Experimental Mycology最新文献

Ashktorab, H., and Cohen, R. J. 1994. Presence of GTP-binding proteins in the plasma membrane of the Phycomyces sporangiophore. Experimental Mycology 18, 139-149. When a plasma membrane-enriched fraction isolated from the sporangiophore of the Zygomycete Phycomyces blakesleeanus was subject to immunoblotting, two polypeptide bands reacted with an antibody directed to a conserved sequence of the ∝ subunit of G-proteins; their apparent molecular masses were 40 and 51 kDa. Upon treating the plasma membrane preparation with cholera toxin, bands at 40 and 51 kDa appeared to be ADP-ribosylated but no band appeared with pertussis toxin incubation. Apparent dissociation constants for the binding of GTPγS were determined for plasma membrane from Phycomyces sporangiophore grown in the light (K_D = 39 ± 16 nM) (±SD) and in the dark (K_D = 11 ± 6 nM). GTP served as a strong competitor for binding as did GDP, although somewhat less well, while ATP competed considerably more weakly. Northern analysis of sporangiophore mRNA displayed two bands hybridizing to the Gα2 probes coding for a G_α subunit from Dictyostelium discoideum. Furthermore, Western blotting of plasma membrane revealed several bands containing polypeptides with presumptive covalently attached immunoreactive flavins. (The prevailing evidence from the action spectra of Phycomyces is that the photoreceptor is a flavoprotein residing in the plasma membrane.) Immunoblotting also detected a H⁺ ATPase similar to the plasma membrane enzyme of yeast, corroborating our isolation of plasma membrane and suggesting another possible player in the signal responses of Phycomyces . This is apparently the first evidence for a G-protein in this class of eukaryotes. G-proteins may serve a role in the flavoprotein-mediated phototransduction system of P. blakesleeanus.

Bistis, G. N. 1994. Retardation of the growth of transplanted apothecia: A manifestation of vegetative incompatibility in Ascobolus stercorarius (Bull.) Schröt. Experimental Mycology 18, 103-110. Two loci, C and D, each with at least two alleles, C¹, C² and D¹, D², control a system of apothecium-transplant incompatibility in the fungus Ascobolus stercorarius. The recognition appears to occur between the sterile tissue of the transplanted apothecium and the vegetative hyphae of the recipient mycelium. When these carry similar C and D alleles the transplanted apothecium grows at a normal rate. If they carry different D alleles the apothecium grows at a subnormal rate. If they carry different C alleles (with like or different Ds) the apothecium grows at a sub-subnormal rate. The C locus, but not the D, also has a detectable effect in vegetative heterokaryons. Two auxotrophic mutants will complement only if they carry like C factors. The two mating-type alleles, A, a, also function as transplant and vegetative incompatibility factors.

Goodwin, S. B., and Fry, W. E. 1994. Genetic analyses of interspecific hybrids between Phytophthora infestans and Phytophthora mirabilis. Experimental Mycology 18, 20-32. Four crosses were made between isolates of two host-specific Phytophthora species. Phytophthora infestans and Phytophthora mirabilis. In the two most successful crosses involving a common P. infestans A2 parent, allozyme analysis confirmed that 79 of 86 progeny were interspecific hybrids, 3 were presumed selfs, and 4 were either selfs or nonrecombinant parental types. Mating type, alleles at the allozyme locus glucose-6-phosphate isomerase, and the + alleles at a number of DNA fingerprinting loci segregated independently according to Mendelian expectation. Three DNA fingerprinting loci were tightly linked in P. mirabilis, but no other linkages were detected among these markers. Mitochondrial DNA was uniparentally inherited, mostly from the P. infestans parent. Growth rate segregated as a quantitative character. None of the 68 progeny tested infected Mirabilis jalapa (the host of P. mirabilis), 3 infected potato, and 4 were weakly pathogenic to tomato. Because most of the F₁ hybrids could not infect any of the hosts infected by the parents, host specialization could provide a postzygotic as well as a prezygotic reproductive isolating mechanism for P. infestans and P. mirabilis in central Mexico. These results indicate that P. mirabilis probably is capable of a regular outcrossing mating system.

Robison, M. M., and Horgen, P. A. (1993). Plasmid loss in Agaricus bitorquis without alterations in homologous mitochondrial sequences. Experimental Mycology , 18, 82-86. An isolate of the basidiomycete Agaricus bitorquis , a common edible lawn mushroom, contains two linear mitochondrial plasmids. With the intent of creating a plasmidless (or "cured") version of this isolate for future studies on a plasmid-homologous mitochondrial sequence, mycelium was grown in the presence of 50 μg/ml ethidium bromide. Regenerates were recovered that had lost only the larger plasmid or both plasmids. No obvious effects on mycelial or mushroom phenotype, associated with plasmid loss, were observed. Restriction fragment length polymorphism analysis of mitochondrial DNAs from 23 regenerates indicated that no apparent deletions or rearrangements of the mitochondrial DNA, particularly the plasmid-homologous mitochondrial sequence, occurred as a result of plasmid loss or ethidium bromide treatment.

