Induced azygospore formation in Mucor (Rhizomucor) pusillus by Absidia corymbifera

Attempts to determine the mating reaction type of heterothallic strains of Mucor pusillus in interspecific contrasts with Mucor strains of known mating reaction type were unsuccessful. Contrasts with Absidia corymbifera strains resulted in the production of azygospores in Mucor pusillus.     

SEXUAL REPRODUCTION AND INTERCROSSING IN VOLVULINA STEINW1

Gametes of Volvulina steinii bear near-apical mating papillae. Zygospore germination yields a single biflagellate cell that develops into a colony xuhose asexual progeny are all of the same mating type. Backcrossing of clones of progeny indicated a 1 :1 ratio of mating types among the progeny. Of 20 clones from a number of localities, none was homothallic and 3 showed no matins: reaction. Mating reactions of clones crossed in all possible combinations indicated the presence of 2 sexually isolated groups of clones producing smooth-walled zygospores and 1 group that produced spiny-walled zygospores. In the latter group weak and nonreciprocal mating reactions occurred in some clone combinations. Failure of germination of spiny-walled zygospores from certain crosses suggests further subdivision into genetically isolated groups.     

Synthesis and turnover of cell body-agglutinin as a pool of flagellar surface-agglutinin inChlamydomonas reinhardii gamete

Chlamydomonas reinhardii cells were broken in a French press and the soluble fraction was tested for agglutination activity. Deflagellated cell bodies ofmt ⁺ andmt ^- gametes yielded soluble fractions that were able to isoagglutinate gametes of the opposite mating type. When the wild-type gametes of opposite mating types were mixed, the cell body-agglutinins were used up during flagellar agglutination and subsequent cell fusion. When thefus mt ⁺ andmt ^- gametes agglutinated without successive fusion, the amount of cell body-agglutinins sharply decreased, then increased and reached the premixing level: the recovery was blocked by cycloheximide. When cells were treated with EDTA or trypsin, the cell body-agglutinins as well as flagellar surface-agglutinins were completely lost without apparent loss of motility. The EDTA extract contained the same amount of agglutinins as observed in the cell bodies before extraction, and this amount was about 100 times higher than that in the EDTA extract of isolated flagella. By the addition of trypsin inhibitor, the trypsinized gametes resynthesized the cell body-agglutinins. The process was sensitive to cycloheximide in both mating type gametes and to tunicamycin inmt ⁺ gametes.Abbreviations mt ^+/- mating type plus or minus - CHI cycloheximide - TI trypsin inhibitor - TM tunicamycin     

A NEW HOMOTHALLIC VARIETY OF CHLAMYDOMONAS MOEWUSH (CHLOROPHYCEAE)1

A new homothallic variety of Chlamydomonas moewusii Gerloff var. monoica is described. When first isolated, the alga exhibited a very strong mating reaction (80–90% zygotes on 2 wk BBM agar slants), but after 2 mo in axenic culture, the reaction was significantly reduced in intensity. Attempts were made to restore the initial mating intensity by varying environmental conditions, but met with limited success. The alga did not grow heterotrophically in carbon-supplemented BBM medium.     

ASYMMETRY OF EYESPOT AND MATING STRUCTURE POSITIONS IN ULVA COMPRESSA (ULVALES,CHLOROPHYTA) REVEALED BY A NEW FIELD EMISSION SCANNING ELECTRON MICROSCOPY METHOD1

Gametes of the marine green alga Ulva compressa L. are biflagellate and pear shaped, with one eyespot at the posterior end of the cell. The species is at an early evolutionary stage between isogamy and anisogamy. In the past, zygote formation of green algae was categorized solely by the relative sizes of gametes produced by two mating types (+ and ?). Recently, however, locations of cell fusion sites and/or mating structures of gametes have been observed to differ between mating types in several green algae (asymmetry of cell fusion site and/or mating structure positions). To use this asymmetry for determining gamete mating type, we explored a new method, field emission scanning electron microscopy (FE‐SEM), for visualizing the mating structure of U. compressa. When gametes were subjected to drying stress in the process of a conventional critical‐point‐drying method, a round structure was observed on the cell surfaces. In the mating type MGEC‐1 (mt⁺), this structure was located on the same side of the cell as the eyespot, whereas it was on the side opposite the eyespot in the mating type MGEC‐2 (mt^?). The gametes fuse at the round structures. TEM showed an alignment of vesicles inside the cytoplasm directly below the round structures, which are indeed the mating structures. Serial sectioning and three‐dimensional construction of TEM micrographs confirmed the association of the mating structure with flagellar roots. The mating structure was associated with 1d root in the MGEC‐1 gamete but with 2d root in the MGEC‐2 gamete.     

