Extensive reprogramming of primary and secondary metabolism by fungal elicitor or infection in parsley cells

The Levels of DAHP Synthase, the First Enzyme of the Shikimate Pathway, Are Related to Free Aromatic Amino Acids and Glutamine Content in Nicotiana plumbaginifolia Cell Cultures

Aromatic amino acid homeostasis was investigated in cell suspension cultures of Nicotiana plumbaginifolia and was related to the activity of the first enzyme in aromatic biosynthesis, 3-deoxy-D-arabino-heptulosonate-7-phosphate (DAHP) synthase. An inverse relationship was found between the intracellular content of free phenylalanine, tyrosine and tryptophan and enzyme specific activity levels, suggesting the occurrence of end-product control mechanisms. Two DAHP synthase isogenes are present in wild tobacco that showed a different expression pattern during the culture growth cycle. Intracellular levels of aromatic amino acids were increased or decreased by adding the culture medium with phenylalanine, tyrosine and tryptophan, or with sublethal doses of the shikimate pathway inhibitor glyphosate, respectively. As a consequence, enzyme levels varied in the opposite direction. The concomitant exogenous supply of glutamine further reduced enzyme activity in mid-log cells, suggesting induction by both aromatic amino acid depletion and nitrogen starvation.

Comparative temporal metabolomics studies to investigate interspecies variation in three Ocimum species

Ocimum is one of the most revered medicinally useful plants which have various species. Each of the species is distinct in terms of metabolite composition as well as the medicinal property. Some basil types are used more often as an aromatic and flavoring ingredient. It would be informative to know relatedness among the species which though belong to the same genera while exclusively different in terms of metabolic composition and the operating pathways. In the present investigation the similar effort has been made in order to differentiate three commonly occurring Ocimum species having the high medicinal value, these are Ocimum sanctum, O. gratissimum and O. kilimandscharicum. The parameters for the comparative analysis of these three Ocimum species comprised of temporal changes in number leaf trichomes, essential oil composition, phenylpropanoid pathway genes expression and the activity of important enzymes. O. gratissimum was found to be richest in phenylpropanoid accumulation as well as their gene expression when compared to O. sanctum while O. kilimandscharicum was found to be accumulating terpenoid. In order to get an overview of this qualitative and quantitative regulation of terpenes and phenylpropenes, the expression pattern of some important transcription factors involved in secondary metabolism were also studied.

Plasma membrane order and fluidity are diversely triggered by elicitors of plant defence

Although plants are exposed to a great number of pathogens, they usually defend themselves by triggering mechanisms able to limit disease development. Alongside signalling events common to most such incompatible interactions, modifications of plasma membrane (PM) physical properties could be new players in the cell transduction cascade. Different pairs of elicitors (cryptogein, oligogalacturonides, and flagellin) and plant cells (tobacco and Arabidopsis) were used to address the issue of possible modifications of plant PM biophysical properties induced by elicitors and their links to other events of the defence signalling cascade. We observed an increase of PM order whatever the elicitor/plant cell pair used, provided that a signalling cascade was induced. Such membrane modification is dependent on the NADPH oxidase-mediated reactive oxygen species production. Moreover, cryptogein, which is the sole elicitor able to trap sterols, is also the only one able to trigger an increase in PM fluidity. The use of cryptogein variants with altered sterol-binding properties confirms the strong correlation between sterol removal from the PM and PM fluidity enhancement. These results propose PM dynamics as a player in early signalling processes triggered by elicitors of plant defence.

Capacity for NADPH regeneration in the leaves of two poplar genotypes differing in ozone sensitivity

Cell capacity for cytosolic NADPH regeneration by NADP-dehydrogenases was investigated in the leaves of two hybrid poplar (Populus deltoides × Populus nigra) genotypes in response to ozone (O3 ) treatment (120 ppb for 17 days). Two genotypes with differential O3 sensitivity were selected, based on visual symptoms and fallen leaves: Robusta (sensitive) and Carpaccio (tolerant). The estimated O3 flux (POD0 ), that entered the leaves, was similar for the two genotypes throughout the treatment. In response to that foliar O3 flux, CO2 assimilation was inhibited to the same extent for the two genotypes, which could be explained by a decrease in Rubisco (EC 4.1.1.39) activity. Conversely, an increase in PEPC (EC 4.1.1.31) activity was observed, together with the activation of certain cytosolic NADP-dehydrogenases above their constitutive level, i.e. NADP-G6PDH (EC 1.1.1.49), NADP-ME (malic enzyme) (EC 1.1.1.40) and NADP-ICDH (NADP-isocitrate dehydrogenase) (EC1.1.1.42). However, the activity of non-phosphorylating NADP-GAPDH (EC 1.2.1.9) remained unchanged. From the 11th fumigation day, NADP-G6PDH and NADP-ME profiles made it possible to differentiate between the two genotypes, with a higher activity in Carpaccio than in Robusta. At the same time, Carpaccio was able to maintain high levels of NADPH in the cells, while NADPH levels decreased in Robusta O3 -treated leaves. All these results support the hypothesis that the capacity for cells to regenerate the reducing power, especially the cytosolic NADPH pool, contributes to improve tolerance to high ozone exposure.

Glucose-6-phosphate dehydrogenase plays a pivotal role in tolerance to drought stress in soybean roots

KEY MESSAGE : Two soybean cultivars showed markedly different drought tolerance. G6PDH plays a central role in the process of H ( 2 ) O ( 2 ) regulated GR, DHAR, and MDHAR activities to maintain GSH and Asc levels. Glucose-6-phosphate dehydrogenase (G6PDH) plays a pivotal role in plant resistance to environmental stresses. In this study, we investigated the role of G6PDH in modulating redox homeostasis under drought stress induced by polyethylene glycol 6000 (PEG6000) in two soybean cultivars JINDOU21 (JD-21) and WDD00172 (WDD-172). The G6PDH activity markedly increased and reached a maximum at 96 h in JD-21 and 72 h in WDD-172 during PEG6000 treatments, respectively. Glucosamine (Glucm, a G6PDH inhibitor) obviously inhibited G6PDH activity in both soybeans under PEG6000 treatments. After PEG6000 treatment, JD-21 showed higher tolerance than WDD-172 not only in higher activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), glutathione reductase (GR), dehydroascorbate reductase (DHAR), and monodehydroascorbate reductase (MDHAR), but also in higher content of glutathione (GSH) and ascorbate (Asc). And we found that hydrogen peroxide (H(2)O(2)) regulated the cell length in root elongation zone. Diphenylene iodonium (DPI, a plasma membrane NADPH oxidase inhibitor) counteracted the PEG6000-induced H(2)O(2) accumulation and decreased the activities of GR, DHAR, and MDHAR as well as GSH and Asc content. Furthermore, exogenous application of H(2)O(2) increased the GR, DHAR, and MDHAR activities that were decreased by Glucm under drought stress. Western blot analysis showed that the G6PDH expression was stimulated by PEG6000 and buthionine sulfoximine (BSO, glutathione biosynthesis inhibitor), and blocked by Glucm, DPI and N-acetyl-L-cysteine (NAC, GSH precursor) in both cultivars. Taken together, our evidence indicates that G6PDH plays a central role in the process of H(2)O(2) regulated GR, DHAR, and MDHAR activities to maintain GSH and Asc levels.

