The effect of polyamine biosynthesis inhibition on growth and differentiation of the phytopathogenic fungus Sclerotinia sclerotiorum

A link between urease and polyamine metabolism in Cryptococcus neoformans

The urease enzyme of Cryptococcus neoformans is linked to different metabolic pathways within the yeast cell, several of which are involved in polyamine metabolism. Cryptococcal biogenic amine production is, however, largely unexplored and is yet to be investigated in relation to urease. The aim of this study was therefore to explore and compare polyamine metabolism in wild-type, urease-negative and urease-reconstituted strains of C. neoformans. Mass spectrometry analysis showed that agmatine and spermidine were the major extra- and intracellular polyamines of C. neoformans and significant differences were observed between 26 and 37 °C. In addition, compared to the wild-type, the relative percentages of extracellular putrescine and spermidine were found to be lower and agmatine higher in cultures of the urease-deficient mutant. The inverse was true for intracellular spermidine and agmatine. Cyclohexylamine was a more potent polyamine inhibitor compared to DL-α-difluoromethylornithine and inhibitory effects were more pronounced at 37 °C than at 26 °C. At both temperatures, the urease-deficient mutant was less susceptible to cyclohexylamine treatment compared to the wild-type. For both inhibitors, growth inhibition was alleviated with polyamine supplementation. This study has provided novel insight into the polyamine metabolism of C. neoformans, highlighting the involvement of urease in biogenic amine production.

High-Yielding Lovastatin Producer Aspergillus terreus Shows Increased Resistance to Inhibitors of Polyamine Biosynthesis

The biosynthesis of pharmaceutically significant secondary metabolites in filamentous fungi is a multistep process that depends on a wide range of various factors, one of which is the intracellular content of polyamines. We have previously shown that in Aspergillus terreus lovastatin high-yielding strain (HY) exogenous introduction of polyamines during fermentation can lead to an increase in the production of lovastatin by 20–45%. However, the molecular mechanisms of this phenomenon have not been elucidated. In this regard, we carried out an inhibitory analysis at the key stage of polyamine biosynthesis, the conversion of L-ornithine to putrescine by the enzyme ornithine decarboxylase (ODC). A. terreus HY strain showed upregulation of genes for biosynthesis of polyamines, 3–10-fold, and increased resistance compared to the original wild-type strain upon inhibition of ODC on synthetic medium with 5 mM α-difluoromethylornithine (DFMO), by 20–25%, and 5 mM 1-aminooxy-3-aminopropane (APA), by 40–45%. The data obtained indicate changes in the metabolism of polyamines in A. terreus HY strain. The observed phenomenon may have a universal character among fungal producers of secondary metabolites improved by classical methods, since previously the increased resistance to ODC inhibitors was also shown for Acremonium chrysogenum, a high-yielding producer of cephalosporin C.

Modulation of plant and bacterial polyamine metabolism during the compatible interaction between tomato and Pseudomonas syringae

The polyamines putrescine, spermidine and spermine participate in a variety of cellular processes in all organisms. Many studies have shown that these polycations are important for plant immunity, as well as for the virulence of diverse fungal phytopathogens. However, the polyamines' roles in the pathogenesis of phytopathogenic bacteria have not been thoroughly elucidated to date. To obtain more information on this topic, we assessed the changes in polyamine homeostasis during the infection of tomato plants by Pseudomonas syringae. Our results showed that polyamine biosynthesis and catabolism are activated in both tomato and bacteria during the pathogenic interaction. This activation results in the accumulation of putrescine in whole leaf tissues, as well as in the apoplastic fluids, which is explained by the induction of its synthesis in plant cells and also on the basis of its excretion by bacteria. We showed that the excretion of this polyamine by P. syringae is stimulated under virulence-inducing conditions, suggesting that it plays a role in plant colonization. However, no activation of bacterial virulence traits or induction of plant invasion was observed after the exogenous addition of putrescine. In addition, no connection was found between this polyamine and plant defence responses. Although further research is warranted to unravel the biological functions of these molecules during plant-bacterial interactions, this study contributes to a better understanding of the changes associated with the homeostasis of polyamines during plant pathogenesis.

