Alteration of chromosome structure in ovarian nurse cells of Drosophila melanogaster by hybrid dysgenesis

The impact of hybrid dysgenesis on the chromosome structure of Drosophila melanogaster ovarian nurse cells was studied. In the examined lines and interlinear hybrids (including those yielded by dysgenic crosses in the P-M and I-R systems of hybrid dysgenesis), disturbed chromosome synapsis was revealed. The disturbance was somewhat similar to that observed in interspecific hybrids. Quantitative analysis showed that the mean frequency of nuclei with defective chromosome pairing ranged from 60.4 to 76%. FISH analysis of ovarian nurse chromosomes of Canton S x Berlin hybrids showed differences in the label localization in asynaptic homologs of arm 2L, which probably results in disrupted homolog pairing and reveal interlinear differences in localization of mobile genetic elements. Our results conform to Sved's model stating that hybrid dysgenesis is based on disorganization of the germline nuclear space.     

Determination of the frequency of wheat-rye chromosome pairing in wheat x rye hybrids with and without chromosome 5B

Genomic in-situ hybridization (GISH) was used to determine the amount of wheat-rye chromosome pairing in wheat (Triticum aestivum) x rye (Secale cereale) hybrids having chromosome 5B present, absent, or replaced by an extra dose of chromosome 5D. The levels of overall chromosome pairing were similar to those reported earlier but the levels of wheat-rye pairing were higher than earlier determinations using C-banding. Significant differences in chromosome pairing were found between the three genotypes studied. Both of the chromosome-5B-deficient hybrid genotypes showed much higher pairing than the euploid wheat hybrid. However, the 5B-deficient hybrid carrying an extra chromosome 5D had significantly less wheat-rye pairing than the simple 5B-deficient genotype, indicating the presence of a suppressing factor on chromosome 5D. Non-homologous/non-homoeologous chromosome pairing was observed in all three hybrid genotypes. The value of GISH for assessing the level of wheat-alien chromosome pairing in wheat/alien hybrids and the effectiveness of wheat genotypes that affect homoeologous chromosome pairing is demonstrated.     

The pattern of polytene chromosome conjugation and crossing-over in interspecific hybrids of Drosophila

Summary The pairing of polytene chromosomes was investigated in the hybrids between three closely related species of Drosophila belonging to the virilis species group. It was found that within the same hybrid different chromosome bands lost the ability to pair by differing degrees. Furthermore, the same chromosome sections paired with different frequencies depending on the hybrid involved. This study revealed that poor polytene chromosome pairing in the hybrids is not due to specific genetic interaction in the hybrids, but depends solely on the properties of the homologous loci themselves. It was also of interest to find whether the pattern of polytene chromosome somatic pairing resembled in some way the picture of chromosome synapsis during meiosis. To obtain evidence for this, crossing-over in the hybrid 5th chromosome was analyzed both genetically and cytologically (from salivary gland chromosome observations). It was found that the sections of the fifth chromosome which were characterized by a high frequency of conjugation in the salivary glands of hybrids also exhibited a high frequency of crossing-over in hybrid females. It may be concluded that sections of the polytene chromosome characterized by a low frequency of conjugation behave in the same manner in meiosis, and thus rarely take part in genetic recombination.     

Absence of qualitative genes controlling interspecific pairing in rye B chromosomes

Summary The meiotic behaviour of hybrids between Secale cereale carrying B chromosomes and S. vavilovii has been studied in order to estimate the effects of B chromosomes on hybrid meiotic pairing. The possible effect of Bs on the meiotic pairing of the offspring from backcrosses with S. vavilovii has been studied also. The results obtained clearly indicate that no detectable differences existed in chromosome pairing of hybrids with or without B chromosomes. The hypothetical existence of epistatic genes on cereale genome masking the effect of Bs has been rejected after the results obtained in backcrosses. Therefore, lack of qualitative genes controlling interspecific pairing on rye B chromosomes has been concluded. A quantitative effect of B chromosomes was detected only when they were in alien cytoplasm.     

