Respiration of wild type and extrachromosomal mutants of Neurospora crassa

Long-oligomer microarray profiling in Neurospora crassa reveals the transcriptional program underlying biochemical and physiological events of conidial germination

To test the inferences of spotted microarray technology against a biochemically well-studied process, we performed transcriptional profiling of conidial germination in the filamentous fungus, Neurospora crassa. We first constructed a 70 base oligomer microarray that assays 3366 predicted genes. To estimate the relative gene expression levels and changes in gene expression during conidial germination, we analyzed a circuit design of competitive hybridizations throughout a time course using a Bayesian analysis of gene expression level. Remarkable consistency of mRNA profiles with previously published northern data was observed. Genes were hierarchically clustered into groups with respect to their expression profiles over the time course of conidial germination. A functional classification database was employed to characterize the global picture of gene expression. Consensus motif searches identified a putative regulatory component associated with genes involved in ribosomal biogenesis. Our transcriptional profiling data correlate well with biochemical and physiological processes associated with conidial germination and will facilitate functional predictions of novel genes in N.crassa and other filamentous ascomycete species. Furthermore, our dataset on conidial germination allowed comparisons to transcriptional mechanisms associated with germination processes of diverse propagules, such as teliospores of the phytopathogenic fungus Ustilago maydis and spores of the social amoeba Dictyostelium discoideum.

Genetical, developmental, and thermal regulation of antioxidant enzymes in Neurospora

Three characteristics of the biochemical genetics of antioxidant enzyme regulation in Neurospora and enteric bacteria are analogous. This paper reports two additional analogies:responsiveness to change in respiratory rate or thermal stress. A negative regulatory Neurospora mutant is defective in those responses. Although several differences are noted, the common denominator of the two organisms is probably an oxy-regulon, a global unit of genetic function. The degree of homology of bacterial and fungal antioxidant enzyme regulatory mechanisms at the molecular-genetic and signal transduction levels of organization remains to be examined. The hypothesis that the genetic control of antioxidant enzymes is a prerequisite for cellular differentiation of Neurospora is discussed.

Mitochondrial biogenesis during fungal spore germination: respiration and cytochrome c oxidase in Neurospora crassa

The germination of conidiospores of wild-type Neurospora crassa was found to be dependent upon the function of the cytochrome-mediated electron transport pathway. The cyanide-insensitive alternate oxidase did not contribute significantly to the respiration of these germinating spores. The dormant spores contained all of the cytochrome components and a catalytically active cytochrome c oxidase required for the activity of the standard respiratory pathway, and these preserved components were responsible for the accelerating rates of oxygen uptake which began immediately upon suspension of the spores in an incubation medium. Mitochondria of the dormant spores contained all of the subunit peptides of the functional cytochrome c oxidase; nevertheless, de novo synthesis of these subunits began at low rates in the first stages of germination. Reactivation of the respiratory system of germinating N. crassa spores seems not to be dependent initially upon the function of either the mitochondrial or cytoplasmic protein-synthesizing systems. The respiratory activity of spores of three mutant cytochrome c oxidase-deficient strains of N. crassa also was found to depend upon the function of the cytochrome electron transport pathway; the dormant and germinating spores of these strains contained a catalytically active cytochrome c oxidase. Cytochrome c oxidase may be present in the dormant and germinating spores of these strains as the result of a developmental-phase-specific synthesis of and requirement for the enzyme.

Ageing of Neurospora crassa. IX. Microviscosity properties of mitochondrial membranes during normal and abnormal growth and development of an inositol auxotroph

