Network analysis of the MVA and MEP pathways for isoprenoid synthesis

Research progress on carotenoid production by Rhodosporidium toruloides

Carotenoids are natural lipophilic pigments, which have been proven to provide significant health benefits to humans, relying on their capacity to efficiently scavenge singlet oxygen and peroxyl radicals as antioxidants. Strains belonging to the genus Rhodosporidium represent a heterogeneous group known for a number of phenotypic traits including accumulation of carotenoids and lipids and tolerance to heavy metals and oxidative stress. As a representative of these yeasts, Rhodosporidium toruloides naturally produces carotenoids with high antioxidant activity and grows on a wide variety of carbon sources. As a result, R. toruloides is a promising host for the efficient production of more value-added lipophilic compound carotenoids, e.g., torulene and torularhodin. This review provides a comprehensive summary of the research progress on carotenoid biosynthesis in R. toruloides, focusing on the understanding of biosynthetic pathways and the regulation of key enzymes and genes involved in the process. Moreover, the relationship between the accumulation of carotenoids and lipid biosynthesis, as well as the stress from diverse abiotic factors, has also been discussed for the first time. Finally, several feasible strategies have been proposed to promote carotenoid production by R. toruloides. It is possible that R. toruloides may become a critical strain in the production of carotenoids or high-value terpenoids by genetic technologies and optimal fermentation processes. KEY POINTS: • Biosynthetic pathway and its regulation of carotenoids in Rhodosporidium toruloides were concluded • Stimulation of abiotic factors for carotenoid biosynthesis in R. toruloides was summarized • Feasible strategies for increasing carotenoid production by R. toruloides were proposed.

Engineering a non-model yeast Rhodotorula mucilaginosa for terpenoids synthesis

Terpenoids have tremendous biological activities and are widely employed in food, healthcare and pharmaceutical industries. Using synthetic biology to product terpenoids from microbial cell factories presents a promising alternative route compared to conventional methods such as chemical synthesis or phytoextraction. The red yeast Rhodotorula mucilaginosa has been widely studied due to its natural production capacity of carotenoid and lipids, indicating a strong endogenous isoprene pathway with readily available metabolic intermediates. This study constructed several engineered strains of R. mucilaginosa with the aim of producing different terpenoids. Monoterpene α-terpineol was produced by expressing the α-terpineol synthase from Vitis vinifera. The titer of α-terpineol was further enhanced to 0.39 mg/L by overexpressing the endogenous rate-limiting gene of the MVA pathway. Overexpression of α-farnesene synthase from Malus domestica, in combination with MVA pathway rate-limiting gene resulted in significant increase in α-farnesene production, reaching a titer of 822 mg/L. The carotenoid degradation product β-ionone was produced at a titer of 0.87 mg/L by expressing the β-ionone synthase from Petunia hybrida. This study demonstrates the potential of R. mucilaginosa as a platform host for the direct biosynthesis of various terpenoids and provides insights for further development of such platforms.

Conversion obstacle from Mg-protoporphyrin IX to protochlorophyllide might be responsible for chlorophyll-deficient phenotype of the Huangjinya's albino offspring

The albino tea cultivar is one of the most important germplasms for key gene mining and high-quality tea producing. In order to elucidate the chlorophyll-deficient mechanism of albino cultivar 'Huangjinya' and its offspring, color difference, photosynthetic pigments and the relevant genes' expression of the tender shoots were comprehensively investigated in this study. Among the tested 16 offspring, 5 exhibited albino phenotype in spring and autumn, 3 showed albino phenotype in spring but normal green in autumn, while the rests were all normal green. The shoot of albino offspring had significantly higher lightness and/or yellowness than that of green ones, and possessed dramatically lower photosynthetic pigments and chlorophyll precursor protochlorophyllide (Pchlide), as well as higher chlorophyll a/chlorophyll b but lower chlorophylls/carotenoids in comparison with green ones. Among the tested genes involved in chlorophyll and carotenoid metabolism pathways, expression of the magnesium protoporphyrin IX monomethyl ester cyclase (CRD), 3,8-divinyl chlorophyllide 8-vinyl reductase (DVR), 5-aminolevulinate dehydratase 1 (HEMB1), 1-deoxy-D-xylulose 5-phosphate synthase 1 (DXS1) and 4-hydroxy-3-methylbut-2-enyl diphosphate reductase (ISPH) was remarkably down-regulated in shoots of the albino offspring. Color difference indices of the offspring were significantly correlated with the levels of photosynthetic pigments and Pchlide, and low level of chlorophylls in shoot of albino offspring was mainly due to conversion obstacle from magnesium protoporphyrin Ⅸ (Mg-Proto IX) to Pchlide which might be attributed to down-regulatory expression of CRD and DVR.

HY5 and PIF antagonistically regulate HMGR expression and sterol biosynthesis in Arabidopsis thaliana

Secondary metabolites play multiple crucial roles in plants by modulating various regulatory networks. The biosynthesis of these compounds is unique to each species and is intricately controlled by a range of developmental and environmental factors. While light's role in certain secondary metabolites is evident, its impact on sterol biosynthesis remains unclear. Previous studies indicate that ELONGATED HYPOCOTYL5 (HY5), a bZIP transcription factor, is pivotal in skotomorphogenesis to photomorphogenesis transition. Additionally, PHYTOCHROME INTERACTING FACTORs (PIFs), bHLH transcription factors, act as negative regulators. To unveil the light-dependent regulation of the mevalonic acid (MVA) pathway, a precursor for sterol biosynthesis, mutants of light signaling components, specifically hy5-215 and the pifq quadruple mutant (pif 1,3,4, and 5), were analyzed in Arabidopsis thaliana. Gene expression analysis in wild-type and mutants implicates HY5 and PIFs in regulating sterol biosynthesis genes. DNA-protein interaction analysis confirms their interaction with key genes like AtHMGR2 in the rate-limiting pathway. Results strongly suggest HY5 and PIFs' pivotal role in light-dependent MVA pathway regulation, including the sterol biosynthetic branch, in Arabidopsis, highlighting a diverse array of light signaling components finely tuning crucial growth pathways.

Plant terpenoid biosynthetic network and its multiple layers of regulation

Terpenoids constitute one of the largest and most chemically diverse classes of primary and secondary metabolites in nature with an exceptional breadth of functional roles in plants. Biosynthesis of all terpenoids begins with the universal five‑carbon building blocks, isopentenyl diphosphate (IPP) and its allylic isomer dimethylallyl diphosphate (DMAPP), which in plants are derived from two compartmentally separated but metabolically crosstalking routes, the mevalonic acid (MVA) and methylerythritol phosphate (MEP) pathways. Here, we review the current knowledge on the terpenoid precursor pathways and highlight the critical hidden constraints as well as multiple regulatory mechanisms that coordinate and homeostatically govern carbon flux through the terpenoid biosynthetic network in plants.

Engineering carbon source division of labor for efficient α-carotene production in Corynebacterium glutamicum

Effective utilization of glucose, xylose, and acetate, common carbon sources in lignocellulose hydrolysate, can boost biomanufacturing economics. However, carbon leaks into biomass biosynthesis pathways instead of the intended target product remain to be optimized. This study aimed to enhance α-carotene production by optimizing glucose, xylose, and acetate utilization in a high-efficiency Corynebacterium glutamicum cell factory. Heterologous xylose pathway expression in C. glutamicum resulted in strain m4, exhibiting a two-fold increase in α-carotene production from xylose compared to glucose. Xylose utilization was found to boost the biosynthesis of pyruvate and acetyl-CoA, essential precursors for carotenoid biosynthesis. Additionally, metabolic engineering including pck, pyc, ppc, and aceE deletion, completely disrupted the metabolic connection between glycolysis and the TCA cycle, further enhancing α-carotene production. This strategic intervention directed glucose and xylose primarily towards target chemical production, while acetate supplied essential metabolites for cell growth recovery. The engineered strain C. glutamicum m8 achieved 30 mg/g α-carotene, 67% higher than strain m4. In fed-batch fermentation, strain m8 produced 1802 mg/L of α-carotene, marking the highest titer reported to date in microbial fermentation. Moreover, it exhibited excellent performance in authentic lignocellulosic hydrolysate, producing 216 mg/L α-carotene, 1.45 times higher than the initial strain (m4). These labor-division strategies significantly contribute to the development of clean processes for producing various valuable chemicals from lignocellulosic resources.

