Fungal Pathogen Infection Research Articles

A novel regulatory element involved in rapid activation of parsley ELI7 gene family members by fungal elicitor or pathogen infection

Abstract In parsley (Petroselinum crispum), members of the ELI7 gene family were rapidly transcriptionally activated following treatment with an elicitor derived from the phytopathogen Phytophthora sojae. Several cDNA and genomic ELI7 clones were isolated. The deduced amino acid sequences revealed close similarity to fatty acid desaturases/hydroxylases, however, the precise functions are still unknown. Analysis of the promoters of two strongly elicitor-induced family members, ELI7.1 and ELI7.2, allowed us to functionally pinpoint a novel, independently acting regulatory region (S box), the only major sequence similarity between the two gene promoters. In situ RNA/RNA hybridization using an ELI7.1 gene-specific probe demonstrated that expression of this gene is rapidly and locally induced around infection sites in planta as well.

Developmental regulated mechanisms affect the ability of a fungal pathogen to infect and colonize tobacco leaves.

During tobacco development, a transition state from susceptibility to resistance to fungal pathogen infection is observed. Leaves acquire resistance to Phytophthora parasistica when the plant becomes committed to flowering. The ability to develop resistance does not imply pathogen-induced defence responses as for the onset of systemic acquired resistance (SAR). Throughout flowering growth, fungal establishment is restrained at two levels. The first level is the control of infection effectiveness. Using the salicylic acid non-accumulating NahG plants, we demonstrate that this control does not require salicylic acid accumulation. The intercellular fluids (IFs) from tobacco leaves committed to flowering exhibit a cytotoxic activity on fungal zoospore cells based on in vitro germination assays. Its accumulation is correlated to the control of infection effectiveness that occurs during flowering growth. The expression of this activity appears to constitute a developmental regulated mechanism that inhibits early steps of fungal pathogen installation. A second level of fungal growth control is the restriction of fungal hyphae expansion. In contrast to infection initiation, fungal hyphae spreading appears to be restricted by similar mechanisms induced during SAR as it is attested by the requirement of salicylic acid accumulation and by the correlating apoplastic accumulation of PR1 proteins. These results provide evidence for the activation of a set of at least two regulatory pathways during flowering growth. This activation leads to the induction of mechanisms which control fungal development by affecting the ability of the fungus to both infect and colonise plant tissues.

Fungistatic Activity of Ruta graveolens Extract and Its Allelochemicals

The biological activity of an extract of Ruta graveolens and its allelochemicals [8-methoxypsoralen (8-MOP), 5-methoxypsoralen (5-MOP) and 4-hydroxycoumarin] (previously isolated) was evaluated gainst pathogenic fungi: Fusarium solani, Pyrenochaeta lycopersici, and Trichoderma viride. In addition a rue lyophilized extract was also tested against Penicillium sp., Thielaviopsis basicola, and Verticillium dahliae. We determined that 5 g rue lyophilized extract/liter, the lowest concentration tested, inhibited the mycelial growth of P. lycopersici and V. dahliae by 63.6% and 47%, respectively, with IC50 (the concentration required to inhibit growth 50%) values of 4.16 and 6.5 g/liter, respectively. Moreover, the rue lyophilized extract was shown to reduce radial growth of all six fungal species significantly at concentrations ranging from 5.0 to 40.0 g/liter. Mycelial growth of Penicillium sp. was promoted at 5.0 g lyophilized rue extract/liter and inhibited at higher concentrations. 4-OH coumarin had no effect on the growth of these fungi at concentrations ranging from 0.32 to 2.60 mg/liter, whereas 8-MOP and 5-MOP inhibited the mycelial growth of F. solani and T. viride with IC50 values of 6 mg/liter (5-MOP) and 27 mg/liter (8-MOP) for both fungi, respectively. A mixture of 5-MOP and 8-MOP, tested at 64.8 mg/liter (as they naturally occur in the crude rue extract) significantly inhibited the growth of all tested fungal species. These results suggest potential role for the rue extract and its allelochemicals in controlling pathogenic fungal infections.

