A polyploid organism by possessing more than two sets of chromosomes from one species （autopolyploidy） or two or more species （allopolyploidy） is known to have evolutionary advantages. However, by what means a pol...A polyploid organism by possessing more than two sets of chromosomes from one species （autopolyploidy） or two or more species （allopolyploidy） is known to have evolutionary advantages. However, by what means a polyploid accommodates increased genetic dosage or divergent genomes （allopolyploidy） in one cell nucleus and cytoplasm constitutes an enormous challenge. Recent years have witnessed efforts and progress in exploring the possible mechanisms by which these seemingly intangible hurdles of polyploidy may be ameliorated or eventually overcome. In particular, the documentation of rapid and extensive non-Mendelian genetic and epigenetic changes that often accompany nascent polyploidy is revealing： the resulting non-additive and novel gene expression at global, regional and local levels, and timely restoration of meiotic chromosomal behavior towards bivalent pairing and disomic inheritance may ensure rapid establishment and stabilization as well as its long-term evolutionary success. Further elucidation on these novel mechanisms underpinning polyploidy will promote our understanding on fundamental issues in evolutionary biology and in our manipulation capacities in future genetic improvement of important crops that are currently polyploids in genomic constitution. This review is intended to provide an updated discussion on these interesting and important issues within the scope of a specific yet one of the most important plant groups--polyploid wheat and its related species.展开更多
The introduction of alien genes or chromosome fragments from wild related species into wheat （Triticum spp.） has been considered valuable for wheat breeding （Valkoun, 2001）. Several relatives, such as Secale cerea...The introduction of alien genes or chromosome fragments from wild related species into wheat （Triticum spp.） has been considered valuable for wheat breeding （Valkoun, 2001）. Several relatives, such as Secale cereale （Gupta and Shepherd, 1993; Ma et al., 2000）, Thinopyrum elongatum （Liu et al., 2008）, Th. intermedium （Cao et al., 2014） and Th. ponticum （Li et al., 2008） showed distinct applications of introgression of interesting genes or traits into wheat. However, there are still some challenges in using these genetic resources. The introgressed alien fragments often bring genes with potentially negative impacts on the traits. In this letter, we mainly focus on multi-strategies for synthesis of polyploids between wheat and rye, Th. elongatum, Th. intermedium and Th. ponticum. We have successfully selected different novel ploidy triticale and trititrigia lines which carried excellent disease-resistance genes and could provide essential genetic resources for wheat breeding.展开更多
In most eukaryotic species, three basic steps of pairing, recombination and synapsis occur during prophase of meiosis I. Homologous chromosomal pairing and recombination are essential for accurate segregation of chrom...In most eukaryotic species, three basic steps of pairing, recombination and synapsis occur during prophase of meiosis I. Homologous chromosomal pairing and recombination are essential for accurate segregation of chromosomes. In contrast to the well-studied processes such as recombination and synapsis, many aspects of chromosome pairing are still obscure. Recent progress in several species indicates that the telomere bouquet formation can facilitate homologous chromosome pairing by bringing chromosome ends into close proximity, but the sole presence of telomere clustering is not sufficient for recognizing homologous pairs. On the other hand, accurate segregation of the genetic material from parent to offspring during meiosis is dependent on the segregation of homologs in the reductional meiotic division （MI） with sister kinetochores exhibiting mono-orientation from the same pole, and the segregation of sister chromatids during the equational meiotic division （MII） with kinetochores showing bi-orientation from the two poles. The underlying mechanism of orientation and segregation is still unclear. Here we focus on recent studies in plants and other species that provide insight into how chromosomes find their partners and mechanisms mediating chromosomal segregation.展开更多
Thinopyrum elongatum （2n = 2x = 14, EE）, a wild relative of wheat, has been suggested as a potentially novel source of resistance to several major wheat diseases including Fusarium Head Blight （FHB）. In this study...Thinopyrum elongatum （2n = 2x = 14, EE）, a wild relative of wheat, has been suggested as a potentially novel source of resistance to several major wheat diseases including Fusarium Head Blight （FHB）. In this study, a series of wheat （cv. Chinese Spring, CS） substitution and ditelosomic lines, including Th. elongatum additions, were assessed for Type II resistance to FHB. Results indicated that the lines containing chromosome 7E of Th. elongatum gave a high level of resistance to FHB, wherein the infection did not spread beyond the inoculated floret. Furthermore, it was determined that the novel resistance gene（s） of 7E was located on the short-ann （7ES） based on sharp difference in FHB resistance between the two 7E ditelosomic lines for each arm. On the other hand, Th. elongatum chromosomes 5E and 6E likely contain gene（s） for susceptibility to FHB because the disease spreads rapidly within the inoculated spikes of these lines. Genomic in situ hybridization （GISH） analysis revealed that the alien chromosomes in the addition and substitution lines were intact, and the lines did not contain discernible genomic aberrations. GISH and multicolor-GISH analyses were further performed on three trans- location lines that also showed high levels of resistance to FHB. Lines TA3499 and TA3695 were shown to contain one pair of wheat-Th. elongatum translocated chromosomes involving fragments of 7D plus a segment of the 7E, while line TA3493 was found to contain one pair of wheat-Th, elongatum translocated chromosomes involving the D- and A-genome chromosomes of wheat. Thus, this study has established that the short-arm of chromosome 7E of Th. elongatum harbors gene（s） highly resistant to the spreading of FHB, and chromatin of 7E introgressed into wheat chromosomes largely retained the resistance, implicating the feasibility of using these lines as novel material for breeding FHB-resistant wheat cultivars.展开更多