Label-free based comparative proteomics approach revealed the changes in proteomic profiles driven by different maturities in two Chinese white truffles, Tuber panzhihuanense and Tuber latisporum

T. panzhihuanense and T. latisporum are white truffle species native to China, of which T. panzhihuanense has significant commercial potential, with high nutritional value and unique flavor. Maturity is an important factor affecting the nutrition and aroma of truffles, which determines their economic status. Here, a label-free-based comparative proteomics method was used to determine the proteomic profiles of T. panzhihuanense and T. latisporum at two different stages of maturity. The results showed that both maturity and species significantly affected the protein expression patterns. T. panzhihuanense responded stronger to maturity than T. latisporum, accompanied by a more complex interaction network between proteins. Some critical proteins were regulated by maturity and variety, including those involved in aroma formation, e.g., S-adenosyl-methionine synthetase. The enrichment of oxidation-reduction processes, glycolysis, and SNARE interactions in vesicular transport were driven by species and maturity. This study provides the first insights into the proteomic profiles of T. panzhihuanense and T. latisporum, revealing the roles of key proteins and biological processes in their maturation.

Genomic analysis based on chromosome-level genome assembly reveals Myrtaceae evolution and terpene biosynthesis of rose myrtle

BACKGROUND

Rose myrtle (Rhodomyrtus tomentosa (Ait.) Hassk), is an evergreen shrub species belonging to the family Myrtaceae, which is enriched with bioactive volatiles (α-pinene and β-caryophyllene) with medicinal and industrial applications. However, the mechanism underlying the volatile accumulation in the rose myrtle is still unclear.

RESULTS

Here, we present a chromosome-level genomic assembly of rose myrtle (genome size = 466 Mb, scaffold N50 = 43.7 Mb) with 35,554 protein-coding genes predicted. Through comparative genomic analysis, we found that gene expansion and duplication had a potential contribution to the accumulation of volatile substances. We proposed that the action of positive selection was significantly involved in volatile accumulation. We identified 43 TPS genes in R. tomentosa. Further transcriptomic and TPS gene family analyses demonstrated that the distinct gene subgroups of TPS may contribute greatly to the biosynthesis and accumulation of different volatiles in the Myrtle family of shrubs and trees. The results suggested that the diversity of TPS-a subgroups led to the accumulation of special sesquiterpenes in different plants of the Myrtaceae family.

CONCLUSIONS

The high quality chromosome-level rose myrtle genome and the comparative analysis of TPS gene family open new avenues for obtaining a higher commercial value of essential oils in medical plants.

Signatures of Adaptation and Purifying Selection in Highland Populations of Dasiphora fruticosa

High mountains harbor a considerable proportion of biodiversity, but we know little about how diverse plants adapt to the harsh environment. Here we finished a high-quality genome assembly for Dasiphora fruticosa, an ecologically important plant distributed in the Qinghai-Tibetan Plateau and lowland of the Northern Hemisphere, and resequenced 592 natural individuals to address how this horticulture plant adapts to highland. Demographic analysis revealed D. fruticosa underwent a bottleneck after Naynayxungla Glaciation. Selective sweep analysis of two pairs of lowland and highland populations identified 63 shared genes related to cell wall organization or biogenesis, cellular component organization, and dwarfism, suggesting parallel adaptation to highland habitats. Most importantly, we found that stronger purging of estimated genetic load due to inbreeding in highland populations apparently contributed to their adaptation to the highest mountain. Our results revealed how plants could tolerate the extreme plateau, which could provide potential insights for species conservation and crop breeding.

The Ginkgo biloba microRNA160-ERF4 module participates in terpene trilactone biosynthesis

Terpene trilactones (TTLs) are important secondary metabolites in ginkgo (Ginkgo biloba); however, their biosynthesis gene regulatory network remains unclear. Here, we isolated a G. biloba ethylene response factor 4 (GbERF4) involved in TTL synthesis. Overexpression of GbERF4 in tobacco (Nicotiana tabacum) significantly increased terpenoid content and upregulated the expression of key enzyme genes (3-hydroxy-3-methylglutaryl-CoA reductase [HMGR], 3-hydroxy-3-methylglutaryl-CoA synthase [HMGS], 1-deoxy-D-xylulose-5-phosphate reductoisomerase [DXR], 1-deoxy-D-xylulose-5-phosphate synthase [DXS], acetyl-CoA C-acetyltransferase [AACT], and geranylgeranyl diphosphate synthase [GGPPS]) in the terpenoid pathway in tobacco, suggesting that GbERF4 functions in regulating the synthesis of terpenoids. The expression pattern analysis and previous microRNA (miRNA) sequencing showed that gb-miR160 negatively regulates the biosynthesis of TTLs. Transgenic experiments showed that overexpression of gb-miR160 could significantly inhibit the accumulation of terpenoids in tobacco. Targeted inhibition and dual-luciferase reporter assays confirmed that gb-miR160 targets and negatively regulates GbERF4. Transient overexpression of GbERF4 increased TTL content in G. biloba, and further transcriptome analysis revealed that DXS, HMGS, CYPs, and transcription factor genes were upregulated. In addition, yeast 1-hybrid and dual-luciferase reporter assays showed that GbERF4 could bind to the promoters of the HMGS1, AACT1, DXS1, levopimaradiene synthase (LPS2), and GGPPS2 genes in the TTL biosynthesis pathway and activate their expression. In summary, this study investigated the molecular mechanism of the gb-miR160-GbERF4 regulatory module in regulating the biosynthesis of TTLs. It provides information for enriching the understanding of the regulatory network of TTL biosynthesis and offers important gene resources for the genetic improvement of G. biloba with high contents of TTLs.

Investigating the spatiotemporal expression of CBTS genes lead to the discovery of tobacco root as a cembranoid-producing organ

Tobacco cembranoids, known for their anti-insect and antifungal properties, were shown to be mainly present on the surface of leaves and flowers, being biosynthesized by their trichomes. It remains unclear whether they could be biosynthesized in other organs without trichomes. Cembratrien-ol synthases (CBTSs) catalyze the conversion of GGPP to CBT-ols and thus play an important role in cembranoid biosynthesis. This study identified the CBTS family genes in tobacco and examined their spatiotemporal expression patterns. The CBTS genes showed diverse expression patterns in tobacco organs, with the majority highly expressed in leaves and a few highly expressed in flowers. The expression of CBTS genes were also correlated with the development of tobacco plants, and most of them showed the highest expression level at the budding stage. Furthermore, their expression is mediated by the JA (jasmonate) signaling in all tobacco organs. Several CBTS genes were found to be highly expressed in tobacco roots that have no trichomes, which prompted us to determine the cembranoid production in roots and other organs. GC-MS and UPLC assays revealed that cembranoids were produced in all tobacco organs, which was supported by the bioactivity assay results that almost all these CBTS enzymes could catalyze CBT-ol biosyntheis in yeast, and that the content ratio of CBT-ols and CBT-diols in tobacco roots was different to that in leaves. This work sheds insights into the expression profiles of tobacco CBTS genes and provides a feasibility to engineer tobacco roots for industrial production of cembranoids.

Windthrow causes declines in carbohydrate and phenolic concentrations and increased monoterpene emission in Norway spruce

With the increasing frequencies of extreme weather events caused by climate change, the risk of forest damage from insect attacks grows. Storms and droughts can damage and weaken trees, reduce tree vigour and defence capacity and thus provide host trees that can be successfully attacked by damaging insects, as often observed in Norway spruce stands attacked by the Eurasian spruce bark beetle Ips typographus. Following storms, partially uprooted trees with grounded crowns suffer reduced water uptake and carbon assimilation, which may lower their vigour and decrease their ability to defend against insect attack. We conducted in situ measurements on windthrown and standing control trees to determine the concentrations of non-structural carbohydrates (NSCs), of phenolic defences and volatile monoterpene emissions. These are the main storage and defence compounds responsible for beetle´s pioneer success and host tree selection. Our results show that while sugar and phenolic concentrations of standing trees remained rather constant over a 4-month period, windthrown trees experienced a decrease of 78% and 37% of sugar and phenolic concentrations, respectively. This strong decline was especially pronounced for fructose (-83%) and glucose (-85%) and for taxifolin (-50.1%). Windthrown trees emitted 25 times greater monoterpene concentrations than standing trees, in particular alpha-pinene (23 times greater), beta-pinene (27 times greater) and 3-carene (90 times greater). We conclude that windthrown trees exhibited reduced resources of anti-herbivore and anti-pathogen defence compounds needed for the response to herbivore attack. The enhanced emission rates of volatile terpenes from windthrown trees may provide olfactory cues during bark beetle early swarming related to altered tree defences. Our results contribute to the knowledge of fallen trees vigour and their defence capacity during the first months after the wind-throw disturbance. Yet, the influence of different emission rates and profiles on bark beetle behaviour and host selection requires further investigation.

