Cytogenetics of Hordeum chilense: current status and considerations with reference to breeding

Hordeum chilense Roem. et Schult. has a number of characteristics interesting for breeding: high crossability with other Triticeae, resistance to biotic and abiotic stresses and high variability for quality traits such as endosperm storage proteins or carotenoid content. xTritordeum, the amphiploids between H. chilense and different Triticum spp, are bridge species which facilitate the transfer of traits from H. chilense to wheat or triticale. The chromosome pairing between H. chilense and wheat chromosomes is very low (if existing) even in the absence of the action of the Ph1 gene. Nevertheless, translocation between H. chilense and wheat chromosomes has been observed frequently in genomic combinations where univalents of both species are present and therefore a method is available for using H. chilense in wheat or triticale breeding. Hybrids and amphiploids with other crop species of the Triticeae, such as rye or barley, have also been obtained, although to date the production of stable introgression stocks has not been completed. The technique of chromosome painting, using both high- and low-repeated DNA sequences in combination with genomic in situ hybridization have been used as effective methods for basic cytogenetic research in H. chilense, allowing analysis of genome evolution, and monitoring H. chilense chromosomes in interspecific hybridization breeding programs.     

Studies on genome relationship and species-specific PCR marker for Dasypyrum breviaristatum in Triticeae

Dasypyrum breviaristatum and nine related species in Triticeae were analyzed using the random amplified polymorphic DNA (RAPD) technique, in order to understand the genetic relationship and to develop species specific markers. The genome relationship dendrogram shows that D. breviaristatum and D. villosum could not be grouped together, indicating that D. breviaristatum was unlikely to be directly derived from D. villosum, while D. breviaristatum was closest to Thinopyrum intermedium, which implied that they might have similar breeding behaviors when introducing their chromatins into wheat. A D. breviaristatum genome specific RAPD product of 1182bp, was cloned and designated as pDb12H. Sequence analysis revealed that pDb12H was strongly homologuos to a long terminal repeat (LTR) Sabrina retrotransposon newly reported in Hordeum. The pDb12H was converted into a PCR based marker, which allows effectively monitoring the D. breviaristatum chromatin introgression into wheat. Fluorescence in situ hybridization (FISH) suggested that pDb12H was specifically hybridized throughout all D. breviaristatum chromosomes arms except for the terminal and centromeric regions, which can be used to characterize wheat -D. breviaristatum chromosome translocation. The genomes repetitive element will also be useful to study gene interactions between the wheat and alien genomes after the polyploidization.     

应用基因组原位杂交鉴定蓝粒小麦及其诱变后代

应用基因组原位杂交技术（GISH）对普通小麦（Triticum aestivumL.)和长穗偃麦草[Agropyron elongatum(Host)Beauv,2n=10x=70]杂交后选育出的蓝粒小麦蓝-58及其诱变后代的染色体组成进行了鉴定。结果表明,GISH可方便地检测到小麦遗传背景中的长穗偃麦草染色体或易位的片段。如前人报道,蓝-58（2n=42)是一个具有2条长穗偃麦草4E染色体的异代换系（4E/4D）。LW004可能是一个具有两对相互易位染色体的纯合系,其田间表现磷高效特性,LW43-3-4为41条染色体的蓝单体（40W 1’4E）,种子颜色为浅蓝色,通过此法还检测出一些染色体结构发生很大变异的材料如4E的单端体（40W 1‘4E),种子颜色为浅蓝色,通过此法还检测出一些染色结构发生很大变异的材料如4E的单端体（40W 1‘t4E)以及组型为39W 1‘4E 1‘t4E的个体,此项研究结果更为直观地表明控制蓝粒体状的基因的确在来自长穗偃麦草的染色体上。同时说明有效的突变方法与灵活方便的检测手段的有机结合在染色体工程材料的创制和染色体工程育种中起着至关重要的作用。     

Genus-specific localization of the TaiI family of tandem-repetitive sequences in either the centromeric or subtelomeric regions in Triticeae species (Poaceae) and its evolution in wheat.

