The use of multiple alien chromosome addition aneuploids facilitates genetic linkage mapping of the Gossypium G genome.

Primary germplasm pools represent the most accessible source of new alleles for crop improvement, but not all effective alleles are available in the primary germplasm pool, and breeders must sometimes confront the difficulties of introgressing genes from the secondary and tertiary germplasm pools in cotton by using synthetic polyploids as introgression bridges. Two parental Gossypium nelsonii x Gossypium australe AFLP genetic linkage maps were used to identify G genome chromosome-specific molecular markers, which in turn were used to track the fidelity and frequency of G. australe chromosome transmission in a Gossypium hirsutum x G. australe hexaploid bridging family. Conversely, when homoeologous recombination is low, first generation aneuploids are useful adjuncts to genetic linkage mapping. Although locus ordering was not possible, the distribution of AFLP markers among 18 multiple chromosome addition aneuploids identified mapping errors among the G. australe and G. nelsonii linkage groups and assigned non-segregating G. australe AFLPs to linkage groups. Four putatively recombined G. australe chromosomes were identified in 5 of the 18 aneuploids. The G. australe and G. nelsonii genetic linkage maps presented here represent the first AFLP genetic linkage maps for the Gossypium G genome.     

Current applications of wheat and wheat–alien precise genetic stocks

A comprehensive collection of wheat aneuploids, whole chromosome substitutions (both intervarietal and interspecific) and wheat–alien addition lines, along with various introgression and near-isogenic lines, has been created over a period of years, primarily to provide the means of localizing the genes underpinning traits and to introduce novel genes into the bread wheat genome. For a time, interest in this class of genetic material was on the wane, but more recently it has revived in the context, for example, of localizing DNA-based markers, designing chromosome-specific bacterial artificial chromosome libraries, and establishing functional differences between alleles and homoeoalleles. Here, a brief review is provided of recent applications of precise genetic stocks in the field of molecular genetics, functional genetics and genomics of the Triticeae species.     

Isolation and characterization of wheat-rye recombinants involving chromosome arm 1DS of wheat

Summary The introgression of genetic material from alien species is assuming increased importance in wheat breeding programs. One example is the translocation of the short arm of rye chromosome 1 (1RS) onto homoeologous wheat chromosomes, which confers disease resistance and increased yield on wheat. However, this translocation is also associated with dough quality defects. To break the linkage between the desirable agronomic traits and poor dough quality, recombination has been induced between 1RS and the homoeologous wheat arm IDS. Seven new recombinants were isolated, with five being similar to those reported earlier and two havina new type of structure. All available recombinantsw ere characterized with DNA probes for the loci Nor-R1, 5SDna-R1, and Tel-R1. Also, the amount of rye chromatin present was quantified with a dispersed rye-specific repetitive DNA sequence in quantitative dot blots. Furthermore, the wheat-rye recombinants were used as a mapping tool to assign two RFLP markers to specific regions on chromosome arms 1DS and 1RS of wheat and rye, respectively.     

The genetic identity of alien chromosomes in potato breeding lines revealed by sequential GISH and FISH analyses using chromosome-specific cytogenetic DNA markers.

Genomic in situ hybridization (GISH) is one of the most popular and effective techniques for detecting alien chromatin introgressed into breeding lines; however, GISH analysis alone does not reveal the genetic identity of the alien chromosomes. We previously isolated a set of bacterial artificial chromosomes (BACs) specific to each of the 12 potato chromosomes. These BAC clones can be used as chromosome-specific cytogenetic DNA markers (CSCDMs) for potato chromosome identification. Here we demonstrate that GISH and fluorescence in situ hybridization (FISH), using CSCDMs, can be performed sequentially on the same chromosome preparations. Somatic metaphase chromosomes prepared using an enzymatic digestion and "flame-drying" procedure allows repeated probing up to five times without significant damage to chromosome morphology. The sequential GISH and FISH analyses reveal the genomic origin and genetic identity of the alien chromosomes in a single experiment and also determine whether an alien chromosome has been added to the genetic background of potato or is substituting for a homoeologous potato chromosome. The sequential GISH and FISH procedures should be widely applicable for germplasm characterization, especially in plant species with small-sized chromosomes.     

