Thinopyrum 7Ai-1-derived small chromatin with Barley Yellow Dwarf Virus (BYDV) resistance gene integrated into the wheat genome with retrotransposon

Thinopyrum intermedium is a useful source of resistance genes for Barley Yellow Dwarf Virus (BYDV), one of the most damaging wheat diseases. In this study, wheat/Th. intermedium translocation lines with a BYDV resistance gene were developed using the Th. intermedium 7Ai-1 chromosome. Genomic in situ hybridization (GISH), using a Th. intermedium total genomic DNA probe, enabled detection of 7Ai-1-derived small chro-matins containing a BYDV resistance gene, which were translocated onto the end of wheat chromosomes in the lines Y95011 and Y960843. Random amplified polymorphic DNA (RAPD) analyses using 120 random 10-mer primers were conducted to compare the BYDV-resistant translocation lines with susceptible lines. Two primers amplified the DNA fragments specific to the resistant line that would be useful as molecular markers to identify 7Ai-1-derived BYDV resistance chromatin in the wheat genome. Additionally, the isolated Th. intermedium-specific retrotransposon-like sequence pTi28 can be used to identify Th. intermedium chromatin transferred to the wheat genome.     

Molecular cytogenetic characterization of two high protein wheat-<Emphasis Type="Italic">Thinopyrum intermedium</Emphasis> partial amphiploids

Fluorescence and genomic in situ hybridization (FISH and GISH) were used to establish the cytogenetic constitution of two wheat × Thinopyrum intermedium partial amphiploids H95 and 55(1-57). Both partial amphiploids are high-protein lines having resistance to leaf rust, yellow rust and powdery mildew and have in total 56 chromosomes per cell. Repetitive DNA probes (pTa71, Afa family and pSc119.2) were used to identify the individual wheat chromosomes and to reveal the distribution of these probes within the alien chromosomes. FISH detected 6B tetrasomy in H95 and a null (1D)-tetrasomy (1B) in 55(1-57). GISH was carried out using biotin labeled Th. intermedium DNA and digoxigenin labeled Pseudoroegneria spicata DNA as probes, subsequently. GISH results revealed 44 wheat chromosomes and four Thinopyrum chromosome pairs, including three S and one J chromosome pairs in line H95. Line 55(1-57), contained 42 wheat chromosomes and six Th. intermedium pairs, including two S and one J^S pairs. Additionally, two identical translocated chromosome pairs with diminished affinity to the alien chromatin were detected in both amphiploids. Another two translocations were found in 55(1-57), with satellite sections from the Thinopyrum J genome.     

Introduction of Thinopyrum intermedium ssp. trichophorum chromosomes to wheat by trigeneric hybridization involving Triticum,Secale and Thinopyrum genera

Main conclusion

Fluorescence in situ hybridization and molecular markers have confirmed that several chromosomes from Thinopyrum intermedium ssp. trichophorum have been added to a wheat background, which originated from a cross between a wheat– Thinopyrum partial amphiploid and triticale. The lines displayed blue grains and resistance to wheat stripe rust.

Thinopyrum intermedium has been used as a valuable resource for improving the disease resistance and yield potential of wheat. With the aim to transfer novel genetic variation from Th. intermedium species for sustainable wheat breeding, a new trigeneric hybrid was produced by crossing an octoploid wheat–Th. intermedium ssp. trichophorum partial amphiploid with hexaploid triticale. Fluorescence in situ hybridization (FISH) revealed that Thinopyrum chromosomes were transmitted preferably and the number of rye chromosomes tended to decrease gradually in the selfed derivatives of the trigeneric hybrids. Four stable wheat–Th. intermedium chromosome substitution, addition and translocation lines were selected, and a 2J^S addition line, two substitution lines of 4J^S(4B) and 4J(4B), and a small 4J.4B translocation line were identified by FISH and molecular markers. It was revealed that the gene(s) responsible for blue grains may located on the FL0.60–1.00 of long arm of Th. intermedium-derived 4J chromosome. Disease resistance screenings indicated that chromosomes 4J^S and 2J^S appear to enhance the resistance to stripe rust in the adult plant stage. The new germplasm with Th. intermedium introgression shows promise for utilization of Thinopyrum chromosome segments in future wheat improvement.

