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Genomic mechanism of aroma terpenoids biosynthesis in plants.

BACKGROUND: Aroma terpenoids are crucial plant secondary metabolites with physiological and commercial importance. Interestingly, both closely and distantly related species can synthesize identical aroma terpenoids. With the development of genome sequencing technology, it has become possible to elucidate the genomic mechanism underlying this phenomenon. AIM: This review highlights whole-genome data as a robust strategy for investigating the genomic mechanism of aroma terpenoids biosynthesis in plants, and provides new perspectives on the origin, evolution, and engineering of terpene synthases (TPSs). This aims to significantly benefit plant breeding and enhance suitability for industrial production. KEY SCIENTIFIC CONCEPTS OF REVIEW: Genomic mechanism of aroma terpenoids biosynthesis in plant genomes is the genetic and evolutionary dynamics. We elaborate the genomic mechanism governing the biosynthesis of plant-derived aroma terpenoids in three dimensions: (1) Genome-wide identification and phylogenetic analyses of TPSs. The same aroma terpenoids were produced by numerous plant species with chromosome-level genomes. Based on 34 plant genomes, we identified 1643 TPSs and classified them into seven subfamilies. (2) Functional and structural basis of TPSs. We found that TPSs with identical functions in distant species exhibit low sequence similarity but conserved active cavity architectures. Conversely, functionally distinct TPSs in closely related species cluster phylogenetically but differ in active cavity structures. (3) Patterns of TPS gene origination. Comparative genomic analyses within and between species revealed three patterns enabling TPSs to acquire the same functions: tandem duplications, dispersed duplications, and genes without duplication.

Terpenes

Gas-liquid chromatography of carotenoids and other terpenoids.

The retention behaviour of over seventy terpenoids on three silicone polymer liquid phases under both isothermal and temperature-programmed conditions is reported. Terpenoids with conjugated unsaturation (e.g., carotenoids) were hydrogenated prior to analysis in order to prevent thermal decomposition. Analyses of the acetates and TMS ethers of both the natural hydroxycarotenoids and their perhydroderivatives are also reported. In addition, a system is described for the routine analysis of terpenols, including those whose pyrophosphates are intermediates in sterol and carotenoid biosynthesis.

Acetylation

Divergent Lineage of Terpene Synthases Establishes Terpenoid Biosynthesis in Brown Macroalgae.

Brown algae of the order Dictyotales uniquely stand out among stramenopiles (heterokonts) as prolific producers of bioactive terpenoid molecules associated with chemical defense and antifouling. Although more than 200 sesquiterpenoids and diterpenoids have been reported, largely from the genera of Dictyota and Dictyopteris, their biosynthetic origin has remained unknown for decades. Leveraging de novo genome and transcriptome sequencing in the nonmodel alga Dictyota coriacea, we identified a brown algal-specific lineage of type I terpene synthases (TSs) that harbors novel catalytic motifs distinct from those characterized in plants, microbes, red algae, and metazoans. Across three brown algal species, we characterized 15 terpene synthases, including DcTS-2, which produces the diterpene alcohol dilophol, a proposed biosynthetic intermediate to the antifouling metabolite pachydictyol A. X-ray crystal structures of the monoterpene synthase DcTS-3 further revealed that the brown algal enzymes retain the canonical terpene synthase fold, and together with mutagenesis studies, suggest the catalytic role of the novel motifs defining this newly established evolutionary lineage. Brown algal terpene synthases separate into two subgroups, with mono- and diTSs containing putative chloroplast-targeting sequences while sesquiTSs lack them, suggesting convergent compartmentalization of terpene biosynthesis with land plants. Together, these findings establish the molecular basis of terpenoid biosynthesis in brown algae and highlight the challenges of adapting established biosynthetic logic to nonmodel marine algae.

Alkyl and Aryl Transferases

A multifunctional sesquiterpene synthase integrates with cytochrome P450s to reinforce the terpenoid defense network in maize.

