Analysis of inheritance of morphological and biochemical characters introgressed into common wheat from Aegilops speltoides Tausch

Genetic control of some morphological traits and the gliadin composition were examined in plants of two lines of common wheat carrying genes introgressed from the wild diploid cereal Aegilops speltoides. Leaf hairiness was shown to be controlled by a single introgressed dominant gene that was not allelic to the known common wheat gene Hl1. Waxlessness of the whole plant is controlled by the introgressed from Ae. speltoides inhibitor gene allelic to gene W1 located on chromosome 2B. This gene was epistatic to the introgressed gene controlling spike waxlessness. The introgressed gene of spike color was shown to be allelic to Rg1 located on chromosome 1B of common wheat. However, the former gene proved to be linked to an allele of the Gli-B1 locus other than in wheat.     

Construction and study of leaf rust-resistant common wheat lines with translocations of Aegilops speltoides Tausch

Genotyping was performed for the leaf rust-resistant line 73/00i (Triticum aestivum x Aegilops speltoides). Fluorescence in situ hybridization (FISH) with probes Spelt1 and pSc119.2 in combination with microsatellite analysis were used to determine the locations and sizes of the Ae. speltoides genetic fragments integrated into the line genome. Translocations were identified in the long arms of chromosomes 5B and 6B and in the short arm of chromosome 1B. The Spelt1 and pSc119.2 molecular cytological markers made it possible to rapidly establish lines with single translocation in the long arms of chromosomes 5B and 6B. The line carrying the T5BS x 5BL-5SL translocation was highly resistant to leaf rust, and the lines carrying the T6BS x 6BL-6SL translocation displayed moderate resistance. The translocations differed in chromosomal location from known leaf resistance genes transferred into common wheat from Ae. speltoides. Hence, it was assumed that new genes were introduced into the common wheat genome from Ae. speltoides. The locus that determined high resistance to leaf rust and was transferred into the common wheat genome from the long arm of Ae. speltoides chromosome 5S by the T5BS x 5BL-5SL translocation was preliminarily designated as LrAsp5.     

The mechanisms of variation of subtelomeric repeats Speltl in the progeny of introgressive line Triticum aestivum L. x Aegilops speltoides Tausch

Quantitative variation of species-specific subtelomeric repeat Speltl was studied in the progeny of an individual accession from the introgressive line Triticum aestivum x Aegilops speltoides. In the progeny, no cases of the Speltl increased content were observed. On the contrary, in some cases statistically significant decrease of the repeat copy number was detected. It seems likely that the mechanisms of the Spelt1 elimination involve either the selection at the gamete level versus the increase of the satellite DNA content in the telomeres, or intramolecular (within one chromatid) homologous recombination.     

BAC libraries of Triticum urartu, Aegilops speltoides and Ae. tauschii, the diploid ancestors of polyploid wheat

Triticum urartu, Aegilops speltoides and Ae. tauschii are respectively the immediate diploid sources, or their closest relatives, of the A, B and D genomes of polyploid wheats. Here we report the construction and characterization of arrayed large-insert libraries in a bacterial artificial chromosome (BAC) vector, one for each of these diploid species. The libraries are equivalent to 3.7, 5.4 and 4.1 of the T. urartu, Ae. speltoides, Ae. tauschii genomes, respectively. The predicted levels of genome coverage were confirmed by library hybridization with single-copy genes. The libraries were used to estimate the proportion of known repeated nucleotide sequences and gene content in each genome by BAC-end sequencing. Repeated sequence families previously detected in Triticeae accounted for 57, 61 and 57% of the T. urartu, Ae. speltoides and Ae. tauschii genomes, and coding regions accounted for 5.8, 4.5 and 4.8%, respectively.     

Molecular marker mapping of the gene resistant to common bunt transferred from Aegilops cylindrica into bread wheat

Introgression lines 5/55-91 and 378/2000 of bread wheat contain the gene of resistance to Tilletia caries (DC.) Tul. transferred from Aegilops cylindrica Host. Using bulked segregant analysis with ISSR and SSR PCR the lincage of microsatellite locus Xgwm 259 with the gene of common bunt resistance has been identified in F2 population of 378/2000 x Lutestens 23397. DNA mapping made it possible to localize this highly effective gene in the intercalary region of the long arm of wheat chromosome 1B at the distance of 7.6-8.5 cM of the microsatellite Xgwm 259 locus which thus can be used in wheat breeding for selection of genotype resistance to common bunt.     