     

Direct evidence for high level of autosyndetic pairing in hybrids of Thinopyrum intermedium and Th. ponticum with Triticum aestivum

 Genomic in situ hybridization (GISH) was used to distinguish autosyndetic from allosyndetic pairing in the hybrids of Thinopyrum intermedium and Th. ponticum with Triticum aestivum cv ‘Chinese Spring’ (CS). All hybrids showed high autosyndetic pairing frequencies among wheat chromosomes and among Thinopyrum chromosomes. The high autosyndetic pairing frequencies among wheat chromosomes in both hybrids suggested that Th. intermedium and Th. ponticum carry promoters for homoeologous chromosome pairing. The higher frequencies of autosyndetic pairing among Thinopyrum chromosomes than among wheat chromosomes in both hybrids indicated that the relationships among the three genomes of Th. intermedium and among the five genomes of Th. ponticum are closer than those among the three genomes of T. aestivum. Received: 19 September 1996 / Accepted: 18 April 1997     

Resistance to eyespot of wheat, caused by Tapesia yallundae, derived from Thinopyrum intermedium homoeologous group 4 chromosome

Thinopyrum intermedium was identified previously as resistant to Tapesia yallundae, cause of eyespot of wheat. Using GUS-transformed isolates of T. yallundae as inoculum, we determined that wheat lines carrying Th. intermedium chromosome 4Ai#2 or the short arm of chromosome 4Ai#2 were as resistant to the pathogen as the eyespot-resistant wheat- Th. ponticum chromosome substitution line SS767 (PI 611939) and winter wheat cultivar Madsen, which carries gene Pch1 for eyespot resistance. Chromosome 4E from Th. elongatum and chromosome 4J from Th. bessarabicum did not confer resistance to T. yallundae. Genome-specific PCR primers confirmed the presence of Thinopyrum chromatin in these wheat- Thinopyrum lines. Genomic in situ hybridization using an St genomic probe from Pseudoroegneria strigosa demonstrated that chromosome 4Ai#2 belongs to the J^s genome of Thinopyrum. The eyespot resistance in the wheat- Th. intermedium lines is thus controlled by the short arm of this J^s chromosome. This is the first report of resistance to T. yallundae controlled by a J^s genome chromosome of Th. intermedium.     

Genomic constitution and variation in five partial amphiploids of wheat–<Emphasis Type="Italic">Thinopyrum intermedium</Emphasis> as revealed by GISH,multicolor GISH and seed storage protein analysis

Genomic in situ hybridization (GISH) and multicolor GISH (mcGISH) methodology were used to establish the cytogenetic constitution of five partial amphiploid lines obtained from wheat × Thinopyrum intermedium hybridizations. Line Zhong 1, 2n=52, contained 14 chromosomes from each of the wheat genomes plus ten Th. intermedium chromosomes, with one pair of A-genome chromosomes having a Th. intermedium chromosomal segment translocated to the short arm. Line Zhong 2, 2n=54, had intact ABD wheat genome chromosomes plus 12 Th. intermedium chromosomes. The multicolor GISH results, using different fluorochrome labeled Th. intermedium and the various diploid wheat genomic DNAs as probes, indicated that both Zhong 1 and Zhong 2 contained one pair of Th. intermedium chromosomes with a significant homology to the wheat D genome. High-molecular-weight (HMW) glutenin and gliadin analysis revealed that Zhong 1 and Zhong 2 had identical banding patterns that contained all of the wheat bands and a specific HMW band from Th. intermedium. Zhong 1 and Zhong 2 had good HMW subunits for wheat breeding. Zhong 3 and Zhong 5, both 2n=56, possessed no gross chromosomal aberrations or translocations that were detectable at the GISH level. Zhong 4 also had a chromosome number of 2n=56 and contained the complete wheat ABD-genome chromosomes plus 14 Th. intermedium chromosomes, with one pair of Th. intermedium chromosomes being markedly smaller. Multicolor GISH results indicated that Zhong 4 also contained two pairs of reciprocally translocated chromosomes involving the A and D genomes. Zhong 3, Zhong 4 and Zhong 5 contained a specific gliadin band from Th. intermedium. Based on the above data, it was concluded that inter-genomic transfer of chromosomal segments and/or sequence introgression had occurred in these newly synthesized partial amphiploids despite their diploid-like meiotic behavior and disomic inheritance.     

