Polyamines and plant disease

Engineered polyamine catabolism preinduces tolerance of tobacco to bacteria and oomycetes

Polyamine oxidase (PAO) catalyzes the oxidative catabolism of spermidine and spermine, generating hydrogen peroxide. In wild-type tobacco (Nicotiana tabacum 'Xanthi') plants, infection by the compatible pathogen Pseudomonas syringae pv tabaci resulted in increased PAO gene and corresponding PAO enzyme activities; polyamine homeostasis was maintained by induction of the arginine decarboxylase pathway and spermine was excreted into the apoplast, where it was oxidized by the enhanced apoplastic PAO, resulting in higher hydrogen peroxide accumulation. Moreover, plants overexpressing PAO showed preinduced disease tolerance against the biotrophic bacterium P. syringae pv tabaci and the hemibiotrophic oomycete Phytophthora parasitica var nicotianae but not against the Cucumber mosaic virus. Furthermore, in transgenic PAO-overexpressing plants, systemic acquired resistance marker genes as well as a pronounced increase in the cell wall-based defense were found before inoculation. These results reveal that PAO is a nodal point in a specific apoplast-localized plant-pathogen interaction, which also signals parallel defense responses, thus preventing pathogen colonization. This strategy presents a novel approach for producing transgenic plants resistant to a broad spectrum of plant pathogens.

Ustilago maydis induced accumulation of putrescine in maize leaves

Polyamines are implicated in the regulation of many processes in the plant cell, including functioning of ion channels, DNA replication, gene transcription, mRNA translation, cell proliferation and programmed cell death. Plant polyamines occur either in free form, covalently bound to proteins, or conjugated to hydroxycinnamic acids forming phenol amides. Ustilago maydis is a dimorphic and biotrophic pathogenic fungus responsible for common smut or “huitlacoche” in maize; and it is considered an excellent model for the study of plant-pathogen interactions. Recently, we reported alterations in polyamine metabolism of maize tumors induced on leaf blades by Ustilago maydis infection. Our data revealed a striking increase in maize polyamine biosynthesis, mainly free and conjugated putrescine in the tumors and in the green plant tissue surrounding the tumor. In this addendum, we describe that changes in polyamine metabolism take place even in earlier stages of maize plant infection with Ustilago maydis .

Spermine signaling plays a significant role in the defense response of Arabidopsis thaliana to cucumber mosaic virus

We have proposed that the polyamine spermine (Spm) functions as a signaling molecule to evoke defense reactions/cell death in avirulent pathogen-attacked tobacco plants. To understand its molecular basis in depth, Spm-responsive genes in Arabidopsis thaliana were identified by SuperSAGE analysis. Close to 90% of the Spm-responsive genes also responded during cucumber mosaic virus (CMV)-elicited hypersensitive response. Spm modulated the expression of genes of redox components, and genes involved in protein folding and secretion, protein degradation and defense. Two other prominent changes, the coordinately enhanced expression of members of the photorespiration pathway and a diversion in electron flow from the primary electron transfer chain of respiration to an alternative oxidase pathway, occurred in response to Spm. Spm activated the expression of 6 transcription factor genes including ZAT7, ZAT12, AtWRKY40 and AtbZIP60, of which the former three genes' products are currently assigned as components of H(2)O(2) signaling pathway, suggesting the involvement of H(2)O(2) in Spm-triggered responses. Since AtbZIP60 plays a proven master role in the unfolded protein response in Arabidopsis thaliana, it may function to control the expression of genes participating in protein folding and secretion, which were mentioned above. Spm induction and CMV-triggered up-regulation of the genes described mainly coincided and their induction was suppressed by inhibitors of Spm oxidation. Furthermore, treatment with those inhibitors prior to CMV inoculation allowed higher viral multiplication in Arabidopsis thaliana plants. These results support the existence of a Spm-signaling pathway in Arabidopsis thaliana and its significant role in defense against CMV.

An integrated genomics approach to define niche establishment by Rhodococcus fascians

Rhodococcus fascians is a Gram-positive phytopathogen that induces shooty hyperplasia on its hosts through the secretion of cytokinins. Global transcriptomics using microarrays combined with profiling of primary metabolites on infected Arabidopsis (Arabidopsis thaliana) plants revealed that this actinomycete modulated pathways to convert its host into a niche. The transcript data demonstrated that R. fascians leaves a very characteristic mark on Arabidopsis with a pronounced cytokinin response illustrated by the activation of cytokinin perception, signal transduction, and homeostasis. The microarray data further suggested active suppression of an oxidative burst during the R. fascians pathology, and comparison with publicly available transcript data sets implied a central role for auxin in the prevention of plant defense activation. Gene Ontology categorization of the differentially expressed genes hinted at a significant impact of infection on the primary metabolism of the host, which was confirmed by subsequent metabolite profiling. The much higher levels of sugars and amino acids in infected plants are presumably accessed by the bacteria as carbon and nitrogen sources to support epiphytic and endophytic colonization. Hexoses, accumulating from a significantly increased invertase activity, possibly inhibited the expression of photosynthesis genes and photosynthetic activity in infected leaves. Altogether, these changes are indicative of sink development in symptomatic tissues. The metabolomics data furthermore point to the possible occurrence of secondary signaling during the interaction, which might contribute to symptom development. These data are placed in the context of regulation of bacterial virulence gene expression, suppression of defense, infection phenotype, and niche establishment.

Mitogen-activated protein kinase cascade in the signaling for polyamine biosynthesis in tobacco

Expression of NtNEK2(DD), a constitutively active mutant of NtMEK2, activates endogenous salicylic acid-induced protein kinase (SIPK) and wounding-induced protein kinase (WIPK), and leads to several stress/defense responses in tobacco. In this study, we used ACP (annealing control primer)-based differential display reverse transcription-PCR to isolate the downstream effectors mediated by the NtMEK2-SIPK/WIPK cascade. The arginine decarboxylase gene (ADC), which is involved in plant putrescine biosynthesis, was one of nine differentially expressed genes. When compared with NtMEK2(KR) plants, NtMEK2(DD) transgenic plants exhibited a significant increase in ADC and ODC (ornithine decarboxylase) transcript levels, as well as in putrescine and its catabolite, gamma-aminobutyric acid, following SIPK/WIPK activation. Taken together, these results suggest that the NtMEK2-SIPK/WIPK cascade is involved in regulating polyamine synthesis, especially putrescine synthesis, through transcriptional regulation of the biosynthetic genes in tobacco.

Modification of the health-promoting value of potato tubers field grown under drought stress: emphasis on dietary antioxidant and glycoalkaloid contents in five native andean cultivars (Solanum tuberosum L.)

