Control of fungal development. II. Kinetics of growth during dikaryosis in Schizophyllum commune

This paper describes a method for mating colonies of Schizophyllum commune so that the mating process in sets of individual colonies occurs synchronously. This technique has permitted us to define the kinetics of growth during dikaryosis, the transition from the homokaryotic to the dikaryotic stage of the life cycle. Homokaryons and established dikaryons have essentially the same exponential growth rates. We find that, during the transition from the homokaryon to the dikaryon, there is a period of distinctly slower growth, and it is during this period that the morphology typical of the dikaryon first becomes apparent. Growth kinetics for the transition from the homokaryon to the common-A heterokaryon are also established. This method will permit us to study sequential biochemical and physiological events occurring during these two developmental transitions.     

Control of arabitol formation in Schizophyllum commune development

Summary Dikaryotic cells of S. commune synthesized polyols throughout the life cycle when grown on glucose, cellobiose, or cellulose. Basidiospores contained arabitol and mannitol which were depleted during germination. The mannitol content of the young germlings rose to normal levels within a day; arabitol accumulation remained depressed for 5 to 7 days and then returned to normal levels characteristic of vegetative cells. Individual homokaryons differed in their production of intracellular polyols, which, unlike germlings, remained constant with cultural age. Homokaryon (str. 699) produced low levels of arabitol but high levels of glycerol while another homokaryon (str. 845) was the reverse. Mixtures of these homokaryons as well as the dikaryon (699×845) produced arabitol and glycerol levels intermediate between the parent homokaryons. High concentrations of glucose did not change the nature of the polyols produced. Arabitol formation could be induced prematurely in germlings or elevated in the dikaryon by growth on acetate or ethanol. Both homokaryons responded to growth on acetate with elevated arabitol production; acetate induction of arabitol formation was repressed in all types of cells if glucose were added simultaneously with acetate. Maltose, cellobiose, and trehalose also stimulated arabitol formation in young germlings, suggesting that glucose repression was the cause of decreased arabitol formation in basidiospore germlings. There was no correlation between the formation of arabitol and the derepression of isocitrate lyase or change in specific activities of alkaline and acid phosphatase in germlings grown on various carbon sources.     

Studies on basidiospore development in Schizophyllum commune.

The time required for synthesis of the spore components and the effect of different environmental conditions on basidiospore production were studied in the basidiomycete Schizophyllum commune. Both exogenous glucose and storage materials were used in the synthesis of spore components, which took 40 to 45 h to complete. A temperature of 30 degrees C, the presence of 5% CO2, a continuous supply of glucose, or a lack of exogenous glucose, had no effect on the rate of spore production. Light, however, was required for sporulation. Darkness inhibited sporulation between karyogamy and the initiation of meiosis: complete inhibition occurred after 48 h in the dark. Spores were produced 5 h after release from dark inhibition.     

Control of erythritol dehydrogenase in Schizophyllum commune

Summary An NAD-dependent erythritol dehydrogenase was detected in cell-extracts of basidiospore germinants of Schizophyllum commune following culture on either meso-erythritol or glycerol as sole carbon sources. Induction of erythritol dehydrogenase was also observed in purely vegetative mycelium (str. 845 or str. 699). Erythritol dehydrogenase was not observed in ungerminated basidiospores or germinants which arose on d-glucose, d-mannitol, sorbitol, ribitol, xylitol, d-arabitol or l-arabitol. NAD-coupled polyol dehydrogenases for all the latter sugar alcohols were observed in ungerminated basidiospores, germinants, and vegetative mycelium of S. commune cultured on d-glucose. Basidiospore germination on d-glucose plus meso-erythritol led to a 90% decrease in erythritol dehydrogenase and the specific activity of ribitol dehydrogenase was directly comparable to that seen in d-glucose germinants. Storage experiments of crude extracts of meso-erythritol germinants indicated differential enzyme decay of dehydrogenases for d-mannitol, sorbitol and erythritol while the respective enzymes could be further distinguished by heat-stability as well as preferential utilization of analogues of NAD. DEAE-cellulose column chromatography led to separation of sorbitol dehydrogenase which was also active with xylitol, erythritol dehydrogenase, and mannitol dehydrogenase which was also active with d-arabitol.     

