DNA nucleotide sequence homologies between some zoosporic fungi

Representative species from the monoflagellate Blastocladiales and the biflagellate Saprolegniales were studied for their DNA base composition, heterogeneity, nucleotide sequence homology and divergence. Intergeneric, intrageneric and interstrain DNAs of Blastocladiales were heterogenous. The G+C values for their main component (average 64 percent) and two minor ones (average 52 and 44 percent) were found to be significantly higher than the corresponding values from the biflagellate Saprolegnia ferax (55, 46 and 36 percent respectively). In Allomyces species, the two hybrid, male and female strains were found to have closer homology with their parental types than these last between themselves. Among Blastocladiales, interspecific similarities between the epigynous A. macrogynus and the hypogynous A. arbuscula were higher (average 75 percent) than intergeneric similarities between Allomyces and Blastocladiella (average 58 percent). The biflagellate S. ferax was found to be distantly related to the uniflagellate Allomyces (average 48 percent similarity). The nucleotide sequence divergences obtained from thermal elution data correlated the hybridization values.

Origin of life. II. From prebiotic replicators to protocells

Primitive microvesicles (coacervates, microspheres, marigranules, etc.), free-born in aqueous media, are only protometabolic proteinoids surrounded by an amphiphilic protomembrane. In contrast, surface-born microvesicles could be initiated in the pores of watered rocks providing primary boundaries coated by amphiphilic compounds and acting as sinks for primitive peptides and their coding nucleobases N-P anchored on polyphosphates. Only presumed replication of these prenucleic infopolymers would qualify the basipetally budded microvesicles as protocells.

Molecular cloning and expression studies of two divergent alpha-tubulin genes in Neurospora crassa

Three alpha-tubulin isoforms were previously detected in Neurospora crassa. We have cloned and analysed two alpha-tubulin cDNAs, Tub alpha A and Tub alpha B that encode polypeptides of 453 and 451 amino acids, respectively. The encoded amino acids exhibit an unusual divergence of 35%. This is the highest divergence ever observed between alpha-tubulins from the same species. The expression of the two genes is developmentally regulated. We did not detect any transcription of the Tub alpha A gene in dormant macroconidia and during the first 30 min of development even though the alpha-tub A protein is already present in the early stage of germination. In contrast, the Tub alpha B gene is continuously transcribed during the vegetative cycle and the expression profile of the protein follows the ones of its mRNA.

Purification of a 47-kDa calmodulin-binding polypeptide as an actin-binding protein from Neurospora crassa

We have enriched a 47-kDa polypeptide (p47) from Neurospora crassa on the basis of its affinity to calmodulin. The p47 was purified to homogeneity by chromatography on a Mono S cation exchange column and evidence is presented that the polypeptide co-sediments specifically with F-actin. The intracellular distribution of p47 and actin was also examined using indirect double immunofluorescence staining of cells at different stages of development. Our results suggest that by altering the conformation binding site of actin to p47, calmodulin could play a regulatory role in the polarized hyphal growth of N. crassa.

A stringent role of F-actin in the ascogonial differentiation of Neurospora crassa fluffy mutant

Cytochalasin D, an inhibitor of actin polymerization, interferes with ascogonial differentiation in the fertile fluffy mutant of Neurospora crassa. As the total level of actin and its mRNA remain unchanged, this suggests that it is in its microfilamentous form (F-form) that actin is stringently required for female differentiation.

Identification and partial purification of calmodulin-binding microtubule-associated proteins from Neurospora crassa

We have purified microtubule-associated proteins from Neurospora crassa on the basis of heat stability and affinity to calmodulin. Two proteins of molecular masses 170 kDa and 190 kDa have been partially purified. A third protein of 145 kDa was purified almost to homogeneity, and we present evidence that this protein is a specific substrate for a Ca2+/calmodulin-dependent protein kinase. The purified 170-, 190-, and 145-kDa proteins induce the assembly of microtubules from purified porcine brain tubulin. We demonstrate that all three proteins are microtubule-associated proteins on the basis of an in vitro microtubule-binding assay.

Molecular cloning of a cDNA encoding calmodulin from Neurospora crassa

A full-length cDNA encoding Neurospora crassa calmodulin was isolated from a lambda ZAP II cDNA expression library. The open reading frame encodes a protein of 148 amino acid residues with a calculated M(r) of 16,865 Da. Using site-directed mutagenesis, the complete cDNA was ligated into a trc promoter-regulated bacterial expression vector to allow expression of N. crassa calmodulin in E. coli. The expressed protein was found to be identical to the native protein on the basis of some of its biochemical properties. Finally, Southern analysis of restriction digests of genomic DNA indicates that calmodulin is encoded by a single-copy gene.