Binding of calmodulin to Nuf1p is required for karyogamy in<Emphasis Type="Italic"> Saccharomyces cerevisiae</Emphasis>

The role of calmodulin (CaM) during mating in Saccharomyces cerevisiae was examined by using a set of Phe-to-Ala substitutions. We identified ten CaM mutants that exhibited significantly reduced mating efficiencies when crossed to a strain of the opposite mating type harboring the same CaM mutation. Most of the mating-defective CaM mutants were bilateral, i.e., they also exhibited mating defects, albeit minor ones, when crossed to the wild type. When strains carrying different bilateral CaM mutations were mated, the mating efficiencies recovered dramatically. We termed this phenomenon "intragenic mating complementation", and classified the mating-defective CaM mutations into two intragenic mating complementation groups. Two mutant alleles belonging to different groups showed minor defects in cell adhesion and cell fusion, but exhibited severe defects in karyogamy. CaM is known to bind to the essential spindle pole body component Nuf1p. This binding appears to be important for karyogamy because the nuf1 ^C911R mutation, which impairs CaM-Nuf1p binding, resulted in a severe defect in karyogamy. Indeed, the two mating-defective CaM mutations were found to compromise formation of the CaM/Nuf1p complex, and the mating defects of these two CaM mutants were suppressible by a dominant, CaM-independent, mutation in NUF1. Taken together, these results suggest that loss of CaM binding to Nuf1p causes a defect in karyogamy, thereby inhibiting productive mating.Communicated by C. P. Hollenberg     

EVIDENCE FOR TUBULAR MATING STRUCTURES INDUCED IN EACH MATING TYPE OF HETEROTHALLIC GONIUM PECTORALE (VOLVOCALES,CHLOROPHYTA)1

Gametes were induced separately in cultures of each mating type of the heterothallic, isogamous colonial volvocalean Gonium pectorale O. F. Müll. to examine the tubular mating structure (TMS) of both mating types plus and minus (plus and minus), referred to as “bilateral mating papillae.” Addition of dibutyryl cyclic adenosine monophosphate (DcAMP or db‐cAMP) and 3‐isobutyl‐1‐methylxanthine (IBMX) to approximately 3‐week‐old cultures of each mating type induced immediate release of naked gametes from the cell walls. Both plus and minus gametes formed a TMS in the anterior region of the protoplasts. Accumulation of actin was visualized by antibody staining in the TMS of both mating types as occurs in the TMS (fertilization tubule) of the plus gametes of the unicellular volvocalean Chlamydomonas reinhardtii P. A. Dang. Induction of naked gametes with a TMS in each mating type will be useful for future cell biological and evolutionary studies of the isogametes of colonial volvocalean algae.     

Two tunicamycin-sensitive components involved in agglutination and fusion ofChlamydomonas reinhardtii gametes

To find out glycoproteins involved in the mating reaction ofChlamydomonas reinhardtii, the effect of tunicamycin (TM), a potent inhibitor of glycosylation of proteins, was studied. TM, when present during gametogenesis, blocked the acquisition of agglutinability ofmt ⁺ cells. TM also inhibited the recovery of agglutinability ofmt ⁺ gamete after trypsin treatment. On the contrary, TM blocked neither the acquisition of agglutination during gametogenesis ofmt ^- cells nor the recovery of their agglutinability after trypsinization. It was found, however, that the TM-treatedmt ^- gametes can agglutinate but do not fuse with non treatedmt ⁺ gametes at all. When gametes of gam-1mt ^-, a conditional mutant strain for cell fusion, were induced at non permissive temperature of 35°C and then transferred to 25°C, the ability of cell fusion was acquired after about 5 h incubation. Presence of TM completely blocked this acquisition. Based on these evidence, we conclude that at least two TM-sensitive glycoproteins are included in the mating reaction. The first component is located on the flagellar surface ofmt ⁺ gamete and responsible for agglutination withmt ^- flagella. The second component occurs on the surface ofmt ^- gamete and plays a role in the fusion withmt ⁺ gamete.Abbreviations CHI cycloheximide - mt mating type - TM tunicamycin     

Some properties ofSaccharomyces kluyveri

Four isolates of aSaccharomyces species which differed fromS. kluyveri by their ability to use cellobiose were analyzed genetically in relation to the latter species. Isolated single spores had low viability. Spore tetrads segregated mating types 2 2, with sexual agglutination occurring between complementary mating types. All single-spore isolates assimilated cellobiose indicating that these isolates were not naturally occurring hybrids betweenS. kluyveri and a cellobiose assimilatingSaccharomyces species.Two cell types were exhibited by single-spore cultures ofS. kluyveri, one granulated (G-type) and one vacuolated (g-type). G-type cultures formed fertile hybrids with complementary mating types of both G- and g-type cultures. Hybrids between two g-type cultures were sterile. They would, however, give fertile hybrids when mixed with G-type cultures.Sporulating hybrids betweenSaccharomyces sp. andS. kluyveri were produced. However the percentage spore germination was low. Single-spore cultures examined had cell types atypical of either parent. The ability to assimilate cellobiose was dominant and appeared to segregate with mating type and cell type.Weak mating reactions occurred when the (+) and (-) mating types ofSaccharomyces sp. were mixed with (a) and () mating types ofS. cerevisiae, respectively.The species ofSaccharomyces isolated from the Pacific Coast are designated as strains ofS. kluyveri.     

