桦纤孔菌有性生殖相关特征及交配型位点分析

对桦纤孔菌菌株MDJCBS88的显微形态、菌丝及担孢子核相进行了观察。采用棉籽壳培养基对担孢子萌发形成的菌株进行栽培试验,筛选出不形成子实体或子实体发育不完整的菌株,将这些菌株在平板上进行了亲和试验,分析桦纤孔菌的有性生殖方式;并基于基因组序列进行交配型基因克隆验证,分析桦纤孔菌的交配型位点结构。显微观察发现,桦纤孔菌菌丝没有锁状联合结构,菌丝细胞无核到多核;子实层担孢子可含0-4个不等的细胞核,不同时期弹射的担孢子含有的细胞核数量不同。桦纤孔菌担孢子萌发率极低,能萌发的担孢子多为早期弹射的担孢子;培养基也影响担孢子的萌发率,与PDA培养基和CYM培养基相比,桦木屑培养基最适合桦纤孔菌担孢子萌发,萌发率为4.55%。从担孢子萌发的96个菌株中获得了2个不结实菌株和9个结实不产孢菌株,占11.5%,这些菌株间亲和试验出现不同的表现特征,包括形成产孢子实体,产生菌丝纽结,相互融合和相互拮抗等现象,认为桦纤孔菌的有性生殖以次级同宗结合为主,并受交配型基因控制。交配型位点克隆测序后分析发现,桦纤孔菌交配型A位点共14 034 bp,含有一个MIP基因和两组HD1和HD2基因;交配型B位点包含3个疑似信息素受体基因和1个信息素前体编码基因。     

Clostridium cellulolyticum Viability and Sporulation under Cellobiose Starvation Conditions

Depending on the moment of cellobiose starvation, Clostridium cellulolyticum cells behave in different ways. Cells starved during the exponential phase of growth sporulate at 30%, whereas exhaustion of the carbon substrate at the beginning of growth does not provoke cell sporulation. Growth in the presence of excess cellobiose generates 3% spores. The response of C. cellulolyticum to carbon starvation involves changes in proteolytic activities; higher activities (20% protein degradation) corresponded to a higher level of sporulation; lower proteolysis (5%) was observed in cells starved during the beginning of exponential growth, when sporulation was not observed; with an excess of cellobiose, an intermediate value (10%), accompanied by a low level of sporulation, was observed in cells taken at the end of the exponential growth phase. The basal percentage of the protein breakdown in nonstarved culture was 4%. Cells lacking proteolytic activities failed to induce sporulation. High concentrations of cellobiose repressed proteolytic activities and sporulation. The onset of carbon starvation during the growth phase affected the survival response of C. cellulolyticum via the sporulation process and also via cell-cellulose interaction. Cells from the exponential growth phase were more adhesive to filter paper than cells from the stationary growth phase but less than cells from the late stationary growth phase.     

Chloroquine, a lysosomotropic agent, inhibits zygote formation in yeast

Haploid cells of opposite mating type of Saccharomyces cerevisiae conjugate to form zygote. During the conjugation process, the degradation or reorganization of the cell wall and the fusion of the two plasma membranes take place. Since chloroquine inhibits cellular events associated with the reorganization of the plasma membrane, the effect of the drug on conjugation was studied. Chloroquine at a concentration, at which cell growth was not retarded, inhibited zygote formation, while it did not affect other mating functions, such as sexual agglutination, production of and response to mating pheromone. Cells in a mating culture containing chloroquine formed no "prezygote" suggesting that they were not prepared for entering into fusion process. The inhibitory effect of chloroquine was reversible as cells formed zygote when they were washed after treatment with chloroquine. Zygote formation was unaffected in cells possessing chloroquine within vacuoles after incubation with the drug in complete medium (YPD) at pH 7.5, followed by washing. This suggests that chloroquine inhibits zygote formation by adsorbing to the plasma membrane of S. cerevisiae.     