Differential effects of anticytoskeletal compounds on the localization and chemical patterns of actin in germinating conidia of Neurospora crassa

Anti-actin drugs, cytochalasins A and B, inhibited both normal single, and benomyl-induced multiple, germ tube outgrowth from conidia of Neurospora crassa. Actin was cytochemically found to be concentrated in each of the benomyl-induced germ tube tips. No significant quantitative changes either in total actin or its isoforms were measured in the inhibitor-treated germlings. While intact microtubules are required for normal, monopolar axiation of the germ tube, they appear not to be necessary for benomyl-induced multipolar outgrowth which, in contrast, still requires intact actin microfilaments. Microfilaments and microtubules thus play complementary roles in the normal germination of conidia.

Immunocharacterization of actin and its immunofluorescent localization during the developmental gametophytic stages of Allomyces arbuscula

Highly specific polyclonal antibodies against actin from Allomyces arbuscula were produced in rabbits, immunopurified by immunoblotting and specified with actin isolated from Neurospora crassa and mouse skeletal muscle. Used as immunofluorescence probes, they allowed localization of actin in the sequential gametophytic stages of the mould.

Localization of actin and characterization of its isoforms in the hyphae of Neurospora crassa

The actin of Neurospora crassa wild type Strain St. Lawrence has been purified, characterized and localized. A fungal 43 kDa protein was isolated by affinity chromatography on DNase I-Sepharose. This protein was identified as actin on immunoblots when an anti-actin monoclonal antibody raised against chicken gizzards was used as a probe. After two-dimensional gel electrophoresis three actin isoforms were detected. The distribution of actin in hyphae was examined by FITC-phalloidin staining of formaldehyde fixed hyphae. F-actin was found to be mainly concentrated in the hyphal tips in which it formed a uniform cap. Apical actin could be involved in hyphal morphogenesis, organelle motility and maintenance of polarity.

Secretion of an Mr 60000 protein by benomyl-treated cells of Neurospora crassa

In the presence of the microtubule inhibitor benomyl at micron concentrations, cells of Neurospora crassa wild type strain St. Lawrence 74A were found to secrete high amounts of an Mr 60 000 protein into the culture medium (about 35 micrograms/ml after a 12 h treatment). The secretion also occurred after treatment with the other antitubulin drugs carbendazim (MBC), nocodazole, thiabendazole, and griseofulvin. This secretion is apparently induced by the specific action of benomyl on N. crassa beta-tubulin as no secretion of the Mr 60 000 protein could be detected after treatment of the benomyl-resistant mutant bml 511 (r), mutated in its beta-tubulin gene (Orbach et al., Mol. Cell. Biol. 6, 2452-2461 (1986)). The secretion was abolished by 12 microM cycloheximide, a protein synthesis inhibitor. The Mr 60 000 protein could be separated into two main and four secondary components by two-dimensional gel electrophoresis (pI 6.67 and 6.52 and pI 6.93, 6.81, 6.44, and 6.32, respectively). The Mr 60 000 protein was not a major intracellular protein of benomyl-treated cells and could only be revealed by immunoblotting with polyclonal antibodies raised against the extracellular form. It was undetectable in untreated cells collected at various stages of vegetative growth or in their culture medium.

Induction of multiple germ tubes in Neurospora crassa by antitubulin agents

The antitubulin fungicide benomyl suppressed the linear growth of Neurospora crassa wild type strain St. Lawrence 74 at micromolar concentrations. The rate of germination of macroconidia was not affected. Macroconidia exposed to 1.7 microM benomyl for 5 h formed multiple germ tubes. When germlings incubated for 4 h were exposed to 1.7 microM benomyl for 3 h, their germ tube stopped growing, swelled and emitted several branches. Normal linear growth was restored after removal of the fungicide. Linear growth of N. crassa was resistant up to 16 microM nocodazole. This drug induced multipolar germination at 8 microM, and griseofulvin only at 140 microM. The microtubule (MT) cytoskeleton of N. crassa could be revealed by indirect immunofluorescence with the monoclonal antibody YOL 1/34 directed against yeast alpha-tubulin. We detected no striking effects of the benomyl treatments on MT organization. The MT-stabilizing agents deuterium oxide (D2O) and cAMP have no antagonistic effects on the benomyl-induced multipolar germination. The positioning of nuclei and mitochondria was determined from the DAPI and Rhodamine 123 fluorescence patterns, respectively. Benomyl inhibited nuclear migration into multiple germ tubes. Quantitative scanning cytophotometry revealed a peak in the intensity of the mitochondria-associated Rhodamine 123 fluorescence near the apex of untreated germlings. This peak disappeared in multiple germ tubes. Benomyl-resistant mutant bml 511 (r), mutated in its beta-tubulin gene, germinated normally in the presence of the fungicide. This strongly suggests that multiple germ tube formation was due to the effect of benomyl on beta-tubulin. Benomyl-resistant strain 74-3, constructed by reintroducing the cloned mutant N. crassa beta-tubulin gene into the cells by transformation, displayed a partial resistance to benomyl with respect to multipolar germination. Its rate of germination was slow (50% germination reached after 4 h at 37 degrees C as compared to 2.5 h for the wild type). In contrast to N. crassa, the other ascomycete Aspergillus nidulans is nocodazole-sensitive (linear growth suppressed at 1.6 microM). It did not respond to the MT inhibitors benomyl and nocodazole with respect to the pattern of germ tube emergence. Our results suggest that microtubule or membrane beta-tubulin is involved in the maintenance of developmental polarity during germ tube emergence and growth of N. crassa.