小麦-鹅观草第一部分同源群染色体渗入系鉴定与基因组归属分析

鹅观草（Roegneria kamoji,2n=42,SSHHYY）是小麦异源六倍体野生近缘种,对小麦赤霉病具有良好抗性,是改良小麦赤霉病抗性的重要遗传资源。通过远缘杂交,将鹅观草第一部分同源群染色体上的抗赤霉病基因Fhb6导入普通小麦。由于第一部分同源群染色体包含1S、1H和1Y三条染色体,为研究这些同源染色体对小麦赤霉病抗性的影响,筛选出4个鹅观草第一部分同源群染色体特异分子标记,通过PCR扩增鹅观草属不同野生种的基因组DNA,明确了抗赤霉病Fhb6基因位于鹅观草1Y#1染色体。进一步利用分子细胞遗传学技术从中国春与鹅观草的后代中选育出5份涉及鹅观草1Y#2和1S#2染色体的渗入系材料。其中：21RK?1为二体异代换系DS1Y#2(1A),21RK?2为二体异代换系DS1S#2（1D）,21RK?3为二体异附加系DA1S#2,21RK?4为1S#2和TW·1S#2S的双单体附加系,21RK?5为纯合TW·1S#2S易位系。这些新种质为小麦抗赤霉病基因的发掘及遗传改良奠定了基础。     

The <Emphasis Type="Italic">Agropyron cristatum</Emphasis> karyotype,chromosome structure and cross-genome homoeology as revealed by fluorescence in situ hybridization with tandem repeats and wheat single-gene probes

Key message

Fluorescence in situ hybridization with probes for 45 cDNAs and five tandem repeats revealed homoeologous relationships of Agropyron cristatum with wheat. The results will contribute to alien gene introgression in wheat improvement.

Abstract

Crested wheatgrass (Agropyron cristatum L. Gaertn.) is a wild relative of wheat and a promising source of novel genes for wheat improvement. To date, identification of A. cristatum chromosomes has not been possible, and its molecular karyotype has not been available. Furthermore, homoeologous relationship between the genomes of A. cristatum and wheat has not been determined. To develop chromosome-specific landmarks, A. cristatum genomic DNA was sequenced, and new tandem repeats were discovered. Their distribution on mitotic chromosomes was studied by fluorescence in situ hybridization (FISH), which revealed specific patterns for five repeats in addition to 5S and 45S ribosomal DNA and rye subtelomeric repeats pSc119.2 and pSc200. FISH with one tandem repeat together with 45S rDNA enabled identification of all A. cristatum chromosomes. To analyze the structure and cross-species homoeology of A. cristatum chromosomes with wheat, probes for 45 mapped wheat cDNAs covering all seven chromosome groups were localized by FISH. Thirty-four cDNAs hybridized to homoeologous chromosomes of A. cristatum, nine hybridized to homoeologous and non-homoeologous chromosomes, and two hybridized to unique positions on non-homoeologous chromosomes. FISH using single-gene probes revealed that the wheat-A. cristatum collinearity was distorted, and important structural rearrangements were observed for chromosomes 2P, 4P, 5P, 6P and 7P. Chromosomal inversions were found for pericentric region of 4P and whole chromosome arm 6PL. Furthermore, reciprocal translocations between 2PS and 4PL were detected. These results provide new insights into the genome evolution within Triticeae and will facilitate the use of crested wheatgrass in alien gene introgression into wheat.