CRISPR （clustered regularly interspaced short palindromic repeats）/Cas9 system, which is a newly developed technology for targeted genome modification, has been successfully used in a number of species. In this stud...CRISPR （clustered regularly interspaced short palindromic repeats）/Cas9 system, which is a newly developed technology for targeted genome modification, has been successfully used in a number of species. In this study, we applied this technology to carry out targeted genome modification in maize. A marker gene Zmzb7 was chosen for targeting. The sgRNA-Cas9 construct was transformed into maize protoplasts, and indel （insertion and deletion） mutations could be detected. A mutant seedling with an expected albino phenotype was obtained from screening 120 seedlings generated from 10 callus events. Mutation efficiency in maize heterochromatic regions was also investigated. Twelve sites with different expression levels in maize centromeres or pericentromere regions were selected. The sgRNA- Cas9 constructs were transformed into protoplasts followed by sequencmg the transformed protoplast genomic DNA. The results show that the genes in heterochromatic regions could be targeted by the CRISPR/Cas9 system efficiently, no matter whether they are expressed or not. Meanwhile, off-target mutations were not found in the similar sites having no PAM （protospacer adjacent motif） or having more than two mismatches. Together. our results show that the CRISPR/Cas9 system is a robust and efficient tool for genome modification in both euchromatic and heterochromatic regions in maize.展开更多
Partial amphiploids created by crossing common wheat （Triticum aestivum L.） and Thinopyrum ponticum （Podp.） Barkworth ＆ D. R. Dewey are important intermediates in wheat breeding because of their resistance to maj...Partial amphiploids created by crossing common wheat （Triticum aestivum L.） and Thinopyrum ponticum （Podp.） Barkworth ＆ D. R. Dewey are important intermediates in wheat breeding because of their resistance to major wheat diseases. In this study, we examined the chromosome compositions of five Xiaoyan-series wheat-Th, ponticum partial amphiploids （Xiaoyan 68, Xiaoyan 693, Xiaoyan 784, Xiaoyan 7430, and Xiaoyan 7631） using GISH, multicolor-GISH, and multicolor-FISH. We found several chromosome changes in these lines. For example, wheat chromosomes 1B and 2B were added in Xiaoyan 68 and Xiaoyan 7430, respectively, while wheat chromosome 6B was eliminated from Xiaoyan 693 and Xiaoyan 7631. Chromosome rearrangements were also detected in these amphiploids, including an interspecific translocation involving chromosome 4D and some intergenomic translocations, such as A--B and A--D translocations, among wheat genomes. Analysis of the Th. ponticum chromosomes in the amphiploids showed that some lines shared the same alien chromosomes. We also evaluated these partial amphiploids for resistance to nine races of stem rust, including TTKSK （commonly known as Ug99）. Three lines, Xiaoyan 68, Xiaoyan 784, and Xiaoyan 7430, exhibited excellent resistance to all nine races, and could therefore be valuable sources of stem rust resistance in wheat breeding.展开更多
Plant centromeres are generally composed of tandem arrays of simple repeats that form a complex chromosome locus where the kinetochore forms and microtubules attach during mitosis and meiosis. Each chromosome has one ...Plant centromeres are generally composed of tandem arrays of simple repeats that form a complex chromosome locus where the kinetochore forms and microtubules attach during mitosis and meiosis. Each chromosome has one centromere region, which is essential for accurate division of the genetic material. Recently, chromosomes containing two centromere regions （called dicentric chromosomes） have been found in maize and wheat. Interestingly, some dicentric chromosomes are stable because only one centromere is active and the other one is inactivated. Because such arrays maintain their typical structure for both active and inactive centromeres, the specification of centromere activity has an epigenetic component independent of the DNA sequence. Under some circumstances, the inactive centromeres may recover centromere function, which is called centromere reactivation. Recent studies have highlighted the important changes, such as DNA methylation and histone modification, that occur during centromere inactivation and reactivation.展开更多
Wheat-rye addition and substitution lines and their self progenies revealed variations in telomeric heterochromatin and centromeres, Furthermore, a mitotically unstable dicentric chromosome and stable multicentric chr...Wheat-rye addition and substitution lines and their self progenies revealed variations in telomeric heterochromatin and centromeres, Furthermore, a mitotically unstable dicentric chromosome and stable multicentric chromosomes were observed in the progeny of a Chinese Spring-lmperial rye 3R addition line. An unstable multicentric chromosome was found in the progeny of a 6R/6D substitution line. Drastic variation of terminal heterochromatin including movement and disappearance of terminal heterochromatin occurred in the progeny of wheat- rye addition line 3R, and the 5RS ditelosomic addition line. Highly stable minichromosomes were observed in the progeny ofa monosomic 4R addition line, a ditelosomic 5RS addition line and a 6R/6D substitution line. Minichromosomes, with and without the FISH signals for telomeric DNA （TTTAGGG）n, derived from a monosomic 4R addition line are stable and transmissible to the next generation. The results indicated that centromeres and terminal heterochromatin can be profoundly altered in wheat-rye hybrid derivatives.展开更多
Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici, is one of the most widely distributed and destructive fungal diseases worldwide. Since 1995, most Chinese wheat cultivars have lost their stripe rust r...Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici, is one of the most widely distributed and destructive fungal diseases worldwide. Since 1995, most Chinese wheat cultivars have lost their stripe rust resistance due to the subsequent emergence of the new races CYR30, CYR31, CYR32, and CYR33 （Han et al., 2010）. Therefore, it is necessary to seek effective resistance genes and develop new resistance germ- plasm for wheat resistance breeding.展开更多
