Development of DNA Markers From Physically Mapped Loci in Aegilops comosa and Aegilops umbellulata Using Single-Gene FISH and Chromosome Sequences

Analysis of a global wheat panel reveals a highly diverse introgression landscape and provides evidence for inter-homoeologue chromosomal recombination

KEY MESSAGE

This study highlights the agronomic potential of rare introgressions, as demonstrated by a major QTL for powdery mildew resistance on chromosome 7D. It further shows evidence for inter-homoeologue recombination in wheat. Agriculturally important genes are often introgressed into crops from closely related donor species or landraces. The gene pool of hexaploid bread wheat (Triticum aestivum) is known to contain numerous such "alien" introgressions. Recently established high-quality reference genome sequences allow prediction of the size, frequency and identity of introgressed chromosome regions. Here, we characterise chromosomal introgressions in bread wheat using exome capture data from the WHEALBI collection. We identified 24,981 putative introgression segments of at least 2 Mb across 434 wheat accessions. Detailed study of the most frequent introgressions identified T. timopheevii or its close relatives as a frequent donor species. Importantly, 118 introgressions of at least 10 Mb were exclusive to single wheat accessions, revealing that large populations need to be studied to assess the total diversity of the wheat pangenome. In one case, a 14 Mb introgression in chromosome 7D, exclusive to cultivar Pamukale, was shown by QTL mapping to harbour a recessive powdery mildew resistance gene. We identified multiple events where distal chromosomal segments of one subgenome were duplicated in the genome and replaced the homoeologous segment in another subgenome. We propose that these examples are the results of inter-homoeologue recombination. Our study produced an extensive catalogue of the wheat introgression landscape, providing a resource for wheat breeding. Of note, the finding that the wheat gene pool contains numerous rare, but potentially important introgressions and chromosomal rearrangements has implications for future breeding.

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.

Chromosome genomics facilitates the marker development and selection of wheat-Aegilops biuncialis addition, substitution and translocation lines

The annual goatgrass, Aegilops biuncialis is a rich source of genes with considerable agronomic value. This genetic potential can be exploited for wheat improvement through interspecific hybridization to increase stress resistance, grain quality and adaptability. However, the low throughput of cytogenetic selection hampers the development of alien introgressions. Using the sequence of flow-sorted chromosomes of diploid progenitors, the present study enabled the development of chromosome-specific markers. In total, 482 PCR markers were validated on wheat (Mv9kr1) and Ae. biuncialis (MvGB642) crossing partners, and 126 on wheat-Aegilops additions. Thirty-two markers specific for U- or M-chromosomes were used in combination with GISH and FISH for the screening of 44 Mv9kr1 × Ae. biuncialis BC3F3 genotypes. The predominance of chromosomes 4M and 5M, as well as the presence of chromosomal aberrations, may indicate that these chromosomes have a gametocidal effect. A new wheat-Ae. biuncialis disomic 4U addition, 4M(4D) and 5M(5D) substitutions, as well as several introgression lines were selected. Spike morphology and fertility indicated that the Aegilops 4M or 5M compensated well for the loss of 4D and 5D, respectively. The new cytogenetic stocks represent valuable genetic resources for the introgression of key genes alleles into wheat.

Chromosome-scale assembly of the wild wheat relative Aegilops umbellulata

Wild wheat relatives have been explored in plant breeding to increase the genetic diversity of bread wheat, one of the most important food crops. Aegilops umbellulata is a diploid U genome-containing grass species that serves as a genetic reservoir for wheat improvement. In this study, we report the construction of a chromosome-scale reference assembly of Ae. umbellulata accession TA1851 based on corrected PacBio HiFi reads and chromosome conformation capture. The total assembly size was 4.25 Gb with a contig N50 of 17.7 Mb. In total, 36,268 gene models were predicted. We benchmarked the performance of hifiasm and LJA, two of the most widely used assemblers using standard and corrected HiFi reads, revealing a positive effect of corrected input reads. Comparative genome analysis confirmed substantial chromosome rearrangements in Ae. umbellulata compared to bread wheat. In summary, the Ae. umbellulata assembly provides a resource for comparative genomics in Triticeae and for the discovery of agriculturally important genes.