In vitro propagation and production of cardiotonic glycosides in shoot cultures of Digitalis purpurea L. by elicitation and precursor feeding

Digitalis purpurea L. (Scrophulariaceae; Foxglove) is a source of cardiotonic glycosides such as digitoxin and digoxin which are commercially applied in the treatment to strengthen cardiac diffusion and to regulate heart rhythm. This investigation deals with in vitro propagation and elicited production of cardiotonic glycosides digitoxin and digoxin in shoot cultures of D. purpurea L. In vitro germinated seedlings were used as a primary source of explants. Multiple shoot formation was achieved for three explant types (nodal, internodal, and leaf) cultured on Murashige and Skoog (MS) medium with several treatments of cytokinins (6-benzyladenine-BA; kinetin-Kin; and thidiazuron-TDZ) and auxins (indole-3-acetic acid-IAA; α-naphthaleneacetic acid-NAA; and 2,4-dichlorophenoxy acetic acid-2,4-D). Maximum multiple shoots (12.7 ± 0.6) were produced from nodal explants on MS + 7.5 μM BA. Shoots were rooted in vitro on MS containing 15 μM IAA. Rooted plantlets were successfully acclimatized. To further maintain the multiple shoot induction, mother tissue was cut into four equal parts and repeatedly sub-cultured on fresh shoot induction liquid medium after each harvest. On adaptation of this strategy, an average of 18 shoots per explant could be produced. This strategy was applied for the production of biomass and glycosides digitoxin and digoxin in shoot cultures on MS medium supplemented with 7.5 μM BA and several treatments with plant growth regulators, incubation period, abiotic (salicylic acid, mannitol, sorbitol, PEG-6000, NaCl, and KCl), biotic (Aspergillus niger, Helminthosporium sp., Alternaria sp., chitin, and yeast extract) elicitors, and precursors (progesterone, cholesterol, and squalene). The treatment of KCl, mycelial mass of Helminthosporium sp., and progesterone were highly effective for the production of cardenolides. In the presence of progesterone (200 to 300 mg/l), digitoxin and digoxin accumulation was enhanced by 9.1- and 11.9-folds respectively.

Glucose-6-phosphate dehydrogenase-dependent hydrogen peroxide production is involved in the regulation of plasma membrane H+-ATPase and Na+/H+ antiporter protein in salt-stressed callus from Carex moorcroftii

Glucose-6-phosphate dehydrogenase (G6PDH) is important for the activation of plant resistance to environmental stresses, and ion homeostasis is the physiological foundation for living cells. In this study, we investigated G6PDH roles in modulating ion homeostasis under salt stress in Carex moorcroftii callus. G6PDH activity increased to its maximum in 100 mM NaCl treatment and decreased with further increased NaCl concentrations. K+/Na+ ratio in 100 mM NaCl treatment did not exhibit significant difference compared with the control; however, in 300 mM NaCl treatment, it decreased. Low-concentration NaCl (100 mM) stimulated plasma membrane (PM) H+-ATPase and NADPH oxidase activities as well as Na+/H+ antiporter protein expression, whereas high-concentration NaCl (300 mM) decreased their activity and expression. When G6PDH activity and expression were reduced by glycerol treatments, PM H+-ATPase and NADPH oxidase activities, Na+/H+ antiporter protein level and K+/Na+ ratio dramatically decreased. Simultaneously, NaCl-induced hydrogen peroxide (H₂O₂) accumulation was abolished. Exogenous application of H₂O₂ increased G6PDH, PM H+-ATPase and NADPH oxidase activities, Na+/H+ antiporter protein expression and K+/Na+ ratio in the control and glycerol treatments. Diphenylene iodonium (DPI), the NADPH oxidase inhibitor, which counteracted NaCl-induced H₂O₂ accumulation, decreased G6PDH, PM H+-ATPase and NADPH oxidase activities, Na+/H+ antiporter protein level and K+/Na+ ratio. Western blot result showed that G6PDH expression was stimulated by NaCl and H₂O₂, and blocked by DPI. Taken together, G6PDH is involved in H₂O₂ accumulation under salt stress. H₂O₂, as a signal, upregulated PM H+-ATPase activity and Na+/H+ antiporter protein level, which subsequently resulted in the enhanced K+/Na+ ratio. G6PDH played a central role in the process.

Elicitation studies in cell suspension cultures of Cannabis sativa L

Cannabis sativa L. plants produce a diverse array of secondary metabolites. Cannabis cell cultures were treated with biotic and abiotic elicitors to evaluate their effect on secondary metabolism. Metabolic profiles analysed by (1)H NMR spectroscopy and principal component analysis (PCA) showed variations in some of the metabolite pools. However, no cannabinoids were found in either control or elicited cannabis cell cultures. Tetrahydrocannabinolic acid (THCA) synthase gene expression was monitored during a time course. Results suggest that other components in the signaling pathway can be controlling the cannabinoid pathway.

Induction of distinct defense-associated protein patterns in Aphanomyces euteiches (Oomycota)-elicited and -inoculated Medicago truncatula cell-suspension cultures: a proteome and phosphoproteome approach

A comprehensive proteomic approach was applied to investigate molecular events occurring upon inoculation of Medicago truncatula cell-suspension cultures with the oomycete root pathogen Aphanomyces euteiches. Establishment of an inoculation assay in the cell cultures allowed a direct comparison between proteins induced by elicitation with a crude culture extract of the oomycete and by inoculation with A. euteiches zoospores representing the natural infection carrier. Oxidative burst assays revealed responsiveness of the cell cultures for perception of elicitation and inoculation signals. The plant "elicitation proteome" resembles the "inoculation proteome" in early incubation stages and includes proteins induced following initial oxidative burst and defense reactions, but also proteins involved in the antioxidative system. However, approximately 2 days after incubation, the inoculation proteome differs drastically from the proteome of elicited cultures, where a cessation of responses assignable to A. euteiches elicitation occurred. The specific protein induction patterns of zoospore-inoculated cells appeared consistent with the protein induction identified in recent studies for an A. euteiches infection in planta and consist of three functional groups: i) pathogenesis-related proteins, ii) proteins associated with secondary phenylpropanoid or phytoalexin metabolism, and, particularly, iii) proteins assigned to carbohydrate metabolism and energy-related cellular processes. Phosphoproteomic analyses revealed consistent and specific activation of these defense-related pathways already at very early timepoints of inoculation, providing evidence that the identified protein profiles are representative for an established A. euteiches infection of M. truncatula.

