New Insights into Stress-Induced β-Ocimene Biosynthesis in Tea (Camellia sinensis) Leaves during Oolong Tea Processing

Integration of digital phenotyping, GWAS, and transcriptomic analysis revealed a key gene for bud size in tea plant (Camellia sinensis)

Tea plant (Camellia sinensis) is among the most significant beverage crops globally. The size of tea buds not only directly affects the yield and quality of fresh leaves, but also plays a key role in determining the suitability of different types of tea. Analyzing the genetic regulation mechanism of tea bud size is crucial for enhancing tea cultivars and boosting tea yield. In this study, a digital phenotyping technology was utilized to collected morphological characteristics of the apical buds of 280 tea accessions of representative germplasm at the 'two and a bud' stage. Genetic diversity analysis revealed that the length, width, perimeter, and area of tea buds followed a normal distribution and exhibited considerable variation across natural population of tea plants. Comparative transcriptomic analysis of phenotypic extreme materials revealed a strong negative correlation between the expression levels of four KNOX genes and tea bud size. A key candidate gene, CsKNOX6, was confirmed by further genome-wide association studies (GWAS). Its function was preliminarily characterized by heterologous transformation of Arabidopsis thaliana. Overexpression of CsKNOX6 reduced the leaf area in transgenic plants, which initially determined that it is a key gene negatively regulating bud size. These findings enhance our understanding of the role of KNOX genes in tea plants and provide some references for uncovering the genetic regulatory mechanisms behind tea bud size.

Revealing the roles of solar withering and shaking processes on oolong tea manufacturing from transcriptome and volatile profile analysis

Solar and indoor withering in the manufacturing process of semi-fermented oolong tea are crucial for aroma formation. While the processes have been established through accumulated experience, the underlying mechanisms remain largely unknown. This study identified pairs of gene and volatile organic compound (VOC) that were significantly correlated and up-regulated during solar withering and the first shaking, including lipoxygenase 8 (LOX8) with 3-hexenyl iso-butyrate, terpene synthase 2 (TPS2) with β-ocimene and linalool, as well as tryptophan synthase β-subunit 2 (TSB2) with indole. Besides, two β-glucosidases (β-GH), β-GH1_1 and β-GH3_1, were up-regulated by more than 30-fold in these stages. When comparing the three manufacturing procedures, indole, nerolidol, β-ocimene, benzyl nitrile, and jasmine lactone, were largely accumulated only in the normal process, where both solar withering and shaking were included. These findings provide insights into the regulation of VOC accumulation under stresses during withering, and highlight the importance of specific manufacturing processes in the formation of oolong tea characteristic aroma.

Multi-Omics analysis reveals the sensory quality and fungal communities of Tibetan teas produced by wet- and dry-piling fermentation

Ya'an Tibetan tea, a dark tea with a rich historical heritage, is typically processed using two primary piling fermentation methods: wet piling with rolled leaves (moisture content around 60%) and dry piling with sun-dried or baked green tea leaves (moisture content below 30%). This study employed sensory evaluation, targeted and non-targeted metabolomics, and fungal Internal Transcribed Spacer (ITS) sequencing to investigate changes in quality components and fungal composition in Tibetan tea processed by both wet and dry-piling methods. The results revealed that 3,7-Dimethyl-1,5,7-octatriene-3-ol and D-limonene were identified as key volatile metabolites contributing to the aroma variations between the dry and wet-piled teas. More pronounced differences were observed in non-volatile components, with 407 differential metabolites identified between the wet- and dry-piled teas. Linear discriminant analysis effect size (LEfSe) identified Rhizomucor, Aspergillus, Thermomyces, Setophoma, and Debaryomyces as the key fungal genera with significant differences between the two piling methods, also dominating in abundance and playing a crucial role in the fermentation process of Tibetan tea. Correlation analysis between microbial communities and differential metabolites showed that Debaryomyces, Thermomyces, and Setophoma were significant contributors to the aroma differences between the teas produced by the two piling methods, while Rhizomucor and Aspergillus had a greater influence on non-volatile metabolites. Since Rhizomucor and Aspergillus were the most dominant fungi in the wet (63.05%) and dry-piled (68.70%) samples, respectively, and showed opposite correlations with major non-volatile differential metabolites, they may underlie the flavor differences between the two piled teas, such as mellowness, thickness, and sweet aftertaste. This study sheds light on the chemical and fungal mechanisms underlying the quality formation of Ya'an Tibetan tea processed by wet and dry piling methods, providing theoretical guidance for the improvement, standardization, and potential enhancement of production efficiency of Ya'an Tibetan tea production.