Genomic characterization and gene bank curation of Aegilops: the wild relatives of wheat

Genetic diversity found in crop wild relatives is critical to preserve and utilize for crop improvement to achieve sustainable food production amid climate change and increased demand. We genetically characterized a large collection of 1,041 Aegilops accessions distributed among 23 different species using more than 45K single nucleotide polymorphisms identified by genotyping-by-sequencing. The Wheat Genetics Resource Center (WGRC) Aegilops germplasm collection was curated through the identification of misclassified and redundant accessions. There were 49 misclassified and 28 sets of redundant accessions within the four diploid species. The curated germplasm sets now have improved utility for genetic studies and wheat improvement. We constructed a phylogenetic tree and principal component analysis cluster for all Aegilops species together, giving one of the most comprehensive views of Aegilops. The Sitopsis section and the U genome Aegilops clade were further scrutinized with in-depth population analysis. The genetic relatedness among the pair of Aegilops species provided strong evidence for the species evolution, speciation, and diversification. We inferred genome symbols for two species Ae. neglecta and Ae. columnaris based on the sequence read mapping and the presence of segregating loci on the pertinent genomes as well as genetic clustering. The high genetic diversity observed among Aegilops species indicated that the genus could play an even greater role in providing the critical need for untapped genetic diversity for future wheat breeding and improvement. To fully characterize these Aegilops species, there is an urgent need to generate reference assemblies for these wild wheats, especially for the polyploid Aegilops.

Comparative genomic analysis of 5Mg chromosome of Aegilops geniculata and 5Uu chromosome of Aegilops umbellulata reveal genic diversity in the tertiary gene pool

Wheat is one of the most important cereal crops for the global food security. Due to its narrow genetic base, modern bread wheat cultivars face challenges from increasing abiotic and biotic stresses. Since genetic improvement is the most sustainable approach, finding novel genes and alleles is critical for enhancing the genetic diversity of wheat. The tertiary gene pool of wheat is considered a gold mine for genetic diversity as novel genes and alleles can be identified and transferred to wheat cultivars. Aegilops geniculata and Ae. umbellulata are the key members of the tertiary gene pool of wheat and harbor important genes against abiotic and biotic stresses. Homoeologous-group five chromosomes (5U^u and 5M^g) have been extensively studied from Ae. geniculata and Ae. umbellulata as they harbor several important genes including Lr57, Lr76, Yr40, Yr70, Sr53 and chromosomal pairing loci. In the present study, using chromosome DNA sequencing and RNAseq datasets, we performed comparative analysis to study homoeologous gene evolution in 5M^g, 5U^u, and group 5 wheat chromosomes. Our findings highlight the diversity of transcription factors and resistance genes, resulting from the differential expansion of the gene families. Both the chromosomes were found to be enriched with the "response to stimulus" category of genes providing resistance against biotic and abiotic stress. Phylogenetic study positioned the M genome closer to the D genome, with higher proximity to the A genome than the B genome. Over 4000 genes were impacted by SNPs on 5D, with 4-5% of those genes displaying non-disruptive variations that affect gene function.

An unusual tandem kinase fusion protein confers leaf rust resistance in wheat

The introgression of chromosome segments from wild relatives is an established strategy to enrich crop germplasm with disease-resistance genes¹. Here we use mutagenesis and transcriptome sequencing to clone the leaf rust resistance gene Lr9, which was introduced into bread wheat from the wild grass species Aegilops umbellulata². We established that Lr9 encodes an unusual tandem kinase fusion protein. Long-read sequencing of a wheat Lr9 introgression line and the putative Ae. umbellulata Lr9 donor enabled us to assemble the ~28.4-Mb Lr9 translocation and to identify the translocation breakpoint. We likewise cloned Lr58, which was reportedly introgressed from Aegilops triuncialis³, but has an identical coding sequence compared to Lr9. Cytogenetic and haplotype analyses corroborate that the two genes originate from the same translocation event. Our work sheds light on the emerging role of kinase fusion proteins in wheat disease resistance, expanding the repertoire of disease-resistance genes for breeding.