Resistance risk assessment for fluazinam in Sclerotinia sclerotiorum

In the current study, sensitivity distribution of Sclerotinia sclerotiorum populations to fluazinam was determined using 103 strains collected from the fields of Jiangsu Province of China in 2016-2017 and the resistance risk of fluazinam was assessed. The average EC₅₀ (50% effective concentration) values and MIC (minimum inhibitory concentration) values of 103 S. sclerotiorum strains against fluazinam were 0.0073±0.0045μg/ml and <0.3μg/ml for mycelial growth, respectively. Nine mutants with low resistance level were obtained from wild type sensitive strains exposed on PDA medium amended with fluazinam and the resistance was stable after their ten transfers on PDA without the fungicide. Compared with the parental strains, the nine fluazinam-resistant mutants decreased in mycelial growth, sclerotial production, pathogenicity and were more sensitive to 0.7M NaCl. In addition, cell membrane permeability of resistant mutants was higher than that of their parental strains. Cross resistance assay showed that there was no cross-resistance between fluazinam and fludioxonil, dimetachlone, prochloraz, tebuconazole, azoxystrobin, or procymidone in S. sclerotiorum. The above results indicated that there was a low resistance risk for fluazinam in S. sclerotiorum. However, the sensitivity of all fluazinam-resistant mutants to fludioxonil decreased. Sequencing alignment results showed that there were no mutations in the two-component histidine kinase gene (Shk1) of the resistant mutants and the expression levels of Shk1 of three resistant mutants were significantly up-regulated while others were almost the same as their parental strains. These results will contribute to evaluating the resistance risk of fluazinam for management of diseases caused by S. sclerotiorum and further increase our understanding about the mode of action of fluazinam.

The Aspergillus flavus Spermidine Synthase (spds) Gene, Is Required for Normal Development, Aflatoxin Production, and Pathogenesis During Infection of Maize Kernels

Aspergillus flavus is a soil-borne saprophyte and an opportunistic pathogen of both humans and plants. This fungus not only causes disease in important food and feed crops such as maize, peanut, cottonseed, and tree nuts but also produces the toxic and carcinogenic secondary metabolites (SMs) known as aflatoxins. Polyamines (PAs) are ubiquitous polycations that influence normal growth, development, and stress responses in living organisms and have been shown to play a significant role in fungal pathogenesis. Biosynthesis of spermidine (Spd) is critical for cell growth as it is required for hypusination-mediated activation of eukaryotic translation initiation factor 5A (eIF5A), and other biochemical functions. The tri-amine Spd is synthesized from the diamine putrescine (Put) by the enzyme spermidine synthase (Spds). Inactivation of spds resulted in a total loss of growth and sporulation in vitro which could be partially restored by addition of exogenous Spd. Complementation of the Δspds mutant with a wild type (WT) A. flavus spds gene restored the WT phenotype. In WT A. flavus, exogenous supply of Spd (in vitro) significantly increased the production of sclerotia and SMs. Infection of maize kernels with the Δspds mutant resulted in a significant reduction in fungal growth, sporulation, and aflatoxin production compared to controls. Quantitative PCR of Δspds mutant infected seeds showed down-regulation of aflatoxin biosynthetic genes in the mutant compared to WT A. flavus infected seeds. Expression analyses of PA metabolism/transport genes during A. flavus-maize interaction showed significant increase in the expression of arginine decarboxylase (Adc) and S-adenosylmethionine decarboxylase (Samdc) genes in the maize host and PA uptake transporters in the fungus. The results presented here demonstrate that Spd biosynthesis is critical for normal development and pathogenesis of A. flavus and pre-treatment of a Δspds mutant with Spd or Spd uptake from the host plant, are insufficient to restore WT levels of pathogenesis and aflatoxin production during seed infection. The data presented here suggest that future studies targeting spermidine biosynthesis in A. flavus, using RNA interference-based host-induced gene silencing approaches, may be an effective strategy to reduce aflatoxin contamination in maize and possibly in other susceptible crops.