The processing of shaking and standing improves the taste quality of summer black tea

Shaking and standing (SS) enhances the aroma intensity and quality of black tea (BT). However, its contribution to the taste remains unknown, and the interaction mechanism between the aroma and taste perception of black tea is also undisclosed. Here, the metabolomics and sensory evaluation-assisted flavor analysis were employed to investigate the changes in non-volatiles induced by SS, and the interaction mechanism between aroma and taste perception. SSBT exhibited considerable reduced bitterness and astringency intensities compared to BT. Notably, the concentrations of contributing compounds such as catechins, proanthocyanidins, theaflavins, anthocyanins, and flavonol glycosides were decreased in SSBT. Sensory experiments further revealed that nine floral and sweet odorants in SSBT exhibited odor-enhancing interactions. Molecular docking validated the binding affinity and interaction forces between mono/di-ligands and OR1G1/OR52D1. Furthermore, the presence of the nine odorants exerted inhibitory effects on the bitterness and astringency of SSBT. These findings provide a novel perspective on the formation of flavor in SSBT.

Exploring the effect of greenhouse covering cultivation on the changes of sensory quality and flavor substances of green tea

To protect tea plant (Camellia sinensis (L.) O. Kuntze) from freezing injury, plastic greenhouse covering is widely used in northern tea areas of China. Currently, there was few researches about the effect of greenhouse covering on tea quality. Our results showed greenhouse covering increased tea yield, changed leaf phenotype and decreased green tea quality. Further analysis revealed greenhouse increased the content of soluble sugars and decreased the content of EGCG and 14 amino acids. Besides, there were 223 differential volatile components were identified in green tea produced by fresh leaves with plastic greenhouse covering (GT) and green tea produced by fresh leaves without plastic greenhouse covering (TT). 81 key aroma components were contributors to the bean-like aroma of TT. 98 key aroma components contributed to the clean aroma of GT. Based on these results, the flavor wheels were constructed, providing a visual presentation of flavor between TT and GT.

The tea cultivar 'Chungui' with jasmine-like aroma: From genome and epigenome to quality

'Chungui' is a newly promoted tea cultivar in China, renowned for producing oolong tea with a distinctive jasmine-like aroma. However, the genetic basis of this unique aroma remains unclear. In this study, the 'Chungui' genome, one of the most complete and well-annotated tea genomes, was assembled using PacBio HiFi reads and Hi-C sequencing. Through comparative analysis with typical jasmine flower volatiles, eight core compounds responsible for this aroma were identified. Further research revealed that the jasmine-like aroma in 'Chungui' is regulated by a coordinated mechanism involving a significant increase in chromatin accessibility and the demethylation of CHH and CHG in the promoter regions of key aroma-related genes during oolong tea processing. The study proposes that the formation of this unique aroma is driven by the synergistic effect of enhanced chromatin accessibility and reduced methylation, which together lead to the robust upregulation of genes involved in the biosynthesis of these core aroma components. These results provide a molecular foundation for understanding the unique jasmine-like aroma of 'Chungui' tea and sets the stage for future studies to explore the roles of these regulatory mechanisms in aroma formation.

The effect of maturity of tea leaves and processing methods on the formation of milky flavor in white tea - A metabolomic study

Targeted metabolomics combined with chemometrics were applied to investigate the flavor profiles of 4 white tea samples, which were produced from different maturity fresh tea leaves with different withering methods. Mature leaves that underwent novel withering process at higher temperature (28-30℃) and humidity (75 ± 3 %) (MN) were characterized by intense milky flavor. The content of free amino acids, catechins, and soluble sugars in MN were significantly lower than that in the other 3 tea samples, resulting in a sweet and mellow taste with low bitterness. Meanwhile, MN possessed the highest intensity of milky aroma, which could be mainly attributed to the existence of dihydro-5-pentyl-2(3H)-furanone and 2-pentyl-furan as the key volatile substances with coconut and creamy fragrance. These findings provide insight into the substance foundations of milky flavor, and identified leaf maturity and processing method as the determining factors of the milk-flavored white tea (MFWT).