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

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

Single-cell transcriptome profiling reveals the spatiotemporal distribution of triterpenoid saponin biosynthesis and transposable element activity in Gynostemma pentaphyllum shoot apexes and leaves

Gynostemma pentaphyllum (Thunb.) Makino is an important producer of dammarene-type triterpenoid saponins. These saponins (gypenosides) exhibit diverse pharmacological benefits such as anticancer, antidiabetic, and immunomodulatory effects, and have major potential in the pharmaceutical and health care industries. Here, we employed single-cell RNA sequencing (scRNA-seq) to profile the transcriptomes of more than 50,000 cells derived from G. pentaphyllum shoot apexes and leaves. Following cell clustering and annotation, we identified five major cell types in shoot apexes and four in leaves. Each cell type displayed substantial transcriptomic heterogeneity both within and between tissues. Examining gene expression patterns across various cell types revealed that gypenoside biosynthesis predominantly occurred in mesophyll cells, with heightened activity observed in shoot apexes compared to leaves. Furthermore, we explored the impact of transposable elements (TEs) on G. pentaphyllum transcriptomic landscapes. Our findings the highlighted the unbalanced expression of certain TE families across different cell types in shoot apexes and leaves, marking the first investigation of TE expression at the single-cell level in plants. Additionally, we observed dynamic expression of genes involved in gypenoside biosynthesis and specific TE families during epidermal and vascular cell development. The involvement of TE expression in regulating cell differentiation and gypenoside biosynthesis warrant further exploration. Overall, this study not only provides new insights into the spatiotemporal organization of gypenoside biosynthesis and TE activity in G. pentaphyllum shoot apexes and leaves but also offers valuable cellular and genetic resources for a deeper understanding of developmental and physiological processes at single-cell resolution in this species.

ApCPS2 contributes to medicinal diterpenoid biosynthesis and defense against insect herbivore in Andrographis paniculata

Kalmegh (Andrographis paniculata) spatiotemporally produces medicinally-important ent-labdane-related diterpenoids (ent-LRDs); andrographolide (AD), 14-deoxy-11,12-didehydroandrographolide (DDAD), neoandrographolide (NAD). ApCPS1 and ApCPS2, the ent-copalyl pyrophosphate (ent-CPP)-producing class II diterpene synthases (diTPSs) were identified, but their contributions to ent-CPP precursor supply for ent-LRD biosynthesis were not well understood. Here, we characterized ApCPS4, an additional ent-CPP-forming diTPS. Further, we elucidated in planta function of the ent-CPP-producing diTPSs (ApCPS1,2,4) by integrating transcript-metabolite co-profiles, biochemical analysis and gene functional characterization. ApCPS1,2,4 localized to the plastids, where diterpenoid biosynthesis occurs in plants, but ApCPS1,2,4 transcript expression patterns and ent-LRD contents revealed a strong correlation of ApCPS2 expression and ent-LRD accumulation in kalmegh. ApCPS1,2,4 upstream sequences differentially activated β-glucuronidase (GUS) in Arabidopsis and transiently-transformed kalmegh. Similar to higher expression of ApCPS1 in kalmegh stem, ApCPS1 upstream sequence activated GUS in stem/hypocotyl of Arabidopsis and kalmegh. However, ApCPS2,4 upstream sequences weakly activated GUS expression in Arabidopsis, which was not well correlated with ApCPS2,4 transcript expression in kalmegh tissues. Whereas, ApCPS2,4 upstream sequences could activate GUS expression at a considerable level in kalmegh leaf and roots/calyx, respectively, suggesting the involvement of transcriptional regulator(s) of ApCPS2,4 that might participate in kalmegh-specific diterpenoid pathway. Interestingly, ApCPS2-silenced kalmegh showed a drastic reduction in AD, DDAD and NAD contents and compromised defense against insect herbivore Spodoptera litura. However, ent-LRD contents and herbivore defense in ApCPS1 or ApCPS4-silenced plants remained largely unaltered. Overall, these results suggested an important role of ApCPS2 in producing ent-CPP for medicinal ent-LRD biosynthesis and defense against insect herbivore.

Methyl-Jasmonate Functions as a Molecular Switch Promoting Cross-Talk between Pathways for the Biosynthesis of Isoprenoid Backbones Used to Modify Proteins in Plants

In plants, the plastidial mevalonate (MVA)-independent pathway is required for the modification with geranylgeranyl groups of CaaL-motif proteins, which are substrates of protein geranylgeranyltransferase type-I (PGGT-I). As a consequence, fosmidomycin, a specific inhibitor of 1-deoxy-d-xylulose (DX)-5 phosphate reductoisomerase/DXR, the second enzyme in this so-called methylerythritol phosphate (MEP) pathway, also acts as an effective inhibitor of protein prenylation. This can be visualized in plant cells by confocal microscopy by expressing GFP-CaM-CVIL, a prenylation sensor protein. After treatment with fosmidomycin, the plasma membrane localization of this GFP-based sensor is altered, and a nuclear distribution of fluorescence is observed instead. In tobacco cells, a visual screen of conditions allowing membrane localization in the presence of fosmidomycin identified jasmonic acid methyl esther (MeJA) as a chemical capable of gradually overcoming inhibition. Using Arabidopsis protein prenyltransferase loss-of-function mutant lines expressing GFP-CaM-CVIL proteins, we demonstrated that in the presence of MeJA, protein farnesyltransferase (PFT) can modify the GFP-CaM-CVIL sensor, a substrate the enzyme does not recognize under standard conditions. Similar to MeJA, farnesol and MVA also alter the protein substrate specificity of PFT, whereas DX and geranylgeraniol have limited or no effect. Our data suggest that MeJA adjusts the protein substrate specificity of PFT by promoting a metabolic cross-talk directing the origin of the prenyl group used to modify the protein. MVA, or an MVA-derived metabolite, appears to be a key metabolic intermediate for this change in substrate specificity.

The identification and functional characterization of the LcMCT gene from Liriodendron chinense reveals its potenatial role in carotenoids biosyanthesis

Terpenoids are not only important component of plant floral scent, but also indispensable elements in the formation of floral color. The petals of Liriodendron chinense are rich in tetraterpene carotenoids and release large amounts of volatile monoterpene and sesquiterpene compounds during full blooming stage. However, the mechanism of terpenoid synthesis is not clear in L. chinense. In this study, we identified a LcMCT gene and characterized its potential function in carotenoids biosynthesis. A total of 2947 up-regulated differentially expressed genes (DEGs) were discerned from the transcriptomic data of L. chinense petals, with a significant enrichment of DEGs related to plant hormone signal transduction and terpenoid backbone biosynthesis. After comprehensive analysis on these DEGs, the LcMCT gene was selected for subsequent function characterization. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) results showed that LcMCT was expressed at the highest level in the petals during full blooming stage, suggesting a possible role in carotenoids biosynthesis and volatile terpenoid biosynthesis. Subcellular localization showed that the LcMCT protein was localized in the chloroplast. Overexpression of LcMCT in Arabidopsis thaliana affected the expression levels of MEP pathway genes. Moreover, the MCT enzyme activity and carotenoids contents in transgenic A. thaliana were increased by 69.27% and 15.57%, respectively. These results suggest that LcMCT promotes the biosynthesis of terpenoid precursors via the MEP pathway. Our work lays a foundation for exploring the mechanism of terpenoid synthesis in L. chinense.

Hydroxamate-Containing Bisphosphonates as Fosmidomycin Analogues: Design, Synthesis, and Proherbicide Activity

Fosmidomycin (FOS) is a natural product inhibiting the DXR enzyme in the MEP pathway and has stimulated interest for finding more suitable FOS analogues. Herein, two series of FOS analogue hydroxamate-containing bisphosphonates as proherbicides were designed, with bisphosphonate replacing the phosphonic unit in FOS while retaining the hydroxamate (BPF series) or replacing it with retro-hydroxamate (BPRF series). The BPF series were synthesized through a three-step reaction sequence including Michael addition of vinylidenebisphosphonate, N-acylation, and deprotection, and the BPRF series were synthesized with a retro-Claisen condensation incorporated into the reaction sequence. Evaluation on model plants demonstrated several compounds having considerable herbicidal activities, and in particular, compound 8m exhibited multifold activity enhancement as compared to the control FOS. The proherbicide properties were comparatively validated. Furthermore, DXR enzyme assay, dimethylallyl pyrophosphate rescue, and molecular docking verified 8m to be a promising proherbicide candidate targeting the DXR enzyme. In addition, 8m also displayed good antimalarial activities.

