Cloning and functional characterization of 2-C-methyl-D-erythritol 4-phosphate cytidyltransferase (GbMECT) gene from Ginkgo biloba

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

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

Cloning and Functional Characterization of 2-C-methyl-D-erythritol-4-phosphate cytidylyltransferase (LiMCT) Gene in Oriental Lily (Lilium 'Sorbonne')

2-C-methyl-D-erythritol-phosphate cytidylyltransferase (MCT) is a key enzyme in the MEP pathway of monoterpene synthesis, catalyzing the generation of 4- (5'-pyrophosphate cytidine)-2-C-methyl-D-erythritol from 2-C-methyl-D-erythritol-4-phosphate. We used homologous cloning strategy to clone gene, LiMCT, in the MEP pathway that may be involved in the regulation of floral fragrance synthesis in the Lilium oriental hybrid 'Sorbonne.' The full-length ORF sequence was 837 bp, encoding 278 amino acids. Bioinformatics analysis showed that the relative molecular weight of LiMCT protein is 68.56 kD and the isoelectric point (pI) is 5.12. The expression pattern of LiMCT gene was found to be consistent with the accumulation sites and emission patterns of floral fragrance monoterpenes in transcriptome data (unpublished). Subcellular localization indicated that the LiMCT protein is located in chloroplasts, which is consistent with the location of MEP pathway genes functioning in plastids to produce isoprene precursors. Overexpression of LiMCT in Arabidopsis thaliana affected the expression levels of MEP and MVA pathway genes, suggesting that overexpression of the LiMCT in A. thaliana affected the metabolic flow of C5 precursors of two different terpene synthesis pathways. The expression of the monoterpene synthase AtTPS14 was elevated nearly fourfold in transgenic A. thaliana compared with the control, and the levels of carotenoids and chlorophylls, the end products of the MEP pathway, were significantly increased in the leaves at full bloom, indicating that LiMCT plays an important role in regulating monoterpene synthesis and in the synthesis of other isoprene-like precursors in transgenic A. thaliana flowers. However, the specific mechanism of LiMCT in promoting the accumulation of isoprene products of the MEP pathway and the biosynthesis of floral monoterpene volatile components needs further investigation.

Structure, synthesis, biosynthesis, and activity of the characteristic compounds from Ginkgo biloba L

Covering: 1928-2021Ginkgo biloba L. is one of the most distinctive plants to have emerged on earth and has no close living relatives. Owing to its phylogenetic divergence from other plants, G. biloba contains many compounds with unique structures that have served to broaden the chemical diversity of herbal medicine. Examples of such compounds include terpene trilactones (ginkgolides), acylated flavonol glycosides (ginkgoghrelins), biflavones (ginkgetin), ginkgotides and ginkgolic acids. The extract of G. biloba leaf is used to prevent and/or treat cardiovascular diseases, while many ginkgo-derived compounds are currently at various stages of preclinical and clinical trials worldwide. The global annual sales of G. biloba products are estimated to total US$10 billion. However, the content and purity of the active compounds isolated by traditional methods are usually low and subject to varying environmental factors, making it difficult to meet the huge demand of the international market. This highlights the need to develop new strategies for the preparation of these characteristic compounds from G. biloba. In this review, we provide a detailed description of the structures and bioactivities of these compounds and summarize the recent research on the development of strategies for the synthesis, biosynthesis, and biotechnological production of the characteristic terpenoids, flavonoids, and alkylphenols/alkylphenolic acids of G. biloba. Our aim is to provide an important point of reference for all scientists who research ginkgo-related compounds for medicinal or other purposes.

