Heritability of fumonisin B1 production in Gibberella fujikuroi mating population A.

Fumonisins are mycotoxins produced by strains belonging to several different mating populations of Gibberella fujikuroi (anamorphs, Fusarium section Liseola), a major pathogen of maize and sorghum worldwide. We studied the heritability of fumonisin production in mating population A by crossing fumonisin-producing strains collected from maize and sorghum in the United States with fumonisin-nonproducing strains collected from maize in Nepal. Random ascospore and tetrad progeny from three of these crosses were analyzed by gas chromatography-mass spectrometry and high-performance liquid chromatography for their ability to produce fumonisins on autoclaved cracked maize. In all three crosses, the ability to produce fumonisins, predominately fumonisin B1, segregated as a single gene or group of closely linked genes. Intercrosses between appropriate progeny and parents were poorly fertile, so we could not determine if the apparent single genes that were segregating in each of these crosses were allelic with one another. Mating type and spore-killer traits were scored in some crosses, and each segregated, as expected, as a single gene that was unlinked to the ability to produce fumonisins. We conclude that G. fujikuroi mating population A provides a powerful genetic system for the study of this important fungal toxin.     

Heritability of fumonisin B1 production in Gibberella fujikuroi mating population A.

Fumonisins are mycotoxins produced by strains belonging to several different mating populations of Gibberella fujikuroi (anamorphs, Fusarium section Liseola), a major pathogen of maize and sorghum worldwide. We studied the heritability of fumonisin production in mating population A by crossing fumonisin-producing strains collected from maize and sorghum in the United States with fumonisin-nonproducing strains collected from maize in Nepal. Random ascospore and tetrad progeny from three of these crosses were analyzed by gas chromatography-mass spectrometry and high-performance liquid chromatography for their ability to produce fumonisins on autoclaved cracked maize. In all three crosses, the ability to produce fumonisins, predominately fumonisin B1, segregated as a single gene or group of closely linked genes. Intercrosses between appropriate progeny and parents were poorly fertile, so we could not determine if the apparent single genes that were segregating in each of these crosses were allelic with one another. Mating type and spore-killer traits were scored in some crosses, and each segregated, as expected, as a single gene that was unlinked to the ability to produce fumonisins. We conclude that G. fujikuroi mating population A provides a powerful genetic system for the study of this important fungal toxin.     

Characterization of single nucleotide polymorphisms for a forward genetics approach using genetic crosses in C57BL/6 and BALB/c substrains of mice

Forward genetics is a powerful approach based on chromosomal mapping of phenotypes and has successfully led to the discovery of many mouse mutations in genes responsible for various phenotypes. Although crossing between genetically remote strains can produce F₂ and backcross mice for chromosomal mapping, the phenotypes are often affected by background effects from the partner strains in genetic crosses. Genetic crosses between substrains might be useful in genetic mapping to avoid genetic background effects. In this study, we investigated single nucleotide polymorphisms (SNPs) available for genetic mapping using substrains of C57BL/6 and BALB/c mice. In C57BL/6 mice, 114 SNP markers were developed and assigned to locations on all chromosomes for full utilization for genetic mapping using genetic crosses between the C57BL/6J and C57BL/6N substrains. Moreover, genetic differences were identified in the 114 SNP markers among the seven C57BL/6 substrains from five production breeders. In addition, 106 SNPs were detected on all chromosomes of BALB/cAJcl and BALB/cByJJcl substrains. These SNPs could be used for genotyping in BALB/cJ, BALB/cAJcl, BALB/cAnNCrlCrlj, and BALB/cCrSlc mice, and they are particularly useful for genetic mapping using crosses between BALB/cByJJcl and other BALB/c substrains. The SNPs characterized in this study can be utilized for genetic mapping to identify the causative mutations of the phenotypes induced by N-ethyl-N-nitrosourea mutagenesis and the SNPs responsible for phenotypic differences between the substrains of C57BL/6 and BALB/c mice.     