Morphogenesis in Schizophyllum commune. I. Effects of White Light

Reproductive differentiation in the basidiomycete Schizophyllum commune Fr. is initiated by plasmogamy and reciprocal nuclear migration and is terminated by the production of basidiospores. The work reported here has analyzed several factors that affect 2 sequential steps in reproductive differentiation: A) the formation of aggregated masses of cells, and B) the subsequent differentiation of fruiting bodies. The 2 steps are both photosensitive: A) light accelerates the formation of aggregated masses of cells; B) a short exposure of light induces nonaggregated dikaryotic cells to form mature fruiting bodies in the dark.     

Origin and ultrastructure of complex septa in Schizophyllum commune development

Summary The mode of origin of cross-walls in living cells of S. commune was studied in basidiospore germinants, vegetative homokaryotic mycelium and the dikaryon of this mushroom. The de novo origin of septa in basidiospore germinants always involved annular ingrowth of cross-walls. The restriction of intercalary growth was observed in the transition from a two-celled hypha to a three-celled unit. Primary branch formation occurred in nonseptate germinants, subterminal cells of the young hypha and in the hyphal apex. Septum formation in purely vegetative homokaryotic mycelium as well as the main cross-wall of the dikaryon was also by annular ingrowth. Ultrastructure studies of the septal pore apparatus revealed no differences in those of germinants, wild-type or morphologically aberrant unilateral diploidizing strains of vegetative mycelium or in the clamp connection of the dikaryon. Simple septa of two general types prevailed in the common-A heterokaryon of S. commune.     

Scooter, a new active transposon in Schizophyllum commune, has disrupted two genes regulating signal transduction

Two copies of scooter, a DNA-mediated transposon in the basidiomycetous fungus Schizophyllum commune, were characterized. Scooter is the first transposon isolated from S. commune. Scooter creates 8-bp target site duplications, comparable to members of the hAT superfamily, and has 32-bp terminal inverted repeats. Both copies of scooter are nonautonomous elements capable of movement. Southern blot hybridizations show that scooter-related sequences are present in all S. commune strains tested. Scooter-1 was identified initially as an insertion in the Bbeta2 pheromone receptor gene, bbr2, leading to a partial defect in mating. Scooter-2 spontaneously disrupted a gene to produce the frequently occurring morphological mutant phenotype known as thin. The scooter-2 insert permitted cloning of the disrupted gene, thn1, which encodes a putative regulator of G protein signaling (RGS) protein. Spontaneous insertion of scooter into genes with identifiable mutant phenotypes constitutes the first evidence of active transposition of a DNA-mediated transposon in a basidiomycete.     

Control of extracellular slime accumulation in monokaryons and resultant dikaryons of Schizophyllum commune.

Extracellular slime accumulation, as alcohol-precipitable material was measured after eight days of growth in glucose-asparagine-salts broth in twenty-two different monokaryons and six resultant dikaryons of Schizophyllum commune. The nutritional control of slime accumulation was also examined in monokaryotic mycelium. Slime occurred after growth in sucrose, glucose, fructose and xylose, with glycerol best. Low inorganic phosphates limited both slime and mycelial growth while limiting MgSO4 decreased growth and enhanced slime. In glucose-asparagine broth, various monokaryons differed widely in slime accumulation, ranging from none (e.g., strain 19) to nearly 800 mg per 100 ml filtrate (strain 1) after eight days growth, followed by a marked decline in slime (eleven days to twenty-one days). Resultant dikaryons all showed less slime accumulation, even when established from two high slime-accumulating monokaryons. In contrast, conditions which arrested dikaryotic fruit-body morphogenesis led to increased slime accumulation.