Overexpression of Ginkgo biloba Hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate reductase 2 gene (GbHDR2) in Nicotiana tabacum cv. Xanthi

2-C-Methyl-d-erythrol-4-phosphate (MEP) pathway in plant supplies isoprene building blocks for carotenoids and chlorophylls essential in photosynthesis as well as plant hormones such as gibberellin and abscisic acid. To assess the effect of overexpression of the terminal enzyme of the MEP pathway, 1-hydroxy-2-methyl-2-(E)-butenyl-4-diphosphate reductase (HDR), transgenic Nicotiana tabacum overexpressing class 2 HDR from Ginkgo biloba (GbHDR2) under the control of 35S promoter was constructed. Contents of chlorophylls a and b in transgenic tobacco were enhanced by 19 and 7%, respectively, compared to those of the wild type. The carotenoid level was also 18% higher than that in the control plant. As a result, photosynthetic rate of the transgenic tobacco was increased by up to 51%. Diterepenoid duvatrienediol content of transgenic tobacco was also elevated by at least sixfold. To explore the molecular basis of the enhanced isoprenoid accumulation, transcript levels of the key genes involved in the isoprenoid biosynthesis were measured. Transcript levels of geranylgeranyl diphosphate synthase (GGPP), kaurene synthase (KS), gibberellic acid 20 oxidase (GA20ox), and phytoene desaturase (PD) genes in the transgenic tobacco leaves were about twofold higher compared to the wild type. Therefore, upregulation of down-stream genes involved in biosynthesis of di- and tetraterpenoids due to GbHDR2 overexpression was responsible for elevated production of isoprenoids and enhanced photosynthetic rate.

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The online version contains supplementary material available at 10.1007/s13205-021-02887-5.

Characterization, Function, and Transcriptional Profiling Analysis of 3-Hydroxy-3-methylglutaryl-CoA Synthase Gene (GbHMGS1) towards Stresses and Exogenous Hormone Treatments in Ginkgo biloba

3-Hydroxy-3-methylglutaryl-CoA synthase (HMGS) is one of the rate-limiting enzymes in the mevalonate pathway as it catalyzes the condensation of acetoacetyl-CoA to form 3-hydroxy-3-methylglutaryl-CoA. In this study, A HMGS gene (designated as GbHMGS1) was cloned from Ginkgo biloba for the first time. GbHMGS1 contained a 1422-bp open-reading frame encoding 474 amino acids. Comparative and bioinformatics analysis revealed that GbHMGS1 was extensively homologous to HMGSs from other plant species. Phylogenetic analysis indicated that the GbHMGS1 belonged to the plant HMGS superfamily, sharing a common evolutionary ancestor with other HMGSs, and had a further relationship with other gymnosperm species. The yeast complement assay of GbHMGS1 in HMGS-deficient Saccharomyces cerevisiae strain YSC6274 demonstrated that GbHMGS1 gene encodes a functional HMGS enzyme. The recombinant protein of GbHMGS1 was successfully expressed in E. coli. The in vitro enzyme activity assay showed that the k_cat and K_m values of GbHMGS1 were 195.4 min⁻¹ and 689 μM, respectively. GbHMGS1 was constitutively expressed in all tested tissues, including the roots, stems, leaves, female flowers, male flowers and fruits. The transcript accumulation for GbHMGS1 was highest in the leaves. Expression profiling analyses revealed that GbHMGS1 expression was induced by abiotic stresses (ultraviolet B and cold) and hormone treatments (salicylic acid, methyl jasmonate, and ethephon) in G. biloba, indicating that GbHMGS1 gene was involved in the response to environmental stresses and plant hormones.

Combining Metabolic Profiling and Gene Expression Analysis to Reveal the Biosynthesis Site and Transport of Ginkgolides in Ginkgo biloba L

The most unique components of Ginkgo biloba extracts are terpene trilactones (TTLs) including ginkgolides and bilobalide. Study of TTLs biosynthesis has been stagnant in recent years. Metabolic profiling of 40 compounds, including TTLs, flavonoids, and phenolic acids, were globally analyzed in leaf, fibrous root, main root, old stem and young stem extracts of G. biloba. Most of the flavonoids were mainly distributed in the leaf and old stem. Most of phenolic acids were generally distributed among various tissues. The total content of TTLs decreased in the order of the leaf, fibrous root, main root, old stem and young stem. The TTLs were further analyzed in different parts of the main root and old stem. The content of TTLs decreases in the order of the main root periderm, the main root cortex and phloem and the main root xylem. In old stems, the content of TTLs in the cortex and phloem was much higher than both the old stem periderm and xylem. The expression patterns of five key genes in the ginkgolide biosynthetic pathway were measured by real-time quantitative polymerase chain reaction (RT-Q-PCR). Combining metabolic profiling and RT-Q-PCR, the results showed that the fibrous root and main root periderm tissues were the important biosynthesis sites of ginkgolides. Based on the above results, a model of the ginkgolide biosynthesis site and transport pathway in G. biloba was proposed. In this putative model, ginkgolides are synthesized in the fibrous root and main root periderm, and these compounds are then transported through the old stem cortex and phloem to the leaves.

