Analysis of intraspecific divergence of hexaploid wheat Triticum spelta L. by chromosome C-banding

Intraspecific divergence of hexaploid wheat Triticum spelta was studied by chromosome C-banding in 41 accessions of different geographic origins. The spelt accessions did not differ in karyotype structure or heterochromatin distribution from common wheat, but showed greater intraspecific polymorphism for chromosome rearrangements (translocations, inversions) and banding patterns. On evidence of C-banding patterns, spelt was assumed to occupy an intermediate position between tetraploid and hexaploid wheat species. Accessions of the Asian spelt subspecies had more diverse banding patterns than European accessions. A relatively high frequency of chromosome rearrangements was observed in Iranian accessions. Visual analysis revealed high uniformity of chromosome banding patterns in T. spelta populations of Afghanistan, Spain, and Germany (Bavarian group), suggesting a significant role of the founder effect in their evolution.     

Analysis of Intraspecific Divergence of Hexaploid Wheat Triticum spelta L. by C-Banding of Chromosomes

Intraspecific divergence of hexaploid wheat Triticum spelta was studied by C-banding method in 41 accessions of different geographic origins. The spelt accessions did not differ in karyotype structure or heterochromatin distribution from common wheat, but showed greater intraspecific polymorphism by chromosome rearrangements (translocations, inversions) and banding patterns. On evidence of C-banding patterns, spelt was assumed to occupy an intermediate position between tetraploid and hexaploid wheat species. Accessions of the Asian spelt subspecies had more diverse banding patterns than European accessions. A relatively high frequency of chromosome rearrangements was observed in Iranian accessions. Visual analysis revealed high uniformity of chromosome banding patterns in T. spelta populations of Afghanistan, Spain, and Germany (Bavarian group), suggesting a significant role of the founder effect in their evolution.     

Analysis of intraspecific diversity of cultivated emmer <Emphasis Type="Italic">Triticum dicoccum</Emphasis> (Schrank.) schuebl using C-banding technique

Ninety-four lines of Triticum dicoccum isolated from 86 wheat accessions from Vavilov All-Russia Research Institute of Plant Industry (VIR, Russia) and INRA (Clermont-Ferrand, France) germ-plasm collections were studied using C-banding technique. Visual comparison of karyotypes of different accessions was performed to establish genetic relationships and evaluate features inherent for ecological-geographical groups. The level of C-banding polymorphism in the whole sample of tetraploid emmer proved to be relatively low. The diversity within groups was higher than the differences between them. The material studied contained 39 lines carrying 16 different types of chromosomal rearrangements including single and multiple translocations and inversions. The level of translocation polymorphism was comparable with that detected earlier for polyploid wheat species. The frequencies of individual translocation types varied from 18 (T7A:5B) to 1 (nine types). Analysis of the distribution of the most frequent translocations 7A:5B suggested that it has significant adaptive value on the territory of Europe. Similarity of the C-banding patterns of European emmer and the accessions with the same translocation of the Asian origin points to their possible common origin. The occurrence of the same translocation in several T. dicoccoides accessions from Syria and Lebanon may indicate that such forms of wild emmer could have taken part in the origin of cultivate emmer from Western Europe. Similarity of the C-banding patterns of some chromosomes of European emmer and spelt could serve as an indirect evidence of their close genetic relationships.     

C-banded wheat chromosomes in wheat and triticale

Summary The C-banding patterns of wheat chromosomes in 7 hexaploid triticale and 7 wheat genotypes are described and compared. All 14 wheat chromosome pairs were individually identified in the triticales and a tetraploid wheat, and all the B and two A genome chromosome pairs in the hexaploid wheat genotypes. Little variation was found between genotypes in the distribution of C-bands but considerable variation was found in their size, total number and total length.     

An improved method of genomic in situ hybridization (GISH) for distinguishing closely related genomes of tetraploid and hexaploid wheat species

An improved modification of genomic in situ hybridization (GISH) was proposed. It allows clear and reproducible discrimination between closely related genomes of both tetraploid and hexaploid wheat species due to preannealing of labeled DNA probes and prehybridization of chromosomal samples with blocking DNA. The method was applied to analyze intergenomic translocations 6A:6B and 1A:6B identified in the IG46147 and IG116188 samples of tetraploid wheat Triticum dicoccoides by C-banding. The structure of the rearranged chromosomes was defined for two translocation variants, and the breakpoints were identified on the chromosome arms. Possible application of the developed GISH variant to study genome reorganizations during speciation of allopolyploid plants in evolution is discussed.     

