The Effect of Substitution of Chromosome 5A with an Extra Chromosome 5B in the Progeny of a Somaclonal Common Wheat Line Monosomic for 5A

Cytogenetic analysis was employed in studying the cause of generation of fertile awned forms in the progeny of plants, which were selected from a speltoid somaclonal wheat line monosomic for chromosome 5A (2n = 41 = 20II + I), had speltoid spikes, and were reproduced by self pollination. On cytogenetic and genetic evidence, chromosome 5A was eliminated and the copy number of chromosome 5B increased in the plants examined. The appearance of an extra chromosome 5B is probably caused by nondisjunction of bivalent 5B in the presence of a telocentric originating from the long arm of chromosome 5A. A difference in meiotic segregation was observed for univalent chromosomes 5A and 5B.     

Genetic analysis of the traits introgressed from <Emphasis Type="Italic">Aegilops speltoides</Emphasis> Tausch. to bread wheat and determined by chromosome 5A genes

A winter bread wheat accession from the Arsenal collection was genetically examined to study the results of introgression, which substantially changed the physiological and morphological traits of the original spring cultivar Rodina. Apart from its winter habit, the accession was characterized by awned speltoid spikes, suggesting introgression into chromosome 5A, which carries marker genes in the order Vrn-A1-Q-B1. Genetic analysis showed that the chromosome fragment introgressed from Aegilops speltoides recombined well with the homeologous region of bread wheat chromosome 5A in the region between the Vrn-A1 and Q genes. Recombination between the Vrn-A1 and B1 genes was not detected, and it was assumed that the order of the marker genes of chromosome 5A was inverted to produce Q-Vrn-A1-B1. When the winter introgression line was crossed with Triticum spelta L., an interaction of two dominant genes determining the spike character was for the first time detected in F₁, increasing the spike length and the number of spikelets, and followed with transgression in F₂. It was assumed that Ae. speltoides had a homeoallelic speltoid gene, which was designated as Q ^S .     

A comparative genetic and cytogenetic mapping of wheat chromosome 5B using introgression lines

The genetic map of chromosome 5B has been constructed by using microsatellite (SSR) analysis of 381 plants from the F2 population produced by cross of the Chinese Spring (CS) and Renan cultivars. Initially, 180 SSR markers for the common wheat 5B chromosome have been used for analysis of these cultivars. The 32 markers able to detect polymorphism between these cultivars have been located on the genetic map of chromosome 5B. Cytogenetic mapping has involved a set of CS 5B chromosome deletion lines. Totally, 51 SSR markers have been located in ten regions (deletion bins) of this chromosome by SSR analysis of these deletion lines. Five genes—TaCBFIIIc-B10, Vrn-B1, Chi-B1, Skr, and Ph1—have been integrated into the cytogenetic map of chromosome 5B using the markers either specific of or tightly linked to the genes in question. Comparison of the genetic and cytogenetic maps suggests that recombination is suppressed in the pericentromeric region of chromosome 5B, especially in the short arm segment. The 18 markers localized to deletion bins 5BL16-0.79-1.00 and 5BL18-0.66-0.79 have been used to analyze common wheat introgression lines L842, L5366-180, L73/00i, and L21-4, carrying fragments of alien genomes in the terminal region of 5B long arm. L5366-180 and L842 lines carry a fragment of the Triticum timopheevii 5GL chromosome, while L73/00i and L21-4 lines, a fragment of the Aegilops speltoides 5SL chromosome. As has been shown, the translocated fragments in these four lines are of different lengths, allowing bin 5BL18-0.66-0.79 to be divided into three shorter regions. The utility of wheat introgression lines carrying alien translocations for increasing the resolution of cytogenetic mapping is discussed.     

Preferential elimination of chromosome 5R of rye in the progeny of 5R5D dimonosomics

Transmission of chromosome 5R of rye (Secale cereale L.) and chromosome 5D of common wheat (Triticum aestivum L.) through gametes of 5R5D dimonosomics (2n = 42, 20W″ + 5R′ + 5D′) was studied. Chromosome 5R was found to have lower competitiveness as compared to 5D. Gametes with the rye chromosome were two times less often involved in the formation of a progeny. The combined frequency of the karyotypes of wheat (5D5D) and wheat monosomics (5D) was 11.6-fold higher than the frequency of the karyotypes of substitution lines (5R5R) and monosomics for the rye chromosome (5R). The karyotypes of 10.38% of hybrid plants had aberrant 5R chromosomes with different translocations formed as a result of breakages in the centromere and in the proximal region of the long arm. Telocentrics for the short arm t5RS, i5RS isochromosomes, and chromosomes with a terminal deletion T5RS.5RL-del were identified. The absence of amplification of SSR markers mapped on 5RS and the detection of PCR products for a number of 5RL markers (including the genome-specific rye marker Xrms115) permitted nine plants carrying only the long arm of chromosome 5R to be revealed. Since t5RL telocentrics were not detected by the cytological analysis, the results obtained allow us to suggest the presence of small intercalary translocations of the long arm of chromosome 5R in chromosome 5D or in other wheat chromosomes.     

