Homoeologous relationships of Aegilops speltoides chromosomes to bread wheat

 Homoeologous pairing at metaphase I was analysed in the standard-type, ph2b and ph1b hybrids of Triticum aestivum (AABBDD) and Aegilops speltoides (SS). Data from relative pairing affinities were used to predict homoeologous relationships of Ae. speltoides chromosomes to wheat. Chromosomes of both species, and their arms, were identified by C-banding. The Ae. speltoides genotype carried genes that induced a high level of homoeologous pairing in the three types of hybrids analyzed. All arms of the seven chromosomes of the S genome showed normal homoeologous pairing, which implies that no apparent chromosome rearrangements occurred in the evolution of Ae. speltoides relative to wheat. A pattern of preferential pairing of two types, A-D and B-S, confirmed that the S genome is very closely related to the B genome of wheat. Although this pairing pattern was also reported in hybrids of wheat with Ae. longissima and Ae. sharonensis, a different behaviour was found in group 5 chromosomes. In the hybrids of Ae. speltoides, chromosome 5B-5S pairing was much more frequent than 5D-5S, while these chromosome associations reached similar frequencies in the hybrids of Ae. longissima and Ae. sharonensis. These results are in agreement with the hypothesis that the B genome of wheat is derived from Ae. speltoides. Received: 8 January 1998 / Accepted: 4 February 1998     

Wheat phylogeny determined by RFLP analysis of nuclear DNA. 3. Intra- and interspecific variations of five Aegilops Sitopsis species

The level of intra- and interspecific variations on nuclear DNA in five Aegilops species of the Sitopsis section were investigated using restriction fragment length polymorphism (RFLP) analysis. A total of 18 accessions, i.e. 7 of Ae. speltoides, 3 of Ae. longissima, 2 of Ae. searsii, 3 of Ae. sharonensis and 3 of Ae. bicornis, were used. One accession each of Triticum aestivum, T. durum, T. urartu and Ae. squarrosa was included as reference material. Five enzymes and 20 probes were used. Among the five Sitopsis species studied, Ae. speltoides had the largest intraspecific variation (=0.061), which was as high as the interspecific variation observed among the other four species. The section Sitopsis was divided into two distinct groups: one containing only Ae. speltoides and the other, Ae. longissima, Ae. searsii, Ae. sharonensis and Ae. bicornis. This grouping by RFLP analysis is in agreement with the taxonomical classification of the subsections.     

Comparative genetic analysis of the Aegilops longissima and Ae. sharonensis genomes with common wheat

Aegilops longissima Schw. et Musch. (2n= 2x=14, S^lS^l) and Aegilops sharonensis Eig. (2n=2x=14, S^lS^l) are diploid species belonging to the section Sitopsis in the tribe Triticeae and potential donors of useful genes for wheat breeding. A comparative genetic map was constructed of the Ae. longissima genome, using RFLP probes with known location in wheat. A high degree of conserved colinearity was observed between the wild diploid and basic wheat genome, represented by the D genome of cultivated wheat. Chromosomes 1S^l, 2S^l, 3S^l, 5S^l and 6S^l are colinear with wheat chromosomes 1D, 2D, 3D, 5D and 6D, respectively. The analysis confirmed that chromosomes 4S^l and 7S^l are translocated relative to wheat. The short arms and major part of the long arms are homoeologous to most of wheat chromosomes 4D and 7D respectively, but the region corresponding to the distal segment of 7D was translocated from 7S^lL to the distal region of 4S^lL. The map and RFLP markers were then used to analyse the genomes and added chromosomes in a set of ’Chinese Spring’ (CS)/Ae. longissima chromosome additions. The study confirmed the availability of disomic CS/Ae. longissima addition lines for chromosomes 1S^l, 2S^l, 3S^l, 4S^l and 5S^l. An as yet unpublished set of Ae. sharonensis chromosome addition lines were also available for analysis. Due to the gametocidal nature of Ae. sharonensis chromosomes 2S^l and 4S^l, additions 1S^l, 3S^l, 5S^l, 6S^l and 7S^l were produced in a (4D)4S^l background, and 2S^l and 4S^l in a euploid wheat background. The analysis also confirmed that the 4/7 translocation found in Ae. longissima was not present in Ae. sharonensis although the two wild relatives of wheat are considered to be closely related. The phenotypes of the Ae. sharonensis addition lines are described in an Appendix. Received: 28 September 2000 / Accepted: 19 January 2001     