The effects of drought stress on dietary antioxidant and glycoalkaloid contents in potato tubers were investigated using a selection of five native Andean cultivars. Both freshly harvested and 4 month-stored tubers were analyzed. Responses to drought stress were highly cultivar-specific. The antioxidant contents of the yellow tuber-bearing cultivars (Sipancachi and SS-2613) were weakly affected by the drought treatment, whereas the pigmented cultivars demonstrated highly cultivar-dependent variations. A drastic reduction of anthocyanins and other polyphenols was revealed in the red- (Sullu) and purple-fleshed (Guincho Negra) cultivars, whereas an increase was shown in the purple-skinned and yellow-fleshed cultivar (Huata Colorada). The hydrophilic antioxidant capacity (evaluated by Folin-Ciocalteu and H-oxygen radical absorbance capacity assays) was highly correlated with the polyphenol content and followed, therefore, the same behavior upon drought. Carotenoid contents, including beta-carotene, as well as vitamin E, tended to increase or remain stable following drought exposure, except for the cultivar Sullu, in which the level of these lipophilic antioxidants was decreased. Vitamin C contents were not affected by drought with the exception of Guincho Negra, in which the level was increased. These variations of health-promoting compounds were associated with increased or stable levels of the toxic glycoalkaloids, alpha-solanine and alpha-chaconine. Storage at 10 degrees C for 4 months tended to decrease the concentrations of all dietary antioxidants, except those of vitamin E. This storage also reduced the drought-induced variations observed in freshly harvested tubers. These results were discussed in terms of their implications for human diet and health as well as in plant stress defense mechanisms.

Plant polyamine catabolism: The state of the art

Polyamines have long been implicated in plant growth and development, as well as adaptation to abiotic and biotic stress. As a general rule of thumb the higher the polyamine titers the better. However, their molecular roles in plant stress responses still remain obscure. It has been postulated that they could act through their catabolism, which generates molecules which may act as secondary messengers signalling networks of numerous developmental and stress adaptation processes. Recently it was shown that plant and mammalian polyamine catabolism share critical features, giving new insight in plant polyamine catabolism. In this review, the advances in genes and proteins of polyamine catabolism in plants is presented and compared to other models.

NtbZIP60, an endoplasmic reticulum-localized transcription factor, plays a role in the defense response against bacterial pathogens in Nicotiana tabacum

A spermine-based signal transduction pathway plays a defensive role against incompatible pathogens. We identified a novel spermine-responsive cDNA from Nicotiana tabacum that encodes a basic region/leucine zipper protein with a putative transmembrane domain. Identity to Arabidopsis thaliana AtbZIP60 was sufficiently high to name the novel cDNA NtbZIP60. Expression analysis revealed that NtbZIP60 is a component of the spermine-signal pathway, and is also involved in the unfolded protein response (UPR), as demonstrated for AtbZIP60. The gene product, NtbZIP60, localizes to the endoplasmic reticulum (ER) in plant cells; once the putative transmembrane domain is eliminated from the intact protein, it targets the nucleus. The putative processed form of NtbZIP60 transactivates target genes through binding to plant-specific UPR cis-elements. Expression of NbbZIP60, an NtbZIP60 ortholog in Nicotiana benthamiana, was significantly up-regulated at 6 h and later time points upon infection with the non-host pathogen Pseudomonas cichorii, while it was unaffected by infection with the compatible pathogen Pseudomonas syringae pv. tabaci. Furthermore, NbbZIP60-silenced N. benthamiana plants allowed higher multiplication of P. cichorii compared to the control plants. Taken together, the results suggest that this ER-localized transcription factor is involved in the spermine-signal transduction pathway and plays an important role in plant innate immunity.

Tapetum-specific location of a cation-dependent O-methyltransferase in Arabidopsis thaliana

Cation- and S-adenosyl-L-methionine (AdoMet)-dependent plant natural product methyltransferases are referred to as CCoAOMTs because of their preferred substrate, caffeoyl coenzyme A (CCoA). The enzymes are encoded by a small family of genes, some of which with a proven role in lignin monomer biosynthesis. In Arabidopsis thaliana individual members of this gene family are temporally and spatially regulated. The gene At1g67990 is specifically expressed in flower buds, and is not detected in any other organ, such as roots, leaves or stems. Several lines of evidence indicate that the At1g67990 transcript is located in the flower buds, whereas the corresponding CCoAOMT-like protein, termed AtTSM1, is located exclusively in the tapetum of developing stamen. Flowers of At1g67990 RNAi-suppressed plants are characterized by a distinct flower chemotype with severely reduced levels of the N ',N ''-bis-(5-hydroxyferuloyl)-N '''-sinapoylspermidine compensated for by N(1),N(5),N(10)-tris-(5-hydroxyferuloyl)spermidine derivative, which is characterized by the lack of a single methyl group in the sinapoyl moiety. This severe change is consistent with the observed product profile of AtTSM1 for aromatic phenylpropanoids. Heterologous expression of the recombinant protein shows the highest activity towards a series of caffeic acid esters, but 5-hydroxyferuloyl spermidine conjugates are also accepted substrates. The in vitro substrate specificity and the in vivo RNAi-mediated suppression data of the corresponding gene suggest a role of this cation-dependent CCoAOMT-like protein in the stamen/pollen development of A. thaliana.

Thermospermine is required for stem elongation in Arabidopsis thaliana

Loss-of-function mutants of the ACAULIS5 (ACL5) gene in Arabidopsis thaliana have severe defects in stem elongation. ACL5 was previously reported as encoding a spermine synthase. A more recent study, however, showed that the bacterial expressed recombinant ACL5 protein catalyzes the conversion of spermidine to thermospermine, a structural isomer of spermine, rather than to spermine. In the present study, we found that thermospermine was detected in wild-type seedlings but was not detectable in the acl5-1 mutant. We further examined the effect of exogenous application of these isomers on the growth of acl5-1. Daily application of 0.1 mM thermospermine onto the shoot apex partially rescued the dwarf phenotype of acl5-1, while that of spermine had no effects on the morphology of the mutant. The acl5-1 transcript level in acl5-1 seedlings, which is much higher than the ACL5 transcript level in wild-type seedlings, was reduced by exogenous thermospermine. Thus we conclude that thermospermine is indeed produced through the action of ACL5 and required for stem elongation in Arabidopsis.

