Tracing the ancestry of modern bread wheats

Development and application of the GenoBaits WheatSNP16K array to accelerate wheat genetic research and breeding

Single-nucleotide polymorphisms (SNPs) are widely used as molecular markers for constructing genetic linkage maps in wheat. Compared with available SNP-based genotyping platforms, a genotyping by target sequencing (GBTS) system with capture-in-solution (liquid chip) technology has become the favored genotyping technology because it is less demanding and more cost effective, flexible, and user-friendly. In this study, a new GenoBaits WheatSNP16K (GBW16K) GBTS array was designed using datasets generated by the wheat 660K SNP array and resequencing platforms in our previous studies. The GBW16K array contains 14 868 target SNP regions that are evenly distributed across the wheat genome, and 37 669 SNPs in these regions can be identified in a diversity panel consisting of 239 wheat accessions from around the world. Principal component and neighbor-joining analyses using the called SNPs are consistent with the pedigree information and geographic distributions or ecological environments of the accessions. For the GBW16K marker panel, the average genetic diversity among the 239 accessions is 0.270, which is sufficient for linkage map construction and preliminary mapping of targeted genes or quantitative trait loci (QTLs). A genetic linkage map, constructed using the GBW16K array-based genotyping of a recombinant inbred line population derived from a cross of the CIMMYT wheat line Yaco"S" and the Chinese landrace Mingxian169, enables the identification of Yr27, Yr30, and QYr.nwafu-2BL.4 for adult-plant resistance to stripe rust from Yaco"S" and of Yr18 from Mingxian169. QYr.nwafu-2BL.4 is different from any previously reported gene/QTL. Three haplotypes and six candidate genes have been identified for QYr.nwafu-2BL.4 on the basis of haplotype analysis, micro-collinearity, gene annotation, RNA sequencing, and SNP data. This array provides a new tool for wheat genetic analysis and breeding studies and for achieving durable control of wheat stripe rust.

Inferring Long-Term and Short-Term Determinants of Genetic Diversity in Honey Bees: Beekeeping Impact and Conservation Strategies

Bees are vital pollinators in natural and agricultural landscapes around the globe, playing a key role in maintaining flowering plant biodiversity and ensuring food security. Among the honey bee species, the Western honey bee (Apis mellifera) is particularly significant, not only for its extensive crop pollination services but also for producing economically valuable products such as honey. Here, we analyzed whole-genome sequence data from four Apis species to explore how honey bee evolution has shaped current diversity patterns. Using Approximate Bayesian Computation, we first reconstructed the demographic history of A. mellifera in Europe, finding support for postglacial secondary contacts, therefore predating human-mediated transfers linked to modern beekeeping. However, our analysis of recent demographic changes reveals significant bottlenecks due to beekeeping practices, which have notably affected genetic diversity. Black honey bee populations from conservatories, particularly those on islands, exhibit considerable genetic loss, highlighting the need to evaluate the long-term effectiveness of current conservation strategies. Additionally, we observed a high degree of conservation in the genomic landscapes of nucleotide diversity across the four species, despite a divergence gradient spanning over 15 million years, consistent with a long-term conservation of the recombination landscapes. Taken together, our results provide the most comprehensive assessment of diversity patterns in honey bees to date and offer insights into the optimal management of resources to ensure the long-term persistence of honey bees and their invaluable pollination services.

Molecular identification of a Pm4 allele conferring powdery mildew resistance in durum wheat DR88

BACKGROUND

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is one of the most destructive wheat diseases worldwide. Durum wheat (Triticum turgidum L. var. durum Desf.) is a crucial gene donor for improving common wheat.

RESULTS

In this study, we investigated a durum wheat accession, DR88, which exhibits broad and high levels of resistance to powdery mildew. Using bulked segregant RNA-Seq (BSR-Seq), we identified a dominant gene, tentatively designated PmDR88, and localized it to 743-776 Mb interval on chromosome arm 2AL according to the reference genome of durum wheat cv. Svevo. Subsequently, PmDR88 was mapped in a genetic region of 3.9 cM flanked by the markers WGRE77410 and WGRC872 at genetic distances of 1.6 and 2.3 cM, respectively; it also co-segregated with JS717×JS718, the diagnostic marker for the Pm4 locus. Genotyping of a large population comprising 5,174 F2:3 families using JS717×JS718 confirmed that PmDR88 is located at the Pm4 locus on 2AL. Sequence alignment revealed that PmDR88 shares identical amino acid sequences with Pm4d, while qRT-PCR analysis suggested distinct expression patterns for PmDR88 compared with previously reported Pm4 alleles. Two complementary DNA markers, including the dominant co-segregating marker JS717×JS718 and a newly developed closely-linked co-dominant marker WGRE77410, were confirmed to be available for efficiently transferring PmDR88 into the tested wheat backgrounds by marker-assisted selection (MAS) strategy.

CONCLUSIONS

PmDR88 was mapped in the Pm4 locus. Despite sharing identical amino acid sequences with Pm4d, PmDR88 exhibits distinct expression patterns. Moreover, DR88 shows broad and high levels of resistance to powdery mildew. Two complementary DNA markers were identified for MAS breeding. The molecular identification of PmDR88 will facilitate transfer of this Pm4 allele into susceptible cultivars for resistance improvement or into resistant cultivars for resistance-enhanced pyramiding breeding.

Assessment of genetic structure and trait associations of Watkins wheat landraces under Egyptian field conditions

Background

Wheat landraces represent a reservoir of genetic diversity that can support wheat improvement through breeding. A core panel of 300 Watkins wheat landraces, as well as 16 non-Watkins landraces and elite wheat cultivars, was grown during the 2020-2021 and 2021-2022 seasons at four Agricultural Research Stations in Egypt, Gemmiza, Nubaria, Sakha, and Sids, to evaluate the core panel for agromorphological and yield-related traits. The genetic population structure within these genotypes were assessed using 35,143 single nucleotide polymorphisms (SNPs).

Results

Cluster analyses using Discriminant Analysis of Principal Components (DAPC) and k-means revealed three clusters with moderate genetic differentiation and population structure, possibly due to wheat breeding systems and geographical isolation. The best ancestry was k = 4, but k = 2 and k = 3 were also significant. A genome-wide association study (GWAS) identified clustered marker trait associations (MTAs) linked to thousand kernel weight on chromosome 5A, plant height on chromosomes 3B and 1D, days to heading on chromosomes 2A, 4B, 5B and 1D, and plant maturity on chromosomes 3A, 2B, and 6B. In the future, these MTAs can be used to accelerate the incorporation of beneficial alleles into locally adapted germplasm through marker-assisted selection. Gene enrichment analysis identified key genes within these loci, including Reduced height-1 (Rht-A1) and stress-related genes.

Conclusion

These findings underscore significant genetic connections and the involvement of crucial biological pathways.

Unveiling RNA structure-mediated regulations of RNA stability in wheat

Despite the critical role of mRNA stability in post-transcriptional gene regulation, research on this topic in wheat, a vital agricultural crop, remains unclear. Our study investigated the mRNA decay landscape of durum wheat (Triticum turgidum L. ssp. durum, BBAA), revealing subgenomic asymmetry in mRNA stability and its impact on steady-state mRNA abundance. Our findings indicate that the 3' UTR structure and homoeolog preference for RNA structural motifs can influence mRNA stability, leading to subgenomic RNA decay imbalance. Furthermore, single-nucleotide variations (SNVs) selected for RNA structural motifs during domestication can cause variations in subgenomic mRNA stability and subsequent changes in steady-state expression levels. Our research on the transcriptome stability of polyploid wheat highlights the regulatory role of non-coding region structures in mRNA stability, and how domestication shaped RNA structure, altering subgenomic mRNA stability. These results illustrate the importance of RNA structure-mediated post-transcriptional gene regulation in wheat and pave the way for its potential use in crop improvement.

A single NLR gene confers resistance to leaf and stripe rust in wheat

Nucleotide-binding leucine-rich repeat (NLR) disease resistance genes typically confer resistance against races of a single pathogen. Here, we report that Yr87/Lr85, an NLR gene from Aegilops sharonensis and Aegilops longissima, confers resistance against both P. striiformis tritici (Pst) and Puccinia triticina (Pt) that cause stripe and leaf rust, respectively. Yr87/Lr85 confers resistance against Pst and Pt in wheat introgression as well as transgenic lines. Comparative analysis of Yr87/Lr85 and the cloned Triticeae NLR disease resistance genes shows that Yr87/Lr85 contains two distinct LRR domains and that the gene is only found in Ae. sharonensis and Ae. longissima. Allele mining and phylogenetic analysis indicate multiple events of Yr87/Lr85 gene flow between the two species and presence/absence variation explaining the majority of resistance to wheat leaf rust in both species. The confinement of Yr87/Lr85 to Ae. sharonensis and Ae. longissima and the resistance in wheat against Pst and Pt highlight the potential of these species as valuable sources of disease resistance genes for wheat improvement.