Environmental cues induce changes of steviol glycosides contents and transcription of corresponding biosynthetic genes in Stevia rebaudiana

Plant growth and secondary metabolism are commonly regulated by external cues such as light, temperature and water availability. In this study, the influences of low and high temperatures, dehydration, photoperiods, and different growing stages on the changes of steviol glycosides (SGs) contents and transcription levels of fifteen genes involved in SGs biosynthesis of Stevia rebaudiana Bertoni were examined using HPLC and RT-PCR. The observations showed that the transcript levels of all the fifteen genes were maximum under 25 °C treatment, and the transcription of SrDXS, SrDXR, SrMCT, SrCMK, SrMDS, SrHDS, SrHDR, SrIDI, SrGGDPS, SrCPPS1, SrUGT85C2 and SrUGT76G1 were restrained both in low temperature (15 °C) and high temperature (35 °C). Most genes in SGs biosynthesis pathway exhibited down-regulation in dehydration. To elucidate the effect of photoperiods, the plants were treated by different simulated photoperiods (8 L/16 D, 1 0L/14 D, 14 L/10 D and 16 L/8 D), but no significant transcription changes were observed. In the study of growing stages, there were evident changes of SGs contents, and the transcript levels of all the fifteen genes were minimal in fast growing period, and exhibited evident increase both in flower-bud appearing stage and flowering stage. The obtained results strongly suggest that the effect of environmental cues on steviol glycosides contents and transcription of corresponding biosynthetic genes in S. rebaudiana is significant. It is worth to study deeply.

Transcriptome analysis of Ginkgo biloba kernels

Ginkgo biloba is a dioecious species native to China with medicinally and phylogenetically important characteristics; however, genomic resources for this species are limited. In this study, we performed the first transcriptome sequencing for Ginkgo kernels at five time points using Illumina paired-end sequencing. Approximately 25.08-Gb clean reads were obtained, and 68,547 unigenes with an average length of 870 bp were generated by de novo assembly. Of these unigenes, 29,987 (43.74%) were annotated in publicly available plant protein database. A total of 3,869 genes were identified as significantly differentially expressed, and enrichment analysis was conducted at different time points. Furthermore, metabolic pathway analysis revealed that 66 unigenes were responsible for terpenoid backbone biosynthesis, with up to 12 up-regulated unigenes involved in the biosynthesis of ginkgolide and bilobalide. Differential gene expression analysis together with real-time PCR experiments indicated that the synthesis of bilobalide may have interfered with the ginkgolide synthesis process in the kernel. These data can remarkably expand the existing transcriptome resources of Ginkgo, and provide a valuable platform to reveal more on developmental and metabolic mechanisms of this species.

Biosynthesis pathways of ginkgolides

The ginkgolides, acting as anti-platelet-activating factors, have been studied for many years. The biosynthetic pathway of ginkgolides is still far away from unveiling at the level of molecular genetics and biochemistry. There are at least 11 kinds of enzymes having been cloned from Ginkgo biloba L., which catalyze the formation of ginkgolides via a series of reactions. Some researchers have indicated that the addition of precursors and elicitors can influence the accumulation of ginkgolides in the suspension cell cultures of G. biloba. There are also other factors that can influence the production of ginkgolides. This review focuses on the aforementioned aspects to discuss the biosynthetic pathways of the ginkgolides.

