Necrotrophic fungi associated with epidermal microcracking caused by chilling injury in pickling cucumber fruit

The objective of this work was to visualize the association between microcracking and other epidermal chilling injury symptoms, and to identify rots in cucumber fruit (Cucumis sativus L.) by scanning electron microscopy (SEM). Depressed epidermal areas and surface cracking due to damages of subepidermal cells characterized the onset of pitting in cucumber fruit. The germination of conidia of Alternaria alternata, with some of them evident on the fractures in the cultivar Trópico, occurred after damaging on the epidermis. Before, the chilling injury symptoms became visible, Stemphylium herbarum conidia germinated, and mycelium penetrated through the hypodermis using the microcracks as pathway. In the cultivar Perichán 121 the fungus was identified as Botrytis cinerea.

Ancient protostome origin of chemosensory ionotropic glutamate receptors and the evolution of insect taste and olfaction.

Ionotropic glutamate receptors (iGluRs) are a highly conserved family of ligand-gated ion channels present in animals, plants, and bacteria, which are best characterized for their roles in synaptic communication in vertebrate nervous systems. A variant subfamily of iGluRs, the Ionotropic Receptors (IRs), was recently identified as a new class of olfactory receptors in the fruit fly, Drosophila melanogaster, hinting at a broader function of this ion channel family in detection of environmental, as well as intercellular, chemical signals. Here, we investigate the origin and evolution of IRs by comprehensive evolutionary genomics and in situ expression analysis. In marked contrast to the insect-specific Odorant Receptor family, we show that IRs are expressed in olfactory organs across Protostomia--a major branch of the animal kingdom that encompasses arthropods, nematodes, and molluscs--indicating that they represent an ancestral protostome chemosensory receptor family. Two subfamilies of IRs are distinguished: conserved "antennal IRs," which likely define the first olfactory receptor family of insects, and species-specific "divergent IRs," which are expressed in peripheral and internal gustatory neurons, implicating this family in taste and food assessment. Comparative analysis of drosophilid IRs reveals the selective forces that have shaped the repertoires in flies with distinct chemosensory preferences. Examination of IR gene structure and genomic distribution suggests both non-allelic homologous recombination and retroposition contributed to the expansion of this multigene family. Together, these findings lay a foundation for functional analysis of these receptors in both neurobiological and evolutionary studies. Furthermore, this work identifies novel targets for manipulating chemosensory-driven behaviours of agricultural pests and disease vectors.

Arbuscular mycorrhizal fungi mediate below-ground plant-herbivore interactions: a phylogenetic study

Ecological interactions are complex networks, but have typically been studied in a pairwise fashion. Examining how third-party species can modify the outcome of pairwise interactions may allow us to better predict their outcomes in realistic systems. For instance, arbuscular mycorrhizal fungi (AMF) can affect plant interactions with other organisms, including below-ground herbivores, but the mechanisms underlying these effects remain unclear. Here, we use a comparative, phylogenetically controlled approach to test the relative importance of mycorrhizal colonization and plant chemical defences (cardenolides) in predicting plant survival and the abundance of a generalist below-ground herbivore across 14 species of milkweeds (Asclepias spp.). Plants were inoculated with a mixture of four generalist AMF species or left uninoculated. After 1month, larvae of Bradysia sp. (Diptera: Sciaridae), a generalist below-ground herbivore, colonized plant roots. We performed phylogenetically controlled analyses to assess the influence of AMF colonization and toxic cardenolides on plant growth, mortality and infestation by fungus gnats. Overall, plants inoculated with AMF exhibited greater survival than did uninoculated plants. Additionally, surviving inoculated plants had lower numbers of larvae in their roots and fewer non-AM fungi than surviving uninoculated plants. In phylogenetic controlled regressions, gnat density in roots was better predicted by the extent of root colonized by AMF than by root cardenolide concentration. Taken as a whole, AMF modify the effect of below-ground herbivores on plants in a species-specific manner, independent of changes in chemical defence. This study adds to the growing body of literature demonstrating that mycorrhizal fungi may improve plant fitness by conferring protection against antagonists, rather than growth benefits. In addition, we advocate using comparative analyses to disentangle the roles of shared history and ecology in shaping trait expression and to better predict the outcomes of complex multitrophic interactions.

