Molecular cloning of hyoscyamine 6 beta-hydroxylase, a 2-oxoglutarate-dependent dioxygenase, from cultured roots of Hyoscyamus niger

Integrated Transcriptomics and Metabolomics Reveal Key Insights into Iridoid Biosynthesis in Gentiana crassicaulis Seeds during Germination

Background:Gentiana crassicaulis Duthie ex Burk., a key species used in traditional Chinese medicine for treating rheumatic pain and stroke, contains iridoids as its primary active component. However, the biosynthetic mechanisms underlying iridoid production are not fully understood. Methods: This study focused on iridoid biosynthesis during the germination of G. crassicaulis seeds, integrating metabolomic and transcriptomic analyses to uncover the underlying pathways and key candidate genes. Results: 196,132 unigenes and 10 iridoid compounds were identified through RNA-seq and ultra performance liquid chromatography-quadrupole time of flight-mass spectrometer (UPLC-Q-TOF-MS), respectively. The intersection of results from Pearson correlation analysis and weighted gene co-expression network analysis (WGCNA) revealed a significant correlation between 26 genes and iridoid levels, suggesting their potential role in the iridoid metabolism. Notably, six highly expressed candidate genes (DL7H, SLS, CYP76, CYP72A2, CYP84A1, and 13-LOX3) and five iridoids (loganic acid, sweroside, swertiamarin, gentiopicroside, and 6'-O-β-D-glucosyl-gentiopicroside) responded to methyl jasmonate stimulation in G. crassicaulis seedlings. Conclusions: by combining the known functions of candidate gene families, It is hypothesized that the CYP716 and LOX families exert indirect influences on iridoid metabolism, while the CYP71, CYP81, CYP72, CYP76, CYP710 families, 2OG-FeII family, and the glucosyltransferase family are likely to play direct roles in the biosynthetic transformations of the five iridoids. This study provides a theoretical basis for further functional gene validation and metabolic engineering aimed at enhancing iridoid production. The insights gained could lead to improved iridoid production efficiency in medicinal plants, ultimately benefiting the quality and efficacy of medicinal materials.

Three-membered ring formation catalyzed by α-ketoglutarate-dependent nonheme iron enzymes

Epoxides, aziridines, and cyclopropanes are found in various medicinal natural products, including polyketides, terpenes, peptides, and alkaloids. Many classes of biosynthetic enzymes are involved in constructing these ring structures during their biosynthesis. This review summarizes our current knowledge regarding how α-ketoglutarate-dependent nonheme iron enzymes catalyze the formation of epoxides, aziridines, and cyclopropanes in nature, with a focus on enzyme mechanisms.

Chemical screening of inhibitors specific for MdDOX-Co that cause an apple columnar tree-shape

MdDOX-Co, the ectopic expression of which is considered to cause the apple columnar tree shape, belongs to the 2-oxoglutarate-dependent dioxygenase (2ODD) family. It adds a hydroxyl group to position 12 of gibberellins (GAs). However, the 2ODD enzymes related to GA biosynthesis and catabolism are phylogenetically distinct from MdDOX-Co. Thus, it is possible that substrates other than GAs exist in MdDOX-Co. To identify the previously unidentified substrate(s) of MdDOX-Co, we searched for MdDOX-Co-specific inhibitors. Chemical screening using gas chromatography-mass spectrometry was performed to investigate the effects of 2400 compounds that inhibited the catalytic reaction of MdDOX-Co, but not the catabolic reaction of GA 2-oxidase, an enzyme involved in GA catabolism. By applying two positive compounds in Arabidopsis, a chemical 3-((2-chloro-6-fluorobenzyl)thio)-5,7-dimethyl-5H-pyrazolo[3,4-e][1,4,2]dithiazine-1,1-dioxide designated as TPDD that did not inhibit GA biosynthesis was selected. The structure-activity relationships among the TPDD analogs were also obtained.

Molecular Mechanisms Regulating the Columnar Tree Architecture in Apple

The columnar apple cultivar ‘McIntosh Wijcik’ was discovered as a spontaneous mutant from the top of a ‘McIntosh’ tree in the early 1960s. ‘McIntosh Wijcik’ exhibits the columnar growth phenotype: compact and sturdy growth, short internodes, and very few lateral shoots. Classical genetic analysis revealed that the columnar growth phenotype of ‘McIntosh Wijcik’ is controlled by a single dominant gene, Co. This review focuses on the advances made toward understanding the molecular mechanisms of columnar growth in the last decade. Molecular studies have shown that an 8.2 kb insertion in the intergenic region of the Co locus is responsible for the columnar growth phenotype of ‘McIntosh Wijcik’, implying that the insertion affects the expression patterns of adjacent genes. Among the candidate genes in the Co region, the expression pattern of MdDOX-Co, putatively encoding 2-oxoglutarate-dependent dioxygenase (DOX), was found to vary between columnar and non-columnar apples. Recent studies have found three functions of MdDOX-Co: facilitating bioactive gibberellin deficiency, increasing strigolactone levels, and positively regulating abscisic acid levels. Consequently, changes in these plant hormone levels caused by the ectopic expression of MdDOX-Co in the aerial organs of ‘McIntosh Wijcik’ can lead to dwarf trees with fewer lateral branches. These findings will contribute to the breeding and cultivation of new columnar apple cultivars with improved fruit quality.

Properties of the Reactants and Their Interactions within and with the Enzyme Binding Cavity Determine Reaction Selectivities. The Case of Fe(II)/2-Oxoglutarate Dependent Enzymes

Fe(II)/2-oxoglutarate dependent dioxygenases (ODDs) share a double stranded beta helix (DSBH) fold and utilise a common reactive intermediate, ferryl species, to catalyse oxidative transformations of substrates. Despite the structural similarities, ODDs accept a variety of substrates and facilitate a wide range of reactions, that is hydroxylations, desaturations, (oxa)cyclisations and ring rearrangements. In this review we present and discuss the factors contributing to the observed (regio)selectivities of ODDs. They span from inherent properties of the reactants, that is, substrate molecule and iron cofactor, to the interactions between the substrate and the enzyme's binding cavity; the latter can counterbalance the effect of the former. Based on results of both experimental and computational studies dedicated to ODDs, we also line out the properties of the reactants which promote reaction outcomes other than the "default" hydroxylation. It turns out that the reaction selectivity depends on a delicate balance of interactions between the components of the investigated system.

Activation modes in biocatalytic radical cyclization reactions

Radical cyclizations are essential reactions in the biosynthesis of secondary metabolites and the chemical synthesis of societally valuable molecules. In this review, we highlight the general mechanisms utilized in biocatalytic radical cyclizations. We specifically highlight cytochrome P450 monooxygenases (P450s) involved in the biosynthesis of mycocyclosin and vancomycin, nonheme iron- and α-ketoglutarate-dependent dioxygenases (Fe/αKGDs) used in the biosynthesis of kainic acid, scopolamine, and isopenicillin N, and radical S-adenosylmethionine (SAM) enzymes that facilitate the biosynthesis of oxetanocin A, menaquinone, and F420. Beyond natural mechanisms, we also examine repurposed flavin-dependent "ene"-reductases (ERED) for non-natural radical cyclization. Overall, these general mechanisms underscore the opportunity for enzymes to augment and enhance the synthesis of complex molecules using radical mechanisms.