Intraspecific karyotype divergence inTriticum araraticum (Poaceae)

Karyotypes of 185 accessions ofTriticum araraticum Jakubz. (2n = 28 = 4x = A^tA^tGG) from Iraq, Iran, Turkey, and Transcaucasia were analyzed using C-banding technique. All accessions showed a certain degree of C-banding polymorphism and further karyotypic diversity was generated by structural rearrangements, mainly translocations. Eighty-one accessions had the normal karyotype similar to that ofT. timopheevii (cultivation), i.e., they showed C-banding polymorphism but no chromosomal rearrangements based on the resolving power of the C-banding technique. One-hundred four accessions showed 34 karyotypic variants, 31 had reciprocal translocations with the breakpoints in the centromeric regions of chromosomes. Three showed reciprocal translocations with the breakpoints in intercalary regions of chromosomes. A paracentric inversion for 7A^t chromosome was observed in some accessions. The rearranged karyotypes differed from the normal by one translocation in 21 variants, by two in 9 variants, by three in 1 variant, and by four in 2 variants of karyotypes. Translocations occurred more frequenty in the chromosomes of G-genome than of A^t-genome. Individual chromosomes differed in the frequencies of their involvement in translocations. Each geographical region contained a unique spectrum of translocations. Karyotypic diversity was the highest in Iraq followed by Transcaucasia and Turkey. Iran showed little karyotypic variation. Based on karyotypic analysis, Iraq should be considered as a centre of origin and primary centre of diversity ofT. araraticum.     

Analysis of intraspecific diversity of cultivated emmer Triticum dicoccum (Schrank.) Schuebl using C-banding technique

Ninety-four lines of Triticum dicoccum isolated from 86 wheat accessions from Vavilov All-Russia Research Institute of Plant Industry (VIR, Russia) and INRA (Clermont-Ferrand, France) germ-plasm collections were studied using C-banding technique. Visual comparison of karyotypes of different accessions was performed to establish genetic relationships and evaluate features inherent for ecological--geographical groups. The level of C-banding polymorphism in the whole sample of tetraploid emmer proved to be relatively low. The diversity within groups was mostly higher than the differences between them. The material studied contained 39 lines carrying 16 different types of chromosomal rearrangements including single and multiple translocations and inversions. The level of translocation polymorphism was comparable with that detected earlier for polyploid wheat species. The frequencies of individual translocation types varied from 18 (T7A:5B) to 1 (nine types). Analysis of the distribution of the most frequent translocations & A:5B suggested that it has significant adaptive value on the territory of Europe. Similarity of the C-banding patterns of European emmer and the accessions with the same translocation of the Asian origin points to their possible common origin. The occurrence of the same translocation in several T. dicoccoides accessions from Syria and Lebanon may indicate that such forms of wild emmer could have taken part in the origin of cultivate emmer from Western Europe. Similarity of the C-banding patterns of some chromosomes of European emmer and spelt could serve as an indirect evidence of their close genetic relationships.     

Physical mapping of translocation breakpoints in rye by means of synaptonemal complex analysis

A physical map including 40 translocation breakpoints has been constructed in rye by means of synaptonemal complex (SC) analysis of well-paired pachytene quadrivalents. The chromosome arms involved in such translocations were previously identified either from mitotic C-banding analysis or from the meiotic configurations observed in the progenies of crosses with a rye line having multiple chromosome rearrangements. The synaptonemal complexes formed by some translocation homozygotes were also analyzed, the relative pachytene SC length of their translocated chromosomes being compared to that observed in the corresponding translocation heterozygotes. In the translocations in which the position of the breakpoint could be well defined from mitotic C-banding analysis, a good correspondence between the relative position of the point showing partner exchange in the pachytene quadrivalents and the actual location of the breakpoint was established. It is concluded that the mapping of translocation breakpoints by SC analysis of pachytene quadrivalents provides a more accurate estimate of the position of the breakpoints than that obtained from mitotic C-banding analysis, due to the lack of evenly-distributed interstitial C-bands in most rye chromosomes. The distribution of the breakpoints along the chromosomes in relation to their spontaneous or induced origin is also discussed.     