GMP-stimulation of the cyanide-insensitive mitochondrial respiration in heat-shocked conidia of Neurospora crassa

In mitochondria of heat-shocked conidia of Neurospora exogenous NADH and succinate were oxidized mainly via the alternative, hydroxamate-sensitive pathway (70%) and only 30% via the cytochromic, cyanide-sensitive pathway which was predominant in untreated conidia; the alternative oxidase pathway was markedly stimulated by guanosine 5'-monophosphate (GMP).

Isolation and characterization of coated vesicles from filamentous fungi

Coated vesicles have been shown to exist in Neurospora crassa (Ascomycetes) and Uromyces phaseoli (Basidiomycetes) growing germlings. Separation of coated vesicles in both fungi was obtained when the high-speed (100,000g) pellet was fractioned on a Sephacryl S-1000 gel filtration column, according to the procedure of Mueller and Branton. Electron micrographs of negatively stained coated vesicles from fractions of gel filtration show the same striking lattice coated vesicles similar to vertebrate coated vesicles. We observe two major size classes of coated vesicles in both fungi: the larger class (100-180 nm) is similar in size to vertebrate coated vesicles; the smaller class (50-80 nm) is mostly found in both fungi. When examined by SDS-PAGE, the Sephacryl column fractions containing the maximum concentration of electron microscopically visible coated vesicles coincide with the bands of the protein coat reported as clathrin. The protein composition on SDS-PAGE of the coated vesicles indicates a major polypeptide species of 180 kDa and minor 30 to 36 kDa species. Polypeptides of 100 kDa and 64 kDa are also found in the fractions containing coated vesicles.

Genetic analysis of transformation in a microconidiating strain of Neurospora crassa

We have characterized Neurospora crassa transformants obtained with plasmid pDV1001 bearing the cloned catabolic dehydroquinase (qa-2+) gene (Hughes et al. 1983a) and fluffy 268 host strain producing only uninucleate microconidia allowing to isolate individual transformation products. The percentage of transformed nuclei in the mycelium and their stability were determined by genetic analysis of microconidia produced on selective or non-selective medium. About half of the transformants originating from mycelial spheroplasts were apparently homokaryotic. Catabolic dehydroquinase activity was in agreement with the proportion of transformed nuclei. The DNAs from four transformants analyzed by Southern hybridization showed restriction fragments expected for integration of pDV1001 into genomic DNA by non-homologous recombination. No plasmids could be rescued from the undigested DNAs of the transformants by transformation of E. coli. One transformant, fl268-6, was unstable and generated a high proportion of segregants. Plasmid pDV1001 sequences were absent in their DNA. Colonies originating from microconidia of strain fl268-6 on selective plates often lost the transformed character. These results suggest that instability in this transformant is due to the loss of integrated plasmid sequences during vegetative growth.

Microcycle conidiation induced by partial nitrogen deprivation in Neurospora crassa

Premature macroconidiation occurs at the tips of germ tubes elongated as presumptive conidiophores from macroconidia of Neurospora crassa incubated at 37 °C in nitrogen-limited shaken cultures. The use of different nitrogen sources indicated that this differentiation process could be induced by ammonium deprivation. This microcycle conidiation was also promoted by carbon deprivation and found not to be strain specific. At 25 °C, microconidia were produced in nutrient-limited shaken cultures. The results present evidence that microcycle conidiation in N. crassa can be obtained by simple manipulation of the conditions of culture.