Polyamine metabolism in maize tumors induced by Ustilago maydis

Alterations occurring in polyamine metabolism of maize in tumors formed during the interaction with the biotrophic pathogenic fungus Ustilago maydis were analyzed. During the process, a striking increase in maize polyamine biosynthesis, mainly free and conjugated putrescine occurred in the tumors induced by the fungus, and in the neighbor plant tissues. This increase correlated with an activation mainly of Adc, Samdc1, Zmsamdc2 and Zmsamdc3, but not of Zmodc, Zmspds1 and Zmspds2 genes, and an elevation in arginine decarboxylase activity, confirming a predominant role of this enzyme in the process. Evidences for a possible contribution of spermidine and spermine degradation by polyamine oxidase activity, probably related to cell wall stiffening or lignification during tumor growth, were also obtained. It is suggested that polyamines, mainly putrescine, might play an active role in the pathosystem maize-U. maydis.

Polyamines: essential factors for growth and survival

Polyamines are low molecular weight, aliphatic polycations found in the cells of all living organisms. Due to their positive charges, polyamines bind to macromolecules such as DNA, RNA, and proteins. They are involved in diverse processes, including regulation of gene expression, translation, cell proliferation, modulation of cell signalling, and membrane stabilization. They also modulate the activities of certain sets of ion channels. Because of these multifaceted functions, the homeostasis of polyamines is crucial and is ensured through regulation of biosynthesis, catabolism, and transport. Through isolation of the genes involved in plant polyamine biosynthesis and loss-of-function experiments on the corresponding genes, their essentiality for growth is reconfirmed. Polyamines are also involved in stress responses and diseases in plants, indicating their importance for plant survival. This review summarizes the recent advances in polyamine research in the field of plant science compared with the knowledge obtained in microorganisms and animal systems.

Characterization of spermidine and spermine synthases in Lotus japonicus: induction and spatial organization of polyamine biosynthesis in nitrogen fixing nodules

The biosynthesis of the polyamines spermidine (Spd) and spermine (Spm) from putrescine (Put) is catalysed by the consequent action of two aminopropyltransferases, spermidine synthase (SPDS EC: 2.5.1.16) and spermine synthase (SPMS EC: 2.5.1.22). Two cDNA clones coding for SPDS and SPMS homologues in the nitrogen-fixing nodules of the model legume Lotus japonicus were identified. Functionality of the encoded polypeptides was confirmed by their ability to complement spermidine and spermine deficiencies in yeast. The temporal and spatial expression pattern of the respective genes was correlated with the accumulation of total polyamines in symbiotic and non-symbiotic organs. Expression of both genes was maximal at early stages of nodule development, while at later stages the levels of both transcripts declined. Both genes were expressed in nodule inner cortical cells, vascular bundles, and central tissue. In contrast to gene expression, increasing amounts of Put, Spd, and Spm were found to accumulate during nodule development and after maturity. Interestingly, nodulated plants exhibited systemic changes in both LjSPDS and LjSPMS transcript levels and polyamine content in roots, stem and leaves, in comparison to uninoculated plants. These results give new insights into the neglected role of polyamines during nodule development and symbiotic nitrogen fixation (SNF).

Pathogenicity of Pseudomonas syringae pv. tomato on tomato seedlings: phenotypic and gene expression analyses of the virulence function of coronatine

Bacterial speck disease, which is caused by Pseudomonas syringae pv. tomato, is an economically important disease on tomato. In the present study, we show that P. syringae pv. tomato DC3000 is a pathogen of tomato seedlings, an aspect of pathogen biology that has not been previously investigated. This resulted in the development of a virulence assay on tomato seedlings that has several advantages over labor-intensive foliar assays, including a shorter growth and incubation period, ease of inoculation and handling, and rapid generation of larger sample sizes per experiment. The utility of this assay was investigated by exploring the virulence function of coronatine (COR) on tomato seedlings. Using the COR- mutant DB29 and a MAPMAN display of transcript data from TOM1 microarrays, COR-dependent expression of genes involved in secondary metabolism, polyamine biosynthesis, reactive oxygen species homeostasis, and the novel transcription factor SlNAC2 were identified. Furthermore, during pathogenesis, genes involved in photosynthetic light reactions and the Calvin-Benson cycle were strongly repressed by COR. In conclusion, we show that P. syringae pv. tomato infects tomato seedlings and that COR is required for virulence in seedlings. The seedling assay can be used in high-throughput screens for the identification of molecular targets for COR and for the identification of genes involved in pathogenesis.

Tomato transcriptional changes in response to Clavibacter michiganensis subsp. michiganensis reveal a role for ethylene in disease development

Clavibacter michiganensis subsp. michiganensis (Cmm) is a gram-positive actinomycete, causing bacterial wilt and canker disease in tomato (Solanum lycopersicum). Host responses to gram-positive bacteria and molecular mechanisms associated with the development of disease symptoms caused by Cmm in tomato are largely unexplored. To investigate plant responses activated during this compatible interaction, we used microarray analysis to monitor changes in host gene expression during disease development. This analysis was performed at 4 d postinoculation, when bacteria were actively multiplying and no wilt symptoms were yet visible; and at 8 d postinoculation, when bacterial growth approached saturation and typical wilt symptoms were observed. Of the 9,254 tomato genes represented on the array, 122 were differentially expressed in Cmm-infected plants, compared with mock-inoculated plants. Functional classification of Cmm-responsive genes revealed that Cmm activated typical basal defense responses in the host, including induction of defense-related genes, production and scavenging of free oxygen radicals, enhanced protein turnover, and hormone synthesis. Cmm infection also induced a subset of host genes involved in ethylene biosynthesis and response. After inoculation with Cmm, Never ripe (Nr) mutant plants, impaired in ethylene perception, and transgenic plants with reduced ethylene synthesis showed significant delay in the appearance of wilt symptoms, compared with wild-type plants. The retarded wilting in Nr plants was a specific effect of ethylene insensitivity, and was not due to altered expression of defense-related genes, reduced bacterial populations, or decreased ethylene synthesis. Taken together, our results indicate that host-derived ethylene plays an important role in regulation of the tomato susceptible response to Cmm.