Distinct expression patterns of two Ginkgo biloba 1-hydroxy-2-methyl-2-(E)-butenyl-4-diphosphate reductase/isopentenyl diphospahte synthase (HDR/IDS) promoters in Arabidopsis model

1-Hydroxy-2-methyl-2-(E)-butenyl-4-diphosphate reductase (HDR) or isopentenyl diphosphate synthase (IDS) is an enzyme at the final step of the MEP pathway. The multi-copy nature of IDS gene in a gymnosperm Ginkgo biloba is known. To evaluate the function of each isogene, the roles of the promoters were examined in Arabidopsis model. Among the promoters of GbIDS series, about 1.3 kb of GbIDS1pro and 1.5 kb of GbIDS2pro were cloned and fused with GUS. The GbIDS1pro::GUS was introduced into Arabidopsis to show GUS expression in most organs except for roots, petals, and stamina, whereas the GbIDS2pro::GUS was expressed only in the young leaves, internodes where the flower and shoot branched, and notably in primary root junction. This pattern of GUS expression correlated with high transcript level of GbIDS2 compared to that of GbIDS1 in Ginkgo roots. Methyl jasmonate (MeJA) treatment resulted in down-regulated GbIDS1pro activity in Arabidopsis leaves and upregulated GbIDS2pro activity in roots. The same pattern of gene regulation in roots was also seen upon treatments of gibberellins, abscisic acid, and indole butyric acid.

Two distinct pathways for essential metabolic precursors for isoprenoid biosynthesis

Isoprenoids are a diverse group of molecules found in all organisms, where they perform such important biological functions as hormone signaling (e.g., steroids) in mammals, antioxidation (e.g., carotenoids) in plants, electron transport (e.g., ubiquinone), and cell wall biosynthesis intermediates in bacteria. All isoprenoids are synthesized by the consecutive condensation of the five-carbon monomer isopentenyl diphosphate (IPP) to its isomer, dimethylallyl diphosphate (DMAPP). The biosynthetic pathway for the formation of IPP from acetyl-CoA (i.e., the mevalonate pathway) had been established mainly in mice and the budding yeast Saccharomyces cerevisiae. Curiously, most prokaryotic microorganisms lack homologs of the genes in the mevalonate pathway, even though IPP and DMAPP are essential for isoprenoid biosynthesis in bacteria. This observation provided an impetus to search for an alternative pathway to synthesize IPP and DMAPP, ultimately leading to the discovery of the mevalonate-independent 2-C-methyl-D-erythritol 4-phosphate pathway. This review article focuses on our significant contributions to a comprehensive understanding of the biosynthesis of IPP and DMAPP.

A raison d'être for two distinct pathways in the early steps of plant isoprenoid biosynthesis?

When compared to other organisms, plants are atypical with respect to isoprenoid biosynthesis: they utilize two distinct and separately compartmentalized pathways to build up isoprene units. The co-existence of these pathways in the cytosol and in plastids might permit the synthesis of many vital compounds, being essential for a sessile organism. While substrate exchange across membranes has been shown for a variety of plant species, lack of complementation of strong phenotypes, resulting from inactivation of either the cytosolic pathway (growth and development defects) or the plastidial pathway (pigment bleaching), seems to be surprising at first sight. Hundreds of isoprenoids have been analyzed to determine their biosynthetic origins. It can be concluded that in angiosperms, under standard growth conditions, C₂₀-phytyl moieties, C₃₀-triterpenes and C₄₀-carotenoids are made nearly exclusively within compartmentalized pathways, while mixed origins are widespread for other types of isoprenoid-derived molecules. It seems likely that this coexistence is essential for the interaction of plants with their environment. A major purpose of this review is to summarize such observations, especially within an ecological and functional context and with some emphasis on regulation. This latter aspect still requires more work and present conclusions are preliminary, although some general features seem to exist.