Tropane alkaloid biosynthesis: a centennial review

Covering: 1917 to 2020Tropane alkaloids (TAs) are a remarkable class of plant secondary metabolites, which are characterized by an 8-azabicyclo[3.2.1]octane (nortropane) ring. Members of this class, such as hyoscyamine, scopolamine, and cocaine, are well known for their long history as poisons, hallucinogens, and anaesthetic agents. Since the structure of the tropane ring system was first elucidated in 1901, organic chemists and biochemists have been interested in how these mysterious tropane alkaloids are assembled in vitro and in vivo. However, it was only in 2020 that the complete biosynthetic route of hyoscyamine and scopolamine was clarified, and their de novo production in yeast was also achieved. The aim of this review is to present the innovative ideas and results in exploring the story of tropane alkaloid biosynthesis in plants from 1917 to 2020. This review also highlights that Robinson's classic synthesis of tropinone, which is one hundred years old, is biomimetic, and underscores the importance of total synthesis in the study of natural product biosynthesis.

Improved tropane alkaloid production and changes in gene expression in hairy root cultures of two Hyoscyamus species elicited by silicon dioxide nanoparticles

Species of Hyoscyamus are rich sources of medicinally important tropane alkaloids, which have anticholinergic, antispasmodic and sedative effects and are competitive inhibitors of acetylcholine. The application of nanotechnology and nanomaterials for elicitation is rapidly expanding and recent research indicates that silicon dioxide nanoparticles (SiO₂ NPs) can be used as an efficient elicitor to increase the production of hyoscyamine and scopolamine in Hyoscyamus species. Thus, in this work, the effect of SiO₂ NPs (0, 25, 50, 100 and 200 mg L^-1) with two treatment times (24 and 48 h) on the growth rate, total phenol and flavonoid content (TPC, TFC), antioxidant enzyme activity, tropane alkaloid yield and pmt (putrescine N-methyltransferase) and h6h (hyoscyamine 6<beta>-hydroxylase) gene expression levels in hairy roots of two Hyoscyamus species (H. reticulatus and H. pusillus) was investigated. The highest TPC and TFC accumulation was obtained in H. reticulatus elicited by SiO₂ NPs (100 and 200 mg L^-1), respectively, at 24 h of treatment. High-performance liquid chromatography (HPLC) revealed the highest amount of hyoscyamine (140.15 μg g^-1 FW) and scopolamine (67.71 μg g^-1 FW) accumulated in H. reticulatus transformed roots treated with 100 mg L^-1 SiO₂ NPs at 24 h, with a respective increase of 1212% and 272% compared to non-treated roots. In H. pusillus, the highest hyoscyamine (7.42 μg g^-1 FW) and scopolamine (15.56 μg g^-1 FW) production (about 82% and 241% higher, respectively, compared to the lowest amounts) was achieved with 25 and 100 mg L^-1 SiO₂ NPs, respectively, at 48 h of treatment. Semi-quantitative RT-PCR analysis determined the highest expression level of pmt and h6h genes in H. reticulatus transformed roots supplemented with 100 mg L^-1 SiO₂ NPs.

Biosynthesis of medicinal tropane alkaloids in yeast

Tropane alkaloids from nightshade plants are neurotransmitter inhibitors that are used for treating neuromuscular disorders and are classified as essential medicines by the World Health Organization1,2. Challenges in global supplies have resulted in frequent shortages of these drugs3,4. Further vulnerabilities in supply chains have been revealed by events such as the Australian wildfires5 and the COVID-19 pandemic6. Rapidly deployable production strategies that are robust to environmental and socioeconomic upheaval7,8 are needed. Here we engineered baker's yeast to produce the medicinal alkaloids hyoscyamine and scopolamine, starting from simple sugars and amino acids. We combined functional genomics to identify a missing pathway enzyme, protein engineering to enable the functional expression of an acyltransferase via trafficking to the vacuole, heterologous transporters to facilitate intracellular routing, and strain optimization to improve titres. Our integrated system positions more than twenty proteins adapted from yeast, bacteria, plants and animals across six sub-cellular locations to recapitulate the spatial organization of tropane alkaloid biosynthesis in plants. Microbial biosynthesis platforms can facilitate the discovery of tropane alkaloid derivatives as new therapeutic agents for neurological disease and, once scaled, enable robust and agile supply of these essential medicines.

Columnar growth phenotype in apple results from gibberellin deficiency by ectopic expression of a dioxygenase gene

The apple cultivar McIntosh Wijcik, which is a mutant of 'McIntosh', exhibits a columnar growth phenotype (short internodes, few lateral branches, many spurs, etc.) that is controlled by a dominant Co gene. The candidate gene (MdDOX-Co), encoding a 2-oxoglutarate-dependent dioxygenase, is located adjacent to an insertion mutation. Non-columnar apples express MdDOX-Co in the roots, whereas columnar apples express MdDOX-Co in the aerial parts as well as in the roots. However, the function of MdDOX-Co remains unknown. Here, we characterized tobacco plants overexpressing MdDOX-Co. The tobacco plants showed the typical dwarf phenotype, which was restored by application of gibberellin A3 (GA3). Moreover, the dwarf tobacco plants had low concentrations of endogenous bioactive gibberellin A1 (GA1) and gibberellin A4 (GA4). Similarly, 'McIntosh Wijcik' contained low endogenous GA4 concentration and its dwarf traits (short main shoot and internodes) were partially reversed by GA3 application. These results indicate that MdDOX-Co is associated with bioactive GA deficiency. Interestingly, GA3 application to apple trees also resulted in an increased number of lateral branches and a decrease in flower bud number, indicating that gibberellin (GA) plays important roles in regulating apple tree architecture by affecting both lateral branch formation (vegetative growth) and flower bud formation (reproductive growth). We propose that a deficiency of bioactive GA by ectopic expression of MdDOX-Co in the aerial parts of columnar apples not only induces dwarf phenotypes but also inhibits lateral branch development and promotes flower bud formation, and assembly of these multiple phenotypes constructs the columnar tree form.

Molecular cloning and functional analysis of hyoscyamine 6β-hydroxylase (H6H) in the poisonous and medicinal plant Datura innoxia mill

Datura innoxia Mill., a traditional Chinese herbal medicine, produces tropane alkaloids such as hyoscyamine and scopolamine. Scopolamine has a larger demand than hyoscyamine due to its stronger pharmacological effects and fewer side reactions. It is extracted from solanaceous plants. However, the content of scopolamine is lower than hyoscyamine in D. innoxia. Hyoscyamine 6β-hydroxylase (H6H, EC1.14.11.11) is the key enzyme which can catalyze hyoscyamine to form scopolamine. In this study, a cDNA encoding H6H was cloned from D. innoxia roots and named Dih6h. The full-length cDNA is 1413 bp in length with a 1044-bp open reading frame encoding 347 amino acids. The deduced protein sequence of D. innoxia H6H (DiH6H) shared high identity with H6Hs from other plants. The DiH6H was heterologously expressed in Escherichia coli and purified via His-tag affinity technique. The recombinant DiH6H showed activity in transforming hyoscyamine to scopolamine. Despite Dih6h mRNA was detected in various tissues, its levels in roots were higher than that in other tissues. Indeed, scopolamine accumulation was low in roots, but it was very high in aerial parts, especially in flowers and seeds. These observations suggest that scopolamine may be synthesized in the roots and subsequently transported to the aerial parts. To further verify in vivo function of DiH6H, the cDNA of DiH6H was overexpressed in D. innoxia hairy roots. As expected, an increase of scopolamine production was observed in the positive transformants. The results provide a potential strategy for increasing scopolamine yield by metabolic engineering of its biosynthetic pathway in D. innoxia.

