Do the beneficial fungi manage phytosanitary problems in the tea agro-ecosystem?

BioControl - In recent years, Fungal Biocontrol Agents (FBCAs) have played a significant role in the biological control of pests and plant pathogens of several economically important crops,...     

Biosynthesis of β-glucans in fungi

Glucans are the most abundant polysaccharides present in fungi. The present review provides updated information on the structure and synthesis of -glucans in fungal cells. Synthesis of these polymers made up of B1,3 chains with a variable degree of B1,6 branching involves several reactions: initiation, chain elongation and branching, of which the most studied one is the elongation step. This reaction, catalyzed by the so-called glucan synthetases, utilizes UDPG as sugar donor. Properties of glucan synthetases are extremely variable depending on the fungal species, and their developmental stage. Because of the importance of these polysaccharides it is anticipated that comprehension of their mechanism of synthesis, is important for the understanding of cell wall assembly and cell growth and morphogenesis, as well as for the design of specific antifungal drugs.Abreviations UDPG uridine-diphospho-glucose - GDPG guanosine-diphospho-glucose - ADPG adenosine-diphospho-glucose - MW molecular weight - mic minimal inhibitory concentration - d.p. degree of polymerization - PAGE polyacrylamide gel electrophoresis - SDS sodium dodecyl sulfate     

Role of odour compounds in the attraction of gamete vectors in endophytic Epichloë fungi

Grass-infecting Epichlo? endophytes (Ascomycota, Calvicipitaceae) depend on Botanophila flies for gamete transfer, while fly larvae feed and develop on the fertilized fungal fruiting structures. Flies are known to be attracted by volatile signals, but the exact mechanisms of chemical communication and the degree of specialization are unknown. Headspace samples collected from five different Epichlo? species were analysed with respect to physiologically active substances using Botanophila flies. In field bioassays using synthetic compounds, their attractiveness and the specificity of the Epichlo?-Botanophila attraction were investigated. The identification of a new natural product, methyl (Z)-3-methyldodec-2-enoate, attracting Botanophila flies is reported here, and chokol K is confirmed as an attractive compound. Different blends of the two compounds attracted Botanophila flies under field conditions, but the three fly taxa present at the study site showed no preference for specific blends of volatiles. Chemical communication in the Epichlo?-Botanophila system relies on a few specific compounds, known as a communication system with 'private channels'. Although ratios of emitted compounds vary in different Epichlo? species, this seems not to lead to specialized attraction of Botanophila flies. Low selective pressure for specialization may have maintained a more generalist interaction between fungi and flies.     

Contributions of the peroxisome and β-oxidation cycle to biotin synthesis in fungi

The first step in the synthesis of the bicyclic rings of D-biotin is mediated by 8-amino-7-oxononanoate (AON) synthase, which catalyzes the decarboxylative condensation of l-alanine and pimelate thioester. We found that the Aspergillus nidulans AON synthase, encoded by the bioF gene, is a peroxisomal enzyme with a type 1 peroxisomal targeting sequence (PTS1). Localization of AON to the peroxisome was essential for biotin synthesis because expression of a cytosolic AON variant or deletion of pexE, encoding the PTS1 receptor, rendered A. nidulans a biotin auxotroph. AON synthases with PTS1 are found throughout the fungal kingdom, in ascomycetes, basidiomycetes, and members of basal fungal lineages but not in representatives of the Saccharomyces species complex, including Saccharomyces cerevisiae. A. nidulans mutants defective in the peroxisomal acyl-CoA oxidase AoxA or the multifunctional protein FoxA showed a strong decrease in colonial growth rate in biotin-deficient medium, whereas partial growth recovery occurred with pimelic acid supplementation. These results indicate that pimeloyl-CoA is the in vivo substrate of AON synthase and that it is generated in the peroxisome via the β-oxidation cycle in A. nidulans and probably in a broad range of fungi. However, the β-oxidation cycle is not essential for biotin synthesis in S. cerevisiae or Escherichia coli. These results suggest that alternative pathways for synthesis of the pimelate intermediate exist in bacteria and eukaryotes and that Saccharomyces species use a pathway different from that used by the majority of fungi.     