Involvement of polyamine oxidase in wound healing

Hydrogen peroxide (H(2)O(2)) is involved in plant defense responses that follow mechanical damage, such as those that occur during herbivore or insect attacks, as well as pathogen attack. H(2)O(2) accumulation is induced during wound healing processes as well as by treatment with the wound signal jasmonic acid. Plant polyamine oxidases (PAOs) are H(2)O(2) producing enzymes supposedly involved in cell wall differentiation processes and defense responses. Maize (Zea mays) PAO (ZmPAO) is a developmentally regulated flavoprotein abundant in primary and secondary cell walls of several tissues. In this study, we investigated the effect of wounding on ZmPAO gene expression in the outer tissues of the maize mesocotyl and provide evidence that ZmPAO enzyme activity, protein, and mRNA levels increased in response to wounding as well as jasmonic acid treatment. Histochemically detected ZmPAO activity especially intensified in the epidermis and in the wound periderm, suggesting a tissue-specific involvement of ZmPAO in wound healing. The role played by ZmPAO-derived H(2)O(2) production in peroxidase-mediated wall stiffening events was further investigated by exploiting the in vivo use of N-prenylagmatine (G3), a selective and powerful ZmPAO inhibitor, representing a reliable diagnostic tool in discriminating ZmPAO-mediated H(2)O(2) production from that generated by peroxidase, oxalate oxidase, or by NADPH oxidase activity. Here, we demonstrate that G3 inhibits wound-induced H(2)O(2) production and strongly reduces lignin and suberin polyphenolic domain deposition along the wound, while it is ineffective in inhibiting the deposition of suberin aliphatic domain. Moreover, ZmPAO ectopic expression in the cell wall of transgenic tobacco (Nicotiana tabacum) plants strongly enhanced lignosuberization along the wound periderm, providing evidence for a causal relationship between PAO and peroxidase-mediated events during wound healing.

Hydrogen peroxide in plants: a versatile molecule of the reactive oxygen species network

Plants often face the challenge of severe environmental conditions, which include various biotic and abiotic stresses that exert adverse effects on plant growth and development. During evolution, plants have evolved complex regulatory mechanisms to adapt to various environmental stressors. One of the consequences of stress is an increase in the cellular concentration of reactive oxygen species (ROS), which are subsequently converted to hydrogen peroxide (H(2)O(2)). Even under normal conditions, higher plants produce ROS during metabolic processes. Excess concentrations of ROS result in oxidative damage to or the apoptotic death of cells. Development of an antioxidant defense system in plants protects them against oxidative stress damage. These ROS and, more particularly, H(2)O(2,) play versatile roles in normal plant physiological processes and in resistance to stresses. Recently, H(2)O(2) has been regarded as a signaling molecule and regulator of the expression of some genes in cells. This review describes various aspects of H(2)O(2) function, generation and scavenging, gene regulation and cross-links with other physiological molecules during plant growth, development and resistance responses.

Aminoaldehyde dehydrogenase activity during wound healing of mechanically injured pea seedlings

Aminoaldehyde dehydrogenase (AMADH, EC 1.2.1.19) is an enzyme that, in association with amine oxidase, participates in polyamine catabolism. In plants, the enzyme is well characterized in pea seedlings. In this study, we used etiolated and light-grown pea seedlings as model plants to evaluate the possible AMADH role in response to stress caused by mechanical damage. In the beginning, the activity distribution of AMADH, amine oxidase and peroxidase in organs of 7-day-old intact pea seedlings was analyzed. To perform mechanical damage, stems of 10-day-old seedlings were each divided into four segments of equal length. The top (=fourth) segments were then longitudinally cut with a lancet. During healing, the injured segments and their control counterparts were harvested in 1-day intervals and analyzed for activity of the above enzymes, polyamine and 4-aminobutyrate (GABA) concentrations. The injury elicited increases in AMADH, amine oxidase and peroxidase activities in both etiolated and green seedlings, accompanied by parallel increases in putrescine, cadaverine, spermidine and GABA content. Histochemical experiments allowed visualization of increased AMADH activity in cross sections obtained from the injured stem segments. The activity was localized in cortical parenchyma and epidermal cells adjacent to the wound site in spatial correlation with an intensive lignification. In the control seedlings, AMADH activity or lignification in these tissues could not be visualized. Thus, we conclude that, in plants, AMADH may participate in processes of adaptation to stress events caused by mechanical injury, which involve polyamine catabolism, GABA production and lignification.

Identification of a novel Cys2/His2-type zinc-finger protein as a component of a spermine-signaling pathway in tobacco

In a previous work, we identified a Cys(2)/His(2)-type zinc-finger transcription repressor, (ZFT1), that functions in a spermine-mediated signal transduction pathway in tobacco plants. Database search disclosed the presence of another Cys(2)/His(2)-type zinc-finger protein ZFP1 (accession number AAC06243) in tobacco plants. In this work, we characterized ZFP1 and investigated whether this protein is also involved in a Spm-signaling pathway. This factor showed the highest identity to petunia ZPT2-2 and higher similarity to petunia ZPT2-3, Arabidopsis STZ/ZAT10, soybean SCOF-1, red pepper CAZFP1/CaPIF1 as well as to tobacco ZFT1. ZFP1 localized to the nucleus and had a specific DNA-binding activity, supportive to be a transcription factor. Furthermore, the protein had a mild repression activity on transcription in plant cells. The expression of ZFP1, encoding ZFP1, was upregulated during tobacco mosaic virus-induced hypersensitive response. ZFP1 expression was also induced by exogenously applied spermine and its induction was repressed by inhibitors of amine oxidase/polyamine oxidase. Collectively, our data indicate that ZFP1 is a new transcription factor which functions in a spermine-signaling pathway in tobacco.

Advances in polyamine research in 2007

Polyamines are small aliphatic amines found in all living organisms except some Archaea. In plants, putrescine, spermidine, and spermine are major components which are not only involved in fundamental cellular processes, for example cell proliferation, differentiation, and programmed cell death, but also in adaptive responses to environmental stress. In this article we review plant polyamine research focusing on recent studies.

Changes in free polyamine titers and expression of polyamine biosynthetic genes during growth of peach in vitro callus

In the present paper, correlation between free polyamines and growth of peach (Prunus persica cv. Yuzora) in vitro callus was investigated. Growth of the callus was divided into three phases based on measurement of fresh weight. Free polyamines, putrescine (Put), spermidine (Spd), and spermine (Spm), could be detected during peach callus growth. Changes in free Put titers followed the callus growth rate, as shown by low and stable levels in the first stage, quick increase at the beginning of the second phase, and slow increase in the last phase, whereas fluctuations of Spd and Spm titers were aberrant from that of Put at early stage. Expressions of five key genes involved in polyamine biosynthesis were characterized, in which only the genes leading to Put synthesis, ADC (arginine decarboxylase) and ODC (ornithine decarboxylase), agreed with callus growth and fluctuation of Put titers. Treatment of the callus with D-arginine, an inhibitor of ADC, led to significant growth inhibition and enormous reduction of endogenous Put, coupled with obvious decrease of mRNA levels of ADC and ODC. Exogenous application of Put partially restored the callus growth, along with resumption of endogenous Put and expression levels of ADC and ODC. Spd and Spm titers experienced minor change in comparison to Put. The data presented here suggested that free Put played an important part in peach callus growth. Putative mechanisms or mode of action underlying the role of Put in peach callus growth and different expression patterns of the genes responsible for polyamine biosynthesis are also discussed.