Molecular cytogenetic characterization of Thinopyrum intermedium-derived wheat germplasm specifying resistance to wheat streak mosaic virus

Thinopyrum intermedium is a promising source of resistance to wheat streak mosaic virus (WSMV), a devastating disease of wheat. Three wheat germplasm lines possessing resistance to WSMV, derived from Triticum aestivum×Th. intermedium crosses, are analyzed by C-banding and genomic in situ hybridization (GISH) to determine the amount and location of alien chromatin in the transfer lines. Line CI15092 was confirmed as a disomic substitution line in which wheat chromosome 4A was replaced by Th. intermedium chromosome 4Ai?2. The other two lines, CI17766 and A29-13-3, carry an identical Robertsonian translocation chromosome in which the complete short arm of chromosome 4Ai?2 was transferred to the long arm of wheat chromosome 4A. Fluorescence in situ hybridization (FISH) using ABD genomic DNA from wheat as a probe and S genomic DNA from Pseudoroegneria stipifolia as the blocker, and vice versa, revealed that the entire short arm of the translocation was derived from the short arm of chromosome 4Ai?2 and the breakpoint was located at the centromere. Chromosomal arm ratios (L/S) of 2.12 in CI17766 and 2.15 in A29-13-3 showed that the translocated chromosome is submetacentric. This translocated chromosome is designated as T4AL?? 4Ai?2S as suggested by Friebe et al. (1991).     

Genomic in situ hybridization (GISH) analyses of Thinopyrum intermedium, its partial amphiploid Zhong 5, and disease-resistant derivatives in wheat

Genomic in situhybridization (GISH) to root-tip cells at mitotic metaphase, using genomic DNA probes from Thinopyrum intermedium and Pseudoroegneria strigosa, was used to examine the genomic constitution of Th. intermedium, the 56-chromosome partial amphiploid to wheat called Zhong 5 and disease-resistant derivatives of Zhong 5, in a wheat background. Evidence from GISH indicated that Th. intermedium contained seven pairs of St, seven J^S and 21 J chromosomes; three pairs of Th. intermedium chromosomes with satellites in their short arms belonging to the St, J, J genomes and homoeologous groups 1, 1, and 5 respectively. GISH results using different materials and different probes showed that seven pairs of added Th. intermedium chromosomes in Zhong 5 included three pairs of St chromosomes, two pairs of J^S chromosomes and two pairs of St-J^S reciprocal tanslocation chromosomes. A pair of chromosomes, which substituted a pair of wheat chromosomes in Yi 4212 and in HG 295 and was added to 21 pairs of wheat chromosomes in the disomic additions Z1, Z2 and Z6, conferred BYDV-resistance and was identical to a pair of St-J^S tanslocation chromosomes (StJ^S) in Zhong 5. The StJ^S chromosome had a special GISH signal pattern and could be easily distinguished from other added chromosomes in Zhong 5; it has not yet been possible to locate the BYDV-resistant gene(s) of this translocated chromosome either in the St chromosome portion belonging to homoeologous group 2 or in the J^S chromosome portion whose homoeologous group relationship is still uncertain. Among 22 chromosome pairs in disomic addition line Z3, the added chromosome pair had satellites and belonged to the St genome and homoeologous group 1. Disomic addition line Z4 carried a pair of added chromosomes which was composed of a group-7 J^S chromosome translocated with a wheat chromosome; this chromosome was different to 7 Ai-1, but was identical to 7 Ai-2. The leaf rust and stem rust resistance genes were located in the distal region of the long arm, whereas the stripe rust resistance gene(s) was located in the short arm or in the proximal region of the long arm of 7 Ai-2. A pair of J^S-wheat translocation chromosomes, which originated from the WJ^S chromosomes in Z4, was added to the disomic addition line Z5; the added chromosomes of Z5 carried leaf and stem rust resistance but not stripe rust resistance; Z5 is a potentially useful source for rust resistance genes in wheat breeding and for cloning these novel rust-resistant genes. GISH analysis using the St genome as a probe has proved advantageous in identifying alien Th. intermedium in wheat. Received: 17 May 1999 / Accepted: 22 June 1999     

