Geranylgeranyl diphosphate synthase from Scoparia dulcis and Croton sublyratus. Plastid localization and conversion to a farnesyl diphosphate synthase by mutagenesis

Elucidation of terpenoid metabolism in Scoparia dulcis by RNA-seq analysis

Scoparia dulcis biosynthesize bioactive diterpenes, such as scopadulcic acid B (SDB), which are known for their unique molecular skeleton. Although the biosynthesis of bioactive diterpenes is catalyzed by a sequence of class II and class I diterpene synthases (diTPSs), the mechanisms underlying this process are yet to be fully identified. To elucidate these biosynthetic machinery, we performed a high-throughput RNA-seq analysis, and de novo assembly of clean reads revealed 46,332 unique transcripts and 40,503 two unigenes. We found diTPSs genes including a putative syn-copalyl diphosphate synthase (SdCPS2) and two kaurene synthase-like (SdKSLs) genes. Besides them, total 79 full-length of cytochrome P450 (CYP450) genes were also discovered. The expression analyses showed selected CYP450s associated with their expression pattern of SdCPS2 and SdKSL1, suggesting that CYP450 candidates involved diterpene modification. SdCPS2 represents the first predicted gene to produce syn-copalyl diphosphate in dicots. In addition, SdKSL1 potentially contributes to the SDB biosynthetic pathway. Therefore, these identified genes associated with diterpene biosynthesis lead to the development of genetic engineering focus on diterpene metabolism in S. dulcis.

A Sweetpotato Geranylgeranyl Pyrophosphate Synthase Gene, IbGGPS, Increases Carotenoid Content and Enhances Osmotic Stress Tolerance in Arabidopsis thaliana

Sweetpotato highly produces carotenoids in storage roots. In this study, a cDNA encoding geranylgeranyl phyrophosphate synthase (GGPS), named IbGGPS, was isolated from sweetpotato storage roots. Green fluorescent protein (GFP) was fused to the C-terminus of IbGGPS to obtain an IbGGPS-GFP fusion protein that was transiently expressed in both epidermal cells of onion and leaves of tobacco. Confocal microscopic analysis determined that the IbGGPS-GFP protein was localized to specific areas of the plasma membrane of onion and chloroplasts in tobacco leaves. The coding region of IbGGPS was cloned into a binary vector under the control of 35S promoter and then transformed into Arabidopsis thaliana to obtain transgenic plants. High performance liquid chromatography (HPLC) analysis showed a significant increase of total carotenoids in transgenic plants. The seeds of transgenic and wild-type plants were germinated on an agar medium supplemented with polyethylene glycol (PEG). Transgenic seedlings grew significantly longer roots than wild-type ones did. Further enzymatic analysis showed an increased activity of superoxide dismutase (SOD) in transgenic seedlings. In addition, the level of malondialdehyde (MDA) was reduced in transgenics. qRT-PCR analysis showed altered expressions of several genes involved in the carotenoid biosynthesis in transgenic plants. These data results indicate that IbGGPS is involved in the biosynthesis of carotenoids in sweetpotato storage roots and likely associated with tolerance to osmotic stress.

Characterization and Functional Identification of a Gene Encoding Geranylgeranyl Diphosphate Synthase from Dunaliella bardawil

Geranylgeranyl diphosphate synthase (GGPS) catalyzes the biosynthesis of geranylgeranyl diphosphate, a key precursor for carotenoid biosynthesis. In this study, a full-length cDNA encoding GGPS from Dunaliella bardawil (DbGGPS) was isolated by rapid amplification of cDNA ends (RACE) for the first time. The full-length cDNA of DbGGPS was 1814 bp, containing a 1074 bp ORF encoding 357 amino acids with a calculated mass of 38.88 kDa. Analysis of DbGGPS genomic DNA revealed that it contained 10 exons and 9 introns. It was predicted that DbGGPS possessed a 48 amino acid transit peptide at its N terminus. Bioinformatic analysis revealed that DbGGPS was a member of a group of polyprenyltransferases with five conserved domains and two highly conserved aspartate-rich motifs. Using heterologous expression, carotenoid complementation assay, and gene deletion analysis, it was shown that the coding region of DbGGPS encodes a functional GGPS. This provides new gene sources for carotenoid genetic engineering.