Sexual development in the homothallic green alga Chlamydomonas monoica Strehlow

In Chlamydomonas monoica, cell division and mating are interdependent processes, since under gametogenic conditions only newly born cells are mating competent. By refeeding nitrogen-starved cells with nitrate or ammonium ions, cell division and mating were synchronized. The mating competence of the progeny cells was dependent on the amount of the nitrogen source parent cells were refed, with an optimum around 0.1 mol·10⁵ cells. A second treatment with nitrate inhibited gametogenesis, but only when applied during the first part of the cell cycle, suggesting that an essential part of sexual development takes place during this period. During the latter part of the cell cycle, cells required light to acquire mating competence.     

Morphological and cytogenetic characteristics of intergroup hybrids between closely related mating groups of the Closterium ehrenbergii species complex (Desmidiales, Chlorophyta)

Five F₁ hybrid strains were established from rare survivors in intergroup crosses between three closely related mating groups (A, B and H) of the Closterium ehrenbergii Meneghini ex Ralfs species complex. Cell sizes of these five strains studied under our standard culture conditions were compared to those of their parental stains and also to the total range of cell-size variation in each mating group. All five F₁ strains were larger in mean cell width than their parental strains. In cell length, three of them were larger than, one was the same as, and the other was intermediate between their parental strains. Their cell sizes were always larger than the range of their respective smaller parental mating group and three of them were larger than the range of their respective larger parental mating group.     

A link between very long chain fatty acid elongation and mating-specific yeast cell cycle arrest

Ceramides and sphingolipid intermediates are well-established regulators of the cell cycle. In the budding yeast Saccharomyces cerevisae, the complex sphingolipid backbone, ceramide, comprises a long chain sphingoid base, a polar head group, and a very long chain fatty acid (VLCFA). While ceramides and long chain bases have been extensively studied as to their roles in regulating cell cycle arrest under multiple conditions, the roles of VLCFAs are not well understood. Here, we used the yeast elo2 and elo3 mutants, which are unable to elongate fatty acids, as tools to explore if maintaining VLCFA elongation is necessary for cell cycle arrest in response to yeast mating. We found that both elo2 and elo3 cells had severely reduced mating efficiencies and were unable to form polarized shmoo projections that are necessary for cell-cell contact during mating. They also lacked functional MAP kinase signaling activity and were defective in initiating a cell cycle arrest in response to pheromone. Additional data suggests that mislocalization of the Ste5 scaffold in elo2 and elo3 mutants upon mating initiation may be responsible for the inability to initiate a cell cycle arrest. Moreover, the lack of proper Ste5 localization may be caused by the inability of mutant cells to mobilize PIP₂. We suggest that VLCFAs are required for Ste5 localization, which is a necessary event for initiating MAP kinase signaling and cell cycle arrest during yeast mating initiation.     

Mating reaction in Saccharomyces cerevisiae VI. Effect of 2-deoxyglucose on conjugation

The effect of 2-deoxyglucose (2-dG) on the mating reaction ofSaccharomyces cerevisiae was investigated and the followingresults were obtained. 1) The cell fusion process of the mating reaction was completelyinhibited by 0.05% 2-dG added to a culture medium containing2% D-glucose. This inhibition was partially reversed by raisingthe glucose concentration in the medium. 2) Sexual cell agglutination was hardly affected by 2-dG. 3) 2-dG at concentrations inhibiting cell fusion considerablysuppressed the incorporation of ¹⁴C-glucose into the cell wallpolysaccharides, glucan and mannan. 4) Glucose uptake and protein synthesis were only slightly inhibitedby 2-dG. 5) No enhancement of bulk polysaccharide synthesis was detectedduring mating. ¹Present address: Biological Institute, Faculty of Science,Nagoya University, Chikusa-ku, Nagoya 464, Japan. (Received April 20, 1974; )     

Factors affecting the kinetics of progeny formation with F′lac in Escherichia coli K12

In matings of F′lac donors with an excess of recipient cells, different donor cells mated at different times. The concentration dependence of mating is incompatible with bimolecular reaction kinetics. In exponentially growing cultures, F′lac transfer from each donor cell continues to occur about once per generation. The establishment of F′lac in some recipient cells may take more than five generations.     