Cytogenetic and molecular identification of novel wheat-Elymus sibiricus addition lines with resistance to leaf rust and the presence of leaf pubescence trait

Introduction

Emerging new races of leaf rust (Puccinia triticina Eriks) are threatening global wheat (Triticum aestivum L.) production. Identifying additional resistance genes from all available gene pools is crucial to expanding wheat resistance to these virulent leaf rust races. Siberian wild rye (Elymus sibiricus L.) possesses numerous beneficial traits that can be valuable in wheat improvement. Three new wheat-E. sibiricus addition lines, O27-2 (BC8), O27-3 (BC12) and O193-3 (BC12), were developed through a backcrossing scheme in this study, using leaf rust field evaluations, molecular marker assays and cytogenetic analysis.

Methods

These three lines were derived from progeny of the bread wheat cultivar 'Obriy' (2n = 6x = 42, AABBDD) and partial octoploid amphiploid wheat-E. sibiricus (2n = 8x = 56, AABBDDStSt).

Results and discussion

The lines (O27-2, O27-3 and O193-3) demonstrated strong specific leaf pubescence (hairiness) and resistance at the adult stage to a local population of leaf rust races. The response to leaf rust in these three lines significantly differed from that of the Lr24 gene, providing evidence for a distinct resistance mechanism associated with the 3St chromosome. This study is the first to report the transfer of an E. sibiricus chromosome into wheat that confers leaf rust resistance. Molecular marker analysis and genomic in situ hybridization confirmed that lines O27-2, O27-3 and O193-3 each possess one pair of E. sibiricus 3St chromosomes. The resistance gene was determined to be on the additional alien chromosome in these lines. Molecular markers (Xwmc221, Lr29F18, Sr24/Lr24) confirmed that the lines O27-2, O27-3, and O193-3 each contain a pair of E. sibiricus 3St chromosomes carrying leaf rust resistance genes. These findings demonstrate that the E. sibiricus 3St chromosome carries the leaf rust resistance gene and that the O27-2, O27-3, and O193-3 lines can serve as novel germplasm sources for introducing this resistance into wheat breeding programs. This study contributes to broadening the genetic diversity of resistance genes available for combating leaf rust in wheat.

On the evolution and genetic diversity of the bread wheat D genome

Bread wheat (Triticum aestivum) became a globally dominant crop after incorporating the D genome from the donor species Aegilops tauschii, but the evolutionary history that shaped the D genome during this process remains to be clarified. Here, we propose a renewed evolutionary model linking Ae. tauschii and the hexaploid wheat D genome by constructing an ancestral haplotype map covering 762 Ae. tauschii and hexaploid wheat accessions. We dissected the evolutionary trajectories of Ae. tauschii lineages and reported a few independent intermediate accessions, demonstrating that low-frequency inter-sublineage gene flow had enriched the diversity of Ae. tauschii. We discovered that the D genome of hexaploid wheat was inherited from a unified ancestral template, but with a mosaic composition that was highly mixed and derived mainly from three Ae. tauschii L2 sublineages located in the Caspian coastal region. This result suggests that early agricultural activities facilitated innovations in D-genome composition and finalized the success of hexaploidization. We found that the majority (51.4%) of genetic diversity was attributed to novel mutations absent in Ae. tauschii, and we identified large Ae. tauschii introgressions from various lineages, which expanded the diversity of the wheat D genome and introduced beneficial alleles. This work sheds light on the process of wheat hexaploidization and highlights the evolutionary significance of the multi-layered genetic diversity of the bread wheat D genome.

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.

Karyotypic and phenotypic condensation in allotetraploid wheats accompanied with reproductive strategy transformation: from natural evolution to domestication

MAIN CONCLUSION

Allotetraploid wheat reflects evolutionary divergence and domestication convergence in the karyotypic and phenotypic evolution, accompanied with the transformation from r- strategy to K- strategy in reproductive fitness. Allotetraploid wheat, the progenitor of hexaploidy bread wheat, has undergone 300,000 years of natural evolution and 10,000 years of domestication. The variations in karyotype and phenotype as well as fertility fitness have not been systematically linked. Here, by combining fluorescent in situ hybridization with the quantification of phenotypic and reproductive traits, we compared the karyotype, vegetative growth phenotype and reproductive fitness among synthesized, wild and domesticated accessions of allotetraploid wheat. We detected that the wild accessions showed dramatically high frequencies of homologous recombination and copy number variations of simple sequence repeats (SSR) comparing with synthetic and domesticated accessions. The phenotypic traits reflected significant differences among the populations shaped by distinct evolutionary processes. The diversity observed in wild accessions was significantly greater than that in domesticated ones, particularly in traits associated with vegetative growth and spike morphology. We found that the active pollen of domesticated accessions exhibited greater potential of germination, despite a lower rate of active pollen compared with the wild accessions, indicating a transformation in reproductive fitness strategy for pollen development in domesticated accessions compared to the wild accessions, from r-strategy to K-strategy. Our results demonstrate the condensation of karyotype and phenotype from natural wild accessions to domesticated accessions in allotetraploid wheats. Ecological strategy transformation should be seriously considered from evolution to domestication in polyploid plants, especially crops, which may provide a perspective on the adaptive evolution of polyploid plants.

Improving wheat grain composition for human health by constructing a QTL atlas for essential minerals

Wheat is an important source of minerals for human nutrition and increasing grain mineral content can contribute to reducing mineral deficiencies. Here, we identify QTLs for mineral micronutrients in grain of wheat by determining the contents of six minerals in a total of eleven sample sets of three biparental populations from crosses between A.E. Watkins landraces and cv. Paragon. Twenty-three of the QTLs are mapped in two or more sample sets, with LOD scores above five in at least one set with the increasing alleles for sixteen of the QTLs being present in the landraces and seven in Paragon. Of these QTLs, the number for each mineral varies between three and five and they are located on 14 of the 21 chromosomes, with clusters on chromosomes 5A (four), 6A (three), and 7A (three). The gene content within 5 megabases of DNA on either side of the marker for the QTL with the highest LOD score is determined and the gene responsible for the strongest QTL (chromosome 5A for Ca) identified as an ATPase transporter gene (TraesCS5A02G543300) using mutagenesis. The identification of these QTLs, together with associated SNP markers and candidate genes, will facilitate the improvement of grain nutritional quality.

Patterns of genomic variation reveal a single evolutionary origin of the wild allotetraploid Mimulus sookensis

Polyploidy occurs across the tree of life and is especially common in plants. Because newly formed cytotypes are often incompatible with their progenitors, polyploidy is also said to trigger "instantaneous" speciation. If a polyploid can self-fertilize or reproduce asexually, it is even possible for one individual to produce an entirely new lineage, but how often this scenario occurs is unclear. Here, we investigate the evolutionary history of the wild allotetraploid Mimulus sookensis, which was formed through hybridization between self-compatible, diploid species in the Mimulus guttatus complex. We generate a chromosome-scale reference assembly for M. sookensis and define its distinct subgenomes. Despite previous reports suggesting multiple origins of this highly selfing polyploid, we discover patterns of population genomic variation that provide unambiguous support for a single origin. One M. sookensis subgenome is clearly derived from the selfer Mimulus nasutus, which organellar variation suggests is the maternal progenitor. The ancestor of the other subgenome is less certain, but it shares variation with both Mimulus decorus and M. guttatus, two outcrossing diploids with geographic ranges that overlap broadly with M. sookensis. This study establishes M. sookensis as an example of instantaneous speciation, likely facilitated by the polyploid's predisposition to self-fertilize.