C-banding analysis on wild Emmer (Triticum dicoccoides Körn) strains with and without spontaneous reciprocal translocations

C-banding polymorphism was analyzed in eight strains of wild Emmer, Triticum dicoccoides Körn, which included six translocation homozygotes reported previously. Polymorphisms were detected in all of the strains examined, and the breakpoints of five spontaneous translocations were successfully identified by C-bands. Of the eight breakpoints that could be precisely identified, one was located in the centromeric region while the remaining seven were located in proximal to distal euchromatic regions. The two breakpoints of one translocation could only be approximately localized to proximal regions due to the scarcity of C-bands. The present results are in contrast with those observed on T. araraticum, another wild tetraploid wheat belonging to the Timopheevi group, in which most of the breakpoints were located in centromeric regions. In T. dicoccoides, the six translocation chromosome types were derived from the standard karyotype primarily by a mechanism other than centric breakage-fusion.     

Chromosome structure of Triticum timopheevii relative to T. turgidum.

The chromosome structure of four different wild populations and a cultivated line of Triticum timopheevii (2n = 28, AtAtGG) relative to Triticum turgidum (2n = 28, AABB) was studied, using genomic in situ hybridisation (GISH) and C-banding analysis of meiotic configurations in interspecific hybrids. Two wild accessions and the cultivated line showed the standard C-banding karyotype. The other two accessions are homozygous for translocation 5At/3G and translocations 1G/2G and 5G/6G. GISH analysis revealed that all the T. timopheevii accessions carry intergenome translocations 6At/1G and 1G/4G and identified the position of the breakpoint in translocation 5At/3G. C-banding analysis of pairing at metaphase I in the hybrids with T. turgidum provides evidence that four species-specific translocations (6AtS/1GS, 1GS/4GS, 4GS/4AtL, and 4AtL/3AtL) exist in T. timopheevii, and that T. timopheevii and T. turgidum differ in the pericentric inversion of chromosome 4A. Bridge plus acentric fragment configurations involving 4AL and 4AtL were identified in cells at anaphase I. This result suggests that the paracentric inversion of 4AL from T. turgidum does not exist in T. timopheevii. Both tetraploid species have undergone independent and distinct evolutionary chromosomal rearrangements. The position, intercalary or subdistal, of the breakpoints in species-specific translocations and inversions contrasts with the position, at or close to the centromere, of intraspecific translocations. Different mechanisms for intraspecific and species-specific chromosome rearrangements are suggested.     

C-banded karyotypes and polymorphisms in hexaploid oat accessions (Avena spp.) using Wright's stain.

A chromosome C-banding protocol using Wright's stain was employed to compare chromosomes in cultivars and wild accessions of several hexaploid oat taxa (Avena spp.). This technique permits the identification of each of the 21 somatic hexaploid oat chromosomes. Digital images of C-banded cells were captured on computer and used to construct karyotypes of several oat accessions. Polymorphisms for C-bands among oat cultivars and wild accessions are described. These banding polymorphisms can be used to trace introgression of chromosomes from wild sources and to provide physical markers on the genetic map for oat. Although C-banding permits the identification of likely C-genome chromosomes based on comparisons with C-banding patterns in diploid and tetraploid Avena species, the A and D genomes cannot be readily differentiated based on their banding patterns.     

Evaluation of phylogenetic relationships between five polyploid Aegilops L. species of the U-genome cluster by means of chromosomal analysis

Four tetraploid (Aegilops ovata, Ae. biuncialis, Ae. columnaris, and Ae. triaristata) and one hexaploid (Ae. recta) species of the U-genome cluster were studied using C-banding technique. All species displayed broad C-banding polymorphism and high frequency of chromosomal rearrangements. Chromosomal rearrangements were represented by paracentric inversions and intragenomic and intergenomic translocations. We found that the processes of intraspecific divergence of Ae. ovata, Ae. biuncialis, and Ae. columnaris were probably associated with introgression of genetic material from other species. The results obtained confirmed that tetraploid species Ae. ovata and Ae. biuncialis occurred as a result of hybridization of a diploid Ae. umbellulata with Ae. comosa and Ae. heldreichii, respectively. The dissimilarity of the C-banding patterns of several chromosomes of these tetraploid species and their ancestral diploid forms indicated that chromosomal aberrations might have taken place during their speciation. Significant differences of karyotype structure, total amount and distribution of C-heterochromatin found between Ae. columnaris and Ae. triaristata, on the one hand, and Ae. ovata and Ae. biuncialis, on the other, evidenced in favor of different origin of these groups of species. In turn, similarity of the C-banding patterns of Ae. columnaris and Ae. triaristata chromosomes suggested that they were derived from a common ancestor. A diploid species Ae. umbellulata was the U-genome donor of Ae. columnaris and Ae. triaristata; however, the donor of the second genome of these species was not determined. We assumed that these tetraploid species occurred as a result of introgressive hybridization. Similarity of the C-banding patterns of chromosomes of Ae. recta and its parental species Ae. triaristata and Ae. uniaristata indicated that the formation of the hexaploid form was not associated with large modifications of the parental genomes.     