Gene organization and plasticity of the β-lactam genes in different filamentous fungi

The genes pcbAB, pcbC and penDE encoding enzymes that catalyze the three steps of the penicillin biosynthesis have been cloned from Penicillium chrysogenum and Aspergillus nidulans. They are located in a cluster in Penicillium chrysogenum, Penicillium notatum, Aspergillus nidulans and Penicillium nalgiovense. The three genes are clustered in chromosome I (10.4 Mb) of P. chrysogenum, in chromosome II of P. notatum (9.6 Mb) and in chromosome VI (3.0 Mb) of A. nidulans. The cluster of the penicillin biosynthetic genes is amplified in strains with high level of antibiotic production. About five to six copies of the cluster are present in the AS-P-78 strain and 11 to 14 copies in the E1 strain (an industrial isolate), whereas only one copy is present in the wild type (NRRL 1951) strain and in the low producer Wis 54-1255 strain. The amplified region in strains AS-P-78 and E1 is arranged in tandem repeats of 106.5 or 57.6-kb units, respectively. In Acremonium chrysogenum the genes involved in cephalosporin biosynthesis are separated in at least two clusters. The pcbAB and pcbC genes are linked in the so-called early cluster of genes involved in the cephalosporin biosynthesis. The late cluster, which includes the cefEF and cefG genes, is involved in the last steps of cephalosporin biosynthesis. The early cluster was located in chromosome VII (4.6 Mb) in the C10 strain and the late cluster in chromosome I (2.2 Mb). Both clusters are present in a single copy in the A. chrysogenum genome, in the wild-type and in the high cephalosporin-producing C10 strains.     

Selection for reduced translation costs at the intronic 5′ end in fungi

It is generally believed that introns are not translated; therefore, the potential intronic features that may be related to the translation step (occurring after splicing) have yet to be thoroughly studied. Here, focusing on four fungi, we performed for the first time a comprehensive study aimed at characterizing how translation efficiency is encoded in introns and affects their evolution. By analysing their intronome we provide evidence of selection for STOP codons close to the intronic 5′ end, and show that the beginning of introns are selected for significantly high translation, presumably to reduce translation and metabolic costs in cases of non-spliced introns. Ribosomal profiling data analysis in Saccharomyces cerevisiae supports the conjecture that in this organism intron retention frequently occurs, introns are partially translated, and their translation efficiency affects organismal fitness. We show that the reported results are more significant in highly translated and highly spliced genes, but are not associated only with genes with a specific function. We also discuss the potential relation of the reported signals to efficient nonsense-mediated decay due to splicing errors. These new discoveries are supported by population-genetics considerations. In addition, they are contributory steps towards a broader understanding of intron evolution and the effect of silent mutations on gene expression and organismal fitness.     

Approaching the taxonomic affiliation of unidentified sequences in public databases – an example from the mycorrhizal fungi

Background  

During the last few years, DNA sequence analysis has become one of the primary means of taxonomic identification of species, particularly so for species that are minute or otherwise lack distinct, readily obtainable morphological characters. Although the number of sequences available for comparison in public databases such as GenBank increases exponentially, only a minuscule fraction of all organisms have been sequenced, leaving taxon sampling a momentous problem for sequence-based taxonomic identification. When querying GenBank with a set of unidentified sequences, a considerable proportion typically lack fully identified matches, forming an ever-mounting pile of sequences that the researcher will have to monitor manually in the hope that new, clarifying sequences have been submitted by other researchers. To alleviate these concerns, a project to automatically monitor select unidentified sequences in GenBank for taxonomic progress through repeated local BLAST searches was initiated. Mycorrhizal fungi – a field where species identification often is prohibitively complex – and the much usedITSlocus were chosen as test bed.     

Do ectomycorrhizal fungi exhibit adaptive tolerance to potentially toxic metals in the environment ?

The effects of potentially toxic metals on ectomycorrhizal (ECM) fungi and their higher plant hosts are examined in this review. Investigations at a species and community level have revealed wide inter- and intraspecific variation in sensitivity to metals. Adaptive and constitutive mechanisms of ECM tolerance are proposed and discussed in relation to proven tolerance mechanisms in bacteria, yeasts and plants. Problems with methodology and research priorities are highlighted. These include the need for a detailed understanding of the genetic basis of tolerance in the ECM symbiosis, and for studies of ECM community dynamics in polluted sites.     