Nuclear transplant studies of the determination of mating type in germ nuclei of Paramecium tetraurelia

The micronucleus from vegetative cells of one mating type (O or E) in Paramecium tetraurelia was transplanted by micropipet into amicronucleate cells of opposite mating type (E or O). When autogamy was induced in the recipient cells, they developed new macronuclei and micronuclei derived from the transplanted micronucleus and usually expressed the same mating type as the recipients. The results indicate that micronuclei in the asexual phase may be undetermined for mating type. Recipient E cells in which the macronucleus had been previously removed were transplanted with a whole macronucleus from an O cell. Their mating type was soon transformed E to O before the occurrence of autogamy, and remained O after autogamy. This demonstrates that the transplanted macronucleus determined the O cytoplasmic state to determine the developing zygotic macronucleus for mating type O. It is unlikely that the micronucleus is determined for mating type in O or E cell during the asexual cycle.     

Mating-type Distribution and Fertility Status in Magnaporthe grisea Populations from Argentina

Isolates of Magnaporthe grisea causing gray leaf spot on rice were collected in Argentina and analyzed for mating distribution and fertility. One hundred and twenty-five isolates of M. grisea were collected from rice plants between 2000 and 2003. Each isolate was tested for mating type through a polymerase chain reaction based assay. All M. grisea isolates from Argentina belonged to a single mating type, MAT1.1. The fertility status of isolates was determined using controlled crosses in vitro, pairing each isolate with GUY11 and KA9 (MAT1.2 standard hermaphroditic testers). Production of perithecia was scarce among isolates of the blast pathogen since a low percentage of them (7.2%) developed perithecia with only one of the fertile tester (KA9); all crosses failed with the other tester strain. Asci and ascospores were not observed. The presence of only one mating type and the absence of female fertile isolates indicate that sexual reproduction is rare or absent in M. grisea populations associated with rice in Argentina.     

Mapping the mating type locus of Tetrahymena thermophila: Meiotic linkage of mat to the ribosomal RNA gene

Tetrahymena thermophila has a multiple mating type system. While a sexually mature cell usually expresses only one mating type, its germline (micronucleus) carries the genetic potential for 5 to 7 mating types. The set of allowed mating types is specified by the mat locus. The choice of which particular mating type is expressed by a cell reflects a somatically inherited, developmentally programmed differentiation of the somatic nucleus (macronucleus). In this work we report that the mat locus maps to the left arm of chromosome 2, as determined by nullisomic deletion mapping. We also report a distance of 29 cM between the mat locus and the ribosomal RNA gene, previously mapped to chromosome 2L. This represents another (rare) case of meiotic linkage in Tetrahymena. © 1992 Wiley-Liss, Inc.     

An inter‐oscillator mechanism modulating circadian clock period in paramecium populations

Abstract

In populations of the ciliate protozoan, Paramecium multimicronucleatum, the circadian‐clock‐con‐trolled mating reaction expressed by a limited number of cells among them feeds back to contribute to coherence of their circadian rhythms of motility and mating reaction. This eventually causes a decrease in the period of the rhythms from the entrained 24h period to a steady‐state period of about 22h, with the rate of decrease depending on the strength of the mating reaction. These results suggest that the interaction among oscillators may be one of the factors which modulate the period of a circadian clock composed of nearly identical oscillators. The clock‐controlled mating reaction provides a promising inter‐oscillator pathway for obtaining more insight into the mechanism of modulation of the period of such circadian clocks through inter‐oscillator interaction.     

A morphological study and hybridization analysis of Caloglossa leprieurii (Ceramiales, Rhodophyta) from Japan, Singapore and Australia

Morphological and hybridization experiments were performed on Caloglossa leprieurii (Montagne) J. Agardh collected from Japan, Singapore and Australia in order to evaluate taxonomic characters of this species. Within C. leprieurii at least four mating groups were recognized from the Indo-Pacific region. These mating groups could be characterized by the blade width at the inter-node and the cell-row numbers on the opposite side derived from the first axial cell at the main axis, though these properties showed a certain variability even in the same plant under both field and culture conditions. The phylogenetic relationship and geographic distribution of the four mating groups are discussed.     

Disentangling signaling gradients generated by equivalent sources

Yeast cells approach a mating partner by polarizing along a gradient of mating pheromones that are secreted by cells of the opposite mating type. The Bar1 protease is secreted by a-cells and, paradoxically, degrades the α-factor pheromones which are produced by cells of the opposite mating type and trigger mating in a-cells. This degradation may assist in the recovery from pheromone signaling but has also been shown to play a positive role in mating. Previous studies suggested that widely diffusing protease can bias the pheromone gradient towards the closest secreting cell. Here, we show that restricting the Bar1 protease to the secreting cell itself, preventing its wide diffusion, facilitates discrimination between equivalent mating partners. This may be mostly relevant during spore germination, where most mating events occur in nature.