The genetic control of cell growth and development in yeast Saccharomyces cerevisiae. Disturbed sporulation in diploids with decreased activity of the Ras/cAMP signal transduction pathway

Seven haploid strains (four with the MAT alpha mating type and three with the MATa mating type) were selected from the Peterhof genetic collection of yeast. Previous phenotypic analysis assigned six of these strains to a physiological group of strains with a lower activity of the Ras/cAMP signal transduction pathway. The haploids were crossed, and the resulting 12 diploids showed higher glycogen accumulation, tolerance to heat shock and nitrogen starvation, and sporulation in complete media. Ten of the diploids expressed the hypersporulation phenotype (higher sporulation efficiency). The phenotypic characters of these ten diploids suggested a reduced activity of the Ras/cAMP pathway. All 12 diploids were tested for sporulation and production of two groups of asci (those with one or two spores and those with three or four spores) as dependent on culture conditions (21, 30, or 34 degrees C; standard sporulation medium or a complete medium containing potassium acetate or glycerol in place of glucose). Sporulation proved to depend on temperature and medium composition. The results are collated with the data on yeast phenotypes associated with a lower activity of the Ras/cAMP signal transduction pathway.     

Metabolism of myo-inositol during sporulation of myo-inositol-requiring Saccharomyces cerevisiae.

We investigated the sporulation properties of a series of diploid Saccharomyces cerevisiae strains homozygous for inositol auxotrophic markers. The strains required different amounts of inositol for the completion of sporulation. Shift experiments revealed two phases of inositol requirement during sporulation which coincided with the two phases of lipid synthesis found by earlier workers. Phase I was at the beginning and during premeiotic deoxyribonucleic acid synthesis; phase II immediately preceded the appearance of mature asci. Of the inositol taken up by sporulating cells, 90% was incorporated into inositol phospholipids. By two-dimensional thin-layer chromatography, eight compounds were resolved, one of which was sporulation specific. The majority of the inositol phospholipids were, however, identical to those found in vegetatively growing cells. In the absence of inositol, the cells did not sporulate but, after a certain time, were unable to return to vegetative growth. These nonsporulating cells did, however, incorporate acetate into lipids and double their deoxyribonucleic acid content in the premeiotic phase. We believe that it is this lack of coordination of biosynthetic events which causes inositol-less death on sporulation media without inositol.     

Factors influencing response of flying Prostephanus truncatus to its male-produced aggregation pheromone

Abstract. The effects of age, sex, mating status, pre-exposure to pheromone, resource (diet) quality, and starvation on the response of Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) to its male-produced aggregation pheromone were investigated.Age was an important factor determining the level of response to pheromone: young adults were more responsive than older adults.The suitability of the resource in which P.truncatus is present affected its dispersal tendency, but not its sensitivity to pheromone per se. Sex, mating status, brief prior exposure to pheromone, and starvation did not influence the response of the larger grain borer to pheromone.The orientation behaviour of the beetle is described, and it is proposed that the pheromone primarily functions as a 'suitable resource location and colonization signal'.     

Role of metabolism of the mating pheromone in sexual differentiation of the heterobasidiomycete Rhodosporidium toruloides.

A trypsin-type endopeptidase (Kamiya et al., Biochem. Biophys. Res. Commun. 94:855-860, 1980) responsible for the metabolism of rhodotorucine A, the farnesyl undecapeptide mating pheromone secreted by mating type A cells of Rhodosporidium toruloides, was biologically characterized. Metabolic activity was found to be present exclusively on the cell surface of the pheromone target cell. The activity was highly specific to the pheromone, and a biologically inactive analog which has the complete amino acid sequence of rhodotorucine A but lacks the farnesyl residue was not metabolized by intact cells. Pheromone metabolism was inhibited by trypsin substrates such as tosyl-L-arginine methyl ester. The presence of tosyl-L-arginine methyl ester strongly inhibited the sexual differentiation induced by the pheromone at a concentration which did not affect the vegetative growth of R. toruloides. Pheromone-induced sexual differentiation was also strongly inhibited by a metabolizable analog, rhodotorucine A S-oxide, but not by a non-metabolizable one. In mutants defective in early processes of mating, the decrease in the pheromone metabolic activity correlated well with the extent of loss of sensitivity to the pheromone. Both the pheromone metabolism and the capacity for sexual differentiation of a sterile mutant were restored concomitantly with reversion from the sterile to the fertile phenotype. These results suggested that metabolism of the mating pheromone plays an essential role in the process of sexual differentiation in R. toruloides.     

