Common Wheat Background Research Articles

The addition of Psathyrostachys Huashanica Keng 6Ns large segment chromosomes has positive impact on stripe rust resistance and plant spikelet number of common wheat

BackgroundDeveloping novel germplasm by using wheat wild related species is an effective way to rebuild the wheat resource bank. The Psathyrostachys huashanica Keng (P. huashanica, 2n = 2x = 14, NsNs) is regarded as a superior species to improve wheat breeding because of its multi-resistance, early maturation and numerous tiller traits. Introducing genetic components of P. huashanica into the common wheat background is the most important step in achieving the effective use. Therefore, the cytogenetic characterization and influence of the introgressed P. huashanica large segment chromosomes in the wheat background is necessary to be explored.ResultsIn this study, we characterized a novel derived line, named D88-2a, a progeny of the former characterized wheat-P. huashanica partial amphiploid line H8911 (2n = 7x = 49, AABBDDNs). Cytological identification showed that the chromosomal composition of D88-2a was 2n = 44 = 22II, indicating the addition of exogenous chromosomes. Genomic in situ hybridization demonstrated that the supernumerary chromosomes were a pair of homologues from the P. huashanica and could be stably inherited in the common wheat background. Molecular markers and 15 K SNP array indicated that the additional chromosomes were derived from the sixth homoeologous group (i.e., 6Ns) of P. huashanica. Based on the distribution of the heterozygous single-nucleotide polymorphism sites and fluorescence in situ hybridization karyotype of each chromosome, this pair of additional chromosomes was confirmed as P. huashanica 6Ns large segment chromosomes, which contained the entire short arm and the proximal centromere portion of the long arm. In terms of the agronomic traits, the addition line D88-2a exhibited enhanced stripe rust resistance, improved spike characteristics and increased protein content than its wheat parent line 7182.ConclusionsThe new wheat germplasm D88-2a is a novel cytogenetically stable wheat-P. huashanica 6Ns large segment addition line, and the introgressed large segment alien chromosome has positive impact on plant spikelet number and stripe rust resistance. Thus, this germplasm can be used for genetic improvement of cultivated wheat and the study of functional alien chromosome segment.

RNA-seq analysis revealed considerable genetic diversity and enabled the development of specific KASP markers for Psathyrostachys huashanica.

Psathyrostachys huashanica, which grows exclusively in Huashan, China, is an important wild relative of common wheat that has many desirable traits relevant for wheat breeding. However, the poorly characterized interspecific phylogeny and genomic variations and the relative lack of species-specific molecular markers have limited the utility of P. huashanica as a genetic resource for enhancing wheat germplasm. In this study, we sequenced the P. huashanica transcriptome, resulting in 50,337,570 clean reads that were assembled into 65,617 unigenes, of which 38,428 (58.56%) matched at least one sequence in public databases. The phylogenetic analysis of P. huashanica, Triticeae species, and Poaceae species was conducted using 68 putative orthologous gene clusters. The data revealed the distant evolutionary relationship between P. huashanica and common wheat as well as the substantial diversity between the P. huashanica genome and the wheat D genome. By comparing the transcriptomes of P. huashanica and Chinese Spring, 750,759 candidate SNPs between P. huashanica Ns genes and their common wheat orthologs were identified. Among the 90 SNPs in the exon regions with different functional annotations, 58 (64.4%) were validated as Ns genome-specific SNPs in the common wheat background by KASP genotyping assays. Marker validation analyses indicated that six specific markers can discriminate between P. huashanica and the other wheat-related species. In addition, five markers are unique to P. huashanica, P. juncea, and Leymus species, which carry the Ns genome. The Ns genome-specific markers in a wheat background were also validated regarding their specificity and stability for detecting P. huashanica chromosomes in four wheat-P. huashanica addition lines. Four and eight SNP markers were detected in wheat-P. huashanica 2Ns and 7Ns addition lines, respectively, and one marker was specific to both wheat-P. huashanica 3Ns, 4Ns, and 7Ns addition lines. These markers developed using transcriptome data may be used to elucidate the genetic relationships among Psathyrostachys, Leymus, and other closely-related species. They may also facilitate precise introgressions and the high-throughput monitoring of P. huashanica exogenous chromosomes or segments in future crop breeding programs.

