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.     

Ustilago maydisMating Hyphae Orient Their Growth toward Pheromone Sources

Snetselaar, K. M., Bölker, M., and Kahmann, R. 1996.Ustilago maydismating hyphae orient their growth toward pheromone sources.Fungal Genetics and Biology20,299–312. When small drops ofUstilago maydissporidia were placed 100–200 μm apart on agar surfaces and covered with paraffin oil, sporidia from one drop formed thin hyphae that grew in a zig-zag fashion toward the other drop if it contained sporidia making the appropriate pheromone. For example,a2b2mating hyphae grew towarda1b1anda1b2mating hyphae, and the filaments eventually fused tip to tip. Time-lapse photography indicated that the mating hyphae can rapidly change orientation in response to nearby compatible sporidia. When exposed to pheromone produced by cells in an adjacent drop, haploid sporidia with thea2allele began elongating before sporidia with thea1allele. Sporidia without functional pheromone genes responded to pheromone although they did not induce a response, and sporidia without pheromone receptors induced formation of mating hyphae although they did not form mating hyphae. Diploid sporidia heterozygous atbbut not ataformed straight, rigid, aerial filaments when exposed to pheromone produced by the appropriate haploid sporidia. Again, thea2a2b1b2strain formed filaments more quickly than thea1a1b1b2strain. Taken together, these results suggest that thea2pheromone diffuses less readily or is degraded more quickly than thea1pheromone.     

Mating agglutination of cilia detached from complementary mating types of Paramecium

Cell-free preparations of mating-reactive cilia were obtained from complementary mating types of Paramecium caudatum with the treatment of the cells in a Triton X-100 solution and then in a Ca solution. When the cilia from both mating types thus obtained were mixed, strong agglutination was observed.     

Changes in photoreceptor currents and their sensitivity to the chemoeffector tryptone during gamete mating in<Emphasis Type="Italic"> Chlamydomonas reinhardtii</Emphasis>

Chlamydomonas reinhardtii Dangeard generates photoreceptor currents (PCs) upon light excitation. These currents play a key role in the signal transduction chain for photomotility responses. We have previously found that inhibition of PCs by tryptone occurs only in gametes that display chemotaxis toward this agent, and is not observed in chemotactically insensitive vegetative cells. Here we show that the sensitivity to tryptone is characteristic of gametes of both mating types, and examine the influence of gamete mating on PCs and their sensitivity to tryptone. The amplitude of PCs increases after cell fusion, but the sensitivity of these currents to tryptone decreases upon flagellar adhesion and/or an increase in the intracellular cAMP concentration. Net chemotaxis toward tryptone is reduced in young zygotes compared to gametes. We conclude that gamete mating leads to rapid inactivation of a gamete-specific chemosensory system.     

Trichoderma hamatum: Its hyphal interactions withRhizoctonia solani andPythium spp.

The mode of hyphal interaction and parasitism ofPythium spp. andRhizoctonia solani byTrichoderma hamatum was studied by both phase-contrast and Nomarski differential interference-contrast microscopy. Directed growth of the mycoparasite toward its host was observed. In the area of interaction,T. hamatum produced appressorial-like structures attached to the host cell wall. Subsequently, several different types of interactions occurred.T. hamatum either grew parallel to and along the host hypha or coiled around its host. In the contrast regions the parasite formed bulbular or hook-like structures that contained granular cytoplasm. In other cases the parasite penetrated into and grew within the mycelium ofR. solani orP. ultimum. As a consequence of the attack, the host hypha became vacuolated, shrank, collapsed, and finally disintegrated. These observations suggest the involvement of parasitism followed by lysis rather than involvement of antibiotics in this host-mycoparasite relationship.     

Mating-type differentiation in ascosporogenous yeasts on the basis of mating-type-specific substances responsible for sexual cell-cell recognition

Summary Sexual agglutination occurred only between cells of opposite mating types of the same species in all the Sacharomyces, Hansenula, Saccharomycodes, and Pichia yeasts tested. We succeeded in solubilizing the sex-specific glycoprotein, cell wall agglutination substance responsible for sexual agglutinability by briefly autoclaving these yeasts. The agglutination substances of all the above yeasts were univalent and sensitive to the enzyme pronase. The formation of complementary complexes was observed only between agglutination substances of opposite mating types of the same species. In general, the agglutination substance of one mating type was more resistant to heat treatment at 100°C in 3% acetic acid and more sensitive to 5% 2-mercaptoethanol treatment than the agglutination substance of the other mating type in these yeasts. On the basis of these results together with the pheromone response and production, we expect that almost all ascosporogenous yeasts can be classified into the two mating types corresponding to a and mating types in Saccharomyces cerevisiae, respectively.     