The Genetic Control of Cell Growth and Development in Yeast Saccharomyces cerevisiae: Disturbed Sporulation in Diploids with a Decreased Activity of the Ras/cAMP Signal Transduction Pathway

Seven haploid strains (four with the MAT mating type and three with the MATa mating type) were selected from the Peterhof genetic collection of yeast. Previous phenotypic analysis assigned six of these strains to a physiological group of strains with changed activity of the Ras/cAMP signal transduction pathway. The haploids were crossed, and the resulting 12 diploids showed higher glycogen accumulation, tolerance to heat shock and nitrogen starvation, and sporulation in complete media. Ten of the diploids expressed the hypersporulation phenotype (higher sporulation efficiency). The phenotypic characters of these ten diploids suggested a reduced activity of the Ras/cAMP pathway. All 12 diploids were tested for sporulation and production of two groups of asci (those with one or two spores and those with three or four spores) as dependent on culture conditions (21, 30, or 34°C; standard sporulation medium or a complete medium containing potassium acetate or glycerol in place of glucose). Sporulation proved to depend on temperature and medium composition. The results are collated with the data on yeast phenotypes associated with a lower activity of the Ras/cAMP signal transduction pathway.     

Influence of glutamate on growth, sporulation, and spore properties of Bacillus cereus ATCC 14579 in defined medium

A chemically defined medium in combination with an airlift fermentor system was used to study the growth and sporulation of Bacillus cereus ATCC 14579. The medium contained six amino acids and lactate as the main carbon sources. The amino acids were depleted during exponential growth, while lactate was metabolized mainly during stationary phase. Two concentrations of glutamate were used: high (20 mM; YLHG) and low (2.5 mM; YLLG). Under both conditions, sporulation was complete and synchronous. Sporulation started and was completed while significant amounts of carbon and nitrogen sources were still present in the medium, indicating that starvation was not the trigger for sporulation. Analysis of amino acids and NH4+ in the culture supernatant showed that most of the nitrogen assimilated by the bacteria was taken up during sporulation. The consumption of glutamate depended on the initial concentration; in YLLG, all of the glutamate was used early during exponential growth, while in YLHG, almost all of the glutamate was used during sporulation. In YLLG, but not in YLHG, NH4+ was taken up by the cells during sporulation. The total amount of nitrogen used by the bacteria in YLLG was less than that used by the bacteria in YLHG, although a significant amount of NH4+ was present in the medium throughout sporulation. Despite these differences, growth and temporal expression of key sigma factors involved in sporulation were parallel, indicating that the genetic time frames of sporulation were similar under both conditions. Nevertheless, in YLHG, dipicolinic acid production started later and the spores were released from the mother cells much later than in YLLG. Notably, spores had a higher heat resistance when obtained after growth in YLHG than when obtained after growth in YLLG, and the spores germinated more rapidly and completely in response to inosine, l-alanine, and a combination of these two germinants.     