     

Establishment of a complete series of a monosomic tomato chromosome addition lines in the cultivated potato using RFLP and GISH analyses

With the aim of establishing a complete monosomic alien tomato chromosome addition series in a potato background, the backcross progenies derived from repeated crossing of potato (+) tomato fusion hybrids to potato were screened through RFLP and GISH analyses. Because of the availability from our previous work of seven of the possible 12 tomato monosomic additions, selected from BC₂ populations, attention was paid to those alien additions that were missing. Thus, since the alien additions were already available for tomato chromosomes 1, 2, 4, 6, 8, 10 and 12, efforts were made to select for chromosomes 3, 5, 7, 9 and 11 by screening specific BC₃ populations. In all, 105 plants from four BC₃ populations were screened through a combination of RFLP and GISH analyses in order to complete the series. Among the newly selected alien addition lines, five were monosomic additions for all the remaining chromosomes and one was a disomic addition for chromosome 11. When using conventional cytogenetics the selection of monosomic alien additions is highly laborious. All the tomato chromosomes showed a variable rate of transmission. Chromosome 6 was transmitted at 29.6% and 81.5% frequency in populations 2705 and 2701 respectively. The present study showed that molecular markers and molecular cytogenetics applied in this study were most efficient and rapid because a pre-selection for the desired genotypes was possible by screening a population with chromosome-specific markers for the presence of one tomato chromosome at a time. Received: 9 January 2001 / Accepted: 26 January 2001     

植物外源基因组成分鉴定方法的研究进展

具外源基因组成分(外源染色体/染色体片段/基因)植株是目前进行基因组学研究以及作物改良的重要材料。迄今为止,已建立了基于性状观测、染色体分析、特异蛋白、DNA序列4种鉴定外源基因组成分的策略。其中,基于DNA序列的分子标记技术是当前鉴定外源基因组成分的主要手段,文中归纳了用于小麦、甘蓝等重要作物外源基因组成分的分子标记,且对简单重复序列(Simple sequence repeat, SSR)、插入缺失(Insertion-deletion,InDel)、单核苷酸多态性(Single nucleotide polymorphism,SNP)等9种标记进行了系统的比较。相比单一的鉴定方法,组合法更全面精准,文中对各组合法的应用情况进行统计和分析,提供了小麦族、芸薹族等作物的最佳鉴定组合。新一代分子标记InDel、SNP易实现高通量检测,对于外源渗入基因的精细定位展现了一定的优越性。此外,可以考虑一些新鉴定方法的加入,如微阵列比较基因组杂交(Microarray-based comparative genomic hybridization,array-CGH)、抑制差减杂交(Suppression subtractive hybridization,SSH)。     

Wheat cytogenetics in the genomics era and its relevance to breeding

Hexaploid wheat is a species that has been subjected to most extensive cytogenetic studies. This has contributed to understanding the mechanism of the evolution of polyploids involving diploidization through genetic restriction of chromosome pairing to only homologous chromosomes. The availability of a variety of aneuploids and the ph mutants (Ph1 and Ph2) in bread wheat also allowed chromosome manipulations leading to the development of alien addition/substitution lines and the introgression of alien chromosome segments into the wheat genome. More recently in the genomics era, molecular tools have been used extensively not only for the construction of molecular maps, but also for identification/isolation of genes/QTLs (including epistatic QTLs, eQTLs and PQLs) for several agronomic traits. It has also been possible to identify gene-rich regions and recombination hot spots in the wheat genome, which are now being subjected to sequencing at the genome level, through development of BAC libraries. In the EST database also, among all plants wheat ESTs are the highest in number, and are only next to those for human, mouse, Ciona intestinalis (a chordate), rat and zebrafish genomes. These ESTs and sequences of several genomic regions have been subjected to a variety of applications including development of perfect markers and establishment of microcollinearity. The technique of in situ hybridization (including FISH, GISH and McFISH) and the development of deletion stocks also facilitated the preparation of physical maps. Molecular markers are also used for marker-assisted selection in wheat breeding programs in several countries. Construction of a wheat DNA chip, which will also become available soon, may further facilitate wheat genomics research. These enormous resources, knowledge base and the fast development of additional molecular tools and high throughput approaches for genotyping will prove extremely useful in future wheat research and will lead to development of improved wheat cultivars.     

