Triticum (Aegilops) tauschii in the natural and artificial synthesis of hexaploid wheat

2008 ◽  
Vol 59 (5) ◽  
pp. 475 ◽  
Author(s):  
G. M. Halloran ◽  
F. C. Ogbonnaya ◽  
E. S. Lagudah
Keyword(s):  
Genetic Variation ◽  
Hexaploid Wheat ◽  
Gene Pool ◽  
Growth Habit ◽  
Tetraploid Wheat ◽  
Systematic Evaluation ◽  
Gene Pools ◽  
Bread Making ◽  
D Genome ◽  
Wheat Improvement

An account is given of the possible time(s) and place(s) of the origin of hexaploid wheat from natural hybridisation between Triticum tauschii (Ae. tauschii) and both wild and cultivated forms of tetraploid wheat. A recapitulation is presented of the likely genotypic and phenotypic status of the newly arisen natural hexaploid and the likely path of hybridisation from whence it arose. Recent substantial contributions of T. tauschii to wheat improvement indicate the likelihood that introgession en masse from T. tauschii has not occurred throughout its natural and agricultural associations with wheat. This has been substantiated in comparative studies revealing higher levels of genetic variation in T. tauschii compared with the D genome of hexaploid wheat. A case is made for a widening of the concept of the gene pool of T. tauschii for wheat improvement and the notion of a secondary gene pool is proposed to include variation in T. tauschii as it occurs in several polyploid forms of ‘grass Triticum’. The likely differentiation of growth habit forms, conditioned by vernalisation (i.e. vrn) genes, in hexaploid wheat synthesis, including the interaction of these genes in hexaploid wheat, is discussed. It is speculated that growth habit differentiation was of significance to the hexaploid’s yield contribution and survival in tetraploid-hexaploid mixtures (likely to be a common constitution of wheat crops of early agriculture), and in the Neolithic spread of agriculture to the higher latitude, and colder environments of NW Europe and central Asia. The significance of the contribution of T. tauschii to the unique milling and bread-making properties of hexaploid wheat is discussed in the light of Roman discernment of its closer fulfilment of the requirements of leavened bread-making compared with tetraploid wheat. The significance of the contribution of T. tauschii to the evolution of wheat appears to have been much delayed (by ~6500 years) in that hexaploid wheat did not receive singular attention and cultivation until during the Roman era, from whence it gradually rose in popularity to eventually achieve its current pre-eminent status. Continuing systematic evaluation of genetic variation in both the primary and secondary gene pools of T. tauschii for wheat improvement, using both conventional and genetic analysis and contemporary genomic tools, is advocated. The latter approach is particularly important for quantitative traits in the light of wide divergence in plant phenotype of their representatives from that of hexaploid wheat.

scholarly journals Conservation and trans-regulation of histone modification in the A and B subgenomes of polyploid wheat during domestication and ploidy transition

BMC Biology ◽  
2021 ◽  
Vol 19 (1) ◽  
Author(s):  
Zhenling Lv ◽  
Zijuan Li ◽  
Meiyue Wang ◽  
Fei Zhao ◽  
Wenjie Zhang ◽  
...  
Keyword(s):  
Gene Expression ◽  
Histone Modification ◽  
Hexaploid Wheat ◽  
Epigenetic Modification ◽  
Expression Profiles ◽  
Tetraploid Wheat ◽  
Gene Expression Profiles ◽  
Great Majority ◽  
D Genome ◽  
Polyploid Wheat

