Cytological investigations of the interspecific hybrids of Nicotiana tabacum L. x N. glauca Grah

Interspecific amphihaploid and amphidiploid hybrids between Nicotiana glauca Grah. (2n = 24) and N. tabacum L. (2n = 48) cultivars BY 103 and K 326 were analysed. F1 amphihaploids (2n = 36) were viable and completely self- and cross-sterile, and mostly univalents were present during meiosis (with pairing range from 0 to 5). In some meiocytes, meiotic irregularities were observed, such as sporadic chromatin bridges and formation of restitution nuclei. The resultant F1 hybrids were easily converted to amphidiploids (2n = 72) via colchicine treatment of seedlings. The number of univalents and the frequency of PMCs containing unpaired chromosomes indicated that amphidiploids N. tabacum cv. BY 103 or K 326 x N. glauca represented quite a high pairing category. However, they were male sterile because pollen mother cells were arrested at the tetrad stage. The termination of development of PMCs, and consequently male sterility, are very rare in this kind of tobacco hybrids.     

Chromosome pairing in meiosis of partially fertile wheat/rye hybrids

The normal course of meiosis depends on regular pairing of homologous chromosomes. In intergeneric hybrids, including those of wheat, there is no chromosome pairing because there are no homologs. In F₁ wheat/rye hybrids, pairing is largely prevented by the pairing homoeologous1 (Ph1) gene. In its presence, there are only rare instances of pairing; most chromosomes are univalent, and their orientation at metaphase I initiates different pathways of the meiotic cycle. The meiotic-like pathway includes a combination of the reductional and the equational + reductional steps at AI followed by the second division. The resulting gametes are mostly non-functional. The mitotic-like pathway involves equational division of univalents at AI and the absence of the second division. Any fertility of wheat/rye hybrids depends on the production of unreduced gametes arising from meiotic restitution (mitotic-like division). We examined the meiotic pairing in wheat/rye hybrids created from wheat lines with single rye chromosome substitutions and Ph1 present. This guaranteed F₁ meiosis with one pair of rye homologs. All hybrids formed bivalents, but proportions of meiocytes with bivalents varied. In the meiocytes where bivalents were present, there was a higher tendency for the meiotic-like pathway, while in meiocytes where bivalent pairing failed, the tendency was stronger for the mitotic-like pathway. Among the equationally dividing cells, we observed more than 90 % of meiocytes without bivalents, where rye homologs did not form bivalents, too. The data indicate a potential application of wheat/rye lines in producing genetic stocks of amphidiploids with designated genomic constitutions.     

Introgression of <Emphasis Type="Italic">Aegilops</Emphasis> genetic material into the genome of hexaploid triticale

Cytological analysis of different meiosis stages was performed in F₄ hybrids in comparison with the F₁ hybrids obtained through crosses between the hexaploid triticale and genome-substitution forms of Aurolata (AABBUU) and Aurosis (AABBS^shS^sh) wheat, in which D genome of common wheat Aurora was substituted for the genomes of Aegilops umbellulata and Ae. sharonensis, respectively. It was demonstrated that in F₄ the level of bivalent conjugation was substantially higher than the expected one. However, the value of meiotic index in F₄ hybrids was still small, pointing to incomplete process of the meiosis stabilization, specifically, of the stages following the metaphase I. Based on the data of morphological and biochemical analyses of the hybrids produced, the forms of triticale carrying some properties of the genus Aegilops, which were of interest for genetic and breeding studies, were isolated.     

Gene silencing in transgenic tobacco hybrids: frequency of the event and visualization of somatic inactivation pattern