The centromere is an essential chromosome site at which the kinetochore forms and loads proteins needed for faithful segregation during the cell cycle and meiosis（Houben et al., 1999;Cleveland et al.,2003;Ma et al.,2...The centromere is an essential chromosome site at which the kinetochore forms and loads proteins needed for faithful segregation during the cell cycle and meiosis（Houben et al., 1999;Cleveland et al.,2003;Ma et al.,2007;Birchler and Han,2009）.Centromere specific sequences such as tandem repeats or transposable elements evolve quickly both within and between the species but have conserved kinetochore proteins（Henikoff and Furuyama,2010）.展开更多
Durum wheat(Triticum durum Desf.,2n=28,AABB),which is mainly used to make pasta,is the second cultivated wheat variety worldwide.However,the durum wheat production is severely affected by a number of diseases,such as ...Durum wheat(Triticum durum Desf.,2n=28,AABB),which is mainly used to make pasta,is the second cultivated wheat variety worldwide.However,the durum wheat production is severely affected by a number of diseases,such as Fusarium head blight(FHB)and stem rust(Klindworth et al.,2017;Zhao et al.,2018).Thinopyrum elongatum(2n=4x=28),a close relative of wheat.展开更多
Recently, engineered minichromosomes have been produced using a telomere-mediated truncation technique in some plants. However, the study on transferring genes to minichromosomes is very limited.Here, telomere-mediate...Recently, engineered minichromosomes have been produced using a telomere-mediated truncation technique in some plants. However, the study on transferring genes to minichromosomes is very limited.Here, telomere-mediated truncation was successfully performed in common wheat（Triticum aestivum）to generate stable truncated chromosomes accompanied by a relatively high frequency of chromosomal rearrangements. After the cross between transgenic parents, a promoter-less DsRed gene in a chromosome from one parent was transferred to another chromosome from the other parent at the site behind a maize ubiquitin promoter via the Cre/lox system. DsRed transcripts and red fluorescent proteins were detected in the recombinant plants. In one such seedling, transgenic signals were detected at the centric terminus of chromosome 4D and the distal terminus of chromosome 3A. Clear translocations could be detected at the transgenic loci of these two chromosomes. Intriguingly, signals of centric-specific sequences were co-localized with the translocated D-group chromosomal segment in the terminal region of chromosome 3A. Our results indicate that the Cre/lox system induces the gene swapping to the target chromosome and non-homologous chromosomal recombination simultaneously. These approaches could offer a platform to transfer large DNA fragments or even terminal chromosomal segments to other chromosomes of the natural genome.展开更多
The Triticum-Aegilops complex groups demonstrated high cross-affinity with each other to overcome the barriers of distant hybridization(Loureiro et al.,2023).Distant hybridization involves two distinct yet closely rel...The Triticum-Aegilops complex groups demonstrated high cross-affinity with each other to overcome the barriers of distant hybridization(Loureiro et al.,2023).Distant hybridization involves two distinct yet closely related events:hybridization and genome doubling.Previous studies have indicated that bursts of transposable elements(TEs)can occur as a consequence or concomitant to hybridization or genome duplication(Parisod et al.,2010).This raises an important scientific question regarding how the TEs-rich centromere region copes with genomic shock(McClintock,1984).The Triticum-Aegilops species complexes,particularly in the F1,So,and subsequent early generations resulting from successive selfcrossing,offer an opportunity to investigate whether the centromere environment undergoes reconstruction and the associated mechanisms that maintain genomic stability.展开更多
Dear Editor,Legumes,including soybean and alfalfa,are vital agricultural crops worldwide,providing high-quality protein and oil sources for humans and animals.In addition,legumes also provide nitrogen for soil improve...Dear Editor,Legumes,including soybean and alfalfa,are vital agricultural crops worldwide,providing high-quality protein and oil sources for humans and animals.In addition,legumes also provide nitrogen for soil improvement,benefiting from their symbiotic associations with nitrogen-fixing bacteria.展开更多
Dear Editor,The 1RS-1BL translocation chromosome,carrying the stripe rust resistance gene Yr9,has shaped global wheat breeding for half a century.The 1RS-1BL translocation chromosome,derived from the exchange between ...Dear Editor,The 1RS-1BL translocation chromosome,carrying the stripe rust resistance gene Yr9,has shaped global wheat breeding for half a century.The 1RS-1BL translocation chromosome,derived from the exchange between rye and wheat chromosomes,not only introduced Yr9into wheat but also incorporated Sr31,Lr26,and Pm8,thereby forming a robust arsenal of disease-resistance genes(Mago et al.,2005).In China,the 1RS-1BL cultivars like "Aimengniu", "Lovrin 10".展开更多
Bread wheat(Triticum aestivum L.)is a major crop that feeds 40%of the world’s population.Over the past several decades,advances in genomics have led to tremendous achievements in understanding the origin and domestic...Bread wheat(Triticum aestivum L.)is a major crop that feeds 40%of the world’s population.Over the past several decades,advances in genomics have led to tremendous achievements in understanding the origin and domestication of wheat,and the genetic basis of agronomically important traits,which promote the breeding of elite varieties.In this review,we focus on progress that has been made in genomic research and genetic improvement of traits such as grain yield,end-use traits,flowering regulation,nutrient use efficiency,and biotic and abiotic stress responses,and various breeding strategies that contributed mainly by Chinese scientists.Functional genomic research in wheat is entering a new era with the availability of multiple reference wheat genome assemblies and the development of cutting-edge technologies such as precise genome editing tools,highthroughput phenotyping platforms,sequencing-based cloning strategies,high-efficiency genetic transformation systems,and speed-breeding facilities.These insights will further extend our understanding of the molecular mechanisms and regulatory networks underlying agronomic traits and facilitate the breeding process,ultimately contributing to more sustainable agriculture in China and throughout the world.展开更多