Hydrogen peroxide, nitric oxide and cytosolic ascorbate peroxidase at the crossroad between defence and cell death

An increase in the production of reactive oxygen species (ROS) is a typical event occurring during different stress conditions and activating conflicting responses in plants. In order to investigate the relevance of different timing and amounts of ROS production, tobacco (Nicotiana tabacum) Bright Yellow-2 (TBY-2) cells were incubated with different amounts of glucose plus glucose oxidase, for generating H(2)O(2) during time, or directly with known amounts of H(2)O(2). Data presented here indicate that, in TBY-2 cells, a difference in H(2)O(2) level is a critical point for shifting metabolic responses towards strengthening of antioxidant defences, or their depletion with consequent cell death. Timing of ROS production is also critical because it can determine programmed cell death (PCD) or necrosis. Depending on the different kinds of activated cell death, ascorbate (ASC) and glutathione (GSH) pools are altered differently. Moreover, an H(2)O(2)-dependent activation of nitric oxide synthesis is triggered only in the conditions inducing PCD. Ascorbate peroxidase (APX) has been analysed under different conditions of H(2)O(2) generation. Under a threshold value of H(2)O(2) overproduction, a transient increase in APX occurs, whereas under conditions inducing cell necrosis, the activity of APX decreases in proportion to cell death without any evident alteration in APX gene expression. Under conditions triggering PCD, the suppression of APX involves both gene expression and alteration of the kinetic characteristics of the enzyme. The changes in ASC, GSH and APX are involved in the signalling pathway leading to PCD, probably contributing to guaranteeing the cellular redox conditions required for successful PCD.

Integrated regulation of the type III secretion system and other virulence determinants in Ralstonia solanacearum

In many plant and animal bacterial pathogens, the Type III secretion system (TTSS) that directly translocates effector proteins into the eukaryotic host cells is essential for the development of disease. In all species studied, the transcription of the TTSS and most of its effector substrates is tightly regulated by a succession of consecutively activated regulators. However, the whole genetic programme driven by these regulatory cascades is still unknown, especially in bacterial plant pathogens. Here, we have characterised the programme triggered by HrpG, a host-responsive regulator of the TTSS activation cascade in the plant pathogen Ralstonia solanacearum. We show through genome-wide expression analysis that, in addition to the TTSS, HrpG controls the expression of a previously undescribed TTSS-independent pathway that includes a number of other virulence determinants and genes likely involved in adaptation to life in the host. Functional studies revealed that this second pathway co-ordinates the bacterial production of plant cell wall-degrading enzymes, exopolysaccharide, and the phytohormones ethylene and auxin. We provide experimental evidence that these activities contribute to pathogenicity. We also show that the ethylene produced by R. solanacearum is able to modulate the expression of host genes and can therefore interfere with the signalling of plant defence responses. These results provide a new, integrated view of plant bacterial pathogenicity, where a common regulator activates synchronously upon infection the TTSS, other virulence determinants and a number of adaptive functions, which act co-operatively to cause disease.

Most pathogenic bacteria have the ability to switch between free-living growth and life within the host tissues. However, the mechanisms that co-ordinate changes in gene expression during the passage between these alternative ecological niches are still largely unknown. A well-studied regulation pathway triggered in response to the host environment is that controlling the transcription of the Type III secretion system (TTSS) genes. The TTSS is a major pathogenicity determinant that delivers bacterial effector proteins directly into the host cell cytosol to promote disease. Here, Valls and colleagues show that the TTSS regulatory pathway is directly connected with other circuits driving the expression of diverse pathogenicity and host-adaptation activities. The authors have identified and characterised the genes co-regulated along with the TTSS via the HrpG regulator. They have found that, in addition to the TTSS, HrpG controls the transcription of a previously unknown TTSS-independent pathway that is essential to pathogenicity and alters the bacterial production of plant cell wall-degrading enzymes, exopolysaccharide, and the phytohormones ethylene and auxin. These findings reveal an important degree of co-ordination between adaptation and virulence functions at the transcriptional level and contribute to a better understanding of the infection process.

Chlorella viruses contain genes encoding a complete polyamine biosynthetic pathway

Two genes encoding the putative polyamine biosynthetic enzymes agmatine iminohydrolase (AIH) and N-carbamoylputrescine amidohydrolase (CPA) were cloned from the chloroviruses PBCV-1, NY-2A and MT325. They were expressed in Escherichia coli to form C-terminal (His)6-tagged proteins and the recombinant proteins were purified by Ni2+-binding affinity chromatography. The biochemical properties of the two enzymes are similar to AIH and CPA enzymes from Arabidopsis thaliana and Pseudomonas aeruginosa. Together with the previously known virus genes encoding ornithine/arginine decarboxlyase (ODC/ADC) and homospermidine synthase, the chloroviruses have genes that encode a complete set of functional enzymes that synthesize the rare polyamine homospermidine from arginine via agmatine, N-carbamoylputrescine and putrescine. The PBCV-1 aih and cpa genes are expressed early during virus infection together with the odc/adc gene, suggesting that biosynthesis of putrescine is important in early stages of viral replication. The aih and cpa genes are widespread in the chlorella viruses.

An investigation of boron toxicity in barley using metabolomics

Boron (B) is an essential micronutrient that affects plant growth at either deficient or toxic concentrations in soil. The aim of this work was to investigate the adaptation of barley (Hordeum vulgare) plants to toxic B levels and to increase our understanding of B toxicity tolerance mechanisms. We used a metabolomics approach to compare metabolite profiles in root and leaf tissues of an intolerant, commercial cultivar (cv Clipper) and a B-tolerant Algerian landrace (cv Sahara). After exposure to elevated B (200 and 1,000 microM), the number and amplitude of metabolite changes in roots was greater in Clipper than in Sahara. In contrast, leaf metabolites of both cultivars only responded following 1,000 microM treatment, at which B toxicity symptoms (necrosis) were visible. In addition, metabolite levels were dramatically altered in the tips of leaves of the sensitive cultivar Clipper after growth in 1,000 microM B compared to those of Sahara. This correlates with a gradual accumulation of B from leaf base to tip in B-intolerant cultivars. Overall, there were always greater differences between tissue types (roots and leaves) than between the two cultivars. This work has provided insights into metabolic differences of two genetically distinct barley cultivars and information about how they respond metabolically to increasing B levels.