C-H Amination via Nitrene Transfer Catalyzed by Mononuclear Non-Heme Iron-Dependent Enzymes

Expanding the reaction scope of natural metalloenzymes can provide new opportunities for biocatalysis. Mononuclear non-heme iron-dependent enzymes represent a large class of biological catalysts involved in the biosynthesis of natural products and catabolism of xenobiotics, among other processes. Here, we report that several members of this enzyme family, including Rieske dioxygenases as well as α-ketoglutarate-dependent dioxygenases and halogenases, are able to catalyze the intramolecular C-H amination of a sulfonyl azide substrate, thereby exhibiting a promiscuous nitrene transfer reactivity. One of these enzymes, naphthalene dioxygenase (NDO), was further engineered resulting in several active site variants that function as C-H aminases. Furthermore, this enzyme could be applied to execute this non-native transformation on a gram scale in a bioreactor, thus demonstrating its potential for synthetic applications. These studies highlight the functional versatility of non-heme iron-dependent enzymes and pave the way to their further investigation and development as promising biocatalysts for non-native metal-catalyzed transformations.

Steric Enforcement of cis-Epoxide Formation in the Radical C-O-Coupling Reaction by Which (S)-2-Hydroxypropylphosphonate Epoxidase (HppE) Produces Fosfomycin

(S)-2-Hydroxypropylphosphonate [(S)-2-HPP, 1] epoxidase (HppE) reduces H₂O₂ at its nonheme-iron cofactor to install the oxirane "warhead" of the antibiotic fosfomycin. The net replacement of the C1 pro-R hydrogen of 1 by its C2 oxygen, with inversion of configuration at C1, yields the cis-epoxide of the drug [(1R,2S)-epoxypropylphosphonic acid (cis-Fos, 2)]. Here we show that HppE achieves ∼95% selectivity for C1 inversion and cis-epoxide formation via steric guidance of a radical-coupling mechanism. Published structures of the HppE·Fe^II·1 and HppE·Zn^II·2 complexes reveal distinct pockets for C3 of the substrate and product and identify four hydrophobic residues-Leu120, Leu144, Phe182, and Leu193-close to C3 in one of the complexes. Replacement of Leu193 in the substrate C3 pocket with the bulkier Phe enhances stereoselectivity (cis:trans ∼99:1), whereas the Leu120Phe substitution in the product C3 pocket diminishes it (∼82:18). Retention of C1 configuration and trans-epoxide formation become predominant with the bulk-reducing Phe182Ala substitution in the substrate C3 pocket (∼13:87), trifluorination of C3 (∼23:77), or both (∼1:99). The effect of C3 trifluorination is counteracted by the more constrained substrate C3 pockets in the Leu193Phe (∼56:44) and Leu144Phe/Leu193Phe (∼90:10) variants. The ability of HppE to epoxidize substrate analogues bearing halogens at C3, C1, or both is inconsistent with a published hypothesis of polar cyclization via a C1 carbocation. Rather, specific enzyme-substrate contacts drive inversion of the C1 radical-as proposed in a recent computational study-to direct formation of the more potently antibacterial cis-epoxide by radicaloid C-O coupling.

Alkaloid chemodiversity in Mandragora spp. is associated with loss-of-functionality of MoH6H, a hyoscyamine 6β-hydroxylase gene

Mandrakes (Mandragora spp., Solanaceae) are known to contain tropane alkaloids and have been used since antiquity in traditional medicine. Tropane alkaloids such as scopolamine and hyoscyamine are used in modern medicine to treat pain, motion sickness, as eye pupil dilators and antidotes against organo-phosphate poisoning. Hyoscyamine is converted to 6β-hydroxyhyoscyamine (anisodamine) and scopolamine by hyoscyamine 6β-hydroxylase (H6H), a 2-oxoglutarate dependent dioxygenase. We describe here a marked chemo-diversity in the tropane alkaloid content in Mandragora spp. M. officinarum and M. turcomanica lack anisodamine and scopolamine but display up to 10 fold higher hyoscyamine levels as compared with M. autumnalis. Transcriptomic analyses revealed that H6H is highly conserved among scopolamine-producing Solanaceae. MoH6H present in M. officinarum differs in several amino acid residues including a homozygotic mutation in the substrate binding region of the protein and its prevalence among accessions was confirmed by Cleaved-Amplified-Polymorphic-Sequence analyses. Functional expression revealed that MaH6H, a gene isolated from M. autumnalis encodes an active H6H enzyme while the MoH6H sequence isolated from M. officinarum was functionally inactive. A single G to T mutation in nucleotide 663 of MoH6H is associated with the lack of anisodamine and scopolamine in M. officinalis.

Metabolic Characterization of Hyoscyamus niger Ornithine Decarboxylase

Ornithine decarboxylase (ODC) catalyzes ornithine decarboxylation to yield putrescine, a key precursor of polyamines, and tropane alkaloids (TAs). Here, to investigate in depth the role of ODC in polyamine/TA biosynthesis and to provide a candidate gene for engineering polyamine/TA production, the ODC gene (HnODC) was characterized from Hyoscyamus niger, a TA-producing plant. Our phylogenetic analysis revealed that HnODC was clustered with ODC enzymes of plants. Experimental work showed HnODC highly expressed in H. niger roots and induced by methyl jasmonate (MeJA). In the MeJA treatment, the production of both putrescine and N-methylputrescine were markedly promoted in roots, while contents of putrescine, spermidine, and spermine were all significantly increased in leaves. By contrast, MeJA did not significantly change the production of either hyoscyamine or scopolamine in H. niger plants. Building on these results, the 50-kDa His-tagged HnODC proteins were purified for enzymatic assays. When ornithine was fed to HnODC, the putrescine product was detected by HPLC, indicating HnODC catalyzed ornithine to form putrescine. Finally, we also investigated the enzymatic kinetics of HnODC. Its K _m, V _max, and K _cat values for ornithine were respectively 2.62 ± 0.11 mM, 1.87 ± 0.023 nmol min^-1 μg^-1 and 1.57 ± 0.015 s^-1, at pH 8.0 and at 30°C. The HnODC enzyme displays a much higher catalytic efficiency than most reported plant ODCs, suggesting it may be an ideal candidate gene for engineering polyamine/TA biosynthesis.

