Plant geranylgeranyl diphosphate synthases: every (gene) family has a story

Chemical structures, biosynthesis, bioactivities, and utilisation values for the diterpenes produced in tobacco trichomes

Cembranoids and labdanes are two important types of diterpenes in tobacco (Nicotiana genus) that are predominantly found in the leaf and flower glandular trichome secretions. This is the first systematic review of the biosynthesis, chemical structures, bioactivities, and utilisation values of cembranoid and labdane diterpenes in tobacco. A total of 131 natural cembranoid diterpenes have been reported in tobacco since 1962; these were summarised and classified according to their chemical structure characteristics as isopropyl cembranoids (1-88), seco-cembranoids (89-103), chain cembranoids (104-123), and polycyclic cembranoids (124-131). Forty natural labdane diterpenes reported since 1961 were also summarised and divided into epoxy side chain labdanes (132-150) and epoxy-free side chain labdanes (151-171). Tobacco cembranoid and labdane diterpenes are both formed via the methylerythritol 4-phosphate pathway and are synthesised from geranylgeranyl diphosphate. Their biosynthetic pathways and the four key enzymes (cembratrienol synthase, cytochrome P450 hydroxylase, copalyl diphosphate synthase, and Z-abienol cyclase) that affect their biosynthesis have been described in detail. A systematic summary of the bioactivity and utilisation values of the cembranoid and labdane diterpenes is also provided. The agricultural bioactivities associated with cembranoid and labdane diterpenes include antimicrobial and insecticidal activities as well as induced resistance, while the medical bioactivities include cytotoxic and neuroprotective activities. Further research into the cembranoid and labdane diterpenes will help to promote their development and utilisation as plant-derived pesticides and medicines.

Liposome-encapsulated cytochrome P450 unleashes enhanced Hg2+ reduction and bacterial gibberellic acid biosynthesis in Priestia megaterium RP1

This study explores the potential of liposome encapsulated silica immobilized cytochrome P450 monooxygenase (LSICY) for bioremediation of mercury (Hg2+). Current limitations in Hg2+ reduction, including sensitivity to factors like pH and cost, necessitate alternative methods. We propose LSICY as a solution, leveraging the enzymatic activities of cytochrome P450 monooxygenase (CYPM) for Hg2+ reduction through hydroxylation and oxygenation. Our investigation employs LSICY to assess its efficacy in mitigating Hg2+ toxicity in Oryza sativa (rice) plants. Gas chromatography confirmed gibberellic acid (GA) presence in the Hg2+ reducing bacteria Priestia megaterium RP1 (PMRP1), highlighting a potential link between CYP450 activity and plant health. This study demonstrates the promise of LSICY as a sustainable and effective approach for Hg2+ bioremediation, promoting a safer soil environment.

Priming avocado with sodium hydrosulfide prior to frost conditions induces the expression of genes involved in protection and stress responses

Priming plants with chemical agents has been extensively investigated as a means for improving their tolerance to many biotic and abiotic stresses. Earlier, we showed that priming young avocado (Persea americana Mill cv. 'Hass') trees with sodium hydrosulfide (NaHS), a donor of hydrogen sulfide, improves the response of photosynthesis to simulated frost (cold followed by high light) conditions. In the current study, we performed a transcriptome analysis to gain insight into the molecular response of avocado 'Hass' leaves to frost, with or without NaHS priming. The analysis revealed 2144 (down-regulated) and 2064 (up-regulated) differentially expressed genes (DEGs) common to both non-primed and primed trees. Non-primed trees had 697 (down) and 559 (up) unique DEGs, while primed trees exhibited 1395 (down) and 1385 (up) unique DEGs. We focus on changes in the expression patterns of genes encoding proteins involved in photosynthesis, carbon cycle, protective functions, biosynthesis of isoprenoids and abscisic acid (ABA), as well as ABA-regulated genes. Notably, the differential expression results depict the enhanced response of primed trees to the frost and highlight gene expression changes unique to primed trees. Amongst these are up-regulated genes encoding pathogenesis-related proteins, heat shock proteins, enzymes for ABA metabolism, and ABA-induced transcription factors. Extending the priming experiments to field conditions, which showed a benefit to the physiology of trees following chilling, suggests that it can be a possible means to improve trees' response to cold stress under natural winter conditions.