Meiosis is a specialized eukaryotic cell division, in which diploid cells undergo a single round of DNA replication and two rounds of nuclear division to produce haploid gametes. In most eukaryotes, the core events of...Meiosis is a specialized eukaryotic cell division, in which diploid cells undergo a single round of DNA replication and two rounds of nuclear division to produce haploid gametes. In most eukaryotes, the core events of meiotic prophase I are chromosomal pairing,synapsis and recombination. To ensure accurate chromosomal segregation, homologs have to identify and align along each other at the onset of meiosis. Although much progress has been made in elucidating meiotic processes, information on the mechanisms underlying chromosome pairing is limited in contrast to the meiotic recombination and synapsis events. Recent research in many organisms indicated that centromere interactions during early meiotic prophase facilitate homologous chromosome pairing, and functional centromere is a prerequisite for centromere pairing such as in maize. Here, we summarize the recent achievements of chromosome pairing research on plants and other organisms, and outline centromere interactions, nuclear chromosome orientation,and meiotic cohesin, as main determinants of chromosome pairing in early meiotic prophase.展开更多
The 7B chromosome of common wheat was microdissected from pollen mother cells of the 7B monosomic line of common wheat cv. Chinese Spring (CS). After proteinase K and DNA topoisomerase Ⅰtreatments, the isolated chrom...The 7B chromosome of common wheat was microdissected from pollen mother cells of the 7B monosomic line of common wheat cv. Chinese Spring (CS). After proteinase K and DNA topoisomerase Ⅰtreatments, the isolated chromosomes were subjected to 1—3 rounds of DOPPCR amplification, which produced continuous DNA fragments ranging from 150 to 700 bp. Genomic Southern hybridization confirmed that the PCR products were originated from the wheat genome. Cloning of portion ( 】 200 bp) of the 3rd round DOP-PCR products (50 μL) could generate about 20 000 recombinant clones. Characterization of 50 randomly chosen clones indicated that 21 clones produced discrete PCR products with the size of 240—600 bp. Dot-blot hybridization showed that among the 21 clones, 11 (～ 55%) were of low-copy nature while 10 (～45%) were repetitive. Southern hybridization with the complete set of the CS 'nullisomic-tetrasomic (NT)' lines demonstrated that all the 6 low-copy clones were specific to either chromosome 7B or the 7th展开更多
Centromeres play a vital role in cellular division by facilitating kinetochore assembly and spindle attachments.Despite their conserved functionality,centromeric DNA sequences exhibit rapid evolution,presenting divers...Centromeres play a vital role in cellular division by facilitating kinetochore assembly and spindle attachments.Despite their conserved functionality,centromeric DNA sequences exhibit rapid evolution,presenting diverse sizes and compositions across species.The functional significance of rye centromeric DNA sequences,particularly in centromere identity,remains unclear.In this study,we comprehensively characterized the sequence composition and organization of rye centromeres.Our findings revealed that these centromeres are primarily composed of long terminal repeat retrotransposons(LTR-RTs)and interspersed minisatellites.We systematically classified LTR-RTs into five categories,highlighting the prevalence of younger CRS1,CRS2,and CRS3 of CRSs(centromeric retrotransposons of Secale cereale)were primarily located in the core centromeres and exhibited a higher association with CENH3 nucleosomes.The minisatellites,mainly derived from retrotransposons,along with CRSs,played a pivotal role in establishing functional centromeres in rye.Additionally,we observed the formation of R-loops at specific regions of CRS1,CRS2,and CRS3,with both rye pericentromeres and centromeres exhibiting enrichment in R-loops.Notably,these R-loops selectively formed at binding regions of the CENH3 nucleosome in rye centromeres,suggesting a potential role in mediating the precise loading of CENH3 to centromeres and contributing to centromere specification.Our work provides insights into the DNA sequence composition,distribution,and potential function of R-loops in rye centromeres.This knowledge contributes valuable information to understanding the genetics and epigenetics of rye centromeres,offering implications for the development of synthetic centromeres in future plant modifications and beyond.展开更多
Non-B-form DNA differs from the classic B-DNA double helix structure and plays a crucial regulatory role in replication and transcription.However,the role of non-B-form DNA in centromeres,especially in polyploid wheat...Non-B-form DNA differs from the classic B-DNA double helix structure and plays a crucial regulatory role in replication and transcription.However,the role of non-B-form DNA in centromeres,especially in polyploid wheat,remains elusive.Here,we systematically analyzed seven non-B-form DNA motif profiles(A-phased DNA repeat,direct repeat,G-quadruplex,inverted repeat,mirror repeat,short tandem repeat,and Z-DNA)in hexaploid wheat.We found that three of these non-B-form DNA motifs were enriched at centromeric regions,especially at the CENH3-binding sites,suggesting that non-B-form DNA may create a favorable loading environment for the CENH3 nucleosome.To investigate the dynamics of centromeric non-B form DNA during the alloploidization process,we analyzed DNA secondary structure using CENH3 ChIP-seq data from newly formed allotetraploid wheat and its two diploid ancestors.We found that newly formed allotetraploid wheat formed more non-B-form DNA in centromeric regions compared with their parents,suggesting that non-B-form DNA is related to the localization of the centromeric regions in newly formed wheat.Furthermore,non-B-form DNA enriched in the centromeric regions was found to preferentially form on young LTR retrotransposons,explaining CENH3's tendency to bind to younger LTR.Collectively,our study describes the landscape of non-B-form DNA in the wheat genome,and sheds light on its potential role in the evolution of polyploid centromeres.展开更多
