The asymmetric meiosis in pentaploid dogroses (Rosa sect. Caninae) is associated with a skewed distribution of rRNA gene families in the gametes

In pentaploid dogroses, Rosa section Caninae (2n=5x=35), the pollen transmits one basic genome (x=7) derived from the seven segregating bivalents, whereas the egg transmits four basic genomes (4x=28) one set derived from the segregation of seven bivalents and three sets of univalent-forming chromosomes. Chromosomes from all five genomes carry 18-5.8-26S nuclear ribosomal DNA (rDNA) sites. This mode of sexual reproduction, known as permanent odd polyploidy, can potentially lead to the independent evolution of rDNA on bivalent- and univalent-forming chromosomes. To test this hypothesis, we analyzed rRNA gene families in pollen and somatic leaf tissue of R. canina, R. rubiginosa and R. dumalis. Six major rRNA gene families (alpha, beta, beta' gamma, delta and epsilon) were identified based on several highly polymorphic sites in the internal transcribed spacers (ITSs). At least two of the major rRNA gene families were found in each species indicating that rDNAs have not been homogenized across subgenomes. A comparison of ITS1 sequences from leaf and pollen showed differences: the shared beta rRNA gene family was more abundant among pollen clones compared to leaf clones and must constitute a major part of the rDNA loci on bivalent-forming chromosomes. The gamma and delta families were underrepresented in pollen genomes and are probably located predominantly (or solely) on the univalents. The results support the hypothesis that pentaploid dogroses inherited a bivalent-forming genome from a common proto-canina ancestor, a likely donor of the beta rDNA family. Allopolyploidy with distantly related species is likely to have driven evolution of Rosa section Caninae.     

Genetic recombination in Sorghum bicolor x S. macrospermum interspecific hybrids

Sorghum has been improved by public and private breeding programs utilizing germplasm mostly from within the species Sorghum bicolor. Until recently, cross-incompatibilities have prevented hybridization of S. bicolor with most other species within the genus Sorghum. Utilizing germplasm homozygous for the iap allele, hybrids were readily produced between S. bicolor (2n = 20; AAB1B1) and S. macrospermum (2n = 40; WWXXYYZZ). These hybrids were intermediate to the parents in chromosome number (2n = 30) and overall morphology. Meiosis in both parents was regular; S. bicolor had 10 bivalents per pollen mother cell (PMC) and S. macrospermum had an average of 19.96 bivalents per PMC. Six hybrids were studied cytologically and meiosis was irregular, with the chromosomes associating primarily as univalents and bivalents. There was an average of 3.54 bivalents per PMC, with a range of 0-8 bivalents, most of which were rods (98%). Using FISH (fluorescent in situ hybridization), moderate levels (2.6 II per PMC) of allosyndetic recombination were observed. Genomic relationships were sufficient to assign S. macrospermum the genomic formula AAB1B1YYZZ (Y and Z remain unknown). Allosyndetic recombination in the interspecific hybrids indicates that introgression through genetic recombination should be possible if viable backcrosses can be recovered.     

FISH-mapping of rDNAs and Arabidopsis BACs on pachytene complements of selected Brassicas.

To improve resolution of physical mapping on Brassica chromosomes, we have chosen the pachytene stage of meiosis where incompletely condensed bivalents are much longer than their counterparts at mitotic metaphase. Mapping with 5S and 45S rDNA sequences demonstrated the advantage of pachytene chromosomes in efficient physical mapping and confirmed the presence of a novel 5S rDNA locus in Brassica oleracea, initially identified by genetic mapping using restriction fragment length polymorphism (RFLP). Fluorescence in situ hybridization (FISH) analysis visualized the presence of the third 5S rDNA locus on the long arm of chromosome C2 and confirmed the earlier reports of two 45S rDNA loci in the B. oleracea genome. FISH mapping of low-copy sequences from the Arabidopsis thaliana bacterial artificial chromosome (BAC) clones on the B. oleracea chromosomes confirmed the expectation of efficient and precise physical mapping of meiotic bivalents based on data available from A. thaliana and indicated conserved organization of these two BAC sequences on two B. oleracea chromosomes. Based on the heterologous in situ hybridization with BACs and their mapping applied to long pachytene bivalents, a new approach in comparative analysis of Brassica and A. thaliana genomes is discussed.     