We have investigated the stability of the expression of different T-DNA-borne genes in hybrid tobacco lines. These lines were constructed to rescue rolC-induced male sterility in kanamycin-resistant P_35s-rolC transgenic tobacco plants by expression of rolC antisense genes. Using five different tester lines, a total of 158 hybrids was obtained. We observed inactivation of transgene expression in 20% of the F₁ progeny and in 35% of the backcrossed F₂ progeny, as indicated by the loss of kanamycin resistance. In 3% of all crosses complete loss of antibiotic resistance was noted, while in most affected hybrid progeny only part of the population became kanamycin sensitive. Single genes could be selectively inactivated on T-DNAs harboring several genes. Gene inactivation was not restricted to one of the two T-DNAs examined. Somatic silencing, visualized by a cell-specific 35SGUSINT marker gene, occurred in a random fashion or exhibited an inherited specific pattern. The type of somatic silencing pattern observed indicated developmental control of the process. Two phenotypic classes could be distinguished with respect to frequency and timing of the inactivation process. Rapid gene inactivation, occurring within a few weeks after germination of hybrid seedlings, was characterized by complete methylation of restriction sites in the promoter of the silenced gene, resetting of gene expression during meiosis, heridity of the developmentally controlled program of gene silencing in subsequent generations, and rapid reactivation of gene expression after genetic separation of the different T-DNAs. In contrast, a slow type of gene inactivation was of a more stochastic nature and was recognized only in hybrids of the backcrossed F₂ generation. In this case the degree of promoter methylation, which could extend beyond the T-DNA borders, was not correlated with the reduction in steady-state poly(A)⁺ mRNA levels, the silenced state was transmitted through meiosis and reactivation lasted several generations. The implications of the observations for our understanding of the gene inactivation process are discussed.     

Reidentification of chromosomal CUP1 translocations in the wine yeasts Saccharomyces cerevisiae

Reciprocal translocations between chromosomes XVI and VIII were revealed in eight Saccharomyces cerevisiae strains (mostly wine ones) using pulse-field electrophoresis of native chromosomal DNAs and their hybridizations with the CUP1 and GAL4 probes. New and reciprocal translocations of at least the gene CUP1 occur at the expense of crossing-over in the hybrids of such strains with the genetic lines of normal karyotype during meiosis. Relationship between these reciprocal translocations and the sulfite (Na₂SO₃) resistance gene SSU1-R is discussed.     

几类异质小麦雄性不育系育性恢复性的细胞遗传学研究

系统调查了4类异质(粘果、易变、偏凸、二角山羊草细胞质)1BL/lRS、非1BL/1RS小麦雄性不育系与其恢复系杂种F减数分裂中期Ⅰ出现单价体细胞频率,以及后期Ⅰ出现落后染色体和染色体桥细胞频率,并对中、后期染色体变异率与杂种F自交结实率进行了相关分析.结果表明(1)1BL/1RS型杂种在中期Ⅰ、后期Ⅰ染色体变异率要明显高于非1BL/1RS杂种;(2)4类异源细胞质在非1BL/1RS杂种中有着明显提高单价体细胞频率的作用;(3)在1BL/1RS杂种中,1B@1BL/1RS杂合核型染色体联会松弛,对单价体频率的影响远大于异源细胞质的影响;(4)1BL/1RS型杂种自交结实率与中期出现单价体细胞频率不直接相关,而与后期出现落后染色体和染色体桥细胞的频率呈高度负相关;(5)非1BL/1RS型杂种在减数分裂中、后期染色体行为相对稳定,易恢复且恢复度高,很有实际利用价值.     

Course of meiosis in F1 interspecific hybrids of Lycopersicon esculentum Mill. × Licopersicon chilense Dun.

A study was conducted into the course of meiosis in F₁ interspecific hybrids of Lycopersicum esculentum Mill (mutant line Mo 638) × Lycopersicum chinense Dul. and its parental forms. An F₁ interspecific hybrid was obtained through the embryo culture technique. A decrease in the chiasma frequency and an increase in the frequency of univalents and meiotic abnormalities compared to their parental forms were detected in hybrid plants. The number of univalents and the percentage of main impairments decreased, as the height of bud tier locations increased. A conclusion was made regarding the connection between the regularity of meiosis in the examined F₁ interspecific hybrids of Lycopersicon esculentum × Lycopersicon chilense, on the one hand, and the hybrid nature of genotypes and the influence of environmental factors, on the other hand.     

RELATIONSHIP OF WOODY PARTHENIUM ARGENTATUM AND HERBACEOUS P. HISPIDUM VAR. AURICULATUM (ASTERACEAE)

Interspecific hybrids between woody Parthenium argentatum Gray (guayule), native to Mexico and Southwest Texas, and herbaceous perennial P. hispidum var. auriculatum (Britton) Rollins, native to the United States, were obtained successfully. The F₁ hybrids were intermediate for most morphological characters with the exception of the short woody stem, yellow pollen color, and the trichome morphology. Chromosome counts revealed the presence of 2n = 36 A-chromosomes in P. argentatum. The same number of A-chromosomes and four B-chromosomes were found in P. hispidum var. auriculatum. Observations of pollen mother cells showed regular meiosis in both parental species. At diakinesis, chiasmata averaged 1.12 and 1.24 per bivalent for P. argentatum and P. hispidum var. auriculatum, respectively. Meiotic behavior of the F₁ hybrids was irregular. F₁ hybrids averaged 4.43 univalents at metaphase I, 1.95 laggards at anaphase I, and 1.62 micronuclei at the tetrad stage. The low pollen stainability (5.1%) in the F₁ hybrids and the limited number of viable BC₁ seeds (4.07%) may be reflections of the irregular meiosis. Although these primary hybrids are partially fertile, they can be used to introduce desirable characteristics of P. hispidum var. auriculatum, such as herbaceous perennial habit, regrowth ability, and cold tolerance into guayule.     