The TaiI family sequences are classified as tandem repetitive DNA sequences present in the genome of tribe Triticeae, and are localized in the centromeric regions of common wheat, but in the subtelomeric heterochromatic regions of Leymus racemosus and related species. In this study, we investigated the chromosomal distribution of TaiI family sequences in other Triticeae species. The results demonstrated a centromeric localization in genera Triticum and Aegilops and subtelomeric localization in other genera, thus showing a genus-dependent localization of TaiI family sequences in one or the other region. The copy numbers of TaiI family sequences in species in the same genus varied greatly, whether in the centromeric or subtelomeric regions (depending on genus). We also examined the evolution of TaiI family sequences during polyploidization of hexaploid common wheat. A comparison of chromosomal locations of the major TaiI family signals in common wheat and in its ancestral species suggested that the centromeric TaiI family sequences in common wheat were inherited from its ancestors with little modification, whereas a mixed origin for the B genome of common wheat was indicated.     

Genetic induction of chromosomal rearrangements in barley chromosome 7H added to common wheat

Chromosome 2C of Aegilops cylindrica induces chromosomal rearrangements in alien chromosome addition lines, as well as in euploid lines, of common wheat. To induce chromosomal rearrangements in barley chromosome 7H, reciprocal crosses were made between a mutation-inducing common wheat line that carries a pair of 7H chromosomes and one 2C chromosome and a 7H disomic addition line of common wheat. Many shrivelled seeds were included in the progeny, which was an indication of the occurrence of chromosome mutations. The chromosomal constitution of the viable progeny was examined by FISH (fluorescence in situ hybridization) using the barley subterminal repeat HvT01 as a probe. Structural changes of chromosome 7H were found in about 15% of the progeny of the reciprocal crosses. The aberrant 7H chromosomes were characterized by a combination of N-banding, FISH and genomic in situ hybridization. Mosaicism for aberrant 7H chromosomes was observed in seven plants. In total, 89 aberrant 7H chromosomes were identified in 82 plants, seven of which had double aberrations. More than half of the plants carried a simple deletion: four short-arm telosomes, one long-arm telosome, and 45 terminal deletions (23 in the short arm, 21 in the long arm, and one involving both arms). About 40% of the aberrations represented translocations between 7H and wheat chromosomes. Twenty of the translocations had wheat centromeres, 12 the 7H centromere, with translocation points in the 7HS (five) and in the 7HL (seven), and the remaining four were of Robertsonian type, three involving 7HS and one with 7HL. In addition, one translocation had a barley segment in an intercalary position of a wheat chromosome, and two were dicentric. The breakpoints of these aberrations were distributed along the entire length of chromosome 7H.     

非Robertsonian类型小黑麦易位系的研究

非Robertsonian类型小黑麦易位系的研究@胡含$中国科学院遗传研究所植物细胞与染色体工程国家重点实验室!北京100101小黑麦;;易位系     

易组"太谷核不育基因"(Ms2)基因定位的研究

将在远缘杂交中由普通小麦（AABBDD）4D染色体易组导入六倍体小黑麦（AABBRR）以及硬粒小麦（AABB）的太谷核不育基因Ms2（原位于普通小麦4D染色体短臂距着丝点31．2cM的显性雄性不育核基因）。重新异回普通小麦染色体组中,所获得携带易组Ms2基因的新型太谷核不育小麦其显性雄性不育特性表达正常,且雄性不育株的雌性可育机制正常,对不育株幼穗花粉母细胞减数分型期染色体构型的观察可见其为整倍体（2n=42),尚未发现回归普通小麦的易组太谷核不育与原位 的太谷核不育基因有不同的表型。采用系统的标志基因测交法对回归普通小麦的易组太谷不育基因进行测交定位,发现易组Ms2基因与普通小麦显性秆标志基因Rht3连锁,从而将其定位于普通小麦4B 色体虎Rht3基因9.7cM处,新位点被命名为Ms2（4BS）,对Ms2基因在六倍体小黑麦与原太谷核不育小麦远缘杂交中位时的走向,普通小麦4A与4B染色体的互换更名以及Ms2（4BS）新位点的开发利用进行了讨论,认为异源多倍体生物核基因的组间易位倾向于从供体染色体向进化亲缘关系较密切,且染色体序数与染色体臂相同的部分同源染色体易位;1988年第7届国际小麦遗传学会对普通小麦4A与4B染色体的互换更名是正确的;Ms2（4BS）作为一个新型的遗传标记,作为小麦族内所有携带B染色体组的物种的育种工具和在拓建各为小麦种质资源的基因库等方面均有广泛的用途。     

Complex genome rearrangements reveal evolutionary dynamics of pericentromeric regions in the Triticeae.