New isolates of ectomycorrhizal fungi and the growth of eucalypt

The objective of this work was to evaluate the efficiency of ectomycorrhizal isolates on root colonization, phosphorus uptake and growth of Eucalyptus dunnii seedlings. Inocula of ten ectomycorrhizal isolates of Chondrogaster angustisporus, Hysterangium gardneri, Pisolithus spp., and Scleroderma spp. were aseptically produced in a peat-vermiculite mixture supplemented with liquid culture medium. Plants grew in a similar substrate supplemented with macro-and micro-nutrients; treatments were randomly distributed in a greenhouse. After three months, seedlings inoculated with three isolates - UFSC-Sc68 (Scleroderma sp.), UFSC-Ch163 (Chondrogaster angustisporus), and UFSC-Pt188 (Pisolithus microcarpus) - had a phosphorus shoot content and a shoot dry matter higher or equivalent to those of noninoculated controls which had been fertilized with a 16-fold phosphorus amount. These isolates were selected for new studies for establishing inoculum production techniques, in order to be applied in reforestation programmes under nursery and field conditions.

Signaling pathways controlling induced resistance to insect herbivores in Arabidopsis.

Insect attack triggers changes in transcript level in plants that are mediated predominantly by jasmonic acid (JA). The implication of ethylene (ET), salicylic acid (SA), and other signals in this response is less understood and was monitored with a microarray containing insect- and defense-regulated genes. Arabidopsis thaliana mutants coi1-1, ein2-1, and sid2-1 impaired in JA, ET, and SA signaling pathways were challenged with the specialist small cabbage white (Pieris rapae) and the generalist Egyptian cotton worm (Spodoptera littoralis). JA was shown to be a major signal controlling the upregulation of defense genes in response to either insect but was found to suppress changes in transcript level only in response to P. rapae. Larval growth was affected by the JA-dependent defenses, but S. littoralis gained much more weight on coi1-1 than P. rapae. ET and SA mutants had an altered transcript profile after S. littoralis herbivory but not after P. rapae herbivory. In contrast, both insects yielded similar transcript signatures in the abscisic acid (ABA)-biosynthetic mutants aba2-1 and aba3-1, and ABA controlled transcript levels both negatively and positively in insect-attacked plants. In accordance with the transcript signature, S. littoralis larvae performed better on aba2-1 mutants. This study reveals a new role for ABA in defense against insects in Arabidopsis and identifies some components important for plant resistance to herbivory.

Molecular characterization and pathogenicity of isolates of Beauveria spp. to fall armyworm

The objective of this work was to evaluate the pathogenicity of 24 Beauveria isolates to Spodoptera frugiperda larvae, and characterize them molecularly through rDNA-ITS sequencing and RAPD markers. Sequencing of rDNA-ITS fragments of 570 bp allowed the identification of isolates as B. bassiana or B. brongniarti by sequence comparison to GenBank. Sixty seven polymorphic RAPD fragments were capable to differentiate 20 among 24 Beauveria isolates, grouping them according to the derived host insect and to pathogenicity against maize fall armyworm larvae. Three RAPD markers were highly associated to the pathogenicity against S. frugiperda, explaining up to 67% of the phenotypic variation. Besides identification and molecular characterization of Beauveria isolates, ITS sequence and RAPD markers proved to be very useful in selecting the isolates potentially effective against S. frugiperda larvae and in monitoring field release of these microorganisms in biocontrol programs.

Insect oral secretions suppress wound-induced responses in Arabidopsis.

