An (E,E)-α-farnesene synthase gene of soybean has a role in defence against nematodes and is involved in synthesizing insect-induced volatiles

First report on the chemical composition of volatile compounds in the essential oils and aromas of Senega adenophora, Senega appressa, and Senega longicaulis (Polygalaceae)

This study presents a comprehensive chemical analysis of the essential oil isolated from Senega longicaulis, and aroma analysis of Senega adenophora and Senega appressa, employing both fresh and dried samples. Notable differences were observed between the fresh and dried samples of essential oil from S. longicaulis. In the fresh sample, the predominant compounds were (E,E)-geranyl linalool (33.21%) and dendrolasin (19.64%), whereas in the dried sample, (E,E)-geranyl linalool increased to 39.19% and dendrolasin to 18.83%. The oxygenated sesquiterpenes were found to be more abundant in the dried sample (81.52%) than in the fresh sample (69.96%). In the case of S. adenophora and S. appressa, the aroma analysis indicated that β-elemene (49.05%) and methyl salicylate (31.13%), respectively, were the primary compounds present in the fresh samples. These findings illustrate how the drying process has the effect of intensifying certain chemical components in the samples of S. longicaulis.

Fine-Tuning the Function of Farnesene Synthases for Selective Synthesis of Farnesene Stereoisomers

Farnesene synthase from Artemisia annua (AaFS) catalyzes the reaction from farnesyl pyrophosphate (FPP) to give the sesquiterpene β-farnesene, a key building block for the biosynthesis of vitamin E. However, an insufficient yield of β-farnesene precludes its industrialization. Understanding the mechanism would be essential for attaining β-farnesene in high yield. Guided by structure-based enzyme engineering, we designed several potent variants, among which L326I increased the β-farnesene yield from 450.65 to 3877.42 mg/L. Furthermore, we found that the function of β-farnesene synthase AaFS can be modulated at two positions; W299 is responsible for tuning the enzyme's function to give its isomeric product α-farnesene and Y402 is the key residue for diverting from the linear farnesene products to the monocyclic α-bisabolol product. These findings provide valuable insights into the catalytic mechanism and functional modulation of farnesene synthases and set the basis for rational engineering of farnesene synthases for selective biosynthesis of diverse sesquiterpene natural products.

Unravelling soybean responses to early and late Tetranychus urticae (Acari: Tetranychidae) infestation

Soybean is a crucial source of food, protein, and oil worldwide that is facing challenges from biotic stresses. Infestation of Tetranychus urticae Koch (Acari: Tetranychidae) stands out as detrimentally affecting plant growth and grain production. Understanding soybean responses to T. urticae infestation is pivotal for unravelling the dynamics of mite-plant interactions. We evaluated the physiological and molecular responses of soybean plants to mite infestation after 5 and 21 days. We employed visual/microscopy observations of leaf damage, H2O2 accumulation, and lipid peroxidation. Additionally, the impact of mite infestation on shoot length/dry weight, chlorophyll concentration, and development stages was analysed. Proteomic analysis identified differentially abundant proteins (DAPs) after early (5 days) and late (21 days) infestation. Furthermore, GO, KEGG, and protein-protein interaction analyses were performed to understand effects on metabolic pathways. Throughout the analysed period, symptoms of leaf damage, H2O2 accumulation, and lipid peroxidation consistently increased. Mite infestation reduced shoot length/dry weight, chlorophyll concentration, and development stage duration. Proteomics revealed 185 and 266 DAPs after early and late mite infestation, respectively, indicating a complex remodelling of metabolic pathways. Photorespiration, chlorophyll synthesis, amino acid metabolism, and Krebs cycle/energy production were impacted after both early and late infestation. Additionally, specific metabolic pathways were modified only after early or late infestation. This study underscores the detrimental effects of mite infestation on soybean physiology and metabolism. DAPs offer potential in breeding programs for enhanced resistance. Overall, this research highlights the complex nature of soybean response to mite infestation, providing insights for intervention and breeding strategies.

Genome-wide identification and tissue expression pattern analysis of TPS gene family in soybean (Glycine max)

The terpene synthase (TPS) plays a pivotal roles in plant growth, development, and enhancing resilience against environmental stresses. Despite this, the bioinformatics analysis of the TPS family gene in soybean (Glycine max) is lacking. In this study, we investigated 36 GmTPS members in soybean, exhibiting a diverse range of protein lengths, spanning from 144 to 835 amino acids. A phylogenetic tree was constructed from these GmTPS genes revealed a classification into five distinct subgroups: Group1, Group2, Group3, Group4 and Group5. Notably, within each subgroup, we identified the motifs of GmTPS proteins were similar, although variations existed among different subfamilies. Gene duplication events analysis demonstrated that TPS genes expand differently in G. max, A. thaliana and O. sativa. Among, both tandem duplication and Whole genome duplication contributive to the expansion of TPS genes in G. max, and Whole genome duplication played a major role. Moreover, the cis-element analysis suggested that TPS is related to hormone signals, plant growth and development and environmental stress. Yeast two-hybrid (Y2H) assay results indicated TPS protein may form heterodimer to function, or may form complex with P450 proteins to function. RNA-seq results revealed a higher expression of most GmTPS genes in flowers, suggesting their potential contribution to flower development. Collectively, these findings offer a provide a holistic knowledge of the TPS gene family in soybean and will facilitate further characterization of TPSs effectively.

Convergence and molecular evolution of floral fragrance after independent transitions to self-fertilization

Studying the independent evolution of similar traits provides valuable insights into the ecological and genetic factors driving phenotypic evolution.1 The transition from outcrossing to self-fertilization is common in plant evolution2 and is often associated with a reduction in floral attractive features such as display size, chemical signals, and pollinator rewards.3 These changes are believed to result from the reallocation of the resources used for building attractive flowers, as the need to attract pollinators decreases.2,3 We investigated the similarities in the evolution of flower fragrance following independent transitions to self-fertilization in Capsella.4,5,6,7,8,9 We identified several compounds that exhibited similar changes in different selfer lineages, such that the flower scent composition reflects mating systems rather than evolutionary history within this genus. We further demonstrate that the repeated loss of β-ocimene emission, one of the compounds most strongly affected by these transitions, was caused by mutations in different genes. In one of the Capsella selfing lineages, the loss of its emission was associated with a mutation altering subcellular localization of the ortholog of TERPENE SYNTHASE 2. This mutation appears to have been fixed early after the transition to selfing through the capture of variants segregating in the ancestral outcrossing population. The large extent of convergence in the independent evolution of flower scent, together with the evolutionary history and molecular consequences of a causal mutation, suggests that the emission of specific volatiles evolved as a response to changes in ecological pressures rather than resource limitation.

Arabidopsis Transcriptomics Reveals the Role of Lipoxygenase2 (AtLOX2) in Wound-Induced Responses

In wounded Arabidopsis thaliana leaves, four 13S-lipoxygenases (AtLOX2, AtLOX3, AtLOX4, AtLOX6) act in a hierarchical manner to contribute to the jasmonate burst. This leads to defense responses with LOX2 playing an important role in plant resistance against caterpillar herb-ivory. In this study, we sought to characterize the impact of AtLOX2 on wound-induced phytohormonal and transcriptional responses to foliar mechanical damage using wildtype (WT) and lox2 mutant plants. Compared with WT, the lox2 mutant had higher constitutive levels of the phytohormone salicylic acid (SA) and enhanced expression of SA-responsive genes. This suggests that AtLOX2 may be involved in the biosynthesis of jasmonates that are involved in the antagonism of SA biosynthesis. As expected, the jasmonate burst in response to wounding was dampened in lox2 plants. Generally, 1 h after wounding, genes linked to jasmonate biosynthesis, jasmonate signaling attenuation and abscisic acid-responsive genes, which are primarily involved in wound sealing and healing, were differentially regulated between WT and lox2 mutants. Twelve h after wounding, WT plants showed stronger expression of genes associated with plant protection against insect herbivory. This study highlights the dynamic nature of jasmonate-responsive gene expression and the contribution of AtLOX2 to this pathway and plant resistance against insects.