Intraspecific divergence of diploid grass Aegilopscomosa is associated with structural chromosome changes

Aegilopscomosa Smith in Sibthorp et Smith, 1806 is diploid grass with MM genome constitution occurring mainly in Greece. Two morphologically distinct subspecies - Ae.c.comosa Chennaveeraiah, 1960 and Ae.c.heldreichii (Holzmann ex Boissier) Eig, 1929 are discriminated within Ae.comosa, however, genetic and karyotypic bases of their divergence are not fully understood. We used Fluorescence in situ hybridization (FISH) with repetitive DNA probes and electrophoretic analysis of gliadins to characterize the genome and karyotype of Ae.comosa to assess the level of their genetic diversity and uncover mechanisms leading to radiation of subspecies. We show that two subspecies differ in size and morphology of chromosomes 3M and 6M, which can be due to reciprocal translocation. Subspecies also differ in the amount and distribution of microsatellite and satellite DNA sequences, the number and position of minor NORs, especially on 3M and 6M, and gliadin spectra mainly in the a-zone. Frequent occurrence of hybrids can be caused by open pollination, which, along with genetic heterogeneity of accessions and, probably, the lack of geographic or genetic barrier between the subspecies, may contribute to extremely broad intraspecific variation of GAA_n and gliadin patterns in Ae.comosa, which are usually not observed in endemic plant species.

Flow Cytometric Analysis and Sorting of Plant Chromosomes

Flow cytometry offers a unique way of analyzing and manipulating plant chromosomes. During a rapid movement in a liquid stream, large populations can be classified in a short time according to their fluorescence and light scatter properties. Chromosomes whose optical properties differ from other chromosomes in a karyotype can be purified by flow sorting and used in a range of applications in cytogenetics, molecular biology, genomics, and proteomics. As the samples for flow cytometry must be liquid suspensions of single particles, intact chromosomes must be released from mitotic cells. This protocol describes a procedure for preparation of suspensions of mitotic metaphase chromosomes from meristem root tips and their flow cytometric analysis and sorting for various downstream applications.

Strategies for utilization of crop wild relatives in plant breeding programs

Crop wild relatives (CWRs) are weedy and wild relatives of the domesticated and cultivated crops, which usually occur and are maintained in natural forms in their centres of origin. These include the ancestors or progenitors of all cultivated species and comprise rich sources of diversity for many important traits useful in plant breeding. CWRs can play an important role in broadening genetic bases and introgression of economical traits into crops, but their direct use by breeders for varietal improvement program is usually not advantageous due to the presence of crossing or chromosome introgression barriers with cultivated species as well as their high frequencies of agronomically undesirable alleles. Linkage drag may subsequently result in unfavourable traits in the subsequent progeny when segments of the genome linked with quantitative trait loci (QTL), or a phenotype, are introgressed from wild germplasm. Here, we first present an overview in regards to the contribution that wild species have made to improve biotic, abiotic stress tolerances and yield-related traits in crop varieties, and secondly summarise the various challenges which are experienced in interspecific hybridization along with their probable solutions. We subsequently suggest techniques for readily harnessing these wild relatives for fast and effective introgression of exotic alleles in pre-breeding research programs.

Pseudorogneria libanotica Intraspecific Genetic Polymorphism Revealed by Fluorescence In Situ Hybridization with Newly Identified Tandem Repeats and Wheat Single-Copy Gene Probes

The genus Pseudoroegneria (Nevski) Löve (Triticeae, Poaceae) with its genome abbreviated 'St' accounts for more than 60% of perennial Triticeae species. The diploid species Psudoroegneria libanotica (2n = 14) contains the most ancient St genome. Therefore, investigating its chromosomes could provide some fundamental information required for subsequent studies of St genome evolution. Here, 24 wheat cDNA probes covering seven chromosome groups were mapped in P. libanotica to distinguish homoelogous chromosomes, and newly identified tandem repeats were performed to differentiate seven chromosome pairs. Using these probes, we investigated intraspecific population chromosomal polymorphism of P. libanotica. We found that (i) a duplicated fragment of the 5St long arm was inserted into the short arm of 2St; (ii) asymmetrical fluorescence in situ hybridization (FISH) hybridization signals among 2St, 5St, and 7St homologous chromosome pairs; and (iii) intraspecific population of polymorphism in P. libanotica. These observations established the integrated molecular karyotype of P. libanotica. Moreover, we suggested heterozygosity due to outcrossing habit and adaptation to the local climate of P. libanotica. Specifically, the generated STlib_96 and STlib_98 repeats showed no cross-hybridization signals with wheat chromosomes, suggesting that they are valuable for identifying alien chromosomes or introgressed fragments of wild relatives in wheat.

