Chromosomes Of Homoeologous Group Research Articles

Gametocidal genes: from a discovery to the application in wheat breeding.

Some species of the genus Aegilops, a wild relative of wheat, carry chromosomes that after introducing to wheat exhibit preferential transmission to progeny. Their selective retention is a result of the abortion of gametes lacking them due to induced chromosomal aberrations. These chromosomes are termed Gametocidal (Gc) and, based on their effects, they are categorized into three types: mild, intense or severe, and very strong. Gc elements within the same homoeologous chromosome groups of Aegilops (II, III, or IV) demonstrate similar Gc action. This review explores the intriguing dynamics of Gc chromosomes and encompasses comprehensive insights into their source species, behavioral aspects, mode of action, interactions, suppressions, and practical applications of the Gc system in wheat breeding. By delving into these areas, this work aims to contribute to the development of novel plant genetic resources for wheat breeding. The insights provided herein shed light on the utilization of Gc chromosomes to produce chromosomal rearrangements in wheat and its wild relatives, thereby facilitating the generation of chromosome deletions, translocations, and telosomic lines. The Gc approach has significantly advanced various aspects of wheat genetics, including the introgression of novel genes and alleles, molecular markers and gene mapping, and the exploration of homoeologous relationships within Triticeae species. The mystery lies in why gametes possessing Gc genes maintain their normality while those lacking Gc genes suffer abnormalities, highlighting an unresolved research gap necessitating deeper investigation.

The Triticeae CBF Gene Cluster-To Frost Resistance and Beyond.

The pivotal role of CBF/DREB1 transcriptional factors in Triticeae crops involved in the abiotic stress response has been highlighted. The CBFs represent an important hub in the ICE-CBF-COR pathway, which is one of the most relevant mechanisms capable of activating the adaptive response to cold and drought in wheat, barley, and rye. Understanding the intricate mechanisms and regulation of the cluster of CBF genes harbored by the homoeologous chromosome group 5 entails significant potential for the genetic improvement of small grain cereals. Triticeae crops seem to share common mechanisms characterized, however, by some peculiar aspects of the response to stress, highlighting a combined landscape of single-nucleotide variants and copy number variation involving CBF members of subgroup IV. Moreover, while chromosome 5 ploidy appears to confer species-specific levels of resistance, an important involvement of the ICE factor might explain the greater tolerance of rye. By unraveling the genetic basis of abiotic stress tolerance, researchers can develop resilient varieties better equipped to withstand extreme environmental conditions. Hence, advancing our knowledge of CBFs and their interactions represents a promising avenue for improving crop resilience and food security.

Insights of auxin signaling F-box genes in wheat (Triticum aestivum L.) and their dynamic expression during the leaf rust infection.

The TRANSPORT INHIBITOR RESPONSE 1/AUXIN SIGNALING F-BOX (TIR1/AFB) protein serves as auxin receptor and links with Aux/IAA repressor protein leading to its degradation via SKP-Cullin-F box (SCFTIR1/AFB) complex in the auxin signaling pathway. Present study revealed 11 TIR1/AFB genes in wheat by genome-wide search using AFB HMM profile. Phylogenetic analysis clustered these genes in two classes. Several phytohormone, abiotic, and biotic stress responsive cis-elements were detected in promoter regions of TIR1/AFB genes. These genes were localized on homoeologous chromosome groups 2, 3, and 5 showing orthologous relation with other monocot plants. Most genes were interrupted by introns and the gene products were localized in cytoplasm, nucleus, and cell organelles. TaAFB3, TaAFB5, and TaAFB8 had nuclear localization signals. The evolutionary constraint suggested paralogous sister pairs and orthologous genes went through strong purifying selection process and are slowly evolving at protein level. Functional annotation revealed all TaAFB genes participated in auxin activated signaling pathway and SCF-mediated ubiquitination process. Furthermore, in silico expression study revealed their diverse expression profiles during various developmental stages in different tissues and organs as well as during biotic and abiotic stress. QRT-PCR based studies suggested distinct expression pattern of TIR1-1, TIR1-3, TaAFB1, TaAFB2, TaAFB3, TaAFB4, TaAFB5, TaAFB7, and TaAFB8 displaying maximum expression at 24 and 48h post inoculation in both susceptible and resistant near isogenic wheat lines infected with leaf rust pathogen. Importantly, this also reflects coordinated responses in expression patterns of wheat TIR1/AFB genes during progression stages of leaf rust infection.