“Cuckoo” Aegilops addition chromosome in wheat ensures its transmission by causing chromosome breaks in meiospores lacking it

In monosomic additions of Aegilops sharonensis to Chinese Spring wheat (2n=42 wheat chromosomes + 1 homoeologous group 4 Aegilops chromosome known as 4S¹), probably all functional gametes carried one Aegilops chromosome. Such preferential transmission is unusual in monosomic alien additions. Male and female meiosis seemed usually normal, but about 75% of embryo sacs and 28% of pollen grains were visibly abnormal near anthesis. Before the first gametophyte mitosis, up to about 13% of megaspores and pollen grains showed abnormalities usual in wheat aneuploids. However, in first mitosis, 50% of megaspores at metaphase and anaphase and 41% of pollen grains at anaphase and telophase contained acentric chromosome (or chromatid) segments of various sizes, up to about 32 in a cell, which were separated from the rest of the chromosome (or chromatid) by a gap or a thin Feulgen-positive thread. Such separated segments (SSs) are not normally seen in wheat and its aneuploids. The data indicat that alien and wheat chromosomes interact in meiocytes so that meiospores with the alien chromosome develop into normal gametophytes, but meiospores lacking the alien chromosome have SSs at first mitosis by whose loss or unequal distribution between daughter nuclei sterilizing deficiencies arise. Thus only gametophytes with the alien chromosome are competent.     

Genetic control of a novel series of trypsin inhibitors in wheat and its relatives

The aneuploids of Chinese Spring wheat have been used to locate the genes(Ti-2) coding for a novel series of trypsin inhibitors to the long arms of the homoeologous group 5 chromosomes. Three allelic variants at the 5D locus were detected in a limited survey among wheat varieties, but no variation at the loci on either chromosome 5A or chromosome 5B was detected. Homoeoloci were found in a number of alien relatives, and in the majority of cases, these were present on the group 5 homoeologue. However, inAegilops umbellulata, theTi-U2 locus was located on a chromosome presumed to belong to homoeologous group 1. NoHordeum vulgare orH. chilense Ti-2 gene was expressed in a wheat background. This new marker will be especially useful as a screening mechanism for nullisomy of chromosome 5B in work aimed at introgression of alien chromatin into wheat.The Agricultural Genetics Company is thanked for financial support.     

Production and identification of wheat-Agropyron cristatum 6P translocation lines

The narrow genetic background of wheat is the primary factor that has restricted the improvement of crop yield in recent years. The kernel number per spike is the most important factor of the many potential characteristics that determine wheat yield. Agropyron cristatum (L.) Gaertn., a wild relative of wheat, has the characteristics of superior numbers of florets and kernels per spike, which are controlled by chromosome 6P. In this study, the wheat-A. cristatum disomic addition and substitution lines were used as bridge materials to produce wheat-A. cristatum 6P translocation lines induced by gametocidal chromosomes and irradiation. The results of genomic in situ hybridization showed that the frequency of translocation induced by gametocidal chromosomes was 5.08%, which was higher than the frequency of irradiated hybrids (2.78%) and irradiated pollen (2.12%). The fluorescence in situ hybridization results of the translocation lines showed that A. cristatum chromosome 6P could be translocated to wheat ABD genome, and the recombination frequency was A genome > B genome > D genome. The alien A. cristatum chromosome 6P was translocated to wheat homoeologous groups 1, 2, 3, 5 and 6. We obtained abundant translocation lines that possessed whole-arm, terminal, segmental and intercalary translocations. Three 6PS-specific and four 6PL-specific markers will be useful to rapidly identify and trace the translocated fragments. The different wheat-A. cristatum 6P translocation lines obtained in this study can provide basic materials for analyzing the alien genes carried by chromosome 6P. The translocation line WAT33-1-3 and introgression lines WAI37-2 and WAI41-1, which had significant characteristics of multikernel (high numbers of kernels per spike), could be utilized as novel germplasms for high-yield wheat breeding.     