Plant terpenes: defense responses, phylogenetic analysis, regulation and clinical applications

The terpenoids constitute the largest class of natural products and many interesting products are extensively applied in the industrial sector as flavors, fragrances, spices and are also used in perfumery and cosmetics. Many terpenoids have biological activities and also used for medical purposes. In higher plants, the conventional acetate-mevalonic acid pathway operates mainly in the cytosol and mitochondria and synthesizes sterols, sesquiterpenes and ubiquinones mainly. In the plastid, the non-mevalonic acid pathway takes place and synthesizes hemi-, mono-, sesqui-, and diterpenes along with carotenoids and phytol tail of chlorophyll. In this review paper, recent developments in the biosynthesis of terpenoids, indepth description of terpene synthases and their phylogenetic analysis, regulation of terpene biosynthesis as well as updates of terpenes which have entered in the clinical studies are reviewed thoroughly.

Molecular cloning, bacterial expression and functional characterisation of cytochrome P450 monooxygenase, CYP97C27, and NADPH-cytochrome P450 reductase, CPR I, from Croton stellatopilosus Ohba

The cDNAs for cytochrome P450 monooxygenase (designated as CYP97C27 by D. Nelson's group) and NADPH-cytochrome P450 reductase (designated as CPR I based on its classification) were isolated from Croton stellatopilosus leaves, which actively biosynthesise plaunotol (18-OH geranylgeraniol). CYP97C27 and CPR I contain open reading frames encoding proteins of 471 and 711 amino acids with predicted molecular masses of 53 and 79kDa, respectively. By aligning the deduced sequences of CYP97C27 and CPR I with other plant species, all functional domains of CYP97C27 (heme and oxygen binding) and CPR I (CYP- and FMN, FAD, and NADPH cofactor binding) were identified. Amino acid sequence comparison indicated that both CYP97C27 (85-93%) and CPR I (79-83%) share high sequence identities with homologous proteins in other plant species, suggesting that CYP97C27 belongs to the CYP97C subfamily and that CPR I belongs to class I of the dicotyledonous CPR. Functional characterisation of both enzymes, produced in Escherichia coli (pET32a/BL21(DE3)) as recombinant proteins, showed that simultaneous incubation of CYP97C27 and CPR I with the substrate geranylgeraniol (GGOH) and coenzyme NADPH led to formation of the product plaunotol. In C. stellatopilosus, the levels of the CYP97C27 and CPR I transcripts were highly correlated with those of several mRNAs involved in the plaunotol biosynthetic pathway, suggesting that CYP97C27 and CPR I are the enzymes that catalyse the last hydroxylation step of the pathway.

Transcriptional activation of a geranylgeranyl diphosphate synthase gene, GGPPS2, isolated from Scoparia dulcis by treatment with methyl jasmonate and yeast extract

A cDNA clone, designated SdGGPPS2, was isolated from young seedlings of Scoparia dulcis. The putative amino acid sequence of the translate of the gene showed high homology with geranylgeranyl diphosphate synthase (GGPPS) from various plant sources, and the N-terminal residues exhibited the characteristics of chloroplast targeting sequence. An appreciable increase in the transcriptional level of SdGGPPS2 was observed by exposure of the leaf tissues of S. dulcis to methyl jasmonate, yeast extract or Ca(2+) ionophore A23187. In contrast, SdGGPPS1, a homologous GGPPS gene of the plant, showed no or only negligible change in the expression level upon treatment with these stimuli. The truncated protein heterologously expressed in Escherichia coli in which the putative targeting domain was deleted catalyzed the condensation of farnesyl diphosphate and isopentenyl diphosphate to liberate geranylgeranyl diphosphate. These results suggested that SdGGPPS2 plays physiological roles in methyl jasmonate and yeast extract-induced metabolism in the chloroplast of S. dulcis cells.

Functional characterization of the Xanthophyllomyces dendrorhous farnesyl pyrophosphate synthase and geranylgeranyl pyrophosphate synthase encoding genes that are involved in the synthesis of isoprenoid precursors