Sequencing chromosome 5D of Aegilops tauschii and comparison with its allopolyploid descendant bread wheat (Triticum aestivum)

Flow cytometric sorting of individual chromosomes and chromosome‐based sequencing reduces the complexity of large, repetitive Triticeae genomes. We flow‐sorted chromosome 5D of Aegilops tauschii, the D genome donor of bread wheat and sequenced it by Roche 454 GS FLX platform to approximately 2.2x coverage. Repetitive sequences represent 81.09% of the survey sequences of this chromosome, and Class I retroelements are the prominent type, with a particular abundance of LTR/Gypsy superfamily. Nonrepetitive sequences were assembled to cover 17.76% of the total chromosome regions. Up to 6188 nonrepetitive gene loci were predicted to be encoded by the 5D chromosome. The numbers and chromosomal distribution patterns of tRNA genes suggest abundance in tRNA^Lys and tRNA^Met species, while the nonrepetitive assembly reveals tRNA^Ala species as the most abundant type. A comparative analysis of the genomic sequences of bread wheat and Aegilops chromosome 5D indicates conservation of gene content. Orthologous unique genes, matching Aegilops 5D sequences, numbered 3730 in barley, 5063 in Brachypodium, 4872 in sorghum and 4209 in rice. In this study, we provide a chromosome‐specific view into the structure and organization of the 5D chromosome of Ae. tauschii, the D genome ancestor of bread wheat. This study contributes to our understanding of the chromosome‐level evolution of the wheat genome and presents a valuable resource in wheat genomics due to the recent hybridization of Ae. tauschii genome with its tetraploid ancestor.     

Genetic analysis of the traits introgressed from <Emphasis Type="Italic">Aegilops speltoides</Emphasis> Tausch. to bread wheat and determined by chromosome 5A genes

A winter bread wheat accession from the Arsenal collection was genetically examined to study the results of introgression, which substantially changed the physiological and morphological traits of the original spring cultivar Rodina. Apart from its winter habit, the accession was characterized by awned speltoid spikes, suggesting introgression into chromosome 5A, which carries marker genes in the order Vrn-A1-Q-B1. Genetic analysis showed that the chromosome fragment introgressed from Aegilops speltoides recombined well with the homeologous region of bread wheat chromosome 5A in the region between the Vrn-A1 and Q genes. Recombination between the Vrn-A1 and B1 genes was not detected, and it was assumed that the order of the marker genes of chromosome 5A was inverted to produce Q-Vrn-A1-B1. When the winter introgression line was crossed with Triticum spelta L., an interaction of two dominant genes determining the spike character was for the first time detected in F₁, increasing the spike length and the number of spikelets, and followed with transgression in F₂. It was assumed that Ae. speltoides had a homeoallelic speltoid gene, which was designated as Q ^S .     

Introgression of an imidazolinone-resistance gene from winter wheat (Triticum aestivum L.) into jointed goatgrass (Aegilops cylindrica Host)

Imidazolinone-resistant winter wheat (Triticum aestivum L.) is being commercialized in the USA. This technology allows wheat growers to selectively control jointed goatgrass (Aegilops cylindrica Host), a weed that is especially problematic because of its close genetic relationship with wheat. However, the potential movement of the imidazolinone-resistance gene from winter wheat to jointed goatgrass is a concern. Winter wheat and jointed goatgrass have the D genome in common and can hybridize and backcross under natural field conditions. Since the imidazolinone-resistance gene (Imi1) is located on the D genome, it is possible for resistance to be transferred to jointed goatgrass via hybridization and backcrossing. To study the potential for gene movement, BC₂S₂ plants were produced artificially using imidazolinone-resistant winter wheat (cv. FS-4) as the female parent and a native jointed goatgrass collection as the male recurrent parent. FS-4, the jointed goatgrass collection, and 18 randomly selected BC₂S₂ populations were treated with imazamox. The percentage of survival was 100% for the FS-4, 0% for the jointed goatgrass collection and 6 BC₂S₂ populations, 40% or less for 2 BC₂S₂ populations, and 50% or greater for the remaining 10 BC₂S₂ populations. Chromosome counts in BC₂S₃ plants showed a restoration of the chromosome number of jointed goatgrass, with four out of four plants examined having 28 chromosomes. Sequencing of AHASL1D in BC₂S₃ plants derived from BC₂S₂-6 revealed the sexual transmission of Imi1 from FS-4 to jointed goatgrass. Imi1 conferred resistance to the imidazolinone herbicide imazamox, as shown by the in vitro assay for acetohydroxyacid synthase (AHAS) activity.     