基金supported by the Program for Changjiang Scholars and Innovative Research Team (PCSIRT) in University in China (No. IRT0519)the National Natural Science Foundation of China (No. 30430060)
文摘A polyploid organism by possessing more than two sets of chromosomes from one species （autopolyploidy） or two or more species （allopolyploidy） is known to have evolutionary advantages. However, by what means a polyploid accommodates increased genetic dosage or divergent genomes （allopolyploidy） in one cell nucleus and cytoplasm constitutes an enormous challenge. Recent years have witnessed efforts and progress in exploring the possible mechanisms by which these seemingly intangible hurdles of polyploidy may be ameliorated or eventually overcome. In particular, the documentation of rapid and extensive non-Mendelian genetic and epigenetic changes that often accompany nascent polyploidy is revealing： the resulting non-additive and novel gene expression at global, regional and local levels, and timely restoration of meiotic chromosomal behavior towards bivalent pairing and disomic inheritance may ensure rapid establishment and stabilization as well as its long-term evolutionary success. Further elucidation on these novel mechanisms underpinning polyploidy will promote our understanding on fundamental issues in evolutionary biology and in our manipulation capacities in future genetic improvement of important crops that are currently polyploids in genomic constitution. This review is intended to provide an updated discussion on these interesting and important issues within the scope of a specific yet one of the most important plant groups--polyploid wheat and its related species.
基金supported by the National High Technology Research and Development Program of China (No. 2010AA100101)
文摘The introduction of alien genes or chromosome fragments from wild related species into wheat （Triticum spp.） has been considered valuable for wheat breeding （Valkoun, 2001）. Several relatives, such as Secale cereale （Gupta and Shepherd, 1993; Ma et al., 2000）, Thinopyrum elongatum （Liu et al., 2008）, Th. intermedium （Cao et al., 2014） and Th. ponticum （Li et al., 2008） showed distinct applications of introgression of interesting genes or traits into wheat. However, there are still some challenges in using these genetic resources. The introgressed alien fragments often bring genes with potentially negative impacts on the traits. In this letter, we mainly focus on multi-strategies for synthesis of polyploids between wheat and rye, Th. elongatum, Th. intermedium and Th. ponticum. We have successfully selected different novel ploidy triticale and trititrigia lines which carried excellent disease-resistance genes and could provide essential genetic resources for wheat breeding.
基金supported by the National Basic Research Program of China(973 Program)(Grant No.2011CB944601)the National Natural Science Foundation of China(Grant No.31320103912)USA National Science Foundation(Grant No.DBI 0922703)
文摘In most eukaryotic species, three basic steps of pairing, recombination and synapsis occur during prophase of meiosis I. Homologous chromosomal pairing and recombination are essential for accurate segregation of chromosomes. In contrast to the well-studied processes such as recombination and synapsis, many aspects of chromosome pairing are still obscure. Recent progress in several species indicates that the telomere bouquet formation can facilitate homologous chromosome pairing by bringing chromosome ends into close proximity, but the sole presence of telomere clustering is not sufficient for recognizing homologous pairs. On the other hand, accurate segregation of the genetic material from parent to offspring during meiosis is dependent on the segregation of homologs in the reductional meiotic division （MI） with sister kinetochores exhibiting mono-orientation from the same pole, and the segregation of sister chromatids during the equational meiotic division （MII） with kinetochores showing bi-orientation from the two poles. The underlying mechanism of orientation and segregation is still unclear. Here we focus on recent studies in plants and other species that provide insight into how chromosomes find their partners and mechanisms mediating chromosomal segregation.
基金supported by the grant of the National High Technology Research and Development Program("863"Program)of China(No.2011AA100101)
文摘Thinopyrum elongatum （2n = 2x = 14, EE）, a wild relative of wheat, has been suggested as a potentially novel source of resistance to several major wheat diseases including Fusarium Head Blight （FHB）. In this study, a series of wheat （cv. Chinese Spring, CS） substitution and ditelosomic lines, including Th. elongatum additions, were assessed for Type II resistance to FHB. Results indicated that the lines containing chromosome 7E of Th. elongatum gave a high level of resistance to FHB, wherein the infection did not spread beyond the inoculated floret. Furthermore, it was determined that the novel resistance gene（s） of 7E was located on the short-ann （7ES） based on sharp difference in FHB resistance between the two 7E ditelosomic lines for each arm. On the other hand, Th. elongatum chromosomes 5E and 6E likely contain gene（s） for susceptibility to FHB because the disease spreads rapidly within the inoculated spikes of these lines. Genomic in situ hybridization （GISH） analysis revealed that the alien chromosomes in the addition and substitution lines were intact, and the lines did not contain discernible genomic aberrations. GISH and multicolor-GISH analyses were further performed on three trans- location lines that also showed high levels of resistance to FHB. Lines TA3499 and TA3695 were shown to contain one pair of wheat-Th. elongatum translocated chromosomes involving fragments of 7D plus a segment of the 7E, while line TA3493 was found to contain one pair of wheat-Th, elongatum translocated chromosomes involving the D- and A-genome chromosomes of wheat. Thus, this study has established that the short-arm of chromosome 7E of Th. elongatum harbors gene（s） highly resistant to the spreading of FHB, and chromatin of 7E introgressed into wheat chromosomes largely retained the resistance, implicating the feasibility of using these lines as novel material for breeding FHB-resistant wheat cultivars.