The yeast Xanthophyllomyces dendrorhous synthesizes the carotenoid astaxanthin, which has applications in biotechnology because of its antioxidant and pigmentation properties. However, wild-type strains produce too low amounts of carotenoids to be industrially competitive. Considering this background, it is indispensable to understand how the synthesis of astaxanthin is controlled and regulated in this yeast. In this work, the steps leading to the synthesis of the carotenoid precursor geranylgeranyl pyrophosphate (GGPP, C20) in X. dendrorhous from isopentenyl pyrophosphate (IPP, C5) and dimethylallyl pyrophosphate (DMAPP, C5) was characterized. Two prenyl transferase encoding genes, FPS and crtE, were expressed in E. coli. The enzymatic assays using recombinant E. coli protein extracts demonstrated that FPS and crtE encode a farnesyl pyrophosphate (FPP, C15) synthase and a GGPP-synthase, respectively. X. dendrorhous FPP-synthase produces geranyl pyrophosphate (GPP, C10) from IPP and DMAPP and FPP from IPP and GPP, while the X. dendrorhous GGPP-synthase utilizes only FPP and IPP as substrates to produce GGPP. Additionally, the FPS and crtE genes were over-expressed in X. dendrorhous, resulting in an increase of the total carotenoid production. Because the parental strain is diploid, the deletion of one of the alleles of these genes did not affect the total carotenoid production, but the composition was significantly altered. These results suggest that the over-expression of these genes might provoke a higher carbon flux towards carotenogenesis, most likely involving an earlier formation of a carotenogenic enzyme complex. Conversely, the lower carbon flux towards carotenogenesis in the deletion mutants might delay or lead to a partial formation of a carotenogenic enzyme complex, which could explain the accumulation of astaxanthin carotenoid precursors in these mutants. In conclusion, the FPS and the crtE genes represent good candidates to manipulate to favor carotenoid biosynthesis in X. dendrorhous.

Metabolic engineering of plant monoterpenes, sesquiterpenes and diterpenes--current status and future opportunities

Terpenoids (a.k.a. isoprenoids) represent the most diverse class of natural products found in plants, with tens of thousands of reported structures. Plant-derived terpenoids have a multitude of pharmaceutical and industrial applications, but the natural resources for their extraction are often limited and, in many cases, synthetic routes are not commercially viable. Some of the most valuable terpenoids are not accumulated in model plants or crops, and genetic resources for breeding of terpenoid natural product traits are thus poorly developed. At present, metabolic engineering, either in the native producer or a heterologous host, is the only realistic alternative to improve yield and accessibility. In this review article, we will evaluate the state of the art of modulating the biosynthetic pathways for the production of mono-, sesqui- and diterpenes in plants.

Molecular cloning and characterization of the promoter of SmGGPPs and its expression pattern in Salvia miltiorrhiza

Geranylgeranyl diphosphate (GGPP) synthase is an important branch point enzyme in terpenoid biosynthesis. It regulates the formation of diterpenoid, such as tanshinones. We cloned a gene for GGPP synthase SmGGPPs involved in diterpenoid biosynthesis from Salvia miltiorrhiza. At 2,767 bp long, this gene comprises an intron and two exons that encode a polypeptide of 364 amino acid residues. Then the 5' flanking sequence of SmGGPPs was characterized by bioinformatics method. Deletion analysis of the promoter of SmGGPPs using tobacco plant displayed that the promoter was induced by heat and cold. To further search these cis-elements involved in induction regulation in the 5' flanking sequence of SmGGPPs, many putative cis-elements were predicted with the PlantCARE and PLACE databases. A group of putative cis-acting elements are involved in induction regulation, including G-Box, WRKY, MYC and ATCT motifs. Real-time PCR analysis revealed that SmGGPPs is mainly expressed in the leaves and can also be induced by various factors, such as NaCl, wounding, high temperature, darkness, pathogen, methyl jasmonate, abscisic acid, salicylic acid, and gibberellins. This study provides useful information for further study of SmGGPPs and its regulator effect on the biosynthetic process of tanshinones so that researchers can improve the tanshinone contents in S. miltiorrhiza.

Structure and dynamics of the isoprenoid pathway network

Isoprenoids are functionally and structurally the most diverse group of plant metabolites reported to date. They can function as primary metabolites, participating in essential plant cellular processes, and as secondary metabolites, of which many have substantial commercial, pharmacological, and agricultural value. Isoprenoid end products participate in plants in a wide range of physiological processes acting in them both synergistically, such as chlorophyll and carotenoids during photosynthesis, or antagonistically, such as gibberellic acid and abscisic acid during seed germination. It is therefore expected that fluxes via isoprenoid metabolic network are tightly controlled both temporally and spatially, and that this control occurs at different levels of regulation and in an orchestrated manner over the entire isoprenoid metabolic network. In this review, we summarize our current knowledge of the topology of the plant isoprenoid pathway network and its regulation at the gene expression level following diverse stimuli. We conclude by discussing agronomical and biotechnological applications emerging from the plant isoprenoid metabolism and provide an outlook on future directions in the systems analysis of the plant isoprenoid pathway network.