The molecular basis of genetic diversity among cytoplasms of Triticum and Aegilops

Summary Many related species and strains of common wheat were compared by matching differences among their mitochondrial genomes with their parent nuclear genomes. We examined three species of Aegilops, section Sitopsis (Ae. bicornis, Ae. sharonensis, and Ae. speltoides), emmer wheat (Triticum dicoccoides, T. dicoccum, and T. durum), common wheat (T. spelta, T. aestivum, and T. compaction), and timopheevi wheat (T. araraticum, T. timopheevi, and T. zhukovskyi). A single source of the cytoplasm was used in all the species, except Ae. speltoides (two sources), T. araraticum (two), and T. aestivum (three). Following restriction endonuclease analyses, the mitochondrial genomes were found to comprise seven types, and a dendrogram showing their genetic relatedness was constructed, based upon the percentage of common restriction fragments. MtDNAs from T. dicoccum, T. durum, T. aestivum, and T. compactum yielded identical restriction fragment patterns; these differed from T. dicoccoides and T. spelta mtDNAs in only 2.3% of their fragments. The fragment patterns of T. timopheevi and T. zhukovskyi were identical, and these differed from T. araraticum mtDNA by only one fragment. In both the emmer-dinkel and timopheevi groups, mitochondrial genome differentiation is evident, suggesting a diphyletic origin of each group. MtDNAs from four accessions of the Sitopsis species of Aegilops differ greatly from one another, but those of Ae. bicornis, Ae. sharonensis, and Ae. searsii, belonging to the same subsection Emarginata, are relatively similar. MtDNAs of timopheevi species are identical, or nearly so, to those of Ae. speltoides accession (09), suggesting that the latter was the cytoplasm donor to the former, polyploid group. The origin of this polyploid group seems to be rather recent in that the diploid and polyploid species possess nearly identical mitochondrial genomes. We cannot determine, with precision, the cytoplasm donor to the emmer-dinkel group. However, our results do suggest that mitochondrial DNAs show larger evolutionary divergence than do the ctDNAs from these same strains.Contribution no. 507 from the Laboratory of Genetics, Faculty of Agriculture, Kyoto University, Japan     

Evidence for AEGILOPS SHARONENSIS Eig as the Donor of the B Genome of Wheat

A number of lines of evidence are advanced for the candidacy of Aegilops sharonensis Eig as the donor of the B genome of wheat. The cytoplasm of Ae. sharonensis is compatible with tetraploid wheat Triticum turgidum dicoccoides, as evidenced by the high level of chromosome pairing and fertility of the amphiploid Ae. sharonensis x T. turgidum dicoccoides. Ae. sharonensis chromosomes exhibit high levels of pairing with those of the B genome of wheat in hybrids with Ph-deficient hexaploid wheat and low levels of homoeologous pairing with T. monococcum chromosomes.——The amphidiploid between Ae. sharonensis and T. monococcum is very similar to T. turgidum dicoccoides in spike, spikelet and grain morphology. The karyotype of Ae. sharonensis resembles more closely that of extrapolated B genome karyotypes of wheat than do the karyotypes of other proposed B-genome donor species of Aegilops. Because of distinctiveness in cytological affinity and karyotype morphology between Ae. sharonensis and Ae. longissima, a separate genome symbol S^sh is proposed for the former species.     

Investigation of a preferentially transmitted Aegilops sharonensis chromosome in wheat

Summary An attempt to produce a set of addition lines of Aegilops sharonensis to the wheat variety Chinese Spring produced only one addition line. This was due to preferential transmission of one chromosome from Ae. sharonensis. This chromosome was studied in detail by established cytological methods of chromosome observation and by the newer techniques of C-banding and in situ hybridization of a cloned DNA sequence. The chromosome was found to be partially homologous to an Ae. sharonensis chromosome of similar behaviour in another wheat addition line. The incomplete homology of the two Ae. sharonensis chromosomes was due to the presence of a translocated segment of a wheat chromosome. — Substitution lines of the Ae. sharonensis chromosome for wheat homoeologous group 4 were produced and the Ae. sharonensis chromosome thereby designated 4 S ^l .     