Changes in Regioselectivity of H Atom Abstraction during the Hydroxylation and Cyclization Reactions Catalyzed by Hyoscyamine 6β-Hydroxylase

Hyoscyamine 6β-hydroxylase (H6H) is an αKG-dependent nonheme iron oxidase that catalyzes the oxidation of hyoscyamine to scopolamine via two separate reactions: hydroxylation followed by oxidative cyclization. Both of these reactions are expected to involve H atom abstraction from each of two adjacent carbon centers (C6 vs C7) in the substrate. During hydroxylation, there is a roughly 85:1 preference for H atom abstraction from C6 versus C7; however, this inverts to a 1:16 preference during cyclization. Furthermore, ¹⁸O incorporation experiments in the presence of deuterated substrate are consistent with the catalytic iron(IV)-oxo complex being able to support the coordination of an additional ligand during hydroxylation. These observations suggest that subtle differences in the substrate binding configuration can have significant consequences for the catalytic cycle of H6H.

Substrate Conformation Correlates with the Outcome of Hyoscyamine 6β-Hydroxylase Catalyzed Oxidation Reactions

Hyoscyamine 6β-hydroxylase (H6H) is an α-ketoglutarate dependent mononuclear nonheme iron enzyme that catalyzes C6-hydroxylation of hyoscyamine and oxidative cyclization of the resulting product to give the oxirane natural product scopolamine. Herein, the chemistry of H6H is investigated using hyoscyamine derivatives with modifications at the C6 or C7 position as well as substrate analogues possessing a 9-azabicyclo[3.3.1]nonane core. Results indicate that hydroxyl rebound is unlikely to take place during the cyclization reaction and that the hydroxylase versus oxidative cyclase activity of H6H is correlated with the presence of an exo-hydroxy group having syn-periplanar geometry with respect to the adjacent H atom to be abstracted.

Molecular Insights into the Involvement of a Never Ripe Receptor in the Interaction Between Two Beneficial Soil Bacteria and Tomato Plants Under Well-Watered and Drought Conditions

Management of plant growth-promoting bacteria (PGPB) can be implemented to deal with sustainable intensification of agriculture. Ethylene is an essential component for plant growth and development and in response to drought. However, little is known about the effects of bacterial inoculation on ethylene transduction pathway. Thus, the present study sought to establish whether ethylene perception is critical for growth induction by two different PGPB strains under drought conditions and the analysis of bacterial effects on ethylene production and gene expression in tomatoes (Solanum lycopersicum). The ethylene-insensitive never ripe (nr) and its isogenic wild-type (wt) cv. Pearson line were inoculated with either Bacillus megaterium or Enterobacter sp. strain C7 and grown until the attainment of maturity under both well-watered and drought conditions. Ethylene perception is crucial for B. megaterium. However, it is not of prime importance for Enterobacter sp. strain C7 PGPB activity under drought conditions. Both PGPB decreased the expression of ethylene-related genes in wt plants, resulting in stress alleviation, while only B. megaterium induced their expression in nr plants. Furthermore, PGPB inoculation affected transcriptomic profile dependency on strain, genotype, and drought. Ethylene sensitivity determines plant interaction with PGPB strains. Enterobacter sp. strain C7 could modulate amino-acid metabolism, while nr mutation causes a partially functional interaction with B. megaterium, resulting in higher oxidative stress and loss of PGPB activity.

Oxidative Cyclization in Natural Product Biosynthesis

Oxidative cyclizations are important transformations that occur widely during natural product biosynthesis. The transformations from acyclic precursors to cyclized products can afford morphed scaffolds, structural rigidity, and biological activities. Some of the most dramatic structural alterations in natural product biosynthesis occur through oxidative cyclization. In this Review, we examine the different strategies used by nature to create new intra(inter)molecular bonds via redox chemistry. This Review will cover both oxidation- and reduction-enabled cyclization mechanisms, with an emphasis on the former. Radical cyclizations catalyzed by P450, nonheme iron, α-KG-dependent oxygenases, and radical SAM enzymes are discussed to illustrate the use of molecular oxygen and S-adenosylmethionine to forge new bonds at unactivated sites via one-electron manifolds. Nonradical cyclizations catalyzed by flavin-dependent monooxygenases and NAD(P)H-dependent reductases are covered to show the use of two-electron manifolds in initiating cyclization reactions. The oxidative installations of epoxides and halogens into acyclic scaffolds to drive subsequent cyclizations are separately discussed as examples of "disappearing" reactive handles. Last, oxidative rearrangement of rings systems, including contractions and expansions, will be covered.

Expression of a putative dioxygenase gene adjacent to an insertion mutation is involved in the short internodes of columnar apples (Malus × domestica)

Determining the molecular mechanism of fruit tree architecture is important for tree management and fruit production. An apple mutant 'McIntosh Wijcik', which was discovered as a bud mutation from 'McIntosh', exhibits a columnar growth phenotype that is controlled by a single dominant gene, Co. In this study, the mutation and the Co gene were analyzed. Fine mapping narrowed the Co region to a 101 kb region. Sequence analysis of the Co region and the original wild-type co region identified an insertion mutation of an 8202 bp long terminal repeat (LTR) retroposon in the Co region. Segregation analysis using a DNA marker based on the insertion polymorphism showed that the LTR retroposon was closely associated with the columnar growth phenotype. RNA-seq and RT-PCR analysis identified a promising Co candidate gene (91071-gene) within the Co region that is specifically expressed in 'McIntosh Wijcik' but not in 'McIntosh'. The 91071-gene was located approximately 16 kb downstream of the insertion mutation and is predicted to encode a 2-oxoglutarate-dependent dioxygenase involved in an unknown reaction. Overexpression of the 91071-gene in transgenic tobaccos and apples resulted in phenotypes with short internodes, like columnar apples. These data suggested that the 8202 bp retroposon insertion in 'McIntosh Wijcik' is associated with the short internodes of the columnar growth phenotype via upregulated expression of the adjacent 91071-gene. Furthermore, the DNA marker based on the insertion polymorphism could be useful for the marker-assisted selection of columnar apples.

Promoting scopolamine biosynthesis in transgenic Atropa belladonna plants with pmt and h6h overexpression under field conditions

Atropa belladonna is one of the most important plant sources for producing pharmaceutical tropane alkaloids (TAs). T1 progeny of transgenic A. belladonna, in which putrescine N-methyltransferase (EC. 2.1.1.53) from Nicotiana tabacum (NtPMT) and hyoscyamine 6β-hydroxylase (EC. 1.14.11.14) from Hyoscyamus niger (HnH6H) were overexpressed, were established to investigate TA biosynthesis and distribution in ripe fruits, leaves, stems, primary roots and secondary roots under field conditions. Both NtPMT and HnH6H were detected at the transcriptional level in transgenic plants, whereas they were not detected in wild-type plants. The transgenes did not influence the root-specific expression patterns of endogenous TA biosynthetic genes in A. belladonna. All four endogenous TA biosynthetic genes (AbPMT, AbTRI, AbCYP80F1 and AbH6H) had the highest/exclusive expression levels in secondary roots, suggesting that TAs were mainly synthesized in secondary roots. T1 progeny of transgenic A. belladonna showed an impressive scopolamine-rich chemotype that greatly improved the pharmaceutical value of A. belladonna. The higher efficiency of hyoscyamine conversion was found in aerial than in underground parts. In aerial parts of transgenic plants, hyoscyamine was totally converted to downstream alkaloids, especially scopolamine. Hyoscyamine, anisodamine and scopolamine were detected in underground parts, but scopolamine and anisodamine were more abundant than hyoscyamine. The exclusively higher levels of anisodamine in roots suggested that it might be difficult for its translocation from root to aerial organs. T1 progeny of transgenic A. belladonna, which produces scopolamine at very high levels (2.94-5.13 mg g(-1)) in field conditions, can provide more valuable plant materials for scopolamine production.