Comprehensive transcriptomic meta-analysis unveils new responsive genes to methyl jasmonate and ethylene in Catharanthusroseus

In Catharanthus roseus, vital plant hormones, namely methyl jasmonate (MeJA) and ethylene, serve as abiotic triggers, playing a crucial role in stimulating the production of specific secondary compounds with anticancer properties. Understanding how plants react to various stresses, stimuli, and the pathways involved in biosynthesis holds significant promise. The application of stressors like ethylene and MeJA induces the plant's defense mechanisms, leading to increased secondary metabolite production. To delve into the essential transcriptomic processes linked to hormonal responses, this study employed an integrated approach combining RNA-Seq data meta-analysis and system biology methodologies. Furthermore, the validity of the meta-analysis findings was confirmed using RT-qPCR. Within the meta-analysis, 903 genes exhibited differential expression (DEGs) when comparing normal conditions to those of the treatment. Subsequent analysis, encompassing gene ontology, KEGG, TF, and motifs, revealed that these DEGs were actively engaged in multiple biological processes, particularly in responding to various stresses and stimuli. Additionally, these genes were notably enriched in diverse biosynthetic pathways, including those related to TIAs, housing valuable medicinal compounds found in this plant. Furthermore, by conducting co-expression network analysis, we identified hub genes within modules associated with stress response and the production of TIAs. Most genes linked to the biosynthesis pathway of TIAs clustered within three specific modules. Noteworthy hub genes, including Helicase ATP-binding domain, hbdA, and ALP1 genes within the blue, turquoise, and green module networks, are presumed to play a role in the TIAs pathway. These identified candidate genes hold potential for forthcoming genetic and metabolic engineering initiatives aimed at augmenting the production of secondary metabolites and medicinal compounds within C. roseus.

Biochemical analysis of the TPS-a subfamily in Medicago truncatula

Terpenes are important mediators of plant chemical response to environmental cues. Here, we describe the genome-wide identification and biochemical characterization of TPS-a members in Medicago truncatula, a model legume crop. Genome mining identified thirty-nine full-length terpene synthases with a significant number predicted to produce monoterpenes and sesquiterpenes. Biochemical characterization of the TPS-a subfamily associated with sesquiterpene biosynthesis revealed such compounds, that exhibit substantial biological activity in other plants. Gene expression analysis using qPCR and the Medicago gene atlas illustrated distinct tissue and time-based variation in expression in leaves and roots. Together our work establishes the gene-to-metabolite relationships for sesquiterpene synthases in M. truncatula. Understanding the biosynthetic capacity is a foundational step to defining the ecological roles of this important family of compounds.

Terpene Synthase Gene Family in Chinese Chestnut (Castanea mollissima BL.) Harbors Two Sesquiterpene Synthase Genes Implicated in Defense against Gall Wasp Dryocosmus kuriphilus

Chinese chestnut (Castanea mollissima BL.) is a well-known fruit tree that has been cultivated in East Asia for millennia. Leaves and buds of the plant can become seriously infested by the gall wasp Dryocosmus kuriphilus (GWDK), which results in gall formation and associated significant losses in fruit production. Herbivore-induced terpenes have been reported to play an important role in plant-herbivory interactions, and in this study, we show that upon herbivory by GWDK, four terpene-related compounds were significantly induced, while the concentrations of these four compounds in intact buds were relatively low. Among these compounds, (E)-nerolidol and (E, E)-α-farnesene have frequently been reported to be involved in plant herbivory defenses, which suggests direct and/or indirect functions in chestnut GWDK defenses. Candidate terpene synthase (TPS) genes that may account for (E)-nerolidol and (E, E)-α-farnesene terpene biosynthesis were characterized by transcriptomics and phylogenetic approaches, which revealed altered transcript levels for two TPSs: CmAFS, a TPS-g subfamily member, and CmNES/AFS, a TPS-b clade member. Both genes were dramatically upregulated in gene expression upon GWDK infestation. Furthermore, Agrobacterium tumefaciens-mediated transient overexpression in Nicotiana benthamiana showed that CmAFS catalyzed the formation of (E, E)-α-farnesene, while CmNES/AFS showed dual (E)-nerolidol and (E, E)-α-farnesene synthase activity. Biochemical assays of the recombinant CmAFS and CmNES/AFS proteins confirmed their catalytic activity in vitro, and the enzymatic products were consistent with two of the major volatile compounds released upon GWDK-infested chestnut buds. Subcellular localization demonstrated that CmAFS and CmNES/AFS were both localized in the cytoplasm, the primary compartment for sesquiterpene synthesis. In summary, we show that two novel sesquiterpene synthase genes CmAFS and CmNES/AFS are inducible by herbivory and can account for the elevated accumulation of (E, E)-α-farnesene and (E)-nerolidol upon GWDK infestation and may be implicated in chestnut defense against GWDK herbivores.

Stressing the importance of plant specialized metabolites: omics-based approaches for discovering specialized metabolism in plant stress responses

Plants produce a diverse range of specialized metabolites that play pivotal roles in mediating environmental interactions and stress adaptation. These unique chemical compounds also hold significant agricultural, medicinal, and industrial values. Despite the expanding knowledge of their functions in plant stress interactions, understanding the intricate biosynthetic pathways of these natural products remains challenging due to gene and pathway redundancy, multifunctionality of proteins, and the activity of enzymes with broad substrate specificity. In the past decade, substantial progress in genomics, transcriptomics, metabolomics, and proteomics has made the exploration of plant specialized metabolism more feasible than ever before. Notably, recent advances in integrative multi-omics and computational approaches, along with other technologies, are accelerating the discovery of plant specialized metabolism. In this review, we present a summary of the recent progress in the discovery of plant stress-related specialized metabolites. Emphasis is placed on the application of advanced omics-based approaches and other techniques in studying plant stress-related specialized metabolism. Additionally, we discuss the high-throughput methods for gene functional characterization. These advances hold great promise for harnessing the potential of specialized metabolites to enhance plant stress resilience in the future.

Secondary Metabolites and Their Role in Strawberry Defense

Strawberry is a high-value commercial crop and a model for the economically important Rosaceae family. Strawberry is vulnerable to attack by many pathogens that can affect different parts of the plant, including the shoot, root, flowers, and berries. To restrict pathogen growth, strawberry produce a repertoire of secondary metabolites that have an important role in defense against diseases. Terpenes, allergen-like pathogenesis-related proteins, and flavonoids are three of the most important metabolites involved in strawberry defense. Genes involved in the biosynthesis of secondary metabolites are induced upon pathogen attack in strawberry, suggesting their transcriptional activation leads to a higher accumulation of the final compounds. The production of secondary metabolites is also influenced by the beneficial microbes associated with the plant and its environmental factors. Given the importance of the secondary metabolite pathways in strawberry defense, we provide a comprehensive overview of their literature and their role in the defense responses of strawberry. We focus on terpenoids, allergens, and flavonoids, and discuss their involvement in the strawberry microbiome in the context of defense responses. We discuss how the biosynthetic genes of these metabolites could be potential targets for gene editing through CRISPR-Cas9 techniques for strawberry crop improvement.