Abscisic Acid-Stress-Ripening Genes Involved in Plant Response to High Salinity and Water Deficit in Durum and Common Wheat.

In the dry and hot Mediterranean regions wheat is greatly susceptible to several abiotic stresses such as extreme temperatures, drought, and salinity, causing plant growth to decrease together with severe yield and quality losses. Thus, the identification of gene sequences involved in plant adaptation to such stresses is crucial for the optimization of molecular tools aimed at genetic selection and development of stress-tolerant varieties. Abscisic acid, stress, ripening-induced (ASR) genes act in the protection mechanism against high salinity and water deficit in several plant species. In a previous study, we isolated for the first time the TtASR1 gene from the 4A chromosome of durum wheat in a salt-tolerant Tunisian landrace and assessed its involvement in plant response to some developmental and environmental signals in several organs. In this work, we focused attention on ASR genes located on the homoeologous chromosome group 4 and used for the first time a Real-Time approach to “in planta” to evaluate the role of such genes in modulating wheat adaptation to salinity and drought. Gene expression modulation was evaluated under the influence of different variables – kind of stress, ploidy level, susceptibility, plant tissue, time post-stress application, gene chromosome location. ASR response to abiotic stresses was found only slightly affected by ploidy level or chromosomal location, as durum and common wheat exhibited a similar gene expression profile in response to salt increase and water deficiency. On the contrary, gene activity was more influenced by other variables such as plant tissue (expression levels were higher in roots than in leaves), kind of stress [NaCl was more affecting than polyethylene glycol (PEG)], and genotype (transcripts accumulated differentially in susceptible or tolerant genotypes). Based on such experimental evidence, we confirmed Abscisic acid, stress, ripening-induced genes involvement in plant response to high salinity and drought and suggested the quantification of gene expression variation after long salt exposure (72 h) as a reliable parameter to discriminate between salt-tolerant and salt-susceptible genotypes in both Triticum aestivum and Triticum durum.

Genome-wide identification and expression analysis of calmodulin and calmodulin-like genes in wheat (Triticum aestivum L.)

ABSTRACT Calmodulin (CaM) and calmodulin-like (CML) genes are widely involved in plant growth and development and mediating plant stress tolerance. However, the whole genome scale studies about CaM and CML gene families have not been done in wheat, and the possible functions of most wheat CaM/CML gene members are still unknown. In this study, a total of 18 TaCaM and 230 TaCML gene members were identified in wheat genome. Among these genes, 28 TaCaM/CML gene members have 74 duplicated copies, while 21 genes have 48 transcript variants, resulting in 321 putative TaCaM/CML transcripts totally. Phylogenetic tree analysis showed that they can be classified into 7 subfamilies. Similar gene structures and protein domains can be found in members of the same gene cluster. The TaCaM/CML genes were spread among all 21 chromosomes with unbalanced distributions, while most of the gene clusters contained 3 homoeologous genes located in the same homoeologous chromosome group. Synteny analysis showed that most of TaCaM/CMLs gene members can be found with 1–4 paralogous genes in T. turgidum and Ae. Tauschii. High numbers of cis-acting elements related to plant hormones and stress responses can be observed in the promoters of TaCaM/CMLs. The spatiotemporal expression patterns showed that most of the TaCaM/TaCML genes can be detected in at least one tissue. The expression levels of TaCML17, 21, 30, 50, 59 and 75 in the root or shoot can be up-regulated by abiotic stresses, suggesting that TaCML17, 21, 30, 50, 59 and 75 may be related with responses to abiotic stresses in wheat. The spatiotemporal expression patterns of TaCaM/CML genes indicated they may be involved widely in wheat growth and development. Our results provide important clues for exploring functions of TaCaMs/CMLs in growth and development as well as responses to abiotic stresses in wheat in the future.