Chromosomal alterations in the karyotype of triticale in comparison with the parental forms

Summary Wheat chromosomes of the primary winter hexaploid and octoploid triticales and of the parental durum and common wheat varieties were studied using morphometric analysis. The size of some heterochromatic segments was shown to change in triticale. Telomeric and intercalary C-bands both increased and decreased in size whereas centromeric bands only increased. The size variability of C-bands in triticale B-genome chromosomes decreased in most of the cases and increased only for several specific C-bands. The C-bands of homologous B-genome chromosomes changed in the same direction in both triticale forms. The changes in size of the C-bands found in R-genome chromosomes detected earlier in these triticale forms (Badaeva et al. 1986) were shown to coincide in their pattern with the size changes of C-bands in homeological B-genome chromosomes. Our data are indicative of regular, directed chromosomal changes in the triticale karyotype.     

八倍体小黑麦×普通小麦杂种后代群体中的染色体易位

用改良的Giemsa C-带技术以单株为基础分析了八倍体小黑麦×普通小麦的杂种BC_1,F_(?)和F_(?)代植株的核型。在鉴定了C-带核型的1098株杂种后代植株中,发现了78条小麦-黑麦和277条黑麦-黑麦易位染色体。在不同的世代和株系中,小麦-黑麦染色体易位率变化在4.35—14.07%之间,平均7.10%;黑麦-黑麦染色体易位率在0.48—52.78%之间,平均25.23%。鉴定的小麦-黑麦易位染色体涉及了黑麦的14条不同的染色体臂和小麦的A、B和D组染色体。易位的48.57%发生在小麦和黑麦的部分同源染色体之间,51.43%发生在非部分同源染色体之间。不同的黑麦染色体臂参与易位的频率不同。小麦-黑麦染色体易位主要发生在杂种的早期世代,使用适当的选择技术在F_3获得了纯合的易位植株。文中讨论了快速选育易位系的技术和它们在小麦育种中的应用问题。     

Detection of intergenomic translocations with centromeric and noncentromeric breakpoints in Triticum araraticum: mechanism of origin and adaptive significance.

Triticum araraticum Jakubz. (2n = 4x = 28, AtAtGG), a wild progenitor of the polyploid cultivated wheat T. timopheevii, shows extensive chromosome translocation polymorphism in natural populations from the Middle East and Transcaucasia. From an extensive survey, eight intergenomic translocation types were observed and their breakpoints analyzed by genomic in situ hybridization. The previously reported species-specific 6At-1G-4G cyclic translocation was found in all accessions studied. In four translocation types, the breakpoints were in interstitial regions of chromosomes and the other four arose via centric-breakage-fusion. A model is presented on the mechanism of origin and the adaptive significance of translocations with centromeric and noncentromeric breakpoints.     

The genetic and molecular characterization of pollen-derived plant lines from octoploid triticale x wheat hybrids

Six doubled-haploid (DH) lines, derived by anther culture from octoploid triticale x wheat hybrids, were characterized using cytological, biochemical and molecular techniques. Lines varied in their wheat and rye genome composition, and were either wheat-rye chromosome multiple addition lines or had spontaneous substitutions and/or wheat-rye translocations. Most of the lines contained a pair of 4R chromosomes, whereas 1R or 7R were present in others. The results are similar to those previously obtained with hexaploid triticale x wheat crosses and indicate that it is possible to produce alien (wheat/rye) addition, substitution, and translocation lines directly from the anther culture of intergeneric hybrids.     

Array painting using microdissected chromosomes to map chromosomal breakpoints

Molecular characterization of breakpoints of chromosomal rearrangements is a successful strategy for the identification of candidate disease genes. Mapping translocation breakpoints and rearranged chromosomal boundaries is labor intensive and/or time consuming. Here, we present a novel and rapid procedure to map such chromosomal breakpoints by hybridizing amplified microdissection derived DNA of aberrant chromosomes to arrays containing genomic clones. We illustrate the potential of the technique by molecularly delineating the breakpoints in five small supernumerary marker chromosomes (sSMC) and mapping the breakpoints of five different chromosomal translocations.     