Activity of a novel strobilurin fungicide benzothiostrobin against Sclerotinia sclerotiorum

Benzothiostrobin is a novel strobilurin fungicide. In this study, baseline sensitivity of Sclerotinia sclerotiorum (Lib.) de Bary to benzothiostrobin was determined using 100 strains collected during 2012 and 2013 from different geographical regions in Jiangsu Province of China, and the average EC50 value was 0.0218 (± 0.0111)μg/mL for mycelial growth. After benzothiostrobin treatment, hyphae were contorted with offshoot of top increasing and cell membrane permeability increased markedly, while sclerotial production and oxalic acid content significantly decreased. Benzothiostrobin strongly inhibited mycelial respiration within 12h and the oxygen consumption of the mycelia could not be inhibited after 24h. On detached rapeseed leaves, the protective and curative activity test of benzothiostrobin suggested that benzothiostrobin had good control efficiency against S. sclerotiorum, and protective activity was better than curative activity. These results will contribute to us evaluating the potential of the new strobilurin fungicide benzothiostrobin for management of diseases caused by S. sclerotiorum and understanding the mode of action of benzothiostrobin against S. sclerotiorum.

Polyamine metabolism in fungi with emphasis on phytopathogenic species

Polyamines are essential metabolites present in all living organisms, and this subject has attracted the attention of researchers worldwide interested in defining their mode of action in the variable cell functions in which they are involved, from growth to development and differentiation. Although the mechanism of polyamine synthesis is almost universal, different biological groups show interesting differences in this aspect that require to be further analyzed. For these studies, fungi represent interesting models because of their characteristics and facility of analysis. During the last decades fungi have contributed to the understanding of polyamine metabolism. The use of specific inhibitors and the isolation of mutants have allowed the manipulation of the pathway providing information on its regulation. During host-fungus interaction polyamine metabolism suffers striking changes in response to infection, which requires examination. Additionally the role of polyamine transporter is getting importance because of its role in polyamine regulation. In this paper we analyze the metabolism of polyamines in fungi, and the difference of this process with other biological groups. Of particular importance is the difference of polyamine biosynthesis between fungi and plants, which makes this process an attractive target for the control of phytopathogenic fungi.

Polyamines stimulate hyphal branching and infection in the early stage of Glomus etunicatum colonization

Polyamines are known to strongly stimulate hyphal growth in arbuscular mycorrhizal fungi. The effect of the polyamines putrescine, spermidine and spermine on spore germination, hyphal elongation and branching by the AM fungus Glomus etunicatum was investigated in this study. The effect of spermine on infection and the development of the host and of daughter spores was further investigated using the dual monoaxenic culture system comprised of Gl. etunicatum fungal cultures in Ri T-DNA transformed carrot hairy roots. Spermidine and spermine showed positive effects on germination and all three polyamines significantly promoted hyphal growth. Hyphal branching was also strongly stimulated by treatment with polyamines, such as an increase in the number of branches. Infection during the early stages of the in vitro co-culture life cycle was enhanced in the presence of spermine, and daughter spores appeared at earlier timepoints compared to the control. Our results demonstrate that polyamines stimulate germination and hyphal branching in the early stage of AM fungal colonization. Moreover, results from the investigations conducted in the fungus-root co-culture suggest that polyamines may be involved in establishing the symbiotic relationship between root and fungus.

Major impacts on the primary metabolism of the plant pathogen Cryphonectria parasitica by the virulence-attenuating virus CHV1-EP713