Greenhouse covering cultivation promotes chlorophyll accumulation of tea plant (Camellia sinensis) by activating relevant gene expression and enzyme activity

BACKGROUND

The tea plant (Camellia sinensis (L.) O. Kuntze) is one of the most economically important woody crops. Plastic greenhouse covering cultivation has been widely used in tea areas of northern China. Chlorophyll is not only the crucial pigment for green tea, but also plays an important role in the growth and development of tea plants. Currently, little is known about the effect of plastic greenhouse covering cultivation on chlorophyll in tea leaves.

RESULTS

To investigate the effect of plastic greenhouse covering cultivation on chlorophyll in tea leaves, color difference values, chlorophyll contents, gene expression, enzyme activities and photosynthetic parameters were analyzed in our study. Sensory evaluation showed the color of appearance, liquor and infused leaves of greenhouse tea was greener than field tea. Color difference analysis for tea liquor revealed that the value of ∆L, ∆b and b/a of greenhouse tea was significantly higher than field tea. Significant increase in chlorophyll content, intracellular CO2, stomatal conductance, transpiration rate, and net photosynthetic rate was observed in greenhouse tea leaves. The gene expression and activities of chlorophyll-metabolism-related enzymes in tea leaves were also activated by greenhouse covering.

CONCLUSION

The higher contents of chlorophyll a, chlorophyll b and total chlorophyll in greenhouse tea samples were primarily due to higher gene expression and activities of chlorophyll-metabolism-related enzymes especially, chlorophyll a synthetase (chlG), pheophorbide a oxygenase (PAO) and chlorophyllide a oxygenase (CAO) in tea leaves covered by greenhouse. In general, our results revealed the molecular basis of chlorophyll metabolism in tea leaves caused by plastic greenhouse covering cultivation, which had great significance in production of greenhouse tea.

Metabolite Profiling Reveals the Dynamic Changes in Non-Volatiles and Volatiles during the Enzymatic-Catalyzed Processing of Aijiao Oolong Tea

The enzymatic reaction stage (ECS) of oolong tea processing plays an important role in the formation of the flavor quality of the oolong tea. To investigate the dynamic changes in the volatile and non-volatile components in the leaves of oolong tea during the ECS, metabolomic studies were carried out using the leaf samples collected at different stages of the ECS of Aijiao oolong tea. Out of the identified 306 non-volatile metabolites and 85 volatile metabolites, 159 non-volatile metabolites and 42 volatile metabolites were screened out as key differential metabolites for dynamic changes during the ECS. A multivariate statistical analysis on the key differential metabolites showed that the accumulations of most metabolites exhibited dynamic changes, while some amino acids, nucleosides, and organic acids accumulated significantly after turning-over treatment. The evolution characteristics of 27 key precursors or transformed VOCs during the ECS of Aijiao oolong tea were clarified, and it was found that the synthesis of aroma substances was mainly concentrated in lipids as precursors and glycosides as precursor pathways. The results revealed the dynamic changes in the flavor metabolites in the ECS during the processing of Aijiao oolong tea, which provided valuable information for the formation of the characteristic flavor of Aijiao oolong tea.

Plant-derived monoterpene S-linalool and β-ocimene generated by CsLIS and CsOCS-SCZ are key chemical cues for attracting parasitoid wasps for suppressing Ectropis obliqua infestation in Camellia sinensis L