Aegilops crassa Boiss. repeatome characterized using low-coverage NGS as a source of new FISH markers: Application in phylogenetic studies of the Triticeae

Aegilops crassa Boiss. is polyploid grass species that grows in the eastern part of the Fertile Crescent, Afghanistan, and Middle Asia. It consists of tetraploid (4x) and hexaploid (6x) cytotypes (2n = 4x = 28, D¹D (Abdolmalaki et al., 2019) X^crX^cr and 2n = 6x = 42, D¹D (Abdolmalaki et al., 2019) X^crX^crD²D (Adams and Wendel, 2005), respectively) that are similar morphologically. Although many Aegilops species were used in wheat breeding, the genetic potential of Ae. crassa has not yet been exploited due to its uncertain origin and significant genome modifications. Tetraploid Ae. crassa is thought to be the oldest polyploid Aegilops species, the subgenomes of which still retain some features of its ancient diploid progenitors. The D¹ and D² subgenomes of Ae. crassa were contributed by Aegilops tauschii (2n = 2x = 14, DD), while the X^cr subgenome donor is still unknown. Owing to its ancient origin, Ae. crassa can serve as model for studying genome evolution. Despite this, Ae. crassa is poorly studied genetically and no genome sequences were available for this species. We performed low-coverage genome sequencing of 4x and 6x cytotypes of Ae. crassa, and four Ae. tauschii accessions belonging to different subspecies; diploid wheatgrass Thinopyrum bessarabicum (J^b genome), which is phylogenetically close to D (sub)genome species, was taken as an outgroup. Subsequent data analysis using the pipeline RepeatExplorer2 allowed us to characterize the repeatomes of these species and identify several satellite sequences. Some of these sequences are novel, while others are found to be homologous to already known satellite sequences of Triticeae species. The copy number of satellite repeats in genomes of different species and their subgenome (D¹ or X^cr) affinity in Ae. crassa were assessed by means of comparative bioinformatic analysis combined with quantitative PCR (qPCR). Fluorescence in situ hybridization (FISH) was performed to map newly identified satellite repeats on chromosomes of common wheat, Triticum aestivum, 4x and 6x Ae. crassa, Ae. tauschii, and Th. bessarabicum. The new FISH markers can be used in phylogenetic analyses of the Triticeae for chromosome identification and the assessment of their subgenome affinities and for evaluation of genome/chromosome constitution of wide hybrids or polyploid species.

Flow karyotyping of wheat-Aegilops additions facilitate dissecting the genomes of Ae. biuncialis and Ae. geniculata into individual chromosomes

Breeding of wheat adapted to new climatic conditions and resistant to diseases and pests is hindered by a limited gene pool due to domestication and thousands of years of human selection. Annual goatgrasses (Aegilops spp.) with M and U genomes are potential sources of the missing genes and alleles. Development of alien introgression lines of wheat may be facilitated by the knowledge of DNA sequences of Aegilops chromosomes. As the Aegilops genomes are complex, sequencing relevant Aegilops chromosomes purified by flow cytometric sorting offers an attractive route forward. The present study extends the potential of chromosome genomics to allotetraploid Ae. biuncialis and Ae. geniculata by dissecting their M and U genomes into individual chromosomes. Hybridization of FITC-conjugated GAA oligonucleotide probe to chromosomes suspensions of the two species allowed the application of bivariate flow karyotyping and sorting some individual chromosomes. Bivariate flow karyotype FITC vs. DAPI of Ae. biuncialis consisted of nine chromosome-populations, but their chromosome content determined by microscopic analysis of flow sorted chromosomes indicated that only 7M^b and 1U^b could be sorted at high purity. In the case of Ae. geniculata, fourteen chromosome-populations were discriminated, allowing the separation of nine individual chromosomes (1M^g, 3M^g, 5M^g, 6M^g, 7M^g, 1U^g, 3U^g, 6U^g, and 7U^g) out of the 14. To sort the remaining chromosomes, a partial set of wheat-Ae. biuncialis and a whole set of wheat-Ae. geniculata chromosome addition lines were also flow karyotyped, revealing clear separation of the GAA-rich Aegilops chromosomes from the GAA-poor A- and D-genome chromosomes of wheat. All of the alien chromosomes represented by individual addition lines could be isolated at purities ranging from 74.5% to 96.6% and from 87.8% to 97.7%, respectively. Differences in flow karyotypes between Ae. biuncialis and Ae. geniculata were analyzed and discussed. Chromosome-specific genomic resources will facilitate gene cloning and the development of molecular tools to support alien introgression breeding of wheat.