Most pericentromeric regions of eukaryotic chromosomes are heterochromatic and are the most rapidly evolving regions of complex genomes. The closely related genomes within hexaploid wheat (Triticum aestivum L., 2n=6x=42, AABBDD), as well as in the related Triticeae taxa, share large conserved chromosome segments and provide a good model for the study of the evolution of pericentromeric regions. Here we report on the comparative analysis of pericentric inversions in the Triticeae, including Triticum aestivum, Aegilops speltoides, Ae. longissima, Ae. searsii, Hordeum vulgare, Secale cereale, and Agropyron elongatum. Previously, 4 pericentric inversions were identified in the hexaploid wheat cultivar 'Chinese Spring' ('CS') involving chromosomes 2B, 4A, 4B, and 5A. In the present study, 2 additional pericentric inversions were detected in chromosomes 3B and 6B of 'CS' wheat. Only the 3B inversion pre-existed in chromosome 3S, 3Sl, and 3Ss of Aegilops species of the Sitopsis section, the remaining inversions occurring after wheat polyploidization. The translocation T2BS/6BS previously reported in 'CS' was detected in the hexaploid variety 'Wichita' but not in other species of the Triticeae. It appears that the B genome is more prone to genome rearrangements than are the A and D genomes. Five different pericentric inversions were detected in rye chromosomes 3R and 4R, 4Sl of Ae. longissima, 4H of barley, and 6E of Ag. elongatum. This indicates that pericentric regions in the Triticeae, especially those of group 4 chromosomes, are undergoing rapid and recurrent rearrangements.     

Mapping quantitative trait loci controlling common bunt resistance in a doubled haploid population derived from the spring wheat cross RL4452 × AC Domain

Wheat resistance to common bunt is a highly desirable trait for environmentally friendly grain grade protection. Valuable breeding achievements have been made to develop wheat varieties with enhanced resistance to the disease, and mapping of race-specific resistance genes has been reported. However, less is known of the chromosomal regions that control non-race specific resistance to common bunt. In this study, we have characterized a segregating population of 185 doubled haploid spring wheat lines derived from the cross RL4452 × AC Domain. Reactions to a mixture of common bunt races were assessed under field simulated spring-sown conditions in greenhouses in two locations over 2 years. A total 369 polymorphic maker loci including 356 microsatellite loci, five expressed sequences tag (ESTs), and eight genes were used to develop a linkage map. Quantitative trait loci (QTL) analysis using composite interval mapping detected three QTLs associated with common bunt resistance, of which two were located on chromosome 1B and one on chromosome 7A. AC Domain alleles contributed the common bunt resistance at all three QTLs. Usefulness of gene tagging within the identified chromosomal regions for common bunt resistance breeding is discussed.     

小麦抗赤霉病外源种质的创制和育种利用

小麦赤霉病是危害小麦安全生产的重要病害之一,种植抗病品种是防治赤霉病最经济有效的手段。目前在生产上应用的抗源很少,越来越多的研究者将目光转移到小麦的近缘属种,寻找新的抗源以及寻求新的育种突破。携带抗性基因的外源染色体可以通过染色体工程手段以附加系、代换系和易位系等形式导入小麦。综述了将大赖草等多个小麦近缘种的抗赤霉病基因导入普通小麦、创制抗病外源种质和育种利用的最新研究进展,以期为小麦抗赤霉病育种提供参考信息。     

Intergenomic rearrangements after polyploidization of Kengyilia thoroldiana (Poaceae: Triticeae) affected by environmental factors