Rapid identification of Psathyrostachys huashanica Keng chromosomes in wheat background based on ND-FISH and SNP array methods

Psathyrostachys huashanica Keng (2n=2x=14, NsNs) is regarded as a valuable wild relative species for common wheat cultivar improvement because of its abundant beneficial agronomic traits. However, although the development of many wheat–P. huashanica-derived lines provides a germplasm base for the transfer of excellent traits, the lag in the identification of P. huashanica chromosomes in the wheat background has limited the study of these lines. In this study, three novel nondenaturing fluorescence in situ hybridization (ND-FISH)-positive oligo probes were developed. Among them, HS-TZ3 and HS-TZ4 could specifically hybridize with P. huashanica chromosomes, mainly in the telomere area, and HS-CHTZ5 could hybridize with the chromosomal centromere area. We sequentially constructed a P. huashanica FISH karyotype and idiogram that helped identify the homologous groups of introduced P. huashanica chromosomes. In detail, 1Ns and 2Ns had opposite signals on the short and long arms, 3Ns, 4Ns, and 7Ns had superposed two-color signals, 5Ns and 6Ns had fluorescent signals only on their short arms, and 7Ns had signals on the intercalary of the long arm. In addition, we evaluated different ways to identify alien introgression lines by using low-density single nucleotide polymorphism (SNP) arrays and recommended the SNP homozygosity rate in each chromosome as a statistical pattern. The 15K SNP array is widely applicable for addition, substitution, and translocation lines, and the 40K SNP array is the most accurate for recognizing transposed intervals between wheat and alien chromosomes. Our research provided convenient methods to distinguish the homologous group of P. huashanica chromosomes in a common wheat background based on ND-FISH and SNP arrays, which is of great significance for efficiently identifying wheat–P. huashanica-derived lines and the further application of Ns chromosomes.

Molecular and Physiological Evaluation of Bread Wheat (Triticum aestivum L.) Genotypes for Stay Green under Drought Stress.

Water availability is considered as the main limiting factor of wheat growth illuminating the need of cultivars best adapted to drought situations for better wheat production and yield. Among these, the stay-green trait is thought to be related to the ability of wheat plants to maintain photosynthesis and CO2 assimilation, and a detailed molecular understanding of this trait may help in the selection of high-yielding, drought-tolerant wheats. The current study, therefore, evaluated the physiological responses of the selected wheat genotypes under pot-induced water stress conditions through different field capacities. The study also focused on exploring the molecular mechanisms involved in drought tolerance conferred due to the stay-green trait by studying the expression pattern of the selected PSI-associated light-harvesting complex I (LHC1) and PSII-associated LHCII gene families related to pigment-binding proteins. The results revealed that the studied traits, including relative water content, membrane stability index and chlorophyll, were variably and negatively affected, while the proline content was positively enhanced in the studied wheats under water stress treatments. Molecular diagnosis of the selected wheat genotypes using the expression profile of 06 genes, viz. TaLhca1, TaLhca2, TaLhca3, TaLhcb1, TaLhcb4 and TaLhcb6 that encodes for the LHCI and LHCII proteins, indicated variable responses to different levels of drought stress. The results obtained showed the relation between the genotypes and the severity of the drought stress condition. Among the studied genotypes, Chirya-1 and SD-28 performed well with a higher level of gene expression under drought stress conditions and may be used in genetic crosses to enrich the genetic background of common wheat against drought stress.