Unity in diversity, a systems approach to regulating plant cell physiology by 2-oxoglutarate-dependent dioxygenases

Could a disjoint group of enzymes synchronize their activities and execute a complex multi-step, measurable, and reproducible response? Here, I surmise that the alpha-ketoglutarate dependent superfamily of non-haem iron (II) dioxygenases could influence cell physiology as a cohesive unit, and that the broad spectra of substrates transformed is an absolute necessity to this portrayal. This eclectic group comprises members from all major taxa, and participates in pesticide breakdown, hypoxia signaling, and osmotic stress neutralization. The oxidative decarboxylation of 2-oxoglutarate to succinate is coupled with a concomitant substrate hydroxylation and, in most cases, is followed by an additional specialized conversion. The domain profile of a protein sequence was used as an index of miscellaneous reaction chemistry and interpreted alongside existent kinetic data in a linear model of integrated function. Statistical parameters were inferred by the creation of a novel, empirically motivated flat-file database of over 3800 sequences (DB2OG) with putative 2-oxoglutarate dependent activity. The collated information was categorized on the basis of existing annotation schema. The data suggests that 2OG-dependent enzymes incorporate several desirable features of a systems level player. DB2OG, is free, accessible without a login to all users, and available at the following URL (http://comp-biol.theacms.in/DB2OG.html).

An active Catharanthus roseus desacetoxyvindoline-4-hydroxylase-like gene and its transcriptional regulatory profile

BACKGROUND

Desacetoxyvindoline-4-hydroxylase is a key enzyme in the biosynthesis of vindoline, the important intermediate leading to vinblastine and vincristine in Catharanthus roseus.

RESULTS

A d4h-like gene has been isolated from C. roseus C₂₀hi cells based on an EST sequence from the Suppression Subtractive Hybridization cDNA library. The full length cDNA of d4h-like was 1427 bp encoding 372 amino acids. It had 66% identities and 80% positives with d4h at the amino acid level. It belonged to 2-oxoglutarate dependent oxygenase superfamily as d4h did. Real-time quantitative PCR analysis revealed that d4h-like was expressed high in roots, flowers and C₂₀hi cells, very low in leaves and stems. Methyl jasmonate could significantly increase the accumulation of d4h-like transcripts. 2,4-D inhibited its expression. An approximate 2,910 bp of 5'-promoter region of d4h-like was obtained, fused to GUS reporter gene and analyzed with fluorescence quantitative assays using transient expression in C. roseus cell suspensions, indicating that d4h-like promoter could drive GUS gene expression in vivo.

CONCLUSION

These results suggest that d4h-like is closely related with d4h in the genetic evolution but with different transcriptional expression profiles. It may be revolved in the hormone-independency of C₂₀hi cells.

Functional diversity of 2-oxoglutarate/Fe(II)-dependent dioxygenases in plant metabolism

Oxidative enzymes catalyze many different reactions in plant metabolism. Among this suite of enzymes are the 2-oxoglutarate/Fe(II)-dependent dioxygenases (2-ODDs). Cytochromes P450 (CYPs) as often considered the most versatile oxidative enzymes in nature, but the diversity and complexity of reactions catalyzed by 2-ODDs is superior to the CYPs. The list of oxidative reactions catalyzed by 2-ODDs includes hydroxylations, demethylations, desaturations, ring closure, ring cleavage, epimerization, rearrangement, halogenation, and demethylenation. Furthermore, recent work, including the discovery of 2-ODDs involved in epigenetic regulation, and others catalyzing several characteristic steps in specialized metabolic pathways, support the argument that 2-ODDs are among the most versatile and important oxidizing biological catalysts. In this review, we survey and summarize the pertinent literature with a focus on several key reactions catalyzed by 2-ODDs, and discuss the significance and impact of these enzymes in plant metabolism.

A root-expressed L-phenylalanine:4-hydroxyphenylpyruvate aminotransferase is required for tropane alkaloid biosynthesis in Atropa belladonna

The tropane alkaloids, hyoscyamine and scopolamine, are medicinal compounds that are the active components of several therapeutics. Hyoscyamine and scopolamine are synthesized in the roots of specific genera of the Solanaceae in a multistep pathway that is only partially elucidated. To facilitate greater understanding of tropane alkaloid biosynthesis, a de novo transcriptome assembly was developed for Deadly Nightshade (Atropa belladonna). Littorine is a key intermediate in hyoscyamine and scopolamine biosynthesis that is produced by the condensation of tropine and phenyllactic acid. Phenyllactic acid is derived from phenylalanine via its transamination to phenylpyruvate, and mining of the transcriptome identified a phylogenetically distinct aromatic amino acid aminotransferase (ArAT), designated Ab-ArAT4, that is coexpressed with known tropane alkaloid biosynthesis genes in the roots of A. belladonna. Silencing of Ab-ArAT4 disrupted synthesis of hyoscyamine and scopolamine through reduction of phenyllactic acid levels. Recombinant Ab-ArAT4 preferentially catalyzes the first step in phenyllactic acid synthesis, the transamination of phenylalanine to phenylpyruvate. However, rather than utilizing the typical keto-acid cosubstrates, 2-oxoglutarate, pyruvate, and oxaloacetate, Ab-ArAT4 possesses strong substrate preference and highest activity with the aromatic keto-acid, 4-hydroxyphenylpyruvate. Thus, Ab-ArAT4 operates at the interface between primary and specialized metabolism, contributing to both tropane alkaloid biosynthesis and the direct conversion of phenylalanine to tyrosine.

2-Oxoglutarate: linking TCA cycle function with amino acid, glucosinolate, flavonoid, alkaloid, and gibberellin biosynthesis

The tricarboxylic acid (TCA) cycle intermediate 2-oxoglutarate (2-OG) is used as an obligatory substrate in a range of oxidative reactions catalyzed by 2-OG-dependent dioxygenases. These enzymes are widespread in nature being involved in several important biochemical processes. We have recently demonstrated that tomato plants in which the TCA cycle enzyme 2-OG dehydrogenase (2-ODD) was antisense inhibited were characterized by early senescence and modified fruit ripening associated with differences in the levels of bioactive gibberellin (GA). Accordingly, there is now compelling evidence that the TCA cycle plays an important role in modulating the rate of flux from 2-OG to amino acid metabolism. Here we discuss recent advances in the biochemistry and molecular biology of 2-OG metabolism occurring in different biological systems indicating the importance of 2-OG and 2-OG dependent dioxygenases not only in glucosinolate, flavonoid and alkaloid metabolism but also in GA and amino acid metabolism. We additionally summarize recent findings regarding the impact of modification of 2-OG metabolism on biosynthetic pathways involving 2-ODDs.