AbstractBackgroundPolyploidy has played a prominent role in the evolution of plants and many other eukaryotic lineages. However, how polyploid genomes adapt to the abrupt presence of two or more sets of chromosomes via genome regulation remains poorly understood. Here, we analyzed genome-wide histone modification and gene expression profiles in relation to domestication and ploidy transition in the A and B subgenomes of polyploid wheat.ResultsWe found that epigenetic modification patterns by two typical euchromatin histone markers, H3K4me3 and H3K27me3, for the great majority of homoeologous triad genes in A and B subgenomes were highly conserved between wild and domesticated tetraploid wheats and remained stable in the process of ploidy transitions from hexaploid to extracted tetraploid and then back to resynthesized hexaploid. However, a subset of genes was differentially modified during tetraploid and hexaploid wheat domestication and in response to ploidy transitions, and these genes were enriched for particular gene ontology (GO) terms. The extracted tetraploid wheat manifested higher overall histone modification levels than its hexaploid donor, and which were reversible and restored to normal levels in the resynthesized hexaploid. Further, while H3K4me3 marks were distally distributed along each chromosome and significantly correlated with subgenome expression as expected, H3K27me3 marks showed only a weak distal bias and did not show a significant correlation with gene expression.ConclusionsOur results reveal overall high stability of histone modification patterns in the A and B subgenomes of polyploid wheat during domestication and in the process of ploidy transitions. However, modification levels of a subset of functionally relevant genes in the A and B genomes weretrans-regulated by the D genome in hexaploid wheat.

Chromosomal rearrangements in wheat: their types and distribution

Genome ◽  
2007 ◽  
Vol 50 (10) ◽  
pp. 907-926 ◽  
Author(s):  
E. D. Badaeva ◽  
O. S. Dedkova ◽  
G. Gay ◽  
V. A. Pukhalskyi ◽  
A. V. Zelenin ◽  
...  
Keyword(s):  
Hexaploid Wheat ◽  
Chromosomal Rearrangements ◽  
Tetraploid Wheat ◽  
Unknown Origin ◽  
D Genome ◽  
Wheat Varieties ◽  
High Frequencies ◽  
C Banding ◽  
B Genome ◽  
Translocation Breakpoints

Four hundred and sixty polyploid wheat accessions and 39 triticale forms from 37 countries of Europe, Asia, and USA were scored by C-banding for the presence of translocations. Chromosomal rearrangements were detected in 70 of 208 accessions of tetraploid wheat, 69 of 252 accessions of hexaploid wheat, and 3 of 39 triticale forms. Altogether, 58 types of major chromosomal rearrangements were identified in the studied material; they are discussed relative to 11 additional translocation types described by other authors. Six chromosome modifications of unknown origin were also observed. Among all chromosomal aberrations identified in wheat, single translocations were the most frequent type (39), followed by multiple rearrangements (9 types), pericentric inversions (9 types), and paracentric inversions (3 types). According to C-banding analyses, the breakpoints were located at or near the centromere in 60 rearranged chromosomes, while in 52 cases they were in interstitial chromosome regions. In the latter case, translocation breakpoints were often located at the border of C-bands and the euchromatin region or between two adjacent C-bands; some of these regions seem to be translocation “hotspots”. Our results and data published by other authors indicate that the B-genome chromosomes are involved in translocations most frequently, followed by the A- and D-genome chromosomes; individual chromosomes also differ in the frequencies of translocations. Most translocations were detected in 1 or 2 accessions, and only 11 variants showed relatively high frequencies or were detected in wheat varieties of different origins or from different species. High frequencies of some translocations with a very restricted distribution could be due to a “bottleneck effect”. Other types seem to occur independently and their broad distribution can result from selective advantages of rearranged genotypes in diverse environmental conditions. We found significant geographic variation in the spectra and frequencies of translocation in wheat: the highest proportions of rearranged genotypes were found in Central Asia, the Middle East, Northern Africa, and France. A low proportion of aberrant genotypes was characteristic of tetraploid wheat from Transcaucasia and hexaploid wheat from Middle Asia and Eastern Europe.

Structural organization of the barley D-hordein locus in comparison with its orthologous regions of wheat genomes

Genome ◽  
2003 ◽  
Vol 46 (6) ◽  
pp. 1084-1097 ◽  
Author(s):  
Yong Qiang Gu ◽  
Olin D Anderson ◽  
Cynthia F Londeorë ◽  
Xiuying Kong ◽  
Ravindra N Chibbar ◽  
...  
Keyword(s):  
Sequence Analysis ◽  
Hexaploid Wheat ◽  
Structural Organization ◽  
Comparative Sequence Analysis ◽  
Cysteine Residue ◽  
Glutenin Subunits ◽  
Bread Making ◽  
D Genome ◽  
Contig Sequence ◽  
Hmw Glutenin