High-Copy Transposons from a Pathogen Give Rise to a Conserved sRNA Family with a Novel Host Immunity Target

Small RNAs (sRNAs) are involved in gene silencing in multiple ways, including through cross-kingdom transfers from parasites to their hosts. Little is known about the evolutionary mechanisms enabling eukaryotic microbes to evolve functional mimics of host small regulatory RNAs. Here, we describe the identification and functional characterization of SINE_sRNA1, an sRNA family derived from highly abundant short interspersed nuclear element (SINE) retrotransposons in the genome of the wheat powdery mildew pathogen. SINE_sRNA1 is encoded by a sequence motif that is conserved in multiple SINE families and corresponds to a functional plant microRNA (miRNA) mimic targeting Tae_AP1, a wheat gene encoding an aspartic protease only found in monocots. Tae_AP1 has a novel function enhancing both pattern-triggered immunity (PTI) and effector-triggered immunity (ETI), thereby contributing to the cross activation of plant defenses. We conclude that SINE_sRNA1 and Tae_AP1 are functional innovations, suggesting the contribution of transposons to the evolutionary arms race between a parasite and its host. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Integrative gene duplication and genome-wide analysis as an approach to facilitate wheat reverse genetics: An example in the TaCIPK family

INTRODUCTION

Reverse genetic studies conducted in the plant with a complex or polyploidy genome enriched with large gene families (like wheat) often meet challenges in identifying the key candidate genes related to important traits and prioritizing the genes for functional experiments.

OBJECTIVE

To overcome the above-mentioned challenges of reverse genetics, this work aims to establish an efficient multi-species strategy for genome-wide gene identification and prioritization of the key candidate genes.

METHODS

We established the integrative gene duplication and genome-wide analysis (iGG analysis) as a strategy for pinpointing key candidate genes deserving functional research. The iGG captures the evolution, and the expansion/contraction of large gene families across phylogeny-related species and integrates spatial-temporal expression information for gene function inference. Transgenic approaches were also employed to functional validation.

RESULTS

As a proof-of-concept for the iGG analysis, we took the wheat calcineurin B-like protein-interacting protein kinases (CIPKs) family as an example. We identified CIPKs from seven monocot species, established the orthologous relationship of CIPKs between rice and wheat, and characterized Triticeae-specific CIPK duplicates (e.g., CIPK4 and CIPK17). Integrated with our analysis of CBLs and CBL-CIPK interaction, we revealed that divergent expressions of TaCBLs and TaCIPKs could play an important role in keeping the stoichiometric balance of CBL-CIPK. Furthermore, we validated the function of TaCIPK17-A2 in the regulation of drought tolerance by using transgenic approaches. Overexpression of TaCIPK17 enhanced antioxidant capacity and improved drought tolerance in wheat.

CONCLUSION

The iGG analysis leverages evolutionary and comparative genomics of crops with large genomes to rapidly highlight the duplicated genes potentially associated with speciation, domestication and/or particular traits that deserve reverse-genetic functional studies. Through the identification of Triticeae-specific TaCIPK17 duplicates and functional validation, we demonstrated the effectiveness of the iGG analysis and provided a new target gene for improving drought tolerance in wheat.

Tagging large CNV blocks in wheat boosts digitalization of germplasm resources by ultra-low-coverage sequencing

BACKGROUND

The massive structural variations and frequent introgression highly contribute to the genetic diversity of wheat, while the huge and complex genome of polyploid wheat hinders efficient genotyping of abundant varieties towards accurate identification, management, and exploitation of germplasm resources.

RESULTS

We develop a novel workflow that identifies 1240 high-quality large copy number variation blocks (CNVb) in wheat at the pan-genome level, demonstrating that CNVb can serve as an ideal DNA fingerprinting marker for discriminating massive varieties, with the accuracy validated by PCR assay. We then construct a digitalized genotyping CNVb map across 1599 global wheat accessions. Key CNVb markers are linked with trait-associated introgressions, such as the 1RS·1BL translocation and 2NvS translocation, and the beneficial alleles, such as the end-use quality allele Glu-D1d (Dx5 + Dy10) and the semi-dwarf r-e-z allele. Furthermore, we demonstrate that these tagged CNVb markers promote a stable and cost-effective strategy for evaluating wheat germplasm resources with ultra-low-coverage sequencing data, competing with SNP array for applications such as evaluating new varieties, efficient management of collections in gene banks, and describing wheat germplasm resources in a digitalized manner. We also develop a user-friendly interactive platform, WheatCNVb ( http://wheat.cau.edu.cn/WheatCNVb/ ), for exploring the CNVb profiles over ever-increasing wheat accessions, and also propose a QR-code-like representation of individual digital CNVb fingerprint. This platform also allows uploading new CNVb profiles for comparison with stored varieties.

CONCLUSIONS

The CNVb-based approach provides a low-cost and high-throughput genotyping strategy for enabling digitalized wheat germplasm management and modern breeding with precise and practical decision-making.

Genome-wide patterns of homoeologous gene flow in allotetraploid coffee

Premise

Allopolyploidy-a hybridization-induced whole-genome duplication event-has been a major driver of plant diversification. The extent to which chromosomes pair with their proper homolog vs. with their homoeolog in allopolyploids varies across taxa, and methods to detect homoeologous gene flow (HGF) are needed to understand how HGF has shaped polyploid lineages.

Methods

The ABBA-BABA test represents a classic method for detecting introgression between closely related species, but here we developed a modified use of the ABBA-BABA test to characterize the extent and direction of HGF in allotetraploid Coffea arabica.

Results

We found that HGF is abundant in the C. arabica genome, with both subgenomes serving as donors and recipients of variation. We also found that HGF is highly maternally biased in plastid-targeted-but not mitochondrial-targeted-genes, as would be expected if plastid-nuclear incompatibilities exist between the two parent species.

Discussion

Together, our analyses provide a simple framework for detecting HGF and new evidence consistent with selection favoring overwriting of paternally derived alleles by maternally derived alleles to ameliorate plastid-nuclear incompatibilities. Natural selection therefore appears to shape the direction and intensity of HGF in allopolyploid coffee, indicating that cytoplasmic inheritance has long-term consequences for polyploid lineages.

Identification of Wheat Glutamate Synthetase Gene Family and Expression Analysis under Nitrogen Stress

Nitrogen (N), as the main component of biological macromolecules, maintains the basic process of plant growth and development. GOGAT, as a key enzyme in the N assimilation process, catalyzes α-ketoglutaric acid and glutamine to form glutamate. In this study, six GOGAT genes in wheat (Triticum aestivum L.) were identified and classified into two subfamilies, Fd-GOGAT (TaGOGAT2s) and NADH-GOGAT (TaGOGAT3s), according to the type of electron donor. Subcellular localization prediction showed that TaGOGAT3-D was localized in mitochondria and that the other five TaGOGATs were localized in chloroplasts. Via the analysis of promoter elements, many binding sites related to growth and development, hormone regulation and plant stress resistance regulations were found on the TaGOGAT promoters. The tissue-specificity expression analysis showed that TaGOGAT2s were mainly expressed in wheat leaves and flag leaves, while TaGOGAT3s were highly expressed in roots and leaves. The expression level of TaGOGATs and the enzyme activity of TaGOGAT3s in the leaves and roots of wheat seedlings were influenced by the treatment of N deficiency. This study conducted a systematic analysis of wheat GOGAT genes, providing a theoretical basis not only for the functional analysis of TaGOGATs, but also for the study of wheat nitrogen use efficiency (NUE).

The wheat powdery mildew resistance gene Pm4 also confers resistance to wheat blast

Wheat blast, caused by the fungus Magnaporthe oryzae, threatens global cereal production since its emergence in Brazil in 1985 and recently spread to Bangladesh and Zambia. Here we demonstrate that the AVR-Rmg8 effector, common in wheat-infecting isolates, is recognized by the gene Pm4, previously shown to confer resistance to specific races of Blumeria graminis f. sp. tritici, the cause of powdery mildew of wheat. We show that Pm4 alleles differ in their recognition of different AVR-Rmg8 alleles, and some confer resistance only in seedling leaves but not spikes, making it important to select for those alleles that function in both tissues. This study has identified a gene recognizing an important virulence factor present in wheat blast isolates in Bangladesh and Zambia and represents an important first step towards developing durably resistant wheat cultivars for these regions.