Insect-induced plant volatile organic compounds (VOCs) may function as either direct defence molecules to deter insects or indirect defence signals to attract the natural enemies of the invading insects. Tea (Camellia sinensis L.), an important leaf-based beverage crop, is mainly infested by Ectropis obliqua which causes the most serious damage. Here, we report a mechanistic investigation of tea plant-derived VOCs in an indirect defence mechanism against E. obliqua. Parasitoid wasp Parapanteles hyposidrae, a natural enemy of E. obliqua, showed strong electrophysiological response and selection behaviour towards S-linalool and β-ocimene, two monoterpenes with elevated emission from E. obliqua-damaged tea plants. Larvae frass of E. obliqua, which also released S-linalool and β-ocimene, was found to attract both mated female or male Pa. hyposidrae according to gas chromatography-electroantennogram detection and Y-tube olfactometer assays. In a field setting, both S-linalool and β-ocimene were effective in recruiting both female and male Pa. hyposidrae wasps. To understand the molecular mechanism of monoterpenes-mediated indirect defence in tea plants, two novel monoterpene synthase genes, CsLIS and CsOCS-SCZ, involved in the biosynthesis of S-linalool or β-ocimene, respectively, were identified and biochemically characterised. When the expression of these two genes in tea plants was inhibited by antisense oligodeoxynucleotide, both volatile emission and attraction of wasps were reduced. Furthermore, gene expression analysis suggested that the expression of CsLIS and CsOCS-SCZ is regulated by the jasmonic acid signalling pathway in the tea plant.

Chemically Mediated Plant-Plant Interactions: Allelopathy and Allelobiosis

Plant-plant interactions are a central driver for plant coexistence and community assembly. Chemically mediated plant-plant interactions are represented by allelopathy and allelobiosis. Both allelopathy and allelobiosis are achieved through specialized metabolites (allelochemicals or signaling chemicals) produced and released from neighboring plants. Allelopathy exerts mostly negative effects on the establishment and growth of neighboring plants by allelochemicals, while allelobiosis provides plant neighbor detection and identity recognition mediated by signaling chemicals. Therefore, plants can chemically affect the performance of neighboring plants through the allelopathy and allelobiosis that frequently occur in plant-plant intra-specific and inter-specific interactions. Allelopathy and allelobiosis are two probably inseparable processes that occur together in plant-plant chemical interactions. Here, we comprehensively review allelopathy and allelobiosis in plant-plant interactions, including allelopathy and allelochemicals and their application for sustainable agriculture and forestry, allelobiosis and plant identity recognition, chemically mediated root-soil interactions and plant-soil feedback, and biosynthesis and the molecular mechanisms of allelochemicals and signaling chemicals. Altogether, these efforts provide the recent advancements in the wide field of allelopathy and allelobiosis, and new insights into the chemically mediated plant-plant interactions.

Understanding the dynamic changes of volatile and non-volatile metabolites in black tea during processing by integrated volatolomics and UHPLC-HRMS analysis

Processing technology has an important effect on the flavor quality of black tea. However, the dynamic changes of volatile and non-volatile metabolites in black tea during processing are poorly understood. In this study, the volatile and non-volatile compounds during black tea processing were comprehensively characterized by integrated volatolomics and UHPLC-Q-Exactive/MS analysis. Volatile and non-volatile metabolites changed continuously throughout the processing process, especially during the withering stage. A total of 178 volatile metabolites and 103 non-volatile metabolites were identified. Among them, 11 volatile components with relative odor activity value greater than 1 (including dimethyl sulfide, 3-methylbutanal, 2-methylbutanal, β-myrcene, β-ocimene, linalool, methyl salicylate, β-cyclocitral, β-citral, citral, and β-ionone) were regarded as key aroma-active components responsible for finished black tea with sweet aroma. This study provides a comprehensive understanding of dynamic evolution trajectory of volatile and non-volatile metabolites during processing, which lays a theoretical foundation for the targeted processing of high-quality black tea.

Recent Progress Regarding Jasmonates in Tea Plants: Biosynthesis, Signaling, and Function in Stress Responses

Tea plants have to adapt to frequently challenging environments due to their sessile lifestyle and perennial evergreen nature. Jasmonates regulate not only tea plants' responses to biotic stresses, including herbivore attack and pathogen infection, but also tolerance to abiotic stresses, such as extreme weather conditions and osmotic stress. In this review, we summarize recent progress about jasmonaic acid (JA) biosynthesis and signaling pathways, as well as the underlying mechanisms mediated by jasmontes in tea plants in responses to biotic stresses and abiotic stresses. This review provides a reference for future research on the JA signaling pathway in terms of its regulation against various stresses of tea plants. Due to the lack of a genetic transformation system, the JA pathway of tea plants is still in the preliminary stages. It is necessary to perform further efforts to identify new components involved in the JA regulatory pathway through the combination of genetic and biochemical methods.