Characterization and subcellular localization of geranylgeranyl diphosphate synthase from Catharanthus roseus

The enzyme geranylgeranyl diphosphate synthase (GGPS: EC 2.5.1.1, EC 2.5.1.10, EC 2.5.1.29) catalyses the formation of geranylgeranyl diphosphate (GGPP) from isopentenyl diphosphate and dimethylallyl diphosphate via three successive condensation reactions. A full-length nucleotide sequence of GGPS (named CrGGPS) was cloned from the medicinal plant Catharanthus roseus. The deduced polypeptide has 383 amino acids with a calculated mass of 41.6 kDa and possesses prenyltransferase signatures characteristic of plant type II GGPS. The enzyme was characterized by functional complementation in carotenoid accumulating strains of Escherichia coli. When cultures of Catharanthus cell lines were treated with methyljasmonate, no specific increase in transcript levels were observed. In plants, GGPS are encoded by a small multigene family and the isoforms have been shown to be localized in three different subcellular compartments: chloroplast, endoplasmic reticulum and mitochondria. We investigated the subcellular distribution of CrGGPS through transient transformations of C. roseus cells with a yellow fluorescent protein-fused construct. Our results clearly indicate that CrGGPS is located to plastids within stroma and stromules.

Cloning and expression of 1-deoxy-d-xylulose 5-phosphate synthase cDNA from Croton stellatopilosus and expression of 2C-methyl-d-erythritol 4-phosphate synthase and geranylgeranyl diphosphate synthase, key enzymes of plaunotol biosynthesis

1-Deoxy-d-xylulose 5-phosphate synthase (DXS, EC: 4.1.3.37), the first enzyme in the 2C-methyl-d-erythritol 4-phosphate (MEP) pathway, is known to be responsible for the rate-limiting step of isoprenoid biosynthesis in Escherichia coli and Arabidopsis thaliana. In this study, the dxs gene from Croton stellatopilosus, designated csdxs, was cloned from leaf tissue using the rapid amplification of cDNA ends (RACE) technique. Leaves of C. stellatopilosus contain plaunotol, an acyclic diterpene alcohol. The csdxs cDNA containing the open reading frame of 2163 base pairs appeared to encode a polypeptide of 720 amino acids. Analysis of the deduced amino acid sequence revealed that the NH(2)-terminus of CSDXS carried a chloroplast transit peptide, a thiamine diphosphate binding site, and a transketolase motif, which are the important characteristics of DXS enzymes in higher plants. Multiple alignments of CSDXS with other plant DXSs have indicated that CSDXS has identity ranging between 68% and 89%. Expression levels of csdxs and genes encoding key enzymes in the plaunotol biosynthetic pathway, namely 2C-methyl-d-erythritol 4-phosphate synthase (meps) and geranylgeranyl diphosphate synthase (ggpps), were analysed by measuring transcript levels in leaves of different developmental stages. The results showed that dxs, meps, and ggpps are all active in young leaves prior to full expansion when plaunotol is synthesised from the DXP precursor in chloroplasts. The dense presence of chloroplasts and oil globules in the palisade cells of these leaves support the view that these genes are involved in plaunotol biosynthesis in chloroplast-containing tissues.

A New Geranylgeranyl Diphosphate Synthase Gene fromGinkgo biloba, which Intermediates the Biosynthesis of the Key Precursor for Ginkgolides

Geranylgeranyl diphosphate synthase (GGPPS, EC: 2.5.1.29) catalyzes the biosynthesis of geranylgeranyl diphosphate (GGPP), which is a key precursor for ginkgolide biosynthesis. Here we reported for the first time the cloning of a new full-length cDNA encoding GGPPS from the living fossil plant Ginkgo biloba. The full-length cDNA encoding G. biloba GGPPS (designated as GbGGPPS) was 1657bp long and contained a 1176bp open reading frame encoding a 391 amino acid protein. Comparative analysis showed that GbGGPPS possessed a 79 amino acid transit peptide at its N-terminal, which directed GbGGPPS to target to the plastids. Bioinformatic analysis revealed that GbGGPPS was a member of polyprenyltransferases with two highly conserved aspartate-rich motifs like other plant GGPPSs. Phylogenetic tree analysis indicated that plant GGPPSs could be classified into two groups, angiosperm and gymnosperm GGPPSs, while GbGGPPS had closer relationship with gymnosperm plant GGPPSs.