Sequences associated with A chromosome centromeres are present throughout the maize B chromosome

Maize chromosome spreads containing the supernumerary B chromosome were hybridized with probes from various repetitive elements including CentC, CRM, and CentA, which have been localized to centromeric regions on the A chromosomes. Repetitive elements that are enriched or found exclusively near the centromeres of A chromosomes hybridized to many sites distinct from the centromere on the B chromosome. To examine whether these elements recruit kinetochore proteins at locations other than the canonical B centromere, cells were labeled with antibodies against CENH3, a key kinetochore protein. No labeling was detected outside the normal centromere and no evidence of B chromosome holocentromeric activity was observed. This finding suggests that, as in other higher eukaryotes, DNA sequence alone is insufficient to dictate kinetochore location in plants. Additionally, examination of the B centromere region in pachytene chromosomes revealed that the B-specific element ZmBs hybridizes to a much larger region than the site of hybridization of CentC, CRM, and CentA and the labeling by anti-CENH3 antibodies.This revised version was published online in December 2004 with corrections to Table 1.     

Assignment of the human gene for hexosaminidase B to chromosome 5

Mouse-human somatic cell hybrids between different mouse and human cells were studied for the expression of human hexosaminidases A and B activities. The expression of human hexosaminidase B in the hybrids was found to segregate concordantly with the presence of the human chromosome 5. Mouse-human hybrid clones containing either the human chromosomes 5 and 7 only or the human chromosome 7 only were also included in this study. Expression of human hexosaminidase B activity was detected only in those clones containing human chromosome 5. These results indicate that the gene(s) for human hexosaminidase B is located on chromosome 5. No hexosaminidase A activity was detected in clones which contained either human chromosomes 5 and 7 or chromosome 7.     

小麦-黑麦附加系的创制及5R抗白粉病新基因的发现

以重复序列pAS1和pSc119.2为探针,对八倍体小黑麦×普通小麦的F5代植株进行了FISH分析,同时对这些材料进行了田间抗病性鉴定。从中鉴定出了1R、2R、3R、4R、5R、6R、7R单体附加系和1R、2R二体附加系,1R和4R附加系出现频率相对较高。5R和6R单体附加系对白粉病免疫,推测5R染色体上带有新的白粉病抗性基因。此外,还检测到不少植株染色体组发生了变异,且小麦4B染色体优先缺失。     

A complete set of maize individual chromosome additions to the oat genome

All 10 chromosomes of maize (Zea mays, 2n = 2x = 20) were recovered as single additions to the haploid complement of oat (Avena sativa, 2n = 6x = 42) among F(1) plants generated from crosses involving three different lines of maize to eight different lines of oat. In vitro rescue culture of more than 4,300 immature F(1) embryos resulted in a germination frequency of 11% with recovery of 379 F(1) plantlets (8.7%) of moderately vigorous growth. Some F(1) plants were sectored with distinct chromosome constitutions among tillers of the same plant and also between root and shoot cells. Meiotic restitution facilitated development of un-reduced gametes in the F(1). Self-pollination of these partially fertile F(1) plants resulted in disomic additions (2n = 6x + 2 = 44) for maize chromosomes 1, 2, 3, 4, 6, 7, and 9. Maize chromosome 8 was recovered as a monosomic addition (2n = 6x + 1 = 43). Monosomic additions for maize chromosomes 5 and 10 to a haploid complement of oat (n = 3x + 1 = 22) were recovered several times among the F(1) plants. Although partially fertile, these chromosome 5 and 10 addition plants have not yet transmitted the added maize chromosome to F(2) offspring. We discuss the development and general utility of this set of oat-maize addition lines as a novel tool for maize genomics and genetics.     