Identification of cytochrome P450 gene family and functional analysis of HgCYP33E1 from Heterodera glycines

The cytochrome P450 (CYP) genes of nematode play a crucial role in the metabolic detoxification of xenobiotics including pesticides. Heterodera glycines, also known as the soybean cyst nematode, is a sedentary endoparasite that infests plant roots, causing high annual economic losses in soybean production regions globally. In this study, we identified 36 CYP genes at a genome-wide level of the H. glycines isolate TN10 using all CYPs from Caenorhabditis elegans as queries. Subsequently, a full-length cDNA of HgCYP33E1 which was significantly up-regulated by the conventional nematicide abamectin was initially cloned from H. glycines. It presented significantly higher expressions in the second-stage juvenile (J2) compared to other parasitic stages of H. glycines. qRT-PCR analysis suggested that the expression of HgCYP33E1 was also xenobiotically induced by soybean root exudate and the metabolites of biocontrol agents. Using RNA interference (RNAi), we investigated the function of HgCYP33E1 in H. glycines parasitism and nematicide selectivity. Compared to the control and dsGFP-treated group, silencing of HgCYP33E1 did not affect the J2 behaviors and the early invasion ability, while it decreased the number of J4s in soybean roots after 18-d inoculation with the dsHgCYP33E1-treated nematodes. In addition, knockdown of HgCYP33E1 in H. glycines resulted in an increase in J2 mortality after 24-h incubation with abamectin compared to the GFP dsRNA-soaked and the control group. These findings revealed the potential role of HgCYP33E1 in the xenobiotic detoxification pathway of H. glycines. Moreover, our data also provided valuable gene information for studying the functions of the CYP family in H. glycines host adaption.

Analysis of Defense-Related Gene Expression and Leaf Metabolome in Wheat During the Early Infection Stages of Blumeria graminis f. sp. tritici

Blumeria graminis f. sp. tritici (Bgt) is an obligate biotrophic fungal pathogen responsible for powdery mildew in bread wheat (Triticum aestivum). Upon Bgt infection, the wheat plant activates basal defense mechanisms, namely PAMP-triggered immunity, in the leaves during the first few days. Understanding this early stage of quantitative resistance is crucial for developing new breeding tools and evaluating plant resistance inducers for sustainable agricultural practices. In this sense, we used a combination of transcriptomic and metabolomic approaches to analyze the early steps of the interaction between Bgt and the moderately susceptible wheat cultivar Pakito. Bgt infection resulted in an increasing expression of genes encoding pathogenesis-related (PR) proteins (PR1, PR4, PR5, and PR8) known to target the pathogen, during the first 48 h postinoculation. Moreover, RT-qPCR and metabolomic analyses pointed out the importance of the phenylpropanoid pathway in quantitative resistance against Bgt. Among metabolites linked to this pathway, hydroxycinnamic acid amides containing agmatine and putrescine as amine components accumulated from the second to the fourth day after inoculation. This suggests their involvement in quantitative resistance via cross-linking processes in cell walls for reinforcement, which is supported by the up-regulation of PAL (phenylalanine ammonia-lyase), PR15 (oxalate oxidase) and POX (peroxidase) after inoculation. Finally, pipecolic acid, which is considered a signal involved in systemic acquired resistance, accumulated after inoculation. These new insights lead to a better understanding of basal defense in wheat leaves after Bgt infection.

Characterization of sandalwood (E,E)-α-farnesene synthase whose overexpression enhances cold tolerance through jasmonic acid biosynthesis and signaling in Arabidopsis

MAIN CONCLUSION

Santalum album (E,E)-α-farnesene synthase catalyzes FPP into (E,E)-α-farnesene. Overexpression of the SaAFS gene positively improved cold stress tolerance through JA biosynthesis and signaling pathways in Arabidopsis. Volatile terpenoids are released from plants that suffer negative effects following exposure to various biotic and abiotic stresses. Recent studies revealed that (E,E)-α-farnesene synthase (AFS) plays a significant role in a plant's defence against biotic attack. However, little is known about whether AFS contributes to plant resistance to cold stress. In this study, a SaAFS gene was isolated from Indian sandalwood (Santalum album L.) and functionally characterized. The SaAFS protein mainly converts farnesyl diphosphate to (E,E)-α-farnesene. SaAFS was clustered into the AFS clade from angiosperms, suggesting a highly conserved enzyme. SaAFS displayed a significant response to cold stress and methyl jasmonate. SaAFS overexpression (OE) in Arabidopsis enhanced cold tolerance by increasing proline content, reducing malondialdehyde content, electrolyte leakage, and accumulating reactive oxygen species. Transcriptomic analysis revealed that upregulated genes related to stress response and JA biosynthesis and signaling were detected in SaAFS-OE lines compared with wild type plants that were exposed to cold stress. Endogenous JA and jasmonoyl-isoleucine content increased significantly in SaAFS-OE lines exposed to cold stress. Collectively considered, these results suggest that the SaAFS gene is a positive regulator during cold stress tolerance via JA biosynthesis and signaling pathways.

Allelic variation of terpene synthases drives terpene diversity in the wild species of the Freesia genus

Terpene synthases (TPSs) play pivotal roles in conferring the structural diversity of terpenoids, which are mainly emitted from flowers, whereas the genetic basis of the release of floral volatile terpenes remains largely elusive. Though quite similar in sequence, TPS allelic variants still function divergently, and how they drive floral terpene diversity in closely related species remains unknown. Here, TPSs responsible for the floral scent of wild Freesia species were characterized, and the functions of their natural allelic variants, as well as the causal amino acid residues, were investigated in depth. Besides the 8 TPSs previously reported in modern cultivars, 7 additional TPSs were functionally evaluated to contribute to the major volatiles emitted from wild Freesia species. Functional characterization of allelic natural variants demonstrated that allelic TPS2 and TPS10 variants changed the enzymatic capacity while allelic TPS6 variants drove the diversity of floral terpene products. Further residue substitution analysis revealed the minor residues determining the enzyme catalytic activity and product specificity. The clarification of TPSs in wild Freesia species reveals that allelic TPS variants evolved differently to determine the interspecific floral volatile terpenes in the genus and might be used for modern cultivar improvement.