Chromosome 5P of Agropyron cristatum induces chromosomal translocation by disturbing homologous chromosome pairing in a common wheat background

Wide hybridization is a strategy for broadening the genetic basis of wheat. Because an efficient method for inducing wheat–alien chromosome translocations will allow producing useful germplasm, it is desirable to discover new genes that induce chromosomal variation. In this study, chromosome 5P from A. cristatum was shown to induce many types of chromosomal structural variation in a common wheat background, including nonhomoeologous chromosome translocations, as revealed by genomic in situ hybridization, fluorescence in situ hybridization, and DNA marker analysis. Aberrant meiosis was associated with chromosomal structural variation, and aberrant meiotic behavior was observed in wheat–A. cristatum 5P monosomic and disomic addition lines, suggesting that the effect of chromosome 5P was independent of the number of chromosome 5P copies. Chromosome 5P disturbed homologous chromosome pairing at pachytene stage in a common wheat background, resulting in a high frequency of univalent formation and reduced crossing over. Thirteen genes involved in DNA repair or chromatin remodeling, including RAD52-like and MSH6 genes, were differentially expressed (upregulated) in wheat–A. cristatum 5P addition lines according to transcriptome analysis, implicating chromosome 5P in the process of meiotic double-strand break repair. These findings provide a new, efficient tool for inducing wheat–alien chromosome translocations and producing new germplasm.

Genetic Mapping and Candidate Gene Prediction of a QTL Related to Early Heading on Wild Emmer Chromosome 7BS in the Genetic Background of Common Wheat

Heading date (HD) is an essential agronomic objective in wheat conventional breeding. Field experiments from several years and locations indicated that the chromosome arm substitution line (CASL) of wild emmer chromosome 7BS in the genetic background of common wheat var. Chinese Spring (CS) always showed a substantially earlier HD than CS planted in different seasons; usually about 8 d earlier than CS grown under a normal autumn sowing season. CASL7BS consistently showed a much earlier HD than CS when treated for vernalization under a long or short photoperiod and then grown under a short or long photoperiod in the growth room. CASL7BS showed faster spike development than CS at the stages before the glume stage when grown under long days, and depicted relatively rapid growth at all stages when grown under short days. To map the early gene in CASL7BS, F2 plants from the cross of CASL7BS and CS were planted in the field and growth room, forming two mapping populations (P1 and P2, respectively). According to the HD distribution of P1, the HD was most likely regulated by a dominant gene. A QTL was detected consistently in the distal region of about 8.94 cM flanked by C268 and C309 with LOD scores of 5–8, explaining 9.14 and 12.35% of the phenotypic variation in the two mapping populations. The QTL was further narrowed down to an interval between ZAFU058724 and ZAFU061354 of 58–61 Mb based on the HD and genotype of F3 and F4 families. A total of 41 genes were located in this region, and eleven of them were thought to be the candidate genes based on the gene functions. According to the HD and mapping location, the QTL identified in this study was a new gene associated with flowering, which will be helpful in understanding the mechanism of wheat flowering and for breeding an early wheat variety.

Molecular cytogenetics and development of St-chromosome-specific molecular markers of novel stripe rust resistant wheat\u2013Thinopyrum intermedium and wheat\u2013Thinopyrum ponticum substitution lines

BackgroundOwing to their excellent resistance to abiotic and biotic stress, Thinopyrum intermedium (2n = 6x = 42, JJJsJsStSt) and Th. ponticum (2n = 10x = 70) are both widely utilized in wheat germplasm innovation programs. Disomic substitution lines (DSLs) carrying one pair of alien chromosomes are valuable bridge materials for transmission of novel genes, fluorescence in situ hybridization (FISH) karyotype construction and specific molecular marker development.ResultsSix wheat–Thinopyrum DSLs derived from crosses between Abbondanza nullisomic lines (2n = 40) and two octoploid Trititrigia lines (2n = 8x = 56), were characterized by sequential FISH–genome in situ hybridization (GISH), multicolor GISH (mc-GISH), and an analysis of the wheat 15 K SNP array combined with molecular marker selection. ES-9 (DS2St (2A)) and ES-10 (DS3St (3D)) are wheat–Th. ponticum DSLs, while ES-23 (DS2St (2A)), ES-24 (DS3St (3D)), ES-25(DS2St (2B)), and ES-26 (DS2St (2D)) are wheat–Th. intermedium DSLs. ES-9, ES-23, ES-25 and ES-26 conferred high thousand-kernel weight and stripe rust resistance at adult stages, while ES-10 and ES-24 were highly resistant to stripe rust at all stages. Furthermore, cytological analysis showed that the alien chromosomes belonging to the same homoeologous group (2 or 3) derived from different donors carried the same FISH karyotype and could form a bivalent. Based on specific-locus amplified fragment sequencing (SLAF-seq), two 2St-chromosome-specific markers (PTH-005 and PTH-013) and two 3St-chromosome-specific markers (PTH-113 and PTH-135) were developed.ConclusionsThe six wheat–Thinopyrum DSLs conferring stripe rust resistance can be used as bridging parents for transmission of valuable resistance genes. The utility of PTH-113 and PTH-135 in a BC1F2 population showed that the newly developed markers could be useful tools for efficient identification of St chromosomes in a common wheat background.