Patterns of gene expression induced by oligoguluronates reveal conserved and environment-specific molecular defense responses in the brown alga Laminaria digitata

* Until now, no information has been available on the transcriptional response to the transduction of defense signals in brown seaweeds that leads to active resistance against pathogens or grazers. * Using a polymerase chain reaction (PCR)-based, subtractive cDNA approach combined with filter arrays we demonstrated that Laminaria digitata exhibits a rapid response to oligoguluronate elicitors. The transcription levels of several genes were validated by quantitative real-time reverse-transcription PCR and further analysed using pharmacological approaches. * Fifty upregulated genes were identified by differential screening in elicited algae over a 24-h time-course. These genes were related to oxidative stress responses, production of antimicrobial secondary compounds or cell wall strengthening. Moreover, pharmacological tests showed that intracellular signal transduction is likely to involve reactive oxygen species. A new oligoguluronate-inducible vanadium-dependent haloperoxidase (vHPO), specific to iodide was also characterized. The transcription of several vHPO genes was shown to be tightly regulated. * Taken together, our data show that early transcriptional defense responses in L. digitata are similar to those in land plants but also include novel defense responses that involve tightly regulated iodine metabolism.

Glucose-6-phosphate dehydrogenase plays a pivotal role in nitric oxide-involved defense against oxidative stress under salt stress in red kidney bean roots

The pivotal role of glucose-6-phosphate dehydrogenase (G-6-PDH)-mediated nitric oxide (NO) production in the tolerance to oxidative stress induced by 100 mM NaCl in red kidney bean (Phaseolus vulgaris) roots was investigated. The results show that the G-6-PDH activity was enhanced rapidly in the presence of NaCl and reached a maximum at 100 mM. Western blot analysis indicated that the increase of G-6-PDH activity in the red kidney bean roots under 100 mM NaCl was mainly due to the increased content of the G-6-PDH protein. NO production and nitrate reductase (NR) activity were also induced by 100 mM NaCl. The NO production was reduced by NaN(3) (an NR inhibitor), but not affected by N(omega)-nitro-L-arginine (L-NNA) (an NOS inhibitor). Application of 2.5 mM Na(3)PO(4), an inhibitor of G-6-PDH, blocked the increase of G-6-PDH and NR activity, as well as NO production in red kidney bean roots under 100 mM NaCl. The activities of antioxidant enzymes in red kidney bean roots increased in the presence of 100 mM NaCl or sodium nitroprusside (SNP), an NO donor. The increased activities of all antioxidant enzymes tested at 100 mM NaCl were completely inhibited by 2.5 mM Na(3)PO(4). Based on these results, we conclude that G-6-PDH plays a pivotal role in NR-dependent NO production, and in establishing tolerance of red kidney bean roots to salt stress.

Ozone has dramatic effects on the regulation of the prechorismate pathway in tobacco (Nicotiana tabacum L. cv. Bel W3)

The accumulation of aromatic secondary metabolites is a well-known element of the plant response to ozone. Most of these metabolites are synthesized via the three aromatic amino acids phenylalanine, tyrosine and tryptophan. Before branching, the biosynthetic pathway to the three amino acids shares seven enzymatic steps, called the prechorismate pathway, catalysed by 3-deoxy-D: -arabino-heptulosonate-7-phosphate (DAHP) synthase [EC 2.5.1.54], 3-dehydroquinate synthase [EC 4.2.3.4], 3-dehydroquinate dehydratase [EC 4.2.1.10]-shikimate 5-dehydrogenase [EC 1.1.1.25], shikimate kinase [EC 2.7.1.71], 5-enolpyruvylshikimate 3-phosphate synthase [EC 2.5.1.19] and chorismate synthase [EC 4.2.3.5]). We have studied the transcript level of these enzymes and the aromatic metabolite profile in the ozone sensitive tobacco cultivar BelW3 (Nicotiana tabacum L. cv Bel W3), when exposed to an acute ozone pulse (160 nl l(-1), 5 h). Specific cDNA-fragments of the corresponding six genes were isolated from tobacco Bel W3 and used as probes for determining the expression of the prechorismate pathway genes. The fully expanded leaves of ozone treated plants, which developed symptoms like necrotic leaf spots and accumulation of aromatic metabolites, showed a clear induction of the shikimate pathway genes; indicating, that this induction is linked to the development of the symptoms. Distinct kinetics and magnitudes were observed in tobacco leaves for the ozone dependent enhanced mRNA accumulation of the aforementioned genes in BelW3. The strongest and earliest induction due to ozone treatment could be observed for DAHP synthase. An isoform-specific analysis of the transcripts showed a strong induction on transcript level only for one of three isoforms, which was followed by the induction of the DAHP synthase also on protein level. The different induction kinetics of the prechorismate pathway genes indicate that their regulation in response to ozone might be regulated by different signals, for example, ethylene, reactive oxygen species or salicylic acid, which also occur with different kinetics and thus may play different roles in the plant response to ozone.

The plant's capacity in regulating resource demand

Regulation of resource allocation in plants is the key to integrate understanding of metabolism and resource flux across the whole plant. The challenge is to understand trade-offs as plants balance allocation between different and conflicting demands, e.g., for staying competitive with neighbours and ensuring defence against parasites. Related hypothesis evaluation can, however, produce equivocal results. Overcoming deficits in understanding underlying mechanisms is achieved through integrated experimentation and modelling the various spatio-temporal scaling levels, from genetic control and cell metabolism towards resource flux at the stand level. An integrated, interdisciplinary research concept on herbaceous and woody plants and its outcome to date are used, while drawing attention to currently available knowledge. This assessment is based on resource allocation as driven through plant-pathogen and plant-mycorrhizosphere interaction, as well as competition with neighbouring plants in stands, conceiving such biotic interactions as a "unity" in the control of allocation. Biotic interaction may diminish or foster effects of abiotic stress on allocation, as changes in allocation do not necessarily result from metabolic re-adjustment but may obey allometric rules during ontogeny. Focus is required on host-pathogen interaction under variable resource supply and disturbance, including effects of competition and mycorrhization. Cost/benefit relationships in balancing resource investments versus gains turned out to be fundamental in quantifying competitiveness when related to the space, which is subject to competitive resource exploitation. A space-related view of defence as a form of prevention of decline in competitiveness may promote conversion of resource turnover across the different kinds of biotic interaction, given their capacity in jointly controlling whole plant resource allocation.