LaMYC7, a positive regulator of linalool and caryophyllene biosynthesis, confers plant resistance to Pseudomonas syringae

Linalool and caryophyllene are the main monoterpene and sesquiterpene compounds in lavender; however, the genes regulating their biosynthesis still remain many unknowns. Here, we identified LaMYC7, a positive regulator of linalool and caryophyllene biosynthesis, confers plant resistance to Pseudomonas syringae. LaMYC7 was highly expressed in glandular trichomes, and LaMYC7 overexpression could significantly increase the linalool and caryophyllene contents and reduce susceptibility to P. syringae in Nicotiana. In addition, the linalool possessed antimicrobial activity against P. syringae growth and acted dose-dependently. Further analysis demonstrated that LaMYC7 directly bound to the promoter region of LaTPS76, which encodes the terpene synthase (TPS) for caryophyllene biosynthesis, and that LaTPS76 was highly expressed in glandular trichomes. Notably, the LaMYC7 promoter contained hormone and stress-responsive regulatory elements and responded to various treatments, including ultraviolet, low temperature, salt, drought, methyl jasmonate, and P. syringae infection treatments. Under these treatments, the changes in the linalool and caryophyllene contents were similar to those in LaMYC7 transcript abundance. Based on the results, LaMYC7 could respond to P. syringae infection in addition to being involved in linalool and caryophyllene biosynthesis. Thus, the MYC transcription factor gene LaMYC7 can be used in the breeding of high-yielding linalool and caryophyllene lavender varieties with pathogen resistance.

Revelation of enzyme/transporter-mediated metabolic regulatory model for high-quality terpene accumulation in developing fruits of Lindera glauca

Lindera glauca with rich resource and fruit terpene has emerged as potential material for utilization in China, but different germplasms show a variation for essential oil content and volatile profiling. This work aimed to determine key regulators (enzymes or transporters) and unravel mechanism of governing high production of essential oil of L. glauca fruit (EO-LGF). Temporal analysis of fruit growth and EO-LGF accumulation (yield, volatile compounds and contents) during development revealed a notable change in the contents of EO-LGF and its 45 compounds in developing fruits, and the major groups were monoterpene and sesquiterpene, showing good antioxidant and antimicrobial activities. To highlight molecular mechanism that govern such difference in terpene content and compound in developing fruits, Genome-wide assay was used to annotate 104 genes for terpene-synthesis pathway based on recent transcriptome data, and the comparative associations of terpene accumulative amount with gene transcriptional level were conducted on developing fruits to identify some crucial determinants (enzymes and transporters) with metabolic regulation model for high-quality terpene accumulation, involving in carbon allocation (sucrose cleavage, glycolysis and OPP pathway), metabolite transport, isoprene precursor production, C5-unit formation (MEP and MVA pathways), and mono-/sesqui-terpene synthesis. Our findings may present strategy for engineering terpene accumulation for utilization.

OXIDOSQUALENE CYCLASE 1 and 2 influence triterpene biosynthesis and defense in Nicotiana attenuata

Triterpenes are a class of bioactive compounds with diverse biological functions, playing pivotal roles in plant defense against biotic stressors. Oxidosqualene cyclases (OSCs) serve as gatekeepers in the biosynthesis of triterpenes. In this study, we utilized a Nicotiana benthamiana heterologous expression system to characterize NaOSC1 from Nicotiana attenuata as a multifunctional enzyme capable of synthesizing lupeol, dammarenediol II, 3-alpha,20-lupanediol, and 7 other triterpene scaffolds. We also demonstrated that NaOSC2 is, in contrast, a selective enzyme, producing only the β-amyrin scaffold. Through virus-induced gene silencing and in vitro toxicity assays, we elucidated the roles of NaOSC1 and NaOSC2 in the defense of N. attenuata against Manduca sexta larvae. Metabolomic and feature-based molecular network analyses of leaves with silenced NaOSC1 and NaOSC2 unveiled 3 potential triterpene glycoside metabolite clusters. Interestingly, features identified as triterpenes within these clusters displayed a significant negative correlation with larval mass. Our study highlights the pivotal roles of NaOSC1 and NaOSC2 from N. attenuata in the initial steps of triterpene biosynthesis, subsequently influencing defense against M. sexta through the modulation of downstream triterpene glycoside compounds.

Preparation and characterization of pickering emulsion stabilized by lovastatin nanoparticles for vaccine adjuvants

While research on mevalonate inhibitors as vaccine adjuvants has made great progress to enhance the effectiveness of the vaccine, co delivery of lovastatin and antigens (OVA) remains an enormous challenge. Here, we encapsulated lovastatin into PLGA nanoparticles. PLGA loading lovastatin was further emulsified with squalene to prepare Pickering emulsion. The emulsification conditions of Pickering emulsion were optimized, and the optimal preparation conditions were obtained. After loading lovastatin and OVA, the size and zeta potential of LS-PPAS/OVA was 1043.33 nm and -22.07 mv, the adsorption rate of OVA was 63.34 %. The adsorbing of LS-PLGA nanoparticles on the surface of squalene in Pickering emulsions was demonstrated by Fluorescent confocal microscopy. After immunization, LS-PPAS enhanced the activation of dendritic cells in lymph nodes, further study found LS-PPAS not only elicited elevated levels of OVA-specific IgG and its subtypes, but also promoted the secretion of TNF-α, IFN-γ, and IL-6 in serum as a marker of cellular immunity. Importantly, LS-PPAS showed sufficient security through monitoring levels of biochemical parameters in serum and pathological observation of organ following vaccinations. LS-PPAS may act as a promising vaccine carrier to produce strong humoral and cellular immunity with acceptable safety.

Overexpression of tocopherol biosynthesis genes in guayule (Parthenium argentatum) reduces rubber, resin and argentatins content in stem and leaf tissues

Natural rubber produced in stems of the guayule plant (Parthenium argentatum) is susceptible to post-harvest degradation from microbial or thermo-oxidative processes, especially once stems are chipped. As a result, the time from harvest to extraction must be minimized to recover high quality rubber, especially in warm summer months. Tocopherols are natural antioxidants produced in plants through the shikimate and methyl-erythtiol-4-phosphate (MEP) pathways. We hypothesized that increased in vivo guayule tocopherol content might protect rubber from post-harvest degradation, and/or allow reduced use of chemical antioxidants during the extraction process. With the objective of enhancing tocopherol content in guayule, we overexpressed four Arabidopsis thaliana tocopherol pathway genes in AZ-2 guayule via Agrobacterium-mediated transformation. Tocopherol content was increased in leaf and stem tissues of most transgenic lines, and some improvement in thermo-oxidative stability was observed. Overexpression of the four tocopherol biosynthesis enzymes, however, altered other isoprenoid pathways resulting in reduced rubber, resin and argentatins content in guayule stems. The latter molecules are mainly synthesized from precursors derived from the mevalonate (MVA) pathway. Our results suggest the existence of crosstalk between the MEP and MVA pathways in guayule and the possibility that carbon metabolism through the MEP pathway impacts rubber biosynthesis.

A diterpene synthase from the sandfly Lutzomyia longipalpis produces the pheromone sobralene

The phlebotomine sandfly, Lutzomyia longipalpis, a major vector of the Leishmania parasite, uses terpene pheromones to attract conspecifics for mating. Examination of the L. longipalpis genome revealed a putative terpene synthase (TPS), which-upon heterologous expression in, and purification from, Escherichia coli-yielded a functional enzyme. The TPS, termed LlTPS, converted geranyl diphosphate (GPP) into a mixture of monoterpenes with low efficiency, of which β-ocimene was the major product. (E,E)-farnesyl diphosphate (FPP) principally produced small amounts of (E)-β-farnesene, while (Z,E)- and (Z,Z)-FPP yielded a mixture of bisabolene isomers. None of these mono- and sesquiterpenes are known volatiles of L. longipalpis. Notably, however, when provided with (E,E,E)-geranylgeranyl diphosphate (GGPP), LlTPS gave sobralene as its major product. This diterpene pheromone is released by certain chemotypes of L. longipalpis, in particular those found in the Ceará state of Brazil. Minor diterpene components were also seen as products of the enzyme that matched those seen in a sandfly pheromone extract.

Deciphering magnesium binding site and structure-function insights in a class II sesquiterpene cyclase

Magnesium ions (Mg2+) are crucial in class II terpene cyclases that utilize substrates with diphosphate groups. Interestingly, these enzymes catalyze reactions without cleaving the diphosphate group, instead initiating the reaction through protonation. In our recent research, we discovered a novel class II sesquiterpene cyclase in Streptomyces showdoensis. Notably, we determined its crystal structure and identified Mg2+ within its active site. This finding has shed light on the previously elusive question of Mg2+ binding in class II terpene cyclases. In this chapter, we outline our methods for discovering this novel enzyme, including steps for its purification, crystallization, and kinetic analysis.