Fine mapping of Pm58 from Aegilops tauschii conferring powdery mildew resistance.

The powdery mildew resistance gene Pm58 was traced to a 141.3-kb interval with the co-segregating marker Xkasp68500 in wheat breeding. Pm58 is a powdery mildew resistance gene identified in Aegilops tauschii accession TA1662 and effective in a common wheat background. To finely map Pm58, an F2 population of 676 plants derived from the cross T093 × TA1662 was used for recombinant screening. We obtained 13 recombinants that occurred between the flanking markers Xhnu670 and Xhnu186. Genotyping and phenotyping these recombinant F2:3 families delimited Pm58 to a 0.22-cM interval (Xsts20220-Xkasp61553) on chromosome arm 2DS. The region carrying the Pm58 locus was approximately 141.3-kb, which contained eight annotated genes according to the reference genome sequence of Ae. tauschii AL8/78. Haplotype analysis of 178 Ae. tauschii accessions using the candidate gene-specific markers identified a disease resistance gene AET2Gv20068500 as a candidate for Pm58. Comparative mapping of the Pm58-containing interval revealed two presence/absence variations (PAVs) between AL8/78 and common wheat Chinese Spring. PAV-1 resides in the 3'-end of AET2Gv20068500. The majority of 158 common wheat cultivars (84.8%) displayed the absence of a 14.1-kb fragment in the PAV-1 region, which was confirmed by aligning the targeted genome sequences of the other sequenced Ae. tauschii accessions and common wheat cultivars. A co-segregating marker Xkasp68500 developed from AET2Gv20068500 can distinguish TA1662 from all randomly selected common wheat cultivars and will be instrumental for tracking Pm58 in breeding programs.

Chromosome Stability of Synthetic-Natural Wheat Hybrids.

Primary allopolyploids are not only ideal materials to study species evolution, but also important bridges in incorporating genetic diversity of wild species into crops. Primary allopolyploids typically exhibit chromosome instability that a disadvantage trait in crop breeding. Newly synthesized hexaploid wheat has been widely used in wheat genetics and breeding studies. To better understand the cytological and genetic basis of chromosome instability, this study investigated the chromosomes of a large number of seeds derived from the synthetic wheat SHW-L1 and its hybrids with natural wheat. SHW-L1 exhibited persistent chromosome instability since we observed a high frequent chromosome variation de novo generated from euploid SHW-L1 plants at the 14th generation of selfing (F14). High frequent chromosome variations were also observed in the F2 hybrids and most of the analyzed recombinant inbred lines (RILs) at F14, derived from the cross of SHW-L1 with common wheat variety Chuanmai 32. Chromosome instability was associated with frequent univalency during meiotic metaphase I. The experiment on reciprocal crosses between SHW-L1 and Chuanmai 32 indicated that cytoplasm has not obvious effects on chromosome instability. An analysis on 48 F14 RILs revealed chromosome variation frequency was not associated with the Ph1 alleles from either SHW-L1 or Chuanmai 32, rejecting the hypothesis that chromosome instability was due to the Ph1 role of synthetic wheat. In the analyzed RILs, chromosome instability influences the phenotype uniformity, showing as obvious trait differences among plants within a RIL. However, the analyzed commercial varieties only containing ∼12.5% genomic components of synthetic wheat were chromosomally stable, indicating that chromosome instability caused by synthetic wheat can be effectively overcome by increasing the genetic background of common wheat.