Chemical profile and analysis of biosynthetic pathways and genes of volatile terpenes in Pityopsis ruthii, a rare and endangered flowering plant

It is critical to gather biological information about rare and endangered plants to incorporate into conservation efforts. The secondary metabolism of Pityopsis ruthii, an endangered flowering plant that only occurs along limited sections of two rivers (Ocoee and Hiwassee) in Tennessee, USA was studied. Our long-term goal is to understand the mechanisms behind P. ruthii's adaptation to restricted areas in Tennessee. Here, we profiled the secondary metabolites, specifically in flowers, with a focus on terpenes, aiming to uncover the genomic and molecular basis of terpene biosynthesis in P. ruthii flowers using transcriptomic and biochemical approaches. By comparative profiling of the nonpolar portion of metabolites from various tissues, P. ruthii flowers were rich in terpenes, which included 4 monoterpenes and 10 sesquiterpenes. These terpenes were emitted from flowers as volatiles with monoterpenes and sesquiterpenes accounting for almost 68% and 32% of total emission of terpenes, respectively. These findings suggested that floral terpenes play important roles for the biology and adaptation of P. ruthii to its limited range. To investigate the biosynthesis of floral terpenes, transcriptome data for flowers were produced and analyzed. Genes involved in the terpene biosynthetic pathway were identified and their relative expressions determined. Using this approach, 67 putative terpene synthase (TPS) contigs were detected. TPSs in general are critical for terpene biosynthesis. Seven full-length TPS genes encoding putative monoterpene and sesquiterpene synthases were cloned and functionally characterized. Three catalyzed the biosynthesis of sesquiterpenes and four catalyzed the biosynthesis of monoterpenes. In conclusion, P. ruthii plants employ multiple TPS genes for the biosynthesis of a mixture of floral monoterpenes and sesquiterpenes, which probably play roles in chemical defense and attracting insect pollinators alike.

Functional Characterization of a (E)-β-Ocimene Synthase Gene Contributing to the Defense against Spodoptera litura

Soybean is a worldwide crop that offers valuable proteins, fatty acids, and phytonutrients to humans but is always damaged by insect pests or pathogens. Plants have captured sophisticated defense mechanisms in resisting the attack of insects and pathogens. How to protect soybean in an environment- or human-friendly way or how to develop plant-based pest control is a hotpot. Herbivore-induced plant volatiles that are released by multiple plant species have been assessed in multi-systems against various insects, of which (E)-β-ocimene has been reported to show anti-insect function in a variety of plants, including soybean. However, the responsible gene in soybean is unknown, and its mechanism of synthesis and anti-insect properties lacks comprehensive assessment. In this study, (E)-β-ocimene was confirmed to be induced by Spodoptera litura treatment. A plastidic localized monoterpene synthase gene, designated as GmOCS, was identified to be responsible for the biosynthesis of (E)-β-ocimene through genome-wide gene family screening and in vitro and in vivo assays. Results from transgenic soybean and tobacco confirmed that (E)-β-ocimene catalyzed by GmOCS had pivotal roles in repelling a S. litura attack. This study advances the understanding of (E)-β-ocimene synthesis and its function in crops, as well as provides a good candidate for further anti-insect soybean improvement.

Understandings and future challenges in soybean functional genomics and molecular breeding

Soybean (Glycine max) is a major source of plant protein and oil. Soybean breeding has benefited from advances in functional genomics. In particular, the release of soybean reference genomes has advanced our understanding of soybean adaptation to soil nutrient deficiencies, the molecular mechanism of symbiotic nitrogen (N) fixation, biotic and abiotic stress tolerance, and the roles of flowering time in regional adaptation, plant architecture, and seed yield and quality. Nevertheless, many challenges remain for soybean functional genomics and molecular breeding, mainly related to improving grain yield through high-density planting, maize-soybean intercropping, taking advantage of wild resources, utilization of heterosis, genomic prediction and selection breeding, and precise breeding through genome editing. This review summarizes the current progress in soybean functional genomics and directs future challenges for molecular breeding of soybean.

Histone deacetylase CsHDA6 mediates the regulated formation of the anti-insect metabolite α-farnesene in tea (Camellia sinensis)

α-Farnesene accumulated in tea plants following infestations by most insects, and mechanical wounding is the common factor. However, the specific mechanism underlying the wounding-regulated accumulation of α-farnesene in tea plants remains unclear. In this study, we observed that histone deacetylase inhibitor treatment induced the accumulation of α-farnesene. The histone deacetylase CsHDA6 interacted directly with CsMYC2, which was an important transcription factor in the jasmonic acid (JA) pathway, and co-regulated the expression of the key α-farnesene synthesis gene CsAFS. Wounding caused by insect infestation affected CsHDA6 production at the transcript and protein levels, while also inhibited the binding of CsHDA6 to the CsAFS promoter. The resulting increased acetylation of histones H3/H4 in CsAFS enhanced the expression of CsAFS and the accumulation of α-farnesene. In conclusion, our study demonstrated the effect of histone acetylation on the production of tea plant HIPVs and revealed the importance of the CsHDA6-CsMYC2 transcriptional regulatory module.

Genome-wide analysis of terpene synthase gene family to explore candidate genes related to disease resistance in Prunus persica

In plants, a family of terpene synthases (TPSs) is responsible for the biosynthesis of terpenes and contributes to species-specific diversity of volatile organic compounds, which play essential roles in fitness of plants. However, little is known about the TPS gene family in peach and/or nectarine (Prunus persica L.). In this study, we identified 40 PpTPS genes in peach genome v2.0. Although these PpTPSs could be clustered into five classes, they distribute in several gene clusters of three chromosomes, share conserved exon-intron organizations, and code similar protein motifs. Thirty-five PpTPSs, especially PpTPS2, PpTPS23, PpTPS17, PpTPS18, and PpTPS19, altered their transcript levels after inoculation with Botryosphaeria dothidea, a cause of peach gummosis, compared to the mock treatments, which might further affect the contents of 133 terpenoids at 48 hours and/or 84 hours post inoculations in the current-year shoots of 'Huyou018', a highly susceptible nectarine cultivar. Moreover, about fifteen PpTPSs, such as PpTPS1, PpTPS2, PpTPS3, and PpTPS5, showed distinct expression patterns during fruit development and ripening in two peach cultivars, yellow-fleshed 'Jinchun' and white-fleshed 'Hikawa Hakuho'. Among them, the transcription level of chloroplast-localized PpTPS3 was obviously related to the content of linalool in fruit pulps. In addition, elevated concentrations (0.1 g/L to 1.0 g/L) of linalool showed antifungal activities in PDA medium. These results improve our understanding of peach PpTPS genes and their potential roles in defense responses against pathogens.

Transcription factor MdLSD1 negatively regulates α-farnesene biosynthesis in apple-fruit skin tissue

α-Farnesene is a sesquiterpene present in plants. It was first discovered in apples. It plays an important role in the plant defence response and is considered a key factor in the occurrence of superficial scald. The gene encoding α-farnesene synthase, which is the last key enzyme in the biosynthetic pathway of α-farnesene in apple fruit, has become the primary target enzyme for controlling the genetic manipulation of α-farnesene biosynthesis. In this study, the yeast one-hybrid assay and the dual luciferase assay were used to ascertain the relationship between MdLSD1 and MdAFS. Real-time PCR was used to analyse the molecular mechanism underlying the regulation of MdAFS by MdLSD1. Our results revealed that transcription factor MdLSD1, which is closely related to programmed cell death in apple fruit tissues, binds to MdAFS. Transient transformation of apple skin with vectors overexpressing MdLSD1 showed that the gene negatively regulates MdAFS. Overall, we suggest that MdLSD1 negatively regulates MdAFS. Our results are of great significance for future research on the transcriptional regulation of the α-farnesene synthase gene and provide a new direction for exploring the specific mechanism of programmed cell death involved in superficial-scald incidence.

