Biomedical subjects

N J Talbot

Publications and source records attributed to N J Talbot.

28 records · Page 2Linked to original sources

PubMed1998

Infection-related development in the rice blast fungus Magnaporthe grisea.

Recent developments have been made in the identification of signal transduction pathways and gene products involved in the infection-related development of the rice blast fungus, Magnaporthe grisea. It has been established that cAMP-dependent and MAP kinase-mediated signaling are both critical for appressorium morphogenesis and function. These signaling pathways may act downstream of hydrophobin-mediated surface sensing by the growing germ tube. Several genes have been identified that are required for invasive growth of M. grisea including genes that allow adaptation of fungal metabolism to growth within plant tissues.

Gene Expression Regulation, Fungal↗

PubMed1997

Growing into the air.

Fungi must grow into the air for reproduction and spore dispersal, and to do this their hyphae contain morphogenetic proteins that respond to the aerial environment. The recent discovery of 'repellent' proteins, however, suggests fungi have more than one mechanism for aerial development.

Air↗

PubMed1997

Characterization of human erythrocyte choline transport in chronic renal failure.

BACKGROUND: Membrane transport of choline cations is elevated in renal failure in erythrocytes and cerebral tissue but the origins and clinical importance of this are unknown. METHODS: The membrane transport changes have been characterized using erythrocytes from patients on maintenance haemodialysis (HD), patients on continuous ambulatory peritoneal dialysis (CAPD), and control subjects. Data were obtained from cells depleted of intracellular choline to create zero-trans (ZT) conditions for choline influx. [14C]-choline influx measurements provided a kinetic description of choline flux as the sum of a saturable transport system (defined by Vmax and Km) and an apparent diffusion pathway. Inhibition of choline transport by hemicholinium-3 (HC-3), quinine and N-ethylmaleimide (NEM) has been studied. Actions of three cationic polyamine putative uraemic toxins (putrescine, spermidine, spermine) were tested in control erythrocytes. RESULTS: Mean (SEM) Vmax (ZT) was increased in HD at 45.0 (3.0) mumol/l cells/h and in CAPD at 46.6 (2.5) mumol/l cells/h compared to controls (30.0 (2.0) mumol/l cells/h). Mean Km (ZT) was not significantly altered in HD or CAPD (HD: 6.1 (1.6) microM; CAPD: 5.5 (0.7) microM; control: 5.1 (0.9) microM). The sensitivity of choline transport to the inhibitors tested was not altered in HD. 1.0 mM quinine, 2.0 mM NEM and 1.0 mM HC-3 caused 75-90% inhibition of transport in both HD and controls. For inhibition of ZT influx of 25 microM choline the mean IC50 of quinine was 90 (9) microM in HD and 101 (13) microM in controls (n.s.). The ZT influx of 200 microM choline was not altered by any of the polyamines at concentrations up to 1.0 mM. CONCLUSIONS: Membrane choline transport in CRF remains protein-mediated and exhibits normal substrate and inhibitor affinities; high values of Vmax seem to occur through increased surface expression of an active normal choline transporter. Increases in plasma polyamines cannot explain the choline transport changes in CRF.

Biological Transport↗

PubMed1996

The influence of genotype and environment on the physiological and metabolic diversity of Fusarium compactum.

Fungal species produce a large variety of secondary metabolites which are of considerable interest to the pharmaceutical industry. It is clear that the secondary metabolite production of a species varies significantly in strains from different geographic locations and from different habitats. The influence of genotype and environment on metabolite production is, however, poorly understood. In this study we examined the influence of genotypic variability, physiological variability, environmental location, and habitat on metabolite production by Fusarium compactum. Isolates of the fungus from two geographic locations and two distinct habitat types were examined for growth on 95 different carbon sources, and genotypic variability was determined using RAPDs and rDNA-RFLP analysis. In a blind test secondary metabolite production was assessed using HPLC profiles of methanolic cell extracts. A number of correlations were observed between genotypic groupings, as determined using parsimony, and specific metabolic production. Similar correlations were also observed with physiological groups although genotypic analysis proved to be a more sensitive predictor of metabolite variability. The data suggest a complex relationship between environment, genotype, and metabolite production but highlight the use of genetic screening as a means of optimizing the changes of identifying a wide range of metabolites from a given species.

Base Sequence↗

PubMed1995

mRNA translocation and microtubules: insect ovary models.

The nurse cells in insect ovarioles supply the developing oocytes with various cellular components, including mRNAs, which pass from one cell to the other through intercellular bridges traversed by microtubules. Best studied of these mRNAs are those that encode the axis-determining factors in Drosophila embryos. These mRNAs are further translocated and localized within the oocyte to sites where the products of their translation will ultimately function. This article explores the evidence supportive of a role for microtubules and motor proteins in these processes.

Journal Article↗

PubMed1995

Having a blast: exploring the pathogenicity of Magnaporthe grisea.

The rice blast fungus Magnaporthe grisea has an exquisite level of pathogenic specialization, allowing it to infect and colonize rice, subvert the metabolism of the host and spread to new hosts. Through a combination of cytology and molecular-genetic analysis, a picture is gradually emerging of the many interlinked processes that are required for successful infection of the plant.