基金supported by the National Natural Science Foundation of China(No.31320103912)
文摘CRISPR （clustered regularly interspaced short palindromic repeats）/Cas9 system, which is a newly developed technology for targeted genome modification, has been successfully used in a number of species. In this study, we applied this technology to carry out targeted genome modification in maize. A marker gene Zmzb7 was chosen for targeting. The sgRNA-Cas9 construct was transformed into maize protoplasts, and indel （insertion and deletion） mutations could be detected. A mutant seedling with an expected albino phenotype was obtained from screening 120 seedlings generated from 10 callus events. Mutation efficiency in maize heterochromatic regions was also investigated. Twelve sites with different expression levels in maize centromeres or pericentromere regions were selected. The sgRNA- Cas9 constructs were transformed into protoplasts followed by sequencmg the transformed protoplast genomic DNA. The results show that the genes in heterochromatic regions could be targeted by the CRISPR/Cas9 system efficiently, no matter whether they are expressed or not. Meanwhile, off-target mutations were not found in the similar sites having no PAM （protospacer adjacent motif） or having more than two mismatches. Together. our results show that the CRISPR/Cas9 system is a robust and efficient tool for genome modification in both euchromatic and heterochromatic regions in maize.
基金supported by the grants from the National Natural Science Foundation of China(No.31171539)the National High-Tech Research and Development Program of China(No.2011AA1001)the National Key Technology R&D Program of China(No.2013BAD05B01)
文摘Partial amphiploids created by crossing common wheat （Triticum aestivum L.） and Thinopyrum ponticum （Podp.） Barkworth ＆ D. R. Dewey are important intermediates in wheat breeding because of their resistance to major wheat diseases. In this study, we examined the chromosome compositions of five Xiaoyan-series wheat-Th, ponticum partial amphiploids （Xiaoyan 68, Xiaoyan 693, Xiaoyan 784, Xiaoyan 7430, and Xiaoyan 7631） using GISH, multicolor-GISH, and multicolor-FISH. We found several chromosome changes in these lines. For example, wheat chromosomes 1B and 2B were added in Xiaoyan 68 and Xiaoyan 7430, respectively, while wheat chromosome 6B was eliminated from Xiaoyan 693 and Xiaoyan 7631. Chromosome rearrangements were also detected in these amphiploids, including an interspecific translocation involving chromosome 4D and some intergenomic translocations, such as A--B and A--D translocations, among wheat genomes. Analysis of the Th. ponticum chromosomes in the amphiploids showed that some lines shared the same alien chromosomes. We also evaluated these partial amphiploids for resistance to nine races of stem rust, including TTKSK （commonly known as Ug99）. Three lines, Xiaoyan 68, Xiaoyan 784, and Xiaoyan 7430, exhibited excellent resistance to all nine races, and could therefore be valuable sources of stem rust resistance in wheat breeding.
基金supported by the grants from the National Natural Science Foundation of China (Nos.31071083 and 31130033)the National Science Foundation of USA (No.DBI 0922703)
文摘Plant centromeres are generally composed of tandem arrays of simple repeats that form a complex chromosome locus where the kinetochore forms and microtubules attach during mitosis and meiosis. Each chromosome has one centromere region, which is essential for accurate division of the genetic material. Recently, chromosomes containing two centromere regions （called dicentric chromosomes） have been found in maize and wheat. Interestingly, some dicentric chromosomes are stable because only one centromere is active and the other one is inactivated. Because such arrays maintain their typical structure for both active and inactive centromeres, the specification of centromere activity has an epigenetic component independent of the DNA sequence. Under some circumstances, the inactive centromeres may recover centromere function, which is called centromere reactivation. Recent studies have highlighted the important changes, such as DNA methylation and histone modification, that occur during centromere inactivation and reactivation.
基金supported by the grants of the National High Technology Research and Development Program("863"Program) of China(No.2011AA100101)the Special Financial Grant from the China Postdoctoral Science Foundation (No.2012T50157),and 2011 Collaborative Innovation Plan of the Ministry Of Education of China
文摘Wheat-rye addition and substitution lines and their self progenies revealed variations in telomeric heterochromatin and centromeres, Furthermore, a mitotically unstable dicentric chromosome and stable multicentric chromosomes were observed in the progeny of a Chinese Spring-lmperial rye 3R addition line. An unstable multicentric chromosome was found in the progeny of a 6R/6D substitution line. Drastic variation of terminal heterochromatin including movement and disappearance of terminal heterochromatin occurred in the progeny of wheat- rye addition line 3R, and the 5RS ditelosomic addition line. Highly stable minichromosomes were observed in the progeny ofa monosomic 4R addition line, a ditelosomic 5RS addition line and a 6R/6D substitution line. Minichromosomes, with and without the FISH signals for telomeric DNA （TTTAGGG）n, derived from a monosomic 4R addition line are stable and transmissible to the next generation. The results indicated that centromeres and terminal heterochromatin can be profoundly altered in wheat-rye hybrid derivatives.