Meiosis in a triploid hybrid of <Emphasis Type="Italic">Gossypium</Emphasis>: high frequency of secondary bipolar spindles at metaphase II

Studies on meiosis in pollen mother cells (PMCs) of a triploid interspecific hybrid (3x = 39 chromosomes, AAD) between tetraploid Gossypium hirsutum (4n = 2x = 52,AADD) and diploid G. arboreum (2n = 2x = 26,AA) are reported. During meiotic metaphase I, 13 AA bivalents and 13 D univalents are expected in the hybrid. However, only 28% of the PMCs had this expected configuration. The rest of the PMCs had between 8 and 12 bivalents and between 12 and 17 univalents. Univalents lagged at anaphase I, and at metaphase II one or a group of univalents remained scattered in the cytoplasm and failed to assemble at a single metaphase plate. Primary bipolar spindles organized around the bivalents and multivalents. In addition to the primary spindle, several secondary and smaller bipolar spindles organized themselves around individual univalents and groups of univalents. Almost all (97%) of the PMCs showed secondary spindles. Each spindle functioned independently and despite their multiple numbers in a cell, meiosis I proceeded normally, with polyad formation. These observations strongly support the view that in plant meiocytes bilateral kinetochore symmetry is not required for establishing a bipolar spindle and that single unpaired chromosomes can initiate and stabilize the formation of a functional bipolar spindle.     

Studies on male and female meiosis in Indian Allium

Male meiosis in autotetraploid Allium tuberosum (4×=32) is fairly regular, keeping in view its cytological status, with 81 percent of the chromosomes associated in quadrivalents and trivalents. About 5% of the cells have 32 univalents. Anaphase segregation is slightly irregular. While 48% of the pollen mitoses show 16 chromosomes, 87% of the mature pollen is viable as indicated by carmine or iodine staining. — Megaspore mother cells have 64 chromosomes associated in 32 bivalents at metaphase I. Anaphase segregation is normal. In three out of 56 cells studied multivalents, bivalents and univalents are observed as in male meiosis. — It is concluded that the species reproduces by pseudogamous parthenogenesis made possible by meiotic modification. This modification is almost perfect and almost completely specific for female meiosis. Slight effects are observed in male meiosis.     

矮牡丹小孢子母细胞减数分裂异常现象的观察

矮牡丹(Paeonia suffruticosa subsp. spontanea)(永济居群)存在多种结构杂合现象,减数分裂存在一些异常:如单价体、异形二价体、互锁四价体、六价体、后期I倒位桥、落后单价体、不均等分离、后期Ⅱ桥和微核等。统计了这些异常现象出现的频率,并对其形成的机制和对正常小孢子形成的影响进行了讨论。从细胞学水平上探讨了矮牡丹可能的濒危机制。同时结合前人的研究,对芍药属内3个组的结构杂合程度进行了比较。     

普通小麦与鹅观草属间杂种F1及BC1的分子细胞遗传学、育性和赤霉病抗性研究

通过胚拯救, 成功获得鹅观草Roegneria kamoji (2n=6x=42, SSHHYY)和普通小麦中国春Triticum aesti-vum (2n=6x=42, AABBDD)的正反交属间杂种F1, 并对这些杂种F1及其BC1的形态学、减数分裂配对行为、育性和赤霉病抗性进行研究。结果表明, (鹅观草×中国春)F1和(中国春×鹅观草)F1的形态介于双亲之间。杂种F1花粉母细胞减数分裂中期I染色体构型分别为40.33I + 0.78II + 0.03III和40.40I + 0.79II 。杂种F1高度雄性不育, 用中国春花粉与其回交可获得BC1代种子。(鹅观草×中国春) F1×中国春BC1植株的染色体数目主要分布在55~63之间, 单价体较多, 植株高度不育; (中国春×鹅观草)F1×中国春BC₁植株染色体数目也主要分布在55~63之间, 但其中部分植株拥有整套小麦染色体且能正常配对、分离, 可形成部分可育花粉粒, 能收到少量自交结实种子。在 (鹅观草×中国春)F1中有1株穗型趋向中国春, 其染色体数目为2n=63, 经染色体分子原位杂交(GISH)检测, 含有42条小麦染色体和21条鹅观草染色体。该杂种F1在减数分裂中期I平均每个花粉母细胞有26.40I+18.30II, 但植株高度雄性不育, 用中国春花粉回交能收到BC₁种子。(鹅观草×中国春) F₁ (2n=63)×中国春BC₁的染色体数目主要分布在40~59之间, 其中的外源染色体已经逐渐减少, 虽然该BC₁的穗型已接近中国春, 但仍然高度不育。赤霉病抗性鉴定结果显示, 所有杂种F1及大部分BC₁对赤霉病均表现出较好的抗性。     

The effect of B chromosomes on homoeologous pairing in species hybrids

The effect of B chromosomes on chromosome pairing at meiosis was investigated in the species hybrid Lolium temulentum x L. perenne at both the diploid and tetraploid level. The presence of B chromosomes drastically reduced association of homoeologous chromosomes in both the diploids and tetraploids. This was evident from the high frequency of univalents recorded in PMC's of diploid hybrids with B's and from the predominantly bivalent association of homologous chromosomes in tetraploids of this type. In the absence of B's homoeologous pairing was extensive giving a high frequency of bivalents in the diploids and multivalents as well as bivalents and univalents in the tetraploids.     