Functional analysis and subcellular localization of two geranylgeranyl diphosphate synthases from Penicillium paxilli

The filamentous fungus Penicillium paxilli contains two distinct geranylgeranyl diphosphate (GGPP) synthases, GgsA and GgsB (PaxG). PaxG and its homologues in Neotyphodium lolii and Fusarium fujikuroi are associated with diterpene secondary metabolite gene clusters. The genomes of other filamentous fungi including Aspergillus fumigatus, Aspergillus nidulans, Aspergillus niger, Aspergillus oryzae and Fusarium graminearum also contain two or more copies of GGPP synthase genes, although the diterpene metabolite capability of these fungi is not known. The objective of this study was to understand the biological significance of the presence of two copies of GGPP synthases in P. paxilli by investigating their subcellular localization. Using a carotenoid complementation assay and gene deletion analysis, we show that P. paxilli GgsA and PaxG have GGPP synthase activities and that paxG is required for paxilline biosynthesis, respectively. In the DeltapaxG mutant background ggsA was unable to complement paxilline biosynthesis. A GgsA-EGFP fusion protein was localized to punctuate organelles and the EGFP-GRV fusion protein, containing the C-terminus tripeptide GRV of PaxG, was localized to peroxisomes. A truncated PaxG mutant lacking the C-terminus tripeptide GRV was unable to complement a DeltapaxG mutant demonstrating that the tripeptide is functionally important for paxilline biosynthesis.

Cloning and characterization of two different types of geranyl diphosphate synthases from Norway spruce (Picea abies)

Geranyl diphosphate (GPP), the universal precursor of monoterpenes, is formed from isopentenyl diphosphate and dimethylallyl diphosphate by the action of geranyl diphosphate synthase, one of the key branchpoint enzymes of terpene biosynthesis. Three types of GPP synthase can be distinguished in plants based on sequence similarity and subunit architecture, but until now individual species have been reported to contain only one of these types. Here we show that the conifer, Norway spruce (Picea abies), contains two different types of GPP synthase belonging to two separate groups of homodimeric proteins. One enzyme, designated PaIDS2 (P. abies isoprenyl diphosphate synthase 2), has high sequence similarity to other gymnosperm GPP synthases. It produces solely GPP in in vitro assays after expression in Escherichia coli and likely participates in monoterpene biosynthesis accompanying induced oleoresin formation, based on dramatic increases in transcript level after methyl jasmonate application. The other enzyme, designated PaIDS3, has highest similarity to the previously reported Arabidopsis thaliana GPP synthase and several other angiosperm sequences, and is not associated with induced oleoresin formation in Norway spruce. In vitro assay of this protein and one encoded by a similar gene sequence from Quercus robur gave substantial amounts of the larger prenyl diphosphates, FPP and GGPP, in addition to GPP. Hence these proteins may not be involved in monoterpene formation and could conceivably form products in addition to GPP in planta.

Biogenesis, molecular regulation and function of plant isoprenoids

Isoprenoids represent the oldest class of known low molecular-mass natural products synthesized by plants. Their biogenesis in plastids, mitochondria and the endoplasmic reticulum-cytosol proceed invariably from the C5 building blocks, isopentenyl diphosphate and/or dimethylallyl diphosphate according to complex and reiterated mechanisms. Compounds derived from the pathway exhibit a diverse spectrum of biological functions. This review centers on advances obtained in the field based on combined use of biochemical, molecular biology and genetic approaches. The function and evolutionary implications of this metabolism are discussed in relation with seminal informations gathered from distantly but related organisms.

A quantitative structure-activity relationship and pharmacophore modeling investigation of aryl-X and heterocyclic bisphosphonates as bone resorption agents