Reproductive isolation in Caenorhabditis: terminal phenotypes of hybrid embryos

SUMMARY Several interspecific combinations of the "elegans" group of Caenorhabditis species are cross-fertile. Most F1 hybrids from these crosses arrest during embryogenesis. Developmental defects observed in hybrid embryos include defects in gastrulation initiation, defects in embryonic compaction, and defects in embryonic elongation. These reproductive barriers have arisen multiple times in the evolution of Caenorhabditis.     

A CYTOGENETIC ANALYSIS OF CERTAIN POLYPLOIDS IN GRINDELIA (COMPOSITAE)

Two diploid taxa, Grindelia procera and G. camporum, and 3 tetraploid ones, G. camporum, G. hirsutula, and G. stricta, have been studied to ascertain their interrelationships. Meiosis in diploid parental strains was regular, the common chromosome configuration being 5 rod bivalents and 1 ring bivalent. The average chiasmata frequency per chromosome was 0.60. Pollen fertility was about 90% in all strains examined. Diploid interspecific hybrids had normal meiosis with an average chiasmata frequency of 0.56 per chromosome. No heterozygosity for inversions or interchanges was detected, and pollen fertility was above 85%. Meiosis in parental tetraploid strains was characterized by the presence of quadrivalents in addition to a complementary number of bivalents. The average chiasmata frequency per chromosome was 0.59 and pollen fertility was generally about 80%. Tetraploid interspecific hybrids also had quadrivalents, normal meiosis, and high pollen fertility. Close genetic relationships between the diploids and between the tetraploids are indicated, and geographical, ecological, and seasonal barriers to gene exchange exist. Attempts to obtain hybrids between diploids and tetraploids were successful in a few cases. The hybrids were tetraploid and had normal meiosis and fertility similar to parental and F₁ tetraploids. Their origin was by the union of unreduced gametes of the diploid female parent and normal pollen from the tetraploid parent. On the basis of chromosome homology, normal meiosis, plus high fertility exhibited in the diploid, tetraploid, and diploid X tetraploid interspecific hybrids, these species of Grindelia are considered to be a part of an autopolyploid complex. Gene exchange between diploids and diploids, tetraploids and tetraploids, and diploids and tetraploids is possible. Tetraploid G. camporum may have originated by hybridization between G. procera and diploid G. camporum with subsequent doubling of chromosomes and selection for the combined characteristics of the diploids.     

小麦的不同染色体组对G、S~v、D~2、M~u型细胞质“中国春”育性的影响

本文以Ｇ、Ｊｖ、Ｄ２、Ｍｕ型异细胞质“中国春”;小麦为母本与１１个不同染色体组类型小麦为父本进行杂交,观察当代的结实率,Ｆ１的育性与性状的变化、减数分裂行为,进一步探讨小麦的细胞质雄性不育与染色体组类型的关系。结果表明：当代结实率主要由父本染色体组类型决定,Ｆ１的育性表现十分复杂,同一父本与不同的异细胞质“中国春”杂交,有的表现可育,有的表现不育,细胞质有一定的影响。Ｆ１的性状,有的与细胞质类型有关,如熟期、雄蕊形态、生长期与抗病性等。选择适宜可获得有明显杂种优势的组合。有的细胞质类型可影响减数分裂行为使中期Ⅰ配对的染色体增加或减少,在四分期出现微核与异常四分孢子。     

Cytology and fertility of viable hybrids of Nicotiana tabacum L. cv. TB-566 with N. alata Link et Otto