D hordein, a prolamin storage protein of barley endosperms, is highly homologous to the high molecular weight (HWM) glutenin subunits, which are the major determinants of bread-making quality in wheat flour. In hexaploid wheat (AABBDD), each genome contains two paralogous copies of HMW-glutenin genes that encode the x- and y-type HMW-glutenin subunits. Previously, we reported the sequence analysis of a 102-kb genomic region that contains the HMW-glutenin locus of the D genome from Aegilops tauschii, the donor of the D genome of hexaploid wheat. Here, we present the sequence analysis of a 120-kb D-hordein region of the barley genome, a more distantly related member of the Triticeae grass tribe. Comparative sequence analysis revealed that gene content and order are generally conserved. Genes included in both of these orthologous regions are arranged in the following order: a Xa21-like receptor kinase, an endosperm globulin, an HMW prolamin, and a serine (threonine) protein kinase. However, in the wheat D genome, a region containing both the globulin and HMW-glutenin gene was duplicated, indicating that this duplication event occurred after the separation of the wheat and barley genomes. The intergenic regions are divergent with regard to the sequence and structural organization. It was found that different types of retroelements are responsible for the intergenic structure divergence in the wheat and barley genomes. In the barley region, we identified 16 long terminal repeat (LTR) retrotransposons in three distinct nested clusters. These retroelements account for 63% of the contig sequence. In addition, barley D hordein was compared with wheat HMW glutenins in terms of cysteine residue conservation and repeat domain organization.Key words: HMW glutenin, evolution, retrotransposon, comparative genomics.

Use of synthetic hexaploid wheat to increase diversity for CIMMYT bread wheat improvement

2008 ◽  
Vol 59 (5) ◽  
pp. 413 ◽  
Author(s):  
S. Dreisigacker ◽  
M. Kishii ◽  
J. Lage ◽  
M. Warburton
Keyword(s):  
Bread Wheat ◽  
Hexaploid Wheat ◽  
Phenotypic Expression ◽  
Germplasm Collection ◽  
Synthetic Hexaploid Wheat ◽  
Selection Marker ◽  
Wheat Cultivars ◽  
D Genome ◽  
Wheat Improvement ◽  
Synthetic Hexaploid

To date, the International Maize and Wheat Improvement Center (CIMMYT) has produced more than 1000 synthetic hexaploid wheats (SHWs), using diverse accessions of the D genome donor species (Aegilops tauschii). Many of these SHWs produced from many different Ae. tauschii have shown resistance or tolerance to various biotic and abiotic stresses, indicating the potential importance of the Ae. tauschii gene pool for breeding purposes. SHWs were backcrossed to CIMMYT improved germplasm to produce synthetic backcross-derived lines (SBLs), which are agronomically similar to the improved parents, but retain the introgressed traits of interest under selection and thereby new diversity. Molecular studies show that SHWs and SBLs are genetically diverse at the DNA level when compared with traditional bread wheat cultivars and preferential transmission of some alleles from the SHW parent has been seen in all genomes, indicating positive selection. Marker analyses of wheat cultivars released over time indicate that SBLs are ideal materials to simultaneously increase yield and diversity for other traits. Following successful diversification of the wheat D genome, CIMMYT has shifted to target improvement of hexaploid wheat via the A and B genomes, focusing on specific traits. Screening the CIMMYT germplasm collection of T. turgidum subsp. dicoccum for Russian wheat aphid resistance and drought tolerance revealed varying levels of phenotypic expression. Promising accessions will be used for the production of new SHWs for future introgressions into elite bread wheat backgrounds.

scholarly journals Dynamic and reversible DNA methylation changes induced by genome separation and merger of polyploid wheat

BMC Biology ◽  
2020 ◽  
Vol 18 (1) ◽  
Author(s):  
Jingya Yuan ◽  
Wu Jiao ◽  
Yanfeng Liu ◽  
Wenxue Ye ◽  
Xiue Wang ◽  
...  
Keyword(s):  
Gene Expression ◽  
Dna Methylation ◽  
Hexaploid Wheat ◽  
Genetic Model ◽  
Tetraploid Wheat ◽  
Epigenetic Changes ◽  
Wheat Evolution ◽  
D Genome ◽  
Polyploid Evolution ◽  
Genome Separation