The induction of plant defences and their subsequent suppression by insects is thought to be an important factor in the evolutionary arms race between plants and herbivores. Although insect oral secretions (OS) contain elicitors that trigger plant immunity, little is known about the suppressors of plant defences. The Arabidopsis thaliana transcriptome was analysed in response to wounding and OS treatment. The expression of several wound-inducible genes was suppressed after the application of OS from two lepidopteran herbivores, Pieris brassicae and Spodoptera littoralis. This inhibition was correlated with enhanced S. littoralis larval growth, pointing to an effective role of insect OS in suppressing plant defences. Two genes, an ERF/AP2 transcription factor and a proteinase inhibitor, were then studied in more detail. OS-induced suppression lasted for at least 48 h, was independent of the jasmonate or salicylate pathways, and was not due to known elicitors. Interestingly, insect OS attenuated leaf water loss, suggesting that insects have evolved mechanisms to interfere with the induction of water-stress-related defences.

Two cases of interferon-alpha-induced sarcoidosis koebnerized along venous drainage lines : new pathogenic insights and review of the literature of interferon-induced sarcoidosis

La sarcoïdose est une affection inflammatoire granuiomateuse systémique d'origine inconnue touchant le plus fréquemment les poumons, le système lymphoïde, le foie, les yeux et la peau. Dans cet article, nous rapportons deux cas de sarcoïdose cutanée touchant les avant-bras de deux patients anciens toxicomanes traités par interféron-a et ribavirine pour une hépatite C chronique. Nous procédons à une revue de la littérature de la sarcoïdose induite par l'interféron et élaborons une nouvelle hypothèse pathogénique de l'effet Koebner dans la sarcoïdose cutanée. Dans le cas des deux patients que nous décrivons, la distribution des lésions cutanées coïncide avec les anciens sites d'injection d'héroïne le long des trajets veineux des deux avant- bras. Cette distribution unique de l'atteinte cutanée suggère que les dommages tissulaires induits par la répétition d'injections percutanées puissent représenter un terrain favorisant au développement local d'une sarcoïdose cutanée. Fait intéressant, il a été récemment démontré que les cellules dendritiques plasmacytoïdes - sous-type de cellules dendritiques généralement absent de la peau - infiltrent rapidement les sites de peau lésée. Ces cellules sont la source d'une production endogène d'interféron-a, cytokine connue pour promouvoir le processus de cicatrisation, mais également pour favoriser le développement de sarcoïdose chez des individus prédisposés. Ainsi, nous postulons que les lésions de sarcoïdose cutanée limitées le long des trajets veineux - sites préalables d'injection percutanée de drogues - peuvent résulter d'une expression locale supplémentaire d'interféron-a. Celle-ci serait en outre favorisée par le traitement de ribavirine dans le cadre de l'hépatite C, connu pour renforcer la production endogène d'interféron-a. L'identification de nombreuses cellules dendritiques plasmacytoïdes circonscrivant l'inflammation granuiomateuse sur la biopsie cutanée de l'un de nos patients semble être un argument dans ce sens, conforté par l'absence de corps étranger détecté en microscopie par lumière polarisée. Cette observation semble pouvoir représenter un point crucial dans la compréhension des mécanismes physiopathologiques à la base de l'infiltration des cicatrices cutanées par la sarcoïdose. Des investigations supplémentaires doivent encore être effectuées afin de confirmer cette hypothèse.

Acclimatization of Tapeinochilos ananassae plantlets in association with arbuscular mycorrhizal fungi

The objective of this work was to assess the potential of three isolates of arbuscular mycorrhizal fungi to promote growth of micropropagated plantlets of Tapeinochilos ananassae during acclimatization. The experiment was carried out in greenhouse, in a completely randomized block design, with four inoculation treatments: non‑inoculated control and plants inoculated with Glomus etunicatum, Acaulospora longula or Gigaspora albida, with ten replicates. After 90 days, the following parameters were evaluated: survival rate, height, leaf and tiller number, leaf area, fresh and dry biomass, contents of macro‑ and micronutrients in the root and shoot, glomerospore number, and mycorrhizal colonization. The survival percentage was 100%, except for plants inoculated with G. albida (80%). The isolate G. etunicatum is more suitable for plant development, since it improves survival, growth, dry matter production, nutritional status, and vigor of T. ananassae micropropagated plants.