Systemic effects of Tuber melanosporum inoculation in two Corylus avellana genotypes

Roots of the European hazelnut (Corylus avellana L.), i.e., one of the most economically important nut species, form symbiosis with ectomycorrhizal (ECM) fungi, including truffles. Although physical interactions only occur in roots, the presence of mycorrhizal fungi can lead to metabolic changes at a systemic level, i.e., in leaves. However, how root colonization by ECM fungi modifies these processes in the host plant has so far not been widely studied. This work aimed to investigate the response in two C. avellana genotypes, focusing on leaves from plants inoculated with the black truffle Tuber melanosporum Vittad. Transcriptomic profiles of leaves of colonized plants were compared with those of non-colonized plants, as well as sugar and polyphenolic content. Results suggested that T. melanosporum has the potential to support plants in stressed conditions, leading to the systemic regulation of several genes involved in signaling and defense responses. Although further confirmation is needed, our results open new perspectives for future research aimed to highlight novel aspects in ECM symbiosis.

Effect of Developmental Stages on Genes Involved in Middle and Downstream Pathway of Volatile Terpene Biosynthesis in Rose Petals

Terpenoids are economically and ecologically important compounds, and they are vital constituents in rose flower fragrance and rose essential oil. The terpene synthase genes (TPSs), trans-prenyltransferases genes (TPTs), NUDX1 are involved in middle and downstream pathway of volatile terpene biosynthesis in rose flowers. We identified 7 complete RcTPTs, 49 complete RcTPSs, and 9 RcNUDX1 genes in the genome of Rosachinensis. During the flower opening process of butterfly rose (Rosachinensis ‘Mutabilis’, MU), nine RcTPSs expressed in the petals of opening MU flowers exhibited two main expression trends, namely high and low, in old and fresh petals. Five short-chain petal-expressed RcTPTs showed expression patterns corresponding to RcTPSs. Analysis of differential volatile terpenes and differential expressed genes indicated that higher emission of geraniol from old MU petals might be related to the RcGPPS expression. Comprehensive analysis of volatile emission, sequence structure, micro-synteny and gene expression suggested that RcTPS18 may encode (E,E)-α-farnesene synthase. These findings may be useful for elucidating the molecular mechanism of terpenoid metabolism in rose and are vital for future studies on terpene regulation.

Biogenic VOCs Emission Profiles Associated with Plant-Pest Interaction for Phenotyping Applications

Pest attacks on plants can substantially change plants' volatile organic compounds (VOCs) emission profiles. Comparison of VOC emission profiles between non-infected/non-infested and infected/infested plants, as well as resistant and susceptible plant cultivars, may provide cues for a deeper understanding of plant-pest interactions and associated resistance. Furthermore, the identification of biomarkers-specific biogenic VOCs-associated with the resistance can serve as a non-destructive and rapid tool for phenotyping applications. This research aims to compare the VOCs emission profiles under diverse conditions to identify constitutive (also referred to as green VOCs) and induced (resulting from biotic/abiotic stress) VOCs released in potatoes and wheat. In the first study, wild potato Solanum bulbocastanum (accession# 22; SB22) was inoculated with Meloidogyne chitwoodi race 1 (Mc1), and Mc1 pathotype Roza (SB22 is resistant to Mc1 and susceptible to pathotype Roza), and VOCs emission profiles were collected using gas chromatography-flame ionization detection (GC-FID) at different time points. Similarly, in the second study, the VOCs emission profiles of resistant ('Hollis') and susceptible ('Alturas') wheat cultivars infested with Hessian fly insects were evaluated using the GC-FID system. In both studies, in addition to variable plant responses (susceptibility to pests), control treatments (non-inoculated or non-infested) were used to compare the VOCs emission profiles resulting from differences in stress conditions. The common VOC peaks (constitutive VOCs) between control and infected/infested samples, and unique VOC peaks (induced VOCs) presented only in infected/infested samples were analyzed. In the potato-nematode study, the highest unique peak was found two days after inoculation (DAI) for SB22 inoculated with Mc1 (resistance response). The most common VOC peaks in SB22 inoculated with both Mc1 and Roza were found at 5 and 10 DAI. In the wheat-insect study, only the Hollis showed unique VOC peaks. Interestingly, both cultivars released the same common VOCs between control and infected samples, with only a difference in VOC average peak intensity at 22.4 min retention time where the average intensity was 4.3 times higher in the infested samples of Hollis than infested samples of Alturas. These studies demonstrate the potential of plant VOCs to serve as a rapid phenotyping tool to assess resistance levels in different crops.

Transcriptome sequencing and differential expression analysis of natural and BTH-treated wound healing in potato tubers (Solanum tuberosum L.)

Background

Wound healing is a representative phenomenon of potato tubers subjected to mechanical injuries. Our previous results found that benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH) promoted the wound healing of potato tubers. However, the molecular mechanism related to inducible wound healing remains unknown.

Results

Transcriptomic evaluation of healing tissues from potato tubers at three stages, namely, 0 d (nonhealing), 5 d (wounded tubers healed for 5 d) and 5 d (BTH-treated tubers healed for 5 d) using RNA-Seq and differentially expressed genes (DEGs) analysis showed that more than 515 million high-quality reads were generated and a total of 7665 DEGs were enriched, and 16 of these DEGs were selected by qRT-PCR analysis to further confirm the RNA sequencing data. Gene ontology (GO) enrichment analysis indicated that the most highly DEGs were involved in metabolic and cellular processes, and KEGG enrichment analysis indicated that a large number of DEGs were associated with plant hormones, starch and sugar metabolism, fatty acid metabolism, phenylpropanoid biosynthesis and terpenoid skeleton biosynthesis. Furthermore, a few candidate transcription factors, including MYB, NAC and WRKY, and genes related to Ca²⁺-mediated signal transduction were also found to be differentially expressed during wound healing. Most of these enriched DEGs were upregulated after BTH treatment.

Conclusion

This comparative expression profile provided useful resources for studies of the molecular mechanism via these promising candidates involved in natural or elicitor-induced wound healing in potato tubers.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08480-1.

Growth regulators promote soybean productivity: a review

Soybean [Glycine max (L.) Merrill] is a predominant edible plant and a major supply of plant protein worldwide. Global demand for soybean keeps increasing as its seeds provide essential proteins, oil, and nutraceuticals. In a quest to meet heightened demands for soybean, it has become essential to introduce agro-technical methods that promote adaptability to complex environments, improve soybean resistance to abiotic stress , and increase productivity. Plant growth regulators are mainly exploited to achieve this due to their crucial roles in plant growth and development. Increasing research suggests the influence of plant growth regulators on soybean growth and development, yield, quality, and abiotic stress responses. In an attempt to expatiate on the topic, current knowledge, and possible applications of plant growth regulators that improve growth and yield have been reviewed and discussed. Notably, the application of plant growth regulators in their appropriate concentrations at suitable growth periods relieves abiotic stress thereby increasing the yield and yield components of soybean. Moreover, the regulation effects of different growth regulators on the morphology, physiology, and yield quality of soybean are discoursed in detail.

Progress in soybean functional genomics over the past decade

Soybean is one of the most important oilseed and fodder crops. Benefiting from the efforts of soybean breeders and the development of breeding technology, large number of germplasm has been generated over the last 100 years. Nevertheless, soybean breeding needs to be accelerated to meet the needs of a growing world population, to promote sustainable agriculture and to address future environmental changes. The acceleration is highly reliant on the discoveries in gene functional studies. The release of the reference soybean genome in 2010 has significantly facilitated the advance in soybean functional genomics. Here, we review the research progress in soybean omics (genomics, transcriptomics, epigenomics and proteomics), germplasm development (germplasm resources and databases), gene discovery (genes that are responsible for important soybean traits including yield, flowering and maturity, seed quality, stress resistance, nodulation and domestication) and transformation technology during the past decade. At the end, we also briefly discuss current challenges and future directions.