Cytoplasmic Inheritance of a Cell Surface Antigen in the Mouse

Mta is a cell surface antigen of the mouse and serves as a target for specific T killer lymphocytes. Using a killer cell assay, the antigen has been found in 72 strains of laboratory mice and, with one exception, in all tested samples of mice caught in the wild or bred from such, including Mus molossinus, Mus castaneus and Mus spretus. Five strains of rats, non-inbred NMRI mice, most substrains of NZB mice and the closely related strain NZO are negative for Mta. In reciprocal F₁ crosses between several Mta⁺ and two Mta^- strains, the antigen is maternally transmitted; that is, Mta⁺ females bear only positive offspring, whereas Mta^- females bear only negative offspring, regardless of the genotype of the male. Since 34 foster-nursed mice had the Mta type of their genetic mothers, the factor that determines expression of Mta must be transmitted before birth and not via the milk. The cytoplasmic genes of Mta⁺ strains have been combined with the chromosomal genes of Mta^- strains, and vice versa, by repeated backcrossing. All progeny retained the Mta type of their maternal lines. Thus, the Mta type is determined solely by maternal inheritance and is not influenced by chromosomal genes. We found no evidence of incompatibility between the cytoplasmic factors and nuclear genes of Mta^- and Mta ⁺ strains.     

Karyotype polymorphism correlates with intraspecific infertility in the homothallic ascomycete Sordaria macrospora

The homothallic fungus Sordaria macrospora produces perithecia with meiotically derived ascospores. In most cases, intraspecies crosses between strains from different culture collections generate fertile hybrid perithecia in the contact zone of two mycelia. However, in some of these crosses we observed a significant decrease in the fertility of the hybrid perithecia when strains of different origin were used for mating. Since we assumed that chromosome variability between the culture collection strains might contribute to this reduction in fertility, we performed pulsed‐field gel electrophoresis. In the course of our study, we were able to identify two major groups of electrophoretic karyotypes in S. macrospora culture collection strains. A quantitative analysis revealed that polymorphic karyotypes contribute to a reduction of fertility in forced crosses between strains carrying differently sized chromosomes. The observed intraspecific chromosome length polymorphism might have consequences on the speciation process of a homothallic fungus capable of sexual but not of asexual spore formation.     

江苏省稻瘟病菌有性态的研究*

用标准菌株对１９９７～１９９９年在江苏省吴江市,宜兴市、通州市、高邮市和赣榆县采集的３２５个猪瘟病菌单孢分离菌株的可育性和交配型进行了测定,结果表明江苏省稻瘟病菌菌株的育性较低,可交配率为２２．７７％,可育率仅为７．０８％。不同年份、不同地区采集的猪瘟病菌茵株的性亲和力和交配型有较大的差异,三年的交配率分别为２６．６１％、８．２６％和３３．６４％;温州地区和赣榆地区菌株的交配率相对较高,分别为２６．１５％和２５．４２％,宜兴地区菌株的交配率较低,只有１５．３８％。江苏省稻瘟病菌菌株的交配型在不同年份亦出现很大差别,１９９７年２９个可交配菌株中有２１个菌株表现为ＭＡＴ１－２ 交配型,而１９９９年３６个可交配茵株均为ＭＡＴ１－１交配型。用江苏省稻瘟病菌的可育菌株进行互交,２５个组合中只有６个组合能产生子囊壳和子囊,但均不产生子囊孢子,提示江苏省稻瘟病菌在田间产生健康有性后代的几率不大。对杂交后代的遗传学分析表明,菌株的交配型是受单基因控制的。     

Altered Mating-Type Identity in the Fungus Podospora Anserina Leads to Selfish Nuclei, Uniparental Progeny, and Haploid Meiosis