Terpenoids, the largest and most structurally diverse class of plant natural products, play essential roles in maize defense and ecological interactions. In this study, we identified and functionally characterized a sesquiterpenoid-based defense pathway in maize centered on α-santalenoic acid, a pathogen-inducible sesquiterpenoid antibiotic. Using a combination of metabolite-based genome-wide association studies (mGWAS), linkage mapping, and heterologous expression assays, we identified ZmTPS9 as a multiproduct terpene synthase that primarily produces α-santalene and β-bisabolene. Sequence analysis and site-directed mutagenesis revealed that threonine at position 413 is critical for enzyme activity, with its deletion resulting in a complete loss of enzyme activity. The sesquiterpene hydrocarbons produced by ZmTPS9 are further oxidized by three cytochrome P450 monooxygenases, ZmCYP71Z16, ZmCYP71Z18, and ZmCYP71Z19, to yield antimicrobial metabolites including α-santalenoic acid, zealexin D1 (ZD1), and zealexin D2 (ZD2). Together, these findings demonstrate a convergent biosynthetic strategy in maize, where multiproduct terpene synthases and promiscuous P450s collaboratively generate a flexible and robust terpenoid defense network.

Zea mays

Terpenoid cyclases: design and function of electrophilic catalysts.

Terpenoid cyclases catalyse the cyclization of the universal acyclic precursors geranyl and farnesyl diphosphate to monoterpenes and sesquiterpenes, respectively. All such cyclases investigated to date are operationally soluble, moderately lipophilic proteins of relative molecular weight 40,000-100,000, requiring no cofactors other than a divalent metal, usually Mg2+ and occasionally Mn2+. The focus of most work has been on the mechanisms of the cyclization reactions themselves. It is currently proposed that the cyclase binds the acyclic substrate in a suitable conformation and initiates the cyclization by ionization of the labile allylic diphosphate moiety. The use of stereospecifically labelled substrates and analysis of the sites of labelling in the derived cyclization products has allowed the proposal of detailed cyclization mechanisms. Further insight into the architecture and function of the cyclase active site has come from the study of substrate and intermediate analogues designed to act as potential inhibitors or anomalous substrates of the normal cyclization reaction. Progress has also been made on the cloning of the relevant structural genes for sesquiterpene cyclases. This has led to new insights into the basic requirements for cyclase catalysis and specificity.

Amino Acid Sequence

Gene flow versus selection pressure and ancestral differentiation in the composition of species: analysis of population variation of Juniperus ashei Buch. using terpenoid data.

Twenty-four populations of Juniperus ashei were sampled throughout the range of this taxon and the terpenoids of the foliage were analyzed by gas/liquid chromatography. Population differentiation was investigated by analysis of variance and numerical taxonomy. Three south Texas and one Mexican population clustered together with the rest of the taxon appearing fairly uniform. No evidence was found of hybridization or introgression with other taxa. Disjunct populations in Oklahoma and the Ozarks, which have been genetically isolated from the central population for thousands of years, showed no signs of differentiation nor genetic drift. The present pattern of distribution probably dates from the Pleistocene. The south Texas and Mexican populations appear to be the primitive elements of the species. Populational differences have apparently been maintained in adjacent populations in spite of seemingly large gene flow and conversely, chemical uniformity is being maintained in many disjunct populations where there is little or no gene flow.

Biological Evolution

Gas chromatographic determination of neuphytadiene as a measure of the terpenoid contribution to experimental tobacco smoke carcinogenesis.

A method for the determination of neophytadiene in the total particulate matter of cigarette smoke was developed and applied to test its relationship to isoprene deliveries. Neophytadiene is suggested as a preferred measure of the contribution of terpenoids to experimental tobacco smoke carcinogenicity. Typical deliveries of neophytadiene are presented.

Carcinogens

[Terpenoids and curcuminoids of the rhizoma of Curcuma xanthorrhiza Roxb].