Homoeologous pairing and recombination in <Emphasis Type="Italic">Solanum lycopersicoides</Emphasis> monosomic addition and substitution lines of tomato

We compared meiotic pairing and recombination between tomato ( Lycopersicon esculentum) and homoeologous Solanum lycopersicoides chromosomes in monosomic additions (MAs) and substitution lines (SLs), each representing a single chromosome of the nightshade in a tomato background. Three configurations of each alien chromosome and its two tomato homoeologues were detected by genomic in situ hybridization in MA-7, -8, and -10 at diakinesis/metaphase-I: 1 trivalent (III), 1 bivalent + 1 univalent (II+I), and 3 univalents (3I). The II+I category was by far the most common, and the univalent was from S. lycopersicoides 91-99.5% of the time, indicating a high degree of preferential (homologous) pairing. In the corresponding substitution lines, association of homoeologous chromosomes was much higher (up to 90% of the cells), presumably due to the absence of homologous partners. However, SL-10 showed a surprisingly high frequency of univalents (about 73%). Genome-wide analysis of chromosome pairing revealed a decrease in the average chiasma frequency for both monosomic additions and substitution lines. Recombination between tomato and the nightshade was restricted in all cases, the reduction being more severe in each monosomic addition than in the corresponding substitution line. Recombination rates in the substitutions were less than those observed for the same chromosomes in the first backcross generation. Chromosomes 8 and 10 showed the highest and the lowest rates of homoeologous recombination, respectively. No recombination was detected between markers on the long arm of chromosome 10, presumably due to the presence of a paracentric inversion differentiating the two genomes in this region. The frequency of homoeologous pairing at diakinesis/metaphase-I was significantly higher than the rate of homoeologous recombination detected in the progeny, suggesting a strong selection against recombinant products in meiotic or post-meiotic stages.     

Alien introgression in rice

Rice (Oryza sativa L.) productivity is affected by several biotic and abiotic stresses. The genetic variability for some of these stresses is limited in the cultivated rice germplasm. Moreover, changes in insect biotypes and disease races are a continuing threat to increased rice production. There is thus an urgent need to broaden the rice gene pool by introgressing genes for such traits from diverse sources. The wild species of Oryza representing AA, BB, CC, BBCC, CCDD, EE, FF, GG and HHJJ genomes are an important reservoir of useful genes. However, low crossability and limited recombination between chromosomes of cultivated and wild species limit the transfer of such genes. At IRRI, a series of hybrids and monosomic alien addition lines have been produced through embryo rescue following hybridization between rice and several distantly related species. Cytoplasmic male sterility and genes for resistance to grassy stunt virus and bacterial blight have been transferred from A genome wild species into rice. Similarly, genes for resistance to brown planthopper, bacterial blight and blast have also been introgressed across crossability barriers from distanly related species into rice. Some of the introgressed genes have been mapped via linkage to molecular markers. One of the genes Xa-21 introgressed from O. longistaminata has been cloned and physically mapped on chromosome 11 of rice using BAC library and flourescence in-situ hybridization. RFLP analysis revealed introgression from 11 of the 12 chromosomes of C genome species into rice. Introgression has also been obtained from other distant genomes (EE, FF, GG) into rice and in majority of the cases one or two RFLP markers were introgressed. Reciprocal replacement of RFLP alleles of wild species with the alleles of O. sativa indicates alien gene transfer through crossing over. The rapid recovery of recurrent phenotypes in BC₂ and BC₃ generations from wide crosses is an indication of limited recombination. Further cytogenetic and molecular investigations are required to determine precisely the mechanism of introgression of small chromosome segments from distant genomes in the face of limited homoeologous chromosome pairing. Future research should focus on enhancing recombination between homoeologous chromosomes. Introgression of QTL from wild species should be attempted to increase the yield potential of rice.     

Molecular cytogenetic characterization of alien introgressions with gene Fhb3 for resistance to Fusarium head blight disease of wheat