白菜型油菜(B. Chinensis)与海甘蓝(Crambe abyssinica)属间杂种的细胞学观察

白菜型油菜与海甘蓝属间杂种F₁代染色体数目早期为2n=55。经多代组培无性繁殖后,杂种染色体大量减少,数目变化于25～28条间,平均为26条。杂种PMC减数分裂中,平均配对构型为0.06Ⅲ+11.26Ⅱ+3.80Ⅰ,二价体数目变化于8～13之间,以10Ⅱ、11Ⅱ、12Ⅱ的细胞出现频率较高,分别为26.60%,23.91%和30.98%,单价体数目变化于0～8个之间。杂种染色体数目减少,二价体个数较高,这说明海甘蓝染色体在大量丢失的同时,白菜型油菜的染色体组发生了自然加倍。在后期Ⅱ观察到三分体、染色体落后、染色体桥等异常现象。      

Comparative physical mapping of the 18S-5.8S-26S rDNA in three sorghum species.

The physical locations of the 18S-5.8S-26S rDNA sequences were examined in three sorghum species by fluorescence in situ hybridization (FISH) using biotin-labeled heterologous 18S-5.8S-26S rDNA probe (pTa71). Each 18S-5.8S-26S rDNA locus occurred at two sites on the chromosomes in Sorghum bicolor (2n = 20) and S. versicolor (2n = 10), but at four sites on the chromosomes of S. halepense (2n = 40) and the tetraploid S. versicolor (2n = 20). Positions of the rDNA loci varied from the interstitial to terminal position among the four accessions of the three sorghum species. The rDNA data are useful for investigation of chromosome evolution and phylogeny. This study excluded S. versicolor as the possible progenitor of S. bicolor.     

Studies on Chromosome Behaviour of F1 and Fertility Restoration in Hybrid of Gossypium hirtutum ×G. bickii

By means of dripping GAs(50 ppm) and NAA(40 ppm) on the hybrid boll-embryo culture in vitro, one F1 plant of G. hirsuturn × G. bickii was obtained in 1982, the Fx plant flowered profusely but failed to produce any seeds when selfed or back crossed. In meiosis of the pollen mother cell (PMC), mean chromosome coniugation was 33.24 Ⅰ +2.67 Ⅱ +0.095 Ⅲ + 0.048 Ⅳ with high frequence (77.6%) of one chiasma attenuated bivalents. Mean number of chiasmta per bivalents was 1.23. The univalents were scattered over the achromatic figure for most PMCs. Although a few of the bivalents were located in' the equatorial region, but they did not form a definite plate. At the second anaphase the distribution of chromosomes was very irregular. In the majority of cases, multipolar distripution of chromosomes was observed. At the completion of meiosis highly abnormal sporads occurred, which contained from 2 ro 13 spores of various sizes. Thus, all of the pollen grains produced were sterile. When the F1 branches were grafted onto the upland cotton and thence they were backcrossed under short day (12 hours) and cold night(15–18℃) exposure, BC1 seeds could be harvested. BC1 and BC2 plants could grow up later. In the BC, generation, the fertility of the hybrid was restored. By 1988, ten pure lines of hybrid with the characers of both male parent (viz.red petal with purple spot and strong fibre) and female parent (white fibre, high yield, earliness ect.) were selected for the first time.     

Cytological studies on F1 hybrids of Solanum integrifolium with S. melongena and S. melongena var. insanum

S. integrifolium (2n = 24) can easily be crossed as the pistillate parent with S. melongena (2n = 24) and S. melongena var. insanum (2n = 24). However, crosses in the other direction do not succeed. Both hybrids are vigorous. Chromosome association at diakinesis and metaphase I was studied. Chromosome associations higher than bivalents were observed in the hybrids indicating structural repatterning of chromosomes. The modal chromosome association in hybrids was twelve bivalents per PMC. This is suggestive of the retention of ancestral chromosome homeologies by the taxa concerned. Despite regular meiosis both hybrids were highly pollen-sterile (about 95%), which was attributed to segregational events of the recombined chromosomes.     