Genetic analysis of grain protein content and dough quality traits in elite spring bread wheat (Triticum aestivum) lines through association study

Wheat quality parameters are complex traits predominantly influenced by the genetic background of varieties. A total of 802 spring bread wheat breeding lines were tested at Marchouch station, Morocco in 2018 aimed at mining invaluable QTNs for grain protein content (PR), gluten content (GL), alveograph strength (W) and zeleny sedimentation test (Z). A single-locus (MLM) and multi-locus (FarmCPU) GWAS models were implemented using 5,095 SNP markers generated from the genotyping-by-sequencing (GBS) platform. A total of 36 and 92 QTNs were detected for the four quality traits from the MLM and FarmCPU GWAS models, respectively. The FarmCPU model detected markers on homoeologous chromosome group one having highly significant QTNs with PR, GL, W and Z traits. The two implemented GWAS models detected significant QTNs on the short arm of homoeologous chromosome groups 2 and 6 for GL, PR, W and Z traits. FarmCPU model detected SNP_615302 marker on chromosome 3B with highly significant MTAs and concurrent effect for PR, GL and W traits. Moreover, significant MTAs were detected on chromosomes 3D, 4A, 4B, 5A, 5B, 7A, 7B and 7D for the four studied quality traits across the two GWAS models. The in-silico gene annotation for QTNs using the high confidence gene models detected genes involved in numerous functions including regulating plant growth, development and tolerance to biotic and abiotic stresses. The identified markers could potentially be useful tool for quality improvement through marker-assisted selection in future breeding programs.

Genome-Wide Identification and Analysis of the NPR1-Like Gene Family in Bread Wheat and Its Relatives.

NONEXPRESSOR OF PATHOGENESIS-RELATED GENES 1 (NPR1), and its paralogues NPR3 and NPR4, are bona fide salicylic acid (SA) receptors and play critical regulatory roles in plant immunity. However, comprehensive identification and analysis of the NPR1-like gene family had not been conducted so far in bread wheat and its relatives. Here, a total of 17 NPR genes in Triticum aestivum, five NPR genes in Triticum urartu, 12 NPR genes in Triticum dicoccoides, and six NPR genes in Aegilops tauschii were identified using bioinformatics approaches. Protein properties of these putative NPR1-like genes were also described. Phylogenetic analysis showed that the 40 NPR1-like proteins, together with 40 NPR1-related proteins from other plant species, were clustered into three major clades. The TaNPR1-like genes belonging to the same Arabidopsis subfamilies shared similar exon-intron patterns and protein domain compositions, as well as conserved motifs and amino acid residues. The cis-regulatory elements related to SA were identified in the promoter regions of TaNPR1-like genes. The TaNPR1-like genes were intensively mapped on the chromosomes of homoeologous groups 3, 4, and 5, except TaNPR2-D. Chromosomal distribution and collinearity analysis of NPR1-like genes among bread wheat and its relatives revealed that the evolution of this gene family was more conservative following formation of hexaploid wheat. Transcriptome data analysis indicated that TaNPR1-like genes exhibited tissue/organ-specific expression patterns and some members were induced under biotic stress. These findings lay the foundation for further functional characterization of NPR1-like proteins in bread wheat and its relatives.

Conservation and differentiation of polyphenol oxidase (PPO) gene introns in Triticum and Aegilops tauschii Coss.