Unexpected genomic variability in clinical and environmental strains of the pathogenic yeast Candida parapsilosis

Invasive candidiasis is the most commonly reported invasive fungal infection worldwide. Although Candida albicans remains the main cause, the incidence of emerging Candida species, such as C. parapsilosis is increasing. It has been postulated that C. parapsilosis clinical isolates result from a recent global expansion of a virulent clone. However, the availability of a single genome for this species has so far prevented testing this hypothesis at genomic scales. We present here the sequence of three additional strains from clinical and environmental samples. Our analyses reveal unexpected patterns of genomic variation, shared among distant strains, that argue against the clonal expansion hypothesis. All strains carry independent expansions involving an arsenite transporter homolog, pointing to the existence of directional selection in the environment, and independent origins of the two clinical isolates. Furthermore, we report the first evidence for the existence of recombination in this species. Altogether, our results shed new light onto the dynamics of genome evolution in C. parapsilosis.

Identification and characterization of pathogenic Pestalotiopsis species to pecan tree in Brazil

The objective of this work was to characterize and cluster isolates of Pestalotiopsis species and to identify those that are pathogenic to pecan, based on morphological and molecular characters. Pestalotiopsis spp. isolates were identified by sequencing the internal transcribed spacer (ITS) and β?tubulin regions. Identification methods were compared to indicate the key morphological characters for species characterization. Thirteen isolates were used for the pathogenicity tests. Morphological characterization was performed using the following variables: mycelial growth rate, sporulation, colony pigmentation, and conidial length and width. Ten pathogenic isolates were identified, three as -tubulin regions. Identification methods were compared to indicate the key morphological characters for species characterization. Thirteen isolates were used for the pathogenicity tests. Morphological characterization was performed using the following variables: mycelial growth rate, sporulation, colony pigmentation, and conidial length and width. Ten pathogenic isolates were identified, three as Pestalotiopsis clavispora and three as P. cocculi. The other isolates remained as an undefined species. The morphological characters were efficient for an initial separation of the isolates, which were grouped according to differences at species level, mainly colony diameter, which was identified as an important morphological describer. Beta-tubulin gene sequencing was less informative than the ITS region sequencing for species identification.

Recognition of insect eggs in Arabidopsis modulates defense responses

Plants activate direct and indirect defenses in response to insect egg deposition. In Arabidopsis thaliana, oviposition by the butterfly Pieris brassicae triggers cellular and molecular changes that are similar to the changes caused by biotrophic pathogens. Even though this innate immune response did not affect egg survival in Arabidopsis, we could show that different insect eggs elicit specific gene expression changes. Additionally, egg- induced necrosis could be observed in a variety of plants from different families ranging from dicotyledonous plants to monocots, suggesting that insect-egg detection by plants is a widespread mechanism and that different insect species contain elicitors of immune responses. Extracts from caterpillars and eggs contain elicitors that co-purified over several extraction steps. Chemical fractionation of caterpillar extracts lead to the characterisation of an active compound that was determined to be a triglyceride by NMR analysis. The exact structure of the side chains as well as the elicitor's presence in insect eggs have yet to be confirmed.We also found that the plant defense signal salicylic acid (SA) accumulates at the site of oviposition. This is unexpected, as the SA pathway controls the defense against fungal and bacterial pathogens whereas it negatively interacts with the jasmonic acid (JA) pathway, which is crucial for the defense against herbivores. Application of P. brassicae or Spodoptera littoralis egg extract onto leaves reduced the induction of insect-responsive genes after challenge with caterpillars, suggesting that egg-derived elicitors suppress plant defense. Consequently, larval growth of the generalist herbivore S. littoralis, but not of the specialist P. brassicae, was significantly higher on plants treated with egg extract than on control plants. In contrast, suppression of gene induction and enhanced S. littoralis performance were not found in the SA-deficient mutant sid2-l, indicating that SA mediates this phenomenon. These data reveal an intriguing facet of the crosstalk between SA- and JA-signalling pathways and suggest that insects have evolved a way to suppress the induction of defense genes by laying eggs that release elicitors. Additionally, we demonstrated that mutants of known crosstalk regulators, including nprl-1, tga2356, ein2-l and wrky70-l, are not affected in egg-induced suppression of herbivore defenses. JA treatment was not able to alleviate this SA/JA negative crosstalk, suggesting that this suppression operates through a novel mechanism downstream of JA biosynthesis.