Mapping genes affecting flowering time and frost resistance on chromosome 5B of wheat

Two populations of single chromosome recombinant lines were used to map genes controlling flowering time on chromosome 5B of wheat, and one of the populations was also used to map a new frost resistance gene. Genetic maps were developed, mainly using microsatellite markers, and QTL analysis was applied to phenotypic data on the performance of each population collected from growth-room tests of flowering time and frost tolerance. Using a recombinant substitution-line mapping population derived from a cross between the substitution-line 'Chinese Spring' ('Cheyenne' 5B) and 'Chinese Spring' (CS), the gene Vrn-B1, affecting vernalization response, an earliness per se locus, Eps-5BL1, and a gene, Fr-B1, affecting frost resistance, were mapped. Using a 'Hobbit Sib' ('Chinese Spring' 5BL) x 'Hobbit Sib' recombinant substitution line mapping population, an earliness per se locus, Eps-5BL2 was mapped. The Vrn-B1 locus was mapped on the distal portion of the long arm of chromosome 5B, to a region syntenous with the segments of chromosomes 5A and 5D containing Vrn-A1 and Vrn-D1 loci, respectively. The two Eps-5BL loci were mapped close to the centromere with a 16-cM distance from each other, one in agreement with the position of a homoeologous locus previously mapped on chromosome 5H of barley, and suggested by the response of 'Chinese Spring' deletion lines. The Fr-B1 gene was mapped on the long arm of chromosome 5B, 40 cM from the centromeric marker. Previous comparative mapping data with rice chromosome 9 would suggest that this gene could be orthologous to the other Fr genes mapped previously by us on chromosomes 5A or 5D of wheat, although in a more proximal position. This study completes the mapping of these homoeoallelic series of vernalization requirement genes and frost resistance genes on the chromosomes of the homoeologous group 5 in wheat.     

Identification and characterization of segregation distortion loci along chromosome 5B in tetraploid wheat

Segregation distortion genes are widespread in plants and animals and function by their effect on competition among gametes for preferential fertilization. In this study, we evaluated the segregation distortion of molecular markers in multiple reciprocal backcross populations derived from unique cytogenetic stocks involving the durum cultivar Langdon (LDN) and wild emmer accessions that allowed us to study the effects of chromosome 5B in isolation. No segregation distortion of female gametes was observed, but three populations developed to analyze segregation of male gametes had genomic regions containing markers with skewed segregation ratios. One region of distortion was due to preferential transmission of LDN alleles over wild emmer alleles through male gametes. Another region required the presence of LDN 5B chromosomes in the female for preferential fertilization by male gametes harboring LDN alleles indicating that the corresponding genes in the female gametes can govern genes affecting segregation distortion of male gametes. A third region of distortion was the result of preferential transmission of wild emmer alleles over LDN alleles through male gametes. These results indicate the existence of different distorter/meiotic drive elements among different genotypes and show that distortion factors along wheat chromosome 5B differ in chromosomal location as well as underlying mechanisms.     

Dissection of barley chromosome 5H in common wheat

We dissected barley chromosome 5H added to common wheat by a genetic method or the gametocidal system. Firstly, we induced chromosomal breaks in the offspring of a 5H addition line of common wheat carrying a gametocidal chromosome and cytologically screened for plants with structural chromosomal changes involving 5H, such as deletions and translocations. Secondly, we screened the progeny of such plants to establish common wheat lines carrying structurally changed chromosomes containing single segments of the dissected 5H. Using 23 representative 5H dissection lines, we physically mapped 97 barley EST markers assigned to 5H. The ESTs fell into 20 regions of 5H between the breakpoints of the 23 dissected segments, distributing rather evenly along the chromosome, with significantly higher frequency in the distal region of the long arm. The ESTs, in turn, allowed us to distinguish the breakpoints of dissected 5H segments. We demonstrated by PCR (polymerase chain reaction), as well as by in situ hybridization, that these dissected 5H segments were stably transmitted in the dissection lines. We discuss the usefulness of the 5H dissection lines for physical mapping of DNA markers. These 5H dissection lines are available from National BioResource Projects-Wheat, Japan.     

Generation of B. nigra-B. rapa chromosome addition stocks: cytology and microsatellite markers (SSRs) based characterization

