Influence of gibberellin and daminozide on the expression of terpene synthases and on monoterpenes in common sage (Salvia officinalis)

Plant In Vitro Cultures of Coleus scutellarioides (L.) Benth. "Electric Lime" and Possibilities of Modification in the Biosynthesis of Volatile Compounds

Coleus scutellarioides (L.) Benth. is a globally spread species, known for its characteristic spectacularly colorful leaves of decorative value. Thanks to its rich chemical composition, the plant is used in ethnopharmacology, and it is also regarded as having high medicinal potential. The application of in vitro cultures enables the acquisition of homogeneous certified material of high quality. Additionally, excluding the effect of biotic and abiotic factors on the plants is a way to fully recognize the influence of phytohormones on the plant morphology and the biosynthetic pathways of compound production. The best way to grow C. scutellarioides "Electric Lime" under in vitro conditions is to use the basic MS medium (Murashige and Skoog medium), enriched with naphthyl-1-acetic acid at a concentration of 0.5 mg dm-3. The analysis of volatile compounds demonstrated that the content of volatile compounds in the plants cultivated under in vivo conditions was expressed at a level of 2848.59 µg g-1, whereas in the plants bred in vitro without supplementation with phytohormones, the level was 8191.47 µg g-1. The highest content was noted for copaene, α-pinene, 1-octene-3-ol, α-selinene, sabinen, γ- and δ-cadinene, 3-octanol, and β-pinene. Aroma profiling revealed a lack of boranyl acetate, 2-hexenal, and 2-hexen-1-ol in the plants cultivated under in vivo conditions. Differences were found in the volatile composition between plants bred in vivo and in vitro, with the most significant recorded for the contents of 1-octen-3-ol and 3-octanol. The addition of plant growth regulators into the basic medium under in vitro conditions affected the percentage ratio and contents of specific compounds in plant tissues. The most intense biosynthesis of volatile compounds took place in the plants cultivated on the medium enriched with NAA at 10,579.11 µg g-1, whereas the least intense was noted for plants cultivated on the medium supplemented with BA, where it was recorded at the level of 5610.02 µg g-1. So far, there has been no research published which would pertain to the profiling of volatile compounds performed using the SPME (solid-phase microextraction) technique. Moreover, the very few studies conducted on the chemical composition of these compounds do not mention the specific variety of C. scutellarioides under analysis.

Physiological, Proteomic, and Resin Yield-Related Genes Expression Analysis Provides Insights into the Mechanisms Regulating Resin Yield in Masson Pine

Masson pine (Pinus massoniana Lamb.) is an important resin-producing conifer species in China. Resin yield is a highly heritable trait and varies greatly among different genotypes. However, the mechanisms regulating the resin yield of masson pine remain largely unknown. In this study, physiological, proteomic, and gene expression analysis was performed on xylem tissues of masson pine with high and low resin yield. Physiological investigation showed that the activity of terpene synthase, as well as the contents of soluble sugar, jasmonic acid (JA), methyl jasmonate (MeJA), gibberellins (GA1, GA4, GA9, GA19, and GA20), indole-3-acetic acid (IAA), and abscisic acid (ABA) were significantly increased in the high yielder, whereas sucrose and salicylic acid (SA) were significantly decreased compared with the low one. A total of 2984 differentially expressed proteins (DEPs) were identified in four groups, which were mainly enriched in the biosynthesis of secondary metabolites, protein processing in the endoplasmic reticulum, carbohydrate metabolism, phytohormone biosynthesis, glutathione metabolism, and plant-pathogen interaction. Integrated physiological and proteomic analysis revealed that carbohydrate metabolism, terpenoid biosynthesis, resistance to stress, as well as JA and GA biosynthesis and signaling, play key roles in regulating resin yield. A series of proteins associated with resin yield, e.g., terpene synthase proteins (TPSs), ATP-binding cassette transporters (ABCs), glutathione S-transferase proteins (GSTs), and heat shock proteins (HSPs), were identified. Resin yield-related gene expression was also associated with resin yield. Our study unveils the implicated molecular mechanisms regulating resin yield and is of pivotal significance to breeding strategies of high resin-yielding masson pine cultivars.

Changes in Metabolite Profiling and Expression Levels of Key Genes Involved in the Terpenoid Biosynthesis Pathway in Garden Sage (Salvia officinalis) under the Effect of Hydrazine Hydrate

Mutagenesis is a highly efficient tool for establishing genetic variation and is widely used for genetic enhancement in various plants. The key benefit of mutation breeding is the prospect of enhancing one or several characteristics of a variety without altering the genetic background. In this study, we exposed the seeds of Salvia officinalis to four concentrations of hydrazine hydrate (HZ), i.e., (0%, 0.1%, 0.2%, and 0.3%) for 6 h. The contents of terpenoid compounds in the S. officinalis plantlets driven from the HZ-treated seeds were determined by GC-MS, which resulted in the identification of a total of 340 phytochemical compounds; 163 (87.48%), 145 (84.49%), 65 (97.45%), and 62 (98.32%), from the four concentrations of HZ (0%, 0.1%, 0.2%, and 0.3%), respectively. Furthermore, we used the qRT-PCR system to disclose the "transcriptional control" for twelve TPS genes related to terpenoid and terpene biosynthesis, namely, SoGPS, SoMYRS, SoNEOD, SoCINS, SoSABS, SoLINS, SoFPPS, SoHUMS, SoTPS6, SoSQUS, SoGGPS, and SoGA2. Altogether, results are likely to ensure some positive relationship between the concentrations of the chemical mutagen HZ used for treating the seeds, the type and amount of the produced terpenes, and the expression of their corresponding genes.