Functional genomics of a living fossil tree, Ginkgo, based on next-generation sequencing technology

Ginkgo biloba is monotypic species native to China and has old, dioecious, medicinally important characteristics. The functional genes related to these characteristics have not been effectively explored due to a limited number of expressed sequence tags (ESTs) from Ginkgo. To discover novel functional genes efficiently and to understand the development of a living fossil tree, Ginkgo, we used massive parallel pyrosequencing on the Roche 454 GS FLX Titanium platform to generate 64 057 ESTs. The ESTs combined with the 21 590 Ginkgo ESTs in genbank were assembled into 22 304 unique putative transcripts, in which 13 922 novel unique putative transcripts were identified by 454 sequencing. After being assigned to putative functions with Gene Ontology terms, a detailed view of the Ginkgo biological systems was displayed, including characterization of unique putative transcripts with homology to known key enzymes and transcription factors involved in ginkgolide/bilobalide and flavonoid biosynthetic pathways, as well as unique putative transcripts related to development, response to disease and defence. The fact that three full-length Ginkgo genes encoding key enzymes were found and cloned, suggests that high-throughput sequencing technology is superior to traditional gene-by-gene approach in discovery of genes. Additionally, a total of 204 simple sequence repeat motifs were detected. Our study not only lays the foundations for transcriptome-led studies in biosynthetic mechanisms, but also contributes significantly to the understanding of functional genomics and development in non-model plants.

Characterization of 1-hydroxy-2-methyl-2-(E)-butenyl-4-diphosphate synthase (HDS) gene from Ginkgo biloba

Diterpene trilactone ginkgolides, one of the major constituents of Ginkgo biloba extract, have shown interesting bioactivities including platelet-activating factor antagonistic activity. 1-Hydroxy-2-methyl-2-(E)-butenyl-4-diphosphate synthase (HDS), converting 2-C-methyl-d-erythritol-2,4-cyclodiphosphate into 1-hydroxy-2-methyl-2-(E)-butenyl-4-diphosphate, is the penultimate enzyme of the seven-step 2-C-methyl-d-erythritol 4-phosphate pathway that supplies building blocks for plant isoprenoids of plastid origin such as ginkgolides and carotenoids. Here, we report on the isolation and characterization of the full-length cDNA encoding HDS (GbHDS, GenBank accession number: DQ251630) from G. biloba. Full-length cDNA of GbHDS, 2,763 bp long, contained an ORF of 2,226 bp encoding a protein composed of 741 amino acids. The theoretical molecular weight and pI of the deduced mature GbHDS of 679 amino acid residues are 75.6 kDa and 5.5, respectively. From 2 weeks after initiation of the culture onward, transcription level of this gene in the ginkgo embryo roots increased to about two times higher than that in the leaves. GbHDS was predicted to possess chloroplast transit peptide of 62 amino acid residues, suggesting its putative localization in the plastids. The transient gene expression in Arabidopsis protoplasts confirmed that the transit peptide was capable of delivering the GbHDS protein from the cytosol into the chloroplasts. The isolation and characterization of GbHDS gene enabled us to further understand the role of GbHDS in the terpenoid biosynthesis in G. biloba.

Optimization of the transient transformation of Catharanthus roseus cells by particle bombardment and its application to the subcellular localization of hydroxymethylbutenyl 4-diphosphate synthase and geraniol 10-hydroxylase

The monoterpene indole alkaloids (MIA) synthesized in Catharanthus roseus are highly valuable metabolites due to their pharmacological properties. In planta, the MIA biosynthetic pathway exhibits a complex compartmentation at the cellular level, whereas subcellular data are sparse. To gain insight into this level of organization, we have developed a high efficiency green fluorescent protein (GFP) imaging approach to systematically localize MIA biosynthetic enzymes within C. roseus cells following a biolistic-mediated transient transformation. The biolistic transformation protocol has been first optimized to obtain a high number of transiently transformed cells with a ~12-fold increase compared to previous protocols and thus to clearly and easily identify the fusion GFP expression patterns in numerous cells. On the basis of this protocol, the subcellular localization of hydroxymethylbutenyl 4-diphosphate synthase (HDS), a methyl erythritol phosphate pathway enzyme and geraniol 10-hydroxylase (G10H), a monoterpene-secoiridoid pathway enzyme has been next characterized. Besides showing the accumulation of HDS within plastids of C. roseus cells, we also provide evidences of the presence of HDS in long stroma-filled thylakoid-free extensions budding from plastids, i.e. stromules that are in close association with other organelles such as endoplasmic reticulum (ER) or mitochondria in agreement with their proposed function in enhancing interorganelle metabolite exchanges. Furthermore, we also demonstrated that G10H is an ER-anchored protein, consistent with the presence of a transmembrane helix at the G10H N-terminal end, which is both necessary and sufficient to drive the ER anchoring.

