, 1,8‐cineole and wine lactone; the sesquiterpene rotundone; and the C₁₃‐norisoprenoids β‐damascenone, β‐ionone, 1,1,6‐trimethyl‐1,2‐dihydronaphthalene and (E)‐1‐(2,3,6‐trimethylphenyl)buta‐1,3‐diene. Their origin, formation and behaviour during winemaking and ageing, and viticultural influences on their concentration, will be discussed, as well as their role in different wine styles.

To elucidate the significant influence of microorganisms on geographically dependent flavor formation by analyzing microbial communities and volatile flavor compounds (VFCs) in cigar tobacco leaves (CTLs) obtained from China, Dominica, and Indonesia. Microbiome analysis revealed that the predominant bacteria in CTLs were Staphylococcus , Aerococcus , Pseudomonas , and Lactobacillus , while the predominant fungi were Aspergillus , Wallemia, and Sampaiozyma . The microbial communities of CTLs from different origins differed to some extent, and the diversity and abundance of bacteria were greater than fungi. Metabolomic analysis revealed that 64 VFCs were identified, mainly ketones, of which 23 VFCs could be utilized to identify the geographical origins of CTLs. Sixteen VFCs with OAV greater than 1, including cedrol, phenylacetaldehyde, damascone, beta-damascone, and beta-ionone, play important roles in shaping the flavor profile of CTLs from different origins. Combined with the correlation analysis, bacterial microorganisms were more closely related to key VFCs and favored a positive correlation. Bacillus , Vibrio , and Sphingomonas were the main flavor-related bacteria. The study demonstrated that the predominant microorganisms were essential for the formation of key flavor qualities in CTLs, which provided a theoretical reference for flavor control of CTLs by microbial technology. Key points • It is the high OAV VFCs that determine the flavor profile of CTLs. • The methylerythritol phosphate (MEP) pathway and the carotenoid synthesis pathway are key metabolic pathways for the formation of VFCs in CTLs. • Microbial interactions influence tobacco flavor, with bacterial microorganisms contributing more to the flavor formation of CTLs. Graphical Abstract

Sichuan dark brick tea (Camellia sinensis) and Sichuan Fuzhuan brick tea have significantly different aroma characteristics although both of them have almost the same processing methods. Thus, these two types of tea were used as the research materials to determine the differences in their aroma compounds. The volatile compounds in the two types of tea were identified and quantified by headspace solid-phase microextraction coupled with gas chromatography–mass spectrometry (HS-SPME–GC–MS), results showed that they both had 37 common volatile compounds. Then the aroma-active components were identified by odour activity value (OAV). It was found that SFBT had 20 aroma-active components, of which β-ionone had the largest OAV (199547.72). SDBT has 21 aroma-active ingredients (including all 20 aroma-active components of SFBT), of which β-ionone again has the largest OAV (114800.66). Finally, the aroma profile differences between the two tea samples were studied by aroma profile tests, and the results showed that the main aroma differences of SDBT and SFBT were caused by β-ionone, epoxydihydrolinalool II, methyl salicylate, geranylacetone, nerolidol, benzaldehyde, benzyl acetate, nonanal, trans,trans-2,4-heptadienal and 1-octen-3-ol, in addition, defined SFBT’s ‘fungi flower aroma’ and SDBT’s ‘aged fragrance’ from the level of aroma monomer.

The sweet osmanthus carotenoid cleavage dioxygenase 4 (OfCCD4) cleaves carotenoids such as β-carotene and zeaxanthin to yield β-ionone. OfCCD4 is a member of the CCD gene family, and its promoter contains a W-box palindrome with two reversely oriented TGAC repeats, which are the proposed binding sites of WRKY transcription factors. We isolated three WRKY cDNAs from the petal of Osmanthus fragrans . One of them, OfWRKY3, encodes a protein containing two WRKY domains and two zinc finger motifs. OfWRKY3 and OfCCD4 had nearly identical expression profile in petals of ‘Dangui’ and ‘Yingui’ at different flowering stages and showed similar expression patterns in petals treated by salicylic acid, jasmonic acid and abscisic acid. Activation of OfCCD4 pro :GUS by OfWRKY3 was detected in coinfiltrated tobacco leaves and very weak GUS activity was detected in control tissues, indicating that OfWRKY3 can interact with the OfCCD4 promoter. Yeast one-hybrid and electrophoretic mobility shift assay showed that OfWRKY3 was able to bind to the W-box palindrome motif present in the OfCCD4 promoter. These results suggest that OfWRKY3 is a positive regulator of the OfCCD4 gene, and might partly account for the biosynthesis of β-ionone in sweet osmanthus.