Molecular analysis of the phylogenetic relationships among the diploid <Emphasis Type="Italic">Aegilops</Emphasis> species of the section <Emphasis Type="Italic">Sitopsis</Emphasis>

RAPD analysis was used to study the intraspecific variation and phylogenetic relationships of Sgenome diploid Aegilops species regarded as potential donors of the B genome of cultivated wheat. In total, 21 DNA specimens from six S-genome diploid species were examined. On a dendrogram, Ae. speltoides and Ae. aucheri formed the most isolated cluster. Among the other species, Ae. searsii was the most distant while Ae. longissima and Ae. sharonensis were the closest species. The maximum difference between individual accessions within one species was approximately the same (0.18–0.22) in Ae. bicornis, Ae. longissima, Ae. sharonensis, and Ae. searsii. The difference between the clusters of questionable species Ae. speltoides and Ae. aucheri corresponded to the intraspecific level; the difference between closely related Ae. longissima and Ae. sharonensis corresponded to the interspecific level.     

The effect of B chromosomes on meiotic and pre-meiotic spindles and chromosome pairing in Triticum/Aegilops hybrids

Diploid populations of Aegilops mutica and Aegilops speltoides containing B chromosomes have been used as male parents in crosses with aneuploid genotypes of Triticum aestivum to investigate the effect of B chromosomes on meiotic homologous and homoeologous chromosome pairing. F₁ hybrids of T. aestivum/Ae. mutica and T. aestivum/Ae. speltoides segregated into four classes with regard to the degree of meiotic chromosome pairing, irrespective of the presence of B chromosomes. The B chromosomes do not introduce factors altering the level of pairing other than that due to the natural allelic and gene variation occurring in the diploids. Similarly no reduction in pairing of homologous chromosomes was observed in genotypes in which pairs of homologues co-existed with B chromosomes. However, a significant drop in chiasma frequency was observed in F₁ hybrids of T. aestivum × Ae. mutica with B chromosomes and T. aestivum × Ae. mutica nullisomic for wheat chromosome 5D with B chromosomes, in temperature regimes of 12° C. No asynapsis occurred in similar hybrids in the absence of Mutica B chromosomes at low temperatures. The low-temperature sensitive phase lies early in the pre-meiotic interphase. In this instance the Mutica B chromosomes are interacting with specific gene loci of the A chromosomes. Synaptic pairing has been observed between A and B chromosomes in Ae. mutica. A high frequency of pollen mother cells with twice the number of chromosomes was observed in hybrids in the presence of Mutica B chromosomes due to failure of spindle formation at the last pre-meiotic mitosis. Meiotic spindle irregularities occurred in hybrids containing Speltoides B chromosomes. Hybrids of Ae. speltoides + B's X Ae. mutica + B's displayed the mitotic and meiotic spindle abnormalities introduced by the presence of the B chromosomes of each parent.     

Microsatellite mapping of <Emphasis Type="Italic">Ae. speltoides</Emphasis> and map-based comparative analysis of the S,G, and B genomes of Triticeae species

The first microsatellite linkage map of Ae. speltoides Tausch (2n = 2x = 14, SS), which is a wild species with a genome closely related to the B and G genomes of polyploid wheats, was developed based on two F₂ mapping populations using microsatellite (SSR) markers from Ae. speltoides, wheat genomic SSRs (g-SSRs) and EST-derived SSRs. A total of 144 different microsatellite loci were mapped in the Ae. speltoides genome. The transferability of the SSRs markers between the related S, B, and G genomes allowed possible integration of new markers into the T. timopheevii G genome chromosomal maps and map-based comparisons. Thirty-one new microsatellite loci assigned to the genetic framework of the T. timopheevii G genome maps were composed of wheat g-SSR (genomic SSR) markers. Most of the used Ae. speltoides SSRs were mapped onto chromosomes of the G genome supporting a close relationship between the G and S genomes. Comparative microsatellite mapping of the S, B, and G genomes demonstrated colinearity between the chromosomes within homoeologous groups, except for intergenomic T6A^tS.1G, T4AL.5AL.7BS translocations. A translocation between chromosomes 2 and 6 that is present in the T. aestivum B genome was found in neither Ae. speltoides nor in T. timopheevii. Although the marker order was generally conserved among the B, S, and G genomes, the total length of the Ae. speltoides chromosomal maps and the genetic distances between homoeologous loci located in the proximal regions of the S genome chromosomes were reduced compared with the B, and G genome chromosomes.     