Cryphonectria parasitica, the chestnut blight fungus, can be infected by virulence-attenuating mycoviruses of the family Hypoviridae. Previous studies have led to the hypothesis that the hypovirus-infected phenotype is partly due to metabolic changes induced by the viral infection. To investigate this, we measured the metabolic rate and respiration of C. parasitica colonies grown on solid medium. These experiments supported historical observations of other fungal species done in liquid cultures that the metabolic rate steadily declines with age and differentiation of the mycelium. Hypovirus infection increased metabolic rate in the youngest mycelium, but a subsequent decline was also observed as the mycelium aged. By measuring both CO(2) production and O(2) consumption, we also observed that changes occur in carbohydrate metabolism as a result of ageing in both infected and uninfected mycelium. Mycelium on the periphery of the colony exploited fermentation pathways extensively, before transitioning to aerobic carbohydrate metabolism and finally lipid metabolism in the interior regions, despite abundant remaining glucose. However, the hypovirus affected the extent of these changes, with infected mycelium apparently unable to utilize lipid-related metabolic pathways, leading to an increased depletion of glucose. Finally, we used metabolic profi fi ling to determine the changes in accumulation of primary metabolites in wild-type and hypovirus-infected mycelium and found that approximately one-third of the 164 detected metabolites were affected. These results are consistent with those expected from the physiological measurements, with significant alterations noted for compounds related to lipid and carbohydrate metabolism. Additionally, we observed an increase in the accumulation of the polyamine spermidine in the presence of hypovirus. Polyamines have been implicated in antiviral responses of mammalian systems; therefore this may suggest a novel antiviral response mechanism in fungi.

Occurrence and Characterization of Dimethachlon Insensitivity in Sclerotinia sclerotiorum in Jiangsu Province of China

Sclerotinia stem rot, caused by Sclerotinia sclerotiorum, is the main fungal disease of oilseed rape (Brassica napus) in China. Numerous fungicide applications are required for control. Dimethachlon, one of the dicarboximide fungicides, has been the major fungicide for disease control after benzimidazole resistance became widespread. Fungal populations were collected throughout Jiangsu Province between 2006 and 2007 in order to determine their sensitivity to dimethachlon. A total of 1,066 single-sclerotium isolates of S. sclerotiorum were collected, and most of the isolates were considered sensitive to dimethachlon. Five isolates collected in Yancheng and Changzhou showed normal growth at 5 μg/ml dimethachlon with the resistance factor ≈10 (resistance factor was estimated as ratios between the EC₅₀ values of resistant isolates and the average EC₅₀ values of sensitive ones) compared to the sensitive isolates (EC₅₀ is the concentration of fungicide causing 50% reduction in growth). Through in vitro selection for resistance to the fungicide, 25 dimethachlon-resistant mutants were derived from 10 wild-type isolates of S. sclerotiorum. The resistance factors for the isolates ranged from 198 to 484, and the isolates were considered highly resistant to dimethachlon. Therefore, at least two different mechanisms of resistance seem to be involved: one that may provide a moderate resistance (insensitivity) and a second that may give a high resistance level under laboratory conditions. There was positive cross-resistance between dimethachlon and other dicarboximide fungicides, such as iprodione and procymidone, in these S. sclerotiorum isolates. The field dimethachlon-insensitive and the laboratory-induced dimethachlon-resistant isolates appeared to have mycelial growth, sclerotial production, and pathogenicity comparable to their wild-type parental isolates. Also, results of osmotic tests showed that there were no significant difference in mycelial radial growth between the field dimethachlon-sensitive and field dimethachlon-insensitive isolates on potato dextrose agar plates amended with 2, 4, 6, or 8% (wt/vol) NaCl, but the laboratory-induced dimethachlon-resistant isolates grew significantly more slowly than their wild-type sensitive parents under all concentrations of NaCl. Because these studies yielded a high frequency of laboratory resistance in S. sclerotiorum, together with the occurrence of field insensitivity, appropriate precautions against resistance development in natural populations should be taken.

In vitro and in vivo inhibition of plant polyamine oxidase activity by polyamine analogues