Interspecies sex-specific growth responses inKluyveromyces

The sex-specific growth factors produced by thea and mating types ofKluyveromyces lactis were examined for interspecies cross-reactivity on growing cells ofKluyveromyces aestuarii andKluyveromyces delphensis. Taxonomically,K. aestuarii is closely related toK. lactis;K. delphensis is more distantly related. Reciprocal growth responses occurred betweenK. aestuarii and the a mating type ofK. lactis; no response was evident betweenK. delphensis and either sex ofK. lactis.     

Multiple allelic incompatibility factors among bifactorial strains of the yeastLeucosporidium (Candida) scottii

A biallelic, unifactorial, sexual incompatibility system, consisting of two mating types, is characteristic of the ascomycetous yeasts, such asSaccharomyces cerevisiae. In addition to the biallelic system, the basidiomycetous yeasts,Rhodosporidium andLeucosporidium have a multiple allelic bifactorial system with 2 A and 2B factors for a total of four mating types. This report presents evidence for an increase in this number of mating types inLeucosporidium scottii due to the presence of a minimum of 5 A and 3 B specificities with linked loci at each factor. These results indicate that sexual incompatibility system in basidiomycetous yeasts is similar to that found in other basidiomycetes such asSchizophyllum commune.     

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     

Hybridization and sexual stimulation inTrichophyton mentagrophytes

Mating and sexual stimulation tests applied to 132 strains of this dermatophyte isolated in Czechoslovakia revealed among them strains ofArthroderma benhamiae (40 strains of the+mating type, one of the—mating type) andA. vanbreuseghemii (three strains of the+type, seven of the-type). No dependence was found concerning the anamorphic variety (T. mentagrophytes var.granulosum, var.interdigitale, var.mentagrophytes, var.quinckeanum), teleomorphic species, mating type and the clinical localization of dermatophytosis. Plausible reasons of different frequencies of the mating types are discussed.     

Molecular Polymorphism in the MTA and MTB Mating Type Genes of Tetrahymena thermophila and Related Asexual Species

Each of the seven mating types of Tetrahymena thermophila is determined by a pair of large genes, MTA and MTB, whose expression peaks at early conjugation. Each protein consists of a mating‐type specific domain and a common transmembrane domain. To assess variation in natural populations, regions of both domains from wild isolates expressing mating types V and VII were analyzed. Corresponding regions of amicronucleates incapable of mating also were examined. MTA and MTB showed high haplotype diversity, with greater sequence variation in MTB. Mating type VII was less variable than mating type V, suggesting more recent origin. No polymorphism distinguished between mat1‐ and mat2‐like alleles encoding different arrays of mating types, nor did polymorphisms give evidence of population structure. MTA and MTB variants have different phylogenies, suggesting independent rather than concerted evolution, and are under weak purifying selection. Codon usage is less biased than for housekeeping genes, and reassigned glutamine encoding stop codons are preferentially used. Amicronucleate T. thermophila and closely related nsp15 and nsp25 have higher levels of nucleotide and amino acid substitution, consistent with cox1 distances. The results suggest that complete sequencing of mating type genes of wild isolates coupled with functional analysis will be informative.     

Role of genital sex pheromones inAmblyomma americanum andA. maculatum (Acari: Ixodidae)

Amblyomma americanum andA. maculatum were studied to determine if genital sex pheromones were present, as reported inDermacentor species. Chemical analysis of methanol extracts of the anterior reproductive tracts (source of the genital sex pheromone) ofA. americanum andA. maculatum confirmed the presence of the same fatty acids that act as components of the genital sex pheromone inDermacentor variabilis andD. andersoni. In bothAmblyomma species, removal of the anterior reproductive-tract of fed females eliminated the male copulatory response. ForA. americanum, use of anterior reproductive tract extracts made with water, methanol, ether and hexane elicited significant probing and copulatory responses by conspecific males. However, inA. maculatum, use of anterior reproductive-tract extracts made with water, methanol, ether, chloroform: methanol (41), hexane and pentane did not restore mating response by males. Treatment with known components ofDermacentor genital sex pheromones elicited weak but significant responses inA. americanum, but did not restore male mating responses inA. maculatum. These results indicate that genital sex pheromones exist inA. americanum and are not restricted to the genusDermacentor. Characteristics of theAmblyomma genital sex pheromone, however, do differ considerably from those inDermacentor. No genital sex pheromone was present inA. maculatum.     