Genomic insights into glume pubescence in durum wheat: GWAS and haplotype analysis implicates TdELD1-1A as a candidate gene

Glume pubescence is an important morphological trait for the characterization of wheat cultivars. It shows tolerance to biotic and abiotic stresses to some extent. Hg1 (formerly named Hg) locus on chromosome 1AS controls glume pubescence in wheat. Its genetic analysis, fine-mapping and candidate gene analysis have been widely studied recently, however, the cloning of Hg1 has not yet been reported. Here, we conducted a GWAS between a dense panel of 171,103 SNPs and glume pubescence (Gp) in a durum wheat population of 145 lines, and further analyzed the candidate genes of Hg1 combined with the gene expression, functional annotation, and haplotype analysis. As a results, TRITD0Uv1G104670 (TdELD1-1A), encoding glycosyltransferase-like ELD1/KOBITO 1, was detected as the most promising candidate gene of Hg1 for glume pubescence in durum wheat. Our findings not only contribute to a deeper understanding of its cloning and functional validation but also underscore the significance of accurate genome sequences and annotations. Additionally, our study highlights the relevance of unanchored sequences in chrUn and the application of bioinformatics analysis for gene discovery in durum wheat.

Domestication caused taxonomical and functional shifts in the wheat rhizosphere microbiota, and weakened the natural bacterial biocontrol against fungal pathogens

Modern crops might have lost some of their functional traits, required for interacting with beneficial microbes, as a result of the genotypic/phenotypic modifications that occurred during domestication. Here, we studied the bacterial and fungal microbiota in the rhizosphere of two cultivated wheat species (Triticum aestivum and T. durum) and their respective ancestors (Aegilops tauschii and T. dicoccoides), in three experimental fields, by using metabarcoding of 16S rRNA genes and ITS2, coupled with co-occurrence network analysis. Moreover, the abundance of bacterial genes involved in N- and P-cycles was estimated by quantitative PCR, and urease, alkaline phosphatase and phosphomonoesterase activities were assessed by enzymatic tests. The relationships between microbiota and environmental metadata were tested by correlation analysis. The assemblage of core microbiota was affected by both site and plant species. No significant differences in the abundance of potential fungal pathogens between wild and cultivated wheat species were found; however, co-occurrence analysis showed more bacterial-fungal negative correlations in the wild species. Concerning functions, the nitrogen denitrification nirS gene was consistently more abundant in the rhizosphere of A. tauschii than T. aestivum. Urease activity was higher in the rhizosphere of each wild wheat species in at least two of the research locations. Several microbiota members, including potentially beneficial taxa such as Lysobacter and new taxa such as Blastocatellaceae, were found to be strongly correlated to rhizospheric soil metadata. Our results showed that a functional microbiome shift occurred as a result of wheat domestication. Notably, these changes also included the reduction of the natural biocontrol potential of rhizosphere-associated bacteria against pathogenic fungi, suggesting that domestication disrupted the equilibrium of plant-microbe relationships that had been established during million years of co-evolution.

Genome-wide association studies reveal novel loci for grain size in two-rowed barley (Hordeum vulgare L.)

KEY MESSAGE

SNP-based and InDel-based GWAS on multi-environment data identified genomic regions associated with barley grain size. Barley yield and quality are greatly influenced by grain size. Improving barley grain size in breeding programs requires knowledge of genetic loci and alleles in germplasm resources. In this study, a collection of 334 worldwide two-rowed barley accessions with extensive genetic diversity was evaluated for grain size including grain length (GL), grain width (GW), and thousand-grain weight (TGW) across six independent field trials. Significant differences were observed in genotype and environments for all measured traits. SNP- and InDel-based GWAS were applied to dissect the genetic architecture of grain size with an SLAF-seq strategy. Two approaches using the FarmCPU model revealed 38 significant marker-trait associations (MTAs) with PVE ranging from 0.01% to 20.68%. Among these MTAs, five were on genomic regions where no previously reported QTL for grain size. Superior alleles of TGW-associated SNP233060 and GL-associated InDel11006 exhibited significantly higher levels of phenotype. The significant MTAs could be used in marker-assisted selection breeding.

A platform for whole-genome speed introgression from Aegilops tauschii to wheat for breeding future crops

Breeding new and sustainable crop cultivars of high yields and desirable traits has been a major challenge for ensuring food security for the growing global human population. For polyploid crops such as wheat, introducing genetic variation from wild relatives of its subgenomes is a key strategy to improve the quality of their breeding pools. Over the past decades, considerable progress has been made in speed breeding, genome sequencing, high-throughput phenotyping and genomics-assisted breeding, which now allows us to realize whole-genome introgression from wild relatives to modern crops. Here, we present a standardized protocol to rapidly introgress the entire genome of Aegilops tauschii, the progenitor of the D subgenome of bread wheat, into elite wheat backgrounds. This protocol integrates multiple modern high-throughput technologies and includes three major phases: development of synthetic octaploid wheat, generation of hexaploid A. tauschii-wheat introgression lines (A-WIs) and homozygosis of the generated A-WIs. Our approach readily generates stable introgression lines in 2 y, thus greatly accelerating the generation of A-WIs and the introduction of desirable genes from A. tauschii to wheat cultivars. These A-WIs are valuable for wheat-breeding programs and functional gene discovery. The current protocol can be easily modified and used for introgressing the genomes of wild relatives to other polyploid crops.

TaRECQ4 contributes to maintain both homologous and homoeologous recombination during wheat meiosis

Introduction

Meiotic recombination (or crossover, CO) is essential for gamete fertility as well as for alleles and genes reshuffling that is at the heart of plant breeding. However, CO remains a limited event, which strongly hampers the rapid production of original and improved cultivars. RecQ4 is a gene encoding a helicase protein that, when mutated, contributes to improve recombination rate in all species where it has been evaluated so far.

Methods

In this study, we developed wheat (Triticum aestivum L.) triple mutant (TM) for the three homoeologous copies of TaRecQ4 as well as mutants for two copies and heterozygous for the last one (Htz-A, Htz-B, Htz-D).

Results

Phenotypic observation revealed a significant reduction of fertility and pollen viability in TM and Htz-B plants compared to wild type plants suggesting major defects during meiosis. Cytogenetic analyses of these plants showed that complete absence of TaRecQ4 as observed in TM plants, leads to chromosome fragmentation during the pachytene stage, resulting in problems in the segregation of chromosomes during meiosis. Htz-A and Htz-D mutants had an almost normal meiotic progression indicating that both TaRecQ4-A and TaRecQ4-D copies are functional and that there is no dosage effect for TaRecQ4 in bread wheat. On the contrary, the TaRecQ4-B copy seems knocked-out, probably because of a SNP leading to a Threonine>Alanine change at position 539 (T539A) of the protein, that occurs in the crucial helicase ATP bind/DEAD/ResIII domain which unwinds nucleic acids. Occurrence of numerous multivalents in TM plants suggests that TaRecQ4 could also play a role in the control of homoeologous recombination.

Discussion

These findings provide a foundation for further molecular investigations into wheat meiosis regulation to fully understand the underlying mechanisms of how TaRecQ4 affects chiasma formation, as well as to identify ways to mitigate these defects and enhance both homologous and homoeologous recombination efficiency in wheat.

Genomic content of wheat has a higher influence than plant domestication status on the ability to interact with Pseudomonas plant growth-promoting rhizobacteria

Plant evolutionary history has had profound effects on belowground traits, which is likely to have impacted the ability to interact with microorganisms, but consequences on root colonization and gene expression by plant growth-promoting rhizobacteria (PGPR) remain poorly understood. Here, we tested the hypothesis that wheat genomic content and domestication are key factors determining the capacity for PGPR interaction. Thus, 331 wheat representatives from eight Triticum or Aegilops species were inoculated under standardized conditions with the generalist PGPR Pseudomonas ogarae F113, using an autofluorescent reporter system for monitoring F113 colonization and expression of phl genes coding for the auxinic inducing signal 2,4-diacetylphloroglucinol. The interaction with P. ogarae F113 was influenced by ploidy level, presence of genomes AA, BB, DD, and domestication. While root colonization was higher for hexaploid and tetraploid species, and phl expression level higher for hexaploid wheat, the diploid Ae. tauschii displayed higher phl induction rate (i.e., expression:colonisation ratio) on roots. However, a better potential of interaction with F113 (i.e., under non-stress gnotobiotic conditions) did not translate, after seed inoculation, into better performance of wheat landraces in non-sterile soil under drought. Overall, results showed that domestication and especially plant genomic content modulate the PGPR interaction potential of wheats.