Background One important metabolic engineering strategy is to localize the enzymes close to their substrates for improved catalytic efficiency. However, localization configurations become more complex the greater the number of enzymes and substrates is involved. Indeed, optimizing synthetic pathways by localizing multiple enzymes remains a challenge. Terpenes are one of the most valuable and abundant natural product groups. Phytoene, lycopene and β-carotene serve as common intermediates for the synthesis of many carotenoids and derivative compounds, which are hydrophobic long-chain terpenoids, insoluble in water and usually accumulate in membrane compartments. Results While β-ionone synthesis by β-carotene cleavage dioxygenase PhCCD1 and astaxanthin synthesis by β-carotene ketolase (CrtW) and β-carotene hydroxylase (CrtZ) differ in complexity (single and multiple step pathways), the productivity of both pathways benefited from controlling enzyme localization to the E. coli cell membrane via a GlpF protein fusion. Especially, the astaxanthin synthesis pathway comprises both CrtW and CrtZ, which perform four interchangeable reactions initiated from β-carotene. Up to four localization strategies of CrtW and CrtZ were exhaustively discussed in this work, and the optimal positioning strategy was achieved. CrtW and CrtZ were linked using a flexible linker and localized to the membrane via a GlpF protein fusion. Enzymes in the optimal localization configuration allowed a 215.4% astaxanthin production increase. Conclusions This work exploits a localization situation involving membrane-bound substrates, intermediates and multiple enzymes for the first time, and provides a workable positioning strategy to solve problems in similar circumstances.

Nutritional antioxidants derived from phytochemicals have been shown to have multifaceted health benefits via the pleiotropic molecular mechanisms. Lycopene is one such aliphatic hydrocarbon carotenoid with no beta-ionone and imparts red coloration to watermelon, tomatoes, and papayas. It is a potent antioxidant and free radical scavenger owing to the presence of 13 carbon–carbon double bonds, out of which 11 are conjugated and the remaining 2 are non-conjugated. It has many biological effects on different types of cancers like prostate, breast, skin, and oral cancer by targeting the Keap1-NF-kB, Keap1-Nrf 2 and PI3K/AKT/m-TOR signalling pathway. In addition to cancer, lycopene also has the ability to modify the gut microbiome, and also work against SARS-CoV-2. This review focuses on the sources, isomers, metabolites, therapeutic targets, mechanistic action, nanoformulations, pharmacokinetics, completed and ongoing clinical trials. In addition to above we are adding the potential ability of lycopene in obesity, infertility, metabolic disorder, gut microbiome, and COVID-19 treatment.

The carotenoids are the most widely distributed secondary metabolites in plants and can be degraded by carotenoid cleavage dioxygenase (CCD) to form apocarotenoids including an important C13 compound beta-ionone. Volatile beta-ionone can confer the violet and woody fragrance to plant essential oils, flowers, fruits, and vegetables, which therefore has been used in various industries. Dendrobium officinale is a traditional medicinal plant. However, there was limited information on the key enzymes involved in the biosynthesis of beta-ionone in D. officinale . In the present study, beta-ionone was detected in stems and leaves of D. officinale and genome-wide identification and expression profiles of CCD genes were subsequently carried out. There were nine DoCCD members in D. officinale . According to the phylogenetic relationship, DoCCD proteins were classified into six subfamilies including CCD1, CCD4, CCD7, CCD8, nine-cis-epoxycarotenoid dioxygenase (NCED) and zaxinone synthase (ZAS). DoCCD genes showed distinctive expression profiles and DoCCD1 gene was abundantly expressed in eight tissues. Induced expression of DoCCD1 gene resulted in discoloration of Escerichia coli strains that can accumulate carotenoids. Analysis of Gas Chromatography/Mass Spectrometer showed that DoCCD1 enzyme can cleave lycopene to produce 6-methyl-5-hepten-2-one and pseudoionone and also catalyze beta-carotene to form beta-ionone. Expression of DoCCD1 gene in Nicotiana benthamiana leaf resulted in production of abundant beta-ionone. Overall, the present study first provides valuable information on the CCD gene family in D. officinale , function of DoCCD1 gene as well as production of beta-ionone through genetic modification.