Polyploidization is a major evolutionary process. Approximately 70–75% species of Triticeae (Poaceae) are polyploids, involving 23 genomes. To investigate intergenomic rearrangements after polyploidization of Triticeae species and to determine the effects of environmental factors on them, nine populations of a typical polyploid Triticeae species, Kengyilia thoroldiana (Keng) J.L.Yang et al. (2n = 6x = 42, StStPPYY), collected from different environments, were studied using genome in situ hybridization (GISH). We found that intergenomic rearrangements occurred between the relatively large P genome and the small genomes, St (8.15%) and Y (22.22%), in polyploid species via various types of translocations compared to their diploid progenitors. However, no translocation was found between the relatively small St and Y chromosomes. Environmental factors may affect rearrangements among the three genomes. Chromosome translocations were significantly more frequent in populations from cold alpine and grassland environments than in populations from valley and lake-basin habitats (P<0.05). The relationship between types of chromosome translocations and altitude was significant (r = 0.809, P<0.01). Intergenomic rearrangements associated with environmental factors and genetic differentiation of a single basic genome should be considered as equally important genetic processes during species'' ecotype evolution.     

Comparative mapping in grasses. Wheat relationships

Conventionally, the genetics of species of the family Gramineae have been studied separately. Comparative mapping using DNA markers offers a method of combining the research efforts in each species. In this study, we developed consensus maps for members of the Triticeae tribe (Triticum aestivum, T. tauschii, andHordeum spp.) and compared them to rice, maize and oat. The aneuploid stocks available in wheat are invaluable for comparative mapping because almost every DNA fragment can be allocated to a chromosome arm, thus preventing erroneous conclusions about probes that could not be mapped due to a lack of polymorphism between mapping parents. The orders of the markers detected by probes mapped in rice, maize and oat were conserved for 93, 92 and 94% of the length of Triticeae consensus maps, respectively. The chromosome segments duplicated within the maize genome by ancient polyploidization events were identified by homoeology of segments from two maize chromosomes to regions of one Triticeae chromosome. Homoeologous segments conserved across Triticeae species, rice, maize, and oat can be identified for each Triticeae chromosome. Putative orthologous loci for several simply inherited and quantitatively inherited traits in Gramineae species were identified.Communicated by H. Saedler     

Analysis of DNA methylation polymorphism in a set of stable chromosome translocation lines

Interspecific hybridization is associated with the origin of novel traits and confers increased vigor compared with the parent lines, although its molecular basis is poorly understood. We report here the identification of genetic and epigenetic changes in a set of wheat–rye translocation lines (R59, R57, and R25) which exhibited novel heritable morphological characteristics compared with the parent lines (MY11 and L155). Genome in situ hybridization and amplified fragment length polymorphism analyses revealed no obvious variations in the primary structure of the genome in different translocation lines, with the exception of the same 1RS chromosome translocation. Global assessment of the extent and pattern of cytosine methylation alterations by methylation-sensitive amplified polymorphism (MSAP) analyses revealed differences in the extent of genomic DNA methylation between the rye and wheat parent lines. Fully-methylated sites were significantly increased and hemi-methylated sites were markedly decreased in the genome of translocation lines compared with the wheat parental cultivar MY11. Comparisons of different MSAP patterns revealed both monomorphic and polymorphic sites between translocation lines and wheat parents. Sequencing of 44 isolated fragments that showed methylation alterations indicated that cellular genes and especially transposable elements were targets for methylation alterations in translocation lines. The present study provides further understanding of the rules governing the distribution and existence of DNA methylation variations induced in the wheat genome during alien germplasm introduction. Furthermore, our study provides insights into the relationship between DNA methylation and hybrid vigor as well as a theoretical basis for further fundamental research and breeding application.     

Development of a wheat single gene FISH map for analyzing homoeologous relationship and chromosomal rearrangements within the Triticeae

Key message

A cytogenetic map of wheat was constructed using FISH with cDNA probes. FISH markers detected homoeology and chromosomal rearrangements of wild relatives, an important source of genes for wheat improvement.