Chromosome pairing in triploid intergeneric hybrids ofFestuca pratensis withLolium multiflorum, revealed by GISH

Genomic in situ hybridisation (GISH) was used to reveal chromosome pairing in two partly fertile, triploid (2n = 3x = 21) hybrids obtained by crossing the diploid (2n = 2x = 14) Festuca pratensis Huds. (designated FpFp), used as a female parent, with the autotetraploid (2n = 4x = 28) Lolium multiflorum Lam. (designated LmLmLmLm), used as a male parent. The pattern of chromosome pairing calculated on the basis of the mean values of chromosome configurations identified in all 100 PMCs analysed, was: 0.71I Lm + 2.24I Fp + 2.18II Lm/Lm + 0.54II Lm/Fp + 4.18III Lm/Lm/Fp. A relatively high number of Lm/Lm bivalents and Fp univalents, and a low number of Lm/Fp bivalents and Lm univalents indicated that the pairing was preferential between L. multiflorum chromosomes. Other observations regarding chromosome pairing within the Lm/Lm/Fp trivalents also confirmed this preferential pairing in the analysed triploids, as the Fp chromosome was not randomly located in the chain- and frying-pan-shaped trivalents. The similarities and differences in chromosome pairing at metaphase I and the level of preferential pairing between Lolium chromosomes in the different triploid Lolium-Festuca hybrids are discussed.     

小麦ph1b突变体与小黑麦杂交的细胞遗传学研究

本文利用普通小麦品系"中国春"(对照)、中国春ph1b突变体分别与八倍体小黑麦、六倍体小黑麦杂交,杂种F1的减数分裂前期Ⅰ染色体行为表现异常,中期Ⅰ出现较多的单价体、棒状二价体和多价体,在后期和末期出现落后染色体、染色体片断和微核。原因是ph1b基因的存在造成染色体联会机制紊乱,致使一些部分同源染色体配对并发生互换,有可能在以后的世代产生染色体易位与基因重组。     

普通小麦与鹅观草属间杂种F1及BC1的分子细胞遗传学、育性和赤霉病抗性研究

通过胚拯救, 成功获得鹅观草Roegneria kamoji (2n=6x=42, SSHHYY)和普通小麦中国春Triticum aesti-vum (2n=6x=42, AABBDD)的正反交属间杂种F1, 并对这些杂种F1及其BC1的形态学、减数分裂配对行为、育性和赤霉病抗性进行研究。结果表明, (鹅观草×中国春)F1和(中国春×鹅观草)F1的形态介于双亲之间。杂种F1花粉母细胞减数分裂中期I染色体构型分别为40.33I + 0.78II + 0.03III和40.40I + 0.79II 。杂种F1高度雄性不育, 用中国春花粉与其回交可获得BC1代种子。(鹅观草×中国春) F1×中国春BC1植株的染色体数目主要分布在55~63之间, 单价体较多, 植株高度不育; (中国春×鹅观草)F1×中国春BC₁植株染色体数目也主要分布在55~63之间, 但其中部分植株拥有整套小麦染色体且能正常配对、分离, 可形成部分可育花粉粒, 能收到少量自交结实种子。在 (鹅观草×中国春)F1中有1株穗型趋向中国春, 其染色体数目为2n=63, 经染色体分子原位杂交(GISH)检测, 含有42条小麦染色体和21条鹅观草染色体。该杂种F1在减数分裂中期I平均每个花粉母细胞有26.40I+18.30II, 但植株高度雄性不育, 用中国春花粉回交能收到BC₁种子。(鹅观草×中国春) F₁ (2n=63)×中国春BC₁的染色体数目主要分布在40~59之间, 其中的外源染色体已经逐渐减少, 虽然该BC₁的穗型已接近中国春, 但仍然高度不育。赤霉病抗性鉴定结果显示, 所有杂种F1及大部分BC₁对赤霉病均表现出较好的抗性。     