Monoterpene synthases of three closely related sage species (Salvia officinalis, S. fruticosa and S. pomifera, Lamiaceae)

The diversity of plant monoterpenes is largely based on the catalytic activity of monoterpene synthases. Additionally, copy number variation of monoterpene synthase genes may contribute to the quantity of transcripts and hence to the essential oil profile. This study used whole-genome sequencing and digital PCR for the measurement of copy number variation and quantification of gene expression in three closely related Salvia species, namely Salvia officinalis, Salvia pomifera and Salvia fruticosa. Twelve, 13 and 15 monoterpene synthase-encoding open-reading frames were predicted for Salvia officinalis, Salvia pomifera and Salvia fruticosa, respectively. In Salvia officinalis, one of the open reading frames was disrupted indicating a pseudogene. Monoterpene synthase genes were generally single copy per haploid genome, only a few were double or triple copy genes. Expression levels of monoterpene synthases in leaves corresponded generally well with essential oil composition. In some cases, a higher expression level of a certain monoterpene synthase could be explained by its duplication or triplication. The very high content of thujones in Salvia pomifera, for example, was accompanied by gene duplication and increased gene expression of (+)-sabinene synthase responsible for the thujone precursor sabinene. In Salvia officinalis, three individuals different in their essential oil profile showed significant differences in their monoterpene synthase expression levels corresponding roughly to the profile of the essential oils. Transcript expression of monoterpene synthase genes were measured in leaf, calyx and corolla. The corolla differed significantly from leaves, while calyces usually showed a profile intermediary between leaf and corolla.

Harvest time explains substantially more variance in yield, essential oil and quality performances of Salvia officinalis than irrigation and putrescine application

Elicitors, irrigation regimes and harvest times influence the content, yield and compound of the essential oil (EO) in Salvia officinalis (sage), through changes in biomass dynamics and biosynthetic pathways. A two-year field experiment was conducted to determine if foliar application of putrescine under optimum and deficit stress conditions would favorably affect EO yield, content and profile of sage harvested in spring and summer. The response of dry weight, EO yield and content, myrcene and borneol concentrations to irrigation regime and putrescine concentration can be expressed by a quadratic model. The maximum dry weight (182.63 g m-2) and EO yield (1.68 g m-2) were predicted under irrigation regimes of 9.06% and 27.75% available soil water depletion (ASWD), respectively. The highest EO content (1.05%) was predicted under 3.04 mM of putrescine. Based on results obtained from GC/MS analyses, 25 compounds (mostly monoterpenes) were identified in the EO of sage. Among EO compounds, α-thujone (54.08%), 1, 8-cineole (17.87%), pinocarvone (14.30%), β-thujone (7.97%) and camphor (8.76%) in turn were the most abundant. The concentration of myrcene was higher in spring than summer under the irrigation regimes of 60% and 80% ASWD. The myrcene concentration reached its maximum (4.53%) under the irrigation regime of 86.5% ASWD. The irrigation regimes of 48.03% and 45.6% ASWD caused the highest borneol concentrations of 1.47% and 1.41% by application of 1.5 mM and 2.25 mM putrescine, respectively. All treatments tested on sage, particularly harvest time, can play an important role in the improvement of EO quality and quantity. Averaged over both years, the irrigation regime of nearly 30% ASWD resulted in the highest EO yield harvested with greater quantity and better quality in summer. The EO content and quality changed slightly with the application of putrescine, without significant effect on yield.

Dynamic regulation of volatile terpenoid production and emission from Chrysanthemum morifolium capitula

Flower-associated communities consist of both mutualistic and antagonistic organisms. We have limited knowledge on how flowers regulate volatiles to balance their defense against antagonists and the attraction of beneficial organisms necessary for reproductive success. Asteraceae is the largest family among flowering plants. Its representatives are characterized by unique inflorescence called capitulum, which has been reduced to a reproduction unit resembling a single flower. Here, we chose Chrysanthemum morifolium, a model species of Asteraceae, to investigate how the capitulum balances the accumulation and emission of floral terpenoid volatiles that are implicated in defense and pollinator attraction, respectively. Our results showed that the capitula of C. morifolium produce and emit complex mixtures of monoterpenoids and sesquiterpenoids. The highest concentrations of terpenoids were detected in the bud stage of the capitula. In contrast, the capitulum reached the highest emission level prior to full blooming. The disc florets were the dominant organs of terpenoid accumulation and emission in the full-openness stage. To understand the molecular basis of volatile terpenoid biosynthesis in C. morifolium, experiments were designed to study terpene synthase (TPS) genes, which are pivotal for terpene biosynthesis. Eight CmCJTPS genes were identified in the transcriptomes of C. morifolium, and the proteins encoded by five genes were found to be biochemically functional. CmCJTPS5 and CmCJTPS8 were the multi-product enzymes catalyzing the monoterpenoid and sesquiterpenoid formation, which closely matched the major terpenoids produced in the flower heads. The five functional terpene synthase genes exhibited similar temporal expression patterns but diverse spatial expression levels, suggesting tissue-specific functions. Altogether, our results illustrate the dynamic patterns of accumulation and emission of floral volatile terpenoids implicated in defense and attracting pollinators in C. morifolium, for which both the regulation of TPS gene expression and the regulation of release may play critical roles.