Calicioid lichens and fungi in amber – Tracing extant lineages back to the Paleogene

Calicioid lichens and fungi are a polyphyletic grouping of tiny ascomycetes that accumulate a persistent spore mass (mazaedium) on top of their usually well-stalked ascomata (‘mazaediate fungi’). In addition to extant forms, six fossils of the group were previously known from European Paleogene amber. Here we report nine new fossils and analyze the preserved features of all fossils to assess their applicability for dating molecular phylogenies. Many fossils are extremely well preserved, allowing detailed comparisons with modern taxa. SEM investigation reveals that even fine details of ascospore wall ultrastructure correspond to those seen in extant specimens. All fossils can confidently be assigned to modern genera: three to Calicium (Caliciaceae, Lecanoromycetes), five to Chaenotheca (Coniocybaceae, Coniocybomycetes), six to Chaenothecopsis (Mycocaliciaceae, Eurotiales), and one to Phaeocalicium (Mycocaliciaceae, Eurotiales). Several Calicium and Chaenotheca fossils are assignable to specific lineages within their genera, while the Chaenothecopsis fossils demonstrate the extent of intraspecific variation within one such lineage. Some features in the morphology of Chaenotheca succina nov. sp. seem to be ancestral as they have not been reported from modern species of the genus.     

Diversity of arbuscular mycorrhizal fungi in the rhizosphere of three host plants in the farming–pastoral zone, north China

The spatial diversity and distribution of AM fungi were investigated in three plots located in farming–pastoral zone, north China. The rhizospheres of Caragana korshinskii, Artemisia sphaerocephala and Salix psammophila were sampled and thirty AM fungal species belonging to five genera were isolated. The study demonstrated that AM fungal diversity and distribution differed significantly among the three host plants and the three studied plots. Spore density of AM fungi ranged between 2 and 22 spores per g^?1 of soil and species richness between 8 and 23. Correlation coefficient analysis demonstrated that spore density was significantly and positively correlated with soil organic matter and available N (P?<?0.01). Species richness was significantly and positively correlated with soil organic matter and available P (P?<?0.01), but significantly and negatively correlated with soil pH (P?<?0.01). Finally, the Shannon–Weiner index was significantly and positively correlated with soil organic matter (P?<?0.05). In this farming–pastoral zone, Glomus reticulatum and G.melanosporum may be more adaptable to the arid conditions than other AM fungal species. This research into AM fungal diversity may lead to exploitation of AM fungi for the mitigation of soil erosion and desertification using mycorrhizal plants, such as C.korshinskii, A.sphaerocephala and S. psammophila. The results of this study support the conclusion that diversity and distribution of AM fungi might be useful to monitor desertification and soil degradation.     

External signal–mediated polarized growth in fungi

As the majority of fungi are nonmotile, polarized growth in response to an external signal enables them to search for nutrients and mating partners, and hence is crucial for survival and proliferation. Although the mechanisms underlying polarization in response to external signals has commonalities with polarization during mitotic division, during budding, and fission growth, the importance of diverse feedback loops regulating external signal–mediated polarized growth is likely to be distinct and uniquely adapted to a dynamic environment. Here, we highlight recent advances in our understanding of the mechanisms that are crucial for polarity in response to external signals in fungi, with particular focus on the roles of membrane traffic, small GTPases, and lipids, as well as the interplay between cell shape and cell growth.     

Occurrence of the toxigenic fungi (producers of aflatoxins and ochratoxin A) in foodstuffs in the Czech Republic 1999–2000

The occurrence of toxigenic fungi producing aflatoxins and ochratoxin A in foodstuffs was studied in the Czech Republic. Twenty five commodities were collected at twelve collection places in the Czech Republic (300 food samples). The presence of potentially toxigenicAspergillus flavus was observed in 28% of the sampled foods (black pepper, caraway seeds, fruit tea, black tea, oat flakes, fine flour, rolled oat flakes and semolina) in the year 1999, and in 25% of the sampled foods (black pepper, black tea, fine flour) in the year 2000.A tamarii (aflatoxins producer) was found in 3 black pepper samples (25%) in both years. Aflatoxins were detected in black pepper and caraway seed samples in the year 1999 and in sweet red pepper in the year 2000.A parasiticus andA nomius were not isolated. Aspergillus section Nigri (potential producer of ochratoxin A) was detected in some foodstuffs. Ochratoxin A was detected in raisins.Penicillium verrucosum andA ochraceus were not isolated from foodstuffs.     