Fusarium head blight (FHB) resistance was identified in the alien species Leymus racemosus, and wheat-Leymus introgression lines with FHB resistance were reported previously. Detailed molecular cytogenetic analysis of alien introgressions T01, T09, and T14 and the mapping of Fhb3, a new gene for FHB resistance, are reported here. The introgression line T09 had an unknown wheat-Leymus translocation chromosome. A total of 36 RFLP markers selected from the seven homoeologous groups of wheat were used to characterize T09 and determine the homoeologous relationship of the introgressed Leymus chromosome with wheat. Only short arm markers for group 7 detected Leymus-specific fragments in T09, whereas 7AS-specific RFLP fragments were missing. C-banding and genomic in situ hybridization results indicated that T09 has a compensating Robertsonian translocation T7AL·7Lr#1S involving the long arm of wheat chromosome 7A and the short arm of Leymus chromosome 7Lr#1 substituting for chromosome arm 7AS of wheat. Introgression lines T01 (2n = 44) and T14 (2n = 44) each had two pairs of independent translocation chromosomes. T01 had T4BS·4BL-7Lr#1S + T4BL-7Lr#1S·5Lr#1S. T14 had T6BS·6BL-7Lr#1S + T6BL·5Lr#1S. These translocations were recovered in the progeny of the irradiated line Lr#1 (T5Lr#1S·7Lr#1S). The three translocation lines, T01, T09, and T14, and the disomic addition 7Lr#1 were consistently resistant to FHB in greenhouse point-inoculation experiments, whereas the disomic addition 5Lr#1 was susceptible. The data indicated that at least one novel FHB resistance gene from Leymus, designated Fhb3, resides in the distal region of the short arm of chromosome 7Lr#1, because the resistant translocation lines share a common distal segment of 7Lr#1S. Three PCR-based markers, BE586744-STS, BE404728-STS, and BE586111-STS, specific for 7Lr#1S were developed to expedite marker-assisted selection in breeding programs.     

Meiotic behaviour of individual chromosomes in allotriploid Alstroemeria hybrids

Chromosome association and chiasma formation were studied in pollen mother cells at metaphase I of four allotriplod BC1 plants (2n=3x=24) obtained from the backcross of the hybrid Alstroemeria aurea x A. inodora with its parent A. inodora. We distinguished the chromosomes of both parental species by genomic in situ hybridization (GISH), whereas the individual chromosomes were identified on the basis of their multicolour FISH banding patterns obtained after a second hybridization with two species-specific satellite repeats as probes. All the four BC1 plants possessed two genomes of A. inodora and one of A. aurea. Variable numbers of recombinant chromosomes, resulting from meiotic recombination in the interspecific hybrid, were present in these plants. The homologous A. inodora chromosomes generally formed bivalents, leaving the homoeologous A. aurea chromosomes unassociated. High frequencies of trivalents were observed for the chromosome sets that contained recombinant chromosomes, even when the recombinant segments were small. Chromosome associations in the trivalents were restricted to homologous segments. The implications of the absence of homoeologous chromosome pairing on gamete constitution and prospects for introgression in Alstroemeria are discussed.     

Evidence for non-disomic inheritance in a Citrus interspecific tetraploid somatic hybrid between C. reticulata and C. limon using SSR markers and cytogenetic analysis

Artificial tetraploid somatic hybrids have been developed for sterile triploid citrus breeding by sexual hybridization between diploid and tetraploid somatic hybrids. The genetic structure of diploid gametes produced by tetraploid genotypes depends on the mode of chromosome association at meiosis. In order to evaluate tetraploid inheritance in a tetraploid interspecific somatic hybrid between mandarin and lemon, we performed segregation studies using cytogenetic and single sequence repeat molecular markers. Cytogenetic analysis of meiosis in the somatic hybrid revealed 11% tetravalents and 76% bivalents. Inheritance of the tetraploid hybrid was analyzed by genotyping the triploid progeny derived from a cross between a diploid pummelo and the tetraploid somatic hybrid, in order to derive genotypes of the meiospores produced by the tetraploid. A likelihood-based approach was used to distinguish between disomic, tetrasomic, and intermediate inheritance models and to estimate the double reduction rate. In agreement with expectations based the cytogenetic data, marker segregation was largely compatible with tetrasomic and inheritance intermediate between disomic and tetrasomic, with some evidence for preferential pairing of homoeologous chromosomes. This has important implications for the design of breeding programs that involve tetraploid hybrids, and underscores the need to consider inheritance models that are intermediate between disomic and tetrasomic.     

Identification and characterization of wheat-wheatgrass translocation lines and localization of barley yellow dwarf virus resistance.