Whole-genome sequencing of diverse wheat accessions uncovers genetic changes during modern breeding in China and the United States

Breeding has dramatically changed the plant architecture of wheat (Triticum aestivum), resulting in the development of high-yielding varieties adapted to modern farming systems. However, how wheat breeding shaped the genomic architecture of this crop remains poorly understood. Here, we performed a comprehensive comparative analysis of a whole-genome resequencing panel of 355 common wheat accessions (representing diverse landraces and modern cultivars from China and the United States) at the phenotypic and genomic levels. The genetic diversity of modern wheat cultivars was clearly reduced compared to landraces. Consistent with these genetic changes, most phenotypes of cultivars from China and the United States were significantly altered. Of the 21 agronomic traits investigated, 8 showed convergent changes between the 2 countries. Moreover, of the 207 loci associated with these 21 traits, more than half overlapped with genomic regions that showed evidence of selection. The distribution of selected loci between the Chinese and American cultivars suggests that breeding for increased productivity in these 2 regions was accomplished by pyramiding both shared and region-specific variants. This work provides a framework to understand the genetic architecture of the adaptation of wheat to diverse agricultural production environments, as well as guidelines for optimizing breeding strategies to design better wheat varieties.

A papain-like cysteine protease-released small signal peptide confers wheat resistance to wheat yellow mosaic virus

Wheat yellow mosaic virus (WYMV), a soil-borne pathogen, poses a serious threat to global wheat production. Here, we identify a WYMV resistance gene, TaRD21A, that belongs to the papain-like cysteine protease family. Through genetic manipulation of TaRD21A expression, we establish its positive role in the regulation of wheat to WYMV resistance. Furthermore, our investigation shows that the TaRD21A-mediated plant antiviral response relies on the release of a small peptide catalyzed by TaRD21A protease activity. To counteract wheat resistance, WYMV-encoded nuclear inclusion protease-a (NIa) suppress TaRD21A activity to promote virus infection. In resistant cultivars, a natural variant of TaRD21A features a glycine-to-threonine substitution and this substitution enables the phosphorylation of threonine, thereby weakening the interaction between NIa and TaRD21A, reinforcing wheat resistance against WYMV. Our study not only unveils a WYMV resistance gene but also offers insights into the intricate mechanisms underpinning resistance against WYMV.

Rht12b, a widely used ancient allele of TaGA2oxA13, reduces plant height and enhances yield potential in wheat

KEY MESSAGE

We identified a new wheat dwarfing allele Rht12b conferring reduced height and higher grain yield, pinpointed its causal variations, developed a breeding-applicable marker, and traced its origin and worldwide distribution. Plant height control is essential to optimize lodging resistance and yield gain in crops. RHT12 is a reduced height (Rht) locus that is identified in a mutationally induced dwarfing mutant and encodes a gibberellin 2-oxidase TaGA2oxA13. However, the artificial dwarfing allele is not used in wheat breeding due to excessive height reduction. Here, we confirmed a stable Rht locus, overlapping with RHT12, in a panel of wheat cultivars and its dwarfing allele reduced plant height by 5.4-8.2 cm, equivalent to Rht12b, a new allele of RHT12. We validated the effect of Rht12b on plant height in a bi-parent mapping population. Importantly, wheat cultivars carrying Rht12b had higher grain yield than those with the contrasting Rht12a allele. Rht12b conferred higher expression level of TaGA2oxA13. Transient activation assays defined SNP-390(C/A) in the promoter of TaGA2oxA13 as the causal variation. An efficient kompetitive allele-specific PCR marker was developed to diagnose Rht12b. Conjoint analysis showed that Rht12b plus the widely used Rht-D1b, Rht8 and Rht24b was the predominant Rht combination and conferred a moderate plant height in tested wheat cultivars. Evolutionary tracking uncovered that RHT12 locus arose from a tandem duplication event with Rht12b firstly appearing in wild emmer. The frequency of Rht12b was approximately 70% (700/1005) in a worldwide wheat panel and comparable to or higher than those of other widely used Rht genes, suggesting it had been subjected to positive selection. These findings not only identify a valuable Rht gene for wheat improvement but also develop a functionally diagnostic tool for marker-assisted breeding.

LHP1-mediated epigenetic buffering of subgenome diversity and defense responses confers genome plasticity and adaptability in allopolyploid wheat

Polyploidization is a major driver of genome diversification and environmental adaptation. However, the merger of different genomes may result in genomic conflicts, raising a major question regarding how genetic diversity is interpreted and regulated to enable environmental plasticity. By analyzing the genome-wide binding of 191 trans-factors in allopolyploid wheat, we identified like heterochromatin protein 1 (LHP1) as a master regulator of subgenome-diversified genes. Transcriptomic and epigenomic analyses of LHP1 mutants reveal its role in buffering the expression of subgenome-diversified defense genes by controlling H3K27me3 homeostasis. Stripe rust infection releases latent subgenomic variations by eliminating H3K27me3-related repression. The simultaneous inactivation of LHP1 homoeologs by CRISPR-Cas9 confers robust stripe rust resistance in wheat seedlings. The conditional repression of subgenome-diversified defenses ensures developmental plasticity to external changes, while also promoting neutral-to-non-neutral selection transitions and adaptive evolution. These findings establish an LHP1-mediated buffering system at the intersection of genotypes, environments, and phenotypes in polyploid wheat. Manipulating the epigenetic buffering capacity offers a tool to harness cryptic subgenomic variations for crop improvement.

Transposable element-initiated enhancer-like elements generate the subgenome-biased spike specificity of polyploid wheat

Transposable elements (TEs) comprise ~85% of the common wheat genome, which are highly diverse among subgenomes, possibly contribute to polyploid plasticity, but the causality is only assumed. Here, by integrating data from gene expression cap analysis and epigenome profiling via hidden Markov model in common wheat, we detect a large proportion of enhancer-like elements (ELEs) derived from TEs producing nascent noncoding transcripts, namely ELE-RNAs, which are well indicative of the regulatory activity of ELEs. Quantifying ELE-RNA transcriptome across typical developmental stages reveals that TE-initiated ELE-RNAs are mainly from RLG_famc7.3 specifically expanded in subgenome A. Acquisition of spike-specific transcription factor binding likely confers spike-specific expression of RLG_famc7.3-initiated ELE-RNAs. Knockdown of RLG_famc7.3-initiated ELE-RNAs resulted in global downregulation of spike-specific genes and abnormal spike development. These findings link TE expansion to regulatory specificity and polyploid developmental plasticity, highlighting the functional impact of TE-driven regulatory innovation on polyploid evolution.

An online database for einkorn wheat to aid in gene discovery and functional genomics studies

Diploid A-genome wheat (einkorn wheat) presents a nutrition-rich option as an ancient grain crop and a resource for the improvement of bread wheat against abiotic and biotic stresses. Realizing the importance of this wheat species, reference-level assemblies of two einkorn wheat accessions were generated (wild and domesticated). This work reports an einkorn genome database that provides an interface to the cereals research community to perform comparative genomics, applied genetics and breeding research. It features queries for annotated genes, the use of a recent genome browser release, and the ability to search for sequence alignments using a modern BLAST interface. Other features include a comparison of reference einkorn assemblies with other wheat cultivars through genomic synteny visualization and an alignment visualization tool for BLAST results. Altogether, this resource will help wheat research and breeding. Database URL  https://wheat.pw.usda.gov/GG3/pangenome.

Genetic diversity and population structure of modern wheat (Triticum aestivum L.) cultivars in Henan Province of China based on SNP markers

BACKGROUND

Henan is the province with the greatest wheat production in China. Although more than 100 cultivars are used for production, many cultivars are still insufficient in quality, disease resistance, adaptability and yield potential. To overcome these limitations, it is necessary to constantly breed new cultivars to maintain the continuous and stable growth of wheat yield and quality. To improve breeding efficiency, it is important to evaluate the genetic diversity and population genetic structure of its cultivars. However, there are no such reports from Henan Province. Therefore, in this study, single nucleotide polymorphism (SNP) markers were used to study the population genetic structure and genetic diversity of 243 wheat cultivars included in a comparative test of wheat varieties in Henan Province, aiming to provide a reference for the utilization of backbone parents and the selection of hybrid combinations in the genetic improvement of wheat cultivars.

RESULTS

In this study, 243 wheat cultivars from Henan Province of China were genotyped by the Affymetrix Axiom Wheat660K SNP chip, and 21 characteristics were investigated. The cultivars were divided into ten subgroups; each subgroup had distinct characteristics and unique utilization value. Furthermore, based on principal component analysis, Zhoumai cultivars were the main hybrid parents, followed by Aikang 58, high-quality cultivars, and Shandong cultivars. Genetic diversity analysis showed that 61.3% of SNPs had a high degree of genetic differentiation, whereas 33.4% showed a moderate degree. The nucleotide diversity of subgenome B was relatively high, with an average π value of 3.91E-5; the nucleotide diversity of subgenome D was the lowest, with an average π value of 2.44E-5.