The Effect of Daminozide, Dark/Light Schedule and Copper Sulphate in Tissue Culture of Triticum timopheevii

Triticum timopheevii Zhuk. is a tetraploid wheat that is utilized worldwide as a valuable breeding source for wheat improvement. Gene-based biotechnologies can contribute to this field; however, T. timopheevii exhibits recalcitrance and albinism in tissue cultures, making this species of little use for manipulation through genetic engineering and genome editing. This study tested various approaches to increasing in vitro somatic embryogenesis and plant regeneration, while reducing the portion of albinos in cultures derived from immature embryos (IEs) of T. timopheevii. They included (i) adjusting the balance between 2,4-D and daminozide in callus induction medium; (ii) cultivation using various darkness/illumination schedules; and (iii) inclusion of additional concentrations of copper ions in the tissue culture medium. We achieved a 2.5-fold increase in somatic embryogenesis (up to 80%) when 50 mg L-1 daminozide was included in the callus induction medium together with 3 mg L-1 2,4-D. It was found that the dark cultivation for 20-30 days was superior in terms of achieving maximum culture efficiency; moreover, switching to light in under 2 weeks from culture initiation significantly increased the number of albino plants, suppressed somatic embryogenesis, and decreased the regeneration of green plants. Media containing higher levels of copper ions did not have a positive effect on the regeneration of green plants; contrarily, the elevated concentrations caused albinism in plantlets. The results and relevant conclusions of the present study might be valuable for establishing an improved protocol for the regeneration of green plants in tissue cultures of T. timopheevii.

Improving water deficit tolerance of Salvia officinalis L. using putrescine

To study the effects of foliar application of putrescine (distilled water (0), 0.75, 1.5, and 2.25 mM) and water deficit stress (20%, 40%, 60%, and 80% available soil water depletion (ASWD)) on the physiological, biochemical, and molecular attributes of Salvia officinalis L., a factorial experiment was performed in a completely randomized design with three replications in the growth chamber. The results of Real-Time quantitative polymerase chain reaction (qRT-PCR) analysis showed that putrescine concentration, irrigation regime, and the two-way interaction between irrigation regime and putrescine concentration significantly influenced cineole synthase (CS), sabinene synthase (SS), and bornyl diphosphate synthase (BPPS) relative expression. The highest concentration of 1,8-cineole, camphor, α-thujone, β-thujone, CS, SS, and BPPS were obtained in the irrigation regime of 80% ASWD with the application of 0.75 mM putrescine. There was high correlation between expression levels of the main monoterpenes synthase and the concentration of main monoterpenes. The observed correlation between the two enzyme activities of ascorbate peroxidase (APX) and catalase (CAT) strongly suggests they have coordinated action. On the other hand, the highest peroxidase (PO) and superoxide dismutase (SOD) concentrations were obtained with the application of 0.75 mM putrescine under the irrigation regime of 40% ASWD. Putrescine showed a significant increase in LAI and RWC under water deficit stress. There was an increasing trend in endogenous putrescine when putrescine concentration was increased in all irrigation regimes. Overall, the results suggest that putrescine may act directly as a stress-protecting compound and reduced H₂O₂ to moderate the capacity of the antioxidative system, maintain the membrane stability, and increase secondary metabolites under water deficit stress.

Water deficit stress responses of monoterpenes and sesquiterpenes in different Iranian cultivars of basil

Ocimum basilicum, a popular aromatic plant, contains aromatic terpenes of terpenoids with in vivo and in vitro verified cytotoxicity. Considering the characteristics and potential of its utilization, it would be attractive to reveal its regulation and biosynthesis, originally at the molecular level under water deficit stress. For this aim, for the first time, the gene encoding the enzyme involved in the end step of the MEP biosynthetic pathways (HDR) was cloned, and the accumulation ratio of linalool, germacrene D and γ-cadinene compounds as well as the expression trait of four critical genes (i.e., HDR, LinS, GerS, and GadS) was assessed under water deficit stress in three Iranian cultivars of basil. The highest value of linalool and γ-cadinene were detected for Cultivar 1 (Cult. 1) under mild stress (W1; 52.6 and 21.1%), while insignificant amounts were obtained for Cultivar 3 (Cult. 3). The germacrene D level of Cultivar 2 (Cult. 2) increased under severe and moderate water stresses as compared with mild water deficit stress. Apart from some expectation, all the studied genes demonstrated divergent transcription ratios under water deficit stress. Principal component analyses (PCA) showed that the relative water content (RWC) and HDR gene expression correlated significantly with essential oil components and gene expression in Cult. 1 and 2, which could represent an elevated demand for corresponding metabolites in the plant tissues. The present work elaborates on the regulation of the mentioned genes, and the results indicate that the production of terpenoids might be a drought stress-dependent and cultivar-dependent procedure.

Concentration-dependent emission of floral scent terpenoids from diverse cultivars of Chrysanthemum morifolium and their wild relatives

Floral scent is an important trait that has a significant influence on the reproduction of many flowering plants and the market value of several ornamental crops. The family of Asteraceae is well known for its unique floral structure (capitulum) that consists of many florets. Although the constituents of either floral essential oils or emitted floral volatiles have been reported in many species of Asteraceae, little information is available on the mechanisms that determine floral volatile emission. In the present study, a total of 44 species/varieties of Chrysanthemum were analyzed to determine the relationship between the internal accumulation of floral terpenoids and their release as volatiles. By performing both headspace collection and organic extraction, it has been found that the emission rates of floral terpenoids are largely correlated to their internal concentrations. Particularly, the flowers of cultivated C. morifolium, when compared to their wild relatives, were found to exhibit lower emission rates that contain lowered concentrations of floral terpenoids. The differences were largely determined by six monoterpenes and five sesquiterpenes that were revealed by principal component analysis. Besides, the relationship between concentrations and emission rates of floral terpenoids as well as the sizes of capitulum was studied in detail. Separated into three different parts, disc florets were found to have a larger contribution to floral volatile emission than ray florets, whereas the phyllaries and receptacles are the main parts of volatiles accumulation. Finally, the potential biosynthetic pathway of the floral terpenoids produced in capitula of Chrysanthemum was proposed. In summary, our findings on the diversity and variations of floral terpenoids in Chrysanthemum reveal correlations between their production and emission. These findings can be useful to develop different plant breeding methods to create novel aromatic cultivars of Chrysanthemum.