Abstract

To transfer agronomically important genes from wild relatives to bread wheat (Triticum aestivum L., 2n = 6x = 42, AABBDD) by induced homoeologous recombination, it is important to know the chromosomal relationships of the species involved. Fluorescence in situ hybridization (FISH) can be used to study chromosome structure. The genomes of allohexaploid bread wheat and other species from the Triticeae tribe are colinear to some extent, i.e., composed of homoeoloci at similar positions along the chromosomes, and with genic regions being highly conserved. To develop cytogenetic markers specific for genic regions of wheat homoeologs, we selected more than 60 full-length wheat cDNAs using BLAST against mapped expressed sequence tags and used them as FISH probes. Most probes produced signals on all three homoeologous chromosomes at the expected positions. We developed a wheat physical map with several cDNA markers located on each of the 14 homoeologous chromosome arms. The FISH markers confirmed chromosome rearrangements within wheat genomes and were successfully used to study chromosome structure and homoeology in wild Triticeae species. FISH analysis detected 1U-6U chromosome translocation in the genome of Aegilops umbellulata, showed colinearity between chromosome A of Ae. caudata and group-1 wheat chromosomes, and between chromosome arm 7S#3L of Thinopyrum intermedium and the long arm of the group-7 wheat chromosomes.     

Cytogenetic and molecular identification of three Triticum aestivum-Leymus racemosus translocation addition lines

Chromosome 2C from Aegilops cylindrica has the ability to induce chromosome breakage in common wheat （Tritivum aestivum）. In the BC1F3 generation of the T. aestivum cv. Chinese Spring and a hybrid between T. aestivum-Leymus racemosus Lr.7 addition line and T. aestivum-Ae, cylindrica 2C addition line, three disomic translocation addition lines （2n = 44） were selected by mitotic chromosome C-banding and genomic in situ hybridization. We further characterized these T. aestivum-L, racemosus translocation addition lines, NAU636, NAU637 and NAU638, by chromosome C-banding, in situ hybridization using the A- and D-genome-specific bacterial artificial chromosome （BAC） clones 676D4 and 9M13; plasmids pAsl and pSc119.2, and 45S rDNA; as well as genomic DNA of L. racemosus as probes, in combination with double ditelosomic test cross and SSR marker analysis. The translocation chromosomes were designated as T3AS-Lr7S, T6BS-Lr7S, and T5DS-Lr7L. The translocation line T3AS-Lr7S was highly resistant to Fusarium head blight and will be useful germplasm for resistance breeding.     

远缘杂交在转移有益基因创造小麦新种质中的潜力

本文概述了小麦远缘杂交技术的发展以及这些技术的应用对以染色体易位方式转移有益基因到普通小麦中的影响。通过对小麦远缘杂交技术的总结得出,普通小麦由于本身的多倍性,对导入的外源基因具有较强的调节能力,是适宜外源有益基因导入的良好受体。而以染色体易位方式转移有益基因是创造小麦新种质的有效方法之一,许多研究也表明以染色体易位导入的外源有益基因更利于表达。近几年,随着细胞遗传学以及其它生物技术的发展,对小麦族进化途径和染色体间的亲缘关系进一步明确,从而更便于进行易位导入的技术选择,也使得染色体易位鉴定方法更趋完善。现在已有更良好的外源导入的工具和方法,使多基因控制的外源优良性状导入成为可能。在小麦远缘杂交中染色体易位所具有的上述优势,在育种实践中逐步显示出来,为开拓小麦种质资源开创了一条新的途径。     

PCR and sequence analysis of barley chromosome 2H subjected to the gametocidal action of chromosome 2C