CONCLUSION

The parents used in wheat cross-breeding in Henan Province are similar, with a relatively homogeneous genetic background and low genetic diversity. These results will not only contribute to the objective evaluation and utilization of the tested cultivars but also provide insights into the current conditions and existing challenges of wheat cultivar breeding in Henan Province, thereby facilitating the scientific formulation of breeding objectives and strategies to improve breeding efficiency.

Deciphering the evolution and complexity of wheat germplasm from a genomic perspective

Bread wheat provides an essential fraction of the daily calorific intake for humanity. Due to its huge and complex genome, progress in studying on the wheat genome is substantially trailed behind those of the other two major crops, rice and maize, for at least a decade. With rapid advances in genome assembling and reduced cost of high-throughput sequencing, emerging de novo genome assemblies of wheat and whole-genome sequencing data are leading to a paradigm shift in wheat research. Here, we review recent progress in dissecting the complex genome and germplasm evolution of wheat since the release of the first high-quality wheat genome. New insights have been gained in the evolution of wheat germplasm during domestication and modern breeding progress, genomic variations at multiple scales contributing to the diversity of wheat germplasm, and complex transcriptional and epigenetic regulations of functional genes in polyploid wheat. Genomics databases and bioinformatics tools meeting the urgent needs of wheat genomics research are also summarized. The ever-increasing omics data, along with advanced tools and well-structured databases, are expected to accelerate deciphering the germplasm and gene resources in wheat for future breeding advances.

Genome-wide identification of ETHYLENE INSENSITIVE 2 in Triticeae species reveals that TaEIN2-4D.1 regulates cadmium tolerance in Triticum aestivum

ETHYLENE INSENSITIVE 2 (EIN2), as the core component of the ethylene signaling pathway, can widely regulate plant growth, development, and stress responses. However, the comprehensive study and function of EIN2 in wheat Cadmium (Cd) stress remain largely unexplored. Here, we identified 33 EIN2 genes and designated as TaEIN2-2B to TaEIN2-Un.3 in Triticum aestivum. The analysis of cis-regulatory elements in promoter regions and RNA-Seq showed that TaEIN2s were functionally related to plant growth and development, as well as the response to biotic and abiotic stress. qRT-PCR analysis of TaEIN2s indicated their sensitivity to Cd stress. Compared with WT plants, TaEIN2-4D.1-RNAi transgenic wheat lines showed enhanced shoot and root elongation, dry weight and chlorophyll accumulation, together with a reduced accumulation of Cd in wheat grain. In addition, TaEIN2-4D.1-RNAi transgenic wheat lines showed enhanced Reactive Oxygen Species (ROS) scavenging capacity compared with WT plants. In conclusion, our research indicates that TaEIN2 plays a key role in response to cadmium stress in wheat, which provides valuable information for crop improvement.

Multi-scale analysis provides insights into the roles of ureide permeases in wheat nitrogen use efficiency

The ureides allantoin and allantoate serve as nitrogen (N) transport compounds in plants, and more recently, allantoin has been shown to play a role in signaling. In planta, tissue ureide levels are controlled by the activity of enzymes of the purine degradation pathway and by ureide transporters called ureide permeases (UPS). Little is known about the physiological function of UPS proteins in crop plants, and especially in monocotyledon species. Here, we identified 13 TaUPS genes in the wheat (Triticum aestivum L.) genome. Phylogenetic and genome location analyses revealed a close relationship of wheat UPSs to orthologues in other grasses and a division into TaUPS1, TaUPS2.1, and TaUPS2.2 groups, each consisting of three homeologs, with a total of four tandem duplications. Expression, localization, and biochemical analyses resolved spatio-temporal expression patterns of TaUPS genes, transporter localization at the plasma membrane, and a role for TaUPS2.1 proteins in cellular import of ureides and phloem and seed loading. In addition, positive correlations between TaUPS1 and TaUPS2.1 transcripts and ureide levels were found. Together the data support that TaUPSs function in regulating ureide pools at source and sink, along with source-to-sink transport. Moreover, comparative studies between wheat cultivars grown at low and high N strengthened a role for TaUPS1 and TaUPS2.1 transporters in efficient N use and in controlling primary metabolism. Co-expression, protein-protein interaction, and haplotype analyses further support TaUPS involvement in N partitioning, N use efficiency, and domestication. Overall, this work provides a new understanding on UPS transporters in grasses as well as insights for breeding resilient wheat varieties with improved N use efficiency.

Einkorn genomics reveals ancient roots of domesticated wheat

Wheat is an important staple food crop that underwent complex genome duplications. During domestication, genetic changes occurred, improving modern wheat, but understanding its phylogenetic history has been lacking. Mahmood and Mansoor discuss a recent publication demonstrating the evolutionary history of domesticated wheat (Triticum monococcum), providing opportunities for advancements in cereal improvement.

Genome-wide association mapping in elite winter wheat breeding for yield improvement

Increased grain yield (GY) is the primary breeding target of wheat breeders. We performed the genome-wide association study (GWAS) on 168 elite winter wheat lines from an ongoing breeding program to identify the main determinants of grain yield. Sequencing of Diversity Array Technology fragments (DArTseq) resulted in 19,350 single-nucleotide polymorphism (SNP) and presence-absence variation (PAV) markers. We identified 15 main genomic regions located in ten wheat chromosomes (1B, 2B, 2D, 3A, 3D, 5A, 5B, 6A, 6B, and 7B) that explained from 7.9 to 20.3% of the variation in grain yield and 13.3% of the yield stability. Loci identified in the reduced genepool are important for wheat improvement using marker-assisted selection. We found marker-trait associations between three genes involved in starch biosynthesis and grain yield. Two starch synthase genes (TraesCS2B03G1238800 and TraesCS2D03G1048800) and a sucrose synthase gene (TraesCS3D03G0024300) were found in regions of QGy.rut-2B.2, QGy.rut-2D.1, and QGy.rut-3D, respectively. These loci and other significantly associated SNP markers found in this study can be used for pyramiding favorable alleles in high-yielding varieties or to improve the accuracy of prediction in genomic selection.

BRI1 EMS SUPPRESSOR1 genes regulate abiotic stress and anther development in wheat (Triticum aestivum L.)

BRI1 EMS SUPPRESSOR1 (BES1) family members are crucial downstream regulators that positively mediate brassinosteroid signaling, playing vital roles in the regulation of plant stress responses and anther development in Arabidopsis. Importantly, the expression profiles of wheat (Triticum aestivum L.) BES1 genes have not been analyzed comprehensively and systematically in response to abiotic stress or during anther development. In this study, we identified 23 BES1-like genes in common wheat, which were unevenly distributed on 17 out of 21 wheat chromosomes. Phylogenetic analysis clustered the BES1 genes into four major clades; moreover, TaBES1-3A2, TaBES1-3B2 and TaBES1-3D2 belonged to the same clade as Arabidopsis BES1/BZR1 HOMOLOG3 (BEH3) and BEH4, which participate in anther development. The expression levels of 23 wheat BES1 genes were assessed using real-time quantitative PCR under various abiotic stress conditions (drought, salt, heat, and cold), and we found that most TaBES1-like genes were downregulated under abiotic stress, particularly during drought stress. We therefore used drought-tolerant and drought-sensitive wheat cultivars to explore TaBES1 expression patterns under drought stress. TaBES1-3B2 and TaBES1-3D2 expression was high in drought-tolerant cultivars but substantially repressed in drought-sensitive cultivars, while TaBES1-6D presented an opposite pattern. Among genes preferentially expressed in anthers, TaBES1-3B2 and TaBES1-3D2 expression was substantially downregulated in thermosensitive genic male-sterile wheat lines compared to common wheat cultivar under sterile conditions, while we detected no obvious differences under fertile conditions. This result suggests that TaBES1-3B2 and TaBES1-3D2 might not only play roles in regulating drought tolerance, but also participate in low temperature-induced male sterility.