In wild-type crosses of the filamentous ascomycete Podospora anserina, after fertilization, only nuclei of opposite mating type can form dikaryons that undergo karyogamy and meiosis, producing biparental progeny. To determine the role played by the mating type in these steps, the four mat genes were mutagenized in vitro and introduced into a strain deleted for its mat locus. Genetic and cytological analyses of these mutant strains, crossed to each other and to wild type, showed that mating-type information is required for recognition of nuclear identity during the early steps of sexual reproduction. In crosses with strains carrying a mating-type mutation, two unusual developmental patterns were observed: monokaryotic cells, resulting in haploid meiosis, and uniparental dikaryotic cells providing, after karyogamy and meiosis, a uniparental progeny. Altered mating-type identity leads to selfish behavior of the mutant nucleus: it migrates alone or paired, ignoring its wild-type partner in all mutant X wild-type crosses. This behavior is nucleus-autonomous because, in the same cytoplasm, the wild-type nuclei form only biparental dikaryons. In P. anserina, mat genes are thus required to ensure a biparental dikaryotic state but appear dispensable for later stages, such as meiosis and sporulation.     

Genetic analysis ofCochliobolus heterostrophus polyoxin-resistant mutants

Nine polyoxin-resistant mutants ofCochliobolus heterostrophus were isolated after ethyl methanesulphonate mutagenesis. All were highly resistant to polyoxin (MIC≥1,600 ppm). Crosses between the mutants and a wild-type strain revealed that the resistance trait was inherited to the offsprings in different fashions. Four of the mutant strains inherited polyoxin resistance in a 1∶1 segregation ratio, indicating that the phenotypes in these strains were due to alteration at a single locus. Allelism tests revealed four new loci,Pol1, Pol2, Pol3 andPol4, for polyoxin resistance in these mutant strains. The genes responsible for the phenotypes of the other five mutant strains were not determined, because of extremely slow growth of progenies in one cross, sterility in another cross, and inexplicable responses to polyoxin of the progenies in the other crosses. No linkage was detected between the genes for polyoxin resistance and mating type.     

C-band polymorphisms in exotic inbred strains of mice: a method for mapping centromeric ends of chromosomes.

The major satellite DNA of Mus musculus appears as a pericentromeric heterochromatin block in all chromosomes but the Y. While C-banding readily reveals the presence of this heterochromatin block, there is considerable polymorphism in C-band size among the chromosomes and among different subspecies. We have studied the distribution of C-band size differences in the chromosomes of 15 exotic inbred laboratory strains and substrains derived from wild populations of different subspecies of M. musculus. The variation in C-band size among these inbred strains can serve as a useful codominant cytological marker for estimating recombinational distances between the centromere and proximal genes in linkage crosses.     

Hybridization between Japanese and North American Chlamydomonas reinhardtii (Volvocales,Chlorophyceae)

The microalga Chlamydomonas reinhardtii is a model organism whose whole genome has been sequenced. Although considered a cosmopolitan species, only eastern North American isolates of C. reinhardtii were available before 2010, when new Japanese isolates were reported. In the study describing the new Japanese isolates, zygote formation between Japanese and North American strains was shown, but germination was not demonstrated. In this study, the germination of intercontinental hybrid zygotes was examined using wild‐type Japanese strains and mutant American strains that cannot utilize nitrate. Several clonal progeny strains were established, and the progeny strains were screened based on mating type and nitrate utilization to confirm their hybrid nature. The establishment of four intercontinental hybrid strains with different phenotypic combinations was confirmed by sequencing mating type‐specific and nitrate reductase‐related genes. The potential for hybrid formation between Japanese and North American strains suggests the existence of a worldwide mating population of C. reinhardtii.     

Neurospora species in bakeries

S. YASSIN AND A. WHEALS. 1992. Neurospora species may occur as spoilage organisms in bakeries and bakery products. A survey of two bakeries over a 4 month period produced 315 individually isolated strains which were characterized with respect to six features: conidial colour, protoperitheciality, mating type and percentage dark-coloured (fertile) ascospores in crosses with type specimens of Neurospora crassa, N. sitophila and N. intermedia. We concluded that (i) N: crassa of both mating types was by far the most abundant but N. sitophila and N. intermedia were also represented; (ii) conidial colour was not a good species criterion; (iii) the percentage of fertile ascospores produced in crosses with several type specimens provided a reliable and simple species indicator; (iv) identification of individuals based on these six characteristics suggested that a large number of genetically different organisms were present in the collection; and (v) bakery infection was not due to endemic contamination in the bakery or in raw materials but from repeated external infection, perhaps on contaminated returned goods.     