Variation in the distribution of a genome-specific DNA sequence on chromosomes reveals evolutionary relationships in the Triticum and Aegilops complex

 The present study analyzed the distribution pattern of the Ae. speltoides–derived repetitive clone pGc1R-1 in the Triticum/Aegilops complex. Fluorescence in situ hybridization analysis showed that clone pGc1R-1 is a S-genome-specific repetitive sequence that hybridized to the S-genome of three species in the section Sitopsis, Aegilops speltoides (S), Ae. longissima (S^l), and Ae. sharonensis (S^sh), but not to Ae. bicornis (S^b) and Ae. searsii (S^s), nor to any other diploid Aegilops species. This clone also hybridized to the very closely related G-genome of T. timopheevii subsp. armeniacum and T. timopheevii ssp. timopheevii, but not to the B-genome of T. turgidum and T. aestivum. Hybridization also was observed in the polyploid Aegilops species, Ae. kotschyi (U^kS^k), Ae. peregrina (U^pS^p), and Ae. vavilovii (X^vaD^vaS^va). Large inter- and intraspecific variations were observed. Our results confirm that the S genome is related more to the S^l and S^sh genomes than to the S^b and S^s genomes; there is a greater affinity between the G and S genomes than between the B and S genomes. Mechanisms to account for the variation in the FISH pattern with different genomes include sequence amplification and deletion. Variation in the distribution of this genome-specific DNA sequence, pGc1R-1, on chromosomes can be used to reveal evolutionary relationships in the Triticum and Aegilops complex. Received April 10, 2002; accepted July 12, 2002 Published online: November 28, 2002 Address of the authors: Peng Zhang, Bernd Friebe (e-mail: friebe@ksu.edu), Bikram S. Gill, Wheat Genetics Resource Center, Department of Plant Pathology, 4024 Throckmorton, Plant Sciences Center, Kansas State University, Manhattan, KS 66506-5502, USA.     

A comparative analysis of the composition and organization of two subtelomeric repeat families in <Emphasis Type="Italic">Aegilops speltoides</Emphasis>Tausch. and related species

The structural organization and evolution of two tandemly repeated families, Spelt1 and Spelt52, located in the subtelomeric regions of Aegilops speltoides chromosomes were studied. The Spelt1 family of sequences with a monomer length of 178 bp was characterized by cloning and sequence analysis of polymerase chain reaction (PCR) products. Members of the Spelt1 family revealed sequence similarities exceeding 95\%. This conservation has remained despite divergence of species in Aegilops section Sitopsis and after independent multiple amplification events in the genome of Ae. speltoides. Sequences representing the Spelt52 family were cloned, sequenced and compared with other sequences in databases. The Spelt52 repeat family contains monomers of two types, Spelt52.1 and Spelt52.2. The two monomers share a homologous stretch of 280 bp and have two regions without sequence similarity of 96 bp and 110 bp, respectively. PCR analysis was conducted to 15 lines in Ae. speltoidesTausch., Ae. longissimaSchw.&Mushc.,Ae. sharonensisEig.,Ae. bicornis(Forssk)Jaub.&Sp., andAe. searsii Feld.&Kis. using primers to the homologous and non- homologous regions of Spelt52 family. Intraspecies and interspecies differences in the occurrence and abundance of combinations of Spelt52.1 and Spelt52.2 monomers were detected. The use of primers to telomeric and subtelomeric repeats followed by Southern hybridization, cloning, and sequence analysis demonstrated that Spelt1 and Spelt52 are localized close to each other and to telomeric repeats. The efficiency of a PCR approach for the analysis of telomeric/subtelomeric junction regions of chromosomes is discussed.     