Harnessing genome-wide genetic diversity, population structure and linkage disequilibrium in Ethiopian durum wheat gene pool

Yanyang Liu, Henan Academy of Agricultural Sciences (HNAAS), China; Landraces are an important genetic source for transferring valuable novel genes and alleles required to enhance genetic variation. Therefore, information on the gene pool's genetic diversity and population structure is essential for the conservation and sustainable use of durum wheat genetic resources. Hence, the aim of this study was to assess genetic diversity, population structure, and linkage disequilibrium, as well as to identify regions with selection signature. Five hundred (500) individuals representing 46 landraces, along with 28 cultivars were evaluated using the Illumina Infinium 25K wheat SNP array, resulting in 8,178 SNPs for further analysis. Gene diversity (GD) and the polymorphic information content (PIC) ranged from 0.13-0.50 and 0.12-0.38, with mean GD and PIC values of 0.34 and 0.27, respectively. Linkage disequilibrium (LD) revealed 353,600 pairs of significant SNPs at a cut-off (r2 > 0.20, P < 0.01), with an average r2 of 0.21 for marker pairs. The nucleotide diversity (π) and Tajima's D (TD) per chromosome for the populations ranged from 0.29-0.36 and 3.46-5.06, respectively, with genome level, mean π values of 0.33 and TD values of 4.43. Genomic scan using the Fst outlier test revealed 85 loci under selection signatures, with 65 loci under balancing selection and 17 under directional selection. Putative candidate genes co-localized with regions exhibiting strong selection signatures were associated with grain yield, plant height, host plant resistance to pathogens, heading date, grain quality, and phenolic content. The Bayesian Model (STRUCTURE) and distance-based (principal coordinate analysis, PCoA, and unweighted pair group method with arithmetic mean, UPGMA) methods grouped the genotypes into five subpopulations, where landraces from geographically non-adjoining environments were clustered in the same cluster. This research provides further insights into population structure and genetic relationships in a diverse set of durum wheat germplasm, which could be further used in wheat breeding programs to address production challenges sustainably.

Triticeae crop genome biology: an endless frontier

Triticeae, the wheatgrass tribe, includes several major cereal crops and their wild relatives. Major crops within the Triticeae are wheat, barley, rye, and oat, which are important for human consumption, animal feed, and rangeland protection. Species within this tribe are known for their large genomes and complex genetic histories. Powered by recent advances in sequencing technology, researchers worldwide have made progress in elucidating the genomes of Triticeae crops. In addition to assemblies of high-quality reference genomes, pan-genome studies have just started to capture the genomic diversities of these species, shedding light on our understanding of the genetic basis of domestication and environmental adaptation of Triticeae crops. In this review, we focus on recent signs of progress in genome sequencing, pan-genome analyses, and resequencing analysis of Triticeae crops. We also propose future research avenues in Triticeae crop genomes, including identifying genome structure variations, the association of genomic regions with desired traits, mining functions of the non-coding area, introgression of high-quality genes from wild Triticeae resources, genome editing, and integration of genomic resources.

Genome wide association and haplotype analyses for the crease depth trait in bread wheat (Triticum aestivum L.)

Wheat grain has a complex structure that includes a crease on one side, and tissues within the crease region play an important role in nutrient transportation during wheat grain development. However, the genetic architecture of the crease region is still unclear. In this study, 413 global wheat accessions were resequenced and a method was developed for evaluating the phenotypic data of crease depth (CD). The CD values exhibited continuous and considerable large variation in the population, and the broad-sense heritability was 84.09%. CD was found to be positively correlated with grain-related traits and negatively with quality-related traits. Analysis of differentiation of traits between landraces and cultivars revealed that grain-related traits and CD were simultaneously improved during breeding improvement. Moreover, 2,150.8-Mb genetic segments were identified to fall within the selective sweeps between the landraces and cultivars; they contained some known functional genes for quality- and grain-related traits. Genome-wide association study (GWAS) was performed using around 10 million SNPs generated by genome resequencing and 551 significant SNPs and 18 QTLs were detected significantly associated with CD. Combined with cluster analysis of gene expression, haplotype analysis, and annotated information of candidate genes, two promising genes TraesCS3D02G197700 and TraesCS5A02G292900 were identified to potentially regulate CD. To the best of our knowledge, this is the first study to provide the genetic basis of CD, and the genetic loci identified in this study may ultimately assist in wheat breeding programs.

Suppressing ASPARTIC PROTEASE 1 prolongs photosynthesis and increases wheat grain weight

The elongation of photosynthesis, or functional staygreen, represents a feasible strategy to propel metabolite flux towards cereal kernels. However, achieving this goal remains a challenge in food crops. Here we report the cloning of wheat CO2 assimilation and kernel enhanced 2 (cake2), the mechanism underlying the photosynthesis advantages and natural alleles amenable to breeding elite varieties. A premature stop mutation in the A-genome copy of the ASPARTIC PROTEASE 1 (APP-A1) gene increased the photosynthesis rate and yield. APP1 bound and degraded PsbO, the protective extrinsic member of photosystem II critical for increasing photosynthesis and yield. Furthermore, a natural polymorphism of the APP-A1 gene in common wheat reduced APP-A1's activity and promoted photosynthesis and grain size and weight. This work demonstrates that the modification of APP1 increases photosynthesis, grain size and yield potentials. The genetic resources could propel photosynthesis and high-yield potentials in elite varieties of tetraploid and hexaploid wheat.

Epigenetic Landscape Is Largely Shaped by Diversiform Transposons in Aegilops tauschii

Transposons (TEs) account for more than 80% of the wheat genome, the highest among all known crop species. They play an important role in shaping the elaborate genomic landscape, which is the key to the speciation of wheat. In this study, we analyzed the association between TEs, chromatin states, and chromatin accessibility in Aegilops tauschii, the D genome donor of bread wheat. We found that TEs contributed to the complex but orderly epigenetic landscape as chromatin states showed diverse distributions on TEs of different orders or superfamilies. TEs also contributed to the chromatin state and openness of potential regulatory elements, affecting the expression of TE-related genes. Some TE superfamilies, such as hAT-Ac, carry active/open chromatin regions. In addition, the histone mark H3K9ac was found to be associated with the accessibility shaped by TEs. These results suggest the role of diversiform TEs in shaping the epigenetic landscape and in gene expression regulation in Aegilops tauschii. This has positive implications for understanding the transposon roles in Aegilops tauschii or the wheat D genome.

Global crotonylatome and GWAS revealed a TaSRT1-TaPGK model regulating wheat cold tolerance through mediating pyruvate

Here, we reported the complete profiling of the crotonylation proteome in common wheat. Through a combination of crotonylation and multi-omics analysis, we identified a TaPGK associated with wheat cold stress. Then, we confirmed the positive role of TaPGK-modulating wheat cold tolerance. Meanwhile, we found that cold stress induced lysine crotonylation of TaPGK. Moreover, we screened a lysine decrotonylase TaSRT1 interacting with TaPGK and found that TaSRT1 negatively regulated wheat cold tolerance. We subsequently demonstrated TaSRT1 inhibiting the accumulation of TaPGK protein, and this inhibition was possibly resulted from decrotonylation of TaPGK by TaSRT1. Transcriptome sequencing indicated that overexpression of TaPGK activated glycolytic key genes and thereby increased pyruvate content. Moreover, we found that exogenous application of pyruvate sharply enhanced wheat cold tolerance. These findings suggest that the TaSRT1-TaPGK model regulating wheat cold tolerance is possibly through mediating pyruvate. This study provided two valuable cold tolerance genes and dissected diverse mechanism of glycolytic pathway involving in wheat cold stress.

Differential alternative polyadenylation of homoeologous genes of allohexaploid wheat ABD subgenomes during drought stress response

Because allohexaploid wheat genome contains ABD subgenomes, how the expression of homoeologous genes is coordinated remains largely unknown, particularly at the co-transcriptional level. Alternative polyadenylation (APA) is an important part of co-transcriptional regulation, which is crucial in developmental processes and stress responses. Drought stress is a major threat to the stable yield of wheat. Focusing on APA, we used poly(A) tag sequencing to track poly(A) site dynamics in wheat under drought stress. The results showed that drought stress led to extensive APA involving 37-47% of differentially expressed genes in wheat. Significant poly(A) site switching was found in stress-responsive genes. Interestingly, homoeologous genes exhibit unequal numbers of poly(A) sites, divergent APA patterns with tissue specificity and time-course dynamics, and distinct 3'-UTR length changes. Moreover, differentially expressed transcripts in leaves and roots used different poly(A) signals, the up- and downregulated isoforms had distinct preferences for non-canonical poly(A) sites. Genes that encode key polyadenylation factors showed differential expression patterns under drought stress. In summary, poly(A) signals and the changes in core poly(A) factors may widely affect the selection of poly(A) sites and gene expression levels during the response to drought stress, and divergent APA patterns among homoeologous genes add extensive plasticity to this responsive network. These results not only reveal the significant role of APA in drought stress response, but also provide a fresh perspective on how homoeologous genes contribute to adaptability through transcriptome diversity. In addition, this work provides information about the ends of transcripts for a better annotation of the wheat genome.