Introduction of chromosome segment carrying the seed storage protein genes from chromosome 1V of Dasypyrum villosum showed positive effect on bread-making quality of common wheat

Key message

Development of wheat- D. villosum 1V#4 translocation lines; physically mapping the Glu - V1 and Gli - V1 / Glu - V3 loci; and assess the effects of the introduced Glu - V1 and Gli - V1 / Glu - V3 on wheat bread-making quality.

Abstract

Glu-V1 and Gli-V1/Glu-V3 loci, located in the chromosome 1V of Dasypyrum villosum, were proved to have positive effects on grain quality. However, there are very few reports about the transfer of the D. villosum-derived seed storage protein genes into wheat background by chromosome manipulation. In the present study, a total of six CS-1V#4 introgression lines with different alien-fragment sizes were developed through ionizing radiation of the mature female gametes of CS––D. villosum 1V#4 disomic addition line and confirmed by cytogenetic analysis. Genomic in situ hybridization (GISH), chromosome C-banding, twelve 1V#4-specific EST–STS markers and seed storage protein analysis enabled the cytological physical mapping of Glu-V1 and Gli-V1/Glu-V3 loci to the region of FL 0.50–1.00 of 1V#4S of D. villosum. The Glu-V1 allele of D. villosum was Glu-V1a and its coded protein was V71 subunit. Quality analysis indicated that Glu-V1a together with Gli-V1/Glu-V3 loci showed a positive effect on protein content, Zeleny sedimentation value and the rheological characteristics of wheat flour dough. In addition, the positive effect could be maintained when specific Glu-V1 and Gli-V1/Glu-V3 loci were transferred to the wheat genetic background as in the case of T1V#4S-6BS·6BL, T1V#4S·1BL and T1V#4S·1DS translocation lines. These results showed that the chromosome segment carrying the Glu-V1 and Gli-V1/Glu-V3 loci in 1V#4S of D. villosum had positive effect on bread-making quality, and the T1V#4S-6BS·6BL and T1V#4S·1BL translocation lines could be useful germplasms for bread wheat improvement. The developed 1V#4S-specific molecular markers could be used to rapidly identify and trace the alien chromatin of 1V#4S in wheat background.     