From heat to flavor: Unlocking new chemical signatures to discriminate Wuyi rock tea under light and moderate roasting

Roasting is crucial for the distinct flavor of Wuyi rock tea (WRT). This study applied untargeted metabolomics to investigate the effects of roasting on 139 WRT samples roasted at light fire (LF) or moderate fire (MF) intensities. Compared to LF, MF roasting led to a decrease in the cis/trans flavanol ratio by 56% and theanine by 85%, while increasing the levels of N-ethyl-2-pyrrolidione-substituted flavanols (EPSFs), flavonol aglycones and flavone C-glycosides. Two new roast markers, 3-p-coumaroyl 1,5-lactone and 4-p-coumaroyl 1,5-lactone, were identified in WRT and their formation increased with roasting temperature. MF roasting facilitated the formation of diverse heterocycles (e.g., pyrazines) and aldehydes (e.g., (Z)-4-heptenal and (E,E)-2.4-decadienal) that contributed to the augmented roasted and fatty odors in WRT. Additionally, the Maillard product furfuryl methyl ether was solely detected in MF samples. These findings provide novel insights into roast markers in WRT with implications for improving quality control measures during tea roasting.

Identification and functional characterization of two trans-isopentenyl diphosphate synthases and one squalene synthase involved in triterpenoid biosynthesis in Platycodon grandiflorus

MAIN CONCLUSION

Two trans-isopentenyl diphosphate synthase and one squalene synthase genes were identified and proved to be involved in the triterpenoid biosynthesis in Platycodon grandiflorus. Platycodon grandiflorus is a commonly used traditional Chinese medicine. The main bioactive compounds of P. grandiflorus are triterpenoid saponins. The biosynthetic pathway of triterpenoid saponins in P. grandiflorus has been preliminarily explored. However, limited functional information on related genes has been reported. A total of three trans-isopentenyl diphosphate synthases (trans-IDSs) genes (PgFPPS, PgGGPPS1 and PgGGPPS2) and one squalene synthase (SQS) gene (PgSQS) in P. grandiflorus were screened and identified from transcriptome dataset. Subcellular localization of the proteins was defined based on the analysis of GFP-tagged. The activity of genes was verified in Escherichia coli, demonstrating that recombinant PgFPPS catalysed the production of farnesyl diphosphate. PgGGPPS1 produced geranylgeranyl diphosphate, whereas PgGGPPS2 did not exhibit catalytic activity. By structural identification of encoding genes, a transmembrane region was found at the C-terminus of the PgSQS gene, which produced an insoluble protein when expressed in E. coli but showed no apparent effect on the enzyme function. Furthermore, some triterpenoid saponin synthesis-related genes were discovered by combining the component content and the gene expression assays at the five growth stages of P. grandiflorus seedlings. The accumulation of active components in P. grandiflorus was closely associated with the expression level of genes related to the synthesis pathway.

The aroma characteristics of oolong tea are jointly determined by processing mode and tea cultivars

This study delved into the aroma characteristics of "Qingxiang" oolong tea, analyzing six different cultivars and their processing modes. The findings showed that both cultivars and processing modes have a significant impact on the oolong tea aroma system. The study identified 18 terpenoid volatiles (VTs), 11 amino-acid-derived volatiles (AADVs), 15 fatty-acid-derived volatiles (FADVs), 3 carotenoid-derived volatiles (CDVs), and 10 other compounds in oolong tea that differentiate it from green and black tea. The turn-over stage was found to be the primary processing stage for oolong tea aroma formation. Molecular sensory analysis revealed that the "fresh" odor attribute is the basis for its aroma, while "floral and fruity" fragrances are its aroma characteristics. The perception of oolong tea as "fresh" and "floral and fruity" is influenced by the interactions of its aroma components. These findings provide a new basis for breed improvement and process enhancement in oolong tea production.