The fresh rhizomes of Curcuma xanthorrhiza Roxb. were investigated for terpenoids and curcuminoids. Nine sesquiterpenoids, alpha-curcumene (1), arturmerone (2), xanthorrhizol (3), germacrone (4), beta-curcumene (6), beta-sesquiphellandrene (9), curzerenone (10), alpha-turmerone (11) and beta-turmerone (12), and three curcuminoids, curcumin (7), mono-demethoxycurcumin (8) and bis-demethoxycurcumin (13), were isolated and one monoterpenoid, camphor (5), was identified by capillary GC-MS. Four species of C. xanthorrhiza could be classified into two chemotypes by their bisabolane-type sesquiterpenoid compositions. The first type contained large amounts of 2, 11 and 12 (CX I type). The second type contained large amounts of 1, 3 and 6, and none of 2, 9, 11 and 12 (CX II type). These two chemotypes, CX I type and CX II type, were compared with the two chemotypes of C. longa L., CL I type and CL II type, on their contents by capillary GC and HPLC analysis. It was found that all of them contained curcuminoids, 7, 8 and 13 and large amounts of various bisabolane-type sesquiterpenoids.

Chromatography, Gas

[Successes in studying the physiological activity of terpenoids and steroids].

Data concerning the structure and function of prenyl proteins and peptides of fungi and animals are reviewed. There exist proteins that are posttranslationally modified by thioether-linked farnesyl- or geranylgeranyl groups; the modification affects the cysteine residue near the C-terminus. Prenylation increases hydrophobicity and is expected to promote protein binding to membrane lipids or other hydrophobic proteins. Isopentenyl-adenylated proteins mediate isoprenoid control over DNA synthesis and are involved in regulation of cell proliferation in animals. Sterols of fungi and plants play a role in regulation of the membrane structure as well as in proliferation. The significance biologically active terpenoids for biotechnology, medicine, and agriculture is discussed.

Animals

Whole-Genome Sequence Dataset of Rhodococcus qingshengii IEGM 267-Terpenoid Biotransformer Toward Genetic Functional Annotation.

Background/Objectives: Microbial biotransformation of monoterpenoids is a promising approach for obtaining bioactive compounds. Rhodococcus species are attractive biocatalysts due to their metabolic versatility and ability to transform hydrophobic substrates. In this study, we investigated the catalytic potential of Rhodococcus qingshengii IEGM 267 toward carveol isomers and explored genomic features that may underlie this activity. Methods: The strain was cultivated in mineral medium supplemented with (-)-trans-carveol. Biotransformation products were analyzed by TLC and GC-MS. The draft genome was sequenced, assembled, taxonomically assigned, and annotated using standard bioinformatics tools. Results: Rhodococcus qingshengii IEGM 267 efficiently converted (-)-trans-carveol to carvone. Genome analysis confirmed the taxonomic assignment of the strain and revealed a large repertoire of oxidoreductases, including monooxygenases, hydroxylases, and dehydrogenases. Seven genes encoding cytochrome P450-dependent oxygenases were identified as candidate enzymes potentially involved in carveol oxidation. Conclusions: R. qingshengii IEGM 267 is an efficient and stereoselective biocatalyst for (-)-trans-carveol oxidation. The results of bioinformatics analysis suggest an alternative enzymatic basis for this transformation and provide a foundation for future functional characterization.

Rhodococcus

Terpenoid biotransformation in mammals. II: Biotransformation of dl-camphene in rabbits.

The biotransformation of dl-camphene in rabbits was investigated. Four neutral metabolites, 6-exo-hydroxycamphene, 10-hydroxycamphene, and diastereoisomers of camphene-2,10-glycol, were identified and two alcohols, 7-hydroxycamphene and 3-hydroxytricyclene, were estimated by IR, UV, NMR, and mass spectra and chemical degradations. The formation of these compounds can be explained through a homoallylic oxidation or an epoxide formation.

Animals