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.

Feedback regulation of the isoprenoid pathway by SsdTPS overexpression has the potential to enhance plant tolerance to drought stress

In order to maintain the dynamic physiological balance, plants are compelled to adjust their energy metabolism and signal transduction to cope with the abiotic stresses caused by complex and changeable environments. The diterpenoid natural compound and secondary metabolites, sclareol, derived from Salvia sclarea, has gained significant attention owing to its economic value as a spice material and diverse physiological activities. Here, we focused on the roles and regulatory mechanisms of the sclareol diterpene synthase gene SsdTPS in the resistance of S. sclarea to abiotic stresses. Our results suggested that abiotic stresses could induce the response and upregulation of SsdTPS expression and isoprenoid pathway in S. sclarea. Ectopic expression of SsdTPS conferred drought tolerance in transgenic Arabidopsis, compared with wild-type. Overexpression of SsdTPS enhanced the transcription of ABA signal transduction synthetic regulators and induced the positive feedback upregulating key regulatory genes in the MEP pathway, thereby promoting the increase of ABA content and improving drought tolerance in transgenic plants. In addition, SsdTPS-overexpressed transgenic Arabidopsis improved the responses of stomatal regulatory genes and ROS scavenging enzyme activities and gene expression to drought stress. This promoted the stomatal closure and ROS reduction, thus enhancing water retention capacity and reducing oxidative stress damage. These findings unveil the potentially positive role of SsdTPS in orchestrating multiple regulatory mechanisms and maintaining homeostasis for improved abiotic stress resistance in S. sclarea, providing a novel insight into strategies for promoting drought resistance and cultivating highly tolerant plants.

Cloning and Expression Analysis of Key Enzyme Gene CoGPPS Involved in Iridoid Glycoside Synthesis in Cornus officinalis

Cornus iridoid glycosides (CIGs), including loganin and morroniside, are the main active components of Cornus officinalis. As one of the key enzymes in the biosynthesis of CIGs, geranyl pyrophosphate synthase (GPPS) catalyzes the formation of geranyl pyrophosphate, which is the direct precursor of CIGs. In this study, the C. officinalis geranyl pyrophosphate synthase (CoGPPS) sequence was cloned from C. officinalis and analyzed. The cDNA sequence of the CoGPPS gene was 915 bp (GenBank No. OR725699). Phylogenetic analysis showed that CoGPPS was closely related to the GPPS sequence of Actinidia chinensis and Camellia sinensis, but relatively distantly related to Paeonia lactiflora and Tripterygium wilfordii. Results from the quantitative real-time PCR showed the spatiotemporal expression pattern of CoGPPS; that is, CoGPPS was specifically expressed in the fruits. Subcellular localization assay proved that CoGPPS was specifically found in chloroplasts. Loganin and morroniside contents in the tissues were detected by high-performance liquid chromatography, and both compounds were found to be at higher levels in the fruits than in leaves. Thus, this study laid the foundation for further studies on the synthetic pathway of CIGs.

Comparative Analysis of Metabolome and Transcriptome in Different Tissue Sites of Aquilaria sinensis (Lour.) Gilg

The resinous stem of Aquilaria sinensis (Lour.) Gilg is the sole legally authorized source of agarwood in China. However, whether other tissue parts can be potential substitutes for agarwood requires further investigation. In this study, we conducted metabolic analysis and transcriptome sequencing of six distinct tissues (root, stem, leaf, seed, husk, and callus) of A. sinensis to investigate the variations in metabolite distribution characteristics and transcriptome data across different tissues. A total of 331 differential metabolites were identified by chromatography-mass spectrometry (GC-MS), of which 22.96% were terpenoids. The differentially expressed genes (DEGs) in RNA sequencing were enriched in sesquiterpene synthesis via the mevalonate pathway. The present study establishes a solid foundation for exploring potential alternatives to agarwood.

The microbial biosynthesis of noncanonical terpenoids

Terpenoids are a class of structurally complex, naturally occurring compounds found predominantly in plant, animal, and microorganism secondary metabolites. Classical terpenoids typically have carbon atoms in multiples of five and follow well-defined carbon skeletons, whereas noncanonical terpenoids deviate from these patterns. These noncanonical terpenoids often result from the methyltransferase-catalyzed methylation modification of substrate units, leading to irregular carbon skeletons. In this comprehensive review, various activities and applications of these noncanonical terpenes have been summarized. Importantly, the review delves into the biosynthetic pathways of noncanonical terpenes, including those with C6, C7, C11, C12, and C16 carbon skeletons, in bacteria and fungi host. It also covers noncanonical triterpenes synthesized from non-squalene substrates and nortriterpenes in Ganoderma lucidum, providing detailed examples to elucidate the intricate biosynthetic processes involved. Finally, the review outlines the potential future applications of noncanonical terpenoids. In conclusion, the insights gathered from this review provide a reference for understanding the biosynthesis of these noncanonical terpenes and pave the way for the discovery of additional unique and novel noncanonical terpenes. KEY POINTS: •The activities and applications of noncanonical terpenoids are introduced. •The noncanonical terpenoids with irregular carbon skeletons are presented. •The microbial biosynthesis of noncanonical terpenoids is summarized.

Transcriptome and volatile compounds analyses of floral development provide insight into floral scent formation in Paeonia lactiflora 'Wu Hua Long Yu'

Herbaceous peony (Paeonia lactiflora) is a well-known ornamental plant in China, celebrated for its beautiful flowers that can emit fragrances. However, exact molecular mechanisms governing synthesis of floral volatiles within herbaceous peony remain unclear. To address this gap in knowledge, our study focused on analyzing the transcriptome and the levels of floral volatile compounds in P. lactiflora 'Wu Hua Long Yu' at different stages of flower development. Using gas chromatography-mass spectrometry (GC-MS), we obtained eighteen major volatile compounds, with monoterpenes being the dominant components among them. Our transcriptome analysis, based on pooled sequencing data, revealed the most differentially expressed genes (DEGs) existed between stages S1 and S3 of flower development. Among these DEGs, we identified 89 functional genes associated with the synthesis of volatile monoterpenes, with 28 of these genes showing a positive correlation with the release of monoterpenes. Specifically, key regulators of monoterpene synthesis in herbaceous peony appear to be 1-deoxy-D-xylulose 5-phosphate synthase (DXS), geranyl pyrophosphate synthase (GPPS), and terpene synthase (TPS). Additionally, our study identified some transcription factors (TFs) that may be involved in the biosynthesis of monoterpenes. These discoveries offer invaluable illumination into the intricate molecular underpinnings orchestrating the generation of floral fragrances in herbaceous peonies, and they offer a foundation for further research to identify and utilize candidate gene resources for this purpose.

Integrating Transcriptome and Chemical Analyses to Provide Insights into Biosynthesis of Terpenoids and Flavonoids in the Medicinal Industrial Crop Andrographis paniculate and Its Antiviral Medicinal Parts

Andrographis paniculata is a medicinal plant traditionally used to produce diterpene lactones and flavonoids, which possess various biological activities. Widely distributed in China, India, and other Southeast Asia countries, A. paniculata has become an important economic crop, significantly treating SARS-CoV-2, and is being cultivated on a large scale in southern China. The biosynthesis of active ingredients in A. paniculata are regulated and controlled by genes, but their specific roles are still not fully understood. To further explore the growth regulation factors and utilization of its medicinal parts of this industrial crop, chemical and transcriptome analyses were conducted on the roots, stems, and leaves of A. paniculata to identify the biosynthesis pathways and related candidate genes of the active ingredients. The chemical analysis revealed that the main components of A. paniculata were diterpene lactones and flavonoids, which displayed potential ability to treat SARS-CoV-2 through molecular docking. Moreover, the transcriptome sequencing annotated a total of 40,850 unigenes, including 7962 differentially expressed genes. Among these, 120 genes were involved in diterpene lactone biosynthesis and 60 genes were involved in flavonoid biosynthesis. The expression of diterpene lactone-related genes was the highest in leaves and the lowest in roots, consistent with our content determination results. It is speculated that these highly expressed genes in leaves may be involved in the biosynthesis pathway of diterpenes. Furthermore, two class Ⅰ terpene synthases in A. paniculata transcriptome were also annotated, providing reference for the downstream pathway of the diterpene lactone biosynthesis. With their excellent market value, our experiments will promote the study of the biosynthetic genes for active ingredients in A. paniculata and provide insights for subsequent in vitro biosynthesis.