Two genes (PPO1 and PPO2), located in the homoeologous chromosome group 2 of common wheat, play an important role in controlling the kernel polyphenol oxidase acitivity, which influence indirectly the time-dependent darkening and discoloration in Asian noodles and other wheat-based products. In the present study, intron sequences of PPO genes (PPO1 and PPO2) in Triticum urartu Tumanian ex Gandilyan, T. monococcum L. and Aegilops tauschii Coss., together with NCBI retrieved wheat PPO sequnces in different ploidy levels, were systematically investigated. The results highlighted that PPO intron sequences are conserved at lower classification levels (species/subspecies level), and the allopolyploidization process of common wheat has little effect on them. Sequence differences in PPO gene introns may occur long before the differentiation of the A and D genome of T. urartu and Ae. tauschii, respectively. It’s interesting that different PPO intron regions vary into two different intron splicing rule within one same gene sequence: intron 1 is all fitted to the “GT-AG” splicing rule while intron 2 is the “GC-AG”. In addition, the phylogenetic analysis showed the obvious differences existed in materials from different geographical distribution in T. monococcum ssp. aegilopoies, which suggest that some of them had close genetic relationship with T. urartu. These findings contribute to the application of PPO gene introns in favorable allele screening, functional molecular marker development, and phylogenetic analysis.

Identification of COS markers specific for Thinopyrum elongatum chromosomes preliminary revealed high level of macrosyntenic relationship between the wheat and Th. elongatum genomes.

Thinopyrum elongatum (Host) D.R. Dewey has served as an important gene source for wheat breeding improvement for many years. The exact characterization of its chromosomes is important for the detailed analysis of prebreeding materials produced with this species. The major aim of this study was to identify and characterize new molecular markers to be used for the rapid analysis of E genome chromatin in wheat background. Sixty of the 169 conserved orthologous set (COS) markers tested on diverse wheat-Th. elongatum disomic/ditelosomic addition lines were assigned to various Th. elongatum chromosomes and will be used for marker-assisted selection. The macrosyntenic relationship between the wheat and Th. elongatum genomes was investigated using EST sequences. Several rearrangements were revealed in homoeologous chromosome groups 2, 5, 6 and 7, while chromosomes 1 and 4 were conserved. Molecular cytogenetic and marker analysis showed the presence of rearranged chromosome involved in 6ES and 2EL arms in the 6E disomic addition line. The selected chromosome arm-specific COS markers will make it possible to identify gene introgressions in breeding programmes and will also be useful in the development of new chromosome-specific markers, evolutionary analysis and gene mapping.

Compensation Ability between the Chromosomes of Homoeologous Group 7 of Triticum aestivum L. and Hordeum marinum ssp. gussoneanum Hudson (2n = 28) and Analysis of the Transmission Frequency of Alien 7H1Lmar Chromosome through Gametes in the Progeny of Wheat–Barley Substitution Lines

On the basis of directed chromosome substitution, ditelosomic (DT) wheat–barley substitution lines (2n = 42 = 40 + 2t) with participation of wild tetraploid barley Hordeum marinum ssp. gussoneanum Hudson (2n = 28) were first obtained and analyzed. GISH analysis of the substitution lines showed that they carried a pair of telocentric barley chromosomes. With the help of ditelosomic analysis, the lines were identified as DT7HILmar(7A) and DT7HILmar(7B). On the basis of the compensation test and the study of meiotic stability of substitution lines, it was demonstrated that 7HILmar chromosome of H. marinum was homoeologous to the group 7 chromosomes of common wheat. Analysis of the gamete transfer frequency in the progeny of reciprocal hybrids between F1 7A-7HILmar, 7B-7HILmar, 7D-7HILmar and Saratovskaya 29 cultivar showed that the gamete with alien chromosome n = 20 + t successfully competed with euploid gamete n = 21 in both macrosporogenesis and microsporogenesis.