Methyl jasmonate and yeast elicitor induce differential transcriptional and metabolic re-programming in cell suspension cultures of the model legume Medicago truncatula

Exposure of cell suspension cultures of Medicago truncatula Gaerth. to methyl jasmonate (MeJA) resulted in up to 50-fold induction of transcripts encoding the key triterpene biosynthetic enzyme beta-amyrin synthase (betaAS; EC 5.4.99.-). Transcripts reached maximum levels at 24 h post-elicitation with 0.5 mM MeJA. The entry point enzymes into the phenylpropanoid and flavonoid pathways, L: -phenylalanine ammonia-lyase (PAL; EC 4.3.1.5) and chalcone synthase (CHS; EC 2.3.1.74), respectively, were not induced by MeJA. In contrast, exposure of cells to yeast elicitor (YE) resulted in up to 45- and 14-fold induction of PAL and CHS transcripts, respectively, at only 2 h post-elicitation. betaAS transcripts were weakly induced at 12 h after exposure to YE. Over 30 different triterpene saponins were identified in the cultures, many of which were strongly induced by MeJA, but not by YE. In contrast, cinnamic acids, benzoic acids and isoflavone-derived compounds accumulated following exposure of cultures to YE, but few changes in phenylpropanoid levels were observed in response to MeJA. DNA microarray analysis confirmed the strong differential transcriptional re-programming of the cell cultures for multiple genes in the phenylpropanoid and triterpene pathways in response to MeJA and YE, and indicated different responses of individual members of gene families. This work establishes Medicago cell cultures as an excellent model for future genomics approaches to understand the regulation of legume secondary metabolism.

Genomics-based selection and functional characterization of triterpene glycosyltransferases from the model legume Medicago truncatula

The biosynthesis of triterpene saponins is poorly characterized in spite of the importance of these glycosylated secondary metabolites for plant defense and animal health. The model legume Medicago truncatula synthesizes more than 30 different saponins based on at least five triterpene aglycones; soyasapogenols B and E, medicagenic acid, hederagenin and bayogenin. We have employed an inducible cell culture system, DNA array-based and in silico transcript profiling, and targeted metabolite profiling, to identify triterpene glycosyltransferases (GTs) from among the more than 300 GTs expressed in M. truncatula. Two uridine diphosphate glucosyltransferases were functionally characterized; UGT73K1 with specificity for hederagenin and soyasapogenols B and E, and UGT71G1 with specificity for medicagenic acid. The latter enzyme also glycosylated certain isoflavones and the flavonol quercetin with higher efficiency than triterpenes; however, integrated transcript and metabolite profiling supported a function for UGT71G1 in terpenoid but not (iso)flavonoid biosynthesis in the elicited cell cultures.

Metabolic profiling of Medicago truncatula cell cultures reveals the effects of biotic and abiotic elicitors on metabolism

GC-MS-based metabolite profiling was used to analyse the response of Medicago truncatula cell cultures to elicitation with methyl jasmonate (MeJa), yeast elicitor (YE), or ultraviolet light (UV). Marked changes in the levels of primary metabolites, including several amino acids, organic acids, and carbohydrates, were observed following elicitation with MeJa. A similar, but attenuated response was observed following YE elicitation, whereas little response was observed following UV elicitation. MeJa induced the accumulation of the triterpene beta-amyrin, a precursor to the triterpene saponins, and LC-MS analysis confirmed the accumulation of triterpene saponins in MeJa-elicited samples. In addition, YE induced a slight, but significant accumulation of shikimic acid, an early precursor to the phenylpropanoid pathway, which was also demonstrated to be YE-inducible by LC-MS analyses. Correlation analyses of metabolite relationships revealed perturbation of the glycine, serine, and threonine biosynthetic pathway, and suggested the induction of threonine aldolase activity, an enzyme as yet uncharacterized from plants. Members of the branched chain amino acid pathway accumulated in a concerted fashion, with the strongest correlation being that between leucine and isoleucine (r2=0.941). While UV exposure itself had little effect on primary metabolites, the experimental procedure, as revealed by control treatments, induced changes in several metabolites which were similar to those following MeJa elicitation. Sucrose levels were lower in MJ- and YE-elicited samples compared with control samples, suggesting that a portion of the effects observed on the primary metabolic pool are a consequence of fundamental metabolic repartitioning of carbon resources rather than elicitor-specific induction. In addition, beta-alanine levels were elevated in all elicited samples, which, when viewed in the context of other elicitation responses, suggests the altered metabolism of coenzyme A and its esters, which are essential in secondary metabolism.

Genome-wide analysis of glucose-6-phosphate dehydrogenases in Arabidopsis

In green tissues of plants under illumination, photosynthesis is the primary source of reduced nicotinamide adenine dinucleotide phosphate (NADPH), which is utilized in reductive reactions such as carbon fixation and nitrogen assimilation. In non-photosynthetic tissues or under non-photosynthetic conditions, the oxidative pentose phosphate pathway contributes to basic metabolism as one of the major sources of NADPH. The first and committed reaction is catalyzed by glucose-6-phosphate dehydrogenase (G6PDH). We characterized the six members of the G6PDH gene family in Arabidopsis. Transit peptide analysis predicted two cytosolic and four plastidic isoforms. Five of the six genes encode active G6PDHs. The recombinant isoforms showed differences in substrate requirements and sensitivities to feedback inhibition. Plastidic isoforms were redox sensitive. One cytosolic isoform was insensitive to redox changes, while the other was inactivated by oxidation. The respective genes had distinct expression patterns that did not correlate with the activity of the proteins, implying a regulatory mechanism beyond the control of mRNA abundance. Two cytosolic and one plastidic isoform were detected in vivo using zymograms, and the respective genes were identified using T-DNA insertion lines. The activity of a plastidic isoform was detected in all tissues including photosynthetic tissues despite its sensitivity to reduction observed in vitro. Genomic data, gene expression, and in vivo enzyme activity data were integrated with in vitro biochemical data to propose in vivo roles for individual G6PDH isoforms in Arabidopsis.