To improve Brassica nigra, the B-genome donor for Brassica juncea through selective introgression of useful variation from A-genome chromosomes, B. nigra-B. rapa chromosome addition stocks were successfully synthesized for the first time. Resynthesized B. juncea was used as B-genome donor species and A-genome addition stocks were developed by hybridizing sesquidiploid plant (ABB) as female and using B. nigra as the male parent. Various cycles of backcrossing and/or selfing were utilized to isolate plants carrying addition of three A-genome chromosomes in the background of B. nigra. These chromosome addition stocks were characterized by chromosome counts, pollen and seed fertility and chromosome specific microsatellite (SSRs) markers. The chromosome number in different backcross/self generations ranged between 2n=26 and 2n=19 with relatively high frequency of univalents (8-10I) at in meiotic configurations observed, suggesting the role of preferential transmission of A-genome chromosomes. SSRs analysis revealed that B. rapa chromosomes 3 and 4 were the first to get eliminated followed by chromosome 10. Remaining chromosomes were maintained till BC(1)F(4). However, second cycle of backcrossing (BC(2)) led to the elimination of chromosome numbers 1 and 2. BC(2)F(2) plants carried the chromosome numbers 6, 7, 8 and 9. Generation BC(3) having plants with 2n=19 carried chromosome numbers 6, 7 and 8. It is possible that chromosomes 6, 7 and 8 had higher transmission frequency and these were better tolerated by the B. nigra genome.     

Assessing the level of collinearity between Arabidopsis thaliana and Brassica napus for A. thaliana chromosome 5.

This study describes a comprehensive comparison of chromosome 5 of the model crucifer Arabidopsis with the genome of its amphidiploid crop relative Brassica napus and introduces the use of in silico sequence homology to identify conserved loci between the two species. A region of chromosome 5, spanning 8 Mb, was found in six highly conserved copies in the B. napus genome. A single inversion appeared to be the predominant rearrangement that had separated the two lineages leading to the formation of Arabidopsis chromosome 5 and its homologues in B. napus. The observed results could be explained by the fusion of three ancestral genomes with strong similarities to modern-day Arabidopsis to generate the constituent diploid genomes of B. napus. This supports the hypothesis that the diploid Brassica genomes evolved from a common hexaploid ancestor. Alignment of the genetic linkage map of B. napus with the genomic sequence of Arabidopsis indicated that for specific regions a genetic distance of 1 cM in B. napus was equivalent to 285 Kb of Arabidopsis DNA sequence. This analysis strongly supports the application of Arabidopsis as a tool in marker development, map-based gene cloning, and candidate gene identification for the larger genomes of Brassica crop species.     

Identification of Brassica oleracea monosomic alien chromosome addition lines with molecular markers reveals extensive gene duplication

Summary Chromosomes of Brassica oleracea (2n=18) were dissected from the resynthesized amphidiploid B. napus Hakuran by repeated backcrosses to B. campestris (2n=20), creating a series of monosomic alien chromosome addition line plants (2n=21). Using morphological, isozyme and restriction fragment length polymorphism markers (RFLPs), 81 putative loci were identified. Of nine possible synteny groups, seven were represented in the 25 monosomic addition plants tested. Sequences homologous to 26% of the 61 DNA clones utilized (80% were cDNA clones) were found on more than one synteny group, indicating a high level of gene duplication. Anomalous synteny associations were detected in four 2n=21 plants. One of these plants showed two markers from one B. oleracea chromosome associated with a second complete B. oleracea synteny group, suggesting translocation or recombination between non-homologous chromosomes in Hakuran or the backcross derivatives. The other three 2n=21 plants each contained two or more B. oleracea synteny groups, suggesting chromosome substitution.     

Use of RFLPs to determine the chromosome composition of tetraploid triticale (A/B)(A/B)RR.

Tetraploid triticale, (A/B)(A/B)RR (2n = 28), is a botanical novelty, an amphiploid composed of a diploid rye and a 14 chromosome wheat genome made up of chromosomes of the A and B genomes of tetraploid wheat. Restriction fragment length polymorphism (RFLP) markers were used to elucidate the chromosome composition of the mixed wheat genome of 35 different tetraploid triticale lines. Of 128 possible A/B chromosome pair combinations, only 6 were found among these lines, with a prevalence of the 1A, 2A, 3B, 4B, 5B, 6B, and 7B karyotype. In most triticale lines stable wheat genomes made up of only homologous A or B genome chromosome pairs were identified, however, in some lines homoeologous chromosome pairs were found. In this paper we demonstrate that RFLPs can be used successfully as an alternative to C-banding for the identification of the chromosome composition of tetraploid triticale and discuss the possible selective advantage of specific chromosome composition.     

Alteration of chromosome behavior and synchronization of parental chromosomes after successive generations in Brassica napus x Orychophragmus violaceus hybrids.