In plants, the oxidative cleavage of carotenoid substrates produces volatile apocarotenoids, including α-ionone, β-ionone, and dihydro-β-ionone, compounds that are important in herbivore-plant communication. For example, β-ionone is part of an induced defense in canola, Brassica napus, and is released following wounding by herbivores. The objectives of the research were to evaluate whether these volatile compounds would: 1) be released in higher quantities from plants through the over-expression of the carotenoid cleavage dioxygenase1 (CCD1) gene and 2) cause herbivores to be repelled or attracted to over-expressing plants relative to the wild-type. In vivo dynamic headspace collection of volatiles coupled with gas chromatography–mass spectrometry was used to determine volatile organic compounds (VOC) in the headspace of the Arabidopsis thaliana ecotype Columbia-0 (L.) over-expressing the AtCCD1 gene. The analytical method allowed the detection of β-ionone in the Arabidopsis headspace where emission rates ranged between 2 and 5-fold higher compared to the wild type, thus corroborating the in vivo enhancement of gene expression. A two chamber choice test between wild type and AtCCD1 plants revealed that crucifer flea beetle Phyllotreta cruciferae (Goeze) adults were repelled by the AtCCD1 plants with the highest transcription and β-ionone levels. α-Ionone and dihydro-β-ionone were not found in the headspace analysis, but solutions of the three compounds were tested in the concentration range of β-ionone found in the Arabidopsis headspace (0.05 to 0.5 ng/μl) in order to assess their biological activity with crucifer flea beetle, two spotted spider mite Tetranychus urticae (Koch), and silverleaf whiteflies Bemisia tabaci (Gennadius). Choice bioassays demonstrated that β-ionone has a strong repellent effect toward both the flea beetle and the spider mite, and significant oviposition deterrence to whiteflies. In contrast, dihydro-β-ionone had attractant properties, especially to the crucifer flea beetle, while α-ionone did not show any significant activity. These findings demonstrate how regulating genes of the carotenoid pathway can increase herbivore deterrent volatiles, a novel tool for insect pest management.

Strigolactones (SLs) are synthesized from all-trans-β-carotene via a pathway involving the b-carotene isomerase DWARF27, the carotenoid cleavage dioxygenases 7 and 8 (CCD7, CCD8), and cytochrome P450 enzymes from the 711 clade (MAX1 in Arabidopsis). The rice enzyme DWARF27 was shown to catalyze the reversible isomerization of all-trans-into 9-cis-β-carotene in vitro. b-carotene occurs in different cis-isomeric forms, and plants accumulate other carotenoids, which may be substrates of DWARF27. Here, we investigated the stereo and substrate specificity of the rice enzyme DWARF27 in carotenoid-accumulating E. coli strains and in in vitro assays performed with heterologously expressed and purified enzyme. Our results suggest that OsDWARF27 is strictly double bond-specific, solely targeting the C9–C10 double bond. OsDWARF27 did not introduce a 9-cis-double bond in 13-cis- or 15-cis-b-carotene. Substrates isomerized by OsDWARF27 are bicyclic carotenoids, including β-, α-acarotene and β,β-cryptoxanthin, that contain at least one unsubstituted β-ionone ring. Accordingly, OsDWARF27 did not produce the abscisic acid precursors 9-cis-violaxanthin or -neoxanthin from the corresponding all-trans-isomers, excluding a direct role in the formation of this carotenoid derived hormone. The conversion of all-trans-α- carotene yielded two different isomers, including 9´-cis-α- carotene that might be the precursor of strigolactones with an ε-ionone ring, such as the recently identified heliolactone.

Odorant binding proteins (OBPs) of insects play a critical role in chemical perceptions and choice of insect host plant. Bemisia tabaci is a notorious insect pest which can damage more than 600 plant species. In order to explore functions of OBPs in B. tabaci, here we investigated binding characteristics and function of odorant-binding protein 3 in B. tabaci (BtabOBP3).The results indicated that BtabOBP3 shows highly similar sequence with OBPs of other insects, including the typical signature motif of six cysteines.The recombinant BtabOBP3 protein was obtained, and the evaluation of binding affinities to tested volatiles of host plant was conducted, then the results indicated that β-ionone had significantly higher binding to BtabOBP3 among other tested plant volatiles. Furthermore, silencing of BtabOBP3 significantly altered choice behavior of B. tabaci to β-ionone. In conclusion, it has been demonstrated that BtabOBP3 exerts function as one carrier of β-ionone and the results could be contributed to reveal the mechanisms of choosing host plant in B. tabaci.