We have used quantitative structure-activity relationship (QSAR) techniques, together with pharmacophore modeling, to investigate the relationships between the structures of a wide variety of geminal bisphosphonates and their activity in inhibiting osteoclastic bone resorption. For aryl-X (X = alkyl, oxyalkyl, and sulfanylalkyl) derivatives of pamidronate and one alendronate, a molecular field analysis (MFA) yielded an R(2) value of 0.900 and an F-test of 54 for a training set of 29 compounds. Using reduced training sets, the activities of 20 such compounds were predicted with an average error of 2.1 over a 4000x range in activity. Such good results were only obtained when using the X-ray crystallographic structure of farnesyl pyrophosphate (FPP) bound to the target enzyme, farnesyl pyrophosphate synthase (FPP synthase), to guide the initial molecular alignment. For a series of heterocyclic bisphosphonates, use of the MFA method yielded an R(2) of 0.873 and an F-test of 36 for a training set of 26 compounds. Using a reduced training set, the activities of 20 compounds were predicted with an average error of 2.5 over a 2000x range in activity. With the heterocyclic compounds, test calculations indicated the importance of correct choice of protonation of the heterocyclic rings. For example, thiazoles, pyrazoles, and triazoles have low ( approximately 2-3) pK(a) values and the derived bisphosphonates are inactive in bone resorption since they cannot readily be side chain protonated and are thus poor carbocation reactive intermediate analogues. On the other hand, aminothiazoles, imidazoles, pyridyl, and aminopyridyl species typically have pK(a) values in the range approximately 5-9 and, in the absence of unfavorable steric interactions, the corresponding bisphosphonates are generally good inhibitors. However, aminoimidazole bisphosphonates are generally less active, since their pK(a)s ( approximately 11) are so high, due to guanidinium-like resonance, that they cannot readily be deprotonated, which we propose results in poor cellular uptake. The results of pharmacophore modeling using the Catalyst program revealed the importance of two negative ionizable and one positive charge feature for both aryl-X and heterocyclic pharmacophores, together with the presence of a distal hydrophobic feature in the aryl bisphosphonate and a more proximal aromatic feature in the heterocyclic bisphosphonate pharmacophores. When taken together, these results show that it is now possible to predict the activity, within a factor of about 2.3, of a wide range of aryl-X and heterocyclic bisphosphonates. The results emphasize the importance of utilizing crystallographic structural information to guide the initial alignment of extended bisphosphonates, and in the case of heterocyclic bisphosphonates, the importance of side chain protonation state. These simple ideas may facilitate the design of other, novel bisphosphonates, of use in bone resorption therapy, and as antiparasitic and immunotherapeutic agents.

Cloning, expression and characterization of a functional cDNA clone encoding geranylgeranyl diphosphate synthase of Hevea brasiliensis

Geranylgeranyl diphosphate (GGPP) synthase catalyzes the condensation of isopentenyl diphosphate (IPP) with allylic diphosphates to give (all-E)-GGPP. GGPP is one of the key precursors in the biosynthesis of biologically significant isoprenoid compounds. In order to examine possible participation of the GGPP synthase in the enzymatic prenyl chain elongation in natural rubber biosynthesis, we cloned, overexpressed and characterized the cDNA clone encoding GGPP synthase from cDNA libraries of leaf and latex of Hevea brasiliensis. The amino acid sequence of the clone contains all conserved regions of trans-prenyl chain elongating enzymes. This cDNA was expressed in Escherichia coli cells as Trx-His-tagged fusion protein, which showed a distinct GGPP synthase activity. The apparent K(m) values for isopentenyl-, farnesyl-, geranyl- and dimethylallyl diphosphates of the GGPP synthase purified with Ni(2+)-affinity column were 24.1, 6.8, 2.3, and 11.5 microM, respectively. The enzyme shows optimum activity at approximately 40 degrees C and pH 8.5. The mRNA expression of the GGPP synthase was detected in all tissues examined, showing higher in flower and leaf than petiole and latex, where a large quantity of natural rubber is produced. On the other hand, expression levels of the Hevea farnesyl diphosphate synthase were significant in latex as well as in flower.

Geranyl diphosphate synthase from Abies grandis: cDNA isolation, functional expression, and characterization

Geranyl diphosphate synthase catalyzes the condensation of dimethylallyl diphosphate and isopentenyl diphosphate to generate geranyl diphosphate, the essential precursor of monoterpene biosynthesis. Using geranylgeranyl diphosphate synthase from Taxus canadensis as a hybridization probe, four full length cDNA clones, sharing high sequence identity to each other (>69%) and to the Taxus geranylgeranyl diphosphate synthase (>66%), were isolated from a grand fir (Abies grandis) cDNA library. When expressed in Escherichia coli, three of the recombinant enzymes produced geranyl diphosphate and one produced geranylgeranyl diphosphate as the dominant product when supplied with isopentenyl diphosphate and dimethylallyl diphosphate as cosubstrates. One enzyme (AgGPPS2) was confirmed as a specific geranyl diphosphate synthase, in that it accepted only dimethylallyl diphosphate as the allylic cosubstrate and it produced exclusively geranyl diphosphate as product, with a k(cat) of 1.8s(-1). Gel filtration experiments performed on the recombinant geranyl diphosphate synthases, in which the plastidial targeting sequences had been deleted, revealed that these enzymes are homodimers similar to other short-chain prenyltransferases but different from the heterotetrameric geranyl diphosphate synthase of mint.