The 4-coumarate:CoA ligase gene family in Arabidopsis thaliana comprises one rare, sinapate-activating and three commonly occurring isoenzymes

4-Coumarate:CoA ligase (4CL; EC 6.2.1.12) has a pivotal role in the biosynthesis of plant secondary compounds at the divergence point from general phenylpropanoid metabolism to several major branch pathways. In Arabidopsis thaliana, we have identified a previously undetected, fourth and final member of the At4CL gene family. The encoded enzyme, At4CL4, exhibits the rare property of efficiently activating sinapate, besides the usual 4CL substrates (4-coumarate, caffeate, and ferulate), indicating a distinct metabolic function. Phylogenetic analysis suggests an early evolutionary and functional divergence of three of the four gene family members, At4CL2-4, whereas At4CL1 appears to have originated much later by duplication of its structurally and functionally closest relative, At4CL2. Various characteristics shared by all known plant 4CL genes, as well as by the encoded proteins, define and delimit the At4CL gene family and distinguish it from the closely related family of "At4CL-like" genes.

Nitric oxide-mediated transcriptional changes in Arabidopsis thaliana

Nitric oxide (NO) is an essential regulatory molecule in several developmental processes and in the stress response in both animal and plant systems. Furthermore, key features of plant resistance to pathogens have been shown to depend on NO production, e.g., defense gene expression and the activation of a hypersensitive reaction (HR) in synergy with reactive oxygen species (ROS). Due to the many possible mechanisms of NO action, a clear picture of its involvement in plant resistance to pathogens is far from being achieved. Transcriptional changes related to NO action are likely to play a significant role in resistance and cell death. We investigated the changes in the expression profiles of Arabidopsis thaliana following infiltration with the NO donor sodium nitroprusside, by cDNA-amplification fragment length polymorphism (AFLP) transcript profiling. Altered expression patterns were detected for 120 of the approximately 2,500 cDNAs examined. Sequence analysis revealed homologies with genes involved in signal transduction, disease resistance and stress response, photosynthesis, cellular transport, and basic metabolism or with sequences coding for unknown proteins. Comparison of the expression profiles with data from public microarray sources revealed that many of the identified genes modulated by NO were previously reported to be modulated in disease-related experiments.

Non-self recognition, transcriptional reprogramming, and secondary metabolite accumulation during plant/pathogen interactions

Disease resistance of plants involves two distinct forms of chemical communication with the pathogen: recognition and defense. Both are essential components of a highly complex, multifaceted defense response, which begins with non-self recognition through the perception of pathogen-derived signal molecules and results in the production, inter alia, of antibiotically active compounds (phytoalexins) and cell wall-reinforcing material around the infection site. To elucidate the molecular details and the genomic basis of the underlying chains of events, we used two different experimental systems: suspension-cultured cells of Petroselinum crispum (parsley) and wild-type as well as mutant plants of Arabidopsis thaliana. Particular emphasis was placed on the structural and functional identification of signal and defense molecules, and on the mechanisms of signal perception, intracellular signal transduction and transcriptional reprogramming, including the structural and functional characterization of the responsible cis-acting gene promoter elements and transacting regulatory proteins. Comparing P. crispum and A. thaliana allows us to distinguish species-specific defense mechanisms from more universal responses, and furthermore provides general insights into the nature of the interactions. Despite the complexity of the pathogen defense response, it is experimentally tractable, and knowledge gained so far has opened up a new realm of gene technology-assisted strategies for resistance breeding of crop plants.

Differential regulation of glucose-6-phosphate dehydrogenase isoenzyme activities in potato

In plants, Glc-6-phosphate dehydrogenase (G6PDH) isoenzymes are present in the cytosol and in plastids. The plastidic enzymes (P1 and P2) are subject to redox regulation, but mechanisms that adjust cytosolic G6PDH activity are largely unknown. We adopted a leaf disc system for monitoring the effects of various conditions on G6PD isoform expression and enzyme activities in potato (Solanum tuberosum). Cytosolic G6PDH activity remained constant during water incubation in the dark. In continuous light or in the presence of metabolizable sugars in the dark, cytosolic G6PDH activity increased 6-fold within 24 h. Cycloheximide incubation demonstrated that enhanced cytosolic G6PDH activity depends on de novo protein synthesis. Osmotic change, phosphate sequestration, or oxidative stress did not affect cytosolic G6PDH activity. Furthermore, enzyme activity and protein contents closely followed the corresponding mRNA levels. Together with the fact that multiple SURE elements are present in the promoter region of the gene, these results suggest that cytosolic G6PDH activity is regulated by sugar availability at the transcriptional level. Plastidic G6PDH activity stayed constant during water incubation in the light and dropped to minimal levels within 6 h in the dark. Conversely, plastidic G6PDH activity of leaf discs incubated on Paraquat rose to 10-fold higher levels, which was not prevented by cycloheximide. Similar increases were found with nitrite, nitrate, or sulfate. No major changes in protein or mRNA contents of the plastidic P1 and P2 isoforms were registered. K(m) (Glc-6-phosphate) values of plastidic G6PDH activity differed between samples incubated on water or Paraquat, suggesting posttranslational modification of the plastidic enzyme(s). Immunoprecipitation of (32)P-labeled samples with P1 isoform-specific antibodies showed that the chloroplast enzyme is subject to protein phosphorylation. Obviously, in extended dark periods, G6PDH activity in the stroma is restricted but can be stimulated in response to high demands for NADPH.

Mitogen-activated protein kinases play an essential role in oxidative burst-independent expression of pathogenesis-related genes in parsley

Plants are continuously exposed to attack by potential phytopathogens. Disease prevention requires pathogen recognition and the induction of a multifaceted defense response. We are studying the non-host disease resistance response of parsley to the oomycete, Phytophthora sojae using a cell culture-based system. Receptor-mediated recognition of P. sojae may be achieved through a thirteen amino acid peptide sequence (Pep-13) present within an abundant cell wall transglutaminase. Following recognition of this elicitor molecule, parsley cells mount a defense response, which includes the generation of reactive oxygen species (ROS) and transcriptional activation of genes encoding pathogenesis-related (PR) proteins or enzymes involved in the synthesis of antimicrobial phytoalexins. Treatment of parsley cells with the NADPH oxidase inhibitor, diphenylene iodonium (DPI), blocked both Pep-13-induced phytoalexin production and the accumulation of transcripts encoding enzymes involved in their synthesis. In contrast, DPI treatment had no effect upon Pep-13-induced PR gene expression, suggesting the existence of an oxidative burst-independent mechanism for the transcriptional activation of PR genes. The use of specific antibodies enabled the identification of three parsley mitogen-activated protein kinases (MAPKs) that are activated within the signal transduction pathway(s) triggered following recognition of Pep-13. Other environmental challenges failed to activate these kinases in parsley cells, suggesting that their activation plays a key role in defense signal transduction. Moreover, by making use of a protoplast co-transfection system overexpressing wild-type and loss-of-function MAPK mutants, we show an essential role for post-translational phosphorylation and activation of MAPKs for oxidative burst-independent PR promoter activation.