A chromosome-level genome assembly of an alpine plant Crucihimalaya lasiocarpa provides insights into high-altitude adaptation

It remains largely unknown how plants adapt to high-altitude habitats. Crucihimalaya (Brassicaceae) is an alpine genus occurring in the Qinghai-Tibet Plateau characterized by cold temperatures and strong ultraviolet radiation. Here, we generated a chromosome-level genome for C. lasiocarpa with a total size of 255.8 Mb and a scaffold N50 size of 31.9 Mb. We first examined the karyotype origin of this species and found that the karyotype of five chromosomes resembled the ancestral karyotype of the Brassicaceae family, while the other three showed strong chromosomal structural variations. In combination with the rough genome sequence of another congener (C. himalaica), we found that the significantly expanded gene families and positively selected genes involved in alpine adaptation have occurred since the origin of this genus. Our new findings provide valuable information for the chromosomal karyotype evolution of Brassicaceae and investigations of high-altitude environment adaptation of the genus.

High-quality evergreen azalea genome reveals tandem duplication-facilitated low-altitude adaptability and floral scent evolution

Azalea belongs to Rhododendron, which is one of the largest genera of flowering plants and is well known for the diversity and beauty in its more than 1000 woody species. Rhododendron contains two distinct groups: the most high-altitude and a few low-altitude species; however, the former group is difficult to be domesticated for urban landscaping, and their evolution and adaptation are little known. Rhododendron ovatum has broad adaptation in low-altitude regions but possesses evergreen characteristics like high-altitude species, and it has floral fragrance that is deficient in most cultivars. Here we report the chromosome-level genome assembly of R. ovatum, which has a total length of 549 Mb with scaffold N50 of 41 Mb and contains 41 264 predicted genes. Genomic micro-evolutionary analysis of R. ovatum in comparison with two high-altitude Rhododendron species indicated that the expansion genes in R. ovatum were significantly enriched in defence responses, which may account for its adaptability in low altitudes. The R. ovatum genome contains much more terpene synthase genes (TPSs) compared with the species that lost floral fragrance. The subfamily b members of TPS are involved in the synthesis of sesquiterpenes as well as monoterpenes and play a major role in flora scent biosynthesis and defence responses. Tandem duplication is the primary force driving expansion of defence-responsive genes for extensive adaptability to the low-altitude environments. The R. ovatum genome provides insights into low-altitude adaptation and gain or loss of floral fragrance for Rhododendron species, which are valuable for alpine plant domestication and floral scent breeding.

Soybean Cyst Nematodes Influence Aboveground Plant Volatile Signals Prior to Symptom Development

Soybean cyst nematode (SCN), Heterodera glycines, is one of the most destructive soybean pests worldwide. Unlike many diseases, SCN doesn't show above ground evidence of disease until several weeks after infestation. Knowledge of Volatile Organic Compounds (VOCs) related to pests and pathogens of foliar tissue is extensive, however, information related to above ground VOCs in response to root damage is lacking. In temporal studies, gas chromatography-mass spectrometry analysis of VOCs from the foliar tissues of SCN infested plants yielded 107 VOCs, referred to as Common Plant Volatiles (CPVs), 33 with confirmed identities. Plants showed no significant stunting until 10 days after infestation. Total CPVs increased over time and were significantly higher from SCN infested plants compared to mock infested plants post 7 days after infestation (DAI). Hierarchical clustering analysis of expression ratios (SCN: Mock) across all time points revealed 5 groups, with the largest group containing VOCs elevated in response to SCN infestation. Linear projection of Principal Component Analysis clearly separated SCN infested from mock infested plants at time points 5, 7, 10 and 14 DAI. Elevated Styrene (CPV11), D-Limonene (CPV32), Tetradecane (CPV65), 2,6-Di-T-butyl-4-methylene-2,5-cyclohexadiene-1-one (CPV74), Butylated Hydroxytoluene (CPV76) and suppressed Ethylhexyl benzoate (CPV87) levels, were associated with SCN infestation prior to stunting. Our findings demonstrate that SCN infestation elevates the release of certain VOCs from foliage and that some are evident prior to symptom development. VOCs associated with SCN infestations prior to symptom development may be valuable for innovative diagnostic approaches.

Functional characterization and substrate promiscuity of sesquiterpene synthases from Tripterygium wilfordii

Acyclic terpenes, commonly found in plants, are of high physiological importance and commercial value, and their diversity was controlled by different terpene synthases. During the screen of sesquiterpene synthases from Tripterygium wilfordii, we observed that Ses-TwTPS1-1 and Ses-TwTPS2 promiscuously accepted GPP, FPP, and GGPP to produce corresponding terpene alcohols (linalool/nerolidol/geranyllinalool). The Ses-TwTPS1-2, Ses-TwTPS3, and Ses-TwTPS4 also showed unusual substrate promiscuity by catalyzing GGPP or GPP in addition to FPP as substrate. Furthermore, key residues for the generation of diterpene product, (E, E)-geranyllinalool, were screened depending on mutagenesis studies. The functional analysis of Ses-TwTPS1-1:V199I and Ses-TwTPS1-2:I199V showed that Val in 199 site assisted the produce of diterpene product geranyllinalool by enzyme mutation studies, which indicated that subtle differences away from the active site could alter the product outcome. Moreover, an engineered sesquiterpene high-yielding yeast that produced 162 mg/L nerolidol in shake flask conditions was constructed to quickly identify the function of sesquiterpene synthases in vivo and develop potential applications in microbial fermentation. Our functional characterization of acyclic sesquiterpene synthases will give some insights into the substrate promiscuity of diverse acyclic terpene synthases and provide key residues for expanding the product portfolio.

Dual Regulation of Cytoplasm and Peroxisomes for Improved Α-Farnesene Production in Recombinant Pichia pastoris

Microbial production of α-farnesene from renewable raw materials is a feasible alternative to traditional petroleum craft. Recently, the research on improving α-farnesene production in Pichia pastoris mainly focused on cytoplasmic engineering, while comprehensive engineering of multiple subcellular compartments is rarely reported. Here, we first sought to confirm that the isopentenol utilization pathway (IUP) could act as a two-step shortcut for IPP synthesis in P. pastoris peroxisomes. In addition, we proposed dual regulation of cytoplasm and peroxisomes to boost α-farnesene synthesis in P. pastoris X33, thus the resultant strain produced 2.18 ± 0.04 g/L, which was 1.3 times and 2.1 times than that of the strain only with peroxisomal or cytoplasmic engineering, respectively. The α-farnesene production achieved 2.56 ± 0.04 g/L in shake flasks after carbon source cofeeding, which was the highest reported production in worldwide literatures to the best of my knowledge. Therefore, we propose these strategies as efficient approaches to enhancing α-farnesene production in P. pastoris, which might bring new ideas for the biosynthesis of high-value compounds.