Fertility and chromosome stability in Brassica napus resynthesised by protoplast fusion

Summary Fertile somatic hybrids between Brassica campestris and B. oleracea have been produced by protoplast fusion. Fusion products were identified by their intermediate protoplast morphology. Heterokaryons were isolated either with micropipettes using a micromanipulator or by flow sorting. About 2% of the obtained calli differentiated to shoots. Of the shoots obtained from manually selected heterokaryons, 100% were true hybrids as confirmed by isozyme analysis while 87% of the flow sorted ones showed a hybrid pattern. Ploidy level of the hybrid plants was determined by chromosome counting and relative DNA-content analysis. The sum of the chromosome number (38) from the two fusion partners were found in 30% of the hybrids; 9% had fewer and 61% had more chromosomes. Pollen viability and seed set varied with ploidy level. Compared to natural B. napus, a pollen viability of 52%–93% and a fertility of 1%–40% was found for the somatic hybrids with normal chromosome number. Restriction enzyme analysis of chloroplast-DNA showed that either B. campestris or B. oleracea chloroplasts were present in the somatic hybrid plants. Of 11 hybrid plants 5 had the campestris and 6 had the oleracea type (11 ratio).     

Production,morphology, and cytogenetic analysis of Elymus caninus (Agropyron caninum) x Triticum aestivum F1 hybrids and backcross-1 derivatives

Summary Intergeneric hybrids were produced between common wheat, Triticum aestivum (2n=6x=42, AABBDD) and wheatgrass, Etymus caninus (Agropyron caninum) (2n=4x=28, SSHH) — the first successful report of this cross. Reciprocal crosses and genotypes differed for percent seed set, seed development and F₁ hybrid plant production. With E. caninus as the pollen parent, there was no hybrid seed set. In the reciprocal cross, seed set was 23.1–25.4% depending upon wheat genotype used. Hybrid plants were produced only by rescuing embryos 12–13 days post pollination with cv Chinese Spring as the wheat parent. Kinetin in the medium facilitated embryo germination but inhibited root development and seedling growth. The hybrids were vigorous, self sterile, and intermediate between parents. These had expected chromosome number (2n=5x=35, ABDSH), very little chromosome pairing (0.51 II, 0.04 III) and some secondary associations. The hybrids were successfully backcrossed with wheat. Chromosome number in the BC₁ derivatives varied 54–58 with 56 as the modal class. The BC₁ derivatives showed unusually high number of rod bivalents or reduced pairing of wheat homologues. These were sterile and BC₂ seed was produced using wheat pollen.     

The genomic relationship between Glycine max (L.) Merr. and G. soja Sieb. and Zucc. as revealed by pachytene chromosome analysis

Summary This study was conducted with the objective of determining the genomic relationship between cultivated soybean (Glycine max) and wild soybean (G. soja) of the subgenus Soja, genus Glycine. Observations on cross-ability rate, hybrid viability, meiotic chromosome pairing, and pollen fertility in F ₁ hybrids of G. max × G. soja and reciprocals elucidated that both species hybridized readily and set mature putative hybrid pods, generated vigorous F₁ plants, had a majority of sporocytes that showed 18II + 1IV chromosome association at diakinesis and metaphase I, and had a pollen fertility that ranged from 49.2% to 53.3%. A quadrivalent was often associated with the nucleolus, suggesting that one of the chromosomes involved in the interchange is a satellited chromosome. Thus, G. max and G. soja genetic stocks used in this study have been differentiated by a reciprocal translocation. Pachytene analysis of F₁ hybrids helped construct chromosome maps based on chromosome length and euchromatin and heterochromatin distribution. Chromosomes were numbered in descending order of 1–20. Pachytene chromosomes in soybean showed heterochromatin distribution on either side of the centromeres. Pachytene analysis revealed small structural differences for chromosomes 6 and 11 which were not detected at diakinesis and metaphase I. This study suggests that G. max and G. soja carry similar genomes and validates the previously assigned genome symbol GG.Research supported in part by the Illinois Agricultural Experiment Station and U.S. Department of Agriculture Competitive Research Grant (85-CRCR-1-1616)     

Chromosome instability in Hordeum vulgare x H. bulbosum hybrids

Chromosome number in Hordeum vulgare x H. bulbosum hybrids ranged between the haploid and diploid number but with peaks in frequency occurring at the 14 and 7 chromosome level. This was reflected in a gradual change from hybrid morphology to that of haploid H. vulgare. The rate of chromosome elimination differed significantly between hybrids, while within each hybrid, differences in mean chromosome number were recorded between and within individual tillers. An increase in temperature from 25–30° C caused a significant increase in the rate of elimination of H. bulbosum chromosomes.     

Genome relationships between Hordeum vulgare L. and H. bulbosum L.