Two immediate-early pathogen-responsive members of the AtCMPG gene family in Arabidopsis thaliana and the W-box-containing elicitor-response element of AtCMPG1

The Arabidopsis thaliana genome contains at least 50 predicted AtCMPG genes. The encoded protein family is defined by a common domain possessing four strictly conserved amino acid residues [Cys, Met, Pro, and Gly (CMPG)] that designate the family. Two members, AtCMPG1 and AtCMPG2, with high sequence similarity to the previously described, immediate-early pathogen-responsive PcCMPG1 gene from Petroselinum crispum were selected for analysis of their expression modes and defense-related promoter elements. Among the most striking similarities with PcCMPG1 were immediate-early transcriptional activation on infection or treatment with a pathogen-derived elicitor and the functional importance of a W-box-containing AtCMPG1 promoter element. Remarkably, this strongly pathogen/elicitor-responsive element, F, did not respond to wounding, in contrast to the AtCMPG1 promoter itself. Comparative analysis, both within the A. thaliana genome and across species, provided further insight into the large structural diversity of W-box-containing elements. Possible roles of AtCMPG proteins in regulatory processes are discussed with reference to a large variety of family members, partly with assigned functions, from plants as well as animals.

Leucine zipper-containing WRKY proteins widen the spectrum of immediate early elicitor-induced WRKY transcription factors in parsley

Two new WRKY transcription factors from parsley (Petroselinum crispum), WRKY4 and WRKY5, were isolated using the yeast one-hybrid system. In yeast, both proteins interacted sequence-specifically with W boxes (TTGACC) and activated transcription. They appear to contain functional leucine zippers, which increase their affinities for W boxes. Co-transfection experiments in parsley protoplasts confirmed their in vivo-binding specificity for W boxes. Elicitor-mediated expression of the WRKY5 gene, the first parsley member of the group III family of WRKY proteins, is extremely transient, with high mRNA levels occurring within a time window of less than 1 h. WRKY4 and -5, as well as the previously identified parsley transcription factors WRKY1 and -3, are encoded by immediate early elicitor-activated genes that differ in their sensitivity to cycloheximide (CHX) and their activation kinetics. We propose that a number of the pathways activated during the plant defense response require the induction of several distinct WRKY transcription factors with different DNA binding-site preferences to fine-tune the activation of a wide spectrum of target genes.

Crosstalk among stress responses in plants: pathogen defense overrides UV protection through an inversely regulated ACE/ACE type of light-responsive gene promoter unit

Plants often have to cope with two or more environmental hazards simultaneously. Such coincidences require instantaneous decisions on relative severity and consequential crosstalk between the respective signaling cascades. Among the frequently encountered threats are pathogen infections and UV irradiation, both of which trigger specifically targeted defense responses by means of changes in gene transcription rates. In Petroselinum crispum, pathogen defense has been shown to be associated with extensive metabolic reprogramming, including strong repression of the UV-protective flavonoid biosynthetic pathway. Here we show that one of the involved genes, encoding acyl-CoA oxidase, responds positively to UV light and negatively to a pathogen-derived elicitor through an inversely regulated promoter unit consisting of two almost identical ACGT-containing elements (ACEs). This unit, when either introduced into an unrelated promoter or generated by mutation of a differently composed unit, confers the same type of response pattern on the recipient genes, confirming its general functionality at a convergence site of two largely distinct signaling pathways. Similarly large, rapid, and partly inverse effects of UV light and elicitor were observed for several mRNAs encoding common plant regulatory factors (CPRFs) that exhibit distinct dimerization and DNA-binding properties. This striking coincidence suggests a major role of common plant regulatory factors in mediating the apparent switch in the function of ACGT-containing elements from positive UV light to negative elicitor or pathogen responsiveness.

Merging molecular and ecological approaches in plant-insect interactions

The singer-song-writer Paul Simon sang about the '50 ways to leave your lover'; plants have at least as many ways of coping with their insect herbivores. Recent research has elucidated the mechanisms of direct and indirect plant defenses, and has provided the first proof of a protective function for indirect defenses in nature. Insect attack elicits a large transcriptional reorganization that differs from that elicited by mechanical wounding. Elicitors in herbivore oral secretions can account for herbivore-specific responses. Patterns of transcriptional changes point to the existence of central herbivore-activated regulators of metabolism.

Oxidative pentose phosphate pathway and pyridine nucleotides in relation to heartwood formation in Robinia pseudoacacia L

Most tree species show in the inner parts of their woody axes often a dark colored zone, the heartwood. Its formation is a genetically determined, programmed cell death which is characterized by the activation of metabolic pathways which lead to the formation of phenolic heartwood extractives. In the present paper we report on the key position of the oxidative pentose phosphate pathway (OPP) for this process. The OPP plays a crucial role in anabolic processes and is involved in the interconversion and rearrangements of sugar-phosphates with the net production of NADPH. In tissues of Robinia pseudoacacia L. which are transferred to heartwood, enhanced activities of glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH) are present. A consequence of these increased enzyme activities is a shift in the pyridine nucleotide pool towards NADP+NADPH at the expense of NAD+NADH. These alterations in the metabolism and the redox status probably provide precursors and reduction equivalents being required for the synthesis of heartwood phenolics. The non heartwood forming species Acer pseudoplatanus L. shows neither a radial gradient nor seasonal changes in the amounts of pyridine nucleotides across the trunkwood. The results are discussed in connection with programmed cell death, mitochondrial activity, and heartwood formation.