Characterization of Fusarium spp. associated with pineapple fruit rot and leaf spot in Peninsular Malaysia

Pineapple (Ananas comosus) is one the important fruit crops planted in Malaysia, and this study was conducted to determine Fusarium spp. associated with diseases of the fruit crop as Fusarium is prevalent in tropical countries. Our objective was to identify and characterize Fusarium spp. associated with pineapple fruit rot and leaf spot mainly found on the fruits and leaves in Peninsular Malaysia. Fusarium isolates (n = 108) associated with pineapple fruit rot and leaf spot were characterized by morphological, molecular and phylogenetic analyses, a mating study and pathogenicity testing. TEF‐1α sequence analysis identified Fusarium proliferatum, Fusarium verticillioides, Fusarium sacchari and Fusarium sp. Mating was successful only between tester strains of F. proliferatum and F. verticillioides. Sexual crosses with standard tester strains showed that 82 isolates of F. proliferatum produced fertile crosses with mating population D (Gibberella intermedia) and three isolates of F. verticillioides were fertile with the tester strain of mating population A (Gibberella moniliformis). All isolates were pathogenic, causing pineapple fruit rot and leaf spot, thus fulfilling Koch's postulates.     

Isolation of plasmids carrying the arginine repressor gene argR of Escherichia coli K12

Summary Twenty-two sexual crosses between strains of Phycomyces blakesleeanus carrying mutations affecting phototropism (madA, madD, madE), synthesis of carotenoids (carA), auxotrophy (leu-51, nicA, pur-51), and resistance to 5-fluorouracil (fur) were studied; mating type was also included as a marker. Recombination frequencies were obtained among the ten genes involved. Linkage was found between mating type and madE; leu-51 and madA; furA401, furB402 and madD. All other gene combinations tested are unliked.     

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.     

Heredity and genetic mapping of domestication-related traits in a temperate japonica weedy rice

Rice is often found as various weedy forms in temperate or newly cultivated rice growing regions throughout the world. The emergence of these forms in the absence of true wild rice remains unclear. A genetic analysis of domestication-related traits (weed syndrome) has been conducted to better understand the appearance of these plants in rice fields. A doubled haploid (DH) population was derived from a cross between a japonica variety and a weedy plant collected in Camargue (France) to set up a genetic linkage map consisting of 68 SSR and 31 AFLP loci. Five qualitative traits related to pigmentation of different organs and 15 developmental and morphological quantitative traits were scored for genes and QTLs mapping. Despite a good reactivity in anther culture and a high fertility of the DH lines, segregation distortions were observed on chromosomal segments bearing gametophytic and sterility genes and corresponded to various QTLs evidenced in indica×japonica distant crosses. Mapping of the coloration genes was found to be in agreement with the presence of several genes previously identified and according to the genetic model governing the synthesis and distribution of anthocyan pigment in the plant. In addition, the main specific traits of weedy forms revealed the same genes/QTLs as progeny derived from a cross between Oryza sativa and its wild progenitor O. rufipogon. A large variation for most characters was found in the DH population, including transgressive variation. Significant correlations were observed between morphology and traits related to weeds and corresponded to a distinct colocalization of most of the QTLs on a limited number of chromosomal regions. The significance of these results on the origin of weedy forms and the de-domestication process is discussed. Received: 25 February 2000 / Accepted: 14 April 2000     

Sexual fertility of fortyFusarium strains from the EuropeanFusarium sambucinum project

Fungus strains designated asFusarium sambucinum, F. torulosum, orFusarium sp. nov. were crossed withMAT1-1 andMAT1–2 tester strains ofGibberella pulicaris. Of the 40 field strains that were crossed with the tester strains, 13 strains produced fertile crosses and 27 strains did not produce fertile crosses. One strain designated asF. torulosum was fertile with a tester strain ofG. pulicaris, suggesting that this is an intraspecies cross and that the strain isG. pulicaris, and, consequently,F. sambucinum rather thanF. torulosum. The lack of fertile crosses between tester strains and 27 of the 40 field strains suggests that these strains are notG. pulicaris. Although the ability to form a fully fertile cross with a tester strain can determine the species of a fertile strain, it is more problematic to exclude a strain only because it is infertile.     