Interrelationships between H. vulgare (2x=14) and H. bulbosum (2x=14; 4x=28) were estimated on the basis of the karyotypes and the pairing behaviour of the chromosomes in diploid, triploid and tetraploid hybrids obtained with the aid of embryo culture. — A comparison of the karyotypes of the two species revealed similarities as well as differences. It was concluded that at least 4 or more of the chromosomes were similar in morphology and probably closely related. — Diploid and tetraploid hybrids are rarely obtained and their chromosome numbers tend to be unstable whereas triploid hybrids (1 vulgare + 2 bulbosum genomes) were stable and relatively easy to produce. In the diploid hybrid only 40% of the meiotic cells contained 14 chromosomes while the numbers ranged from 7 to 16 in other cells. All hybrids exhibited pairing between the chromosomes of the two species. Diploid hybrids had a mean of 5.0 and a maximum of 7 bivalents per cell in those cells having 14 chromosomes. Triploid hybrids from crosses between 2x H. vulgare and 4x H. bulbosum exhibited a mean of 1.5 and a maximum of 5 trivalents per cell. In a hexaploid sector found following colchicine treatment of a triploid the mean frequencies of chromosome associations per cell were: 5.5_I+8.0_II+0.7_III+3.7_IV+0.3_V+0.4_VI. One unstable 27 chromosome hybrid obtained from crosses between the autotetraploid forms had a mean of 1.1 and a maximum of 4 quadrivalents per cell. The chromosome associations observed in these hybrids are consistent and are taken as evidence of homoeologous pairing between the chromosomes of the two species. Interspecific hybridization between these two species also reveals that chromosome stable hybrids are only obtained when the genomes are present in a ratio of 1 vulgare2 bulbosum. Based upon the results obtained, the possibility of transferring genetic characters from H. bulbosum into cultivated barley is discussed.     

C-banding in 6x-Triticale xSecale cereale L. hybrid cytogenetics

Summary The meiotic behaviour of F₁ hybrids of hexaploid Triticale that differed in their genotypic or chromosomic constitution, and diploid rye, was investigated. Meiotic analysis were done by Feulgen and C-banding staining methods. A differential desynaptic effect in the hybrids was detected and explained in terms of genetic differences in pairing regulators. The high homoeologous pairing (A-B wheat chromosomes and wheat-rye chromosomes) observed in the hybrids can be explained in terms of an inhibition of the effect of a single dose of thePh allele of the 5B chromosome produced by two doses of the 5R chromosome. The higher homoeologous pairing detected in the hybrid 188 x Canaleja could be the overall result of the balance between thePh diploidizing system (1 dose), the pairing promoter of the 5R chromosome (2 doses) and that of the 3D chromosome (1 dose coming from the parental line Triticale with the substitution 3R by 3D).     

Interspecific hybridization and the analysis of meiotic chromosome pairing inDahlia (Asteraceae — Heliantheae) species with x = 16

The successful production of a large number of artificial hybrids betweenDahlia species based on x = 16 has allowed a detailed study of their genomic relationships. Chromosome behaviour in these artificial hybrids was extremely similar to that observed in parental species suggesting that there is a considerable degree of homology between the genomes of theseDahlia species. Using GISH it can be demonstrated that in these hybrids bivalent formation involved pairing only between parental genomes. The ability of GISH to differentiate between parental genomes in artificial hybrids was variable, indicating that molecular divergence of highly repeated sequences has accompanied the evolution of these species. However, the extent of chromosome pairing and chiasma formation in the hybrids does not reflect the differences that can be detected by GISH. Seyeral of the new hybrid combinations have resulted in horticulturally interesting plants.     

Genetic Control of Embryo Lethality in Crosses between Common Wheat and Rye

The phenotypic manifestation and genetic control of embryo lethality observed in crosses between common wheat and rye were studied. It was found that crosses between common wheat and inbred self-fertile rye lines L2 and 535 gave rise to ungerminating grains, in which the development and differentiation of the hybrid embryo are arrested. Study of the degree of embryo development in the hybrid grains obtained by crossing common wheat varieties with inbred rye lines L2 and 535 showed that genotypes of the parents affected the ratio between undifferentiated embryos of various sizes. Analysis of this trait was performed by test crosses according to a novel pedigree program with the use of interlinear hybrids and a set of fourth-generation hybrid recombinant inbred lines. Rye line L2 was shown to bear the Eml (Embryo lethality) gene, which terminates the development of the hybrid embryo in amphihaploids. The suggestion of complementary interaction between wheat and rye genes during formation of a “new” character in wheat-rye F₁ hybrids is discussed. A method of detecting an allele not complementary to the rye Eml allele in wheat is proposed. The proposed test program allows appropriate study of the system of wheat and rye genes involved in complementary interaction in the genotype of a distant hybrid.__________Translated from Genetika, Vol. 41, No. 8, 2005, pp. 1075–1083.Original Russian Text Copyright © 2005 by Tikhenko, Tsvetkova, Voylokov.     