Multiple factors influence the role of arbuscular mycorrhizal fungi in soil aggregation—a meta-analysis

Background and aims

Soil aggregation is a crucial aspect of ecosystem functioning in terrestrial ecosystems. Arbuscular mycorrhizal fungi (AMF) play a key role in soil aggregate formation and stabilization. Here we quantitatively analyzed the importance of experimental settings as well as biotic and abiotic factors for the effectiveness of AMF to stabilize soil macroaggregates.

Methods

We gathered 35 studies on AMF and soil aggregation and tested 13 predictor variables for their relevance with a boosted regression tree analysis and performed a meta-analysis, fitting individual random effects models for each variable.

Results and conclusions

The overall mean effect of inoculation with AMF on soil aggregation was positive and predictor variable means were all in the range of beneficial effects. Pot studies and studies with sterilized sandy soil, near neutral soil pH, a pot size smaller than 2.5 kg and a duration between 2.2 and 5 months were more likely to result in stronger effects of AMF on soil aggregation than experiments in the field, with non-sterilized or fine textured soil or an acidic pH. This is the first study to quantitatively show that the effect of AMF inoculation on soil aggregation is positive and context dependent. Our findings can help to improve the use of this important ecosystem process, e.g. for inoculum application in restoration sites.     

Biodiversity of palm fungi in the tropics: are global fungal diversity estimates realistic?

Two questions are addressed: 'How many species of fungi can occur on a single host palm?' and 'What are the implications of this for global estimates of fungal diversity?' Fungal diversity estimates found in the literature are reviewed. Data on the numbers of fungi occurring on the above-ground tissues of six individual palms in the genus Licuala in Australia and Brunei Darussalam (Borneo) are provided. A total of 189 species of fungi were isolated and/or collected from the six palms. In addition, 53 'morphospecies' of mycelia sterilia were isolated, giving a total of 242 taxa from the 2672 isolates/collections made. The three palms in Australia (sampled once) yielded 100 species (each palm supporting an average of 54.7 taxa), while the three palms in Brunei Darussalam (sampled three times) yielded 172 species in total (approximately 111.3 taxa each). The magnitude of global fungal diversity, estimated at 1.5 million species, is discussed. Our results indicate that 33 to 1 would be a more accurate estimate (than 5.7 to 1) of the ratio of host specific fungal to palm species in the tropics. We therefore propose that global estimates of fungal diversity, based on temperate studies, require revision upwards.     

Mycotoxins and fungi in wheat harvested during 1990 in test plots in the state of São Paulo,Brazil

Wheat from two cultivars with contrasting characteristics were harvested in ten experimental plots located in wheat producing areas of the State of São Paulo, Brazil. The samples (10 of each cultivar) were analyzed by a gaschromatographic method for deoxynivalenol (DON), nivalenol (NIV), diacetoxyscirpenol (DAS), toxins T-2 (T-2) and HT-2, T-2 tetraol, T-2 triol, and by a thin-layer chromatographic method for zearalenone (ZEN), aflatoxins B₁, B₂, G₁, G₂, ochratoxin A and sterigmatocystin. No mycotoxins were detected in 13 samples. DON was found in four samples (0.47–0.59 µg/g), NIV in three samples (0.16–0.40 µg/g), T-2 in two samples (0.40, 0.80 µg/g), DAS in one sample (0.60 µg/g), and ZEN in three samples (0.04–0.21 µg/g). The wheat samples were also examined for the incidence of fungi.Alternaria, Drechslera, Epicoccum andCladosporium were the prevailing genera. Among theFusarium spp.,F. semitectum was present in 19 samples andF. moniliforme in 18 samples. NoF. graminearum was isolated in the samples.Abbreviations DAS diacetoxyscirpenol - DON deoxynivalenol - NIV nivalenol - T-2 T-2 toxin - ZEN zearalenone