Phylogenetic relationships of the intercellular fish pathogenIchthyophonus hoferi and fungi, choanoflagellates and the rosette agent

Ichthyophonus hoferi Plehn and Mulsow, 1911 is thought to be one of the few pathogenic fungal infections of marine fish. The result of an attack is severe epizootics in herring stocks with drastic reduction in the population as a consequence. The exact phylogenetic position of the genusIchthyophonus is not known. In the present study, a combination of molecular data, ultrastructure and biochemical characters were utilized to investigate the phylogeny ofI.hoferi. The genomic DNA encoding the small subunit ribosomal RNA (18S rRNA) was amplified and sequenced. Comparisons with other eukaryotic 18S rRNA sequences indicate thatI. hoferi is not a member of the Fungi. In both the parsimony and the neighborjoining trees,I. hoferi is the sister taxon to the rosette agent. The clade encompassingI.hoferi and the rosette organism is the sister group to the chanoflagellate clade in the neighbor-joining tree, while in the parsimony tree theI. hoferi/rosette clade is equally distant to both the choanoflagellate and animal clades. Transmission electron microscopy showed thatI. hoferi has a defined cell wall, an endoplasm that consists of a fine granulated matrix with numerous ribosomes, several nuclei, vacuoles of varying density distributed throughout the cell, and mitochondria with tubular cristae. The cell wall ofI. hoferi contains chitin.

Micro Morphological and Chemical Investigation into the Effects of Fungal Diseases on Melissa officinals L., Mentha×Piperita L. and Salvia officinalis L.

AbstractA micro‐morphological study of infected tissues and a chemical investigation into the volatile fraction of secretory tissues of healthy and infected plants were carried out. The botanic species were: Melissa officinalis L. (infected by Erysiphe galeopsidis and Septoria melissae); Salvia officinalis L. (infected by Erysiphe salviae); Mentha piperita L. (infected by Puccinia menthae).The results show that pathogenic fungal infection seriously damages the secretory tissues and stomata, causing a decrease in the amount of essential oil contained in infected plants, and modifying the composition of the plant's volatile fraction.

Phytotoxic and antimicrobial activity of 5,7-dihydroxychromone from peanut shells

A flavonoid decomposition product that is present in peanut (Arachis hypogaea) shells, 5,7-dihydroxychromone (DHC), was found to inhibit the radial growth of cultures of the soil pathogenic fungiRhizoctonia solani andSclerotium rolfsii with I50 (the concentrations of DHC required to inhibit growth 50%) values of 18 and 26µM, respectively. Radicle elongation of velvetleaf, corn, peanut, and wheat was inhibited by DHC with I50 values of 30, 50, 65 and 200µM, respectively. DHC had no effect on the growth ofBradyrhizobium sp. at 10µM in medium containing low (1.0 g/liter) mannitol as the carbon source, although the related flavones luteolin and chrysin each promoted bacterial growth at 10µM 48 hr after inoculation. When tested in high (10.0 g/liter) mannitol medium, DHC initially inhibited growth ofBradyrhizobium sp., but 120 hr after inoculation the growth of all treatments were similar. These results suggest a role for DHC released from peanut shells in suppressing pathogenic fungal infection and competing plant growth but not forBradyrhizobium growth promotion.

Insects and fungi on a C3 sedge and a C4 grass exposed to elevated atmospheric CO2 concentrations in open‐top chambers in the field

ABSTRACTThe effects of elevated atmospheric CO2 concentration on plant‐fungi and plant‐insect interactions were studied in an emergent marsh in the Chesapeake Bay. Stands of the C3 sedge Scirpus olneyi Grey, and the C4 grass Spartina patens (Ait.) Muhl. have been exposed to elevated atmospheric CO2 concentrations during each growing season since 1987. In August 1991 the severities of fungal infections and insect infestations were quantified. Shoot nitrogen concentration ([N]) and water content (WC) were determined. In elevated concentrations of atmospheric CO2, 32% fewer S. olneyi plants were infested by insects, and there was a 37% reduction in the severity of a pathogenic fungal infection, compared with plants grown in ambient CO2 concentrations. S. olneyi also had reduced [N], which correlated positively with the severities of fungal infections and insect infestations. Conversely, S. patens had increased WC but unchanged [N] in elevated concentrations of atmospheric CO2 and the severity of fungal infection increased. Elevated atmospheric CO2 concentration increased or decreased the severity of fungal infection depending on at least two interacting factors, [N] and WC; but it did not change the number of plants that were infected with fungi. In contrast, the major results for insects were that the number of plants infected with insects decreased, and that the amount of tissue that each insect ate also decreased.

Molecular approaches to identify novel targets for future development of antifungal agents