Characterization of HMW-GSs and their gene inaction in tetraploid wheat

In this study, we report the expression of HMW-GSs in 87 accessions of tetraploid wheat, the characterization of three inactive and one active HMW glutenin genes, and the functional verification of HMW-GSs by promoter–GUS expression. SDS-PAGE profiles revealed that tetraploid wheat has many different combinations of HMW-GSs and the number of subunits varies from 1 to 4. HMW glutenin genes at the Glu-A1x, Glu-A1y and Glu-B1y loci exhibited different frequencies of inaction while the Glu-B1x allele was expressed in all 87 accessions. Gene cloning showed that only 1Bx (Tdu-e) could express a full-length protein and its deduced protein sequence has the typical primary structure but with fewer cysteine residues. The expression of the other three HMW glutenin genes has been disrupted by stop codons in their repetitive domains. Besides short indels or mutations of one or more bases, an 85-bp deletion and a 185-bp insertion were found in the promoter regions of 1Ay (Tdu-s) and 1Bx (Tdu-e). The transient expression of promoter–GUS constructs indicated that the 1Ay promoter can drive expression of the GUS gene. We conclude that defects (stop codons or the insertion of large transposon-like elements) in the coding regions may be the most probable cause for the inaction of the HMW glutenin genes.     

Molecular characterisation of the amino- and carboxyl-domains in different Glu-A1x alleles of Triticum urartu Thum. ex Gandil.

The wild diploid wheat (Triticum urartu Thum. ex Gandil.) is a potential gene source for wheat breeding, as this species has been identified as the A-genome donor in polyploid wheats. One important wheat breeding trait is bread-making quality, which is associated in bread wheat (T. aestivum ssp. aestivum L. em. Thell.) with the high-molecular-weight glutenin subunits. In T. urartu, these proteins are encoded by the Glu-A1x and Glu-A1Ay genes at the Glu-A ^u 1 locus. The Glu-A1x genes of 12 Glu-A ^u 1 allelic variants previously detected in this species were analysed using PCR amplification and sequencing. Data showed wide diversity for the Glu-A1x alleles in T. urartu, which also showed clear differences to the bread wheat alleles. This variation could enlarge the high-quality genetic pool of modern wheat and be used to diversify the bread-making quality in durum (T. turgidum ssp. durum Desf. em. Husn.) and common wheat.     

The detection of a de novo allele of the Glu-1Dx gene in wheat–rye hybrid offspring

Key message

This study provides a link between a de novo gene and novel phenotype in wheat–rye hybrids that can be used as a model for induced de novo genetic variation.

Abstract

Wide hybridization can produce de novo DNA variation that may cause novel phenotypes. However, there is still a lack of specific links between changed genes and novel phenotypes in wide hybrids. The well-studied high-molecular-weight glutenin subunit (HMW-GS) genes in tribe Triticeae provide a useful model for addressing this issue. In this study, we investigated the feasibility of a wheat–rye hybridization method for inducing de novo phenotypes using the Glu-1Dx2.2 subunit as an example. We developed three hexaploid wheat lines with normal fertility and a Glu-1Dx2.2 variant, named Glu-1Dx2.2 ^v , derived from three F₁ hybrids. The wild-type Glu-1Dx2.2 has two direct repeats of 295 bp length separated by an intervening 101 bp in its central repetitive region. In the mutant Glu-1Dx2.2 ^v , one copy of the repeats and the intervening sequence were deleted, probably through homology-dependent illegitimate recombination (IR). This study provides a direct link between a de novo allele and novel phenotype. Our results indicate that the wheat–rye method may be a useful tool to induce de novo genetic variations that broaden the genetic diversity for wheat improvement.     

Mapping of a BYDV resistance gene from Thinopyrum intermedium in wheat background by molecular markers

The wheat line H960642 is a homozygous wheat-Thinopyrum intermedium translocation line with resistance to BYDV by genomicin situ hybridization (GISH) and RFLP analysis. The genomic DNA ofTh. intermedium was used as a probe, and common wheat genomic DNA as a blocking in GISH experiment. The results showed that the chromosome segments ofTh. intermedium were transferred to the distal end of a pair of wheat chromosomes. RFLP analysis indicated that the translocation line H960642 is a T7DS-7DL-7XL translocation by using 8 probes mapped on the homoeologous group 7 in wheat. The translocation breakpoint is located between Xpsr680 and Xpsr965 about 90–99 cM from the centromere. The RFLP markers psr680 and psr687 were closely linked with the BYDV resistance gene. The gene is located on the distal end of 7XL around Xpsr680 and Xpsr687. Project supported by the 863 program and the National Natural Science Foundation of China (Grant No. 39680027).     