Polyamine oxidase from Avena sativa L. cv. Cristal seedlings was purified to homogeneity using a simple four-step purification protocol including an infiltration washing technique. The enzyme had a high affinity for spermidine and spermine (K(m) approximately 5.5 and 1.2 microM, respectively), and also oxidized norspermidine (K(m) approximately 64.0 microM). Natural and synthetic diamines, cyclohexylamine, the putrescine analogue 1-aminooxy-3-aminopropane, and several polyamine analogues had inhibitory effects on polyamine oxidase activity and none were substrates. No inhibitory effect was observed on spermidine oxidation when the reaction product 1,3-diaminopropane was added. By contrast, 1-aminooxy-3-aminopropane showed mixed inhibition kinetics and a K(i) value of 0.113 mM. In addition, in vitro enzymatic activity assays showed that the oligoamine [3,8,13,18,23,28,33,38,43,48-deca-aza-(trans-25)-pentacontene], the tetramine 1,14-bis-[ethylamino]-5,10-diazatetradecane, and the pentamine 1,19-bis-[ethylamino]-5,10,15-triazanonadecane, displayed potent competitive inhibitory activities against polyamine oxidase with K(i) values of 5.8, 110.0 and 7.6 nM, respectively, where cyclohexylamine was a weak competitive inhibitor with a K(i) value of 0.5 mM. These analogues did not inhibit mycelial growth of the fungus Sclerotinia sclerotiorum (Lib.) De Bary and the bacterium Pseudomonas viridiflava (Burkholder) Dowson in vitro. On the contrary, with concentrations similar to those used for polyamine analogues, guazatine (a well-known fungicide and at the same time, a polyamine oxidase inhibitor) inhibited ( approximately 85%) S. sclerotiorum mycelial growth on Czapek-Dox medium. Finally, the analogue 1,19-bis-ethylamino-5,10,15-triazanonadecane inhibited polyamine oxidase activity observed in segments of maize leaves in vivo. The results obtained provide insights into research on the influence of polyamine oxidase activity on plant biotic and abiotic stresses.

Apoplastic polyamine oxidation plays different roles in local responses of tobacco to infection by the necrotrophic fungus Sclerotinia sclerotiorum and the biotrophic bacterium Pseudomonas viridiflava

The role of polyamine (PA) metabolism in tobacco (Nicotiana tabacum) defense against pathogens with contrasting pathogenic strategies was evaluated. Infection by the necrotrophic fungus Sclerotinia sclerotiorum resulted in increased arginine decarboxylase expression and activity in host tissues, as well as putrescine and spermine accumulation in leaf apoplast. Enhancement of leaf PA levels, either by using transgenic plants or infiltration with exogenous PAs, led to increased necrosis due to infection by S. sclerotiorum. Specific inhibition of diamine and PA oxidases attenuated the PA-induced enhancement of leaf necrosis during fungal infection. When tobacco responses to infection by the biotrophic bacterium Pseudomonas viridiflava were investigated, an increase of apoplastic spermine levels was detected. Enhancement of host PA levels by the above-described experimental approaches strongly decreased in planta bacterial growth, an effect that was blocked by a PA oxidase inhibitor. It can be concluded that accumulation and further oxidation of free PAs in the leaf apoplast of tobacco plants occurs in a similar, although not identical way during tobacco defense against infection by microorganisms with contrasting pathogenesis strategies. This response affects the pathogen's ability to colonize host tissues and results are detrimental for plant defense against necrotrophic pathogens that feed on necrotic tissue; on the contrary, this response plays a beneficial role in defense against biotrophic pathogens that depend on living tissue for successful host colonization. Thus, apoplastic PAs play important roles in plant-pathogen interactions, and modulation of host PA levels, particularly in the leaf apoplast, may lead to significant changes in host susceptibility to different kinds of pathogens.

Calcium Restores Prepenetration Morphogenesis Abolished by Methylglyoxal-Bis-Guanyl Hydrazone in Cochliobolus miyabeanus Infecting Rice

ABSTRACT Cochliobolus miyabeanus forms a specialized infection structure, an appressorium, to infect its host rice plants. Curtailment of prepenetration development by spermidine and spermine was more evident in appressorium development and germination remained unaffected, whereas putrescine and methylglyoxal-bis-guanyl hydrazone (MGBG) impaired both morphogenetic events. Exogenous calcium nullified the inhibitory effect of MGBG on the prepenetration development in vitro and in vivo and the disease progression. High levels of polyamines were detected in freshly collected conidia, but the amounts were reduced during germination and appressorium formation. MGBG fortified the decrease of polyamines within conidia under development and calcium amendment did not affect the reduction. Hard-surface contact augmented messenger RNA synthesis of calmodulin gene (CmCaM) and protein kinase C (PKC) activity in germinating or appressorium-forming conidia. Calcium restored transcription of CmCaM and upregulation of PKC activity suppressed by MGBG. Taken together, fine-tuning of intracellular polyamine transition is indispensable for the conidial germination and appressorium formation in C. miyabeanus. Biochemical and molecular analyses revealed that the MGBG-acting site or sites are upstream of Ca(2+)-dependent signaling pathways regulating prepenetration morphogenesis of C. miyabeanus causing rice brown leaf spot.