Chromosome painting reveals inter-chromosomal rearrangements and evolution of subgenome D of wheat

Aegilops species represent the most important gene pool for breeding bread wheat (Triticum aestivum). Thus, understanding the genome evolution, including chromosomal structural rearrangements and syntenic relationships among Aegilops species or between Aegilops and wheat, is important for both basic genome research and practical breeding applications. In the present study, we attempted to develop subgenome D-specific fluorescence in situ hybridization (FISH) probes by selecting D-specific oligonucleotides based on the reference genome of Chinese Spring. The oligo-based chromosome painting probes consisted of approximately 26 000 oligos per chromosome and their specificity was confirmed in both diploid and polyploid species containing the D subgenome. Two previously reported translocations involving two D chromosomes have been confirmed in wheat varieties and their derived lines. We demonstrate that the oligo painting probes can be used not only to identify the translocations involving D subgenome chromosomes, but also to determine the precise positions of chromosomal breakpoints. Chromosome painting of 56 accessions of Ae. tauschii from different origins led us to identify two novel translocations: a reciprocal 3D-7D translocation in two accessions and a complex 4D-5D-7D translocation in one accession. Painting probes were also used to analyze chromosomes from more diverse Aegilops species. These probes produced FISH signals in four different genomes. Chromosome rearrangements were identified in Aegilops umbellulata, Aegilops markgrafii, and Aegilops uniaristata, thus providing syntenic information that will be valuable for the application of these wild species in wheat breeding.

Mapping of the novel powdery mildew resistance gene Pm2Mb from Aegilops biuncialis based on ph1b-induced homoeologous recombination

A novel powdery mildew resistance gene Pm2Mb from Aegilops biuncialis was transferred into common wheat and mapped to chromosome 2M^bL bin FL 0.49-0.66 by molecular cytogenetic analysis of 2M^b recombinants. Aegilops biuncialis, a wild relative of common wheat, is highly resistant to powdery mildew. Previous studies identified that chromosome 2M^b in Chinese Spring (CS)-Ae. biuncialis 2M^b disomic addition line TA7733 conferred high resistance to powdery mildew, and the resistance gene was temporarily designated as Pm2Mb. In this study, a total of 65 CS-Ae. biuncialis 2M^b recombinants were developed by ph1b-induced homoeologous recombination and they were grouped into 12 different types based on the presence of different markers of 2M^b-specificity. Segment sizes and breakpoints of each 2M^b recombinant type were further characterized using in situ hybridization and molecular marker analyses. Powdery mildew responses of each type were assessed by inoculation of each 2M^b recombinant-derived F₂ progenies using the isolate E05. Combined analyses of in situ hybridization, molecular markers and powdery mildew resistance data of the 2M^b recombinants, the gene Pm2Mb was cytologically located to an interval of FL 0.49-0.66 in the long arm of 2M^b, where 19 2M^b-specific markers were located. Among the 65 2M^b recombinants, T-11 (T2DS.2DL-2M^bL) and T-12 (Ti2DS.2DL-2M^bL-2DL) contained a small 2M^bL segment harboring Pm2Mb. Besides, a physical map of chromosome 2M^b was constructed with 70 2M^b-specific markers in 10 chromosomal bins and the map showed that submetacentric chromosome 2M^b of Ae. biuncialis was rearranged by a terminal intrachromosomal translocation. The newly developed 2M^b recombinants with powdery mildew resistance, the 2M^b-specific molecular markers and the physical map of chromosome 2M^b will benefit wheat disease breeding as well as fine mapping and cloning of Pm2Mb.