Functional characterization of a geranylgeranyl diphosphate synthase in the leaf beetle Monolepta hieroglyphica

Geranylgeranyl diphosphate synthase (GGPPS) as the short-chain prenyltransferases for catalyzing the formation of the acyclic precursor (E)-GGPP has been extensively investigated in mammals, plants, and microbes, but its functional plasticity is poorly understood in insect species. Here, a single GGPPS in leaf beetle Monolepta hieroglyphica, MhieGGPPS, was functionally investigated. Phylogenetic analysis showed that MhieGGPPS was clustered in one clade with homologs and had six conserved motifs. Molecular docking results indicated that binding sites of dimethylallyl diphosphate (DMAPP), (E)-geranyl pyrophosphate (GPP), and (E)-farnesyl pyrophosphate (FPP) were in the chain-length determination region of MhieGGPPS, respectively. In vitro, recombiant MhieGGPPS could catalyze the formation of (E)-geranylgeraniol against different combinations of substrates including isopentenyl pyrophosphate (IPP)/DMAPP, IPP/(E)-GPP, and IPP/(E)-FPP, suggesting that MhieGGPPS could not only use (E)-FPP but also (E)-GPP and DMAPP as the allylic cosubstrates. In kinetic analysis, the (E)-FPP was most tightly bound to MhieGGPPS than that of others. It was proposed that MhieGGPPS as a multifunctional enzyme is differentiated from the other GGPPSs in the animals and plants, which only accepted (E)-FPP as the allylic cosubstrate. These findings provide valuable insights into understanding the functional plasticity of GGPPS in M. hieroglyphica and the novel biosynthesis mechanism in the isoprenoid pathway.

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.

Comprehensive and evolutionary analysis of Spodoptera litura-inducible Cytochrome P450 monooxygenase gene family in Glycine max elucidate their role in defense

Plants being sessile organisms and lacking both circulating phagocytic cells and somatic adaptive immune response, have thrived on various defense mechanisms to fend off insect pests and invasion of pathogens. CYP450s are the versatile enzymes, which thwart plants against insect pests by ubiquitous biosynthesis of phytohormones, antioxidants, and secondary metabolites, utilizing them as feeding deterrents and direct toxins. Therefore, a comprehensive analysis of biotic stress-responsive CYPs from Glycine max was performed to ascertain their function against S. litura-infestation. Phylogenetic analysis and evolutionary studies on conserved domains and motifs disclosed the evolutionary correspondence of these GmCYPs with already characterized members of the CYP450 superfamily and close relatedness to Medicago truncatula. These GmCYPs were mapped on 13 chromosomes; they possess 1-8 exons; they have evolved due to duplication and are localized in endoplasmic reticulumn. Further, identification of methyl-jasmonate, salicylic acid, defense responsive and flavonoid biosynthesis regulating cis-acting elements, their interaction with biotic stress regulating proteins and their differential expression in diverse types of tissues, and during herbivory, depicted their responsiveness to biotic stress. Three-dimensional homology modelling of GmCYPs, docking with heme cofactor required for their catalytic activity and enzyme-substrate interactions were performed to understand the functional mechanism of their action. Moreover, to gain insight into their involvement in plant defense, gene expression analysis was evaluated, which revealed differential expression of 11 GmCYPs upon S. litura-infestation, 12 GmCYPs on wounding while foliar spray of ethylene, methyl-jasmonate and salicylic acid differentially regulated 11 GmCYPs, 6 GmCYPs, and 10 GmCYPs respectively. Our study comprehensively analysed the underlying mechanism of GmCYPs function during S. litura-infestation, which can be further utilized for functional characterization to develop new strategies for enhancing soybean resistance to insect pests.

Differential roles of Cassia tora 1-deoxy-D-xylulose-5-phosphate synthase and 1-deoxy-D-xylulose-5-phosphate reductoisomerase in trade-off between plant growth and drought tolerance

Due to global climate change, drought is emerging as a major threat to plant growth and agricultural productivity. Abscisic acid (ABA) has been implicated in plant drought tolerance, however, its retarding effects on plant growth cannot be ignored. The reactions catalyzed by 1-deoxy-D-xylulose-5-phosphate synthase (DXS) and 1-deoxy-D-xylulose-5-phosphate reductoisomerase (DXR) proteins are critical steps within the isoprenoid biosynthesis in plants. Here, five DXS (CtDXS1-5) and two DXR (CtDXR1-2) genes were identified from Cassia tora genome. Based on multiple assays including the phylogeny, cis-acting element, expression pattern, and subcellular localization, CtDXS1 and CtDXR1 genes might be potential candidates controlling the isoprenoid biosynthesis. Intriguingly, CtDXS1 transgenic plants resulted in drought tolerance but retardant growth, while CtDXR1 transgenic plants exhibited both enhanced drought tolerance and increased growth. By comparison of β-carotene, chlorophyll, abscisic acid (ABA) and gibberellin 3 (GA3) contents in wild-type and transgenic plants, the absolute contents and (or) altered GA3/ABA levels were suggested to be responsible for the balance between drought tolerance and plant growth. The transcriptome of CtDXR1 transgenic plants suggested that the transcript levels of key genes, such as DXS, 9-cis-epoxycarotenoid dioxygenases (NCED), ent-kaurene synthase (KS) and etc, involved with chlorophyll, β-carotene, ABA and GA3 biosynthesis were induced and their contents increased accordingly. Collectively, the trade-off effect induced by CtDXR1 was associated with redesigning architecture in phytohormone homeostasis and thus was highlighted for future breeding purposes.