Use of cDNA microarrays to monitor transcriptional responses of the chestnut blight fungus Cryphonectria parasitica to infection by virulence-attenuating hypoviruses

Hypoviruses are a family of cytoplasmically replicating RNA viruses of the chestnut blight fungus Cryphonectria parasitica. Members of this mycovirus family persistently alter virulence (hypovirulence) and related fungal developmental processes, including asexual and sexual sporulation. In order to gain a better understanding of the molecular basis for these changes, we have developed a C. parasitica cDNA microarray to monitor global transcriptional responses to hypovirus infection. In this report, a spotted DNA microarray representing approximately 2,200 C. parasitica genes was used to monitor changes in the transcriptional profile after infection by the prototypic hypovirus CHV1-EP713. Altered transcript abundance was identified for 295 clones (13.4% of the 2,200 unique cDNAs) as a result of CHV1-EP713 infection-132 up-regulated and 163 down-regulated. In comparison, less than 20 specific C. parasitica genes were previously identified by Northern analysis and mRNA differential display as being responsive to hypovirus infection. A 93% validation rate was achieved between real-time reverse transcription-PCR results and microarray predictions. Differentially expressed genes represented a broad spectrum of biological functions, including stress responses, carbon metabolism, and transcriptional regulation. These findings are consistent with the view that infection by a 12.7-kbp hypovirus RNA results in a persistent reprogramming of a significant portion of the C. parasitica transcriptome. The potential impact of microarray studies on current and future efforts to establish links between hypovirus-mediated changes in cellular gene expression and phenotypes is discussed.

Polyamine metabolism during the germination of Sclerotinia sclerotiorum ascospores and its relation with host infection

• Polyamine biosynthesis inhibitors were used to study polyamine metabolism during the germination of Sclerotinia sclerotiorum ascospores, and to evaluate the potential of polyamine biosynthesis inhibition for the control of ascospore-borne diseases in plants. • The effects of inhibitors on ascospore germination, free polyamine levels, ornithine decarboxylase activity and development of disease symptoms on tobacco (Nicotiana tabacum) leaf discs inoculated with ascospores were determined. • α-Difluoromethylornithine inhibited ornithine decarboxylase and decreased free spermidine levels, but had no effect on ascospore germination. Both, the spermidine synthase inhibitor cyclohexylamine and the S-adenosyl-methionine decarboxylase inhibitor methylglyoxal bis-[guanyl hydrazone] decreased free spermidine levels, but only the latter inhibited ascospore germination, at concentrations of 5 mm or higher. Lesion development on leaf discs was reduced by cyclohexylamine and methylglyoxal bis-[guanyl hydrazone], but not by α-difluoromethylornithine. In the absence of inhibitors, dormant ascospores contained higher polyamine levels than mycelium. • Ascospore germination did not depend on ornithine decarboxylase activity and inhibitors of this enzyme will probably have a limited potential for the control of ascospore-borne plant diseases. On the contrary, spermidine synthase and S-adenosyl-methionine decarboxylase could be more suitable targets for fungicidal action. The relative insensitivity of ascospore germination to polyamine biosynthesis inhibitors may be caused by their high polyamine content.