Physical mapping of chromosome 7J and a purple coleoptile gene from Thinopyrum intermedium in the common wheat background.

A physical map of Thinopyrum intermedium chromosome 7J was constructed using translocation mapping, and a new seedling purple coleoptile gene was mapped to the bin of FL 0.35-0.63 of 7JS. Thinopyrum intermedium (2n = 6x = 42, JJJsJsStSt), a wild relative of common wheat, harbors numerous beneficial genes for wheat improvement. Previous studies showed that wheat-Th. intermedium partial amphiploid TAF46 and its derived addition line L1 had a purple coleoptile, which was derived from Th. intermedium chromosome 7J. To identify and physically map the purple coleoptile gene, 12 wheat-Th. intermedium 7J translocation lines were analyzed by sequential multicolor fluorescence in situ hybridization (mc-FISH), PCR-based landmark unique gene (PLUG) and intron targeting (IT) markers. A physical map of the 7J chromosome was constructed, consisting of eight chromosomal bins with 89 markers. Seedling evaluation of the coleoptile colors of all tested materials indicated that the purple coleoptile gene was located to the bin with a fraction length (FL) of 0.35-0.63 on chromosome 7JS. Furthermore, based on the syntenic relationships between Th. intermedium and wheat chromosomes, we developed a new chromosome 7J-specific EST-PCR marker from the chromosomal region corresponding to the purple coleoptile gene through the Triticeae multi-omics database. The approach of designing chromosome-specific markers has facilitated fine mapping of the Thinopyrum-specific purple coleoptile gene, and these translocation lines will be valuable for studying the function of the purple coleoptile gene in anthocyanin biosynthesis.

Enriching LMW-GS alleles and strengthening gluten properties of common wheat through wide hybridization with wild emmer.

Two advanced lines (BAd7-209 and BAd7-213) with identical high-molecular-weight glutenin subunit composition were obtained via wide hybridization between low-gluten cultivar chuannong16 (CN16) and wild emmer D97 (D97). BAd7-209 was better than BAd7-213, and both of them were much better than CN16 in a dough quality test. We found that BAd7-209 had more abundant and higher expression levels of low-molecular-weight glutenin subunit (LMW-GS) proteins than those of BAd7-213. Twenty-nine novel LMW-GS genes at Glu-A3 locus were isolated from BAd7-209, BAd7-213 and their parents. We found that all 29 LMW-GS genes possessed the same primary structure shared by other known LMW-GSs. Twenty-seven genes encode LMW-m-type subunits, and two encode LMW-i-type subunits. BAd7-209 had a higher number of LMW-GS genes than BAd7-213, CN16, and D97. Two wild emmer genes MG574329 and MG574330 were present in the two advanced lines. Most of the LMW-m-type genes showed minor nucleotide variations between wide hybrids and their parents that could be induced through the wide hybridization process. Our results demonstrated that the wild emmer LMW-GS alleles could be feasibly transferred and integrated into common wheat background via wide hybridization and the potential value of the wild emmer LMW-GS alleles in breeding programs designed to improve wheat flour quality.

Development of wheat—Hordeum chilense Chromosome 2Hch Introgression Lines Potentially Useful for Improving Grain Quality Traits