Genetics and metabolic responses of Artemisia annua L to the lake of phosphorus under the sparingly soluble phosphorus fertilizer: evidence from transcriptomics analysis

The medicinal herb Artemisia annua L. is prized for its capacity to generate artemisinin, which is used to cure malaria. Potentially influencing the biomass and secondary metabolite synthesis of A. annua is plant nutrition, particularly phosphorus (P). However, most soil P exist as insoluble inorganic and organic phosphates, which results to low P availability limiting plant growth and development. Although plants have developed several adaptation strategies to low P levels, genetics and metabolic responses to P status remain largely unknown. In a controlled greenhouse experiment, the sparingly soluble P form, hydroxyapatite (Ca5OH(PO4)3/CaP) was used to simulate calcareous soils with low P availability. In contrast, the soluble P form KH2PO4/KP was used as a control. A. annua's morphological traits, growth, and artemisinin concentration were determined, and RNA sequencing was used to identify the differentially expressed genes (DEGs) under two different P forms. Total biomass, plant height, leaf number, and stem diameter, as well as leaf area, decreased by 64.83%, 27.49%, 30.47%, 38.70%, and 54.64% in CaP compared to KP; however, LC-MS tests showed an outstanding 37.97% rise in artemisinin content per unit biomass in CaP contrary to KP. Transcriptome analysis showed 2015 DEGs (1084 up-regulated and 931 down-regulated) between two P forms, including 39 transcription factor (TF) families. Further analysis showed that DEGs were mainly enriched in carbohydrate metabolism, secondary metabolites biosynthesis, enzyme catalytic activity, signal transduction, and so on, such as tricarboxylic acid (TCA) cycle, glycolysis, starch and sucrose metabolism, flavonoid biosynthesis, P metabolism, and plant hormone signal transduction. Meanwhile, several artemisinin biosynthesis genes were up-regulated, including DXS, GPPS, GGPS, MVD, and ALDH, potentially increasing artemisinin accumulation. Furthermore, 21 TF families, including WRKY, MYB, bHLH, and ERF, were up-regulated in reaction to CaP, confirming their importance in P absorption, internal P cycling, and artemisinin biosynthesis regulation. Our results will enable us to comprehend how low P availability impacts the parallel transcriptional control of plant development, growth, and artemisinin production in A. annua. This study could lay the groundwork for future research into the molecular mechanisms underlying A. annua's low P adaptation.

Comparative transcriptomics of two Salvia subg. Perovskia species contribute towards molecular background of abietane-type diterpenoid biosynthesis

Tanshinones, are a group of diterpenoid red pigments present in Danshen - an important herbal drug of Traditional Chinese Medicine which is a dried root of Salvia miltiorrhiza Bunge. Some of the tanshinones are sought after as pharmacologically active natural products. To date, the biosynthetic pathway of tanshinones has been only partially elucidated. These compounds are also present in some of the other Salvia species, i.a. from subgenus Perovskia, such as S. abrotanoides (Kar.) Sytsma and S. yangii B.T. Drew. Despite of the close genetic relationship between these species, significant qualitative differences in their diterpenoid profile have been discovered. In this work, we have used the Liquid Chromatography-Mass Spectrometry analysis to follow the content of diterpenoids during the vegetation season, which confirmed our previous observations of a diverse diterpenoid profile. As metabolic differences are reflected in different transcript profile of a species or tissues, we used metabolomics-guided transcriptomic approach to select candidate genes, which expression possibly led to observed chemical differences. Using an RNA-sequencing technology we have sequenced and de novo assembled transcriptomes of leaves and roots of S. abrotanoides and S. yangii. As a result, 134,443 transcripts were annotated by UniProt and 56,693 of them were assigned as Viridiplantae. In order to seek for differences, the differential expression analysis was performed, which revealed that 463, 362, 922 and 835 genes indicated changes in expression in four comparisons. GO enrichment analysis and KEGG functional analysis of selected DEGs were performed. The homology and expression of two gene families, associated with downstream steps of tanshinone and carnosic acid biosynthesis were studied, namely: cytochromes P-450 and 2-oxoglutarate-dependend dioxygenases. Additionally, BLAST analysis revealed existence of 39 different transcripts related to abietane diterpenoid biosynthesis in transcriptomes of S. abrotanoides and S. yangii. We have used quantitative real-time RT-PCR analysis of selected candidate genes, to follow their expression levels over the vegetative season. A hypothesis of an existence of a multifunctional CYP76AH89 in transcriptomes of S. abrotanoides and S. yangii is discussed and potential roles of other CYP450 homologs are speculated. By using the comparative transcriptomic approach, we have generated a dataset of candidate genes which provides a valuable resource for further elucidation of tanshinone biosynthesis. In a long run, our investigation may lead to optimization of diterpenoid profile in S. abrotanoides and S. yangii, which may become an alternative source of tanshinones for further research on their bioactivity and pharmacological therapy.

Design and synthesis of fosmidomycin analogs containing aza-linkers and their biological activity evaluation

BACKGROUND

The enzymes involved in the 2-C-methyl-d-erythritol 4-phosphate (MEP) pathway are attractive targets of a new mode of action for developing anti-infective drugs and herbicides, and inhibitors against 1-deoxy-d-xylulose 5-phosphate reductoisomerase (IspC), the second key enzyme in the pathway, have been intensively investigated; however, few works are reported regarding IspC inhibitors designed for new herbicide discovery.

RESULTS

A series of fosmidomycin (FOS) analogs were designed with nitrogen-containing linkers replacing the trimethylene linker between the two active substructures of FOS, phosphonic acid and hydroxamic acid. Synthesis followed a facile three-step route of sequential aza-Michael addition of α-amino acids to dibenzyl vinylphosphonate, amidation of the amino acid carboxyl with O-benzyl hydroxylamine, and simultaneous removal of the benzyl protective groups. Biological activity evaluation of IspC and model plants revealed that some compounds had moderate enzyme and model plant growth inhibition effects. In particular, compound 10g, which has a N-(4-fluorophenylethyl) nitrogen-containing linker, exhibited the best plant inhibition activities, superior to the control FOS against the model plants Arabidopsis thaliana, Brassica napus L., Amaranthus retroflexus and Echinochloa crus-galli. A dimethylallyl pyrophosphate rescue assay on A. thaliana confirmed that both 10g and FOS exert their herbicidal activity by blocking the MEP pathway. This result consistent with molecular docking, which confirmed 10g and FOS binding to the IspC active site in a similar way.

CONCLUSION

Compound 10g has excellent herbicidal activity and represents the first herbicide lead structure of a new mode of action that targets IspC enzyme in the MEP pathway. © 2023 Society of Chemical Industry.

YGL3 Encoding an IPP and DMAPP Synthase Interacts with OsPIL11 to Regulate Chloroplast Development in Rice

As the source of isoprenoid precursors, the plastidial methylerythritol phosphate (MEP) pathway plays an essential role in plant development. Here, we report a novel rice (Oryza sativa L.) mutant ygl3 (yellow-green leaf3) that exhibits yellow-green leaves and lower photosynthetic efficiency compared to the wild type due to abnormal chloroplast ultrastructure and reduced chlorophyll content. Map-based cloning showed that YGL3, one of the major genes involved in the MEP pathway, encodes 4-hydroxy-3-methylbut-2-enyl diphosphate reductase, which is localized in the thylakoid membrane. A single base substitution in ygl3 plants resulted in lower 4-hydroxy-3-methylbut-2-enyl diphosphate reductase activity and lower contents of isopentenyl diphosphate (IPP) compared to the wild type. The transcript levels of genes involved in the syntheses of chlorophyll and thylakoid membrane proteins were significantly reduced in the ygl3 mutant compared to the wild type. The phytochrome interacting factor-like gene OsPIL11 regulated chlorophyll synthesis during the de-etiolation process by directly binding to the promoter of YGL3 to activate its expression. The findings provides a theoretical basis for understanding the molecular mechanisms by which the MEP pathway regulate chloroplast development in rice.

Integrated metabolomic and transcriptomic analyses revealed metabolite variations and regulatory networks in Cinnamomum cassia Presl from four growth years

To understand the mechanism of the dynamic accumulation of active ingredients in Cinnamomum cassia Presl, metabolomic and transcriptomic analyses of 5~8 years old C. cassia were performed. A total of 72 phenylpropanoids, 146 flavonoids, and 130 terpenoids showed marked changes. Most phenylpropanoids and flavonoids showed markedly higher abundances in 6-year-old C. cassia than in others, which was related to the higher expression of genes that synthesize and regulate phenylpropanoids and flavonoid. We identified transcription factors (TFs) and genes involved in phenylpropanoids and flavonoids synthesis and regulation through co-expression network analyses. Furthermore, most of the terpenoids in 5-year-old C. cassia showed markedly higher abundances than in others, which was due to the differentially expressed genes upstream of the terpenoids pathway. The results of our study provide new insights into the synthesis and accumulation of phenylpropanoid, flavonoids and terpenoids in C. cassia at four growth stages.