Isolation and characterization of novel defence-related genes induced by copper, salicylic acid, methyl jasmonate, abscisic acid and pathogen infection in Brassica carinata

Summary To examine the defence response in Brassica carinata we differentially screened a cDNA library made from CuCl(2)-treated (Cu) leaves. The sequence of 17 of the 27 cDNA clones examined that showed Cu-induction had a high similarity to defence genes from other plant species. Among other clones that showed higher expression in the Cu leaves were two cDNAs encoding polypeptides of 351 and 250 amino acids, designated BcCJS1 and BcCJAS1. BcCJS1 had similarity to S-adenosyl-l-methionine: salicylic acid carboxyl methyltransferase from Clarkia breweri. However, the enzyme activity was not found in extracts from E. coli expressing BcCJS1. BcCJAS1 did not show extensive similarity to any genes with known function in the databases but it did contain three regions of amino acid sequence that are frequently found in amidotransferases. A third Cu-induced mRNA, Bcp6PGL, showed very high (86%) similarity to a putative 6-phosphogluconolactonase (6PGL) from Arabidopsis thaliana. In addition to Cu induction, BcCJS1 expression was induced by methyl jasmonate (MeJA) and salicylic acid (SA), BcCJAS1 expression by MeJA, SA and abscisic acid and Bcp6PGL expression by MeJA. The expression of all three genes increased after Alternaria brassicae infection. BcCJS1 and BcCJAS1 were induced within 1 h after MeJA- but not until 3 h after SA-treatment. The expression of both genes was systemically induced after infection with a compatible or incompatible fungal pathogen. SA systemically induced only BcCJAS1. The effects of various inhibitors of signalling pathways on expression of the three genes were studied.

A highly specific pathogen-responsive promoter element from the immediate-early activated CMPG1 gene in Petroselinum crispum

Within the complex signalling network from pathogen-derived elicitor perception to defense-related gene activation, some immediate-early responding genes may have pivotal roles in downstream transcriptional regulation. We have identified the parsley (Petroselinum crispum) ELI17 gene as a particularly fast-responding gene possessing a new type of W box-containing, elicitor-responsive promoter element, E17. Highly selective E17-mediated reporter gene expression at pathogen infection sites in transgenic Arabidopsis thaliana plants demonstrated the potential of this promoter element for designing new strategies in resistance breeding as well as for further analysis of the early components of defense-related gene activation mechanisms. The protein encoded by the ELI17 gene exhibits various structural characteristics of established transcription factors and is designated as a CMPG protein according to the first four strictly conserved amino acids defining a newly emerging class of plant-specific proteins.

Molecular interactions between the specialist herbivore Manduca sexta (Lepidoptera, Sphingidae) and its natural host Nicotiana attenuata. I. Large-scale changes in the accumulation of growth- and defense-related plant mRNAs

Plants respond to herbivore attack with a dramatic functional reorganization that involves the activation of direct and indirect defenses and tolerance, which in turn make large demands on primary metabolism. Here we provide the first characterization of the transcriptional reorganization that occurs after insect attack in a model plant-herbivore system: Nicotiana attenuata Torr. ex Wats.-Manduca sexta. We used mRNA differential display to characterize one-twentieth of the insect-responsive transcriptome of N. attenuata and verified differential expression for 27 cDNAs. Northern analyses were used to study the effects of folivory and exposure to airborne methyl jasmonate and for kinetic analyses throughout a 16-h- light/8-h-dark cycle. Sequence similarity searches allowed putative functions to be assigned to 15 transcripts. Genes were related to photosynthesis, electron transport, cytoskeleton, carbon and nitrogen metabolism, signaling, and a group responding to stress, wounding, or invasion of pathogens. Overall, transcripts involved in photosynthesis were strongly down-regulated, whereas those responding to stress, wounding, and pathogens and involved in shifting carbon and nitrogen to defense were strongly up-regulated. The majority of transcripts responded similarly to airborne methyl jasmonate and folivory, and had tissue- and diurnal-specific patterns of expression. Transcripts encoding Thr deaminase (TD) and a putative retrotransposon were absent in control plants, but were strongly induced after herbivory. Full-length sequences were obtained for TD and the pathogen-inducible alpha-dioxygenase, PIOX. Effects of abiotic and biotic stimuli were investigated for transcripts encoding TD, importin alpha, PIOX, and a GAL83-like kinase cofactor.

Accumulation of soluble and wall-bound indolic metabolites in Arabidopsis thaliana leaves infected with virulent or avirulent Pseudomonas syringae pathovar tomato strains

The chemical structures and accumulation kinetics of several major soluble as well as wall-bound, alkali-hydrolyzable compounds induced upon infection of Arabidopsis thaliana leaves with Pseudomonas syringae pathovar tomato were established. All identified accumulating products were structurally related to tryptophan. Most prominent among the soluble substances were tryptophan, beta-d-glucopyranosyl indole-3-carboxylic acid, 6-hydroxyindole-3-carboxylic acid 6-O-beta-d-glucopyranoside, and the indolic phytoalexin camalexin. The single major accumulating wall component detectable under these conditions was indole-3-carboxylic acid. All of these compounds increased more rapidly, and camalexin as well as indole-3-carboxylic acid reached much higher levels, in the incompatible than in the compatible P. syringae/A. thaliana interaction. The only three prominent phenylpropanoid derivatives present in the soluble extract behaved differently. Two kaempferol glycosides remained largely unaffected, and sinapoyl malate decreased strongly upon bacterial infection with a time course inversely correlated with that of the accumulating tryptophan-related products. The accumulation patterns of both soluble and wall-bound compounds, as well as the disease resistance phenotypes, were essentially the same for infected wild-type and tt4 (no kaempferol glycosides) or fah1 (no sinapoyl malate) mutant plants. Largely different product combinations accumulated in wounded or senescing A. thaliana leaves. It seems unlikely that any one of the infection-induced compounds identified so far has a decisive role in the resistance response to P. syringae.

Accumulation of soluble and wall-bound indolic metabolites in Arabidopsis thaliana leaves infected with virulent or avirulent Pseudomonas syringae pathovar tomato strains

The chemical structures and accumulation kinetics of several major soluble as well as wall-bound, alkali-hydrolyzable compounds induced upon infection of Arabidopsis thaliana leaves with Pseudomonas syringae pathovar tomato were established. All identified accumulating products were structurally related to tryptophan. Most prominent among the soluble substances were tryptophan, beta-d-glucopyranosyl indole-3-carboxylic acid, 6-hydroxyindole-3-carboxylic acid 6-O-beta-d-glucopyranoside, and the indolic phytoalexin camalexin. The single major accumulating wall component detectable under these conditions was indole-3-carboxylic acid. All of these compounds increased more rapidly, and camalexin as well as indole-3-carboxylic acid reached much higher levels, in the incompatible than in the compatible P. syringae/A. thaliana interaction. The only three prominent phenylpropanoid derivatives present in the soluble extract behaved differently. Two kaempferol glycosides remained largely unaffected, and sinapoyl malate decreased strongly upon bacterial infection with a time course inversely correlated with that of the accumulating tryptophan-related products. The accumulation patterns of both soluble and wall-bound compounds, as well as the disease resistance phenotypes, were essentially the same for infected wild-type and tt4 (no kaempferol glycosides) or fah1 (no sinapoyl malate) mutant plants. Largely different product combinations accumulated in wounded or senescing A. thaliana leaves. It seems unlikely that any one of the infection-induced compounds identified so far has a decisive role in the resistance response to P. syringae.