Overproduction of α-Farnesene in Saccharomyces cerevisiae by Farnesene Synthase Screening and Metabolic Engineering

Maximizing the flux of farnesyl diphosphate (FPP) to farnesene biosynthesis is the main challenge of farnesene overproduction in Saccharomyces cerevisiae. In this study, we screened α-farnesene synthase from soybean (Fsso) with a higher catalytic ability. Combining the overexpression of the mevalonate (MVA) pathway with the expression of Fsso, an engineered yeast strain producing 190.5 mg/L α-farnesene was screened with poor growth. By decreasing the copies of 3-hydroxy-3-methylglutaryl-coenzyme (HMGR) overexpressed, the titer was increased to 417.8 mg/L. Then, the coexpression of Fsso and HMGR under the control of the GAL promoter and inactivation of lipid phosphate phosphatase encoded by DPP1 promoted the titer to 1163.7 mg/L. The titer was further increased to 1477.2 mg/L at the shake flask level with better growth by the construction of a prototrophic strain. Finally, the highest α-farnesene production of 10.4 g/L in S. cerevisiae was obtained by fed-batch fermentation in a 5 L bioreactor.

Five TPSs are responsible for volatile terpenoid biosynthesis in Albizia julibrissin

Silk tree, Albizia julibrissin Duraz, is an old ornamental plant and extensively cultivated in Asia. Previous works have discovered that the terpenoids were the dominating compounds in the floral VOC of A. julibrissin, however the biosynthesis of these terpenoids was poorly understood so far. Here, 11 terpene synthase genes (TPSs) were identified by transcriptome sequencing that fell into TPS-a, TPS-b and TPS-g subfamilies. The enzymatic activity tests showed that five genes were functional: AjTPS2 was a sesquiterpene synthase and produced α-farnesene and (Z, E)-β-farnesene; AjTPS5 was able to catalyze the formation of five monoterpenes and nine sesquiterpenes; AjTPS7, AjTPS9 and AjTPS10 were dedicated monoterpene synthases, as AjTPS7 and AjTPS10 formed the single product β-ocimene and linalool, respectively, and AjTPS9 produced γ-terpinene with other three monoterpenes. More importantly, the main catalytic products of the characterized AjTPSs were consistent with the terpenoids observed in A. julibrissin volatiles. Combining terpene chemistry, TPSs biochemical activities and gene expression analysis, we demonstrate that AjTPS2, AjTPS5, AjTPS7, AjTPS9 and AjTPS10 are responsible for the volatile terpenoids biosynthesis in A. julibrissin.

De novo transcriptome assembly of transgenic tobacco (Nicotiana tabacum NC89) with early senescence characteristic

The enzyme, α-farnesene synthase (AFS), which synthesizes α-farnesene, is the final enzyme in α-farnesene synthesis pathway. We overexpressed the α-farnesene synthase gene (previously cloned in our lab from apple peel) and ectopically expressed it in tobacco (Nicotiana tabacum NC89). Then, the transgenic plants showed an accelerated developmental process and bloomed about 7 weeks earlier than the control plants. We anticipate that de novo transcriptomic analyses of N. tabacum may provide useful information on isoprenoid biosynthesis, growth, and development. We generated 318,925,338 bp sequencing data using Illumina paired-end sequencing from the cDNA library of the apical buds of transgenic line and the wild-type line. We annotated and functionally classified the unigenes in a nucleotide and protein database. Differentially expressed unigenes may be involved in carbohydrate metabolism, nitrogen metabolism, transporter activity, hormone signal transduction, antioxidant systems and transcription regulator activity particularly related to senescence. Moreover, we analyzed eight genes related to terpenoid biosynthesis using qRT-PCR to study the changes in growth and development patterns in the transgenic plants. Our study shows that transgenic plants show premature senescence.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-00953-z.

Identification and characterization of two sesquiterpene synthase genes involved in volatile-mediated defense in tea plant (Camellia sinensis)

Terpenes and their derivatives are vital components of tea aroma. Their constitution and quantity are highly important criteria for the sensory evaluation of teas. Biologically, terpenes are involved in chemical resistance of tea plant against biotic and/or abiotic stresses. The goal of this study is to identify volatile terpenes of tea plants implicated in defense against herbivores and to identify terpene synthase (TPS) genes for their biosynthesis. Upon herbivory by tea geometrid (Ectropis obliqua Prout), tea plants were found to emit two sesquiterpenes, (E, E)-α-farnesene and (E)-nerolidol, which were undetectable in intact tea plants. The induced emission of (E, E)-α-farnesene and (E)-nerolidol suggests that they function in either direct or indirect defense of tea plants against the tea geometrid. Candidate TPS genes were identified from the transcriptomes of tea plants infested by tea geometrids. Two dedicated sesquiterpene synthases, CsAFR and CsNES2, were identified. CsAFR belongs to the TPS-b clade and can catalyze the formation of (E, E)-α-farnesene from (E, E)-FPP. CsNES2 belongs to the TPS-g clade and can synthesize (E)-nerolidol using (E, E)-FPP. The two genes were also both dramatically upregulated by herbivore damage. In summary, we showed that two novel sesquiterpene synthase genes CsAFR and CsNSE2 are inducible by herbivory and responsible for the elevated emission of herbivore-induced (E, E)-α-farnesene and (E)-nerolidol, which are implicated in tea plant defense against herbivores.

MdMYC2 and MdERF3 Positively Co-Regulate α-Farnesene Biosynthesis in Apple

α-Farnesene, a sesquiterpene volatile compound plays an important role in plant defense and is known to be associated with insect attraction and with superficial scald of apple and pear fruits during cold storage. But the mechanism whereby transcription factors regulate apple α-farnesene biosynthesis has not been clarified. Here, we report that two transcription factors, MdMYC2 and MdERF3 regulated α-farnesene biosynthesis in apple fruit. Dual-luciferase assays and Y1H assays indicated that MdMYC2 and MdERF3 effectively trans-activated the MdAFS promoter. EMSAs showed that MdERF3 directly binds the DRE motif in the MdAFS promoter. Subsequently, overexpression of MdMYC2 and MdERF3 in apple calli markedly activated the transcript levels of MdHMGR2 and MdAFS. Furthermore, transient overexpression of MdMYC2 and MdERF3 in apple fruit significantly increased MdAFS expression and hence, α-farnesene production. These results indicate that MdMYC2 and MdERF3 are positive regulators of α-farnesene biosynthesis and have important value in genetic engineering of α-farnesene production.

Production of multiple terpenes of different chain lengths by subcellular targeting of multi-substrate terpene synthase in plants

Multi-substrate terpene synthases (TPSs) are distinct from typical TPSs that react with a single substrate. Although in vitro activity of few multi-substrate TPSs have been reported, in vivo characterization has not been well investigated for most of them. Here, a new TPS from Cananga odorata, CoTPS5, belonging to TPS-f subfamily was functionally characterized in vitro as well as in vivo. CoTPS5 reacted with multiple prenyl-pyrophosphate substrates of various chain lengths as a multi-substrate TPS. It catalyzed the formation of (E)-β-ocimene, (E,E)-α-farnesene and α-springene from geranyl pyrophosphate, (E,E)-farnesyl pyrophosphate and geranylgeranyl pyrophosphate, respectively. Upon transient expression in Nicotiana benthamiana, CoTPS5 localized to cytosol and produced only (E,E)-α-farnesene. However, expression of plastid-targeted CoTPS5 in N. benthamiana resulted in biosynthesis of all three compounds, (E)-β-ocimene, (E,E)-α-farnesene and α-springene. Similarly, transgenic Arabidopsis plants overexpressing plastid-targeted CoTPS5 showed stable and sustainable production of (E)-β-ocimene, (E,E)-α-farnesene and α-springene. Moreover, their production did not affect the growth and development of transgenic Arabidopsis plants. Our results demonstrate that redirecting multi-substrate TPS to a different intracellular compartment could be an effective way to prove in vivo activity of multi-substrate TPSs and thereby allowing for the production of multiple terpenoids simultaneously in plants.