Characterization of a fermented dairy, sour cream: Lipolysis and the release profile of flavor compounds

Lipolysis and flavor development during fermentation of sour cream were studied by evaluating the physicochemical changes, sensory differences and volatile components. The fermentation caused significant changes in pH, viable count and sensory evaluation. The peroxide value (POV) decreased after reaching the maximum value of 1.07 meq/kg at 15 h, while thiobarbituric acid reactive substances (TBARS) increased continuously with the accumulation of secondary oxidation products. The Free fatty acids (FFAs) in sour cream were mainly myristic, palmitic and stearic. GC-IMS was used to identify the flavor properties. A total of 31 volatile compounds were identified, among which the contents of characteristic aromatic substances such as ethyl acetate, 1-octen-3-one and hexanoic acid were increased. The results suggest that lipid changes and flavor formation in sour cream are influenced by fermentation time. Furthermore, flavor compounds may be related to lipolysis such as 1-octen-3-one and 2- heptanol were also observed.

Biosynthesis and the Transcriptional Regulation of Terpenoids in Tea Plants (Camellia sinensis)

Terpenes, especially volatile terpenes, are important components of tea aroma due to their unique scents. They are also widely used in the cosmetic and medical industries. In addition, terpene emission can be induced by herbivory, wounding, light, low temperature, and other stress conditions, leading to plant defense responses and plant-plant interactions. The transcriptional levels of important core genes (including HMGR, DXS, and TPS) involved in terpenoid biosynthesis are up- or downregulated by the MYB, MYC, NAC, ERF, WRKY, and bHLH transcription factors. These regulators can bind to corresponding cis-elements in the promoter regions of the corresponding genes, and some of them interact with other transcription factors to form a complex. Recently, several key terpene synthesis genes and important transcription factors involved in terpene biosynthesis have been isolated and functionally identified from tea plants. In this work, we focus on the research progress on the transcriptional regulation of terpenes in tea plants (Camellia sinensis) and thoroughly detail the biosynthesis of terpene compounds, the terpene biosynthesis-related genes, the transcription factors involved in terpene biosynthesis, and their importance. Furthermore, we review the potential strategies used in studying the specific transcriptional regulation functions of candidate transcription factors that have been discriminated to date.

Identification of QTL controlling volatile terpene contents in tea plant (Camellia sinensis) using a high-aroma 'Huangdan' x 'Jinxuan' F1 population

Aroma is an important factor affecting the character and quality of tea. The improvement of aroma trait is a crucial research direction of tea plant breeding. Volatile terpenes, as the major contributors to the floral odors of tea products, also play critical roles in the defense responses of plants to multiple stresses. However, previous studies have largely focused on the aroma formation during the manufacture of tea or the comparison of raw tea samples. The mechanisms causing different aroma profiles between tea cultivars have remained underexplored. In the current study, a high-density genetic linkage map of tea plant was constructed based on an F₁ population of 'Huangdan' × 'Jinxuan' using genotyping by sequencing. This linkage map covered 1754.57 cM and contained 15 linkage groups with a low inter-marker distance of 0.47 cM. A total of 42 QTLs associated with eight monoterpene contents and 12 QTLs associated with four sesquiterpenes contents were identified with the average PVE of 12.6% and 11.7% respectively. Furthermore, six candidate genes related to volatile terpene contents were found in QTL cluster on chromosome 5 by RNA-seq analysis. This work will enrich our understanding of the molecular mechanism of volatile terpene biosynthesis and provide a theoretical basis for tea plant breeding programs for aroma quality improvement.

Metabolomics integrated with machine learning to discriminate the geographic origin of Rougui Wuyi rock tea

The geographic origin of agri-food products contributes greatly to their quality and market value. Here, we developed a robust method combining metabolomics and machine learning (ML) to authenticate the geographic origin of Wuyi rock tea, a premium oolong tea. The volatiles of 333 tea samples (174 from the core region and 159 from the non-core region) were profiled using gas chromatography time-of-flight mass spectrometry and a series of ML algorithms were tested. Wuyi rock tea from the two regions featured distinct aroma profiles. Multilayer Perceptron achieved the best performance with an average accuracy of 92.7% on the training data using 176 volatile features. The model was benchmarked with two independent test sets, showing over 90% accuracy. Gradient Boosting algorithm yielded the best accuracy (89.6%) when using only 30 volatile features. The proposed methodology holds great promise for its broader applications in identifying the geographic origins of other valuable agri-food products.