The chromosome 2Hch of Hordeum chilense. has the potential to improve seed carotenoid content in wheat as it carries a set of endosperm carotenoid-related genes. We have obtained structural changes in chromosome 2Hch in a common wheat (Triticum aestivum L. “Chinese Spring”) background by crossing a wheat double disomic substitution 2Hch(2D) and 7Hch(7D) line with a disomic addition line carrying chromosome 2Cc from Aegilops cylindrica Host.. Seven introgressions of chromosome 2Hch into wheat were characterized by fluorescence in situ hybridization (FISH) and DNA markers. Chromosome-specific simple sequence repeats (SSRs) were used for identifying wheat chromosomes. In addition, we tested 82 conserved orthologous set (COS) markers for homoeologous group 2, of which 65 amplified targets in H. chilense and 26 showed polymorphism between H. chilense and wheat. A total of 24 markers were assigned to chromosome 2Hch with eight allocated to 2HchS and 16 to 2HchL. Among the seven introgressions there was a disomic substitution line 2Hch(2D), a ditelosomic addition line for the 2HchL arm, an isochromosome for the 2HchL arm, a homozygous centromeric 2HchS·2DL translocation, a double monosomic 2HchS·2DL plus 7HchS·D translocation, a homozygous centromeric 7HchS·2HchL translocation and, finally, a 2HchL·7HchL translocation. Wheat—H. chilense macrosyntenic comparisons using COS markers revealed that H. chilense chromosome 2Hch exhibits synteny to wheat homoeologous group 2 chromosomes, and the COS markers assigned to this chromosome will facilitate alien gene introgression into wheat. The genetic stocks developed here include new wheat—H. chilense recombinations which are useful for studying the effect of chromosome 2Hch on grain quality traits.

Characterization of New Wheat-Dasypyrum breviaristatum Introgression Lines with Superior Gene(s) for Spike Length and Stripe Rust Resistance

Dasypyrum breviaristatum (genome V^bV^b) contains potentially important traits for commercial wheat production. Chromosome 2V^b of D. breviaristatum carries several desirable agronomic characters, including long spike length as well as enhanced resistance to stripe rust, which are expressed in a common wheat background. In this study, wheat-D. breviaristatum 2V^b deletion lines were produced and identified by fluorescence in situ hybridization (FISH), and 74 molecular markers specific to D. breviaristatum chromosome 2V^b were physically localized in 4 distinct chromosomal regions. New wheat-D. breviaristatum 2V^b translocation lines were also characterized by FISH. The breakpoint of the translocation T3AS.3AL-2V^bS was determined by physically mapped molecular markers. Field evaluation revealed that genes affecting plant height and spike length are located on fraction length (FL) 0.65-1.00 of 2V^bS, while the stripe rust resistance gene(s) are located on FL 0.40-1.00 of D. breviaristatum chromosome 2V^bL. The newly characterized wheat-Dasypyrum chromosomal introgressions are of potential value for the improvement of the yield and disease resistance of wheat.

Identification and genetic analysis of multiple P chromosomes of Agropyron cristatum in the background of common wheat

Agropyron cristatum, a wild relative of common wheat (Triticum aestivum L.), provides many desirable genetic resources for wheat improvement, such as tolerance to cold, drought, and disease. To transfer and utilize these desirable genes, in this study, two wheat-A. cristatum derivatives II-13 and II-23 were identified and analyzed. We found that the number of root tip cell chromosomes was 44 in both II-13 and II-23, but there were four and six P genome chromosomes in II-13 and II-23, respectively, based on genomic in situ hybridization (GISH). The chromosome configurations of II-13 and II-23 were both 2n=22II by the meiotic analysis of pollen mother cells (PMCs) at metaphase I, indicating that there were two and three pairs of P chromosomes in II-13 and II-23, respectively. Notably, wheat chromosome 7D was absent in derivative line II-13 while II-23 lacked chromosomes 4B and 7A based on SSR analysis combining fluorescence in situ hybridization (FISH) analysis with pAs1 and pSc119.2 as probes. Chromosomes 2P and 7P were detected in both II-13 and II-23. Another pair of P genome chromosomes in II-23 was determined to be 4P based on expressed-sequences tags-sequence tagged sites (EST-STS) markers specific to A. cristatum and FISH with probes pAcTRT1 and pAcpCR2. Overall, these results suggest that II-13 was a 7P (7D) substitution line with one pair of additional 2P chromosomes and II-23 was a multiple 4P (4B), 7P (7A) substitution line with one pair of additional 2P chromosomes. Moreover, we obtained six alien disomic addition lines and five alien disomic substitution lines by backcrossing. These new materials will allow desirable genes from A. cristatum to be used in common wheat.

