Sensitivity distribution of phytopathogenic bacteria and fungi to antibiotics.
The minimal inhibitory concentrations (MIC) of various antibiotics and fungicides for Erwinia carotovora, Pseudomonas coronafaciens var. atropurpurea, P. lachrymans, Alternaria mali, A. kikuchiana, Pyricularia oryzae, Botrytis sp. and Sclerotinia sp. isolated from diseased plants in various localities of Japan were examined to enable the isolates to be gruoped into sensitive and resistant strains. To minimize the effects of various variable conditions, MIC of isolates were pooled for either 2 or 3 years and were plotted in a single figure. The grouping values were determined on the basis of MIC values of the antibiotics and agricultural chemicals on phytopathogenic bacteria and fungi under investigations. The relationships between grouping values for isolates of bacteria and fungi and the control of disease on the plants correlated to each other were studied. (+info)
Multiple epoxide hydrolases in Alternaria alternata f. sp. lycopersici and their relationship to medium composition and host-specific toxin production.
The production of Alternaria alternata f. sp. lycopersici host-specific toxins (AAL toxins) and epoxide hydrolase (EH) activity were studied during the growth of this plant-pathogenic fungus in stationary liquid cultures. Media containing pectin as the primary carbon source displayed peaks of EH activity at day 4 and at day 12. When pectin was replaced by glucose, there was a single peak of EH activity at day 6. Partial characterization of the EH activities suggests the presence of three biochemically distinguishable EH activities. Two of them have a molecular mass of 25 kDa and a pI of 4.9, while the other has a molecular mass of 20 kDa and a pI of 4.7. Each of the EH activities can be distinguished by substrate preference and sensitivity to inhibitors. The EH activities present at day 6 (glucose) or day 12 (pectin) are concomitant with AAL toxin production. (+info)
Insertional mutagenesis and cloning of the genes required for biosynthesis of the host-specific AK-toxin in the Japanese pear pathotype of Alternaria alternata.
The Japanese pear pathotype of Alternaria alternata causes black spot of Japanese pear by producing a host-specific toxin known as AK-toxin. Restriction enzyme-mediated integration (REMI) mutagenesis was used to tag genes required for toxin biosynthesis. Protoplasts of a wild-type strain were treated with a linearized plasmid along with the restriction enzyme used to linearize the plasmid. Of 984 REMI transformants recovered, three produced no detectable AK-toxin and lost pathogenicity on pear leaves. Genomic DNA flanking the integrated plasmid was recovered from one of the mutants. With the recovered DNA used as a probe, a cosmid clone of the wild-type strain was isolated. Structural and functional analyses of an 8.0-kb region corresponding to the tagged site indicated the presence of two genes. One, designated AKT1, encodes a member of the class of carboxyl-activating enzymes. The other, AKT2, encodes a protein of unknown function. The essential roles of these two genes in both AK-toxin production and pathogenicity were confirmed by transformation-mediated gene disruption experiments. DNA gel blot analysis detected AKT1 and AKT2 homologues not only in the Japanese pear pathotype strains but also in strains from the tangerine and strawberry pathotypes. The host-specific toxins of these two pathotypes are similar in structure to AK-toxin. Homologues were not detected in other pathotypes or in non-pathogenic strains of A. alternata, suggesting acquisition of AKT1 and AKT2 by horizontal transfer. (+info)
Requirement of functional ethylene-insensitive 2 gene for efficient resistance of Arabidopsis to infection by Botrytis cinerea.
Inoculation of wild-type Arabidopsis plants with the fungus Alternaria brassicicola results in systemic induction of genes encoding a plant defensin (PDF1.2), a basic chitinase (PR-3), and an acidic hevein-like protein (PR-4). Pathogen-induced induction of these three genes is almost completely abolished in the ethylene-insensitive Arabidopsis mutant ein2-1. This indicates that a functional ethylene signal transduction component (EIN2) is required in this response. The ein2-1 mutants were found to be markedly more susceptible than wild-type plants to infection by two different strains of the gray mold fungus Botrytis cinerea. In contrast, no increased fungal colonization of ein2-1 mutants was observed after challenge with avirulent strains of either Peronospora parasitica or A. brassicicola. Our data support the conclusion that ethylene-controlled responses play a role in resistance of Arabidopsis to some but not all types of pathogens. (+info)
A longevity assurance gene homolog of tomato mediates resistance to Alternaria alternata f. sp. lycopersici toxins and fumonisin B1.