Solid-phase synthesis and antibacterial activity of hydroxycinnamic acid amides and analogues against methicillin-resistant Staphylococcus aureus and vancomycin-resistant S. aureus

A library of hydroxycinnamic acid amides (HCAAs) and analogues were synthesized using solid-phase synthesis technique. These compounds were screened for antibacterial against methicillin-resistant Staphylococcus aureus (MRSA) (11 strains) and vancomycin-resistant S. aureus (VRSA) (4 strains). Dihydrocaffeoyl analogues showed activity against VRSA which were better than the reference drugs, vancomycin and oxacillin. These compounds also exhibited antibacterial activity against MRSA, which were more potent than oxacillin.

Branched-chain aminotransferase4 is part of the chain elongation pathway in the biosynthesis of methionine-derived glucosinolates in Arabidopsis

As part of our analysis of branched-chain amino acid metabolism in plants, we analyzed the function of Arabidopsis thaliana BRANCHED-CHAIN AMINOTRANSFERASE4 (BCAT4). Recombinant BCAT4 showed high efficiency with Met and its derivatives and the corresponding 2-oxo acids, suggesting its participation in the chain elongation pathway of Met-derived glucosinolate biosynthesis. This was substantiated by in vivo analysis of two BCAT4 T-DNA knockout mutants, in which Met-derived aliphatic glucosinolate accumulation is reduced by approximately 50%. The increase in free Met and S-methylmethionine levels in these mutants, together with in vitro substrate specificity, strongly implicate BCAT4 in catalysis of the initial deamination of Met to 4-methylthio-2-oxobutyrate. BCAT4 transcription is induced by wounding and is predominantly observed in the phloem. BCAT4 transcript accumulation also follows a diurnal rhythm, and green fluorescent protein tagging experiments and subcellular protein fractions show that BCAT4 is located in the cytosol. The assignment of BCAT4 to the Met chain elongation pathway documents the close evolutionary relationship of this pathway to Leu biosynthesis. In addition to BCAT4, the enzyme methylthioalkylmalate synthase 1 has been recruited for the Met chain elongation pathway from a gene family involved in Leu formation. This suggests that the two pathways have a common evolutionary origin.

Heterologous expression and biochemical characterization of a polyamine oxidase from Arabidopsis involved in polyamine back conversion

Polyamine oxidase (PAO) is a flavin adenine dinucleotide-dependent enzyme involved in polyamine catabolism. Animal PAOs oxidize spermine (Spm), spermidine (Spd), and/or their acetyl derivatives to produce H2O2, an aminoaldehyde, and Spd or putrescine, respectively, thus being involved in a polyamine back-conversion pathway. On the contrary, plant PAOs that have been characterized to date oxidize Spm and Spd to produce 1,3-diaminopropane, H2O2, and an aminoaldehyde and are therefore involved in the terminal catabolism of polyamines. A database search within the Arabidopsis (Arabidopsis thaliana) genome sequence showed the presence of a gene (AtPAO1) encoding for a putative PAO with 45% amino acid sequence identity with maize (Zea mays) PAO. The AtPAO1 cDNA was isolated and cloned in a vector for heterologous expression in Escherichia coli. The recombinant protein was purified by affinity chromatography on guazatine-Sepharose 4B and was shown to be a flavoprotein able to oxidize Spm, norspermine, and N1-acetylspermine with a pH optimum at 8.0. Analysis of the reaction products showed that AtPAO1 produces Spd from Spm and norspermidine from norspermine, demonstrating a substrate oxidation mode similar to that of animal PAOs. To our knowledge, AtPAO1 is the first plant PAO reported to be involved in a polyamine back-conversion pathway.

Rapid screening of ascorbic acid, glycoalkaloids, and phenolics in potato using high-performance liquid chromatography

Evaluation of phenolic metabolism in potato tubers (Solanum tuberosum) would be facilitated by faster analytical methods. A high-throughput HPLC method was developed for the qualitative and quantitative determination in potato of numerous phenolic compounds, the sum of the glycoalkaloids chaconine and solanine, plus ascorbic acid. Following a fast extraction, HPLC run times of 12 min were achieved with the use of a monolithic RP C18 column. UV and MS analyses were used to characterize the phenolic complement in extracts from two white-fleshed varieties. Over 30 compounds were identified, some of which are thought to possess either nutritional value or are involved in plant disease resistance. This method is expected to be useful for germplasm mining and for varietal development programs in which large numbers of lines are generated.

BUD2, encoding an S-adenosylmethionine decarboxylase, is required for Arabidopsis growth and development

Polyamines are implicated in regulating various developmental processes in plants, but their exact roles and how they govern these processes still remain elusive. We report here an Arabidopsis bushy and dwarf mutant, bud2, which results from the complete deletion of one member of the small gene family that encodes S-adenosylmethionine decarboxylases (SAMDCs) necessary for the formation of the indispensable intermediate in the polyamine biosynthetic pathway. The bud2 plant has enlarged vascular systems in inflorescences, roots, and petioles, and an altered homeostasis of polyamines. The double mutant of bud2 and samdc1, a knockdown mutant of another SAMDC member, is embryo lethal, demonstrating that SAMDCs are essential for plant embryogenesis. Our results suggest that polyamines are required for the normal growth and development of higher plants.

A novel R2R3 MYB transcription factor NtMYBJS1 is a methyl jasmonate-dependent regulator of phenylpropanoid-conjugate biosynthesis in tobacco

Target metabolic and large-scale transcriptomic analyses of tobacco (Nicotiana tabacum L.) Bright Yellow-2 (BY-2) cells were employed to identify novel gene(s) involved in methyl jasmonate (MJ)-dependent function in plants. At the metabolic level, we describe the specific accumulation of several phenylpropanoid-polyamine conjugates in MJ-treated BY-2 cells. Furthermore, global gene expression analysis of MJ-treated cells using a 16K cDNA microarray containing expressed sequence tags (ESTs) from BY-2 cells revealed 828 genes that were upregulated by MJ treatment within 48 h. Using time-course expression data we identified a novel MJ-inducible R2R3 MYB-type transcription factor (NtMYBJS1) that was co-expressed in a close temporal pattern with the core phenylpropanoid genes phenylalanine ammonia-lyase (PAL) and 4-coumarate:CoA ligase (4CL). Overexpression of NtMYBJS1 in tobacco BY-2 cells caused accumulation of specific phenylpropanoid conjugates in the cells. Subsequent microarray analysis of NtMYBJS1 transgenic lines revealed that a limited number of genes, including PAL and 4CL, were specifically induced in the presence of the NtMYBJS1 transgene. These results, together with results of both antisense expression analysis and of gel mobility shift assays, strongly indicate that the NtMYBJS1 protein functions in tobacco MJ signal transduction, inducing phenylpropanoid biosynthetic genes and the accumulation of phenylpropanoid-polyamine conjugates during stress.