Development of EST-PCR markers specific to the long arm of chromosome 6V of Dasypyrum villosum

Expressed sequence tags-derived polymerase chain reaction (EST-PCR) molecular markers specific for alien chromosomes can be used to not only monitor the introgressed alien chromatin in wheat background, but also provide the evidence of the syntenic relationship between homoeologous chromosomes. In the present study, in order to develop high density and evenly distributed molecular markers specific for chromosome 6VL of Dasypyrum villosum, 297 primer pairs were designed based on the expressed sequence tags (EST) sequences, which were previously mapped in different bins of the long arms of wheat homoeologous 6AL, 6BL, and 6DL. By using the Triticum aestivum, D. villosum, T. durum-D. villosum amphiploid, and T. aestivum-D. villosum alien chromosome lines involving chromosome 6V, it was found that 32 (10.77%) primers could amplify specific bands for chromosome 6V, and 31 could be allocated to chromosome arm 6VL. These 6VL specific markers provided efficient tools for the characterization of structural variation involving the chromosome 6VL in common wheat background as well as for the selection of useful genes located on 6VL in breeding programs.

Enriching novel Glu-Ax alleles and significantly strengthening gluten properties of common wheat through wide hybridization with wild emmer

Two hybrids, BAd7-209 and BAd7-210, were obtained by wide hybridization between wild emmer D97 and weak gluten cultivar CN16. They had a genetic background of common wheat, resulting from continuous selfing over nine times. These hybrids were better than CN16 in dough quality and processing quality tests. BAd7-210 was better than medium gluten wheat cultivar MM37, and BAd7-209 was far better than moderate to strong gluten wheat cultivar SM482. Through chromosome engineering, BAd7-210 possessed the 1Ax2.2 of male D97, and BAd7-209 had the 1Ax1.2 which was caused by complex variation because of cross-parents’ genomic asymmetry. The open reading frames (ORFs) of two novel active Glu-Ax alleles 1Ax2.2 and 1Ax1.2 were 2496 bp and 2514 bp, encoding 830 and 836 amino acid residues, respectively. The 1Ax1.2 was the second longest Glu-Ax gene discovered to date, and it had two deletions and one insertion besides many single nucleotide polymorphisms (SNPs) compared with the 1Ax2.2 and 1Ax1. The longer polypeptide of 1Ax1.2 should explain why BAd7-209 has better processing quality than BAd7-210. Therefore, wild emmer could be effectively utilized to enrich the 1Ax alleles of common wheat through direct cross transferring and generating novel allele variation, which could significantly enhance the gluten strength.

Characterization of a set of common wheat–Hordeum chilense chromosome 7Hch introgression lines and its potential use in research on grain quality traits

AbstractChromosome 7Hch from Hordeum chilense has potential for improving seed carotenoid content in wheat as it carries a Phytoene synthase 1 (Psy1) gene, which has a major role in this trait. Structural changes in chromosome 7Hch were obtained in common wheat background by crossing the wheat disomic substitution line 7Hch(7D) with a disomic addition line carrying chromosome 2Cc from Aegilops cylindrica in common wheat cv. ‘Chinese Spring’. Rearranged 7Hch chromosomes were cytologically characterized by FISH. A set of 24 molecular markers and the Psy1 gene were used to identify the H. chilense chromosome segments involved in the introgressions. Six structural rearrangements of chromosome 7Hch were identified. They included three homozygous wheat–H. chilense centromeric translocations, one involving the 7HchS arm (T‐7HchS·A/B) and two involving the 7HchL arm (T1‐7HchL·A/B and T2‐7HchL·A/B). In addition, one 7HchS arm deletion, one 7HchL·7HchL isochromosome and one 7HchS telosome were obtained in hemizygous condition. These genetic stocks will be useful for studying the effect of chromosome 7Hch on wheat flour colour.