An atypical pattern of accumulation of scopolamine and other tropane alkaloids and expression of alkaloid pathway genes in Hyoscyamus senecionis

A cDNA encoding hyoscyamine 6β-hydroxylase (H6H, EC 1.14.11.11), a bifunctional enzyme catalyzing the last two steps in the scopolamine biosynthetic pathway, was isolated from Hyoscyamus senecionis, a medicinal plant endemic to the Iranian plateau. Expression analysis indicates that Hsh6h is expressed in all tested organs of H. senecionis including roots, rhizomes, leaves, stems and flowers unlike the other tropane alkaloid producing species. In parallel to this, in leaves, levels of scopolamine, the product of H6H, were higher than the substrate hyoscyamine. These data suggest that not only does the conversion of hyoscyamine to scopolamine take place in the root, followed by translocation to aerial parts, but also accumulated hyoscyamine in the aerial parts may be converted to scopolamine by activity of HsH6H. Analysis of expression profiles of putrescine N-methyltransferase and tropinone reductase I and II genes also indicates the organ-independent expression of these genes. Here we also introduce H. senecionis as an important tropane alkaloid producing species with its thick underground parts as a source of hyoscyamine, while its leaves can be considered as a source of scopolamine.

Distribution and prediction of catalytic domains in 2-oxoglutarate dependent dioxygenases

BACKGROUND

The 2-oxoglutarate dependent superfamily is a diverse group of non-haem dioxygenases, and is present in prokaryotes, eukaryotes, and archaea. The enzymes differ in substrate preference and reaction chemistry, a factor that precludes their classification by homology studies and electronic annotation schemes alone. In this work, I propose and explore the rationale of using substrates to classify structurally similar alpha-ketoglutarate dependent enzymes.

FINDINGS

Differential catalysis in phylogenetic clades of 2-OG dependent enzymes, is determined by the interactions of a subset of active-site amino acids. Identifying these with existing computational methods is challenging and not feasible for all proteins. A clustering protocol based on validated mechanisms of catalysis of known molecules, in tandem with group specific hidden markov model profiles is able to differentiate and sequester these enzymes. Access to this repository is by a web server that compares user defined unknown sequences to these pre-defined profiles and outputs a list of predicted catalytic domains. The server is free and is accessible at the following URL (http://comp-biol.theacms.in/H2OGpred.html).

CONCLUSIONS

The proposed stratification is a novel attempt at classifying and predicting 2-oxoglutarate dependent function. In addition, the server will provide researchers with a tool to compare their data to a comprehensive list of HMM profiles of catalytic domains. This work, will aid efforts by investigators to screen and characterize putative 2-OG dependent sequences. The profile database will be updated at regular intervals.

Functional characterization of recombinant hyoscyamine 6β-hydroxylase from Atropa belladonna

(-)-Hyoscyamine, the enantiomerically pure form of atropine, and its derivative scopolamine are tropane alkaloids that are extensively used in medicine. Hyoscyamine 6β-hydroxylase (H6H, EC 1.14.11.11), a monomeric α-ketoglutarate dependent dioxygenase, converts (-)-hyoscyamine to its 6,7-epoxy derivative, scopolamine, in two sequential steps. In this study, H6H of Atropa belladonna (AbH6H) was cloned, heterologously expressed in Escherichia coli, purified and characterized. The catalytic efficiency of AbH6H, especially for the second oxidation, was found to be low, and this may be one of the reasons why Atropa belladonna produces less scopolamine than other species in the same family. 6,7-Dehydrohyoscyamine, a potential precursor for the last step of epoxidation, was shown not to be an obligatory intermediate in the biosynthesis of scopolamine using purified AbH6H with an in vitro (18)O labeling experiment. Moreover, the nitrogen atom in the tropane ring of (-)-hyoscyamine was found to play an important role in substrate recognition.

A 2-oxoglutarate-dependent dioxygenase from Ruta graveolens L. exhibits p-coumaroyl CoA 2'-hydroxylase activity (C2'H): a missing step in the synthesis of umbelliferone in plants

Coumarins are important compounds that contribute to the adaptation of plants to biotic or abiotic stresses. Among coumarins, umbelliferone occupies a pivotal position in the plant phenylpropanoid network. Previous studies indicated that umbelliferone is derived from the ortho-hydroxylation of p-coumaric acid by an unknown biochemical step to yield 2,4-dihydroxycinnamic acid, which then undergoes spontaneous lactonization. Based on a recent report of a gene encoding a 2-oxoglutarate-dependent dioxygenase from Arabidopsis thaliana that exhibited feruloyl CoA 6'-hydroxylase activity (Bourgaud et al., 2006), we combined a bioinformatic approach and a cDNA library screen to identify an orthologous ORF (Genbank accession number JF799117) from Ruta graveolens L. This ORF shares 59% amino acid identity with feruloyl CoA 6'-hydroxylase, was functionally expressed in Escherichia coli, and converted feruloyl CoA into scopoletin and p-coumaroyl CoA into umbelliferone with equal activity. Its bi-functionality was further confirmed in planta: transient expression of JF799117 in Nicotiana benthamiana yielded plants with leaves containing high levels of umbelliferone and scopoletin when compared to control plants, which contained barely detectable traces of these compounds. The expression of JF799117 was also tightly correlated to the amount of umbelliferone that was found in UV-elicited R. graveolens leaves. Therefore, JF799117 encodes a p-coumaroyl CoA 2'-hydroxylase in R. graveolens, which represents a previously uncharacterized step in the synthesis of umbelliferone in plants. Psoralen, which is an important furanocoumarin in R. graveolens, was found to be a competitive inhibitor of the enzyme, and it may exert this effect through negative feedback on the enzyme at an upstream position in the pathway.

Chromium-induced tropane alkaloid production and H6H gene expression in Atropa belladonna L. (Solanaceae) in vitro-propagated plantlets

Hyoscyamine and scopolamine tropane alkaloids found in several solanaceous plants are anticholinergic drugs. Hyoscyamine 6β-hydroxylase (H6H) catalyzes two consecutive oxidation reactions. The first reaction is the hydroxylation of hyoscyamine to 6β-hydroxyhyoscyamine and the second is epoxidation of 6β-hydroxyhyoscyamine yielding scopolamine that is the final metabolite in the tropane alkaloid biosynthetic pathway. The effects of trivalent chromium as KCr (SO4)(2) on the production of tropane alkaloids and the expression of hyoscyamine 6β-hydroxylase gene (h6h) were studied in micro-propagated Atropa belladonna L. plantlets. The results showed that chromium treatment decreased the growth parameters (weights and lengths of the plantlets) and chlorophyll contents and increased proline contents. Moreover, semiquantitave RT-PCR analysis showed that the transcript level of H6H increased under chromium treatment. This treatment also increased hyoscyamine and scopolamine contents as shown by HPLC analysis. Changes of scopolamine contents correlate with the expression levels of h6h gene under different concentrations of chromium.