Integrated transcriptomic and metabolomic analyses reveal regulation of terpene biosynthesis in the stems of Sindora glabra

Sesquiterpenes are important defensive secondary metabolites that are synthesized in various plant organs. Methyl jasmonate (MeJA) plays a key role in plant defense responses and secondary metabolism. Sindora glabra Merr. ex de Wit produces abundant sesquiterpenes in its trunks, and was subjected to investigation after MeJA treatment in order to characterize the molecular mechanisms underlying the regulation of sesquiterpene biosynthesis in plant stems and further our understanding of oleoresin production in trees. A total of 14 types of sesquiterpenes in the stems of mature S. glabra trees were identified. The levels of two sesquiterpenes, α-copaene and β-caryophyllene, significantly increased after MeJA treatment. Differentially expressed genes involved in terpenoid backbone biosynthesis were significantly enriched over time, while the expression of JAZ genes involved in the jasmonic acid signaling pathway and TGA genes involved in the salicylic acid signaling pathway was significantly enriched at later time points after treatment. Two new terpene synthase genes, SgSTPS4 and SgSTPS5, were also identified. Following MeJA treatment, the expression levels of SgSTPS1, SgSTPS2 and SgSTPS4 decreased, while SgSTPS5 expression increased. The major enzymatic products of SgSTPS4 were identified as β-elemene and cyperene, while SgSTPS5 was identified as a bifunctional mono/sesquiterpene synthase that could catalyze farnesyl pyrophosphate to produce nine types of sesquiterpenes, including α-copaene and β-caryophyllene, while SgSTPS5 could also use geranyl pyrophosphate to produce geraniol. Dramatic changes in the amounts of α-copaene and β-caryophyllene in response to MeJA were correlated with transcriptional expression changes of SgSTPS5 in the wood tissues. In addition, the transcription factors MYB, NAC, ARF, WRKY, MYC, ERF and GRAS were co-expressed with terpene biosynthesis genes and might potentially regulate terpene biosynthesis. Metabolite changes were further investigated with UPLC-TOF/MS following MeJA treatment. These results contribute to the elucidation of the molecular mechanisms of terpene biosynthesis and regulation as well as to the identification of candidate genes involved in these processes.

The effects of water deficit on the expression of monoterpene synthases and essential oils composition in Salvia ecotypes

The medicinal sage plant (Salvia spp.), belonging to Lamiaceae family, is one of the most important medicinal and aromatic plants. The members of this genus are globally known due to its antimicrobial, antioxidant, astringent, spasmolytic, antihidrotic and specific sensorial properties. In this study, we investigated the potential impact of water deficit on transcript abundance, and essential oil composition of five major metabolites, i.e. 1-8 cineole, α-β-thujone, camphor, and borneol in three genotypes of Salvia spp. Results showed that relative expression of three genes and their corresponding metabolites increased together at three stages under drought condition, but the CS gene transcript decreased independently from 1,8-cineole in garden sage. Furthermore, borneol changed differently compared to the BS gene expression in control and drought treatment plants of S. reuterana (Yasuj). The competitive synthesis of ß-thujone, and α-thujone by SS gene were demonstrated in S. officinalis and Yasuj ecotype of S. reuterana; whereas, no change was observed for Urmia ecotype of S. reuterana. There was no precursor shortage to synthesis of borneol and camphor in garden sage; however increasing the BS led to high production of borneol and low camphor in S. reuterana under drought stress. As a mechanism, secondary metabolites enable the plants to cope with unfavorable conditions, but genetic differences might affect the quantity and quality of these compounds.

Biosynthetic pathways and metabolic engineering of spice flavors

Historically, spices have played an important economic role, due to their large applications and unique flavor. The supply and cost of spice materials and their corresponding natural products are often affected by environmental, geopolitical and climatic conditions. Secondary metabolite composition, including certain flavor compounds in spice plants, is recognized and considered closely related to plant classification. Both genes and enzymes involved in the biosynthesis of spice flavors are constantly identified, which provides insight into metabolic engineering of flavor compounds (i.e. aroma and pungent compounds) from spice plants. In this review, a systematic meta-analysis was carried out based on a comprehensive literature survey of the flavor profiles of 36 spice plants from nine families. We also reviewed typical biosynthetic pathways and metabolic engineering of most representative aroma and pungent compounds that may assist in the future study of spice plants as biosynthetic factories facing a new challenge in creating spice products.