Allelic Variants of Glutamine Synthetase and Glutamate Synthase Genes in a Collection of Durum Wheat and Association with Grain Protein Content

Wheat is one of the most important crops grown worldwide. Despite the fact that it accounts for only 5% of the global wheat production, durum wheat (Triticum turgidum L. subsp. durum) is a commercially important tetraploid wheat species, which originated and diversified in the Mediterranean basin. In this work, the candidate gene approach has been applied in a collection of durum wheat genotypes; allelic variants of genes glutamine synthetase (GS2) and glutamate synthase (GOGAT) were screened and correlated with grain protein content (GPC). Natural populations and collections of germplasms are quite suitable for this approach, as molecular polymorphisms close to a locus with evident phenotypic effects may be closely associated with their character, providing a better physical resolution than genetic mapping using ad hoc constituted populations. A number of allelic variants were detected both for GS2 and GOGAT genes, and regression analysis demonstrated that some variations are positively and significantly related to the GPC effect. Additionally, these genes map into homoeologous chromosome groups 2 and 3, where several authors have localized important quantitative trait loci (QTLs) for GPC. The information outlined in this work could be useful in breeding and marker-assisted selection programs.

Flow sorting of C-genome chromosomes from wild relatives of wheat Aegilops markgrafii, Ae. triuncialis and Ae. cylindrica, and their molecular organization.

Aegilops markgrafii (CC) and its natural hybrids Ae. triuncialis (U(t)U(t)C(t)C(t)) and Ae. cylindrica (D(c)D(c)C(c)C(c)) represent a rich reservoir of useful genes for improvement of bread wheat (Triticum aestivum), but the limited information available on their genome structure and the shortage of molecular (cyto-) genetic tools hamper the utilization of the extant genetic diversity. This study provides the complete karyotypes in the three species obtained after fluorescent in situ hybridization (FISH) with repetitive DNA probes, and evaluates the potential of flow cytometric chromosome sorting. The flow karyotypes obtained after the analysis of 4',6-diamidino-2-phenylindole (DAPI)-stained chromosomes were characterized and the chromosome content of the peaks on the flow karyotypes was determined by FISH. Twenty-nine conserved orthologous set (COS) markers covering all seven wheat homoeologous chromosome groups were used for PCR with DNA amplified from flow-sorted chromosomes and genomic DNA. FISH with repetitive DNA probes revealed that chromosomes 4C, 5C, 7C(t), T6U(t)S.6U(t)L-5C(t)L, 1C(c) and 5D(c) could be sorted with purities ranging from 66 to 91%, while the remaining chromosomes could be sorted in groups of 2-5. This identified a partial wheat-C-genome homology for group 4 and 5 chromosomes. In addition, 1C chromosomes were homologous with group 1 of wheat; a small segment from group 2 indicated 1C-2C rearrangement. An extensively rearranged structure of chromosome 7C relative to wheat was also detected. The possibility of purifying Aegilops chromosomes provides an attractive opportunity to investigate the structure and evolution of the Aegilops C genome and to develop molecular tools to facilitate the identification of alien chromatin and support alien introgression breeding in bread wheat.

Evolutionary history of Methyltransferase 1 genes in hexaploid wheat.