Calmodulin-stimulated cyclic nucleotide phosphodiesterase from Neurospora crassa

Cyclic nucleotide phosphodiesterase has been partially purified by calmodulin-Sepharose affinity chromatography from a soluble extract of Neurospora crassa. The phosphodiesterase activity remained bound to the affinity column even in the presence of 6 M urea and could only be eluted by calcium chelation. The enzyme exhibits cAMP and cGMP phosphodiesterase activities. Both activities can be enhanced by calmodulin in a Ca2+-dependent manner. Stimulation of cyclic nucleotide phosphodiesterase by calmodulin can be inhibited by calmodulin antagonists such as pimozide, trifluoperazine and chlorpromazine.

Ultrastructural cytochemistry of perinucleolar dense spots in heat-treated macroconidia of Neurospora crassa

Upon heat treatment at 46 degrees C of Neurospora macroconidia, numerous dense sports appear around the nucleolus but disappear completely 5 h after shift-down to normal temperature. Cytochemical reactions and high-resolution autoradiography after pulse-labeling with tritiated uridine indicate that these dense sports contain RNA (perhaps pre-rRNA), RNP and other proteins, but no DNA.

Heat-induced changes in respiratory pathways and mitochondrial structure during microcycle conidiation of Neurospora crassa

Changes in both respiratory pathways and mitochondrial structure of Neurospora crassa occurred under conditions of microcycle conidiation. Upon heat-treatment at 46 degrees C, conidia developed a highly cyanide-insensitive, hydroxamate-sensitive respiration associated with morphological alterations in mitochondrial membranes; such changes were time-dependent. When heat-treated conidia were shifted down to 25 degrees C, the alternate, hydroxamate-sensitive respiration decreased significantly, paralleling the recovery of well-cristated mitochondria with an electron-dense matrix in the germ tubes. The decrease in hydroxamate-sensitivity was associated with two periods of increase in cyanide sensitivity corresponding to the events of germination and precocious proconidial budding.

Conidiogenous loss of structuro-functional polarity in the hyphal tips of Sclerotinia fructigena

Ultrastructural depolarization in the conidiogenously induced hyphal tips is initiated by Spitzenkörper (apical body) disintegration, followed by spreading of wall-associated vesicles and migration of mitochondria and lipid granules into the exclusion zone of the vegetative apices.

Ultrastructure de l'hyphe végétatif de Sclerotinia fructigena

Vegetative hyphae of Sclerotinia (Monilia) fructigena (Ader and Ruhl) show a sharply polarized distribution of their organelles. In their tip, the "Spitzenkörper" made up of a microvesicular aggregate is well delimitated and surrounded by apical vesicles which can fuse with the plasmalemma. Excluded from the hyphal tip, mitochondria are elongated in the apicobasal polarity and in contact with numerous and often voluminous lipid globules. It appears that these lipid globules originate from the endomembranous system of the hyphae. The endoplasmic reticulum extends into pseudogolgi cisternae apparently generating apical vesicles. In the new hyphal branches, polarity seems to be initiated by the newly oriented endoplasmic reticulum from which originate microvesicles later aggregating into the new "Spitzenkörper." An elaborate system of microtubules also seems implicated in the further maintenance of the polarity of the growing hyphae. Microbodies with pseudocrystalline inclusions are also oriented according to the developmental polarity.

Differential deoxyribonucleic acid synthesis during microcycle conidiation in Neurospora crassa

In conidia of Neurospora crassa germinating at 25 degrees C, DNA synthesis measured by incorporation of tritiated adenosine reaches a maximum soon after the outgrowth of the germ tube (6--7 h after inoculation). In conidia heat-treated at 46 degrees C (for 15 h), a maximum of incorporation of the DNA precursor occurs already 1 h after inoculation, then the incorporation progressively declines until the end of the heat-shock. When such conidia are shifted to 25 degrees C, a maximum of DNA synthesis occurs during the development of the presumptive conidiophore as at the outgrowth of normal germ tubes. This wave of DNA synthesis is followed by a second maximum of DNA synthesis, occurring only in the microcyclized cultures, when the premature differentiation of proconidia takes place. Prevention of this second wave of DNA synthesis with hydroxyurea or 5-fluorodeoxyuridine respectively reduces or fully inhibits such induced conidial differentiation.