Metaphase I bound arms frequency and genome analysis in wheat-Aegilops hybrids

Summary Meiotic associations of different wheat-Aegilops variabilis and wheat-Ae. kotschyi hybrid combinations with low and high homoeologous pairing were analyzed at metaphase I. Five types of pairing involving wheat and Aegilops genomes were identified by using C-banding. A genotype that seems to promote homoeologous pairing has been found in Ae. variabilis var. cylindrostachys. Its effect is detectable in the low pairing hybrids but not in the high ones. Pairing affinity has been analyzed on the basis of metaphase I associations in the low and high homoeologous pairing hybrids, and in bivalents and multivalents in the high pairing hybrids. The results indicate that the amount of bound arms of each type of identifiable association relative to the total associations formed (relative contribution) was not maintained, either between the different levels of pairing (low and high) or between different meiotic configurations (bivalents and multivalents). These findings seem to indicate that quantifications of genomic relationships based on the amount of chromosome pairing at metaphase I must be carefully done in this type of hybrid combinations.     

Cytological analysis of tetraploid hybrids between sweet potato and diploid Ipomoea trifida (H. B. K.) Don.

Summary Tetraploid F₁ hybrids between Ipomoea batatas, sweet potato (2n = 6x = ca. 90), and diploid (2n = 2x = 30) I. trifida (H. B. K.) Don. showed various degrees of fertility reduction. The present study aimed to clarify its causes by cytological analysis of meiotic chromosome behavior in the diploid and sweet potato parents and their tetraploid hybrids. The diploid parents showed exclusively 15 bivalents, and the sweet potato parents exhibited almost perfect chromosome pairing along with predominant multivalent formation. Their hybrids (2n = 4x= 57–63) formed 2.6–5.0 quadrivalents per cell, supporting the autotetraploid nature. The meiotic aberratios of the hybrids were characterized by the formation of univalents, micronuclei, and abnormal sporads (monad, dyad, triad, and polyad). The causes underlying these aberrations were attributed in part to the multivalent formation, and in part to a disturbance in the spindle function. Three hybrids showing serious meiotic aberrations were very low in fertility. The utilization of the sweet potato-diploid I. trifida hybrids for sweet potato improvement is described and, further, the role of interploidy hybridization in the study of the sweet potato evolution is discussed.     

The genetics of meiotic chromosome pairing in Lolium temulentum x Lolium perenne tetraploids

Summary The degree of preferential pairing of homologous chromosomes was estimated in a series of tetraploid hybrids of Lolium temulentum x Lolium perenne by means of cytological and genetic analyses. The correlations between the frequency of bivalents at first metaphase of meiosis in the hybrid tetraploids and the degree of preferential pairing calculated from the segregation pattern of isozyme alleles in a test cross was extremely high. The results showed clearly that suppression of heterogenetic pairing in these Lolium tetraploids is achieved by a genetic system involving the A chromosomes as well as the B chromosome system which has been known for some time. Certain similarities with the genetic system controlling pairing in polyploid wheats are discussed.     

Comparative analysis of the meiotic effects of wheat ph1b and ph2b mutations in wheat×rye hybrids

 Wheat-wheat and wheat-rye homoeologous pairing at metaphase I and wheat-rye recombination at anaphase I were examined by genomic in situ hybridization (GISH) in wild-type (Ph1Ph2) and mutant ph1b and ph2b wheat×rye hybrids. The metaphase-I analysis revealed that the relative contribution of wheat-rye chromosome associations in ph2b wheat×rye was similar to that of the wild-type hybrid genotype but differed from the effect of the ph1b mutation. The greater pairing promotion effect of the ph1b mutation appears to be relatively more on distant homoeologous partner metaphase-I associations, whereas the lower promoting effect of ph2b is evenly distributed among all types of homoeologous associations. This finding reveals that distinct mechanisms are involved in the control of wheat homoeologous pairing by the two Ph genes. The frequency of wheat-rye recombination calculated from anaphase-I analysis was lower than expected from the metaphase-I data. A greater discrepancy was found in ph2b than in ph1b wheat×rye hybrids, which may suggest a more distal chiasma localization in the former hybrid genotype. Received: 20 June 1997 / Accepted: 9 December 1997     