BackgroundPlant and animal methyltransferases are key enzymes involved in DNA methylation at cytosine residues, required for gene expression control and genome stability. Taking advantage of the new sequence surveys of the wheat genome recently released by the International Wheat Genome Sequencing Consortium, we identified and characterized MET1 genes in the hexaploid wheat Triticum aestivum (TaMET1).ResultsNine TaMET1 genes were identified and mapped on homoeologous chromosome groups 2A/2B/2D, 5A/5B/5D and 7A/7B/7D. Synteny analysis and evolution rates suggest that the genome organization of TaMET1 genes results from a whole genome duplication shared within the grass family, and a second gene duplication, which occurred specifically in the Triticeae tribe prior to the speciation of diploid wheat. Higher expression levels were observed for TaMET1 homoeologous group 2 genes compared to group 5 and 7, indicating that group 2 homoeologous genes are predominant at the transcriptional level, while group 5 evolved into pseudogenes. We show the connection between low expression levels, elevated evolution rates and unexpected enrichment in CG-dinucleotides (CG-rich isochores) at putative promoter regions of homoeologous group 5 and 7, but not of group 2 TaMET1 genes. Bisulfite sequencing reveals that these CG-rich isochores are highly methylated in a CG context, which is the expected target of TaMET1.ConclusionsWe retraced the evolutionary history of MET1 genes in wheat, explaining the predominance of group 2 homoeologous genes and suggest CG-DNA methylation as one of the mechanisms involved in wheat genome dynamics.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-922) contains supplementary material, which is available to authorized users.

Flow cytometric chromosome sorting from diploid progenitors of bread wheat, T. urartu, Ae. speltoides and Ae. tauschii

Chromosomes 5A (u) , 5S and 5D can be isolated from wild progenitors, providing a chromosome-based approach to develop tools for breeding and to study the genome evolution of wheat. The three subgenomes of hexaploid bread wheat originated from Triticum urartu (A(u)A(u)), from a species similar to Aegilops speltoides (SS) (progenitor of the B genome), and from Ae. tauschii (DD). Earlier studies indicated the potential of chromosome genomics to assist gene transfer from wild relatives of wheat and discover novel genes for wheat improvement. This study evaluates the potential of flow cytometric chromosome sorting in the diploid progenitors of bread wheat. Flow karyotypes obtained by analysing DAPI-stained chromosomes were characterized and the contents of the chromosome peaks were determined. FISH analysis with repetitive DNA probes proved that chromosomes 5A(u), 5S and 5D could be sorted with purities of 78-90 %, while the remaining chromosomes could be sorted in groups of three. Twenty-five conserved orthologous set (COS) markers covering wheat homoeologous chromosome groups 1-7 were used for PCR with DNA amplified from flow-sorted chromosomes and genomic DNA. These assays validated the cytomolecular results as follows: peak I on flow karyotypes contained chromosome groups 1, 4 and 6, peak II represented homoeologous group 5, while peak III consisted of groups 2, 3 and 7. The isolation of individual chromosomes of wild progenitors provides an attractive opportunity to investigate the structure and evolution of the polyploid genome and to deliver tools for wheat improvement.

Homoeologous chromosomes of Xenopus laevis are highly conserved after whole-genome duplication

It has been suggested that whole-genome duplication (WGD) occurred twice during the evolutionary process of vertebrates around 450 and 500 million years ago, which contributed to an increase in the genomic and phenotypic complexities of vertebrates. However, little is still known about the evolutionary process of homoeologous chromosomes after WGD because many duplicate genes have been lost. Therefore, Xenopus laevis (2n=36) and Xenopus (Silurana) tropicalis (2n=20) are good animal models for studying the process of genomic and chromosomal reorganization after WGD because X. laevis is an allotetraploid species that resulted from WGD after the interspecific hybridization of diploid species closely related to X. tropicalis. We constructed a comparative cytogenetic map of X. laevis using 60 complimentary DNA clones that covered the entire chromosomal regions of 10 pairs of X. tropicalis chromosomes. We consequently identified all nine homoeologous chromosome groups of X. laevis. Hybridization signals on two pairs of X. laevis homoeologous chromosomes were detected for 50 of 60 (83%) genes, and the genetic linkage is highly conserved between X. tropicalis and X. laevis chromosomes except for one fusion and one inversion and also between X. laevis homoeologous chromosomes except for two inversions. These results indicate that the loss of duplicated genes and inter- and/or intrachromosomal rearrangements occurred much less frequently in this lineage, suggesting that these events were not essential for diploidization of the allotetraploid genome in X. laevis after WGD.