The phytopathogenic fungus Alternaria alternata f. sp. lycopersici (AAL) produces toxins that are essential for pathogenicity of the fungus on tomato (Lycopersicon esculentum). AAL toxins and fumonisins of the unrelated fungus Fusarium moniliforme are sphinganine-analog mycotoxins (SAMs), which cause inhibition of sphingolipid biosynthesis in vitro and are toxic for some plant species and mammalian cell lines. Sphingolipids can be determinants in the proliferation or death of cells. We investigated the tomato Alternaria stem canker (Asc) locus, which mediates resistance to SAM-induced apoptosis. Until now, mycotoxin resistance of plants has been associated with detoxification and altered affinity or absence of the toxin targets. Here we show that SAM resistance of tomato is determined by Asc-1, a gene homologous to the yeast longevity assurance gene LAG1 and that susceptibility is associated with a mutant Asc-1. Because both sphingolipid synthesis and LAG1 facilitate endocytosis of glycosylphosphatidylinositol-anchored proteins in yeast, we propose a role for Asc-1 in a salvage mechanism of sphingolipid-depleted plant cells. (+info)
Cloning and characterization of a cyclic peptide synthetase gene from Alternaria alternata apple pathotype whose product is involved in AM-toxin synthesis and pathogenicity.
Afternaria afternata apple pathotype causes Alternaria blotch of susceptible apple cultivars through the production of a cyclic peptide host-specific toxin, AM-toxin. PCR (polymerase chain reaction), with primers designed to conserved domains of peptide synthetase genes, amplified several products from A. alternata apple pathotype that showed high similarity to other fungal peptide synthetases and were specific to the apple pathotype. Screening of a Lambda Zap genomic library with these PCR-generated probes identified overlapping clones containing a complete cyclic peptide synthetase gene of 13.1 kb in length with no introns. Disruption of this gene, designated AM-toxin synthetase (AMT), by transformation of wild-type A. afternata apple pathotype with disruption vectors resulted in toxin-minus mutants, which were also unable to cause disease symptoms on susceptible apple cultivars. AM-toxin synthetase is therefore a primary determinant of virulence and specificity in the A. alternata apple pathotype/apple interaction. (+info)
Report of successful prolonged antifungal therapy for refractory allergic fungal sinusitis.
Allergic fungal sinusitis (AFS) is an increasingly recognized cause of refractory chronic sinusitis in the young immunocompetent host, analogous to allergic bronchopulmonary aspergillosis (ABPA), a related process in the lower respiratory tract. Most patients experience remittent disease despite corticosteroid therapy and aggressive sinus surgery. Because controlled trials have shown adjunctive antifungal therapy to be of benefit in treating ABPA, long-term oral itraconazole was used in a young man with remittent AFS, which was able to break the cycle of relapsing disease. (+info)
Structural and functional complexity of the genomic region controlling AK-toxin biosynthesis and pathogenicity in the Japanese pear pathotype of Alternaria alternata.
The Japanese pear pathotype of Alternaria alternata produces host-specific AK-toxin and causes black spot of Japanese pear. Previously, a cosmid clone, pcAKT-1, was isolated that contains two genes, AKT1 and AKT2, within a 5.0-kb region required for AK-toxin biosynthesis. The wild-type strain has multiple, nonfunctional copies of these genes. In the present study, two additional genes, AKTR-1 and AKT3-1, downstream of AKT2 were identified. Transformation of the wild type with AKTR-1- and AKT3-1-targeting vectors produced toxin-deficient (Tox-), nonpathogenic mutants. DNA gel blot analysis, however, demonstrated that the fragments targeted in Tox- mutants were different from those containing AKTR-1 and AKT3-1 on the transforming vectors. A cosmid clone, pcAKT-2, containing the targeted DNA was isolated and shown to carry two genes, AKTR-2 and AKT3-2, with high similarity to AKTR-1 and AKT3-1, respectively. Transcripts from not only AKTR-2 and AKT3-2 but also AKTR-1 and AKT3-1 were found in the wild type. DNA gel blot analysis with pulsed-field gel electrophoresis showed that AKT1, AKT2, AKT3, and AKTR and their homologues are on a single chromosome. These results indicate the structural and functional complexity of the genomic region controlling AK-toxin biosynthesis. (+info)