Gametocidal (Gc) chromosomes induce various types of chromosomal mutations during gametogenesis in the chromosomes of common wheat and alien chromosomes added to common wheat. However, it is not yet known whether the Gc chromosome causes aberrations at the nucleotide level because mutations caused by Gc chromosomes have been studied only by cytological screening. In order to know whether the Gc chromosome induces point mutations, we conducted PCR analysis and sequencing with the progeny of a common wheat line that is disomic for barley chromosome 2H and monosomic for Gc chromosome 2C. We analyzed 18 2H-specific EST sequences using 81 progeny plants carrying a cytologically normal-appearing 2H chromosome and found no nucleotide changes in the analyzed 1,419 sequences (in total 647,075 bp). During this analysis, we found six plants for which some ESTs could not be PCR amplified, suggesting the presence of chromosomal mutations in these plants. The cytological and PCR analyses of the progeny of the six plants confirmed the occurrence of chromosomal mutations in the parental plants. These results suggested that the Gc chromosome mostly induced chromosomal aberrations, not nucleotide changes, and that the Gc-induced chromosomal mutations in the six plants occurred after fertilization.     

Fixation of translocation 2A·4B infers the monophyletic origin of Ethiopian tetraploid wheat

Analysis of structural chromosomal polymorphism revealed the presence of a previously reported 2A·4B translocation common to all 15 strains of Ethiopian tetraploid wheat examined. Using the C-banding technique, we found two new translocations,T1B·6B and T5B·6B, and a pericentric inversion of chromosome 5A. The C-banding pattern indicated that in all three translocations the breakpoint was located in the centromeric region. Sequential N-banding and genomic in situ hybridization (GISH) confirmed the location of the breakpoint of translocation 2A·4B, and revealed that the breakpoint of another known translocation, 2A-2B, was in the proximal region of 2BL. The fixation of the 2A·4B translocation indicates the monophyletic origin of Ethiopian tetraploid wheat and the presence of a very severe bottleneck effect during its dispersal. Received: 29 June 1999 / Accepted: 18 February 2000     

Molecular and physical mapping of a barley gene on chromosome arm 1 HL that causes sterility in hybrids with wheat.

Addition of the long arm of barley chromosome 1H (1HL) to wheat causes severe meiotic abnormalities and complete sterility of the plants. To map the barley gene responsible for the 1H-induced sterility of wheat, a series of addition lines of translocated 1H chromosomes were developed from the crosses between the wheat 'Shinchunaga' and five reciprocal translocation lines derived from the barley line St.13559. Examination of the seed fertility of the addition lines revealed that the sterility gene is located in the interstitial 25% region of the 1HL arm. The genetic location of the sterility gene was also estimated by physically mapping sequence-tagged site (STS) markers and simple-sequence repeat (SSR) markers with known map locations. The sterility gene is designated Shw (sterility in hybrids with wheat). Comparison of the present physical map of 1HL with two previously published genetic maps revealed a paucity of markers in the proximal 30% region and non-random distribution of SSR markers. Two inconsistencies in marker order were found between the present physical map and the consensus genetic map of group 1 chromosomes of Triticeae. On the basis of the effects on meiosis and chromosomal location, the relationship of the present sterility gene with other fertility-related genes of Triticeae is discussed.     

黑麦碱基因（Sec–1）表达缺失的1RS／1BL易位系的鉴定

用改良的Giemsa C－带技术、DNA原位杂交和酸性聚丙烯酰胺凝胶电泳（A-PAGE）对来源于小麦品种绵阳11与不同黑麦自交系远缘杂交获得的高代株系（BC1F7）的染色体结构和醇溶蛋白进行了研究。结果发现,在鉴定的200个株系中,有45个株系经C-带和A-PAGE检测均一致地发现它们含有一对1RS /1BL易位染色体,而一个株系843-1-1,C-带鉴定、原位杂交结果均证明它含有一对1RS/1BL易位染色体,但A-PAGE醇溶蛋白图谱却不具有黑麦1RS染色体臂的黑麦碱特征带,而表达出既不同于黑麦碱又不同于亲本绵阳11的醇溶蛋白带型。这一结果表明,利用不同的黑麦亲本资源,可以获得黑麦碱基因Sec-1表达缺失的新的1RS/1BL易位系。这种新的1RS/1BL易位系缺失了影响小麦品质的黑麦碱蛋白,因此是进一步研究1RS/1BL 易位对小麦品质影响的珍贵材料。研究指出,在利用外源基因的植物育种中,外源种供体材料的遗传多样性是值得重视的基因资源。