一种新的六倍体细胞类型水生薏苡的细胞遗传学鉴定

通过醋酸洋红压片和荧光原位杂交技术(包括基因组原位杂交技术),确定在我国广西西南部地区广泛分布着的水生薏苡(Coix aquatica Roxb.)属于一种新的六倍体细胞类型.这种水生薏苡与已报道的几种水生薏苡细胞类型的染色体数目均不相同,它的染色体数目是2n=30,在减数分裂前期Ⅰ和中期Ⅰ的细胞中形成10个二价体和10个单价体.基因组原位杂交结果表明,这种水生薏苡的20条染色体与四倍体的薏苡(C.lacryma-jobi,2n＝20)的基因组DNA是高度同源的.45S和5S rDNA分别杂交到这种水生薏苡的两条染色体上,其中各有一条染色体与薏苡中携带45S和5S rDNA杂交信号的染色体具有相同的形状和信号的分布状态.据此推测:四倍体的薏苡可能是这种新的水生薏苡细胞类型的一个亲本,它的另一个亲本可能是八倍体的水生薏苡(C.aquatica,2n＝40),因为这种八倍体的水生薏苡在核型、植株形态及生长环境等方面与新的六倍体细胞类型的水生薏苡相似.     

The use of double fluorescence in situ hybridization to physically map the positions of 5S rDNA genes in relation to the chromosomal location of 18S-5.8S-26S rDNA and a C genome specific DNA sequence in the genus Avena.

A physical map of the locations of the 5S rDNA genes and their relative positions with respect to 18S-5.8S-26S rDNA genes and a C genome specific repetitive DNA sequence was produced for the chromosomes of diploid, tetraploid, and hexaploid oat species using in situ hybridization. The A genome diploid species showed two pairs of rDNA loci and two pairs of 5S loci located on both arms of one pair of satellited chromosomes. The C genome diploid species showed two major pairs and one minor pair of rDNA loci. One pair of subtelocentric chromosomes carried rDNA and 5S loci physically separated on the long arm. The tetraploid species (AACC genomes) arising from these diploid ancestors showed two pairs of rDNA loci and three pairs of 5S loci. Two pairs of rDNA loci and 2 pairs of 5S loci were arranged as in the A genome diploid species. The third pair of 5S loci was located on one pair of A-C translocated chromosomes using simultaneous in situ hybridization with 5S rDNA genes and a C genome specific repetitive DNA sequence. The hexaploid species (AACCDD genomes) showed three pairs of rDNA loci and six pairs of 5S loci. One pair of 5S loci was located on each of two pairs of C-A/D translocated chromosomes. Comparative studies of the physical arrangement of rDNA and 5S loci in polyploid oats and the putative A and C genome progenitor species suggests that A genome diploid species could be the donor of both A and D genomes of polyploid oats. Key words : oats, 5S rDNA genes, 18S-5.8S-26S rDNA genes, C genome specific repetitive DNA sequence, in situ hybridization, genome evolution.     

不同染色技术和双色荧光原位杂交技术对宽翅菘蓝 （Isatis violascens Bunge）的细胞遗传学分析

为了解十字花科菘蓝属植物宽翅菘蓝(宽翅菘蓝,Isatis violascens Bunge)的染色体结构,本文利用45SrDNA和5SrDNA双色荧光原位杂交、银染技术和CMA3对宽翅菘蓝进行分子细胞遗传学研究。45SrDNA和5SrDNA荧光原位杂交结果显示宽翅菘蓝染色体上有1对45SrDNA信号和1对5SrDNA信号;银染结果显示其中期染色体有1对银染点;CMA3染色结果发现宽翅菘蓝中期染色体存在1对CMA3信号。     

Physical mapping of 5S and 18S-25S rDNA and repetitive DNA sequences in Aegilops umbellulata.

An accurate physical map of the location of the 5S and the 18S-5.8S-25S rRNA genes and a repetitive DNA sequence has been produced on Aegilops umbellulata Zhuk., (2n = 2x = 14) chromosomes by in situ hybridization. Chromosome morphology together with the hybridization pattern of pSc119.2, a DNA sequence from rye, allowed identification and discrimination of different chromosomes; pSc119.2 hybridizes with all Ae. umbellulata chromosomes at the telomeres, except for the short arm of chromosome 6U, and shows intercalary sites on the long arms of chromosomes 6U and 7U. The 5S and 18S-25S rDNA have been mapped physically only on the short arms of chromosomes 1U and 5U. On chromosome 1U the order of the genes is 5S rDNA subterminal and 18S-25S rDNA more proximal, while on chromosome 5U the position of the genes is reversed. The relative order of the genes, together with the hybridization pattern of the pSc119.2, is useful in identifying whole chromosomes or chromosome segments from Ae. umbellulata in recombinant or addition lines with wheat. The data help link the physical organization of chromosomes to the genetic map. Other members of the Triticeae vary in the presence and order of the 5S and 18S-25S rDNA sequences on groups 1 and 5, indicating multiple and complex evolutionary rearrangements of the chromosome arms.