Microviscosity of mitochondrial membranes of an inositol auxotroph of Neurospora was measured by the method of Shinitzky, employing the fluorescent probe diphenyl-hexatriene. With high concentration of inositol, growth, morphogenesis, and cellular and biochemical phenotypes of the auxotroph are normal; whereas with low concentrations, these characteristics become abnormal and cellular and clonal senescence ensue. During normal growth and development, the critical temperatures of phase transition, the energies and volumes of fusion (delta E, V), and the microviscosities (n) at low and high temperatures changed in a cyclical "gaussian" manner; whereas the microviscosity at 25 degrees C remained constant. The normal developmental changes of the microviscosity properties were consistent with Brody's molecular packaging hypothesis, whereby the biochemical properties of conidia are pre-determined in conidiogenic hyphae. The microviscosity properties and their developmental change were closely correlated with other biochemical and biological properties such as the critical extremities of growth temperature, activity of membrane-bound cytochrome oxidase, and the stages of cellular differentiation. The thermodynamic properties of the membrane microviscosity support the genetic hypothesis that conidia and conidiogenic hyphae are more highly differentiated than growing hyphae. During abnormal growth and development, delta E and V of the liquid-crystalline phase underwent a precocious, but otherwise normal change at an early age; whereas subsequent cellular and mitochondrial senescence was accompanied by an abnormal increase of microviscosity and abnormally small delta E and V. With the results of other experiments and by analogy to proposed structural determinants of microviscosity properties of other biological membranes, a tentative interpretation of the molecular basis of the microviscosity properties and their normal and abnormal changes is derived. The effects of phospholipase treatment indicated that electrostatic interaction of phospholipid polar groups with membrane proteins may restrict mobility, increasing microviscosity and decreasing energies of fusion. Abnormal development or ageing of the membranes, leading to abnormally large n and small delta E, is probably a consequence of excessive lipid peroxidation and related abnormal changes of their structure.

Cytochrome abnormalities and cyanide-resistant respiration in extranuclear mutants of Aspergillus nidulans

The cytochrome spectra of two extranuclear mutants of Aspergillus nidulans and the double-mutant recombinant formed from them have been examined both at room temperature and at the temperature of liquid N2 and compared with those of the wild-type strain. The oligomycin-resistant, slow growing mutant contained an increased amount of cytochrome c without any loss of cytochromes b and a,a3. The cold-sensitive mutant, apparently normal when grown at 37 C, showed an increased amount of cytochrome c and a partial loss of cytochromes b and a,a3 when grown at 20 C. A combination of these effects was observed in the double-mutant recombinant. Cyanide-resistant respiration was present in both mutant strains and in the recombinant at much higher levels than in the wild-type strain. In the oligomycin-resistant mutant, this was usually present together with cyanide-sensitive respiration, whereas in the cold-sensitive mutant and recombinant grown at 20 C cyanide-resistant approached 100%. Inhibitor and growth yield studies indicated that the cyanide-resistant pathway was not used by the cold-sensitive mutant during growth at 20 C.

Glucose utilization and ethanolic fermentation by wild type and extrachromosomal mutants of Neurospora crassa

Logarithmic growth rates, maximal biomass, specific glucose utilization rates, and ethanol accumulation were measured in aerobic cultures of wild type and extrachromosomal mutants of Neurospora crassa. Maximal biomass and ethanol accumulation of wild type and [mi-1] were proportional to the initial glucose concentration in the range of 2 to 10%. The specific rates of glucose utilization by the mutants were 13- to 20-fold greater than those of wild type in young cultures. The specific rates of glucose utilization by wild type, however, were increased threefold by increasing the ammonium ion concentration in the preculture medium. The suppressor gene f(+) suppressed the excessive glucose utilization and enhanced the growth rate and maximal biomass of [mi-1]. When the mutants were utilizing glucose at excessive rates, ethanol did not appear in the culture medium. Ethanol accumulation was maximum at stationary phase or thereafter, but there was little difference between the maxima of the mutants and wild type. The molar efficiency of the conversion of glucose to ethanol during the entire culture period of wild type and mutants was about 50% and, in the latter stages of fermentation, approached 100%. Replacement of ammonium ion by nitrate in the culture medium suppressed ethanol accumulation by wild type. The relationship of these results to previous observations on respiratory adaptation are discussed. We suggest that the Pasteur effect, the inhibition of fermentation by respiration, may be operative in N. crassa. Factors such as nitrogen source and concentration and oxygen tension, which may serve primarily to regulate the amount and form of respiration would, therefore, indirectly regulate fermentation. The mutants, although transiently deficient in terminal respiratory activity, do not accumulate more ethanol than wild type and, therefore, apparently do not ferment in excess to obtain additional adenosine 5'-triphosphate. We suggest that the excess activity of the alternate form of respiration of the mutants may be related to their excessive rate of glucose utilization by way of the pentose phosphate pathway and the oxidation of excess reduced nicotinamide adenine dinucleotide.