Characterization of the Biogenic Volatile Organic Compounds (BVOCs) and Analysis of the PR1 Molecular Marker in Vitis vinifera L. Inoculated with the Nematode Xiphinema index

Upon pathogen attack, plants very quickly undergo rather complex physico-chemical changes, such as the production of new chemicals or alterations in membrane and cell wall properties, to reduce disease damages. An underestimated threat is represented by root parasitic nematodes. In Vitis vinifera L., the nematode Xiphinema index is the unique vector of Grapevine fanleaf virus, responsible for fanleaf degeneration, one of the most widespread and economically damaging diseases worldwide. The aim of this study was to investigate changes in the emission of biogenic volatile organic compounds (BVOCs) in grapevines attacked by X. index. BVOCs play a role in plant defensive mechanisms and are synthetized in response to biotic damages. In our study, the BVOC profile was altered by the nematode feeding process. We found a decrease in β-ocimene and limonene monoterpene emissions, as well as an increase in α-farnesene and α-bergamotene sesquiterpene emissions in nematode-treated plants. Moreover, we evaluated the PR1 gene expression. The transcript level of PR1 gene was higher in the nematode-wounded roots, while in the leaf tissues it showed a lower expression compared to control grapevines.

Formation of α-Farnesene in Tea (Camellia sinensis) Leaves Induced by Herbivore-Derived Wounding and Its Effect on Neighboring Tea Plants

Herbivore-induced plant volatiles (HIPVs) play important ecological roles in defense against stresses. In contrast to model plants, reports on HIPV formation and function in crops are limited. Tea (Camellia sinensis) is an important crop in China. α-Farnesene is a common HIPV produced in tea plants in response to different herbivore attacks. In this study, a C. sinensis α-farnesene synthase (CsAFS) was isolated, cloned, sequenced, and functionally characterized. The CsAFS recombinant protein produced in Escherichia coli was able to transform farnesyl diphosphate (FPP) into α-farnesene and also convert geranyl diphosphate (GPP) to β-ocimene in vitro. Furthermore, transient expression analysis in Nicotiana benthamiana plants indicated that CsAFS was located in the cytoplasm and could convert FPP to α-farnesene in plants. Wounding, to simulate herbivore damage, activated jasmonic acid (JA) formation, which significantly enhanced the CsAFS expression level and α-farnesene content. This suggested that herbivore-derived wounding induced α-farnesene formation in tea leaves. Furthermore, the emitted α-farnesene might act as a signal to activate antibacterial-related factors in neighboring undamaged tea leaves. This research advances our understanding of the formation and signaling roles of common HIPVs in crops such as tea plants.

Phytoparasitic Nematode Control of Plant Hormone Pathways

Phytoparasitic nematodes use multiple tactics to influence phytohormone physiology and alter plant developmental programs to establish feeding sites.

Acibenzolar-S-Methyl Reprograms Apple Transcriptome Toward Resistance to Rosy Apple Aphid

Acibenzolar-S-methyl (ASM) is a chemical compound, which is able to induce resistance in several model and non-model plants, but the end-players of this induced defense remain ill-defined. Here, we test the hypothesis that treatment with ASM can protect apple (Malus × domestica) against the rosy apple aphid (Dysaphis plantaginea) and investigate the defense molecules potentially involved in resistance. We measured aphid life traits and performed behavioral assays to study the effect of ASM on plant resistance against the aphid, and then combined transcriptomic, bioinformatics, metabolic and biochemical analyses to identify the plant compounds involved in resistance. Plants treated with ASM negatively affected several life traits of the aphid and modified its feeding and host seeking behaviors. ASM treatment elicited up-regulation of terpene synthase genes in apple and led to the emission of (E,E)-α-farnesene, a sesquiterpene that was repellent to the aphid. Several genes encoding amaranthin-like lectins were also strongly up-regulated upon treatment and the corresponding proteins accumulated in leaves, petioles and stems. Our results link the production of specific apple proteins and metabolites to the antibiosis and antixenosis effects observed against Dysaphis plantaginea, providing insight into the mechanisms underlying ASM-induced herbivore resistance.

A laboratory high-throughput glass chamber using dynamic headspace TD-GC/MS method for the analysis of whole Brassica napus L. plantlet volatiles under cadmium-related abiotic stress

INTRODUCTION

The dynamic headspace sampling technique using thermal desorption, gas chromatography-mass spectrometry (TD-GC/MS) is a powerful method for analysing plant emissions of volatile organic compounds (VOCs), and experiments performed in sterile and controlled conditions can be useful for VOC metabolism investigations.

OBJECTIVE

The main purpose of this study was to set up a laboratory high-throughput glass chamber for whole plant volatiles analysis. Brassica napus L. plantlets were tested with the developed system to better understand the relationship between low emission of induced terpene and cadmium (Cd)-related abiotic stress.

METHODOLOGY

VOCs emitted by 28-day-old Brassica napus L. plantlets cultivated in vitro were trapped with our device using adsorbent cartridges that were desorbed with a thermal desorption unit before cryofocusing with a cooled injection system and programmable temperature vaporising inlet into an HP-5 ms GC column. Terpene detection and quantitation from chromatogram profiles were acquired using selected ion monitoring (SIM) mode during full scan analysis and mass spectra were obtained with a quadrupole-type mass spectrometer.

RESULTS

The new trapping method produced reliable qualitative profiles of oilseed rape VOCs. Typical emissions of monoterpenes (myrcene, limonene) and sesquiterpenes (β-elemene, (E,E)-α-farnesene) were found for the different concentrations tested. One-way analysis of variance for quantitative results of (E,E)-α-farnesene emission rates showed a Cd concentration effect.

CONCLUSION

This inexpensive glass chamber has potential for wide application in laboratory sterile approach and replicated research. Moreover, the non-invasive dynamic sampling technique could also be used to analyse volatiles under both abiotic and biotic stresses.

UV-B irradiation differentially regulates terpene synthases and terpene content of peach

Plants generate protective molecules in response to ultraviolet (UV) light. In laboratory experiments, 48 h UV-B irradiation of peach fruits and leaves reduced the flavour-related monoterpene linalool by 60%. No isoprene was detected, but other terpenoids increased significantly, including a threefold accumulation of the sesquiterpene (E,E)-α-farnesene, which was also increased by jasmonic acid treatment. RNA sequencing revealed altered transcript levels for two terpene synthases (TPSs): PpTPS1, a TPS-g subfamily member, decreased by 86% and PpTPS2, a TPS-b subfamily member, increased 80-fold. Heterologous expression in Escherichia coli and transient overexpression in tobacco and peach fruits showed PpTPS1 was localized in plastids and associated with production of linalool, while PpTPS2 was responsible for (E,E)-α-farnesene biosynthesis in the cytoplasm. Candidate regulatory genes for these responses were identified. Commercial peach production in Asia involves fruit bagging to maintain marketable yield and quality. TPS gene expression and volatile terpenoid production in field experiments, using bags transmitting high UV-B radiation, showed similar effects on peach volatiles to those from laboratory experiments. Bags transmitting less UV-B light ameliorated the reduction in the flavour volatile linalool, indicating that flavour components of peach fruits can be modulated by selecting an appropriate source of environmental screening material.