Tracing 100 million years of grass genome evolutionary plasticity

Grasses derive from a family of monocotyledonous plants that includes crops of major economic importance such as wheat, rice, sorghum and barley, sharing a common ancestor some 100 million years ago. The genomic attributes of plant adaptation remain obscure and the consequences of recurrent whole genome duplications (WGD) or polyploidization events, a major force in plant evolution, remain largely speculative. We conducted a comparative analysis of omics data from ten grass species to unveil structural (inversions, fusions, fissions, duplications, substitutions) and regulatory (expression and methylation) basis of genome plasticity, as possible attributes of plant long lasting evolution and adaptation. The present study demonstrates that diverged polyploid lineages sharing a common WGD event often present the same patterns of structural changes and evolutionary dynamics, but these patterns are difficult to generalize across independent WGD events as a result of non-WGD factors such as selection and domestication of crops. Polyploidy is unequivocally linked to the evolutionary success of grasses during the past 100 million years, although it remains difficult to attribute this success to particular genomic consequences of polyploidization, suggesting that polyploids harness the potential of genome duplication, at least partially, in lineage-specific ways. Overall, the present study clearly demonstrates that post-polyploidization reprogramming is more complex than traditionally reported in investigating single species and calls for a critical and comprehensive comparison across independently polyploidized lineages.

High density mapping of wheat stripe rust resistance gene QYrXN3517-1BL using QTL mapping, BSE-Seq and candidate gene analysis

Fine mapping of a major stripe rust resistance locus QYrXN3517-1BL to a 336 kb region that includes 12 candidate genes. Utilization of genetic resistance is an effective strategy to control stripe rust disease in wheat. Cultivar XINONG-3517 (XN3517) has remained highly resistant to stripe rust since its release in 2008. To understand the genetic architecture of stripe rust resistance, Avocet S (AvS) × XN3517 F₆ RIL population was assessed for stripe rust severity in five field environments. The parents and RILs were genotyped by using the GenoBaits Wheat 16 K Panel. Four stable QTL from XINONG-3517 were detected on chromosome arms 1BL, 2AL, 2BL, and 6BS, named as QYrXN3517-1BL, QYrXN3517-2AL, QYrXN3517-2BL, and QYrXN3517-6BS, respectively. Based on the Wheat 660 K array and bulked segregant exome sequencing (BSE-Seq), the most effective QTL on chromosome 1BL is most likely different from the known adult plant resistance gene Yr29 and was mapped to a 1.7 cM region [336 kb, including twelve candidate genes in International Wheat Genome Sequencing Consortium (IWGSC) RefSeq version 1.0]. The 6BS QTL was identified as Yr78, and the 2AL QTL was probably same as QYr.caas-2AL or QYrqin.nwafu-2AL. The novel QTL on 2BL was effective in seedling stage against the races used in phenotyping. In addition, allele-specifc quantitative PCR (AQP) marker nwafu.a5 was developed for QYrXN3517-1BL to assist marker-assisted breeding.

Allelic variation of TaWD40-4B.1 contributes to drought tolerance by modulating catalase activity in wheat

Drought drastically restricts wheat production, so to dissect allelic variations of drought tolerant genes without imposing trade-offs between tolerance and yield is essential to cope with the circumstance. Here, we identify a drought tolerant WD40 protein encoding gene TaWD40-4B.1 of wheat via the genome-wide association study. The full-length allele TaWD40-4B.1^C but not the truncated allele TaWD40-4B.1^T possessing a nonsense nucleotide variation enhances drought tolerance and grain yield of wheat under drought. TaWD40-4B.1^C interacts with canonical catalases, promotes their oligomerization and activities, and reduces H₂O₂ levels under drought. The knock-down of catalase genes erases the role of TaWD40-4B.1^C in drought tolerance. TaWD40-4B.1^C proportion in wheat accessions is negatively correlative with the annual rainfall, suggesting this allele may be selected during wheat breeding. The introgression of TaWD40-4B.1^C enhances drought tolerance of the cultivar harboring TaWD40-4B.1^T. Therefore, TaWD40-4B.1^C could be useful for molecular breeding of drought tolerant wheat.

Population genomics unravels the Holocene history of bread wheat and its relatives

Deep knowledge of crop biodiversity is essential to improving global food security. Despite bread wheat serving as a keystone crop worldwide, the population history of bread wheat and its relatives, both cultivated and wild, remains elusive. By analysing whole-genome sequences of 795 wheat accessions, we found that bread wheat originated from the southwest coast of the Caspian Sea and underwent a slow speciation process, lasting ~3,300 yr owing to persistent gene flow from its relatives. Soon after, bread wheat spread across Eurasia and reached Europe, South Asia and East Asia ~7,000 to ~5,000 yr ago, shaping a diversified but occasionally convergent adaptive landscape in novel environments. By contrast, the cultivated relatives of bread wheat experienced a population decline by ~82% over the past ~2,000 yr due to the food choice shift of humans. Further biogeographical modelling predicted a continued population shrinking of many bread wheat relatives in the coming decades because of their vulnerability to the changing climate. These findings will guide future efforts in protecting and utilizing wheat biodiversity to enhance global wheat production.

Wheat genome architecture influences interactions with phytobeneficial microbial functional groups in the rhizosphere

Wheat has undergone a complex evolutionary history, which led to allopolyploidization and the hexaploid bread wheat Triticum aestivum. However, the significance of wheat genomic architecture for beneficial plant-microbe interactions is poorly understood, especially from a functional standpoint. In this study, we tested the hypothesis that wheat genomic architecture was an overriding factor determining root recruitment of microorganisms with particular plant-beneficial traits. We chose five wheat species representing genomic profiles AA (Triticum urartu), BB {SS} (Aegilops speltoides), DD (Aegilops tauschii), AABB (Triticum dicoccon) and AABBDD (Triticum aestivum) and assessed by quantitative polymerase chain reaction their ability to interact with free-nitrogen fixers, 1-aminocyclopropane-1-carboxylate deaminase producers, 2,4-diacetylphloroglucinol producers and auxin producers via the phenylpyruvate decarboxylase pathway, in combination with Illumina MiSeq metabarcoding analysis of N fixers (and of the total bacterial community). We found that the abundance of the microbial functional groups could fluctuate according to wheat genomic profile, as did the total bacterial abundance. N fixer diversity and total bacterial diversity were also influenced significantly by wheat genomic profile. Often, rather similar results were obtained for genomes DD (Ae. tauschii) and AABBDD (T. aestivum), pointing for the first time that the D genome could be particularly important for wheat-bacteria interactions.

Crossover patterning in plants

KEY MESSAGE

Chromatin state, and dynamic loading of pro-crossover protein HEI10 at recombination intermediates shape meiotic chromosome patterning in plants. Meiosis is the basis of sexual reproduction, and its basic progression is conserved across eukaryote kingdoms. A key feature of meiosis is the formation of crossovers which result in the reciprocal exchange of segments of maternal and paternal chromosomes. This exchange generates chromosomes with new combinations of alleles, increasing the efficiency of both natural and artificial selection. Crossovers also form a physical link between homologous chromosomes at metaphase I which is critical for accurate chromosome segregation and fertility. The patterning of crossovers along the length of chromosomes is a highly regulated process, and our current understanding of its regulation forms the focus of this review. At the global scale, crossover patterning in plants is largely governed by the classically observed phenomena of crossover interference, crossover homeostasis and the obligatory crossover which regulate the total number of crossovers and their relative spacing. The molecular actors behind these phenomena have long remained obscure, but recent studies in plants implicate HEI10 and ZYP1 as key players in their coordination. In addition to these broad forces, a wealth of recent studies has highlighted how genomic and epigenomic features shape crossover formation at both chromosomal and local scales, revealing that crossovers are primarily located in open chromatin associated with gene promoters and terminators with low nucleosome occupancy.