The transcriptome of Arabidopsis thaliana during systemic acquired resistance

Infected plants undergo transcriptional reprogramming during initiation of both local defence and systemic acquired resistance (SAR). We monitored gene-expression changes in Arabidopsis thaliana under 14 different SAR-inducing or SAR-repressing conditions using a DNA microarray representing approximately 25-30% of all A. thaliana genes. We derived groups of genes with common regulation patterns, or regulons. The regulon containing PR-1, a reliable marker gene for SAR in A. thaliana, contains known PR genes and novel genes likely to function during SAR and disease resistance. We identified a common promoter element in genes of this regulon that binds members of a plant-specific transcription factor family. Our results extend expression profiling to definition of regulatory networks and gene discovery in plants.

Two differentially regulated class II chitinases from parsley

Two distinct cDNA clones, PcCHI1 and PcCHI2, with high sequence similarity to plant chitinases were isolated from parsley (Petroselinum crispum), expressed in Escherichia coli, and the encoded proteins functionally identified as endochitinases. Different expression patterns of the corresponding mRNAs and proteins in infected and uninfected parsley plants indicated distinct roles of the two isoforms in both pathogen defense and plant development. Infection of parsley leaf buds with Phytophthora sojae resulted in the rapid, transient and highly localized accumulation of PcCHI1 mRNA and protein around infection sites, whereas PcCHI2 mRNA and protein were systemically induced at later infection stages. Similar differences in the timing of induction were observed in elicitor-treated, suspension-cultured parsley cells. In uninfected plants, PcCHI1 mRNA was particularly abundant in the transmitting tract of healthy flowers, suggesting a role in the constitutive protection of susceptible transmitting tissue of the style against pathogen ingress and/or in the fertilization process, possibly by affecting pollen tube growth. Localization of PcCHI2 mRNA and protein in the parenchymatic collenchyme of young pedicels may indicate a function in the constitutive protection of this tissue. In addition to such distinct roles of PcCHI1 and PcCHI2 in preformed and induced pathogen defense, both chitinases may have endogenous regulatory functions in plant development.

UV light selectively coinduces supply pathways from primary metabolism and flavonoid secondary product formation in parsley

The UV light-induced synthesis of UV-protective flavonoids diverts substantial amounts of substrates from primary metabolism into secondary product formation and thus causes major perturbations of the cellular homeostasis. Results from this study show that the mRNAs encoding representative enzymes from various supply pathways are coinduced in UV-irradiated parsley cells (Petroselinum crispum) with two mRNAs of flavonoid glycoside biosynthesis, encoding phenylalanine ammonia-lyase and chalcone synthase. Strong induction was observed for mRNAs encoding glucose 6-phosphate dehydrogenase (carbohydrate metabolism, providing substrates for the shikimate pathway), 3-deoxyarabinoheptulosonate 7-phosphate synthase (shikimate pathway, yielding phenylalanine), and acyl-CoA oxidase (fatty acid degradation, yielding acetyl-CoA), and moderate induction for an mRNA encoding S-adenosyl-homocysteine hydrolase (activated methyl cycle, yielding S-adenosyl-methionine for B-ring methylation). Ten arbitrarily selected mRNAs representing various unrelated metabolic activities remained unaffected. Comparative analysis of acyl-CoA oxidase and chalcone synthase with respect to mRNA expression modes and gene promoter structure and function revealed close similarities. These results indicate a fine-tuned regulatory network integrating those functionally related pathways of primary and secondary metabolism that are specifically required for protective adaptation to UV irradiation. Although the response of parsley cells to UV light is considerably broader than previously assumed, it contrasts greatly with the extensive metabolic reprogramming observed previously in elicitor-treated or fungus-infected cells.

Altering expression of cinnamic acid 4-hydroxylase in transgenic plants provides evidence for a feedback loop at the entry point into the phenylpropanoid pathway

Pharmacological evidence implicates trans-cinnamic acid as a feedback modulator of the expression and enzymatic activity of the first enzyme in the phenylpropanoid pathway, L-phenylalanine ammonia-lyase (PAL). To test this hypothesis independently of methods that utilize potentially non-specific inhibitors, we generated transgenic tobacco lines with altered activity levels of the second enzyme of the pathway, cinnamic acid 4-hydroxylase (C4H), by sense or antisense expression of an alfalfa C4H cDNA. PAL activity and levels of phenylpropanoid compounds were reduced in leaves and stems of plants in which C4H activity had been genetically down-regulated. However, C4H activity was not reduced in plants in which PAL activity had been down-regulated by gene silencing. In crosses between a tobacco line over-expressing PAL from a bean PAL transgene and a C4H antisense line, progeny populations harboring both the bean PAL sense and C4H antisense transgenes had significantly lower extractable PAL activity than progeny populations harboring the PAL transgene alone. Our data provide genetic evidence for a feedback loop at the entry point into the phenylpropanoid pathway that had previously been inferred from potentially artifactual pharmacological experiments.

Regulation and functional expression of cinnamate 4-hydroxylase from parsley

A previously isolated parsley (Petroselinum crispum) cDNA with high sequence similarity to cinnamate 4-hydroxylase (C4H) cDNAs from several plant sources was expressed in yeast (Saccharomyces cerevisiae) containing a plant NADPH:cytochrome P450 oxidoreductase and verified as encoding a functional C4H (CYP73A10). Low genomic complexity and the occurrence of a single type of cDNA suggest the existence of only one C4H gene in parsley. The encoded mRNA and protein, in contrast to those of a functionally related NADPH:cytochrome P450 oxidoreductase, were strictly coregulated with phenylalanine ammonia-lyase mRNA and protein, respectively, as demonstrated by coinduction under various conditions and colocalization in situ in cross-sections from several different parsley tissues. These results support the hypothesis that the genes encoding the core reactions of phenylpropanoid metabolism form a tight regulatory unit.