Ascomycota↗

PubMed1993

Identification and characterization of MPG1, a gene involved in pathogenicity from the rice blast fungus Magnaporthe grisea.

Differential cDNA cloning was used to identify genes expressed during infectious growth of the fungal pathogen Magnaporthe grisea in its host, the rice plant. We characterized one of these genes, MPG1, in detail. Using a novel assay to determine the proportion of fungal biomass present in the plant, we determined that the MPG1 transcript was 60-fold more abundant during growth in the plant than in culture. Mpg1 mutants have a reduced ability to cause disease symptoms that appears to result from an impaired ability to undergo appressorium formation. MPG1 mRNA was highly abundant very early in plant infection concomitant with appressorium formation and was also abundant at the time of symptom development. The MPG1 mRNA was also expressed during conidiation and in mycelial cultures starved for nitrogen or carbon. MPG1 potentially encodes a small, secreted, cysteine-rich, moderately hydrophobic protein with the characteristics of a fungal hydrophobin. Consistent with the role of the MPG1 gene product as a hydrophobin, Mpg1 mutants show an "easily wettable" phenotype. Our results suggest that hydrophobins may have a role in the elaboration of infective structures by fungi and may fulfill other functions in fungal phytopathogenesis.

Amino Acid Sequence↗

PubMed1993

Karyotypic Variation within Clonal Lineages of the Rice Blast Fungus, Magnaporthe grisea.

We have analyzed the karyotype of the rice blast fungus, Magnaporthe grisea, by using pulsed-filed gel electrophoresis. We tested whether the electrophoretic karyotype of an isolate was related to its pathotype, as determined by infection assays, or its genetic lineage, as determined by DNA fingerprinting. Highly reproducible electrophoretic karyotypes were obtained for a collection of U.S. and Chinese isolates representing a diverse collection of pathotypes and genetic lineages. Chromosomes ranged in size from 3 to 10 Mb. Although chromosome number was largely invariant, chromosome length polymorphisms were frequent. Minichromosomes were also found, although their presence was not ubiquitous. They ranged in number from 1 to 3 and in size from 470 kb to 2.2 Mb. Karyotypes were sufficiently variable as to obscure the obvious relatedness of isolates on the basis of pathogenicity assays or genetic lineage analysis by DNA fingerprinting. We documented that the electrophoretic karyotype of an isolate can change after prolonged serial transfer in culture and that this change did not alter the isolate's pathotype. The mechanisms bringing about karyotype variability involve deletions, translocations, and more complex rearrangements. We conclude that karyotypic variability in the rice blast fungus is a reflection of the lack of sexuality in wild populations which leads to the maintenance of neutral genomic rearrangements in clones of the fungus.

Journal Article↗

PubMed1991

Pulsed field gel electrophoresis reveals chromosome length differences between strains of Cladosporium fulvum (syn. Fulvia fulva).

Methods are described for the electrophoretic separation of chromosome-sized DNA molecules from the fungal tomato pathogen Cladosporium fulvum (syn. Fulvia fulva). Using a hexagonal electrode array and switching times of 75 min at 45 V for 14 days, nine bands could be resolved. By comparison with co-electrophoresed Aspergillus nidulans chromosomal DNA (which was resolved into seven bands), the sizes of the C. fulvum bands are estimated to be between 1.9 Mb and 5.4 Mb. The two largest bands are believed to be doublets, giving a minimum genome size of 44 Mb. Cloned probes for the ribosomal DNA repeat, an anonymous single copy fragment and a newly discovered retrotransposon were hybridized to blots of the pulsed field gels, demonstrating the use of this technique for genomic mapping. Most strains of C. fulvum had an identical pattern of bands. Two strains exhibited two polymorphisms which could be due to a translocation.

Blotting, Southern↗

PubMedDate not supplied

Expression of reverse transcriptase genes in Fulvia fulva.

Antibodies raised against intercellular fluid antigens isolated from diseased tomato leaves have revealed that the fungal pathogen Fulvia fulva expresses genes for a fungal reverse transcriptase (RNA-dependent DNA polymerase). This enzyme is required for the replication of retroviruses and retroviral-like transposable elements and could provide a mechanism for increasing the mutation rate of fungal pathogens, perhaps explaining their ability to evolve new races rapidly. We report here the DNA sequence of a 225-bp clone from a lambda gt11 genomic library of F. fulva. This clone, designated P5, exhibits a high degree of sequence homology with the reverse transcriptase (pol) gene of the Drosophila melanogaster copia-like retrotransposon 17.6. Southern blot analysis of genomic DNA of F. fulva showed that P5-related sequences are moderately reiterated with 30-100 copies, some of which exhibit restriction fragment length polymorphism in different races of the pathogen. Western blot analysis of extracts from F. fulva with antibodies raised to purified reverse transcriptase (from human immunodeficiency virus-1) revealed immunoreactive proteins. Reverse transcriptase previously has been detected in a variety of organisms including yeast, insects, protozoa, and mammals, but to our knowledge, this is the first report of its occurrence in filamentous fungi.

Amino Acid Sequence↗