Sequencing and variation of terpene synthase gene (TPS2) as the major gene in biosynthesis of thymol in different Thymus species

Thyme (Thymus spp.) is a valuable genus of Lamiaceae family with different pharmaceutical and food properties. Thymol has also been considered as the major essential oil compound in most of the studied Thymus species. In this research, the gene encoding γ-terpinene synthase (Ttps2) was sequenced in T. vulgaris and in eight Iranian thymes including T. carmanicus, T. daenensis, T. fedtschenkoi, T. kotschyanus, T. migricus, T. pubescens, T. serpyllum, and T. trautvetteri. Genetic relationships based on terpene synthase genes were also determined among the studied species. Rapid Amplification of cDNA Ends (RACE) PCR was done to complete the sequence of all species. The cDNA of the studied species possessed an open reading frame ranging from 1788 to 1794 bp that encode for a protein of 596-598 amino acids, presenting all the conserved motifs characteristics of monoterpene synthases. The taxonomic status of Thymus species was determined based on eight reported sections. The species were classified in three major groups. The first and second group comprised species of Micantes and Mastichina sections. The third cluster included the species belonging to Serpyllum and Pseudothymbra sections. Overall, phylogenetic analysis according to whole sequence of Ttps2 gene can help providing insights in respect to its evolutionary process. Finally, clustering based on the amount of main essential oils components (thymol and carvacrol) was compared with that based on Ttps2 gene classification in the studied Thymus species, showing that clustering is not always in accordance.

Regulation of endogenous phytohormones alters the fluoranthene content in Arabidopsis thaliana

Phytohormones are crucial endogenous modulators that regulate and integrate plant growth and responses to various environmental pollutants, including the uptake of pollutants into the plant. However, possible links between endogenous phytohormone pathways and pollutant accumulation are unclear. Here we describe the fluoranthene uptake, plant growth, and superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and glutathione S-transferase (GST) activities in relation to different endogenous phytohormones and different levels in Arabidopsis thaliana. Three phytohormone inhibitors-N-1-naphthyl-phthalamic acid (NPA), daminozide (DZ), and silver nitrate (SN)-were used to regulate endogenous auxin, gibberellin, and ethylene levels, respectively. Fluoranthene inhibited plant growth and root proliferation while increasing GST and SOD activity. The three inhibitors reduced fluoranthene levels in Arabidopsis by either affecting plant growth or modulating antioxidant enzyme activity. NPA reduced plant growth and increased CAT activity. SN promoted plant growth and increased POD and CAT activity, whereas DZ increased POD activity.

Biogenic Synthesis and Spatial Distribution of Endogenous Phytohormones and Ginsenosides Provide Insights on Their Intrinsic Relevance in Panax ginseng

Ginseng, the root and rhizome of Panax ginseng C. A. Mey., is a well-known and valuable traditional Chinese medicine. The pharmacological activities of ginseng are mainly attributed to the presence of ginsenosides, which are considered to be critical biomarkers for evaluating ginseng quality. The biosynthesis of triterpenes, which serve defensive functions in plants, is regulated by endogenous phytohormones that play key roles in growth and defense of plant populations. However, the role of major hormones that are closely related to secondary metabolism pathways in P. ginseng is poorly understood. To gain insight into their potential correlation, we performed a spatial synthesis analysis and studied the distribution of endogenous phytohormones and ginsenosides in different tissue regions of the entire P. ginseng plant. Gibberellins are growth hormones that accumulate in the fiber root. In contrast, abscisic acid (ABA), salicylic acid (SA), and jasmonic acid (JA), which are considered stress hormones, were predominantly found in the leaf and leaf peduncle. We observed a tissue-specific distribution of phytohormones consistent with the expression of genes involved in hormone biosynthesis that influenced ginsenoside synthesis and distribution. The aim of this study was to investigate the role of different endogenous phytohormones on triterpene metabolites in ginseng innate immunity.

De novo transcriptome sequencing and metabolite profiling analyses reveal the complex metabolic genes involved in the terpenoid biosynthesis in Blue Anise Sage (Salvia guaranitica L.)

Many terpenoid compounds have been extracted from different tissues of Salvia guaranitica. However, the molecular genetic basis of terpene biosynthesis pathways is virtually unknown. In this study, approximately 4 Gb of raw data were generated from the transcriptome of S. guaranitica leaves using Illumina HiSeq 2000 sequencing. After filtering and removing the adapter sequences from the raw data, the number of reads reached 32 million, comprising 186 million of high-quality nucleotide bases. A total of 61,400 unigenes were assembled de novo and annotated for establishing a valid database for studying terpenoid biosynthesis. We identified 267 unigenes that are putatively involved in terpenoid metabolism (including, 198 mevalonate and methyl-erythritol phosphate (MEP) pathways, terpenoid backbone biosynthesis genes and 69 terpene synthases genes). Moreover, three terpene synthase genes were studied for their functions in terpenoid biosynthesis by using transgenic Arabidopsis; most transgenic Arabidopsis plants expressing these terpene synthetic genes produced increased amounts of terpenoids compared with wild-type control. The combined data analyses from the transcriptome and metabolome provide new insights into our understanding of the complex metabolic genes in terpenoid-rich blue anise sage, and our study paves the way for the future metabolic engineering of the biosynthesis of useful terpene compounds in S. guaranitica.