Functional characterization of a terpene synthase responsible for (E)-β-ocimene biosynthesis identified in Pyrus betuleafolia transcriptome after herbivory

(E)-β-ocimene, a ubiquitous monoterpene volatile in plants, is emitted from flowers to attract pollinators and/or from vegetative tissues as part of inducible defenses mediated by complex signaling networks when plants are attacked by insect herbivores. Wild pear species Pyrus betuleafolia used worldwide as rootstock generally displays valuable pest-resistant traits and is a promising genetic resource for pear breeding. In the current study, transcriptional changes in this wild pear species infested with a polyphagous herbivore Spodoptera litura and the underlying molecular mechanisms were fully investigated. A total of 3,118 differentially expressed genes (DEGs) were identified in damaged pear leaf samples. Spodoptera litura larvae infestation activated complex phytohormonal signaling networks in which jasmonic acid, ethylene, brassinosteroids, cytokinin, gibberellic acid and auxin pathways were induced, whereas salicylic acid and abscisic acid pathways were suppressed. All DEGs associated with growth-related photosynthesis were significantly downregulated, whereas most DEGs involved in defense-related early signaling events, transcription factors, green leaf volatiles and volatile terpenes were significantly upregulated. The PbeOCS (GWHGAAYT028729), a putative (E)-β-ocimene synthase gene, was newly identified in P. betuleafolia transcriptome. The upregulation of PbeOCS in S. litura-infested pear leaves supports a potential role for PbeOCS in herbivore-induced plant defenses. In enzyme-catalyzed reaction, recombinant PbeOCS utilized only geranyl pyrophosphate but not neryl diphosphate, farnesyl pyrophosphate or geranylgeranyl diphosphate as a substrate, producing (E)-β-ocimene as the major product and a trace amount of (Z)-β-ocimene. Moreover, as a catalytic product of PbeOCS, (E)-β-ocimene showed repellent effects on larvae of S. litura in dual-choice bioassays. What is more, (E)-β-ocimene increased mortalities of larvae in no-choice bioassays. These findings provide an overview of transcriptomic changes in wild pears in response to chewing herbivores and insights into (E)-β-ocimene biosynthesis in pear plants, which will help elucidate the molecular mechanisms underlying pear-insect interactions.

Quantitative Measurement Reveals Dynamic Volatile Changes and Potential Biochemical Mechanisms during Green Tea Spreading Treatment

Quantitative data provide clues for biochemical reactions or regulations. The absolute quantification of volatile compounds in tea is complicated by their low abundance, volatility, thermal liability, matrix complexity, and instrumental sensitivity. Here, by integrating solvent-assisted flavor evaporation extraction with a gas chromatography-triple quadrupole mass spectrometry platform, we successfully established a method based on multiple reaction monitoring (MRM). The method was validated by multiple parameters, including the linear range, limit of detection, limit of quantification, precision, repeatability, stability, and accuracy. This method was then applied to measure temporal changes of endogenous volatiles during green tea spreading treatment. In total, 38 endogenous volatiles were quantitatively measured, which are derived from the shikimic acid pathway, mevalonate pathway, 2-C-methylerythritol-4-phosphate pathway, and fatty acid derivative pathway. Hierarchical clustering and heat-map analysis demonstrated four different changing patterns during green tea spreading treatment. Pathway analysis was then conducted to explore the potential biochemistry underpinning these dynamic change patterns. Our data demonstrated that the established MRM method showed high selectivity and sensitivity for quantitative tea volatile measurement and offered novel insights about volatile formation during green tea spreading.

Study on the Suitability of Tea Cultivars for Processing Oolong Tea from the Perspective of Aroma Based on Olfactory Sensory, Electronic Nose, and GC-MS Data Correlation Analysis