Functions of amine oxidases in plant development and defence

Copper amine oxidases and flavin-containing amine oxidases catalyse the oxidative de-amination of polyamines, which are ubiquitous compounds essential for cell growth and proliferation. Far from being only a means of degrading cellular polyamines and, thus, contributing to polyamine homeostasis, amine oxidases participate in important physiological processes through their reaction products. In plants, the production of hydrogen peroxide (H(2)O(2)) deriving from polyamine oxidation has been correlated with cell wall maturation and lignification during development as well as with wound-healing and cell wall reinforcement during pathogen invasion. As a signal molecule, H(2)O(2) derived from polyamine oxidation mediates cell death, the hypersensitive response and the expression of defence genes. Furthermore, aminoaldehydes and 1,3-diaminopropane from polyamine oxidation are involved in secondary metabolite synthesis and abiotic stress tolerance.

Self-assembly of fatty acid-alkylboladiamine salts

Long-chain fatty acids are insoluble in aqueous solution and form crystal precipitates. It is then of particular importance to determine the physicochemical parameters allowing their dispersion in water to improve their bioavailability and their utilization as surfactants. Herein, we report a study on salt-free catanionic systems in aqueous solution made of mixtures between palmitic or stearic fatty acids and alkylboladiamines (Abd's) differing by their alkyl chain length. Phase contrast microscopy, solid-state NMR, Fourier transform infrared spectroscopy, and small-angle neutron scattering were used to characterize the phase behavior of these systems at molar ratio of fatty acid to Abd of 1 and 2. Whatever the Abd and the molar ratio, fatty acids were embedded at low temperature in a bilayer gel phase which crystallizes after a period of rest. At an equimolar ratio, the gel phases transited upon raising the temperature to an isotropic phase made of worm-like micelles except in the case of the ethylenediamine chain for which a lamellar fluid phase was observed. At a molar ratio of 2 and high temperature, fatty acids were embedded in a lamellar fluid phase which self-orients with its stacking axis perpendicular to the magnetic field. However, for a long alkylboladiamine such as spermine, worm-like micelles formed. The phase behavior at high temperature is discussed in terms of molecular volume.

Tobacco ZFT1, a transcriptional repressor with a Cys2/His2 type zinc finger motif that functions in spermine-signaling pathway

We previously proposed that a spermine (Spm)-mediated signal transduction pathway is involved in the hypersensitive response induced by Tobacco mosaic virus (TMV) in tobacco plants. To identify regulatory component(s) of this pathway, we surveyed a tobacco cDNA library and found that the ZFT1 gene, which encodes a Cys2/His2 type zinc-finger protein, is Spm-responsive. ZFT1 was not induced by two other polyamines, putrescine and spermidine, or by salicylic acid (SA), jasmonic acid or ethylene. Furthermore, ZFT1 was upregulated in TMV- inoculated tobacco plants in an N gene-dependent manner. Notably, induction of ZFT1 by Spm and by TMV infection was unimpaired in NahG-transgenic tobacco plants, indicating that cross-talk with an SA signaling pathway is not involved in this response. Within the Spm-signaling pathway, we found that ZFT1 functioned downstream of both mitochondrial dysfunction and mitogen-activated protein kinase activation. The ZFT1 protein has two zinc finger motifs and shows a high degree of similarity to ZPT2-3 in petunia and SCOF1 in soybean. However, unlike the latter two proteins, ZFT1 binds to the EP1S sequence and functions as a transcription repressor. Moreover, interestingly, ZFT1 overexpression rendered tobacco plants more tolerant to TMV. Based on the results presented here, we propose that ZFT1 functions as a transcription repressor in a Spm signaling pathway, thereby accelerating necrotic local region formation in tobacco leaves.

Influence of cultivar and germination on bioactive amines in soybeans (Glycine max L. Merril)

The levels of amines in soybeans as affected by cultivar in two consecutive years and by germination were investigated. Spermidine, spermine, putrescine, agmatine, and cadaverine were detected, whereas tyramine, histamine, tryptamine, serotonine, and phenylethylamine were not. Spermidine was the predominant amine followed by spermine. High concentrations of these amines confirmed soybean as a rich source. Cadaverine was confirmed to be inherent to soybean. The percent contribution of spermidine and spermine to total levels was not affected by cultivar in either years. However, amine levels were affected by cultivars in different ways in the consecutive years. Cadaverine was affected more by the cultivar, whereas spermidine, spermine, and agmatine were affected by harvest year. During germination the levels of amines from soybean increased significantly, except for agmatine. Spermidine and spermine accumulated in the cotyledon, whereas cadaverine and putrescine accumulated in the radicle and hypocotyl.

Polyamine profiles of healthy and parasite-infected Vaccinium myrtillus plants under nitrogen enrichment

Addition of nitrogen (N) to the field layer of boreal forests has been shown to increase the occurrence of the parasitic fungus Valdensia heterodoxa on Vaccinium myrtillus plants. We investigated whether N addition to soil alters the levels of polyamines in V. myrtillus shoots, and discuss here whether such changes could promote the spread of the parasitic fungus on V myrtillus. Using HPLC, we analyzed the concentrations of free and conjugated polyamines in healthy and naturally V. heterodoxa-infected V. myrtillus plants, which had received a moderate or high dose of N fertilizer, or no additional N. Fertilization with N increased the concentrations of free diamines (putrescine and diaminopropane), but had no significant effect on conjugated amines. Thus, N-induced changes in the constitutive levels of soluble conjugated amines do not seem to explain the increased parasite susceptibility of V. myrtillus under N enrichment. Generally, the concentrations of free diamines and insoluble conjugated putrescine were higher in diseased than in healthy shoots, suggesting parasite-induced accumulation of diamines. Free spermine seemed to accumulate in unfertilized, diseased plants, but in fertilized plants this induction was dampened, suggesting that N-induced alterations in spermine metabolism may promote the spread of parasites on V. myrtillus under N-enrichment.

Boron deficiency increases putrescine levels in tobacco plants

Polyamine concentrations were determined in leaves and roots of tobacco plants (Nicotiana tabacum L.) subjected to a short-term boron deficiency. A decrease in the growth of shoots and, especially, roots was found under this mineral deficiency. Boron deficiency did not lead to a significant decrease in leaf or root ion concentrations when compared to control treatment; however, as expected, leaf boron concentration was lower in boron-deficient plants in comparison to the control. In leaves, the levels of free putrescine and spermidine were similar in both treatments. In roots, a short-term boron deficiency caused an increase in free putrescine. Moreover, boron-deficient plants had higher conjugated polyamine concentration than boron-sufficient plants, which was especially evident for conjugated putrescine in leaves. A possible link between boron and polyamine levels is proposed and discussed.