A vigorous hybrid (N. tabacum cv. TB-566 tetra x N. alata) x N. alata was obtained by backcrossing a partly viable sesquidiploid hybrid N. tabacum cv. TB-566 tetra x N. alata to N. alata. The hybrid was a 35-chromosome near-amphihaploid with a pair of N. alata chromosomes in disomic condition. It was completely self- and cross-sterile and formed from 7 to 8 bivalents in pollen mother cells. By using stem pith culture, polyploidized regenerants were obtained from the 35-chromosome hybrid with somatic chromosome numbers from 65 to 70. These regenerants showed fairly regular meiosis with the number of bivalents in pollen mother cells ranging from 27.3 to 30.4. Irregularities in meiosis included a high number of univalents, aberrant tetrads, and a high frequency of micronuclei. The percentage of acetocarmine-stainable pollen ranged from 22.1 to 78.4. A 66-chromosome regenerant showed fairly regular meiosis and was self-fertile but could not be backcrossed to N. tabacum. This barrier seems to be caused by genic imbalance rather than irregularities of meiotic divisions. Hence transfer programs based on the introgression of entire linkage groups (sexual and somatic hybridization) seem to be of little use in the case of that species.     

Development of monosomic alien addition lines and introgression of genes from Oryza australiensis Domin. to cultivated rice O. sativa L.

Oryza australiensis, a diploid wild relative of cultivated rice, is an important source of resistance to brown planthopper (BPH) and bacterial blight (BB). Interspecific hybrids between three breeding lines of O. sativa (2n=24, AA) and four accessions of O. australiensis (2n=24, EE) were obtained through embryo rescue. The crossability ranged from 0.25% to 0.90%. The mean frequency of bivalents at diakinesis/metaphase I in F₁ hybrids (AE) was 2.29 to 4.85 with a range of 0–8 bivalents. F₁ hybrids were completely male sterile. We did not obtain any BC₁ progenies even after pollinating 20,234 spikelets of AE hybrids with O. sativa pollen. We crossed the artificially induced autotetraploid of an elite breeding line (IR31917-45-3-2) with O. australiensis (Acc. 100882) and, following embryo rescue, produced six F₁ hybrid plants (AAE). These triploid hybrids were backcrossed to O. sativa. The chromosome number of 16 BC₁ plants varied from 28 to 31, and all were male sterile. BC₂ plants had 24–28 chromosomes. Eight monosomic alien addition lines (MAALs) having a 2n chromosome complement of O. sativa and one chromosome of O. australiensis were selected from the BC₂ F₂ progenies. The MAALs resembled the primary trisomies of O. sativa in morphology, and on the basis of this morphological similarity the MAALs were designated as MAAL-1, -4, -5, -7, -9, -10, -11, and -12. The identity of the alien chromosome was verified at the pachytene stage of meiosis. The alien chromosomes paired with the homoeologous pairs to form trivalents at a frequency of 13.2% to 24.0% at diakinesis and 7.5% to 18.5% at metaphase I. The female transmission rates of alien chromosomes varied from 4.2% to 37.2%, whereas three of the eight MAALs transmitted the alien chromosome through the male gametes. BC₂ progenies consisting of disomic and aneuploid plants were examined for the presence of O. australiensis traits. Alien introgression was detected for morphological traits, such as long awns, earliness, and Amp-3 and Est-2 allozymes. Of the 600 BC₂ F₄ progenies 4 were resistant to BPH and 1 to race 6 of BB. F₃ segregation data suggest that earliness is a recessive trait and that BPH resistance is monogenic recessive in two of the four lines but controlled by a dominant gene in the other two lines.     

Reduced meiotic fitness in hybrids with heterozygosity for heterochromatin in the speciating<Emphasis Type="Italic">Mus terricolor</Emphasis> complex

Mus terricolor I, II and III are the three chromosomal species which differ in stable autosomal short-arm heterochromatin variations established in homozygous condition. Analysis of meiosis in the laboratory-generated F₁ male hybrids from crosses (both ways) betweenM. terricolor I and II and betweenM. terricolor I and III shows high frequencies of pairing abnormalities at pachytene. The backcross (N3 generation) male hybrids betweenM. terricolor I and II have meiotic abnormalities as in the F₁male hybrids, though to a lesser extent. They show difference in pairing abnormalities in the different karyotypic forms; the backcross hybrids heterozygous for the heterochromatic short arms have more anomalies compared to the homokaryotypic hybrids. This suggests a negative influence of the heterochromatin heterozygosity in meiotic pairing. The results indicate a role for heterochromatin variations in the development of a reproductive barrier in the speciatingM. terricolor complex.     