基金supported by the grants from the National High Technology Research and Development Program of China (No. 2011AA100102)the Chinese Academy of Sciences (No. KSCX2-EW-N-02)
文摘Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici, is one of the most widely distributed and destructive fungal diseases worldwide. Since 1995, most Chinese wheat cultivars have lost their stripe rust resistance due to the subsequent emergence of the new races CYR30, CYR31, CYR32, and CYR33 （Han et al., 2010）. Therefore, it is necessary to seek effective resistance genes and develop new resistance germ- plasm for wheat resistance breeding.
文摘The centromere is an essential chromosome site at which the kinetochore forms and loads proteins needed for faithful segregation during the cell cycle and meiosis（Houben et al., 1999;Cleveland et al.,2003;Ma et al.,2007;Birchler and Han,2009）.Centromere specific sequences such as tandem repeats or transposable elements evolve quickly both within and between the species but have conserved kinetochore proteins（Henikoff and Furuyama,2010）.
基金supported by the’Strategic Priority Research Program’of the Chinese Academy of Sciences(XDA08010204)the National Key Research and Development Program of China(2016YFD0102001).
文摘Durum wheat(Triticum durum Desf.,2n=28,AABB),which is mainly used to make pasta,is the second cultivated wheat variety worldwide.However,the durum wheat production is severely affected by a number of diseases,such as Fusarium head blight(FHB)and stem rust(Klindworth et al.,2017;Zhao et al.,2018).Thinopyrum elongatum(2n=4x=28),a close relative of wheat.
基金supported by the National Key Research and Development Program of China(2016YFD0102003)the Ministry of Science and Technology(MOST)Project(2016ZX08010002 and 2014ZX0801006B)
文摘Recently, engineered minichromosomes have been produced using a telomere-mediated truncation technique in some plants. However, the study on transferring genes to minichromosomes is very limited.Here, telomere-mediated truncation was successfully performed in common wheat（Triticum aestivum）to generate stable truncated chromosomes accompanied by a relatively high frequency of chromosomal rearrangements. After the cross between transgenic parents, a promoter-less DsRed gene in a chromosome from one parent was transferred to another chromosome from the other parent at the site behind a maize ubiquitin promoter via the Cre/lox system. DsRed transcripts and red fluorescent proteins were detected in the recombinant plants. In one such seedling, transgenic signals were detected at the centric terminus of chromosome 4D and the distal terminus of chromosome 3A. Clear translocations could be detected at the transgenic loci of these two chromosomes. Intriguingly, signals of centric-specific sequences were co-localized with the translocated D-group chromosomal segment in the terminal region of chromosome 3A. Our results indicate that the Cre/lox system induces the gene swapping to the target chromosome and non-homologous chromosomal recombination simultaneously. These approaches could offer a platform to transfer large DNA fragments or even terminal chromosomal segments to other chromosomes of the natural genome.
基金the National Natural Science Foundation of China(31991212)the National Key Research and Development Program of China(2022YFF1003303).
文摘The Triticum-Aegilops complex groups demonstrated high cross-affinity with each other to overcome the barriers of distant hybridization(Loureiro et al.,2023).Distant hybridization involves two distinct yet closely related events:hybridization and genome doubling.Previous studies have indicated that bursts of transposable elements(TEs)can occur as a consequence or concomitant to hybridization or genome duplication(Parisod et al.,2010).This raises an important scientific question regarding how the TEs-rich centromere region copes with genomic shock(McClintock,1984).The Triticum-Aegilops species complexes,particularly in the F1,So,and subsequent early generations resulting from successive selfcrossing,offer an opportunity to investigate whether the centromere environment undergoes reconstruction and the associated mechanisms that maintain genomic stability.
基金supported by grants from the Biological Breeding-National Science and Technology Major Project(2024ZD04079)the National Natural Science Foundation of China(32370261).
文摘Dear Editor,Legumes,including soybean and alfalfa,are vital agricultural crops worldwide,providing high-quality protein and oil sources for humans and animals.In addition,legumes also provide nitrogen for soil improvement,benefiting from their symbiotic associations with nitrogen-fixing bacteria.
基金supported by the National Natural Science Foundation of China (NSFC31991212)the National Key Research and Development Program of China (2022YFF1003303)。
文摘Dear Editor,The 1RS-1BL translocation chromosome,carrying the stripe rust resistance gene Yr9,has shaped global wheat breeding for half a century.The 1RS-1BL translocation chromosome,derived from the exchange between rye and wheat chromosomes,not only introduced Yr9into wheat but also incorporated Sr31,Lr26,and Pm8,thereby forming a robust arsenal of disease-resistance genes(Mago et al.,2005).In China,the 1RS-1BL cultivars like "Aimengniu", "Lovrin 10".
基金This work was supported by the National Natural Science Foundation of China(31788103,31970529,32125030,31921005,31961143013,32072660)the Key Research and Development Program of Ministry of Science and Technology of China(2021YFF1000200)the Strategic Priority Research Program of Chinese Academy of Sciences(XDA24010202).
文摘Bread wheat(Triticum aestivum L.)is a major crop that feeds 40%of the world’s population.Over the past several decades,advances in genomics have led to tremendous achievements in understanding the origin and domestication of wheat,and the genetic basis of agronomically important traits,which promote the breeding of elite varieties.In this review,we focus on progress that has been made in genomic research and genetic improvement of traits such as grain yield,end-use traits,flowering regulation,nutrient use efficiency,and biotic and abiotic stress responses,and various breeding strategies that contributed mainly by Chinese scientists.Functional genomic research in wheat is entering a new era with the availability of multiple reference wheat genome assemblies and the development of cutting-edge technologies such as precise genome editing tools,highthroughput phenotyping platforms,sequencing-based cloning strategies,high-efficiency genetic transformation systems,and speed-breeding facilities.These insights will further extend our understanding of the molecular mechanisms and regulatory networks underlying agronomic traits and facilitate the breeding process,ultimately contributing to more sustainable agriculture in China and throughout the world.