Gibberellic acid 3 enhanced the anticancer activity of Abeliophyllum distichum adventitious roots by activating the diterpenoid biosynthesis pathway

The industrial value of various plants has been improved through the of plant cell culture systems with elicitation. In this study, the adventitious root of Abeliophyllum distichum (AdAR) was treated with gibberellic acid 3 (GA3) to improve its anticancer property. The hexane fraction of the GA3-treated A. distichum adventitious root exhibited a stronger cytotoxic activity against A549 cells than the hexane fraction of AdAR. Through GC/MS and principal component analysis, we identified ferruginol and sugiol as anticancer compounds, which were induced by GA3 treatment in AdAR. Gene expression analysis combined with functional characterisation suggests that the GA3 treatment increased the transcription of geranylgeranyl pyrophosphate synthases and copalyl diphosphate synthase, which led to the accumulation of diterpenoids, including ferruginol and sugiol. Overall, these findings can contribute to the advancement of metabolic engineering for enhancing the biosynthesis of active diterpenoids, and facilitate the large-scale production of bioactive compounds sourced from A. distichum.

Tomato geranylgeranyl diphosphate synthase isoform 1 is involved in the stress-triggered production of diterpenes in leaves and strigolactones in roots

Carotenoids are photoprotectant pigments and precursors of hormones such as strigolactones (SL). Carotenoids are produced in plastids from geranylgeranyl diphosphate (GGPP), which is diverted to the carotenoid pathway by phytoene synthase (PSY). In tomato (Solanum lycopersicum), three genes encode plastid-targeted GGPP synthases (SlG1 to SlG3) and three genes encode PSY isoforms (PSY1 to PSY3). Here, we investigated the function of SlG1 by generating loss-of-function lines and combining their metabolic and physiological phenotyping with gene co-expression and co-immunoprecipitation analyses. Leaves and fruits of slg1 lines showed a wild-type phenotype in terms of carotenoid accumulation, photosynthesis, and development under normal growth conditions. In response to bacterial infection, however, slg1 leaves produced lower levels of defensive GGPP-derived diterpenoids. In roots, SlG1 was co-expressed with PSY3 and other genes involved in SL production, and slg1 lines grown under phosphate starvation exuded less SLs. However, slg1 plants did not display the branched shoot phenotype observed in other SL-defective mutants. At the protein level, SlG1 physically interacted with the root-specific PSY3 isoform but not with PSY1 and PSY2. Our results confirm specific roles for SlG1 in producing GGPP for defensive diterpenoids in leaves and carotenoid-derived SLs (in combination with PSY3) in roots.

A quantitative method to measure geranylgeranyl diphosphate (GGPP) and geranylgeranyl monophosphate (GGP) in tomato (Solanum lycopersicum) fruit

BACKGROUND

Isoprenoids are a very large class of metabolites playing a key role in plant physiological processes such as growth, stress resistance, fruit flavor, and color. In chloroplasts and chromoplasts, the diterpene compound geranylgeranyl diphosphate (GGPP) is the metabolic precursor required for the biosynthesis of tocopherols, plastoquinones, phylloquinone, chlorophylls, and carotenoids. Despite its key role for the plant metabolism, reports on GGPP physiological concentrations in planta have been extremely scarce.

RESULTS

In this study, we developed a method to quantify GGPP and its hydrolysis product geranylgeranyl monophosphate (GGP) from tomato fruit, using ultra-high performance liquid chromatography coupled with tandem mass spectrometry (UHPLC-MS/MS). Quantification was done by external calibration and the method was validated in terms of specificity, precision, accuracy, and detection and quantitation limits. We further demonstrate the validity of our approach by analysing GGPP contents in the ripe fruits of wild-type tomatoes and mutants defective in GGPP production. Finally, we also show that the sample preparation is key to prevent GGPP hydrolysis and mitigate its conversion to GGP.

CONCLUSION

Our study provides an efficient tool to investigate the metabolic fluxes required for GGPP supply and consumption in tomato fruit.