Identifying Loci Influencing 1,000-Kernel Weight in Wheat by Microsatellite Screening for Evidence of Selection during Breeding

Chinese wheat mini core collection (262 accessions) was genotyped at 531 microsatellite loci representing a mean marker density of 5.1 cM. One-thousand-kernel weights (TKW) of lines were measured in five trials (three environments in four growing seasons). Structure analysis based on 42 unlinked SSR loci indicated that the materials formed two sub-populations, viz., landraces and modern varieties. A large difference in TKW (7.08 g, P<0.001) was found between the two sub-groups. Therefore, TKW is a major yield component that was improved in the past 6 decades; it increased from a mean 31.5 g in the 1940s to 44.64 g in the 2000s, representing a 2.19 g increase in each decade. Analyses based on a mixed linear model (MLM), population structure (Q) and relative kinship (K) revealed 22 SSR loci that were significantly associated with mean TKW (MTKW) of the five trials estimated by the best linear unbiased predictor (BLUP) method. They were mainly distributed on chromosomes of homoeologous groups 1, 2, 3, 5 and 7. Six loci, cfa2234-3A, gwm156-3B, barc56-5A, gwm234-5B, wmc17-7A and cfa2257-7A individually explained more than 11.84% of the total phenotypic variation. Favored alleles for breeding at the 22 loci were inferred according to their estimated effects on MTKW based on mean difference of varieties grouped by genotypes. Statistical simulation showed that these favored alleles have additive genetic effects. Frequency changes of alleles at loci associated with TKW are much more dramatic than those at neutral loci between the sub-groups. The numbers of favored alleles in modern varieties indicate there is still considerable genetic potential for their use as markers for genome selection of TKW in wheat breeding. Alleles that can be used globally to increase TKW were inferred according to their distribution by latitude and frequency of changes between landraces and the modern varieties.

Meta-analysis of QTLs Involved in Pre-harvest Sprouting Tolerance and Dormancy in Bread Wheat

In common wheat, meta-analysis of quantitative trait loci (QTL) associated with pre-harvest sprouting tolerance (PHST) and dormancy was carried out using results of 15 studies involving 15 different mapping populations. The study was restricted to only four chromosomes including three chromosomes of homoeologous group 3 (3A, 3B and 3D) and the chromosome 4A, since QTLs for PHST and dormancy on these four chromosomes were reported in several earlier studies, thus making these chromosomes suitable for meta-QTL analysis. The software BioMercator 2.1 was used to build a consensus map, and QTLs were projected on to this map for conducting meta-analysis. Using 36 of the 50 original QTLs, 8 meta-QTLs (MQTLs) were identified: 7 MQTLs were located on chromosomes of homoeologous group 3 including 3A (2 MQTL), 3B (3 MQTL) and 3D (2 MQTL), 1 MQTL was located on chromosome 4A. Confidence intervals (C.I.) for each of these 8 MQTLs were particularly narrow. The mapping information for 50 QTLs was also used for “overview” analysis to visualize important genomic regions carrying the MQTLs for PHST and dormancy. Co-localizations between candidate genes for dormancy/PHST ( taVP1 and TaGA20 - ox1 ) and MQTL positions appeared globally significant, although these candidate genes deserve further investigation. Markers associated with 8 MQTLs identified during the present study should prove helpful for introgression of tolerance against pre-harvest sprouting (PHS) into high yielding wheat varieties through marker-assisted selection (MAS).