Ornithine and arginine decarboxylase activities and effect of some polyamine biosynthesis inhibitors on Gigaspora rosea germinating spores

The pathways for putrescine biosynthesis and the effects of polyamine biosynthesis inhibitors on the germination and hyphal development of Gigaspora rosea spores were investigated. Incubation of spores with different radioactive substrates demonstrated that both arginine and ornithine decarboxylase pathways participate in putrescine biosynthesis in G. rosea. Spermidine and spermine were the most abundant polyamines in this fungus. The putrescine biosynthesis inhibitors alpha-difluoromethylarginine and alpha-difluoromethylornithine, as well as the spermidine synthase inhibitor cyclohexylamine, slightly decreased polyamine levels. However, only the latter interfered with spore germination. The consequences of the use of putrescine biosynthesis inhibitors for the control of plant pathogenic fungi on the viability of G. rosea spores in soil are discussed.

Spermidine metabolism in parasitic protozoa--a comparison to the situation in prokaryotes, viruses, plants and fungi

Targeting polyamines of parasitic protozoa in chemotherapy has attracted attention because polyamines might reveal novel drug targets for antiparasite therapies (Müller et al. 2001). The biological function of the triamine spermidine in parasitic protozoa has not been studied in great detail although the results obtained mainly imply three different functions, i.e., cell proliferation, cell differentiation, and biosynthesis of macromolecules. Sequence information from the malaria genome project databases and inhibitor studies provide evidence that the current status of spermidine research has to be extended since enzymes of spermidine metabolism are present in the parasite (Kaiser et al. 2001). Isolation and characterisation of these enzymes, i.e., deoxyhypusine synthase (EC 1.1.1.249) (DHS) and homospermidine synthase (EC 2.5.1.44) (HSS) might lead to valuable new targets in drug therapy. Currently research on spermidine metabolism is based on the deposition of the deoxyhypusine synthase nucleic acid sequence in GenBank while the activity of homospermidine synthase was deduced from inhibitor studies. Spermidine biosynthesis is catalyzed by spermidine synthase (EC 2.5.1.16) which transfers an aminopropyl moiety from decarboxylated S-adenosylmethionine to putrescine. Spermidine is also an important precursor in the biosynthesis of the unusual amino acid hypusine (Wolff et al. 1995) and the uncommon triamine homospermidine in eukaryotes, in particular in pyrrolizidine alkaloid-producing plants (Ober and Hartmann 2000). Hypusine is formed by a two-step enzymatic mechanism starting with the transfer of an aminobutyl moiety from spermidine to the epsilon-amino group of one of the lysine residues in the precursor protein of eukaryotic initiation factor eIF5A by DHS (Lee and Park 2000). The second step of hypusinylation is completed by deoxyhypusine hydroxylase (EC 1.14.9929) (Abbruzzese et al. 1985). Homospermidine formation in eukaryotes parallels deoxyhypusine formation in the way that in an NAD(+)-dependent reaction an aminobutyl moiety is transferred from spermidine. In the case of homospermidine synthase, however the acceptor is putrescine. Thus the triamine homospermidine consists of two symmetric aminobutyl moieties while there is one aminobutyl and one aminopropyl moiety present in spermidine. Here, we review the metabolism of the triamine spermidine with particular focus on the biosynthesis of hypusine and homospermidine in parasitic protozoa, i.e., Plasmodium, Trypanosoma and Leishmania, compared to that in prokaryotes i.e., Escherichia coli, a phytopathogenic virus and pyrrolizidine alkaloid-producing plants (Asteraceae) and fungi.

An update on pollen and fungal spore aerobiology

Changes in climate are altering pollen distribution. Predictive modeling can be used to forecast long- and short-term changes in pollen concentrations. Increasing evidence confirms the presence of pollen allergens on small, respirable particles in the air, explaining the occurrence of pollen-season increases in asthma. Like pollens, aboveground indoor fungal aerosols primarily reflect outdoor concentrations. Basement spore concentrations might be higher and reflective of local sources. Fungal presence in the indoor or outdoor air can be monitored on an area basis or with personal monitors. The samples can be analyzed by means of microscopy, culture, DNA probes, HPLC, or immunodetection. Total fungal biomass can be estimated on the basis of measurements of ergosterol or glucan in environmental samples. Unfortunately, there are no generally accepted standards for interpretation of fungal levels in indoor or outdoor air. At present, the best approach to indoor fungal control is moisture control in the indoor environment. This will essentially prevent fungal growth, except from extraordinary events.