Karlsson, J.-O. 1994. Genetic variation in Heterobasidion annosum detected with M13 fingerprinting and ribosomal DNA probes. Experimental Mycology 18, 48-56. Mitochondrial and nuclear DNA diversity were analyzed in 54 strains of the forest pathogen Heterobasidion annosum (Fr.) Bref. from Northern Europe. Restriction-fragment-length polymorphisms were detected with three different probes on Southern blots of DNA restricted with Hae III. Intersterility groups were clearly differentiated based on the UPGMA clustering of M13 minisatellite bands, and strains with the same geographic origin tended to form clusters. Average band share values were 0.80 and 0.68 within S- and P-groups, respectively, and 0.49 between groups. When the ribosomal mitochondrial ML 5-8 region was used as a probe the two types of patterns observed were in accordance with the results of the mating tests and the UPGMA clustering of fingerprints. No variability was detected in ribosomal nuclear ITS 1-4 region.

Li, J., and Heath, I. B. 1994. The behavior of F-actin during the zoosporic phases of the chytridiomycete gut fungi Neocallimastix and Orpinomyces; Experimental Mycology 18, 57-69. The changing patterns of F-actin were shown with rhodamine-labeled phalloidin staining of cells fixed at different stages of their development cycle. Zoospores were permeated by diffuse F-actin which was more concentrated at the plasmalemma and in amoeboid projections, suggestive of a role in zoospore morphogenesis. Upon encystment, nuclei became enclosed in a perinuclear shell of F-actin which persisted throughout vegetative growth, including mitosis. We suggest that this shell, and cytoplasmic F-actin filaments, function in nuclear motility and positioning, and the former may also generate nuclear shape at mitosis. Also present during growth were peripheral F-actin plaques specifically associated with both diffuse cell wall deposition over the entire surface of the expanding cell body and localized deposition at rhizoid tips. Similar plaques are previously reported associated with localized wall synthesis in other fungi; their occurrence is now extended to the chytridiomycetes with their diffuse pattern of wall synthesis. During zoosporogenesis, cytoplasmic cleavage vacuoles were associated with extensive F-actin sheets which presumably generate or direct their expansion. Presumptive initials of these vacuoles are also F-actin-rich, consistent with an F-actin role in their initial clustering around the centrioles. Comparison of these observations with previous ones on similar stages in the unrelated oomycetes shows similarities in F-actin associated with wall synthesis, zoospore morphogenesis, and cytokinesis but differences in nuclear-associated F-actin, suggesting that an F-actin role in the former processes is a widespread and ancient phenomenon.

Olsson, S. 1994. Uptake of glucose and phosphorus by growing colonies of Fusarium oxysporum as quantified by image analysis. Experimental Mycology 18, 33-47. The simplest of all heterogeneous environments for fungal colony growth is the petri dish with an agar medium. As the colony grows there will be a depression of nutrient concentrations under the colony caused by the uptake of nutrients by the growing colony. Image analysis methods have been developed for measuring medium concentrations of glucose and phosphorus with simultaneous biomass density determinations in agar systems. Maps of the concentrations in the agar medium under the colony and of colony biomass density were produced. A new method for weighing fungal colonies grown on agar is also presented. For Fusarium oxysporum phosphorus and glucose uptake from the medium was the same irrespective of the C/mineral ratios in the medium within the measured range of ratios. Even the concentration profiles of the nutrients under the colony were the same irrespective of nutrient ratios. Distribution of biomass density was affected by differences in glucose concentrations, being highest at the colony margin at the lower concentrations. The results indicate that the fungal colony is able to take up nutrients at the margin in excess of the local needs.

Moragues, M. D., Estevez, J. J., Rementerı́a, A., and Sevilla, M. J. 1994. Effect of n-alkanols on acidification curves of Aureobasidium pullulans suspensions. Experimental Mycology 18, 1-6. n -Alkanols, from methanol to 1-hexanol, induce yeast-to-hyphae transition in the dimorphic fungus Aureobasidium pullulans. In order to elucidate whether triggering of the morphogenetic event is membrane related, we have studied the effect of the morphogenetic n-alkanols on the pH of suspensions of A. pullulans, with no external carbon source. n -Alkanols, at their hyphal inducing concentration or higher, caused a decrease in the initial acidification rate (C) of yeast-phase cell suspensions of A. pullulans. From this effect on C, an inhibition coefficient (K) was deduced, specific for each alcohol. These coefficients were directly related to the lipid/buffer partition coefficients of the alkanols. On the other hand, germ tubes of A. pullulans, obtained in the presence of n-propanol, showed a much slower acidification rate in water than yeast cells. Moreover, 1-propanol or 1-butanol did not significantly affect the initial acidification rate of germ tubes. The latter observation was interpreted as an adaptation of cells grown in the presence of alcohol. The results of all these experiments support our hypothesis that the plasma membrane is a target of the morphogenetic effects of n-alkanols.