The Effect of Ochre Suppression on Meiosis and Ascospore Formation in Saccharomyces

The effect of altered tyrosyl-tRNAs on the developmental process of sporulation was examined. Mutations in eight independent loci resulting in tyrosine-inserting nonsense suppressor were tested for their effects on sporulation. Different levels of inhibition were found ranging from SUP3-omicron, which caused the greatest reduction of sporulation (7-17% of wild type), to SUP11-omicron which caused no reduction in sporulation. Since the SUP3-omicron mutation exhibited the greatest effect, it was studied in detail. Although SUP3-omicron is a dominant nonsense suppressor, its effect on sporulation is recessive. Expression of the sporulation deficiency is dependent upon the stage of transfer from glucose growth medium (i.e., log, early stationary, etc.) to sporulation medium. SUP3-omicron/SUP3-omicron diploid cells transferred from log or early stationary phase are capable of sporulation, whereas cells transferred after early stationary phase (i.e., after adaptation to respiration) exhibit poor sporulative ability. Sporulation events were examined under restrictive conditions to observe those events completed by SUP3-omicron/SUP3-omicron diploids. The early events of sporulation occur in these cells. Later events are completed by progressively fewer cells. Premeiotic DNA synthesis occurred in approximately 40% of the cells, nuclear segregation occurred in 20%, and finally, only 2% formed asci. The fact that fewer late-sporulation events occur under restrictive conditions can be explained by increased efficiency of suppression.     

In vivo regulation of histidine ammonia-lyase activity from Streptomyces griseus.

The enzyme histidine ammonia-lyase (histidase) is required for growth of Streptomyces griseus on L-histidine as the sole source of nitrogen. Histidase was induced by the inclusion of histidine in the medium, regardless of the presence of other carbon and nitrogen sources. Histidase activity was increased by a shift of culture incubation temperature from 30 to 37 degrees C. Conversely, upon induction of sporulation by either phosphate starvation or nutritional downshift, histidase underwent rapid inactivation. Nutrient replenishment fully reversed histidase inactivation while simultaneously permitting reinitiation of vegetative growth. In contrast to histidase inactivation during sporulation, histidase was activated after transition of a vegetatively growing culture to stationary phase. Although neither activation nor inactivation required de novo protein synthesis, inactivation appeared to involve a heat-labile protein. The results indicate that histidase activity is regulated in vivo by a process that responds to changes in the growth phase of the organism.     

Methionine Induces Sexual Development in the Fission Yeast Schizosaccharomyces pombe via an ste11-Dependent Signalling Pathway

Methionine added to minimal medium overcomes the repressing effects of ammonium and cyclic AMP (cAMP) on sexual development and efficiently induces mating and sporulation in homothallic strains of Schizosaccharomyces pombe. In heterothallic strains it induces G₁ arrest when cells enter stationary phase. We show that methionine reduces the intracellular cAMP pool and induces the expression of at least two cAMP-repressible genes, including fbp1 and ste11. The easiest interpretation of the results is that methionine induces sexual development via a cAMP-dependent ste11 signalling pathway.     

Transient increase of Ca2+ uptake as a signal for mating pheromone-induced differentiation in the heterobasidiomycetous yeast Rhodosporidium toruloides.

The role of Ca2+ for the signaling of rhodotorucine A, a mating pheromone of Rhodosporidium toruloides, was investigated. The efficiency with which the target cells responded to the mating pheromone was dependent on the Ca2+ concentration in the medium. The pheromone induced a very rapid and transient increase of Ca2+ uptake in the recipient cell. We concluded that the transient increase in the intracellular Ca2+ concentration could play an essential role in the control of differentiation by the pheromone.     

Rapamycin specifically interferes with the developmental response of fission yeast to starvation.