Regulation of resin acid synthesis in Pinus densiflora by differential transcription of genes encoding multiple 1-deoxy-D-xylulose 5-phosphate synthase and 1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate reductase genes

Pinus densiflora Siebold et Zucc. is the major green canopy species in the mountainous area of Korea. To assess the response of resin acid biosynthetic genes to mechanical and chemical stimuli, we cloned cDNAs of genes encoding enzymes involved in the 2-C-methyl-d-erythritol 4-phosphate (MEP) pathway (1-deoxy-d-xylulose 5-phosphate synthase (PdDXS), 1-deoxy-d-xylulose 5-phosphate reductoisomerase (PdDXR) and 1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate reductase (PdHDR)) by the rapid amplification of cDNA ends (RACE) technique. In addition, we cloned the gene encoding abietadiene synthase (PdABS) as a marker for the site of pine resin biosynthesis. PdHDR and PdDXS occurred as two gene families. In the phylogenetic trees, PdDXSs, PdDXR and PdHDRs each formed a separate clade from their respective angiosperm homologs. PdDXS2, PdHDR2 and PdDXR were most actively transcribed in stem wood, whereas PdABS was specifically transcribed. The abundance of PdDXS2 transcripts in wood in the resting state was generally 50-fold higher than the abundance of PdDXS1 transcripts, and PdHDR2 transcripts were more abundant by an order of magnitude in wood than in other tissues, with the ratio of PdHDR2 to PdHDR1 transcripts in wood being about 1. Application of 1 mM methyl jasmonate (MeJA) selectively enhanced the transcript levels of PdDXS2 and PdHDR2 in wood. The ratios of PdDXS2 to PdDXS1 and PdHDR2 to PdHDR1 reached 900 and 20, respectively, on the second day after MeJA treatment, whereas the transcript level of PdABS increased twofold by 3 days after MeJA treatment. Wounding of the stem differentially enhanced the transcript ratios of PdDXS2 to PdDXS1 and PdHDR2 to PdHDR1 to 300 and 70, respectively. The increase in the transcript levels of the MEP pathway genes in response to wounding was accompanied by two orders of magnitude increase in PdABS transcripts. These observations indicated that resin acid biosynthesis activity, represented by PdABS transcription, was correlated with the selective transcriptions of PdDXS2 and PdHDR2. Introduction of PdDXS2, PdHDR1 and PdHDR2 rescued their respective knockout Escherichia coli mutants, confirming that at least these three genes were functionally active. Intracellular targeting of the green fluorescent protein fused to the N-terminal 100 amino acid residues of these genes in the Arabidopsis transient expression system showed that the proteins were all targeted to the chloroplasts. Our results suggest that the MEP pathway regulates resin biosynthesis in the wood of P. densiflora by differential transcription of the multiple PdDXS and PdHDR genes.

Two copies of 4-(cytidine 5'-diphospho)-2-C-methyl-D-erythritol kinase (CMK) gene in Ginkgo biloba: molecular cloning and functional characterization

4-(Cytidine 5'-diphospho)-2-C-methyl-D-erythritol kinase (CMK or YchB), the fourth enzyme of the 2-C-methyl-D-erythritol 4-phosphate pathway, phosphorylates the 2-hydroxyl group of 4-(cytidine 5'-diphospho)-2-C-methyl-D-erythritol in the presence of ATP. Two isogenes encoding CMK (GbCMK1 and GbCMK2) were cloned and characterized from Ginkgo biloba. The activities of both isozymes were confirmed by complementation assay using Escherichia coli NMW29, a ychB knock-out mutant. The transcript profiles of GbCMKs in the radicles and the cotyledons of the cultured Ginkgo biloba embryos demonstrated that the transcript levels of GbCMK1 were similar in both organs, whereas that of GbCMK2 was predominantly high in the ginkgolide-synthesizing radicles. Selective increases in the transcript abundance of GbCMK2 in the radicles, induced by light and methyl jasmonate treatments, were observed. These differential induction patterns of the transcripts imply GbCMK1 and GbCMK2 respectively have high correlations with the primary and the secondary metabolisms. The transit peptides of both isozymes delivered the fused green fluorescent protein (GFP) into the chloroplast in the Arabidopsis and the Nicotiana transient expression systems; interestingly, the transit peptide of GbCMK1 delivered the GFP protein into the cytosol and the nucleus in addition to the chloroplasts.