The genotypic control of homoeologous chromosome association in Lolium temulentum × Lolium perenne interspecific hybrids

Two contrasting genotypes of Lolium perenne and two inbred lines of L. temulentum were examined with regard to their effect on homoeologous chromosome pairing in interspecific hybrids derived from them. Substantial differences in chiasma frequency were observed between the hybrid progeny of the different parental types. The background genes involved were found to operate in the presence and in the absence of B chromosomes. The combination of A chromosome genes present in some of the 0B hybrids was found to result in a considerable suppression of chiasma formation at the diploid level, and the restriction of pairing to strict homologues at the tetraploid level. It appears, therefore, that genes are present within the diploid species of the genus Lolium which are capable of performing a function similar to that of the Ph locus in wheat.     

Control of conformation changes associated with homologue recognition during meiosis

During early meiosis, chromosomes pair via their telomeres and centromeres. This pairing induces a conformational change which propagates from these regions along each chromosome, making the chromatin of the partners accessible for intimate pairing. In the present study, we show by exploiting wheat–rye hybrids that the signal is initiated in both the presence and absence of either the Ph1 or Ph2 locus. However, the chromatin change only continues to propagate through rye telomeric heterochromatin when Ph1 is absent. This failure to propagate the chromatin change through the rye heterochromatin in the absence of Ph2 correlates with a subsequent lack of wheat–rye chromosome association at metaphase I.     

Expression of nuclear-cytoplasmic genomic incompatibility in interspecific Petunia somatic hybrid plants

Summary Somatic hybrid plants were regenerated following calcium-high pH fusion of the unidirectional, sexually incompatible cross of Petunia parodii wild-type leaf mesophyll protoplasts with protoplasts from a cytoplasmic determined chlorophyll-deficient mutant of P. inflata. Genic complementation to chlorophyll synthesis and sustained growth in the selective medium was used to visually identify hybrid calluses. Hybrid calluses were subsequently regenerated to shoots, rooted, and confirmed as somatic hybrids by their intermediate floral and leaf morphology based on comparison to the 2 _n = 4 _x = 28 sexual counterpart, dominant anthocyanin expression in the corolla, chromosome number, and peroxidase and maleic dehydrogenase isozyme patterns. Certain cytologically stable somatic hybrids displayed aberrant reproductive and floral morphologies including subtle to moderate corolla and leaf pigment variegation, floral dimension changes and reduced pollen viability. In contrast, cytologically unstable somatic hybrids showed various degrees of aneuploidy coupled with corolla splitting, and irregularities in reproductive organs such as double stigmas and styles in addition to reduced pollen viability. Postulated mechanisms to account for these phenotypic changes in stable and unstable somatic hybrids include nuclear-cytoplasmic genomic incompatibility, chromosome loss in a biparental cytoplasm, or a phenomenon similar to hybrid dysgenesis occurring as a result of somatic fusion.Michigan Agricultural Experiment Station Journal Article No. 11376. Supported by Grant No. I-134-79 from BARD — The United States — Israel Binational Agricultural Research and Development Fund, and by grant 11-77-4 from American Florists Endowment     

Chromosomal analysis of Nicotiana asymmetric somatic hybrids by dot blotting and in situ hybridization

Summary A species-specific, dispersed repetitive DNA sequence was cloned from Nicotiana plumbaginifolia and used in dot blots and in situ hybridizations to analyze asymmetric somatic hybrids of N. tabacum(+)kanamycin-resistant N. plumbaginifolia. Dot blot hybridization data, using the cloned, species-specific repetitive DNA as a probe, showed that some of the hybrids contain only 1%–5% N. plumbaginifolia DNA, whereas others contain 15%–25%. In situ hybridization of the probe to chromosome spreads showed that the extremely asymmetric hybrids retain a single N. plumbaginifolia chromosome; the hybrids with higher dot blot values were found to have 8 to 12 N. plumbaginifolia chromosomes and chromosome fragments. In situ hybridization also revealed translocations between N. plumbaginifolia and N. tabacum chromosomes in 3 of 8 hybrids studied. RFLP analysis using a 5S gene probe showed the presence of N. plumbaginifolia-specific 5S banding patterns in most hybrids examined, including those that retain only a single N. plumbaginifolia chromosome.