Stable introgression of agronomically important traits into crop plants through wide crossing often requires the generation and identification of translocation lines. However, the low efficiency of identifying lines containing translocations is a significant limitation in utilizing valuable alien chromatin-derived traits. Selection of putative wheatgrass-wheat translocation lines based on segregation ratios of progeny from gamma-irradiated seed using a standard phenotypic analysis resulted in a low 4% success rate of identifying barley yellow dwarf virus (BYDV) resistant and susceptible translocation lines. However, 58% of the susceptible progeny of this irradiated seed contained a Thinopyrum intermedium chromosome-specific repetitive sequence, which indicated that gamma-irradiation-induced translocations occurred at high rate. Restriction fragment length polymorphism (RFLP) analysis of susceptible lines containing alien chromatin, their resistant sister lines and other resistant lines showed that more than one third of the progeny of gamma-irradiated double monosomic seeds contained wheatgrass-wheat translocations. Genomic in situ hybridization (GISH) analysis of selected lines confirmed that these were wheatgrass-wheat translocation lines. This approach of initially identifying BYDV susceptible deletion lines using an alien chromosome-specific repetitive sequence followed by RFLP analysis of their resistant sister lines efficiently identified resistant translocation lines and localized the BYDV resistance to the distal end of the introgressed Th. intermedium chromosome.     

Karyotype and identification of all homoeologous chromosomes of allopolyploid Brassica napus and its diploid progenitors

Investigating recombination of homoeologous chromosomes in allopolyploid species is central to understanding plant breeding and evolution. However, examining chromosome pairing in the allotetraploid Brassica napus has been hampered by the lack of chromosome-specific molecular probes. In this study, we establish the identification of all homoeologous chromosomes of allopolyploid B. napus by using robust molecular cytogenetic karyotypes developed for the progenitor species Brassica rapa (A genome) and Brassica oleracea (C genome). The identification of every chromosome among these three Brassica species utilized genetically mapped bacterial artificial chromosomes (BACs) from B. rapa as probes for fluorescent in situ hybridization (FISH). With this BAC-FISH data, a second karyotype was developed using two BACs that contained repetitive DNA sequences and the ubiquitous ribosomal and pericentromere repeats. Using this diagnostic probe mix and a BAC that contained a C-genome repeat in two successive hybridizations allowed for routine identification of the corresponding homoeologous chromosomes between the A and C genomes of B. napus. When applied to the B. napus cultivar Stellar, we detected one chromosomal rearrangement relative to the parental karyotypes. This robust novel chromosomal painting technique will have biological applications for the understanding of chromosome pairing, homoeologous recombination, and genome evolution in the genus Brassica and will facilitate new applied breeding technologies that rely upon identification of chromosomes.     

利用RFLP分子标记确定导入小麦的鹅观草(R. kamoji)染色体的部分同源群归属

选用来自小麦族7个部分同源群的26个DNA探针对45个小麦-鹅观草衍生后代株系及鹅观草、中国春和扬麦5号亲本进行RFLP分析,结果表明16个小麦-鹅观草异附加系、异代换系或可能的易位系中所涉及鹅观草染色体分别属于第1、3、5、6、7部分同源群。小麦-鹅观草异染色体系中导入的成对鹅观草染色体能够较稳定地遗传给后代。K139、K141、K214、K218、K219、K224二体附加系所添加的鹅观草染色体属第1部分同源群,但K214和K218所添加的鹅观草染色体与K219、K224的添加的鹅观草染色体分别来自鹅观草不同的染色体组。K147端体添加系涉及鹅观草第1部分同源群染色体长臂,而K139、K141和K147所涉及的鹅观草染色体长臂分别来自鹅观草3个不同的染色体组。鹅观草U染色体与小麦第1部分同源群有同源关系,属第1部分同源群的鹅观草染色体尤其是其长臂与赤霉病抗性有关。鹅观草第1部分同源群与第6部分同源群染色体之间可能涉及重排。K203添加的2条鹅观草染色体分别与第1和6部分同源群同源。K166导入鹅观草染色体涉及第5部分同源群短臂。K177（2n=41,20Ⅱ I）中,所渗入的鹅观草染色质涉及第5（5L）、6（6S）、7（SL）部分同源群。鹅观草S、H和Y3个染色体组间具部分同源性。