Mating Reaction and its Daily Rhythm in Euplotes crassus*†

The agglutinative mating reaction of Euplotes crassus occurred without lag if complementary mating types were brought together under appropriate conditions. Only a small fraction of the cell population reacted at the beginning but the number of reacting cells steadily increased until firmly united pairs were formed after ～30 min. The intensity of the initial mating reaction changed rhythmically; the rhythm appeared circadian. Mating-type-specific soluble factors did not appear to participate in this reaction. The results strongly support the positive-feedback hypothesis of the mating reaction presented by Heckmann & Siegel in 1964. Patterns of preconjugant cell interactions of different ciliates are discussed.     

Leucosporidium gen. n., the heterobasidiomycetous stage of several yeasts of the genusCandida

Investigation of yeasts from Antarctic regions revealed that certain species ofCandida have heterobasidiomycetous life cycles. Two distinct but overlapping groups of species were found: heterothallic and self-sporulating species.Candida scottii is a heterothallic species with the following life cycle: opposite mating types will conjugate and develop a dikaryotic mycelium with clamp connections. Karyogamy occurs in the teliospore which germinates and produces a promycelium. Meiosis takes place in the promycelium, followed by development of haploid sporidia to complete the life cycle. In addition,C. scottii has a self-sporulating phase. From a single cell, in the apparent absence of mating, a uninucleate mycelium is produced that lacks clamp connections. Teliospores, promycelia and sporidia develop that appear similar to those produced from dikaryotic mycelium.The self-sporulating species have life histories similar to the self-sporulating phase ofC. scottii; except that heterothallism has not been observed.Based on these life histories the new genusLeucosporidium is proposed with two heterothallic species (Leu. scottii andLeu. capsuligenum) and five self-sporulating species (Leu. antarcticum, Leu. frigidum, Leu. gelidum, Leu. nivalis andLeu. stokesii. Leu. antarcticum) andLeu. stokesii have not been described under the genusCandida.Contribution No. 1138 from the Institute of Marine Sciences, University of Miami, Fla.This study was supported by the National Science Foundation through the Office of Antarctic Programs, Grant GA-3957. The authors are grateful to Dr. E. Marelli for editing the Latin diagnosis.     

Agglutinative mating types ofSaccharomyces transvaalensis

Agglutinative mating types ofSaccharomyces transvaalensis have been recovered from the type strain of this species. These mating types react with the corresponding opposite mating types obtained from two other strains of this species but do not react with one-spore cultures of the physiologically similar species,Saccharomyces dairensis. The dissimilarity of these two species is further confirmed by differences in the structure of their ascospores as observed in ultrathin sections by electron microscopy.     

Isolation of the mating-inducing factor of the ciliate Euplotes

Numerous strains of different mating types of the marine ciliate Euplotes raikovi have been found to be autonomous excreters into the surrounding medium of specific mating-inducing factors (gamones) (Luporini, P et al., J exp zool 226 (1983) 1 [9]). The gamone from the mating type represented by strain 13 has been isolated and identified as a glycoprotein with a molecular weight (MW) of about 12 kD and a pI of 4. It has been termed euplomone r 13. At a concentration of 3 × 10⁻¹² M, euplomone r 13 specifically induces cells of a complementary mating type to unite in conjugation within 2 h.     