The expression of monoterpene synthase genes and their respective end products are affected by gibberellic acid in Thymus vulgaris

Thymus vulgaris L. (Lamiaceae), a well-known aromatic medicinal herb, has many important essential constituents in its oil, including γ-terpinene, carvacrol, thymol, and p-cymene. Gibberellins comprise hundreds of components, which regulate several various growths and underlying developmental processes, such as cell division and elongation, shoot elongation, seed germination, and gene expression. In this study, we investigated the influence of sprayed gibberellic acid (GA₃) treatments on the internode length, leaf morphology, length of new shoot, expression of monoterpene synthase genes and monoterpenes content during two plant growth stages. Our results showed that increasing of internode length was a clear effect of GA₃ that was varied with internode position. The results also showed that all internodes displayed a dramatic increase in the highest concentration of GA₃. Also, the foliar application of GA₃ resulted in not only an increased expression level of monoterpene synthase genes, but also the improved production of a monoterpene, especially in the moderate concentration of GA₃ that they were up-regulated. In the lowest GA₃ concentrations, relative expression levels were similar or lower than the control plants and a notable downregulation in those genes was observed in the application of the highest concentration of GA₃ rather than the moderate concentrations. Overall, the expression of two out of five monoterpene synthase genes, TPS and CYP71D181, showed a correlation with the level of γ-terpinene and carvacrol, respectively, indicating that they are regulated at the transcriptional levels.

Comparative metabolomic responses to gibberellic acid and 6-benzylaminopurine in Cunila menthoides Benth. (Lamiaceae): a contribution to understand the metabolic pathways

Gibberellic acid elicited synthesis of many phenols from different classes and enhanced production of sesquiterpenoids, polyterpenoids, steroids and monoterpenoids compared to control and 6-benzylaminopurine. Little is known about the effects of 6-benzylaminopurine (BA) and gibberellic acid (GA3) on the synthesis of secondary metabolites in species of Lamiaceae. In this study, for the first time, the profile of secondary metabolites in plantlets of Cunila menthoides was characterized, using UPLC-ESI-Qq-oaTOF-MS. Ninety metabolites were identified, including polyphenols and terpenes. BA down-regulated most of the identified molecules in relation to GA3 and MS0 (control). The results showed that GA3 elicited synthesis of many phenols from different classes, and seemed to play a major role in the shikimate pathway in relation to BA. GA3 enhanced production of sesquiterpenoids, polyterpenoids, steroids and monoterpenoids compared to MS0 and BA, and also seemed to positively influence the MEP/DOXP and MVA pathways. These data show the most comprehensive metabolomic profile of Cunila menthoides to date, and the effects of BA and GA3 on the synthesis of secondary metabolites, modulating quantitative aspects of metabolism in Lamiaceae.

Daminozide reduces red color intensity in herbaceous peony (Paeonia lactiflora Pall.) flowers by inhibiting the expression of flavonoid biosynthetic genes

Daminozide is a plant growth retardant that inhibits 2-oxoglutarate-dependent dioxygenase activity in the gibberellin biosynthesis pathway, but few studies have focused on its effect on the flavonoid biosynthesis pathway involved in flower color. In the present study, the effect of daminozide on the regulation of flower color was investigated. An herbaceous peony (Paeonia lactiflora Pall.) cultivar 'Fenzhu Pan' was used as the material and treated with daminozide. Color parameters of petals were measured; flavonoid composition and content as well as flavonoid biosynthetic gene expression were monitored. The results showed that daminozide treatment caused less red coloration in herbaceous peony. The content of total anthocyanins was decreased by 23%, and the content of total anthoxanthins was increased by 8%; thus, it appeared that less red coloration in daminozide-treated flowers was associated with restricted anthocyanin accumulation. Furthermore, the gene expression patterns of flavonoid 3'-hydroxylase, dihydroflavonol 4-reductase and anthocyanidin synthase were lower after daminozide treatment, which could decrease anthocyanin accumulation and lead to less red coloration in flowers. These findings would improve our understanding of daminozide regulation of flower color in herbaceous peony.

Transcriptome and metabolite analyses reveal the complex metabolic genes involved in volatile terpenoid biosynthesis in garden sage (Salvia officinalis)

A large number of terpenoid compounds have been extracted from different tissues of S. officinalis. However, the molecular genetic basis of terpene biosynthesis pathways is virtually unknown. In this study, approximately 6.6 Gb of raw data were generated from the transcriptome of S. officinalis leaves using Illumina HiSeq 2000 sequencing. After filtering and removing the adapter sequences from the raw data, the number of reads reached 21 million, comprising 98 million of high-quality nucleotide bases. 48,671 unigenes were assembled de novo and annotated for establishing a valid database for studying terpenoid biosynthesis. We identified 135 unigenes that are putatively involved in terpenoid metabolism, including 70 mevalonate and methyl-erythritol phosphate pathways, terpenoid backbone biosynthesis genes, and 65 terpene synthase genes. Moreover, five terpene synthase genes were studied for their functions in terpenoid biosynthesis by using transgenic tobacco; most transgenic tobacco plants expressing these terpene synthetic genes produced increased amounts of terpenoids compared with wild-type control. The combined data analyses from the transcriptome and metabolome provide new insights into our understanding of the complex metabolic genes in terpenoid-rich sage, and our study paves the way for the future metabolic engineering of the biosynthesis of useful terpene compounds in S. officinalis.

Impact of drought stress on specialised metabolism: Biosynthesis and the expression of monoterpene synthases in sage (Salvia officinalis)

In previous experiments, we demonstrated that the amount of monoterpenes in sage is increased massively by drought stress. Our current study is aimed to elucidate whether this increase is due, at least in part, to elevated activity of the monoterpene synthases responsible for the biosynthesis of essential oils in sage. Accordingly, the transcription rates of the monoterpene synthases were analyzed. Salvia officinalis plants were cultivated under moderate drought stress. The concentrations of monoterpenes as well as the expression of the monoterpene synthases were analyzed. The amount of monoterpenes massively increased in response to drought stress; it doubled after just two days of drought stress. The observed changes in monoterpene content mostly match with the patterns of monoterpene synthase expressions. The expression of bornyl diphosphate synthase was strongly up-regulated; its maximum level was reached after two days. Sabinene synthase increased gradually and reached a maximum after two weeks. In contrast, the transcript level of cineole synthase continuously declined. This study revealed that the stress related increase of biosynthesis is not only due to a "passive" shift caused by the stress related over-reduced status, but also is due - at least in part-to an "active" up-regulation of the enzymes involved.