The oolong tea aroma is shown to consist of cultivar aroma and technical aroma in this study based on the aroma differences between oolong tea products of cultivars of different suitability, as determined by correlation analysis of olfactory, sensory, electronic nose, and GC-MS data. Human senses were significantly affected by the aroma components, which included eight terpene metabolites (β-Ocimene, (Z)-Furan linalool oxide, linalool, (3E)-4,8-Dimethyl-1,3,7-nonatriene, (E)-Pyranoid linalool oxide, γ-Elemene, Humulene, (Z,E)-α-Farnesene), three carotenoid metabolites (β-Ionone, (Z)-Geranylacetone and 6-methyl-5-Hepten -2-one), three lipid metabolites ((Z)-3-Hexenyl (Z)-3-hexenoate, Butanoic acid hexyl ester, and (Z)-Jasmone), four amino acid metabolites (Methyl salicylate, Geranyl isovalerate, indole, and Phenylethyl alcohol), and six thermal reaction products (2-Pentylfuran, Octanal, Decanal, (E,E)-2,4-Nonadienal, (Z)-2-Decenal, and (E)-2-Undecenal). Meanwhile, several aroma compounds (such as (E)-Nerolidol and α-Farnesene), mainly comprising the “technical aroma” formed in the processing mode, were noted to be less closely related to cultivar suitability. This study sheds light on the aroma characteristics of different tea cultivars for oolong tea processing.

Comparative transcriptomics of Pinus massoniana organs provides insights on terpene biosynthesis regulation

Terpenoids are the most important natural products collected from conifer species. However, the molecular mechanisms and core factors underlying terpenoid biosynthesis in Pinus massoniana remain unclear. To clarify these mechanisms, this study aimed to identify potential genes that might participate in the terpenoid biosynthesis of P. massoniana. In this study, single molecule real-time (SMRT) sequencing and expression analysis were used to confirm the expression patterns of genes involved in the cones, immature needles, mature needles, immature branches, and mature branches of P. massoniana. A total of 31,331 lncRNAs and 71,240 mRNAs were identified from these organs, and the greatest number of differentially expressed genes (DEGs) was discovered between needles and branches. Weighted gene coexpression network analysis (WGCNA) classified all expressed genes into nine typical modules with 11 kinds of transcription factors (TFs), namely, AP2-ERF, ARF, AUX-IAA, C2H2, Dof, F-box, SBP, WRKY, bHLH, bZIP, and GRAS, and seven kinds of functional genes, namely, ABC transporter, cellulose synthase (CesA), leucine-rich repeats (LRR), cytochrome P450 (CYT P450), pathogenesis-related protein (PR), terpene synthase (TPS), and chlorophyllase enzyme. A molecular network was constructed for hub genes, TFs, and functional genes in three modules. The potential function of eight candidate genes, including PmbHLH2, PmERF1, PmRGA, PmGAI, PmbZIP1, PmLOB1, PmMADS1, and PmMYB1, was validated through correlation analysis between terpenoid contents and expression levels, subcellular localization, and transcriptional activation activity, which provides us with probable regulators of terpenoid biosynthesis in conifers.

A monoterpene synthase gene cluster of tea plant (Camellia sinensis) potentially involved in constitutive and herbivore-induced terpene formation

Monoterpenes and sesquiterpenes are the most abundant volatiles in tea plants and have dual functions in aroma quality formation and defense responses in tea plants. Terpene synthases (TPS) are the key enzymes for the synthesis of terpenes in plants; however, the functions of most of them in tea plants are still unknown. In this study, six putative terpene biosynthesis gene clusters were identified from the tea plant genome. Then we cloned three new TPS-b subfamily genes, CsTPS08, CsTPS10 and CsTPS58. In vitro enzyme assays showed that CsTPS08 and CsTPS58 are two multiple-product terpene synthases, with the former synthesizing linalool as the main product, and β-myrcene, α-phellandrene, α-terpinolene, D-limonene, cis-β-ocimene, trans-β-ocimene and (4E,6Z)-allo-ocimene as minor products are also detected, while the latter catalyzing the formation of α-pinene and D-limonene using GPP as the substrate. No product of CsTPS10 was detected in the prokaryotic expression system, but geraniol production was detected when transiently expressed in tobacco leaves. CsTPS08 and CsTPS10 are two functional members of a monoterpene synthase gene cluster, which were significantly induced during both Ectropis oblique feeding and fresh leaf spreading treatments, suggesting that they have dual functions involved in tea plant pest defense and tea aroma quality regulation. In addition, the differences in their expression levels in different tea plant cultivars provide a possibility for the subsequent screening of tea plant resources with a specific aroma flavor. Our results deepen the understanding of terpenoid synthesis in tea plants.