Cloning of resistance gene analogs located on the alien chromosome in an addition line of wheat-Thinopyrum intermedium

Homology-based gene/gene-analog cloning method has been extensively applied in isolation of RGAs (resistance gene analogs) in various plant species. However, serious interference of sequences on homoeologous chromosomes in polyploidy species usually occurred when cloning RGAs in a specific chromosome. In this research, the techniques of chromosome microdissection combined with homology-based cloning were used to clone RGAs from a specific chromosome of Wheat-Thinopyrum alien addition line TAi-27, which was derived from common wheat and Thinopyrum intermedium with a pair of chromosomes from Th. intermedium. The alien chromosomes carry genes for resistance to BYDV. The alien chromosome in TAi-27 was isolated by a glass needle and digested with proteinase K. The DNA of the alien chromosome was amplified by two rounds of Sau3A linker adaptor-mediated PCR. RGAs were amplified by PCR with the degenerated primers designed based on conserved domains of published resistance genes (R genes) by using the alien chromosome DNA, genomic DNA and cDNA of Th. intermedium, TAi-27 and 3B-2 (a parent of TAi-27) as templates. A total of seven RGAs were obtained and sequenced. Of which, a constitutively expressed single-copy NBS-LRR type RGA ACR3 was amplified from the dissected alien chromosome of TAi-27, TcDR2 and TcDR3 were from cDNA of Th. intermedium, AcDR3 was from cDNA of TAi-27, FcDR2 was from cDNA of 3B-2, AR2 was from genomic DNA of TAi-27 and TR2 was from genomic DNA of Th. intermedium. Sequence homology analyses showed that the above RGAs were highly homologous with known resistance genes or resistance gene analogs and belonged to NBS-LRR type of R genes. ACR3 was recovered by PCR from genomic DNA and cDNA of Th. intermedium and TAi-27, but not from 3B-2. Southern hybridization using the digested genomic DNA of Th. intermedium, TAi-27 and 3B-2 as the template and ACR3 as the probe showed that there is only one copy of ACR3 in the genome of Th. intermedium and TAi-27, but it is absent in 3B-2. The ACR3 could be used as a specific probe of the R gene on the alien chromosome of TAi-27. Results of Northern hybridization suggested that ACR3 was constitutively expressed in Th. intermedium and TAi-27, but not 3B-2, and expressed higher in leaves than in roots. This research demonstrated a new way to clone RGAs located on a specific chromosome. The information reported here should be useful to understand the resistance mechanism of, and to clone resistant genes from, the alien chromosome in TAi-27.     

Radiation-induced nonhomoeologous wheat-Agropyron intermedium chromosomal translocations conferring resistance to leaf rust

Summary The Agropyron intermedium chromosome 7Ai #2 is the source of the leaf rust resistance gene Lr38 which was transferred to wheat by irradiation. The chromosomal constitutions of eight radiation-induced rust-resistant wheat-Agropyron intermedium derivatives were analyzed by C-banding and genomic in-situ hybridization (GISH). Five lines were identified as wheat Ag. intermedium chromosome translocation lines with the translocation chromosomes T2AS·2AL-7Ai#2L, T5AL · 5AS-7Ai # 2L, T1DS · 1DL-7Ai # 2L, T3DL · 3DS-7Ai#2L, and T6DS · 6DL-7Ai#2L. The sizes of the 7Ai#2L segments in mitotic metaphases of these translocations are 2.42 m, 4.20 m, 2.55 m, 2.78 m, and 4.19 m, respectively. One line was identified as a wheat-Ag. intermedium chromosome addition line. The added Ag. intermedium chromosome in this line is different from 7Ai # 2. This line has resistance to leaf rust and stem rust. Based on the rust reactions, and the C-banding and GISH results, the remaining two lines do not contain any Ag. intermedium-derived chromatin.     