Isolation and Characterization of Three New Monoterpene Synthases from Artemisia annua

Artemisia annua, an annual herb used in traditional Chinese medicine, produces a wealth of monoterpenes and sesquiterpenes, including the well-known sesquiterpene lactone artemisinin, an active ingredient in the treatment for malaria. Here we report three new monoterpene synthases of A. annua. From a glandular trichome cDNA library, monoterpene synthases of AaTPS2, AaTPS5, and AaTPS6, were isolated and characterized. The recombinant proteins of AaTPS5 and AaTPS6 produced multiple products with camphene and 1,8-cineole as major products, respectively, and AaTPS2 produced a single product, β-myrcene. Although both Mg(2+) and Mn(2+) were able to support their catalytic activities, altered product spectrum was observed in the presence of Mn(2+) for AaTPS2 and AaTPS5. Analysis of extracts of aerial tissues and root of A. annua with gas chromatography-mass spectrometry detected more than 20 monoterpenes, of which the three enzymes constituted more than 1/3 of the total. Mechanical wounding induced the expression of all three monoterpene synthase genes, and transcript levels of AaTPS5 and AaTPS6 were also elevated after treatments with phytohormones of methyl jasmonate, salicylic acid, and gibberellin, suggesting a role of these monoterpene synthases in plant-environment interactions. The three new monoterpene synthases reported here further our understanding of molecular basis of monoterpene biosynthesis and regulation in plant.

Expression, crystallization and structure elucidation of γ-terpinene synthase from Thymus vulgaris

The biosynthesis of γ-terpinene, a precursor of the phenolic isomers thymol and carvacrol found in the essential oil from Thymus sp., is attributed to the activitiy of γ-terpinene synthase (TPS). Purified γ-terpinene synthase from T. vulgaris (TvTPS), the Thymus species that is the most widely spread and of the greatest economical importance, is able to catalyze the enzymatic conversion of geranyl diphosphate (GPP) to γ-terpinene. The crystal structure of recombinantly expressed and purified TvTPS is reported at 1.65 Å resolution, confirming the dimeric structure of the enzyme. The putative active site of TvTPS is deduced from its pronounced structural similarity to enzymes from other species of the Lamiaceae family involved in terpenoid biosynthesis: to (+)-bornyl diphosphate synthase and 1,8-cineole synthase from Salvia sp. and to (4S)-limonene synthase from Mentha spicata.

Susceptibility to Verticillium longisporum is linked to monoterpene production by TPS23/27 in Arabidopsis

The fungus Verticillium longisporum is a soil-borne plant pathogen of increasing economic importance, and information on plant responses to it is limited. To identify the genes and components involved in the early stages of infection, transcripts in roots of V. longisporum-challenged Arabidopsis Col-0 and the susceptible NON-RACE SPECIFIC DISEASE RESISTANCE 1 (ndr1-1) mutant were compared using ATH1 gene chips. The analysis revealed altered transcript levels of several terpene biosynthesis genes, including the monoterpene synthase TPS23/27. When transgenic 35S:TPS23/27 and TPS23/27-amiRNA plants were monitored the over-expresser line showed enhanced fungal colonization whereas the silenced genotype was indistinguishable from Col-0. Transcript analysis of terpene biosynthesis genes suggested that only the TPS23/27 pathway is affected in the two transgenic genotypes. To confirm changes in monoterpene production, emitted volatiles were determined using solid-phase microextraction and gas chromatography-mass spectrometry. Levels of all identified TPS23/27 monoterpene products were significantly altered in the transgenic plants. A stimulatory effect on conidial germination and hyphal growth of V. longisporum was also seen in co-cultivation with 35S:TPS23/27 plants and upon exposure to 1,8-cineole, the main product of TPS23/27. Methyl jasmonate treatments of myc2-1 and myc2-2 mutants and analysis of TPS23/27:uidA in the myc2-2 background suggested a dependence on jasmonic acid mediated by the transcription factor MYC2. Taken together, our results show that TPS23/27-produced monoterpenes stimulate germination and subsequent invasion of V. longisporum in Arabidopsis roots.

Identification and characterization of a second isogene encoding γ-terpinene synthase in Thymus caespititius

Thymus caespititius Brot. is an Iberian endemic species, whose essential oils possess high polymorphism. They consist mostly of mono- and sesquiterpene, some of them with interest for the pharmaceutical and food industries. The search for terpene synthase genes was performed in three in vitro T. caespititius genotypes. For these plants, the expression of a previously described γ-terpinene synthase gene, Tctps2, was confirmed, occurring concomitantly with a new gene encoding an enzyme with similar activity, named Thymus caespititius terpene synthase 4 (Tctps4). The two isogenes were isolated and functionally characterized in the three plant genotypes. Alignment of the two Tctps revealed a transit peptide much shorter in Tctps4 than in Tctps2 (3-4 amino acids instead of 47). The Tctps4 open reading frame is shorter than Tctps2 (1665 bp versus 1794 bp). The amino acid sequence of both γ-terpinene synthases shared an 88% pairwise identity. The fact that T. caespititius carries two isogenes for γ-terpinene synthases, suggests gene duplication along the evolutionary process, followed by mutations leading to the differentiation of both genes. These mutations didn't compromise protein activity. A high accumulation of transcripts from both genes was found in shoots of in vitro plantlets, while in roots they could not be detected. Still, γ-terpinene levels in aerial parts were reduced, probably due to fast conversion into carvacrol and thymol, the main components from T. caespititius essential oils. This study is a contribution to the identification of terpene synthase genes in Lamiaceae.

