The small GTP-binding protein Rho is expressed differentially during spore germination of Phycomyces blakesleeanus. (1/78)

Evidence has been obtained for the presence of the small 22 kDa GTP-binding Rho protein in dormant spores of Phycomyces blakesleeanus. Immunoblotting with a polyclonal antibody against RhoA revealed a soluble and membrane-associated 22 kDa protein. When [32P]ADP-ribosylated by Clostridium botulinum C3 exotoxin the protein had a pI of 5.7, a value similar to that reported for other RhoA proteins. The 22 kDa protein was expressed at all stages of growth investigated, but radiolabelling of the [32P]ADP-ribosylated protein increased when tube-formation occurred and decreased as the hyphae branched. Localization of RhoA during spore germination studied by immunofluorescence microscopy revealed the presence of RhoA in the cell membrane of the spore. When the spore started to swell, RhoA was observed as patches in the cell membrane which become concentrated in the neck region of the site of the protuberation tube, but this protein was never observed at the point of growth of the hyphal tip. The above results suggest that RhoA associated with one or more membrane proteins could participate in the molecular mechanism involved in maintaining cell integrity during the extrusion of the germ-tube of P. blakesleeanus.  (+info)

Meiosis in Phycomyces. (2/78)

A four-factor cross between two strains of Phycomyces involving two auxotrophic, one color, and the mating type marker is described. Samples of 40 germspores from 84 individual fertile germsporangia were characterized. The results show: (i) The germspores of a germsporangium are derived from one meiosis in approximately 78% of the cases. (ii) The four markers are on separate chromosomes. They are nonselective. (iii) Analysis of a large sample of germspores from 106 pooled germsporangia confirms that the four markers are unlinked. (iv) From the ditype/tetratype ratios it is inferred that each marker is located about 15 map units from its centromere.  (+info)

Responses of Phycomyces indicating optical excitation of the lowest triplet state of riboflavin. (3/78)

Phototropic and light growth responses of the sporangiophore of Phycomyces have been elicited using tunable laser stimulation from 575 to 630 nm. The growth response shows additional components of the action spectrum with a sharp peak at 595 nm, a sharp cut-off at 585 nm, and a tail extending beyond 630 nm. The integral over the electronic transition (f-value) is 1.5 X 10(-9) times that at 455 nm. These parameters indicate a direct transition from the ground state to the lowest triplet state of riboflavin.  (+info)

Interaction between gravitropism and phototropism in sporangiophores of Phycomyces blakesleeanus. (4/78)

The interaction between gravitropism and phototropism was analyzed for sporangiophores of Phycomyces blakesleeanus. Fluence rate-response curves for phototropism were generated under three different conditions: (a) for stationary sporangiophores, which reached photogravitropic equilibrium; (b) for sporangiophores, which were clinostated head-over during phototropic stimulation; and (c) for sporangiophores, which were subjected to centrifugal accelerations of 2.3g to 8.4g. For blue light (454 nm), clinostating caused an increase of the slope of the fluence rate-response curves and an increase of the maximal bending angles at saturating fluence rates. The absolute threshold remained, however, practically unaffected. In contrast to the results obtained with blue light, no increase of the slope of the fluence rate-response curves was obtained with near-ultraviolet light at 369 nm. Bilateral irradiation with near-ultraviolet or blue light enhanced gravitropism, whereas symmetric gravitropic stimulation caused a partial suppression of phototropism. Gravitropism and phototropism appear to be tightly linked by a tonic feedback loop that allows the respective transduction chains a mutual influence over each other. The use of tropism mutants allowed conclusions to be drawn about the tonic feedback loop with the gravitropic and phototropic transduction chains. The results from clinostating mutants that lack octahedral crystals (implicated as statoliths) showed that these crystals are not involved in the tonic feedback loop. At elevated centrifugal accelerations, the fluence-rate-response curves for photogravitropic equilibrium were displaced to higher fluence rates and the slope decreased. The results indicate that light transduction possesses a logarithmic transducer, whereas gravi-transduction uses a linear one.  (+info)