Transcriptomic Insights into the Enhanced Aroma of Guangdong Oolong Dry Tea (Camellia sinensis cv. Yashixiang Dancong) in Winter

Winter dry tea (WDT) exhibits a more intense and lasting aroma compared to dry tea from other seasons; however, this conclusion is solely based on sensory outcomes and lacks corroborative theoretical evidence. Our study aimed to analyze the aroma compounds in WDT and investigate the causes behind the formation of WDT's aroma by analyzing the volatile organic compounds (VOCs) in WDT, spring dry tea (SDT), winter fresh leaves (WFLs) and spring fresh leaves (SFLs) by gas chromatography-mass spectrometry (GC-MS), complemented by an analysis of gene expression pertinent to WFLs and SFLs by using transcriptomic analysis. The results revealed a significant increase in total VOCs in WDT compared to SDT, with WDT exhibiting distinct woody aromas as indicated by a higher α-muurolene content. In WFL, the contents of aldehydes and ketones were richer than those in SFL. Notably, the study found that UDP-glycosyltransferase genes in WFLs were significantly up-regulated, potentially promoting the synthesis of terpene glycosides. These terpene glycosides can release terpene aroma compounds during processing, contributing significantly to the intense and lasting aroma of WDT. Overall, this research provides valuable insights into the mechanism behind aroma formation in Guangdong oolong tea harvested during winter.

Diversification of Plastid Structure and Function in Land Plants

Plastids represent a largely diverse group of organelles in plant and algal cells that have several common features but also a broad spectrum of morphological, ultrastructural, biochemical, and physiological differences. Plastids and their structural and metabolic diversity significantly contribute to the functionality and developmental flexibility of the plant body throughout its lifetime. In addition to the multiple roles of given plastid types, this diversity is accomplished in some cases by interconversions between different plastids as a consequence of developmental and environmental signals that regulate plastid differentiation and specialization. In addition to basic plastid structural features, the most important plastid types, the newly characterized peculiar plastids, and future perspectives in plastid biology are also provided in this chapter.

Astaxanthin from microalgae: A review on structure, biosynthesis, production strategies and application

Astaxanthin is a red-colored secondary metabolite with excellent antioxidant properties, typically finds application as foods, feed, cosmetics, nutraceuticals, and medications. Astaxanthin is usually produced synthetically using chemicals and costs less as compared to the natural astaxanthin obtained from fish, shrimps, and microorganisms. Over the decades, astaxanthin has been naturally synthesized from Haematococcus pluvialis in commercial scales and remains exceptional, attributed to its higher bioactive properties as compared to synthetic astaxanthin. However, the production cost of algal astaxanthin is still high due to several bottlenecks prevailing in the upstream and downstream processes. To that end, the present study intends to review the recent trends and advancements in astaxanthin production from microalgae. The structure of astaxanthin, sources, production strategies of microalgal astaxanthin, and factors influencing the synthesis of microalgal astaxanthin were discussed while detailing the pathway involved in astaxanthin biosynthesis. The study also discusses the relevant downstream process used in commercial scales and details the applications of astaxanthin in various health related issues.

Establishment and validation of a callus tissue transformation system for German chamomile (Matricaria chamomilla L.)

BACKGROUND

German chamomile (Matricaria chamomilla L.) is an important medicinal plant, and the essential oils in the flowers have various biological activities. Genetic transformation systems are important for plant quality improvement and molecular research. To the best of our knowledge, a genetic transformation system has not yet been reported for German chamomile.

RESULTS

In this study, we developed Agrobacterium-mediated transformation protocols for German chamomile callus tissues. This involved optimizing key parameters, such as hygromycin and cefotaxime concentrations, bacterial density, and infection and co-culture durations. We also performed gas chromatography-mass spectrometry analysis to identify volatile compounds in non-transgenic and transgenic callus and hairy root tissues. Furthermore, to compare and verify the callus transformation system of German chamomile, we transferred McFPS to the hairy roots of German chamomile. The results showed that the optimal conditions for Agrobacterium-mediated callus tissue transformation were as follows: explant, petiole; cefotaxime concentration, 300 mg/L; hygromycin concentration, 10 mg/L; and bacterial solution concentration, OD600 = 0.6; callus transformation efficiency was the highest when the co-culture time was 3 days.

CONCLUSIONS

Establishment of a high-efficiency callus transformation system will lay the foundation for gene function identification in German chamomile.

Miltiradiene Production by Cytoplasmic Metabolic Engineering in Nicotiana benthamiana

Plant natural products are important sources of innovative drugs, but the extraction and isolation of medicinal natural products from plants is challenging as these compounds have complex structures that are difficult to synthesize chemically. Therefore, utilizing heterologous expression systems to produce medicinal natural products in plants is a novel, environmentally friendly, and sustainable method. In this study, Nicotiana benthamiana was used as the plant platform to successfully produce miltiradiene, the key intermediate of tanshinones, which are the bioactive constituents of the Chinese medicinal plant Salvia miltiorrhiza. The yield of miltiradiene was increased through cytoplasmic engineering strategies combined with the enhancement of isoprenoid precursors. Additionally, we discovered that overexpressing SmHMGR alone accelerated apoptosis in tobacco leaves. Due to the richer membrane systems and cofactors in tobacco compared to yeast, tobacco is more conducive to the expression of plant enzymes. Therefore, this study lays the foundation for dissecting the tanshinone biosynthetic pathway in tobacco, which is essential for subsequent research. Additionally, it highlights the potential of N. benthamiana as an alternative platform for the production of natural products in plants.

Single-cell RNA sequencing reveals a hierarchical transcriptional regulatory network of terpenoid biosynthesis in cotton secretory glandular cells

Plants can synthesize a wide range of terpenoids in response to various environmental cues. However, the specific regulatory mechanisms governing terpenoid biosynthesis at the cellular level remain largely elusive. In this study, we employed single-cell RNA sequencing to comprehensively characterize the transcriptome profile of cotton leaves and established a hierarchical transcriptional network regulating cell-specific terpenoid production. We observed substantial expression levels of genes associated with the biosynthesis of both volatile terpenes (such as β-caryophyllene and β-myrcene) and non-volatile gossypol-type terpenoids in secretory glandular cells. Moreover, two novel transcription factors, namely GoHSFA4a and GoNAC42, are identified to function downstream of the Gossypium PIGMENT GLAND FORMATION genes. Both transcription factors could directly regulate the expression of terpenoid biosynthetic genes in secretory glandular cells in response to developmental and environmental stimuli. For convenient retrieval of the single-cell RNA sequencing data generated in this study, we developed a user-friendly web server . Our findings not only offer valuable insights into the precise regulation of terpenoid biosynthesis genes in cotton leaves but also provide potential targets for cotton breeding endeavors.

Subcellular compartmentalization in the biosynthesis and engineering of plant natural products

Plant natural products (PNPs) are specialized metabolites with diverse bioactivities. They are extensively used in the pharmaceutical, cosmeceutical and food industries. PNPs are synthesized in plant cells by enzymes that are distributed in different subcellular compartments with unique microenvironments, such as ions, co-factors and substrates. Plant metabolic engineering is an emerging and promising approach for the sustainable production of PNPs, for which the knowledge of the subcellular compartmentalization of their biosynthesis is instrumental. In this review we describe the state of the art on the role of subcellular compartments in the biosynthesis of major types of PNPs, including terpenoids, phenylpropanoids, alkaloids and glucosinolates, and highlight the efforts to target biosynthetic pathways to subcellular compartments in plants. In addition, we will discuss the challenges and strategies in the field of plant synthetic biology and subcellular engineering. We expect that newly developed methods and tools, together with the knowledge gained from the microbial chassis, will greatly advance plant metabolic engineering.