Molecular cytogenetics identification of a wheat –Leymus mollisdouble disomic addition line with stripe rust resistance

Leymus mollis (Trin.) Pilg. (2n = 4x = 28, NsNsXmXm) possesses a number of valuable genes against biotic and abiotic stress, which could be transferred into common wheat background for wheat improvement. In the present study, we determined the karyotypic constitution of a wheat - L. mollis double disomic addition line, M11003-4-4-1-1, selected from the F5 progeny of a stable wheat - L. mollis derivative M39 (2n = 56) × Triticum aestivum cultivar 7182, by morphological and cytogenetic identification, GISH (genomic in situ hybridization), FISH (fluorescent in situ hybridization), molecular markers analysis, and stripe rust resistance evaluation. Cytological studies demonstrated that M11003-4-4-1-1 had a chromosome karyotype of 2n = 46 with 23 bivalents, while GISH and FISH analysis indicated that this line contained 42 common wheat chromosomes and two pairs of L. mollis chromosomes. DNA markers showed that the alien chromosomes from L. mollis belonged to homoeologous groups 5 and 6. Evaluation of the agronomic traits revealed that M11003-4-4-1-1 was resistant to stripe rust at the adult stage, while the plant height was reduced and the 1000-grain weight was increased significantly. Therefore, the new line M11003-4-4-1-1 could be exploited as an important bridge material in chromosome engineering and wheat breeding.

Physical mapping of Agropyron cristatum chromosome 6P using deletion lines in common wheat background.

Genetically stable deletion lines of Agropyron cristatum chromosome 6P in common wheat background were generated, which allowed for physical mapping of 255 6P-specific STS markers and leaf rust resistance gene(s). Chromosomal deletion lines are valuable tools for gene discovery and localization. The chromosome 6P of Agropyron cristatum (2n = 4x = 28, PPPP) confers many desirable agronomic traits to common wheat, such as higher grain number per spike, multiple fertile tiller number, and enhanced resistance to certain diseases. Although many elite genes from A. cristatum have been identified, their chromosomal locations were largely undetermined due to the lack of A. cristatum 6P deletion lines. In this study, various A. cristatum 6P deletion lines were developed using a wheat-A. cristatum 6P disomic addition line 4844-12 subjected to (60)Co-γ irradiation as well as an Aegilops cylindrica gametocidal chromosome. Twenty-six genetically stable A. cristatum 6P deletion lines in the genetic background of common wheat were obtained, and their genetic constitutions were elucidated by genomic in situ hybridization (GISH) and sequence-tagged site (STS) markers specific to A. cristatum chromosome 6P. Moreover, 255 novel chromosome 6P-specific STS markers were physically mapped to 14 regions of chromosome 6P. Field evaluation of leaf rust resistance of various deletion lines and BC1F2 populations indicated that the A.cristatum chromosome 6P-originated leaf rust resistance gene(s) was located in the region 6PS-0.81-1.00. This study will provide not only useful tools for characterization and utilization of wheat materials with alien chromosomal segments, but also novel wheat germplasms potentially valuable in wheat breeding and improvement.

Cytological identification of an Aegilops variabilis chromosome carrying stripe rust resistance in wheat.

Aegilops variabilis (UUSvSv), an important sources for wheat improvement, originated from chromosome doubling of a natural hybrid between Ae. umbellulata (UU) with Ae. longissima (SlSl). The Ae. variabilis karyotype was poorly characterized by fluorescent in situ hybridization (FISH). The FISH probe combination of pSc119.2, pTa71 and pTa-713 identified each of the 14 pairs of Ae. variabilis chromosomes. Our FISH ideogram was further used to detect an Ae. variabilis chromosome carrying stripe rust resistance in the background of wheat lines developed from crosses of the stripe rust susceptible bread wheat cultivar Yiyuan 2 with a resistant Ae. variabilis accession. Among the 15 resistant BC1F7 lines, three were 2Sv + 4Sv addition lines (2n = 46) and 12 were 2Sv(2B) or 2Sv(2D) substitution lines that were confirmed with SSR markers. SSR marker gwm148 can be used to trace 2Sv in common wheat background. Chromosome 2Sv probably carries gametocidal(Gc) gene(s) since cytological instability and chromosome structural variations, including non-homologous translocations, were observed in some lines with this chromosome. Due to the effects of photoperiod genes, substitution lines 2Sv(2D) and 2Sv(2B) exhibited late heading with 2Sv(2D) lines being later than 2Sv(2B) lines. 2Sv(2D) substitution lines were also taller and exhibited higher spikelet numbers and longer spikes.