Centromere-Specific Single-Copy Sequences of Secale Species

Single-copy FISH analysis is a useful tool to physically locate a given sequence on chromosome. Centromeric single-copy sequences can be used to locate the position of centromere and disclose the subtle differences among different centromeres. Nine centromeric single-copy sequences 1R1, 3R1, 4R1, 4R2, 5R1, 5R2, 6R2, 6R3, and 7R1 were cloned from Kustro (Secale cereale L.). FISH analysis using these sequences as probes indicated that the signals of 1R1, 3R1, 4R1, 4R2, 5R1, 5R2, 6R1, 6R2, and 7R1 were located in the centromeric regions of rye 1R, 3R, 4R, 4R, 5R, 5R, 6R, 6R, and 7R chromosomes, respectively. In addition, for each of the centromeric single-copy sequences, high sequence similarity was observed among different Secale species. Combined with rye genomic sequence, single-copy FISH analysis indicated that the 1BL.1RS translocations in wheat cultivar CN17 and wheat line 20T363-4 contained the centromeric segment of 1R chromosome from 349,498,361 to 349,501,266 bp, and the 1BL.1RS translocations in the other two wheat cultivars did not contain this segment. The nine sequences are useful in determining the centromere location on rye chromosomes, and they have the potential to disclose the accurate structural differences of centromeres among the wheat-rye centric fusion translocation chromosomes; therefore, more centromeric single-copy sequences are needed.

Transfer of the ph1b Deletion Chromosome 5B From Chinese Spring Wheat Into a Winter Wheat Line and Induction of Chromosome Rearrangements in Wheat-Aegilops biuncialis Hybrids

Effective utilization of genetic diversity in wild relatives to improve wheat requires recombination between wheat and alien chromosomes. However, this is suppressed by the Pairing homoeologous gene, Ph1, on the long arm of wheat chromosome 5B. A deletion mutant of the Ph1 locus (ph1b) has been used widely to induce homoeologous recombination in wheat × alien hybrids. However, the original ph1b mutation, developed in Chinese Spring (CS) background has poor agronomic performance. Hence, alien introgression lines are first backcrossed with adapted wheat genotypes and after this step, alien chromosome segments are introduced into breeding lines. In this work, the ph1b mutation was transferred from two CSph1b mutants into winter wheat line Mv9kr1. Homozygous genotypes Mv9kr1 ph1b/ph1b exhibited improved plant and spike morphology compared to Chinese Spring. Flow cytometric chromosome analysis confirmed reduced DNA content of the mutant 5B chromosome in both wheat genotype relative to the wild type chromosome. The ph1b mutation in the Mv9kr1 genotype allowed wheat-alien chromosome pairing in meiosis of Mv9kr1ph1b_K × Aegilops biuncialis F₁ hybrids, predominantly with the M^b-genome chromosomes of Aegilops relative to those of the U^b genome. High frequency of wheat-Aegilops chromosome interactions resulted in rearranged chromosomes identified in the new Mv9kr1ph1b × Ae. Biuncialis amphiploids, making these lines valuable sources for alien introgressions. The new Mv9kr1ph1b mutant genotype is a unique resource to support alien introgression breeding of hexaploid wheat.