Unraveling the secret lives of bacteria: use of in vivo expression technology and differential fluorescence induction promoter traps as tools for exploring niche-specific gene expression

A major challenge for microbiologists is to elucidate the strategies deployed by microorganisms to adapt to and thrive in highly complex and dynamic environments. In vitro studies, including those monitoring genomewide changes, have proven their value, but they can, at best, mimic only a subset of the ensemble of abiotic and biotic stimuli that microorganisms experience in their natural habitats. The widely used gene-to-phenotype approach involves the identification of altered niche-related phenotypes on the basis of gene inactivation. However, many traits contributing to ecological performance that, upon inactivation, result in only subtle or difficult to score phenotypic changes are likely to be overlooked by this otherwise powerful approach. Based on the premise that many, if not most, of the corresponding genes will be induced or upregulated in the environment under study, ecologically significant genes can alternatively be traced using the promoter trap techniques differential fluorescence induction and in vivo expression technology (IVET). The potential and limitations are discussed for the different IVET selection strategies and system-specific variants thereof. Based on a compendium of genes that have emerged from these promoter-trapping studies, several functional groups have been distinguished, and their physiological relevance is illustrated with follow-up studies of selected genes. In addition to confirming results from largely complementary approaches such as signature-tagged mutagenesis, some unexpected parallels as well as distinguishing features of microbial phenotypic acclimation in diverse environmental niches have surfaced. On the other hand, by the identification of a large proportion of genes with unknown function, these promoter-trapping studies underscore how little we know about the secret lives of bacteria and other microorganisms.

A Dopaquinone Model That Mimics the Water Addition Step of Cofactor Biogenesis in Copper Amine Oxidases

The consensus mechanism for biogenesis of the 2,4,5-trihydroxyphenylalanine quinone (TPQ) cofactor in copper amine oxidases involves a key water addition to the dopaquinone intermediate. Although hydration of o-quinones seems straightforward and was implicated previously in aqueous autoxidation of catechols to give ultimately hydroxyquinones, a recent study (Mandal, S.; Lee, Y.; Purdy, M. M.; Sayre, L. M. J. Am. Chem. Soc. 2000, 122, 3574-3584) showed that the observed hydroxyquinones arise not from hydration, but from addition to the o-quinones of H(2)O(2) generated during autoxidation of the catechols. In the enzyme case, hydration of dopaquinone is proposed to be mediated by the active site Cu(II). To establish precedent for this mechanism, we engineered a catechol tethered to a Cu(II)-coordinating unit, such that the corresponding o-quinone could be generated in situ by oxidation with periodate (to avoid generation of H(2)O(2)). Thus, coordination of 4-((2-(bis(2-pyridylmethyl)amino)ethylamino)methyl)-1,2-benzenediol (1) to Cu(II) and subsequent addition of periodate resulted in rapid formation of the TPQ-like corresponding hydroxyquinone. Hydroxyquinone formation was seen also using Zn(II) and Ni(II), but not in the absence of M(II). Under the same conditions, periodate oxidation of the simple catechol 4-tert-butylcatechol does not give hydroxyquinone in the presence or absence of Cu(II). M(II)OH(2) pK(a) data for the Cu(II), Zn(II), and Ni(II) complexes with the pendant tetradentate ligand in the masked (dimethyl ether) catechol form, and kinetic pH-rate profiles of the metal-dependent hydroxyquinone formation from periodate oxidation of catechol 1, suggested a rate-limiting addition step of the ligand-coordinated M(II)OH to the o-quinone intermediate. This study represents the first chemical demonstration of a true o-quinone hydration, which occurs in cofactor biogenesis in copper amine oxidases.

A leader intron and 115-bp promoter region necessary for expression of the carnation S-adenosylmethionine decarboxylase gene in the pollen of transgenic tobacco

The expression of CSDC9 encoding S-adenosylmethionine decarboxylase (SAMDC) is developmentally and spatially regulated in carnation. To examine the regulation of the SAMDC gene, we analyzed the spatial expression of CSDC9 with a 5'-flanking beta-glucuronidase fusion in transgenic tobacco plants. GUS was strongly expressed in flower, pollen, stem and vein of cotyledons. Expression in both anther and stigma was under developmental control; analysis of a series of mutants with deletions of the 5'-flanking region demonstrated differential activation in petal, anther, stigma and pollen grains. All the major cis-regulatory elements required for pollen-specific transcription were located in the upstream region between -273 and -158. This region contains four putative elements related to gibberellin induction (pyrimidine boxes, TTTTTTCC and CCTTTT) and pollen-specific expression (GTGA and AGAAA). In addition, the first 5'-leader intron was necessary for tissue-specific expression.

A subset of hypersensitive response marker genes, including HSR203J, is the downstream target of a spermine signal transduction pathway in tobacco

A cellular signal transduction pathway induced by the polyamine, spermine (Spm), and transmitted by mitochondrial dysfunction is proposed in tobacco. In this investigation, we further resolve the pathway by identifying a subset of hypersensitive response (HR) marker genes as downstream components. In a previous report, we identified harpin-induced 1 (HIN1) and two closely related genes as responsive to Spm. Other HR marker genes, HSR203J, HMGR, HSR201, and HSR515, are also Spm-responsive. Induction of these HR marker genes, including HIN1, by Spm was suppressed by pre-treatment with antioxidants, calcium channel blockers, inhibitor of mitochondrial permeability transition pore openings, and blockers of amine oxidase/polyamine oxidase. Such quenching is also observed for Spm-induced activation of two mitogen-activated protein kinases (MAPKs), salicylic acid-induced protein kinase (SIPK), and wound-induced protein kinase (WIPK), and upregulation of the WIPK gene, suggesting that all these components are part of the same signaling pathway. Furthermore, gain-of-function and loss-of-function studies on MAPK cascade members reveal that the expression of Spm-induced HR marker genes varies with respect to involvement of SIPK/WIPK activation.

Efficient Syntheses of Oncinotine and Neooncinotine

We have synthesized two natural alkaloids, oncinotine (1) and neooncinotine (2), by means of efficient ring-closing metathesis (RCM) reactions. The required dienes for RCM were assembled from three basic components: 2-allylpiperidine (5), 9-decenoic acid (6), and diamines 7. We developed two different methods to achieve the linkage: the Michael addition of acrylamide and two amidations of succinic anhydride. The Grubbs catalyst was used to form the 17- and 18-membered lactams in 50% and 68% yields, respectively.