[Studies on the conidial differentiation of "Neurospora crassa" -- VII. -- Alcoholic regulation and conidiogenous capacity (wild-type and "fluffy" mutant) (authors transl)]

Sucrose consumption by the wild-type Neurospora crassa is quicker, with much more ethanol produced, in the ammonium medium than in nitrate as single N source. On low sugar concentration which is quickly nullified, little alcohol is produced and early conidiation can develop. The higher the initial sugar concentration, the higher is the alcoholigenic coefficient defined as the efficiency of alcoholic glycolysis per unit of sugar consumed, and the more complete is the conidial "repression" in ammonium medium. The nitrate counteracts this catabolic repression effect and, depressing the alcoholigenic coefficients, permits conidiation even on high sugar (8 %) medium. The "fluffy" mutant produces relatively less ethanol (average 2-3 times less) in all cases even though it increases its alcoholigenic coefficient with the increased sugar concentration. Surprisingly, it is not induced to alcoholigenic glycolytic disinhibition by ammonium and produces even more alcohol in nitrate than in ammonium media, thus revealing an inability to benefit from the antiglycolytic, normally conidiogenous, effect of nitrate. Suggestion is made that this amacroconidial mutant is defective in its metabolic regulation related to the Pasteur effect which is required for conidiogenic expression in the wild type.

Loss of rRNA genes during a phenotypic, masculinizing mutation in Allomyces arbuscla

Saturation hybridization of 3H rRNA from Allomyces arbuscula Bali wild-type to homologous DNA and to DNA preparations from Allomyces arbuscula Bali X-ray induced male mutant and an interspecific male hybrid (Allomyces arbuscula X Allomyces macrogynus Emerson and Wilson) has shown approximately 50--60% reduction in the cistrons coding for rRNA in the masculinized strains.

Ultrastructural study of microcyclic macroconidiation in Neurospora crassa

Heat-shock of macroconidia of Neurospora crassa at 46 degrees C followed by shift-down to 25 degrees C determines premature conidiogenesis. The nuclei and cytoplasmof heat-treated, swollen conidia contain spots of a dense material especially concentrated around the nucleolus in short time treated ones. In the first proconidium apically budding on the enlarged tip of the premature conidiophore, small vesicles are later seen lining the initially simple septum separating the proconidial units into conidia. The doubling of this interconidial septum is surface viewn as a thick annulus. Disarticulation of the conidial untis intervenes along a septal furrow of electroluscent material. Interconidial continuity through the septal proes is transiently insured by a connective which is ruptured for final liberation of the conidia.

Characterization of Allomyces genome

Allomyces arbuscula DNA isolated from whole cells (bulk DNA) is composed of a major (alpha) and two minor components (beta & gamma) with buoyant densities in neutral CsCl corresponding to 1.721, 1.710 and 1.702 g/cm3, respectively. The DNA obtained from purified nuclei contains alpha component only. The beta component corresponds to mitochondrial DNA. The gamma component is also extra-nuclear but has not been characterized. The reassociation kinetics of sheared, bulk and nuclear DNA show that (i) 25 % bulk and 10% of nuclear DNA reanneal very rapidly and contain highly repeated sequences; (ii) moderately repeated sequences, accounting for 15% of both bulk and nuclear DNA, have a sequence complexity of approximately 7.2-10(6) daltons and are repeated about 320 times; (iii) the slow reannealing fraction accounts for about 60% of the genome and has kinetic properties similar to single copy sequences. The sequence complexity of this fraction was determined in relation to that of Escherichia coli. After a correction for the size of the repeated sequences the genome size of A. arbuscula was calculated to be 1.7-10(10) daltons.

Ribosomal RNA cistrons in Allomyces arbuscula

Bulk and nuclear DNA have been fractionated by preparative neutral CsCl equilibrium density gradient centrifugation and each fraction hybridized to labeled rRNA (25 + 18 S). The cistrons coding for rRNA appeared on the light side of the main peak. Hybridization of the nuclear DNA fractionated by preparative Ag+-Cs2SO4 gradients at different pHs showed that the banding profile did not change as compared to the CsCl pattern. In Hg2+-Cs2SO4 gradients, however, the peak of the fRNA-DNA hybrids shifted on the heavier side of the profile. This indicates that the ribosomal RNA cistrons in Allomyces are A-T-rich. Hybridization with homologous rRNA showed that, at saturation, 3.25% of the DNA is complementary to rRNA. With the genome size of 1.7-10(10) daltons, the multiplicity of rRNA cistrons has been found to be close to 270.

Release of RNA--DNA-protein complex during differentiation of the water mould Allomyces arbuscula

A correlation between release of a nucleic acid protein complex into the external medium and sporangial differentiation was found. Conditions preventing differentiation also stopped the release. Lethal lysis is not involved in this release process. Extracellular nucleic acids are very heterogenous, consisting of nucleotides as well as acid-precipitable nucleic acids. RNA was found to be associated with proteins and a hetero-duplex RNA--DNA associated with this nucleoprotein. Some speculations are presented about possible correlation between the release of nucleoprotein complexes and the intracellular events of differentiation.