Stacking small segments of the 1D chromosome of bread wheat containing major gluten quality genes into durum wheat: transfer strategy and breeding prospects

Using a chromosome engineering strategy, we previously developed two durum wheat recombinant lines, each containing on chromosome 1A a short segment of bread wheat chromosome 1D with either the Glu-D1 (PL line) or the Gli-D1/Glu-D3 (PS line) genes. Since PL and PS transfers produced substantial but different effects on durum gluten properties, in the present work stacking of their 1DS and 1DL segments into the same chromosome 1A was undertaken to investigate their combined effect in durum wheat and to potentially widen the spectrum of the crop end-uses. Development of genetic and genomic in situ hybridization (GISH)-based physical maps of PS and PL recombinant arms facilitated selection of carriers of the double-recombinant (PS?+?PL) 1A chromosome among F₂ progeny from the PS?×?PL cross. With the 1DS transfer spanning the terminal 17% of recombinant 1AS, and the interstitial 1DL segment occupying 16% of recombinant 1AL, PS?+?PL chromosomes were generated by pairing events occurred with a 68.4% frequency in 1A regions shared by parental chromosomes. Homozygous double-recombinant F₃ plants exhibited no significant differences for relevant agronomic traits compared to sib lines possessing either one or no 1D segment. Among quality parameters preliminarily assessed, SDS sedimentation values increased by 12% in PS and by over 32 and 38% in PL and PS?+?PL lines, respectively, compared to null controls. As a whole, the novel recombinant genotype offers good prospects for direct exploitation in breeding, and hence for an effective contribution to the enhancement of the crop value.     

Isolation and characterization of novel Glu-St1 alleles from Pseudoroegneria spicata and Pd. strigosa

Pseudoroegneria is a small genus of the Triticeae tribe; its St genome is present in over half of allopolyploid Triticeae species. The high molecular weight (HMW) subunits of glutenin (GS) encoded by the St genome are not well described. In this paper, we report the characterization of fourteen alleles of HMW-GS genes from the two species Pd. spicata and Pd. strigosa. Analysis shows that all fourteen sequences possess a typical primary structure shared by other known HMW-GS, but with some unique modifications. All fourteen Glu-St1 alleles are significantly smaller than normal Glu-1 genes due to fewer repeat motifs in a repetitive region with no indication of large deletion in other conserved regions. Thus, the small size is a common feature of HMW-GS encoded by Glu-St1 loci of Pseudoroegneria species. Sequence analysis indicated that all fourteen Glu-St1 alleles were intermediate type between x- and y-type, which represent an intermediate stage in the evolutionary divergence of x- and y-type subunits.     

Genetic mapping of a putative Thinopyrum intermedium-derived stripe rust resistance gene on wheat chromosome 1B

Key message

Stripe rust resistance transferred from Thinopyrum intermedium into common wheat was controlled by a single dominant gene, which mapped to chromosome 1B near Yr26 and was designated YrL693.

Abstract

Stripe rust caused by Puccinia striiformis f. sp. tritici (Pst) is a highly destructive disease of wheat (Triticum aestivum). Stripe rust resistance was transferred from Thinopyrum intermedium to common wheat, and the resulting introgression line (L693) exhibited all-stage resistance to the widely virulent and predominant Chinese pathotypes CYR32 and CYR33 and to the new virulent pathotype V26. There was no cytological evidence that L693 had alien chromosomal segments from Th. intermedium. Genetic analysis of stripe rust resistance was performed by crossing L693 with the susceptible line L661. F₁, F₂, and F_2:3 populations from reciprocal crosses showed that resistance was controlled by a single dominant gene. A total 479 F_2:3 lines and 781 pairs of genomic simple sequence repeat (SSR) primers were employed to determine the chromosomal location of the resistance gene. The gene was linked to six publicly available and three recently developed wheat genomic SSR markers. The linked markers were localized to wheat chromosome 1B using Chinese Spring nulli-tetrasomic lines, and the resistance gene was localized to chromosome 1B based on SSR and wheat genomic information. A high-density genetic map was also produced. The pedigree, molecular marker data, and resistance response indicated that the stripe rust resistance gene in L693 is a novel gene, which was temporarily designated YrL693. The SSR markers that co-segregate with this gene (Xbarc187-1B, Xbarc187-1B-1, Xgwm18-1B, and Xgwm11-1B) have potential application in marker-assisted breeding of wheat, and YrL693 will be useful for broadening the genetic basis of stripe rust resistance in wheat.     