Enhancing the scopolamine production in transgenic plants of Atropa belladonna by overexpressing pmt and h6h genes

Atropa belladonna is officially deemed as the commercial plant to produce scopolamine in China. In this study we report the simultaneous overexpression of two functional genes involved in biosynthesis of scopolamine, which encode the upstream key enzyme putrescine N-methyltransferase (PMT) and the downstream key enzyme hyoscyamine 6β-hydroxylase (H6H), respectively, in transgenic herbal plants Atropa belladonna. Analysis of gene expression profile indicated that both pmt and h6h were expressed at a higher level in transgenic lines, which would be favorable for biosynthesis of scopolamine. High-performance liquid chromatography result suggested that transgenic lines could produce higher accumulation of scopolamine at different levels compared with wild-type lines. Scopolamine content increased to 7.3-fold in transgenic line D9 compared with control lines. This study not only confirms that co-overexpression of pmt and h6h is an ideal method to improve the biosynthetic capacity of scopolamine but also successfully cultivates the transgenic line D9, which significantly enhanced the scopolamine accumulation. Our research can serve as an alternative choice to provide scopolamine resources for relative industry, which is more competitive than conventional market.

Functional identification of hyoscyamine 6β-hydroxylase from Anisodus acutangulus and overproduction of scopolamine in genetically-engineered Escherichia coli

Hyoscyamine 6β-hydroxylase (H6H; EC 1.14.11.11) converts hyoscyamine to scopolamine in the last step of scopolamine biosynthetic pathway. The gene encoding H6H in Anisodus acutangulus was cloned and expressed in Escherichia coli and the recombinant proteins fused with His-tag or GST-tag at its N-terminal were purified and then confirmed by Western bolt analysis. The biofunctional assay revealed that the His-AaH6H and GST-AaH6H converted hyoscyamine (40 mg/l) to scopolamine at 32 and 31 mg/l, respectively. This is the first report on AaH6H expression, purification and functional characterization facilitates further genetic improvement of scopolamine yield in A. acutangulus.

Genome mining in Streptomyces. Elucidation of the role of Baeyer-Villiger monooxygenases and non-heme iron-dependent dehydrogenase/oxygenases in the final steps of the biosynthesis of pentalenolactone and neopentalenolactone

The pentalenolactone biosynthetic gene clusters have been cloned and sequenced from two known producers of the sesquiterpenoid antibiotic pentalenolactone, Streptomyces exfoliatus UC5319 and Streptomyces arenae TÜ469. The recombinant enzymes PenE and PntE, from S. exfoliatus and S. arenae, respectively, catalyze the flavin-dependent Baeyer-Villiger oxidation of 1-deoxy-11-oxopentalenic acid (7) to pentalenolactone D (8). Recombinant PenD, PntD, and PtlD, the latter from Streptomyces avermitilis, each catalyze the Fe(2+)-α-ketoglutarate-dependent oxidation of pentalenolactone D (8) to pentalenolactone E (15) and pentalenolactone F (16). Incubation of PenD, PntD, or PtlD with the isomeric neopentalenolactone D (9) gave PL308 (12) and a compound tentatively identified as neopentalenolactone E (14). These results are corroborated by analysis of the ΔpenD and ΔpntD mutants of S. exfoliatus and S. arenae, respectively, both of which accumulate pentalenolactone D but are blocked in production of pentalenolactone as well as the precursors pentalenolactones E and F. Finally, complementation of the previously described S. avermitilis ΔptlE ΔptlD deletion mutant with either penE or pntE gave pentalenolactone D (8), while complemention of the ΔptlE ΔptlD double mutant with pntE plus pntD or penE plus pntD gave pentalenolactone F (16).

Biochemical and structural characterization of recombinant hyoscyamine 6β-hydroxylase from Datura metel L

Hyoscyamine 6β-hydroxylase (H6H; EC 1.14.11.11), an important enzyme in the biosynthesis of tropane alkaloids, catalyzes the hydroxylation of hyoscyamine to give 6β-hydroxyhyoscyamine and its epoxidation in the biosynthetic pathway leading to scopolamine. Datura metel produces scopolamine as the predominant tropane alkaloid. The cDNA encoding H6H from D. metel (DmH6H) was cloned, heterologously expressed and biochemically characterized. The purified recombinant His-tagged H6H from D. metel (DmrH6H) was capable of converting hyoscyamine to scopolamine. The functionally expressed DmrH6H was confirmed by HPLC and ESI-MS verification of the products, 6β-hydroxyhyoscyamine and its derivative, scopolamine; the DmrH6H epoxidase activity was low compared to the hydroxylase activity. The K(m) values for both the substrates, hyoscyamine and 2-oxoglutarate, were 50μM each. The CD (circular dichroism) spectrum of the DmrH6H indicated a preponderance of α-helicity in the secondary structure. From the fluorescence studies, Stern-Volmer constants for hyoscyamine and 2-oxoglutarate were found to be 0.14M(-1) and 0.56M(-1), respectively. These data suggested that the binding of the substrates, hyoscyamine and 2-oxoglutarate, to the enzyme induced significant conformational changes.

Norcoclaurine synthase is a member of the pathogenesis-related 10/Bet v1 protein family

Norcoclaurine synthase (NCS) catalyzes the first committed step in the biosynthesis of benzylisoquinoline alkaloids (BIAs). NCS from Thalictrum flavum (Tf NCS), Papaver somniferum (Ps NCS1 and Ps NCS2), and Coptis japonica (Cj PR10A) share substantial identity with pathogen-related 10 (PR10) and Bet v1 proteins, whose functions are not well understood. A distinct enzyme (Cj NCS1) with similarity to 2-oxoglutarate-dependent dioxygenases was suggested as the bona fide NCS in C. japonica. Here, we validate the exclusive role of PR10/Bet v1-type NCS enzymes in BIA metabolism. Immunolocalization of Ps NCS2 revealed its cell type-specific occurrence in phloem sieve elements, which contain all other known BIA biosynthetic enzymes. In opium poppy, NCS transcripts and proteins were abundant in root and stem, but at low levels in leaf and carpel. Silencing of NCS in opium poppy profoundly reduced alkaloid levels compared with controls. Immunoprecipitation of NCS from total protein extracts of T. flavum cells resulted in a nearly complete attenuation of NCS activity. A Ps NCS2-green fluorescent protein fusion introduced by microprojectile bombardment into opium poppy cells initially localized to the endoplasmic reticulum but subsequently sorted to the vacuole. In our hands, Cj NCS1 did not catalyze the formation of (S)-norcoclaurine from dopamine and 4-hydroxyphenylacetaldehyde.

Molecular cloning and characterization of two tropinone reductases in Anisodus acutangulus and enhancement of tropane alkaloid production in AaTRI-transformed hairy roots

Tropane alkaloids are used medicinally as anticholinergic agents with increasing market demand, so the improvement and production of active components from medicinal plants using molecular biotechnology show great potential for applications that should benefit human healthcare. Two tropinone reductases constitute a branching point in the biosynthesis of tropane alkaloids. In the present paper, we report for the first time the cloning and characterization of two fulllength cDNAs encoding TRI (tropinone reductase I) (GenBank accession number EU424321) and TRII (tropinone reductase II) (GenBank(R) accession number EU424322) from the solanaceous plant Anisodus acutangulus by rapid amplification of cDNA ends. Sequence comparison indicated that AaTRI (A. acutangulus TRI) and AaTRII (A. acutangulus TRII) had high homology with other tropinone reductases from Hyoscyamus niger, Datura stramonium etc., but AaTRI and AaTRII showed identity of only 60.8%. Phylogenetic-tree analysis showed that AaTRI and AaTRII belong to different clusters and have the closest relationship with H. niger TRI and TRII respectively. Expression-pattern analysis showed that AaTRI and AaTRII were expressed in all tissues tested, including root, stem and leaf, but the transcript level of AaTRI was much lower than AaTRII. Expression of AaTRI and AaTRII could be enhanced by methyl jasmonate, with a weak effect for AaTRI and a strong effect for AaTRII. AaTRI-transformed hairy-root lines were accompanied by a mean 1.87-fold higher level of hyoscyamine and a mean 8-fold higher level of scopolamine compared with control roots, indicating that AaTRI is a promising target for genetic engineering to increase tropane alkaloid in A. acutangulus.