Rapamycin is a microbial macrolide which belongs to a family of immunosuppressive drugs that suppress the immune system by blocking stages of signal transduction in T lymphocytes. In Saccharomyces cerevisiae cells, as in T lymphocytes, rapamycin inhibits growth and cells become arrested at the G1 stage of the cell cycle. Rapamycin is also an effective antifungal agent, affecting the growth of yeast and filamentous fungi. Unexpectedly, we observed that rapamycin has no apparent effect on the vegetative growth of Schizosaccharomyces pombe. Instead, the drug becomes effective only when cells experience starvation. Under such conditions, homothallic wild-type cells will normally mate and undergo sporulation. In the presence of rapamycin, this sexual development process is strongly inhibited and cells adopt an alternative physiological option and enter stationary phase. Rapamycin strongly inhibits sexual development of haploid cells prior to the stage of sexual conjugation. In contrast, the drug has only a slight inhibitory effect on the sporulation of diploid cells. A genetic approach was applied to identify the signal transduction pathway that is inhibited by rapamycin. The results indicate that either rapamycin did not suppress the derepression of sexual development of strains in which adenylate cyclase was deleted or the cyclic AMP-dependent protein kinase encoded by pka1 was mutated. Nor did rapamycin inhibit the unscheduled meiosis observed in pat1-114 mutants. Overexpression of ras1+, an essential gene for sexual development, did not rescue the sterility of rapamycin-treated cells. However, expression of the activated allele, ras1Val17, antagonized the effect of rapamycin and restored the ability of the cells to respond to mating signals in the presence of the drug. We discuss possible mechanisms for the inhibitory effect of rapamycin on sexual development in S. pombe.     

Sexual co-flocculation by heterothallic cells of the fission yeast Schizosaccharomyces pombe modulated by medium constituents

Novel simple synthetic media for inducing sexual co-flocculation in a short time after mixing heterothallic fission-yeast (Schizosaccharomyces pombe) cells of h^- and h⁺ were devised; The most effective of these, mannose synthetic medium (MSM), contains 0.4% mannose as a carbon source in addition to galactose, KH₂PO₄ (pH4.0) and 4 vitamins. The addition of galactose to the medium suppressed the asexual self-flocculation but rather promoted the sexual co-flocculation. By transferring and mixing h^- and h⁺ cells grown in malt-extract broth plus galactose into MSM, these heterothallic strains were revealed to be sexually ready through a long period of the log to stationary phases. Furthermore, a variety of C sources and NH₄Cl at various concentrations in various media were examined for their effects upon sexual co-flocculation, conjugation and sporulation; it was found that the sugar concentration strictly affected the progress of the sequence of sexual reproduction at 26°C but not 30°C and that sexual co-flocculation of the heterothallic strains was induced only under lower concentrations of C and N source than that for the homothallic one.     

Mutants of the fission yeast Schizosaccharomyces pombe which alter the shift between cell proliferation and sporulation

Summary Mutants of S. pombe have been isolated which undergo conjugation and sporulation in rich medium, conditions which are normally inhibitory for these processes. Two of these mutants are also able to sporulate from the haploid state in the absence of heterozygosity at the mating type locus. These recessive mutants define a single nuclear gene called ran1 which is unlinked to mating type. It is proposed that the ran1 gene codes for an inhibitor in the control of the initiation of conjugation and sporulation. In wild type cells the inhibitory effect is released by nutritional starvation and heterozygosity at the mating type locus. This allows the cells to proceed to sporulation. The ran1 mutants are unusual in that they attempt to undergo a reductional meiotic division from the haploid state. They are also genetically unstable and generate extragenic suppressors at high frequency.     

Antagonism between sexual and natural selection in experimental populations of Saccharomyces cerevisiae

Trade-offs between life-history components are a central concept of evolution and ecology. Sexual and natural selection seem particularly apt to impose antagonistic selective pressures. When sex is not integrated into reproduction, as in Saccharomyces cerevisiae, natural selection can impair or even eliminate it. In this study, a genetic trade-off between the sexual and asexual phases of the yeast life cycle was suggested by sharp declines in the mating and sporulation abilities of unrelated genotypes that were propagated asexually in minimal growth medium and in mice. When sexual selection was applied to populations that had previously evolved asexually, sexual fitness increased but asexual fitness declined. No such negative correlation was observed when sexual selection was applied to an ancestral strain: sexual and asexual fitness both increased. Thus, evolutionary history affected the evolution of genetic correlations, as fitness increases in a population already well adapted to the environment were more likely to come at the expense of sexual functions.