STRONG ASSORTATIVE MATING BY DIET,COLOR, SIZE,AND MORPHOLOGY BUT LIMITED PROGRESS TOWARD SYMPATRIC SPECIATION IN A CLASSIC EXAMPLE: CAMEROON CRATER LAKE CICHLIDS

Models predict that sympatric speciation depends on restrictive parameter ranges, such as sufficiently strong disruptive selection and assortative mating, but compelling examples in nature have rarely been used to test these predictions. I measured the strength of assortative mating within a species complex of Tilapia in Lake Ejagham, Cameroon, a celebrated example of incipient sympatric adaptive radiation. This species complex is in the earliest stages of speciation: morphological and ecological divergence are incomplete, species differ primarily in breeding coloration, and introgression is common. I captured 27 mated pairs in situ and measured the diet, color, size, and morphology of each individual. I found strong assortative mating by color, size, head depth, and dietary source of benthic or pelagic prey along two independent dimensions of assortment. Thus, Ejagham Tilapia showed strong assortative mating most conducive to sympatric speciation. Nonetheless, in contrast to a morphologically bimodal Sarotherodon cichlid species pair in the lake, Ejagham Tilapia show more limited progress toward speciation, likely due to insufficient strength of disruptive selection on morphology estimated in a previous study (γ = 0.16). This supports the predicted dependence of sympatric speciation on strong assortment and strong disruptive selection by examining a potentially stalled example in nature.     

Members of two gene families encoding ubiquitin-conjugating enzymes, AtUBC1-3 and AtUBC4-6, fromArabidopsis thaliana are differentially expressed

Covalent attachment of ubiquitin to other intracellular proteins is essential for many physiological processes in eukaryotes, including selective protein degradation. Selection of proteins for ubiquitin conjugation is accomplished, in part, by a group of enzymes designated E2s or ubiquitin-conjugating enzymes (UBCs). At least six types of E2s have been identified in the plantArabidopsis thaliana; each type is encoded by a small gene family. Previously, we described the isolation and characterization of two three-member gene families, designatedAtUBC1-3 andAtUBC4-6, encoding two of these E2 types. Here, we investigated the expression patterns, of theAtUBC1-3 andAtUBC4-6 genes by the histochemical analysis of transgenicArabidopsis containing the corresponding promoters fused to the -glucuronidase-coding region. Staining patterns showed that these genes are active in many stages of development and some aspects of cell death, but are not induced by heat stress. Within the two gene families, individual members exhibited both overlapping and complementary expression patterns, indicating that at least one member of each gene family is expressed in most cell types and at most developmental stages. Different composite patterns of expression were observed between theAtUBC1-3 andAtUBC4-6 families, suggesting distinct biochemical and/or physiological functions for the encoded E2s inArabidopsis.     

Stable soil pH of thai mangroves in dry and rainy seasons and its relation to zonal distribution of mangroves

Soil characteristics of mangrove forests at Amphur Laemngob, Trat Province, east Thailand were investigated in both dry andrainy seasons. Sonneratia alba, Avicennia alba andRhizophora mucronata mainly grew as seaward mangroves.Rhizophora apiculata, Ceriops tagal, Excoecaria agallocha andBruguiera gymnorrhiza grew as meso mangroves in most cases.Lumnitzera racemosa was found as a landward mangrove. The salinity of the soil in which these 8 species grew was significantly higher in the dry season than in the rainy season. Soil pH did not change irrespective of the season. Each species seemed to grow at inherent soil pH. Bruguiera gymnorrhiza, Sonneratia alba andAvicennia marina were found both in Japan and Thailand. The soil pH of each mangrove species was similar in Japan and Thailand. The soil salinity of each mangrove species in Japan was similar to that in Thailand in the dry season. It was suggested that soil pH and salinity in the dry season are the important factors governing the zonal distribution of mangroves.     

Genetic analysis of mating type differentiation in Paramecium tetraurelia. III. A mutation restricted to mating type E and affecting the determination of mating type

In P. tetraurelia each cell is determined to express only one of the two complementary mating types, O and E. This determination is under cytoplasmic control and seems to be achieved only by the commitment or noncommitment to the expression of mating type E. All the previously known mutations affecting the differentiation of mating type prevent the expression of the E mating type (O-restricted mutations) without affecting the determination process. An E-restricted mutation was obtained: mtF^E. Its phenotypic properties indicate that the mutation affects the determination process itself. When an O cell becomes mtF^E/mtF^E it acquires the E mating type and an E-determining cytoplasm. We propose that this constitutive determination for the E mating type is due to the inefficiency of a factor which is normally active in an O cell. This factor would act like a repressor and stabilize the E functions under an inactive state.