Next‐generation sequencing and syntenic integration of flow‐sorted arms of wheat chromosome 4A exposes the chromosome structure and gene content

Wheat is the third most important crop for human nutrition in the world. The availability of high-resolution genetic and physical maps and ultimately a complete genome sequence holds great promise for breeding improved varieties to cope with increasing food demand under the conditions of changing global climate. However, the large size of the bread wheat (Triticum aestivum) genome (approximately 17 Gb/1C) and the triplication of genic sequence resulting from its hexaploid status have impeded genome sequencing of this important crop species. Here we describe the use of mitotic chromosome flow sorting to separately purify and then shotgun-sequence a pair of telocentric chromosomes that together form chromosome 4A (856 Mb/1C) of wheat. The isolation of this much reduced template and the consequent avoidance of the problem of sequence duplication, in conjunction with synteny-based comparisons with other grass genomes, have facilitated construction of an ordered gene map of chromosome 4A, embracing ≥85% of its total gene content, and have enabled precise localization of the various translocation and inversion breakpoints on chromosome 4A that differentiate it from its progenitor chromosome in the A genome diploid donor. The gene map of chromosome 4A, together with the emerging sequences of homoeologous wheat chromosome groups 4, 5 and 7, represent unique resources that will allow us to obtain new insights into the evolutionary dynamics between homoeologous chromosomes and syntenic chromosomal regions.

Chromosome synteny of the a genome of two evolutionary wheat lines

In order to estimate synteny between A(t) and A polyploid wheat genomes belonging to different evolutionary lines (Timopheevi and Emmer), saturation of chromosome maps of Triticum timopheevii A(t) genome by molecular markers has been conducted. Totally, 179 EST-SSR and 48 genomic SSR-markers have been used with the following integration of 13 and 7 markers correspondingly into chromosome maps of A(t) genome. EST-SSR showed higher transferability and lower polymorphism than genomic SSR markers. The chromosome maps designed were compared to maps of homoeologous chromosome group of the T. aestivum A genome. No disturbances of colinearity, i.e., of the order of markers within the chromosome segments on which they had been previously mapped, were observed. According to the quantity assessment of markers amplifying in homoeologous chromosomes, the maximum divergence was detected in two groups (4A(t)/4A and 3A(t)/3A) among the seven chromosomes examined in the A(t) and A genomes. Comparison of molecular genetic mapping results with the published results of studying meiosis of F1 hybrids and the frequency of chromosomes substitution in introgressive T. aestivum x T. timopheevii lines suggest that individual chromosomes of the At and A genomes evolve differently. Translocations were shown to introduce the major impact on the divergence of 4A(t)/4A and 6A(t)/6A chromosomes, while mutations of the primary DNA structure, on the divergence of homoeologous group 3 chromosomes. The level of reorganization of other chromosomes during the evolution in the A(t) and A genomes was significantly lower.

Highly Conserved UFD1 Proteins Among Eukaryotes Exhibit Considerable C-Terminus Diversity in Different Taxa

The UFD1 protein is an important ubiquitin recognition component in the ubiquitin-mediated degradation pathway. To investigate the conservation of UFD1 genes among eukaryotes and their differentiation, two UFD1 paralogs from wheat were identified and mapped to homoeologous chromosome groups 6 and 2, respectively. TaUFD1a-6B and TaUFD1b-2D were cloned, and both genes consist of eight introns and of the same intron phases. These genes were compared with those in Arabidopsis, rice, polar, yeast, and mammals for their sequence, chromosome organization, and primary protein structure. The sequence structure, especially those corresponding to the fourth, fifth, and sixth exons of UFD1 genes, is highly conserved across these taxa. However, unlike yeast and mammals having a single UFD1 gene, higher angiosperm species have two ancient UFD1 paralogs. Besides the evolutionarily conserved ubiquitin-binding domain at the N-terminus, plant UFD1 proteins have three conserved C-terminal motifs. Motif I, near the UFD1 domain, displays a high level of similarity to the mammalian p97-binding site, and motif III is likely responsible for endoplasmic reticulum membrane retention. TaUFD1a-6B and TaUFD1b-2D are ubiquitously expressed in different plant tissues. A green fluorescent protein-transient expression assay in epidermal cells of onion demonstrated that TaUFD1 proteins primarily accumulate in the nucleus.