Homoeologous relationships of Triticum sharonense chromosomes to T. aestivum

 Homoeologous pairing at metaphase I was analyzed in standard-type, ph2b, and ph1b hybrids of Triticum aestivum (common, bread or hexaploid wheat) and T. sharonense in order to establish the homoeologus relationships of T. sharonense chromosomes to hexaploid wheat. Chromosomes of both species, and their arms, were identified by C-banding. Normal homoeologous relationships for the seven chromosomes of the S^sh genome, and their arms, were revealed, which implies that no apparent chromosome rearrangement occurred in the evolution of T. sharonense relative to wheat. All three types of hybrids with low-, intermediate-, and high-pairing level showed preferential pairing between A-D and B-S^sh. A close relationship of the S^sh genome to the B genome of bread wheat was confirmed, but the results provide no evidence that the B genome was derived from T. sharonense. Data on the pairing between individual chromosomes of T. aestivum and T. sharonense provide an estimate of interspecific homoeologous recombination. Received: 14 October 1996 / Accepted: 25 October 1996     

Insight into the genetic variability analysis and relationships among some Aegilops and Triticum species,as genome progenitors of bread wheat,using SCoT markers

We assessed the molecular genetic diversity and relationships among some Aegilops and Triticum species using 15 start codon-targeted (SCoT) polymorphism markers. A total of 166 bands amplified, of which 164 (98.79%) were polymorphic. Analysis of molecular variance and inter-population differentiation (Gst) indicated high genetic variation within the studied populations. Our analyses revealed high genetic diversity in T. boeoticum, Ae. cylindrica, T. durum and Ae. umbellulata, low diversity in Ae. crassa, Ae. caudata and Ae. speltoides, and a close relationship among Ae. tauschii, T. aestivum, T. durum, T. urartu, and T. boeoticum. Cluster analysis indicated 180 individuals divided into 8 genome homogeneous clades and 11 sub-groups. T. aestivum and T. durum accessions were grouped together, and accessions with the C and U genomes were grouped into the same clade. Our results support the hypothesis that T. urartu and Ae. tauschii are two diploid ancestors of T. aestivum, and also that Ae. caudata and Ae. umbellulata are putative donors of C and U genomes for other Aegilops species that possess these genomes. Our results also revealed that the SCoT technique is informative and can be used to assess genetic relationships among wheat germplasm.     

The effect of ph mutations on homoeolgous pairing in hybrids of wheat with Triticum longissimum

Homoeologous pairing at metaphase-I was analyzed in wild-type, ph2b, and ph1b hybrids of wheat and a low-pairing type of T. longissimum in order to study the effect of ph mutations on the pairing of T. longissimum chromosomes with wheat chromosomes. Chromosomes of both species, and their arms, were identified by C-banding. The three types of hybrids, with low-, intermediate-, and high-pairing levels, respectively, exhibited a very similar pairing pattern which was characterized by the existence of two types, A-D and B-S¹, of preferential pairing. These results confirm that the S¹ genome of T. longissimum is closely related to the B genome of wheat. The possible use of ph1b and ph2b mutations in the transfer to wheat of genes from related species is discussed.     

Chromosome structure of Triticum longissimum relative to wheat

Homoeologous pairing at meiotic metaphase I was analyzed in T. longissimum x T. aestivum hybrids in order to reconfirm the homoeologous relationships of T. longissimum chromosomes to wheat. Hybrids between T. longissimum and Chinese Spring carrying the Ph1 gene or theph1b mutation, which showed low and high pairing levels, respectively, were used. Chromosome arms associated at metaphase I were identified by C-banding. The homoeology of chromosomes 1S ^l , 2S ^l , 3S ^l , 5S ^l and 6S ^l to wheat group 1,2, 3, 5, and 6 chromosomes, respectively, was confirmed. Chromsome arms 4S ^l S and 7S ^l S showed normal homoeologous relationships to wheat. The 4S ^l L arm carries a translocated segment from 7S ^l L relative to wheat. The 7S ^l L arm seldom paired, likely because this arm lost a relatively long segment and received a very short segment in the interchange with 4S ^l L. Available data suggest that translocation 4S ^l L/7S ^l L arose in the evolution of T. longissimum, which implies that this species was not the donor of the B genome of wheat.     