Biosynthesis of sesquiterpenes in grape berry exocarp of Vitis vinifera L.: evidence for a transport of farnesyl diphosphate precursors from plastids to the cytosol

The participation of the mevalonic acid (MVA) and 1-deoxy-d-xylulose 5-phosphate/2-C-methyl-d-erythritol-4-phosphate (DOXP/MEP) pathways in sesquiterpene biosynthesis of grape berries was investigated. There is an increasing interest in this class of terpenoids, since the oxygenated sesquiterpene rotundone was identified as the peppery aroma impact compound in Australian Shiraz wines. To investigate precursor supply pathway utilization, in vivo feeding experiments were performed with the deuterium labeled, pathway specific, precursors [5,5-(2)H2]-1-deoxy-d-xylulose and [5,5-(2)H2]-mevalonic acid lactone. Head Space-Solid Phase Micro Extraction-Gas Chromatography-Mass Spectrometry (HS-SPME-GC-MS) analysis of the generated volatile metabolites demonstrated that de novo sesquiterpene biosynthesis is mainly located in the grape berry exocarp (skin), with no detectable activity in the mesocarp (flesh) of the Lemberger variety. Interestingly, precursors from both the (primarily) cytosolic MVA and plastidial DOXP/MEP pathways were incorporated into grape sesquiterpenes in the varieties Lemberger, Gewürztraminer and Syrah. Our labeling data provide evidence for a homogenous, cytosolic pool of precursors for sesquiterpene biosynthesis, indicating that a transport of precursors occurs mostly from plastids to the cytosol. The labeling patterns of the sesquiterpene germacrene D were in agreement with a cyclization mechanism analogous to that of a previously cloned enantioselective (R)-germacrene D synthase from Solidago canadensis. This observation was subsequently confirmed by enantioselective GC-MS analysis demonstrating the exclusive presence of (R)-germacrene D, and not the (S)-enantiomer, in grape berries.

Genomic characterization, molecular cloning and expression analysis of two terpene synthases from Thymus caespititius (Lamiaceae)

The identification, isolation and functional characterization of two genes encoding two monoterpene synthases-γ-terpinene synthase (Tctps2) and α-terpineol synthase (Tctps5)-from three chemically distinct Thymus caespititius (Lamiaceae) genotypes were performed. Genomic exon-intron structure was also determined for both terpene synthase genes, revealing an organization with seven exons and six introns. The cDNA of Tctps2 was 2,308 bp long and had an open reading frame of 1,794 bp encoding for a protein with 598 amino acids. Tctps5 was longer, mainly due to intron sequences, and presented high intraspecific variability on the plants analyzed. It encoded for a protein of 602 amino acids from an open reading frame of 1,806 bp comprising a total of 2,507 bp genomic sequence. The amino acid sequence of these two active Tctps genes shared 74 % pairwise identity, ranging between 42 and 94 % similarity with about 50 known terpene synthases of other Lamiaceae species. Gene expression revealed a multi-product Tctps2 and Tctps5 enzymes, producing γ-terpinene and α-terpineol as major components, respectively. These enzymatic results were consistent with the monoterpene profile present in T. caespititius field plants, suggesting a transcriptional regulation in leaves. Herewith reported for the first time for this species, these two newly characterized Tctps genes improve the understanding of the molecular mechanisms of reaction responsible for terpene biosynthesis and chemical diversity found in T. caespititius.

Seasonal influence on gene expression of monoterpene synthases in Salvia officinalis (Lamiaceae)

Garden sage (Salvia officinalis L., Lamiaceae) is one of the most important medicinal and aromatic plants and possesses antioxidant, antimicrobial, spasmolytic, astringent, antihidrotic and specific sensorial properties. The essential oil of the plant, formed mainly in very young leaves, is in part responsible for these activities. It is mainly composed of the monoterpenes 1,8-cineole, α- and β-thujone and camphor synthesized by the 1,8-cineole synthase, the (+)-sabinene synthase and the (+)-bornyl diphosphate synthase, respectively, and is produced and stored in epidermal glands. In this study, the seasonal influence on the formation of the main monoterpenes in young, still expanding leaves of field-grown sage plants was studied in two cultivars at the level of mRNA expression, analyzed by qRT-PCR, and at the level of end-products, analyzed by gas chromatography. All monoterpene synthases and monoterpenes were significantly influenced by cultivar and season. 1,8-Cineole synthase and its end product 1,8-cineole remained constant until August and then decreased slightly. The thujones increased steadily during the vegetative period. The transcript level of their corresponding terpene synthase, however, showed its maximum in the middle of the vegetative period and declined afterwards. Camphor remained constant until August and then declined, exactly correlated with the mRNA level of the corresponding terpene synthase. In summary, terpene synthase mRNA expression and respective end product levels were concordant in the case of 1,8-cineole (r=0.51 and 0.67 for the two cultivars, respectively; p<0.05) and camphor (r=0.75 and 0.82; p<0.05) indicating basically transcriptional control, but discordant for α-/β-thujone (r=-0.05 and 0.42; p=0.87 and 0.13, respectively).