In an earlier study, the progenies of intergeneric hybrids Brassica napus (2n = 38) x Orychophragmus violaceus (2n = 24) were investigated in successive generations (F1-F4) for the cytological phenomenon of parental genome separation during mitotic and meiotic division. In the present study, inbred lines (F5-F8) derived from 1 such hybrid were characterized for morphology, chromosome pairing behaviour, and genome composition. One F5 plant (2n = 31) with slightly yellow petals and 12:19 and 15:16 segregation ratios in its pollen mother cells (PMCs) produced F6 plants with distinct morphological characteristics and wide variations in fertility and chromosome numbers (2n = 25-38). F7 and F8 lines with distinctive morphology and wide ranges in chromsome numbers were established. In PMCs of F7 plants from 4 F6 plants, 0-12 labelled chromosomes from O. violaceus, which predominantly appeared as bivalents, were identified by genomic in situ hybridization. They behaved synchronously with B. napus chromosomes during meiotic division. The results provide molecular cytogenetic evidence of the inclusion of O. violaceus chromosomes in the original hybrids and the cytology in the hybrids documented earlier. They also show that chromosome behaviour was altered and the parental chromosomes became synchronized after successive generations.     

Effect of the 5R(5A) alien chromosome substitution on the growth habit and winter hardiness of wheat

The growth habit, ear emergence time, and frost tolerance of wheat/rye substitution lines have been studied in cultivars Rang and Mironovskaya Krupnozernaya whose chromosome 5A is substituted with chromosome 5R of Onkhoyskaya rye. Hybrid analysis has demonstrated that the spring habit of the recipient cultivars Rang and Mironovskaya Krupnozernaya is controlled by dominant gene Vrn-A1 located in chromosome 5A. Onokhoyskaya rye has a dominant gene for the spring habit (Sp1) located in chromosome 5R. It has been found that the resultant 5R(5A) alien-substitution lines have a winter type of development and ears do not emerge during summer in plants sown in spring. The change in growth habit has been shown to be related to the absence of the rye Spl gene expression in the substitution lines. The winter hardiness of winter 5R(5A) alien-substitution lines has been studied under the environmental conditions of Novosibirsk. Testing the lines in the first winter demonstrated that their winter survival is 20-27%. The possible presence of the frost resistance gene homeoallelic to the known genes Fr1 and Fr2 of the common wheat located on chromosomes 5A and 5D, respectively, is discussed.     

Identification of a QTL conferring seedling and adult plant resistance to eyespot on chromosome 5A of Cappelle Desprez

Eyespot is an economically important fungal disease of wheat and other cereals caused by two fungal species: Oculimacula yallundae and Oculimacula acuformis. However, only two eyespot resistance genes have been characterised and molecular markers made available to plant breeders. These resistances are Pch1, introduced into wheat from the relative Aegilops ventricosa, and Pch2, originally identified in the cultivar Cappelle Desprez (CD). There are drawbacks associated with both resistances; Pch1 is linked to deleterious traits carried on the Ae. ventricosa introgression and Pch2 has been shown to have limited effectiveness. An additional resistance has been reported on chromosome 5A of CD that confers resistance to eyespot in adult plants. In the present study, we demonstrate that resistance on this chromosome is effective against both O. yallundae and O. acuformis eyespot pathogens and confers resistance at both seedling and adult plant stages. This resistance was mapped in both seedling bioassays and field trials in a 5A recombinant population derived from a cross between CD and a CD single chromosome substitution line carrying 5A from the susceptible line Bezostaya. The resistance was also mapped using seedling bioassays in a 5A recombinant population derived from a cross between the susceptible line Chinese Spring (CS) and a single chromosome substitution line carrying 5A from CD. A single major QTL on the long arm of chromosome 5A was detected in all experiments. Furthermore, the SSR marker Xgwm639 was found to be closely associated with the resistance and could be used for marker-assisted selection of the eyespot resistance by plant breeders.     

Characterization of a maize chromosome 4 centromeric sequence: evidence for an evolutionary relationship with the B chromosome centromere

Previous work has identified sequences specific to the B chromosome that are a major component of the B centromere. To address the issue of the origin of the B and the evolution of centromere-localized sequences, DNA prepared from plants without B chromosomes was probed to seek evidence for related sequences. Clones were isolated from maize line B73 without B chromosomes by screening DNA at reduced stringency with a B centromeric probe. These clones were localized to maize centromere 4 using fluorescence in situ hybridization. They showed homology to a maize centromere-mapped sequence, to maize B chromosome centromere sequences, and to a portion of the unit repeat of knobs, which act as neocentromeres in maize. A representative copy was used to screen a BAC library to obtain these sequences in a larger context. Each of the six positive BACs obtained was analyzed to determine the nature of centromere 4-specific sequences present. Fifteen subclones of one BAC were sequenced and the organization of this chromosome 4-specific repeat was examined.