The functional evolution of architecturally different plant geranyl diphosphate synthases from geranylgeranyl diphosphate synthase

Terpenoids constitute the largest class of plant primary and secondary metabolites with a broad range of biological and ecological functions. They are synthesized from isopentenyl diphosphate and dimethylallyl diphosphate, which in plastids are condensed by geranylgeranyl diphosphate synthases (GGPPSs) to produce GGPP (C20) for diterpene biosynthesis and by geranyl diphosphate synthases (GPPSs) to form GPP (C10) for monoterpene production. Depending on the plant species, unlike homomeric GGPPSs, GPPSs exist as homo- and heteromers, the latter of which contain catalytically inactive GGPPS-homologous small subunits (SSUs) that can interact with GGPPSs. By combining phylogenetic analysis with functional characterization of GGPPS homologs from a wide range of photosynthetic organisms, we investigated how different GPPS architectures have evolved within the GGPPS protein family. Our results reveal that GGPPS gene family expansion and functional divergence began early in nonvascular plants, and that independent parallel evolutionary processes gave rise to homomeric and heteromeric GPPSs. By site-directed mutagenesis and molecular dynamics simulations, we also discovered that Leu-Val/Val-Ala pairs of amino acid residues were pivotal in the functional divergence of homomeric GPPSs and GGPPSs. Overall, our study elucidated an evolutionary path for the formation of GPPSs with different architectures from GGPPSs and uncovered the molecular mechanisms involved in this differentiation.

Knockdown of NtCPS2 promotes plant growth and reduces drought tolerance in Nicotiana tabacum

Drought stress is one of the primary environmental stress factors that gravely threaten crop growth, development, and yields. After drought stress, plants can regulate the content and proportion of various hormones to adjust their growth and development, and in some cases to minimize the adverse effects of drought stress. In our previous study, the tobacco cis-abienol synthesis gene (NtCPS2) was found to affect hormone synthesis in tobacco plants. Unfortunately, the role of NtCPS2 genes in the response to abiotic stress has not yet been investigated. Here, we present data supporting the role of NtCPS2 genes in drought stress and the possible underlying molecular mechanisms. NtCPS2 gene expression was induced by polyethylene glycol, high-temperature, and virus treatments. The results of subcellular localization showed that NtCPS2 was localized in the cell membrane. The NtCPS2-knockdown plants exhibited higher levels of gibberellin (GA) content and synthesis pathway genes expression but lower abscisic acid (ABA) content and synthesis pathway genes expression in response to drought stress. In addition, the transgenic tobacco lines showed higher leaf water loss and electrolyte loss, lower soluble protein and reactive oxygen species content (ROS), and lower antioxidant enzyme activity after drought treatment compared to wild type plants (WT). In summary, NtCPS2 positively regulates drought stress tolerance possibly by modulating the ratio of GA to ABA, which was confirmed by evidence of related phenotypic and physiological indicators. This study may provide evidence for the feedback regulation of hormone to abiotic and biotic stresses.

Transient expression systems to rewire plant carotenoid metabolism

Enrichment of foodstuffs with health-promoting metabolites such as carotenoids is a powerful tool to fight against unhealthy eating habits. Dietary carotenoids are vitamin A precursors and reduce risk of several chronical diseases. Additionally, carotenoids and their cleavage products (apocarotenoids) are used as natural pigments and flavors by the agrofood industry. In the last few years, major advances have been made in our understanding of how plants make and store carotenoids in their natural compartments, the plastids. In part, this knowledge has been acquired by using transient expression systems, notably agroinfiltration and viral vectors. These techniques allow profound changes in the carotenoid profile of plant tissues at the desired developmental stage, hence preventing interference with normal plant growth and development. Here we review how transient expression approaches have contributed to learn about the structure and regulation of plant carotenoid biosynthesis and to rewire carotenoid metabolism and storage for efficient biofortification of plant tissues.

Plant carotenoids: recent advances and future perspectives

Carotenoids are isoprenoid metabolites synthesized de novo in all photosynthetic organisms. Carotenoids are essential for plants with diverse functions in photosynthesis, photoprotection, pigmentation, phytohormone synthesis, and signaling. They are also critically important for humans as precursors of vitamin A synthesis and as dietary antioxidants. The vital roles of carotenoids to plants and humans have prompted significant progress toward our understanding of carotenoid metabolism and regulation. New regulators and novel roles of carotenoid metabolites are continuously revealed. This review focuses on current status of carotenoid metabolism and highlights recent advances in comprehension of the intrinsic and multi-dimensional regulation of carotenoid accumulation. We also discuss the functional evolution of carotenoids, the agricultural and horticultural application, and some key areas for future research.