Engineering Nannochloropsis oceanica for the production of diterpenoid compounds

Photosynthetic microalgae like Nannochloropsis hold enormous potential as sustainable, light-driven biofactories for the production of high-value natural products such as terpenoids. Nannochloropsis oceanica is distinguished as a particularly robust host with extensive genomic and transgenic resources available. Its capacity to grow in wastewater, brackish, and sea waters, coupled with advances in microalgal metabolic engineering, genome editing, and synthetic biology, provides an excellent opportunity. In the present work, we demonstrate how N. oceanica can be engineered to produce the diterpene casbene-an important intermediate in the biosynthesis of pharmacologically relevant macrocyclic diterpenoids. Casbene accumulated after stably expressing and targeting the casbene synthase from Daphne genkwa (DgTPS1) to the algal chloroplast. The engineered strains yielded production titers of up to 0.12 mg g-1 total dry cell weight (DCW) casbene. Heterologous overexpression and chloroplast targeting of two upstream rate-limiting enzymes in the 2-C-methyl- d-erythritol 4-phosphate pathway, Coleus forskohlii 1-deoxy- d-xylulose-5-phosphate synthase and geranylgeranyl diphosphate synthase genes, further enhanced the yield of casbene to a titer up to 1.80 mg g-1 DCW. The results presented here form a basis for further development and production of complex plant diterpenoids in microalgae.

NtMYB1 and NtNCED1/2 control abscisic acid biosynthesis and tepal senescence in Chinese narcissus (Narcissus tazetta)

Chinese narcissus (Narcissus tazetta var. chinensis cv. 'Jinzhanyintai') is one of the 10 most famous traditional flowers of China, having a beautiful and highly ornamental flower with a rich fragrance. However, the flower longevity affects its commercial appeal. While petal senescence in Narcissus is ethylene-independent and abscisic acid-dependent, the regulatory mechanism has yet to be determined. In this study, we identified a R2R3-MYB gene (NtMYB1) from Narcissus tazetta and generated oeNtMYB1 and Ntmyb1 RNA interference mutants in Narcissus as well as an oeNtMYB1 construct in Arabidopsis. Overexpressing NtMYB1 in Narcissus or Arabidopsis led to premature leaf yellowing, an elevated level of total carotenoid, a reduced level of chlorophyll b, and a decrease in photosystem II fluorescence (Fv/Fm). A dual-luciferase assay and chromatin immunoprecipitation-quantitative PCR revealed that NtMYB1 directly binds to the promoter of NtNCED1 or NtNCED2 and activates NtNCED1/2 gene expression both in vitro and in vivo. Moreover, overexpressing NtMYB1 accelerated abscisic acid biosynthesis, up-regulated the content of zeatin and abscisic acid, and down-regulated the level of β-carotene and gibberellin A1, leading to petal senescence and leaf yellowing in Narcissus. This study revealed a regulatory process that is fundamentally different between non-photosynthetic organs and leaves.

The Capsicum terpenoid biosynthetic module is affected by spider-mite herbivory

In response to herbivory, Capsicum annuum leaves adapt their specialized metabolome that may protect the plant against herbivore feeding either directly or indirectly through volatile metabolites acting as cues for natural enemies of the herbivore. The volatile blend of spider-mite infested leaves differs from non-challenged leaves predominantly by a higher contribution of mono- and sesquiterpenes. In addition to these terpenoids released into the headspace, the terpenoid composition of the leaves alters upon herbivory. All this suggests an important role for terpenoids and their biosynthetic machinery in the defence against herbivory. Here, we show that the C. annuum genome contains a terpene synthase (TPS) gene family of 103 putative members of which structural analysis revealed that 27 encode functional enzymes. Transcriptome analysis showed that several TPS loci were differentially expressed upon herbivory in leaves of two C. annuum genotypes, that differ in susceptibility towards spider mites. The relative expression of upstream biosynthetic genes from the mevalonate and the methylerythritol phosphate pathway also altered upon herbivory, revealing a shift in the metabolic flux through the terpene biosynthetic module. The expression of multiple genes potentially acting downstream of the TPSs, including cytochrome P450 monooxygenases, UDP-glucosyl transferases, and transcription factors strongly correlated with the herbivory-induced TPS genes. A selection of herbivory-induced TPS genes was functionally characterized through heterologous expression and the products that these enzymes catalysed matched with the volatile and non-volatile terpenoids induced in response to herbivory.

Unraveling the terpene synthase family and characterization of BsTPS2 contributing to (S)-( +)-linalool biosynthesis in Boswellia

Boswellia tree bark exudes oleo-gum resin in response to wounding, which is rich in terpene volatiles. But, the molecular and biochemical basis of wound-induced formation of resin volatiles remains poorly understood. Here, we combined RNA-sequencing (RNA-seq) and metabolite analysis to unravel the terpene synthase (TPS) family contributing to wound-induced biosynthesis of resin volatiles in B. serrata, an economically-important Boswellia species. The analysis of large-scale RNA-seq data of bark and leaf samples representing more than 600 million sequencing reads led to the identification of 32 TPSs, which were classified based on phylogenetic relationship into various TPSs families found in angiosperm species such as TPS-a, b, c, e/f, and g. Moreover, RNA-seq analysis of bark samples collected at 0-24 h post-wounding shortlisted 14 BsTPSs that showed wound-induced transcriptional upregulation in bark, suggesting their important role in wound-induced biosynthesis of resin volatiles. Biochemical characterization of a bark preferentially-expressed and wound-inducible TPS (BsTPS2) in vitro and in planta assays revealed its involvement in resin terpene biosynthesis. Bacterially-expressed recombinant BsTPS2 catalyzed the conversion of GPP and FPP into (S)-( +)-linalool and (E)-(-)-nerolidol, respectively, in vitro assays. However, BsTPS2 expression in Nicotiana benthamiana found that BsTPS2 is a plastidial linalool synthase. In contrast, cytosolic expression of BsTPS2 did not form any product. Overall, the present work unraveled a suite of TPSs that potentially contributed to the biosynthesis of resin volatiles in Boswellia and biochemically characterized BsTPS2, which is involved in wound-induced biosynthesis of (S)-( +)-linalool, a monoterpene resin volatile with a known role in plant defense.

An Investigation of the JAZ Family and the CwMYC2-like Protein to Reveal Their Regulation Roles in the MeJA-Induced Biosynthesis of β-Elemene in Curcuma wenyujin

β-Elemene (C15H24), a sesquiterpenoid compound isolated from the volatile oil of Curcuma wenyujin, has been proven to be effective for multiple cancers and is widely used in clinical treatment. Unfortunately, the β-elemene content in C. wenyujin is very low, which cannot meet market demands. Our previous research showed that methyl jasmonate (MeJA) induced the accumulation of β-elemene in C. wenyujin. However, the regulatory mechanism is unclear. In this study, 20 jasmonate ZIM-domain (JAZ) proteins in C. wenyujin were identified, which are the core regulatory factors of the JA signaling pathway. Then, the conservative domains, motifs composition, and evolutionary relationships of CwJAZs were analyzed comprehensively and systematically. The interaction analysis indicated that CwJAZs can form homodimers or heterodimers. Fifteen out of twenty CwJAZs were significantly induced via MeJA treatment. As the master switch of the JA signaling pathway, the CwMYC2-like protein has also been identified and demonstrated to interact with CwJAZ2/3/4/5/7/15/17/20. Further research found that the overexpression of the CwMYC2-like gene increased the accumulation of β-elemene in C. wenyujin leaves. Simultaneously, the expressions of HMGR, HMGS, DXS, DXR, MCT, HDS, HDR, and FPPS related to β-elemene biosynthesis were also up-regulated by the CwMYC2-like protein. These results indicate that CwJAZs and the CwMYC2-like protein respond to the JA signal to regulate the biosynthesis of β-elemene in C. wenyujin.

Growth inhibitory, immunosuppressive, cytotoxic, and genotoxic effects of γ-terpinene on Zeugodacus cucurbitae (Coquillett) (Diptera: Tephritidae)

γ-Terpinene, a monoterpene widely present in essential oils of many medicinal and aromatic plants with numerous biological properties, was evaluated for its insecticidal activity against melon fruit fly, Zeugodacus cucurbitae (Coquillett). Different concentrations (5, 25, 125, 625, and 3125 ppm) of γ-terpinene along with control were fed to larvae of melon fly. The number of pupae formed and adults emerged declined significantly after treatment. Morphologically deformed adults and pupae were also observed. The developmental duration too prolonged in treated larvae. Food assimilated, mean relative growth rate, larval weight gain, and pupal weight also declined. In the larvae treated with LC30 and LC50 concentrations, there was a decline in the titers of phenoloxidase and total hemocyte count, and variations were observed in the differential hemocyte count, suggesting an immunosuppressive effect of γ-terpinene on melon fly. Both concentrations also led to an increase in the apoptotic and necrotic cells as well as decrease in the viable hemocytes in the circulating hemolymph of treated larvae. Comet parameters (tail length, % tail DNA, tail moment, and olive tail moment) of γ-terpinene fed larvae increased significantly. Given the observed effects of γ-terpinene on normal developmental and nutritional physiology, its immunosuppressive properties, and its potential for genome damage, it can be considered for incorporation into integrated pest management strategies for controlling Z. cucurbitae.