Arbuscular mycorrhizal fungi in soil aggregates from fields of "murundus" converted to agriculture

The objective of this work was to evaluate the spore density and diversity of arbuscular mycorrhizal fungi (AMF) in soil aggregates from fields of "murundus" (large mounds of soil) in areas converted and not converted to agriculture. The experiment was conducted in a completely randomized design with five replicates, in a 5x3 factorial arrangement: five areas and three aggregate classes (macro-, meso-, and microaggregates). The evaluated variables were: spore density and diversity of AMF, total glomalin, total organic carbon (TOC), total extraradical mycelium (TEM), and geometric mean diameter (GMD) of soil aggregates. A total of 21 AMF species was identified. Spore density varied from 29 to 606 spores per 50 mL of soil and was higher in microaggregates and in the area with 6 years of conversion to agriculture. Total glomalin was higher between murundus in all studied aggregate classes. The area with 6 years showed lower concentration of TOC in macroaggregates (8.6 g kg-1) and in microaggregates (10.1 g kg-1). TEM was greater at the top of the murundus in all aggregate classes. GMD increased with the conversion time to agriculture. The density and diversity of arbuscular mycorrhizal spores change with the conversion of fields of murundus into agriculture.

Phylogenetic position of Fit insect toxin producing pseudomonads

Fit produced by Pseudomonas fluorescens CHA0 is a novel insect toxin in root colonizing pseudomonads, of which a homologue is described in Photorhabdus species.However, occurrence and abundance of insect pathogenicity in plant-associated pseudomonads is still unclear. An extensive screening outside the P. fluorescens complex identified strains of Pseudomonas chlororaphis as further Fit toxin producing candidates. Sequences of five different P. chlororaphis strains generated in this study were used to reconstruct the evolutionary history of the Fit toxin gene and to analyse its mode of evolution. We found that P. chlororaphis is closely associated with a small subgroup of 2,4-diacetylphloroglucinol and pyoluteorin- producing pseudomonads, both when analyzing four housekeeping genes and the nucleotide sequences for the Fit toxin gene. Additionally, we identified purifying selection to be the predominant mode of Fit toxin evolution.

Taking the fungal highway: mobilization of pollutant-degrading bacteria by fungi.

The capacity of fungi to serve as vectors for the dispersion of pollutant-degrading bacteria was analyzed in laboratory model systems mimicking water-saturated (agar surfaces) and unsaturated soil environments (glass-bead-filled columns). Two common soil fungi (Fusarium oxysporum and Rhexocercosporidium sp.) forming hydrophilic and hydrophobic mycelia, respectively, and three polycyclic aromatic hydrocarbon degrading bacteria (Achromobacter sp. SK1, Mycobacterium frederiksbergense LB501TG, and Sphingomonas sp. L138) were selected based on the absence of mutual antagonistic effects. It was shown that fungal hyphae act as vectors for bacterial transport with mobilization strongly depending on the specific microorganisms chosen: The motile strain Achromobacter sp. SK1 was most efficiently spread along hyphae of hydrophilic F. oxysporum in both model systems with transport velocities of up to 1 cm d(-1), whereas no dispersion of the two nonmotile strains was observed in the presence of F. oxysporum. By contrast, none of the bacteria was mobilized along the hydrophobic mycelia of Rhexocercosporidium sp. growing on agar surfaces. In column experiments however, strain SK1 was mobilized by Rhexocercosporidium sp. It is hypothesized that bacteria may move by their intrinsic motilitythrough continuous (physiological) liquid films forming around fungal hyphae. The results of this study suggest that the specific stimulation of indigenous fungi may be a strategy to mobilize pollutant-degrading bacteria leading to their homogenization in polluted soil thereby improving bioremediation.