Abstract Background Wheat is a powerful genetic model for studying polyploid evolution and crop domestication. Hexaploid bread wheat was formed by two rounds of interspecific hybridization and polyploidization, processes which are often accompanied by genetic and epigenetic changes, including DNA methylation. However, the extent and effect of such changes during wheat evolution, particularly from tetraploid-to-hexaploid wheat, are currently elusive. Results Here we report genome-wide DNA methylation landscapes in extracted tetraploid wheat (ETW, AABB), natural hexaploid wheat (NHW, AABBDD), resynthesized hexaploid wheat (RHW, AABBDD), natural tetraploid wheat (NTW, AABB), and diploid (DD). In the endosperm, levels of DNA methylation, especially in CHG (H=A, T, or C) context, were dramatically decreased in the ETW relative to natural hexaploid wheat; hypo-differentially methylated regions (DMRs) (850,832) were 24-fold more than hyper-DMRs (35,111). Interestingly, those demethylated regions in ETW were remethylated in the resynthesized hexaploid wheat after the addition of the D genome. In ETW, hypo-DMRs correlated with gene expression, and TEs were demethylated and activated, which could be silenced in the hexaploid wheat. In NHW, groups of TEs were dispersed in genic regions of three subgenomes, which may regulate the expression of TE-associated genes. Further, hypo-DMRs in ETW were associated with reduced H3K9me2 levels and increased expression of histone variant genes, suggesting concerted epigenetic changes after separation from the hexaploid. Conclusion Genome merger and separation provoke dynamic and reversible changes in chromatin and DNA methylation. These changes correlate with altered gene expression and TE activity, which may provide insights into polyploid genome and wheat evolution.

scholarly journals Polyploidization enhancing genetic recombination of the ancestral diploid genome in the evolution of hexaploid wheat

2020 ◽  
Author(s):  
Hongshen Wan ◽  
Jun Li ◽  
Shengwei Ma ◽  
Qin Wang ◽  
Xinguo Zhu ◽  
...  
Keyword(s):  
Hexaploid Wheat ◽  
Genetic Recombination ◽  
Aegilops Tauschii ◽  
Tetraploid Wheat ◽  
Synthetic Hexaploid Wheat ◽  
Evolutionary Potential ◽  
D Genome ◽  
Diploid Genome ◽  
Synthetic Hexaploid ◽  
The Impact

AbstractAllopolyploidy increases its evolutionary potential by fixing heterosis and the advantage of gene redundancy. Allelic combinations generated from genetic recombination potentially provide many variations to the selection pools for evolution. May there be any relationship between allopolyploidization and genetic recombination? To study the impact of polyploidy on genetic recombination, we selected wheat as a model and simulated its evolution pathway of allopolyploidy by developing synthetic hexaploid wheat. The change of homologous chromosome recombination were investigated on their diploid DD and tetraploid AABB genomes after their allohexaploidization, respectively. The genetic recombination of the ancestral diploid genome of Aegilops tauschii was enhanced significantly more than 2 folds after their hexaploidization. Hexaploidization enhancing genetic recombination of the ancestral diploid D genome was firstly reported to be a new way to increase evolutionary potential of wheat, which is beneficial for wheat to conquer their narrow origination of D genome, quickly spread and make it a major crop of the world. Finally, re-synthetizing hexaploid wheat using diverse Ae. tauschii species with tetraploid wheat can be considered as a pleiotropic strategy to speed adaptive evolution of bread wheat in breeding processes by increasing both gene allele types and genetic recombination variations.

scholarly journals Histone acetyltransferase TaHAG1 acts as a crucial regulator to strengthen salt tolerance of hexaploid wheat

2021 ◽  
Author(s):  
Mei Zheng ◽  
Jingchen Lin ◽  
Xingbei Liu ◽  
Wei Chu ◽  
Jinpeng Li ◽  
...  
Keyword(s):  
Salt Tolerance ◽  
Bread Wheat ◽  
Hexaploid Wheat ◽  
Histone Acetyltransferase ◽  
Tetraploid Wheat ◽  
Triticum Aestivum L ◽  
Ros Production ◽  
Signal Specificity ◽  
H3 Acetylation