普通小麦1BL—1RS K,V型雄性不育体系育性恢复的研究

对１ＢＬ－１ＲＳ Ｋ,Ｖ型雄性不育系及其保持素与中国春及其第一部分同源群染色体全部６个缺－四体杂种Ｆ１的育性恢复进行了研究。结果表明：Ｋ型杂种的育笥恢复主要受１ＢＳ上Ｒｆｖ１基因的控制;而Ｖ杂种则受Ｒｆｖ１的１Ｄ染色上育性恢复基因的共同控制;在保持１Ｄ正常剂量的情况下,使恢复系中载有Ｒｆｖ１的１Ｂ染色体（片段）加倍,如１Ａ缺体－１Ｂ四体能使Ｋ,Ｖ型杂种1Ｆ的育性完全恢复。     

Meiotic restriction in emmer wheat is controlled by one or more nuclear genes that continue to function in derived lines

Highly fertile F₁ hybrids were made between Triticum turgidum L. ssp. turgidum (2n = 28, AABB) and Aegilops tauschii Coss. (2n = 14, DD) without embryo rescue and hormone treatment. The F₁ plants had an average seed set of 25%. Approximately 96% of the F₂ seeds were able to germinate normally and about 67% of the F₂ plants were spontaneous amphidiploid (2n = 42, AABBDD). Cytological analysis of male gametogenesis of the F₁ plants showed that meiotic restitution is responsible for the high fertility. A mitosis-like meiosis led to meiotic restitution at either of the two meiotic divisions resulting in unreduced gametes. Test crosses of the T. t. turgidum–Ae. tauschii amphidiploid with Ae. variabilis and rye suggested that the mitosis-like meiosis is controlled by one or more nuclear genes that continue to function in derived lines. This discovery indicates a potential application of such genes in producing double haploids.     

Meiotic restitution in amphihaploids in the tribe Triticeae

In haploid and diploid organisms of the plant kingdom, meiotic division of diploid cells proceeds in two consecutive stages, with DNA replicating only once. In amphihaploids (interspecific or intergeneric hybrids), where homologs are absent, the reduction of the chromosome number does not occur, meiosis is abnormal, and the plants are sterile. Gamete viability in F₁ hybrids is ensured by a single division when chromosomes are separated into sister chromatids in either the first or the second division. Such gametes ensure partial fertility of amphihaploids, thereby facilitating their survival and stabilization of the polygenome. The frequency of the formation of viable gametes varies from a few cases to 98.8% in different anthers of the hybrids. Here, studies on the cytological mechanisms and genetic control of chromosome unreduction or restitution in different amphihaploids of the tribe Triticeae are reviewed. The current notions on the control of formation of restitution nuclei based on the principles of a prolonged metaphase I and different types of meiocytes. The main terms used for systematization of restitution mechanisms are first-division restitution (FDR), single-division meiosis (SDM), and unreductional meiotic cell division (UMCD). It has been assumed that archesporial cells of wide hybrids may have two cell division programs, the meiotic and the mitoyic ones The possible approaches to the analysis of the genetic control of chromosome restitution in amphihaploids are discussed.     

Autosyndetic pairing in Gibasis (Commelinaceae) hybrids revealed by C-banding

Two closely related species of Gibasis, G. karwinskyana and G. consobrina, and their F₁ hybrids were studied cytologically at the diploid and tetraploid level. Despite similarity in their basic karyotype, pairing was extremely limited in the diploid hybrid and almost exclusively autosyndetic in the tetraploid, except for multivalent formation due to interchange heterozygosity. The analysis was considerably facilitated by the use of C-banding techniques at meiosis, by which the chromosomes of each species could be readily identified. In the parents, quadrivalents were formed between homologous but non-identical chromosomes, which also formed autosyndetic bivalents in the hybrids. Meiotic pairing in the hybrids was unaffected by polytypy for C-bands among different populations of the parental species.     

Predicting mean and variance of all possible lines and hybrids from designs with partially inbred progenies

Two-factor mating designs at consecutive S_n and S_(n+1) levels (S₀ and S₁ S₁ and S₂, or F₂ and F₃) allow estimation of all components of the variation among homozygous lines and F₁ hybrids that can be derived from a given population. They also allow for the prediction of the mean of these lines and single-cross hybrids. Some tests for the presence of epistasis are possible at the levels of means and of variances. Such mating designs can be very useful for predicting the value of the best possible lines or the best possible F₁ hybrids when it is difficult to produce, at an experimental level for exploratory purposes, either lines or hybrids.