A single gene for lycopene cyclase, phytoene synthase, and regulation of carotene biosynthesis in Phycomyces. (5/78)

Previous complementation and mapping of mutations that change the usual yellow color of the Zygomycete Phycomyces blakesleeanus to white or red led to the definition of two structural genes for carotene biosynthesis. We have cloned one of these genes, carRA, by taking advantage of its close linkage to the other, carB, responsible for phytoene dehydrogenase. The sequences of the wild type and six mutants have been established, compared with sequences in other organisms, and correlated with the mutant phenotypes. The carRA and carB coding sequences are separated by 1,381 untranslated nucleotides and are divergently transcribed. Gene carRA contains separate domains for two enzymes, lycopene cyclase and phytoene synthase, and regulates the overall activity of the pathway and its response to physical and chemical stimuli from the environment. The lycopene cyclase domain of carRA derived from a duplication of a gene from a common ancestor of fungi and Brevibacterium linens; the phytoene synthase domain is similar to the phytoene and squalene synthases of many organisms; but the regulatory functions appear to be specific to Phycomyces.  (+info)

Intersexual partial diploids of phycomyces. (6/78)

Sexual interaction between strains of opposite sex in many fungi of the order Mucorales modifies hyphal morphology and increases the carotene content. The progeny of crosses of Phycomyces blakesleeanus usually include a small proportion of anomalous segregants that show these signs of sexual stimulation without a partner. We have analyzed the genetic constitution of such segregants from crosses that involved a carF mutation for overaccumulation of beta-carotene and other markers. The new strains were diploids or partial diploids heterozygous for the sex markers. Diploidy was unknown in this fungus and in the Zygomycetes. Random chromosome losses during the vegetative growth of the diploid led to heterokaryosis in the coenocytic mycelia and eventually to sectors of various tints and mating behavior. The changes in the nuclear composition of the mycelia could be followed by selecting for individual nuclei. The results impose a reinterpretation of the sexual cycle of Phycomyces. Some of the intersexual strains that carried the carF mutation contained 25 mg beta-carotene per gram of dry mass and were sufficiently stable for practical use in carotene production.  (+info)

Role of nitric oxide synthase in the light-induced development of sporangiophores in Phycomyces blakesleeanus. (7/78)

Blue light controls the development of sporangiophores in the zygomycete Phycomyces blakesleeanus Burgeff. Light represses the production of microsporangiophores and enhances the development of macrosporangiophores. Inhibition of the biosynthesis of tetrahydrobiopterin, a cofactor of NO synthase, inhibits this photomorphogenesis. Light induces production of citrulline from arginine in the mycelium and in sporangiophores. The citrulline-forming activity is dependent on NADPH, independent of calcium, and inhibited by NO synthase inhibitors. It is reduced in tetrahydrobiopterin-depleted mycelium. Light induces emission of NO from the developing fungus in the same order of magnitude as citrulline formation from arginine. The NO donor sodium nitroprusside can replace the light effect on sporangiophore development, and inhibitors of NO synthase repress it. We suggest that a fungal NO synthase is involved in sporangiophore development and propose its participation in light signaling.  (+info)

Glyceraldehyde-3-phosphate dehydrogenase is negatively regulated by ADP-ribosylation in the fungus Phycomyces blakesleeanus. (8/78)

Dormant spores of Phycomyces blakesleeanus contain a 37 kDa protein that is endogenously mono-ADP-ribosylated. This protein was purified and identified as glyceraldehyde-3-phosphate dehydrogenase (GAPDH) by N-terminal sequencing and homology analysis. GAPDH enzymic activity changed dramatically upon spore germination, being maximal at stages where ADP-ribosylation was nearly undetectable. The presence of glyceraldehyde 3-phosphate in this reaction affected the [(32)P]ADP-ribosylation of the GAPDH. ADP-ribosylation of the GAPDH occurred by transfer of the ADP-ribose moiety from NAD to an arginine residue. A model for the regulation of GAPDH activity and its role in spore germination in P. blakesleeanus is proposed.  (+info)