The specific activity of ribulose-1,5-bisphosphate carboxylase in relation to genotype in wheat

The specific activity of ribulose-1,5-bisphosphate carboxylase (RuBPCase; EC 4.1.1.39) in crude extracts of leaves from euploid, amphiploid and alloplasmic lines of wheat fell into high or low categories (3.75 or 2.70 mol·mg^–1·min^–1, 30°C). For the alloplasmic lines, where the same hexaploid nuclear genome was substituted into different cytoplasms, the specific activity of RuBPCase was consistent with the type of cytoplasm (high for the B and S cytoplasms and low for the A and D cytoplasms). There was no evidence from the euploid and amphiploid lines that small subunits encoded in different nuclear genomes influenced the specific activity. High specific activity was conferred by possession of the chloroplast genome of the B-type cytoplasm which encodes the large subunit of RuBPCase. All lines with a cytoplasm derived from the Sitopsis section of wheat, with the exception of Aegilops longissima and A. speltoides 18940, had RuBPCase with high specific activity. In contrast with the euploid lines of A. longissima, the alloplasmic line containing A. longissima cytoplasm from a different source had RuBPCase with high specific activity. The difference in specific activity found here in-vitro was not apparent in-vivo when leaf gas exchange was measured.Abbreviation RuBP(Case) ribulose-1,5-bisphosphate (carboxylase)     

Production and cytogenetic analysis of BC1, BC2, and BC3 progenies of an intergeneric hybrid between Triticum aestivum (L.) Thell. and tetraploid Agropyron cristatum (L.) Gaertn.

Summary Intergeneric hybrids between Triticum aestivum cv Chinese Spring and Agropyron cristatum 4x (2n= 5x=35, ABDPP genomes) with a high level of homoeologous meiotic pairing between the wheat chromosomes were backcrossed 3 times to wheat. Pollination of the F₁ hybrid with Chinese Spring resulted in 22 BC₁ seeds with an average seed set of 1.52%. Five BC₁ plants with 39–41 chromosomes were raised using embryo rescue techniques. Chromosome pairing in the BC₁ was characterized by a high frequency of multivalent associations, but in spite of this there was no evidence of homoeologous pairing between chromosomes of wheat and those of Agropyron. All of the plants were self sterile. The embryo rescue technique was again essential to produce 39 BC₂ plants with chromosome numbers ranging from 37 to 67. The phenomenon of meiotic non-reduction was also observed in the BC₃ progenies. In this generation male and female fertility greatly increased, and meiotic pairing was fairly regular. Some monosomic (2n=43) and double monosomic (2n=44) lines were produced. Analysis of these progenies should permit the extraction of the seven possible wheat-Agropyron disomic addition lines including those with the added chromosomes carrying the genes involved in meiotic non-reduction and in suppression of Ph activity.     

The genetic control of grain esterases in hexaploid wheat

Summary A comparison of EST-5 grain esterase phenotypes from wheat-alien amphiploid, addition and substitution genotypes, resolved by flat-bed isoelectric focusing identified homoeologous Est-5 loci on chromosome 3H of Hordeum vulgare, 3H^ch of H. chilense, 3S^b of Aegilops bicornis, 3S¹ of Ae. sharonensis and Ae. longissima and 6R of Secale cereale and 6R^m of S. montanum. The Est-5 genes in alien species provide evidence for chromosome homoeology with wheat.     

Transfer of Ph I genes promoting homoeologous pairing from Triticum speltoides to common wheat

Diploid-like chromosome pairing in polyploid wheat is controlled by several Ph (pairing homoeologous) genes with major and minor effects. Homoeologous pairing occurs in either the absence of these genes or their inhibition by genes from other species (Ph ^I genes). We transferred Ph ^I genes from Triticum speltoides (syn Aegilops speltoides) to T. aestivum, and on the basis of further analysis it appears that two duplicate and independent Ph ^I genes were transferred. Since Ph ^I genes are epistatic to the Ph genes of wheat, homoeologous pairing between the wheat and alien chromosomes occurs in the F₁ hybrids. Using the Ph ^I gene stock, we could demonstrate homoeologous pairing between the wheat and Haynaldia villosa chromosomes. Since homoeologous pairing occurs in F₁ hybrids and no cytogenetic manipulation is needed, the Ph ^I gene stock may be a versatile tool for effecting rapid and efficient alien genetic transfers to wheat.Contribution no. 93-435-J from the Kansas Agricultural Experiment Station, Kansas State University, Manhattan, KS 66506-5502, USA