Insights of interaction between small and large subunits of ADP-glucose pyrophosphorylase from bread wheat (Triticum aestivum L.)

Lack of knowledge of three dimensional structures of small and large subunits of ADP- glucose pyrophosphorylase (AGPase) in wheat has hindered efforts to understand the binding specifities of substrate and catalytic mechanism. Thus, to understand the structure activity relationship, 3D structures were built by homology modelling based on crystal structure of potato tuber ADP-glucose pyrophosphorylase. Selected models were refined by energy minimization and further validated by Procheck and Prosa-web analysis. Ramachandran plot showed that overall main chain and side chain parameters are favourable. Moreover, Z-score of the models from Prosa-web analysis gave the conformation that they are in the range of the template. Interaction analysis depicts the involvement of six amino acids in hydrogen bonding (AGP-SThr422-AGP-LMet138, AGP- SArg420-AGP-LGly47, AGP-SSer259-AGP-LSer306, AGP-SGlu241-AGP-LIle311, AGPSGln113- AGP-LGlu286 and AGP-SGln70-AGP-LLys291). Fifteen amino acids of small subunit were able to make hydrophobic contacts with seventeen amino acids of large subunit. Furthermore, decrease in the solvent accessible surface area in the amino acids involved in interaction were also reported. All the distances were formed in between 2.27 to 3.78Å. The present study focussed on heterodimeric structure of (AGPase). This predicted complex not only enhance our understanding of the interaction mechanism between these subunits (AGP-L and AGP-S) but also enable to further study to obtain better variants of this enzyme for the improvement of the plant yield.     

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.     

Chromosomal location of genomic SSR markers associated with yellow rust resistance in Turkish bread wheat (Triticum aestivum L.)

We have previously reported Xgwm382 as a diagnostic marker for disease resistance against yellow rust in Izgi2001 × ES14 F₂ population. Among the same earlier tested 230 primers, one SSR marker (Xgwm311) also amplified a fragment which is present in the resistant parent and in the resistant bulks, but absent in the susceptible parent and in the susceptible bulks. To understand the chromosome group location of these diagnostic markers, Xgwm382 and Xgwm311, in the same population, we selected 16 SSR markers mapped only in one genome of chromosome group 2 around 1–21 cM distance to these diagnostic markers based on the SSR consensus map of wheat. Out of 16 SSRs, Xwmc658 identified resistant F₂ individuals as a diagnostic marker for yellow rust disease and provided the location of Xgwm382 and Xgwm311 on chromosome 2AL in our plant material.     

Molecular characterization and mapping of ALMT1, the aluminium-tolerance gene of bread wheat (Triticum aestivum L.).

The major aluminum (Al) tolerance gene in wheat ALMT1 confers. An Al-activated efflux of malate from root apices. We determined the genomic structure of the ALMT1 gene and found it consists of 6 exons interrupted by 5 introns. Sequencing a range of wheat genotypes identified 3 alleles for ALMT1, 1 of which was identical to the ALMT1 gene from an Aegilops tauschii accession. The ALMT1 gene was mapped to chromosome 4DL using 'Chinese Spring' deletion lines, and loss of ALMT1 coincided with the loss of both Al tolerance and Al-activated malate efflux. Aluminium tolerance in each of 5 different doubled-haploid populations was found to be conditioned by a single major gene. When ALMT1 was polymorphic between the parental lines, QTL and linkage analyses indicated that ALMT1 mapped to chromosome 4DL and cosegregated with Al tolerance. In 2 populations examined, Al tolerance also segregated with a greater capacity for Al-activated malate efflux. Aluminium tolerance was not associated with a particular coding allele for ALMT1, but was significantly correlated with the relative level of ALMT1 expression. These findings suggest that the Al tolerance in a diverse range of wheat genotypes is primarily conditioned by ALMT1.     

Pm34: a new powdery mildew resistance gene transferred from Aegilops tauschii Coss. to common wheat (Triticum aestivum L.)