Molecular cytogenetic evidence for a high level of chromosome pairing among different genomes in Triticum aestivum–Thinopyrum intermedium hybrids

Intergeneric hybrids (ABDJJ^sS genomes) were made between Triticum aestivum cv. Chinese Spring (CS) and Thinopyrum intermedium. Genomic in situ hybridization (GISH) using genomic DNA probes from Pseudoroegneria libanotica (Hackel) D.R. Dewey (genome S, 2n = 14) was used to study chromosome pairing among J, J^s, S and wheat ABD genomes in the hybrids. It was shown that in the hexaploid (ABDJJ^sS) hybrids, high pairing occurred among wheat chromosomes and among Thinopyrum chromosomes. A closer relationship was observed among the three genomes of Th. intermedium than among the three genomes of T. aestivum. It was further discerned that S genome chromosomes paired with J- and J^s-genome chromosomes at a high frequency. The frequency of heterologous pairing between S and J or S and J^s chromosomes was higher than those between J and J^s chromosomes, indicating that the S-genome was more closely related with these two genomes. Our results provided direct molecular cytogenetic evidence for the hypothesis that S-genome chromosomes are genetically similar to the J-genome chromosomes and, therefore, genetic exchange between these genomes is possible. The discovery of a close relationship among S, J and J^s genomes provides valuable markers for molecular cytogenetic analyses using S-genomic DNA probes in monitoring the transfer of useful traits from Thinopyrum species into wheat. Received: 23 August 2000 / Accepted: 5 September 2000     

The Pontin series of recombinant alien translocations in bread wheat: single translocations integrating combinations of Bdv2, Lr19 and Sr25 disease-resistance genes from Thinopyrum intermedium and Th. ponticum

Two bread wheat lines each with a translocation on chromosome 7DL from either Thinopyrum intermedium (TC5 and TC14) or Thinopyrum ponticum (T4m), were hybridized in a ph1b mutant background to enhance recombination between the two translocated chromosomal segments. The frequency of recombinants was high in lines derived from the larger and similar-sized translocations (TC5/T4m), but much lower when derived from different-sized translocations (TC14/T4m). Recombinant translocations contained combinations of resistance genes Bdv2, Lr19 and Sr25 conferring resistance to Barley yellow dwarf virus (BYDV), leaf rust and stem rust, respectively. Their genetic composition was identified using bioassays and molecular markers specific for the two progenitor Thinopyrum species. This set of 7DL Th. ponticum/intermedium recombinant translocations was termed the Pontin series. In addition to Thinopyrum markers, the size of the translocation was estimated with the aid of wheat markers mapped on each of the 7DL deletion bins. Bioassays for BYDV, leaf rust and stem rust were performed under greenhouse and field conditions. Once separated from ph1b background, the Pontin recombinant translocations were stable and showed normal inheritance in successive backcrosses. The reported Pontin translocations integrate important resistance genes in a single linkage block which will allow simultaneous selection of disease resistance. Combinations of Bdv2 + Lr19 or Lr19 + Sr25 in both long and short translocations, are available to date. The smaller Pontins, comprising only 20 % of the distal portion of 7DL, will be most attractive to breeders.