The mycological characteristics of fungi causing infections in humans, and the clinical features of the infections they cause, present unique parasite-host interactions that make them valuable research models to study. On the basis of biochemical analyses, antifungal drugs currently in clinical use have been developed for their capacity to inhibit enzymatic activities present in fungi but not in the host. Nowadays, the treatment of systemic mycoses depends largely on three classes of structurally related compounds: polyene antibiotics, flucytosine and azoles. The antifungal activity of polyene antibiotics, amphotericin B and nystatin, is due to the binding to sterols present in fungal cell membranes. Flucytosine, a synthetic nucleoside, by converting itself into 5-fluorouracil, interferes with fungal protein synthesis. Finally, the synthetic imidazole antifungals presumably act by inhibiting cytochrome P-450 sterol demethylase. However, these drugs have drawbacks associated with their usage, such as high toxicity for the kidney, high mortality rate (amphotericin B), and other problems associated with the use of flucytosine, such as resistance developing during therapy. Azoles usually have low toxicity, are fungistatic, but their use is not recommended for long-term treatment such as that required in AIDS patients. While further studies are being performed on some of these compounds to have a better understanding of their mode of action, there is also an urgent need for the development of new classes of antifungal drugs. Recent studies of known antifungals, together with new approaches based on the latest advances in molecular biology aimed at the identifcation of new targets that represent the basis for the synthesis of novel classes of fungal antibiotics, are reported. The principal objective of this approach is to identify and clone specific genes that are absent or whose products have low amino acid homology with corresponding human proteins, to selectively inhibit a fungal cellular function. However, this approach will rely not only on a better understanding of the mode of infection of pathogenic fungi, but also on the significance of 'virulence factors' which have been attributed to activities that, in the past few years, have been associated with some specific fungal gene products. Most of the studies performed to date on host-parasite relationships have been based on the elucidation of the mechanisms used by the human immune system to circumvent fungal infection, but too little is known of the molecular processes used by the fungus to invade a human host and establish infection, both in normal as well as in immunocompromised patients. This comprehension is definitely needed in order to

Echinocandins - a breakthrough in antifungal therapy?

The increase in life-threatening opportunistic and pathogenic fungal infections has spurred the search for new targets of antifungal attack. A promising new approach focuses on the complex polysaccharide cell wall of fungi. In this respect, a class of agents known as the echinocandins are showing considerable promise, particularly the 2nd generation agents which have improved aqueous solubility and a broader spectrum of activity. Progress with these agents was reported at the 33rd Interscience Conference on Antimicrobial Agents and Chemotherapy held in New Orleans, US, and the International Summit on Cutaneous Antifungal Therapy in San Francisco, US, last month.

OTHER FUNGAL ARTHRITIDES

Fungi are not a common cause of musculoskeletal infection; however, reports of fungal bone and joint infections have lately surged and are expected to increase more. There is evidence of an increasing incidence of pathogenic and opportunistic fungal infections and emergence of new species of disease-causing fungi, particularly in immunosuppressed patients. Distribution is worldwide, signs of infection can be mild, and chronic evolution as well as delayed diagnosis are common.

Ultraviolet-induced autofluorescence of arbuscular mycorrhizal root infections: an alternative to clearing and staining methods for assessing infections

Arbuscules in vesicular–arbuscular mycorrhizal (VAM) infections in untreated roots autofluoresced when viewed with an epifluorescence microscope. Ultraviolet-induced fluorescence was observed with the same filtering system used to detect fluorescein staining. Plant roots were examined from five plant families, grown under a variety of conditions, and infected with several species of VAM fungi. In every case, autofluorescent arbuscules were observed. Vesicles, spores, and hyphae did not autofluoresce under these same conditions. Fluorescence was not observed in ectomycorrhizae or pathogenic fungal infections. Cut mycorrhizal root segments from greenhouse- and field-grown plants were evaluated for infection using ultraviolet light and clearing and staining. No significant differences were found in the percent VAM infection as determined by the two methods on the same root segments. Applications and considerations in the use of the ultraviolet method for measuring infections as well as some preliminary observations on using fluorescein diacetate are discussed.

Schadbild und Ätiologie des Tannensterbens

Abstract Symptoms and etiology of dieback of silver fir (fir dying). II. On the mycorrhizal and pathogenic status in fine roots in relation to symptoms of fir dying. Investigations of the fine roots revealed, that pathogenic fungal infections contributed to the dying of feeder roots and the necrosis of woody fine roots. Root damage was associated with a decrease in the root storage capacity and therefore, root regeneration of affected trees was markedly reduced.

Treatment of chronic otitis externa with Trichophyton, Oidiomycetes, Epidermophyton antigen.

Chronic otitis externa may be a sensitivity (dermatophytid) reaction from a distant pathogenic superficial fungal infection, eg, tinea pedis and monilial vaginitis, which are often difficult to eradicate. Skin testing is done with a combined antigenic extract of TOE (Trichophyton; Oidiomycetes, ie, Monilia or Candida albicans; and Epidermophyton). The serial dilution titration method of skin testing is done, and the end point of reaction is determined. Treatment is begun on a weekly basis, with subcutaneous administration of 0.3 cc of a TOE extract two dilutions weaker than the end point. Symptomatic improvement is usually noted within two to four weeks, with objective improvement within eight weeks. After a variable maintenance period, the injections are spaced at less frequent intervals.