Cloning, characterization and analysis of expression profiles of a cDNA encoding a hyoscyamine 6beta-hydroxylase (H6H) from Atropa baetica Willk

A new cDNA encoding hyoscyamine 6beta-hydroxylase (H6H, EC 1.14.11.11), a bifunctional enzyme catalyzing the last two steps in the biosynthesis of scopolamine, was isolated from Atropa baetica roots (GenBank accession no. EF442802). The full cDNA sequence showed an ORF of 1035bp, coding for a protein with 344 amino acid residues. Sequence analyses at the nucleotide level showed that this ORF shares high identity with other H6H from different plant species, such as Anisodus tanguticus and Hyoscyamus niger with 90% identity, and an almost total identity with A. belladonna (98%). Tissue expression analyses showed that the gene transcript was tissue dependent, appearing exclusively in roots, thus being the only biosynthetic site for the production of scopolamine. Furthermore, Southern hybridization experiments revealed that this gene was not part of a multigene family as appears in low copy number. Phylogenetic tree analysis indicated that A. baetica H6H had a very close relationship with A. belladonna and to a lesser extent with H. niger.

The promoter from SlREO, a highly-expressed, root-specific Solanum lycopersicum gene, directs expression to cortex of mature roots

Root-specific promoters are valuable tools for targeting transgene expression, but many of those already described have limitations to their general applicability. We present the expression characteristics of SlREO, a novel gene isolated from tomato (Solanum lycopersicum L.). This gene was highly expressed in roots but had a very low level of expression in aerial plant organs. A 2.4-kb region representing the SlREO promoter sequence was cloned upstream of the uidA GUS reporter gene and shown to direct expression in the root cortex. In mature, glasshouse-grown plants this strict root specificity was maintained. Furthermore, promoter activity was unaffected by dehydration or wounding stress but was somewhat suppressed by exposure to NaCl, salicylic acid and jasmonic acid. The predicted protein sequence of SlREO contains a domain found in enzymes of the 2-oxoglutarate and Fe(II)-dependent dioxygenase superfamily. The novel SlREO promoter has properties ideal for applications requiring strong and specific gene expression in the bulk of tomato root tissue growing in soil, and is also likely to be useful in other Solanaceous crops.

Scopoletin is biosynthesized via ortho-hydroxylation of feruloyl CoA by a 2-oxoglutarate-dependent dioxygenase in Arabidopsis thaliana

Coumarins are derived via the phenylpropanoid pathway in plants. The 2H-1-benzopyran-2-one core structure of coumarins is formed via the ortho-hydroxylation of cinnamates, trans/cis isomerization of the side chain, and lactonization. Ortho-hydroxylation is a key step in coumarin biosynthesis as a branch point from lignin biosynthesis; however, ortho-hydroxylation of cinnamates is not yet fully understood. In this study, scopoletin biosynthesis was explored using Arabidopsis thaliana, which accumulates scopoletin and its beta-glucopyranoside scopolin in its roots. T-DNA insertion mutants of caffeoyl CoA O-methyltransferase 1 (CCoAOMT1) showed significant reduction in scopoletin and scopolin levels in the roots, and recombinant CCoAOMT1 exhibited 3'-O-methyltransferase activity on caffeoyl CoA to feruloyl CoA. These results suggest that feruloyl CoA is a key precursor in scopoletin biosynthesis. Ortho-hydroxylases of cinnamates were explored in the oxygenase families in A. thaliana, and one of the candidate genes in the Fe(II)- and 2-oxoglutarate-dependent dioxygenase (2OGD) family was designated as F6'H1. T-DNA insertion mutants of F6'H1 showed severe reductions in scopoletin and scopolin levels in the roots. The pattern of F6'H1 expression is consistent with the patterns of scopoletin and scopolin accumulation. The recombinant F6'H1 protein exhibited ortho-hydroxylase activity for feruloyl CoA (K(m) = 36.0 +/- 4.27 microM; k(cat) = 11.0 +/- 0.45 sec(-1)) to form 6'-hydroxyferuloyl CoA, but did not hydroxylate ferulic acid. These results indicate that Fe(II)- and 2-oxoglutarate-dependent dioxygenase is the pivotal enzyme in the ortho-hydroxylation of feruloyl CoA in scopoletin biosynthesis.

Hyoscyamine biosynthesis in Datura stramonium hairy root in vitro systems with different ploidy levels

Hyoscyamine biosynthesis in Datura stramonium hairy roots with different ploidy levels was investigated. For the first time, we report that hairy roots undergo endoreduplication and therefore consist mainly of cells with doupled sets of chromosomes of primary plant tissues, used for Agrobacterium transformation. The alkaloid profiles of hairy roots obtained from diploid and tetraploid plants were similar in terms of the major compounds, but they differed significantly with respect to the minor compounds (here defined as those that accounted for <1% of the total ion current of the alkaloid mixture in gas chromatography-mass spectrometric analyses). Significant differences in the effects of the main nutrients on the growth of the hairy roots obtained from diploid and tetraploid plants and their hyoscyamine contents were observed. The maximal yield of hyoscyamine (177 mg/L) was obtained when hairy roots from tetraploid plants were cultivated in Murashige-Skoog nutrient medium supplemented with 6% sucrose. Time courses of utilization of the main nutrients in the medium during cultivation of D. stramonium hairy root cultures are also presented.

Expression of Brugmansia candida Hyoscyamine 6beta-Hydroxylase gene in Saccharomyces cerevisiae and its potential use as biocatalyst

Background

Tropane alkaloids, mainly hyoscyamine and scopolamine, are widely used in medicine due to their anticholinergic activity. Scopolamine has a higher demand being the more valuable alkaloid due to its fewer side effects and higher physiological activity. Anisodamine (6β-hydroxyhyoscyamine) is the intermediate in the conversion of hyoscyamine into scopolamine. Current studies report that this alkaloid is potentially applicable in medicine. The gene that codifies for Hyoscyamine 6-β hydroxylase, the enzyme responsible for hyoscyamine hydroxylation and epoxidation, leading to scopolamine was isolated from Brugmansia candida.

Results

The h6hcDNA was cloned into pYES2.1 and pYES2.1/V5-His-TOPO vectors to produce an untagged and a tagged protein, respectively. The H6H enzyme was produced in Saccharomyces cerevisiae in order to obtain a biological catalyst for potential industrial applications. Protein extracts of the induced yeast were analyzed by Western blot. The expression was detected 4 h after induction and no degradation was observed during the period assayed. The tagged and the untagged proteins were able to transform hyoscyamine, showing a functional expression of the h6hcDNA.

Conclusion

The strains obtained in this work are promising and potentially applicable in biocatalytic processes.