基金supported by the National Natural Science Foundation of China(31600994.31630049)
文摘Meiosis is a specialized eukaryotic cell division, in which diploid cells undergo a single round of DNA replication and two rounds of nuclear division to produce haploid gametes. In most eukaryotes, the core events of meiotic prophase I are chromosomal pairing,synapsis and recombination. To ensure accurate chromosomal segregation, homologs have to identify and align along each other at the onset of meiosis. Although much progress has been made in elucidating meiotic processes, information on the mechanisms underlying chromosome pairing is limited in contrast to the meiotic recombination and synapsis events. Recent research in many organisms indicated that centromere interactions during early meiotic prophase facilitate homologous chromosome pairing, and functional centromere is a prerequisite for centromere pairing such as in maize. Here, we summarize the recent achievements of chromosome pairing research on plants and other organisms, and outline centromere interactions, nuclear chromosome orientation,and meiotic cohesin, as main determinants of chromosome pairing in early meiotic prophase.
文摘The 7B chromosome of common wheat was microdissected from pollen mother cells of the 7B monosomic line of common wheat cv. Chinese Spring (CS). After proteinase K and DNA topoisomerase Ⅰtreatments, the isolated chromosomes were subjected to 1—3 rounds of DOPPCR amplification, which produced continuous DNA fragments ranging from 150 to 700 bp. Genomic Southern hybridization confirmed that the PCR products were originated from the wheat genome. Cloning of portion ( 】 200 bp) of the 3rd round DOP-PCR products (50 μL) could generate about 20 000 recombinant clones. Characterization of 50 randomly chosen clones indicated that 21 clones produced discrete PCR products with the size of 240—600 bp. Dot-blot hybridization showed that among the 21 clones, 11 (～ 55%) were of low-copy nature while 10 (～45%) were repetitive. Southern hybridization with the complete set of the CS 'nullisomic-tetrasomic (NT)' lines demonstrated that all the 6 low-copy clones were specific to either chromosome 7B or the 7th
基金supported by the National Natural Science Foundation of China(31991212,31920103006)。
文摘Centromeres play a vital role in cellular division by facilitating kinetochore assembly and spindle attachments.Despite their conserved functionality,centromeric DNA sequences exhibit rapid evolution,presenting diverse sizes and compositions across species.The functional significance of rye centromeric DNA sequences,particularly in centromere identity,remains unclear.In this study,we comprehensively characterized the sequence composition and organization of rye centromeres.Our findings revealed that these centromeres are primarily composed of long terminal repeat retrotransposons(LTR-RTs)and interspersed minisatellites.We systematically classified LTR-RTs into five categories,highlighting the prevalence of younger CRS1,CRS2,and CRS3 of CRSs(centromeric retrotransposons of Secale cereale)were primarily located in the core centromeres and exhibited a higher association with CENH3 nucleosomes.The minisatellites,mainly derived from retrotransposons,along with CRSs,played a pivotal role in establishing functional centromeres in rye.Additionally,we observed the formation of R-loops at specific regions of CRS1,CRS2,and CRS3,with both rye pericentromeres and centromeres exhibiting enrichment in R-loops.Notably,these R-loops selectively formed at binding regions of the CENH3 nucleosome in rye centromeres,suggesting a potential role in mediating the precise loading of CENH3 to centromeres and contributing to centromere specification.Our work provides insights into the DNA sequence composition,distribution,and potential function of R-loops in rye centromeres.This knowledge contributes valuable information to understanding the genetics and epigenetics of rye centromeres,offering implications for the development of synthetic centromeres in future plant modifications and beyond.
基金supported by the National Natural Science Foundation of China(31991212)the National Key Research and Development Program of China(2022YFF1003303)。
文摘Non-B-form DNA differs from the classic B-DNA double helix structure and plays a crucial regulatory role in replication and transcription.However,the role of non-B-form DNA in centromeres,especially in polyploid wheat,remains elusive.Here,we systematically analyzed seven non-B-form DNA motif profiles(A-phased DNA repeat,direct repeat,G-quadruplex,inverted repeat,mirror repeat,short tandem repeat,and Z-DNA)in hexaploid wheat.We found that three of these non-B-form DNA motifs were enriched at centromeric regions,especially at the CENH3-binding sites,suggesting that non-B-form DNA may create a favorable loading environment for the CENH3 nucleosome.To investigate the dynamics of centromeric non-B form DNA during the alloploidization process,we analyzed DNA secondary structure using CENH3 ChIP-seq data from newly formed allotetraploid wheat and its two diploid ancestors.We found that newly formed allotetraploid wheat formed more non-B-form DNA in centromeric regions compared with their parents,suggesting that non-B-form DNA is related to the localization of the centromeric regions in newly formed wheat.Furthermore,non-B-form DNA enriched in the centromeric regions was found to preferentially form on young LTR retrotransposons,explaining CENH3's tendency to bind to younger LTR.Collectively,our study describes the landscape of non-B-form DNA in the wheat genome,and sheds light on its potential role in the evolution of polyploid centromeres.