Abstract Polyploidy occurs prevalently and plays an important role during plant speciation and evolution. This phenomenon suggests polyploidy could develop novel features that enable them to adapt wider range of environmental conditions compared with diploid progenitors. Bread wheat (Triticum aestivum L., BBAADD) is a typical allohexaploid species and generally exhibits greater salt tolerance than its tetraploid wheat progenitor (BBAA). However, little is known about the underlying molecular basis and the regulatory pathway of this trait. Here, we show that the histone acetyltransferase TaHAG1 acts as a crucial regulator to strengthen salt tolerance of hexaploid wheat. Salinity-induced TaHAG1 expression was associated with tolerance variation in polyploidy wheat. Overexpression, silencing and CRISPR-mediated knockout of TaHAG1 validated the role of TaHAG1 in salinity tolerance of wheat. TaHAG1 contributed to salt tolerance by modulating ROS production and signal specificity. Moreover, TaHAG1 directly targeted a subset of genes that are responsible for hydrogen peroxide production, and enrichment of TaHAG1 triggered increased H3 acetylation and transcriptional upregulation of these loci under salt stress. In addition, we found the salinity-induced TaHAG1-mediated ROS production pathway is involved in salt tolerance difference of wheat accessions with varying ploidy. Our findings provide insight into the molecular mechanism of how an epigenetic regulatory factor facilitates adaptability of polyploidy wheat and highlights this epigenetic modulator as a strategy for salt tolerance breeding in bread wheat.

scholarly journals Genetic Diversity of Landraces and Improved Varieties of Rice (Oryza sativa L.) in Taiwan

Rice ◽  
2020 ◽  
Vol 13 (1) ◽  
Author(s):  
Ai-ling Hour ◽  
Wei-hsun Hsieh ◽  
Su-huang Chang ◽  
Yong-pei Wu ◽  
Han-shiuan Chin ◽  
...  
Keyword(s):  
Genetic Diversity ◽  
Genetic Variation ◽  
Indigenous Peoples ◽  
Oryza Sativa L ◽  
Crop Improvement ◽  
Genetic Erosion ◽  
Germplasm Conservation ◽  
Gene Pools ◽  
Improved Varieties ◽  
Breeding Goals

Abstract Background Rice, the most important crop in Asia, has been cultivated in Taiwan for more than 5000 years. The landraces preserved by indigenous peoples and brought by immigrants from China hundreds of years ago exhibit large variation in morphology, implying that they comprise rich genetic resources. Breeding goals according to the preferences of farmers, consumers and government policies also alter gene pools and genetic diversity of improved varieties. To unveil how genetic diversity is affected by natural, farmers’, and breeders’ selections is crucial for germplasm conservation and crop improvement. Results A diversity panel of 148 rice accessions, including 47 cultivars and 59 landraces from Taiwan and 42 accessions from other countries, were genotyped by using 75 molecular markers that revealed an average of 12.7 alleles per locus with mean polymorphism information content of 0.72. These accessions could be grouped into five subpopulations corresponding to wild rice, japonica landraces, indica landraces, indica cultivars, and japonica cultivars. The genetic diversity within subpopulations was: wild rices > landraces > cultivars; and indica rice > japonica rice. Despite having less variation among cultivars, japonica landraces had greater genetic variation than indica landraces because the majority of Taiwanese japonica landraces preserved by indigenous peoples were classified as tropical japonica. Two major clusters of indica landraces were formed by phylogenetic analysis, in accordance with immigration from two origins. Genetic erosion had occurred in later japonica varieties due to a narrow selection of germplasm being incorporated into breeding programs for premium grain quality. Genetic differentiation between early and late cultivars was significant in japonica (FST = 0.3751) but not in indica (FST = 0.0045), indicating effects of different breeding goals on modern germplasm. Indigenous landraces with unique intermediate and admixed genetic backgrounds were untapped, representing valuable resources for rice breeding. Conclusions The genetic diversity of improved rice varieties has been substantially shaped by breeding goals, leading to differentiation between indica and japonica cultivars. Taiwanese landraces with different origins possess various and unique genetic backgrounds. Taiwanese rice germplasm provides diverse genetic variation for association mapping to unveil useful genes and is a precious genetic reservoir for rice improvement.

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