Chloroplast localization of methylerythritol 4-phosphate pathway enzymes and regulation of mitochondrial genes in ispD and ispE albino mutants in Arabidopsis

Plant isoprenoids are derived from two independent pathways, the cytosolic mevalonate pathway and the plastid methylerythritol 4-phosphate (MEP) pathway. We used green fluorescent fusion protein assays to demonstrate that the Arabidopsis MEP pathway enzymes are localized to the chloroplast. We have also characterized three Arabidopsis albino mutants, ispD-1, ispD-2 and ispE-1, which have T-DNA insertions in the IspD and IspE genes of the MEP pathway. Levels of photosynthetic pigments are almost undetectable in these albino mutants. Instead of thylakoids, the ispD and ispE mutant chloroplasts are filled with large vesicles. Impairments in chloroplast development and functions may signal changes in the expression of nuclear, chloroplast and mitochondrial genes. We used northern blot analysis to examine the expression of photosynthetic and respiratory genes in the ispD and ispE albino mutants. Steady-state mRNA levels of nucleus- and chloroplast-encoded photosynthetic genes are significantly decreased in the albino mutants. In contrast, transcript levels of nuclear and mitochondrial genes encoding subunits of the mitochondrial electron transport chain are increased or not affected in these mutants. Genomic Southern blot analysis revealed that the DNA amounts of mitochondrial genes are not enhanced in the ispD and ispE albino mutants. These results support the notion that the functional state of chloroplasts may affect the expression of nuclear and mitochondrial genes. The up-regulation of mitochondrial genes in the albino mutants is not caused by changes of mitochondrial DNA copy number in Arabidopsis.

1-Hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate reductase (IDS) is encoded by multicopy genes in gymnosperms Ginkgo biloba and Pinus taeda

Isoprenoids are synthesized through the condensation of five-carbon intermediates, isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP), derived from two distinct biosynthetic routes: cytosolic mevalonate (MVA) and plastidial 2-C-methyl-D: -erythritol 4-phosphate (MEP) pathways. 1-Hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate reductase (IDS; EC 1.17.1.2), which catalyzes the last step of MEP pathway, was cloned as a multicopy gene from gymnosperms Ginkgo biloba (GbIDS1, GbIDS2, and GbIDS2-1) and Pinus taeda (PtIDS1 and PtIDS2), and characterized. Phylogenetic tree constructed with other plant IDSs demonstrated gymnosperm IDSs were distinctively different from angiosperm IDSs. The gymnosperm IDS clade contained two subclades, one composed of GbIDS1 and PtIDS1, and the other composed of GbIDS2, GbIDS2-1, and PtIDS2. G. biloba IDSs, except GbIDS2-1, successfully complemented Escherichia coli DLYT1, a lytB disruptant, confirming the in vivo competency of isozymes. During the 4 weeks study period, although transcript levels of GbIDS1s were similar both in roots and leaves of cultured G. biloba embryo, the transcripts of GbIDS2 predominantly occurred in the embryo roots, where diterpene ginkgolides are biosynthesized. Levels of PtIDS2 transcripts in the diterpenoid resin-producing wood were 4-5 times higher than those in other tissues. Higher levels of GbIDS1 transcripts were induced by light, whereas those of GbIDS2 were increased by methyl jasmonate treatment. These results strongly imply GbIDS2 and PtIDS2 have high correlation with secondary metabolism. In Arabidopsis transient expression system, N-terminal 100 amino acid residues of GbIDS1 delivered fused GFP protein into chloroplast as well as cytosol and nucleus, whereas those of GbIDS2, GbIDS2-1, and two PtIDSs delivered GFP only into chloroplast.