Crossing analysis of sorbose resistant mutants of Neurospora crassa

Summary After treatment of the conidia of Neurospora crassa with nitrous acid 19 of the resulting mutants were selected for their resistance to sorbose, an agent which has a toxic effect on the wild type. The selected sorbose resistant mutants were analyzed genetically by crossing them with tester strains containing known markers. Mutational sites were thus found to be located on at least 5 of the full complement of 7 linkage groups. 9 sites were found to be located on the left arm of linkage group VI near the ylo-marker. These were so far not separable by recombinational analysis and therefore seem to represent a single gene-locus (A). Other sorbose resistant sites were mapped on linkage groups I, III (gene C), V and VII (gene B). Another site which has not yet been definitely located is not closely linked to any of the aforementioned. One site each on linkage groups I and VI were mapped more precisely by means of 3-point crosses. These crosses permitted the location of these sites of sorbose resistance in regard to neighbouring markers. From these crosses it is concluded that the mutation of any 1 of at least 6 different chromosomal genes can cause the formation of a sorbose resistant phenotype. The mutation of any 1 of 4 of these genes could result in a mutant with an altered sorbose permease system or containing a suppressor which decreases the efficiency of the permease system.

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I. Teil einer Habilitationsschrift bei der Naturwissenschaftlichen Fakultät der Universität München.     

GENETIC AND ENVIRONMENTAL DETERMINANTS OF FOOD PREFERENCE IN DROSOPHILA TRIPUNCTATA

Mark-release-recapture field experiments involving two isofemale strains of Drosophila tripunctata revealed that strain identity strongly and consistently affected the preferences of both males and females for mushrooms versus tomatoes. Females, but not males, showed an augmented preference for the type of food on which they had been kept prior to release. The behavior of F2 flies from reciprocal crosses between the two strains demonstrated that genetic variation for food preference is autosomal and largely additive. Because mating often occurs in the vicinity of food in the wild, positive assortative mating with respect to genes for food preference may lead to greater phenotypic variance in preference, which could increase the variety of food resources used by a population.     

Effect of auxotrophic starvation on mitochondrial marker transmission in the cdc8 mutant of Saccharomyces cerevisiae

Summary Crosses were made using strains of S. cerevisiae which carried mitochondrial markers conferring resistance to erythromycin and chloramphenicol. The effect of auxotrophic starvation of one parent prior to mating on the transmission of its mitochondrial markers was studied in different crosses relative to the presence of the cdc8 nuclear mutation (a temperature-sensitive DNA replication).In crosses between two cdc8 mutant strains, auxotrophic starvation of one of the haploid parental strains prior to mating caused a marked decrease of its mitochondrial marker transmission to the diploid progeny of the cross. The transmission decreased as a function of the time of starvation. This effect was not observed in the cross between two wild type strains and in crosses of starved cdc8 phenotypic revertants with cdc8 mutant strains. Only a small, if any, effect of starvation on mitochonrial marker transmission was observed when starved cdc8 mutant strains were crossed either with their phenotypic revettants or with the wild-type strains.In one of the haploid parental strains the starvation increased the frequency of petites as a function of starvation time, while in the other this effect was not observed.In the progeny of cdc8xcdc8 crosses (both in starvation experiments and in control crosses) an increased frequency of diploid petite cells accompanied by a decreased frequency of recombination between mitochondrial markers was noticed.The influence of the cdc8 mutation on the transmission of mitochondrial markers is discussed in terms of high frequency of ^– molecule formation in cdc8 strains.