Powdery mildew is a major fungal disease in wheat growing areas worldwide. A novel source of resistance to wheat powdery mildew present in the germplasm line NC97BGTD7 was genetically characterized as a monogenic trait in greenhouse and field trials using F₂ derived lines from a NC97BGTD7 X Saluda cross. Microsatellite markers were used to map and tag this resistance gene, now designated Pm34. Three co-dominant microsatellite markers linked to Pm34 were identified and their most likely order was established as: Xbarc177-5D, 5.4cM, Pm34, 2.6cM, Xbarc144-5D, 14cM, Xgwm272-5D. These microsatellite markers were previously mapped to the long arm of the 5D chromosome and their positions were confirmed using Chinese Spring nullitetrasomic Nulli5D-tetra5A and ditelosomic Dt5DL lines. Pm2, the only other known Pm gene on chromosome 5D, has been mapped to the short arm and its specificity is different from that of Pm34.     

Genetic and in silico comparative mapping of the polyphenol oxidase gene in bread wheat (Triticum aestivum L.)

Polyphenol oxidases (PPOs) are involved in the time-dependent darkening and discolouration of Asian noodles and other wheat end products. In this study, a doubled haploid (DH) population derived from Chara (moderately high PPO activity)/WW2449 (low PPO activity) was screened for PPO activity based on l-DOPA and l-tyrosine assays using whole seeds. Both these assays were significantly genetically correlated (r=0.91) in measuring the PPO activity in this DH population. Quantitative trait loci (QTLs) analysis utilising a skeleton map enabled us to identify a major QTL controlling PPO activity based on l-DOPA and l-tyrosine on the long arm of chromosome 2A. The simple sequence repeat (SSR) marker GWM294b explained over 82% of the line mean phenotypic variation from samples collected in both 2000 and 2003. Four SSR markers were validated for PPO linkage in genetically diverse backgrounds and proven to correctly predict the PPO activity in more than 92% of wheat lines. Physical mapping using deletion lines of Chinese Spring has confirmed the location of the GWM294b, GWM312 and WMC170 on chromosome 2AL, between deletion breakpoints 2AL-C to 0.85. In order to identify functional gene markers, data searches for alignments between rice BAC/PAC clones assembled on chromosome 1 and 4, chromosome 7, and (1) the wheat expressed sequence tags mapped in deletion bin (2AL-C to 0.85) and (2) the coding sequence of a previously cloned wheat PPO gene were made and found significant sequence similarities with the PPO gene or common central domain of tyrosinase. Available PPO gene sequences in the National Centre for Biotechnology Information (NCBI) database have revealed that there is a significant molecular diversity at the nucleotide and amino acid level in the wheat PPO genes.Electronic Supplementary Material Supplementary material is available for this article at .     

Leaf rust resistance gene Lr1, isolated from bread wheat (Triticum aestivum L.) is a member of the large psr567 gene family

In hexaploid wheat, leaf rust resistance gene Lr1 is located at the distal end of the long arm of chromosome 5D. To clone this gene, an F₁-derived doubled haploid population and a recombinant inbred line population from a cross between the susceptible cultivar AC Karma and the resistant line 87E03-S2B1 were phenotyped for resistance to Puccinia triticina race 1-1 BBB that carries the avirulence gene Avr1. A high-resolution genetic map of the Lr1 locus was constructed using microsatellite, resistance gene analog (RGA), BAC end (BE), and low pass (LP) markers. A physical map of the locus was constructed by screening a hexaploid wheat BAC library from cultivar Glenlea that is known to have Lr1. The locus comprised three RGAs from a gene family related to RFLP marker Xpsr567. Markers specific to each paralog were developed. Lr1 segregated with RGA567-5 while recombinants were observed for the other two RGAs. Transformation of the susceptible cultivar Fielder with RGA567-5 demonstrated that it corresponds to the Lr1 resistance gene. In addition, the candidate gene was also confirmed by virus-induced gene silencing. Twenty T ₁ lines from resistant transgenic line T ₀-938 segregated for resistance, partial resistance and susceptibility to Avr1 corresponding to a 1:2:1 ratio for a single hemizygous insertion. Transgene presence and expression correlated with the phenotype. The resistance phenotype expressed by Lr1 seemed therefore to be dependant on the zygosity status. T ₃-938 sister lines with and without the transgene were further tested with 16 virulent and avirulent rust isolates. Rust reactions were all as expected for Lr1 thereby providing additional evidence toward the Lr1 identity of RGA567-5. Sequence analysis of Lr1 indicated that it is not related to the previously isolated Lr10 and Lr21 genes and unlike these genes, it is part of a large gene family. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. The Canadian Crown's right to retain a non-exclusive, royalty-free licence in and to any copyright is acknowledged.