Identification of New QTLs for Dietary Fiber Content in Aegilops biuncialis

Grain dietary fiber content is an important health-promoting trait of bread wheat. A dominant dietary fiber component of wheat is the cell wall polysaccharide arabinoxylan and the goatgrass Aegilops biuncialis has high β-glucan content, which makes it an attractive gene source to develop wheat lines with modified fiber composition. In order to support introgression breeding, this work examined genetic variability in grain β-glucan, pentosan, and protein content in a collection of Ae. biuncialis. A large variation in grain protein and edible fiber content was revealed, reflecting the origin of Ae. biuncialis accessions from different eco-geographical habitats. Association analysis using DArTseq-derived SNPs identified 34 QTLs associated with β-glucan, pentosan, water-extractable pentosan, and protein content. Mapping the markers to draft chromosome assemblies of diploid progenitors of Ae. biuncialis underlined the role of genes on chromosomes 1M^b, 4M^b, and 5M^b in the formation of grain β-glucan content, while other QTLs on chromosome groups 3, 6, and 1 identified genes responsible for total- and water-extractable pentosan content. Functional annotation of the associated marker sequences identified fourteen genes, nine of which were identified in other monocots. The QTLs and genes identified in the present work are attractive targets for chromosome-mediated gene transfer to improve the health-promoting properties of wheat-derived foods.

Variation of Chromosome Composition in a Full-Sib Population Derived From 2x × 3x Interploidy Cross of Populus

Interploidy cross commonly results in complex chromosome number and structural variations. In our previous study, a progeny with segregated ploidy levels was produced by an interploidy cross between diploid female parent Populus tomentosa × Populus bolleana clone TB03 and triploid male parent Populus alba × Populus berolinensis 'Yinzhong'. However, the chromosome compositions of aneuploid genotypes in the progeny were still unclear. In the present study, a microsatellite DNA allele counting-peak ratios (MAC-PR) method was employed to analyze allelic configurations of each genotype to clarify their chromosome compositions, while 45S rDNA fluorescence in situ hybridization (FISH) analysis was used to reveal the mechanism of chromosome number variation. Based on the MAC-PR analysis of 47 polymorphic simple sequence repeat (SSR) markers distributed across all 19 chromosomes of Populus, both chromosomal number and structural variations were detected for the progeny. In the progeny, 26 hypo-triploids, 1 hyper-triploid, 16 hypo-tetraploids, 10 tetraploids, and 5 hyper-tetraploids were found. A total of 13 putative structural variation events (duplications and/or deletions) were detected in 12 genotypes, involved in chromosomes 3, 6, 7, 14, 15, 16, and 18. The 46.2% (six events) structural variation events occurred on chromosome 6, suggesting that there probably is a chromosome breakpoint near the SSR loci of chromosome 6. Based on calculation of the allelic information, the transmission of paternal heterozygosity in the hypo-triploids, hyper-triploid, hypo-tetraploids, tetraploids, and hyper-tetraploids were 0.748, 0.887, 0.830, 0.833, and 0.836, respectively, indicating that the viable pollen gains of the male parent 'Yinzhong' were able to transmit high heterozygosity to progeny. Furthermore, 45S rDNA-FISH analysis showed that specific-chromosome segregation feature during meiosis and chromosome appointment in normal and fused daughter nuclei of telophase II of 'Yinzhong,' which explained that the formation of aneuploids and tetraploids in the progeny could be attributed to imbalanced meiotic chromosomal segregation and division restitution of 'Yinzhong,' The data of chromosomal composition and structural variation of each aneuploid in the full-sib progeny of TB03 × 'Yinzhong' lays a foundation for analyzing mechanisms of trait variation relying on chromosome or gene dosages in Populus.

Turf performance and physiological responses of native Poa species to summer stress in Northeast China

Rapid rise in temperature in summer causes severe injury to cool-season turfgrass of both native species and introduced ones in Heilongjiang of Northeast China. The objectives of this study were to compare physiological responses to seasonal heat stresses and turf performances between native and introduced commercial Poa accessions. Three Chinese native Poa species (i.e., P. pratensis, P. sibirica and P. sphondylodes) and three USA Kentucky bluegrass cultivars (ie. 'Midnight', 'Moonlight' and 'BlueChip') were evaluated under field conditions in 2017 and 2018. All accessions showed unique characteristics and considerable seasonal differences in response to temperatures. However, performances over all accessions were largely similar in early spring and autumn. In summer, native P. pratensis performed similar to 'Midnight', 'Moonlight' or 'BlueChip', with respect to such traits or parameters as quality, coverage, color intensity, growth rate, osmolytes, ROS and anti-oxidant production. Native P. pratensis could be used as a new turf resource for further improvement and application under the specific climatic conditions in Heilongjiang; native P. sphondylodes may be used in repairing damaged environments or for alternative seasonal greenness.