Chromosomal distributions of breakpoints in cancer,infertility, and evolution

We extract 11 genome-wide sets of breakpoint positions from databases on reciprocal translocations, inversions and deletions in neoplasms, reciprocal translocations and inversions in families carrying rearrangements and the human-mouse comparative map, and for each set of positions construct breakpoint distributions for the 44 autosomal arms. We identify and interpret four main types of distribution: (i) a uniform distribution associated both with families carrying translocations or inversions, and with the comparative map, (ii) telomerically skewed distributions of translocations or inversions detected consequent to births with malformations, (iii) medially clustered distributions of translocation and deletion breakpoints in tumor karyotypes, and (iv) bimodal translocation breakpoint distributions for chromosome arms containing telomeric proto-oncogenes.     

Structural variation and rates of genome evolution in the grass family seen through comparison of sequences of genomes greatly differing in size

Homology was searched with genes annotated in the Aegilops tauschii pseudomolecules against genes annotated in the pseudomolecules of tetraploid wild emmer wheat, Brachypodium distachyon, sorghum and rice. Similar searches were performed with genes annotated in the rice pseudomolecules. Matrices of collinear genes and rearrangements in their order were constructed. Optical BioNano genome maps were constructed and used to validate rearrangements unique to the wild emmer and Ae. tauschii genomes. Most common rearrangements were short paracentric inversions and short intrachromosomal translocations. Intrachromosomal translocations outnumbered segmental intrachromosomal duplications. The densities of paracentric inversion lengths were approximated by exponential distributions in all six genomes. Densities of collinear genes along the Ae. tauschii chromosomes were highly correlated with meiotic recombination rates but those of rearrangements were not, suggesting different causes of the erosion of gene collinearity and evolution of major chromosome rearrangements. Frequent rearrangements sharing breakpoints suggested that chromosomes have been rearranged recurrently at some sites. The distal 4 Mb of the short arms of rice chromosomes Os11 and Os12 and corresponding regions in the sorghum, B. distachyon and Triticeae genomes contain clusters of interstitial translocations including from 1 to 7 collinear genes. The rates of acquisition of major rearrangements were greater in the large wild emmer wheat and Ae. tauschii genomes than in the lineage preceding their divergence or in the B. distachyon, rice and sorghum lineages. It is suggested that synergy between large quantities of dynamic transposable elements and annual growth habit have been the primary causes of the fast evolution of the Triticeae genomes.     

Translocations and other karyotypic structural changes in wheat x rye hybrids regenerated from tissue culture

Summary The spontaneous occurrence of chromosome breaks, deletions, and translocations in plant tissue cultures is well documented. This study investigated the usefulness of tissue culture as a method of introgressing alien genes into wheat. Wheat X rye hybrids were regenerated from embryo scutellar calli maintained in culture for 222 days. The regenerated seedlings then were treated with colchicine to produce amphidiploids (AABBDDRR). The karyotypes of ten amphidiploids were analyzed by C-banding to determine chromosome structural changes that occurred during tissue culture. Three wheat/rye and one wheat/wheat chromosome translocations, seven deletions, and five amplifications of heterochromatin bands of rye chromosomes were identified. One amphidiploid contained a reciprocal translocation between wheat chromosome 4D and rye chromosome 1R. Non-reciprocal translocations between 2B and 3R, and between an unidentified wheat chromosome and 2R, were found independently in two amphidiploids. An additional plant had a translocation between wheat chromosomes 6B and 5A. All deletions involving rye chromosomes were noted in all 10 amphidiploids. Twelve of the 13 breakpoints in chromosomes involved in translocations and deletions occurred in heterochromatin. Amplification of heterochromatin bands on 2RL and 7RL chromosome arms also was observed in five plants. These results indicate a high degree of chromosome structural change induced by tissue culture. Therefore, tissue culture may be a useful tool in alien gene introgression and manipulation of heterochromatin in triticale improvement.Contribution No. 84-188-J, Kansas Agricultural Experiment Station, Kansas State University. Research was supported by the Science and Education Administration of the U.S. Department of Agriculture under Grant No. 59-2201-1-1-639-0 from Competitive Research Grants Office to R.G.S.