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Pangenomes are collections of annotated genome sequences of multiple individuals of a species 1 . The structural variants uncovered by these datasets are a major asset to genetic analysis in crop plants 2 . Here we report a pangenome of barley comprising long-read sequence assemblies of 76 wild and domesticated genomes and short-read sequence data of 1,315 genotypes. An expanded catalogue of sequence variation in the crop includes structurally complex loci that are rich in gene copy number variation. To demonstrate the utility of the pangenome, we focus on four loci involved in disease resistance, plant architecture, nutrient release and trichome development. Novel allelic variation at a powdery mildew resistance locus and population-specific copy number gains in a regulator of vegetative branching were found. Expansion of a family of starch-cleaving enzymes in elite malting barleys was linked to shifts in enzymatic activity in micro-malting trials. Deletion of an enhancer motif is likely to change the developmental trajectory of the hairy appendages on barley grains. Our findings indicate that allelic diversity at structurally complex loci may have helped crop plants to adapt to new selective regimes in agricultural ecosystems., Competing Interests: Competing interests: K.B., C.D., M.E.J., S.M.K., Q.L., E.M., P.R.P., B.S., H.C.T., M.T.S.N., C.V. and M.W.R. are current or previous Carlsberg A/S employees. P.A.P. and D.V. are SECOBRA Recherches employees. The other authors declare no competing interests., (© 2024. The Author(s).)

Better understanding of the mechanistic basis of plant plasticity will enhance efforts to breed crops resilient to predicted climate change. However, complexity in plasticity's conceptualisation and measurement may hinder fruitful crossover of concepts between disciplines that would enable such advances. We argue active adaptive plasticity is particularly important in shaping the fitness of wild plants, representing the first line of a plant's defence to environmental change. Here, we define how this concept may be applied to crop breeding, suggest appropriate approaches to measure it in crops, and propose a refocussing on active adaptive plasticity to enhance crop resilience. We also discuss how the same concept may have wider utility, such as in ex situ plant conservation and reintroductions., (Copyright © 2022 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Flowering plants reproduce sexually by combining a haploid male and female gametophyte during fertilization. Male gametophytes are localized in the anthers, each containing reproductive (meiocyte) and non-reproductive tissue necessary for anther development and maturation. Meiosis, where chromosomes pair and exchange their genetic material during a process called recombination, is one of the most important and sensitive stages in breeding, ensuring genetic diversity. Most anther development studies have focused on transcript variation, but very few have been correlated with protein abundance. Taking advantage of a recently published barley anther transcriptomic (BAnTr) dataset and a newly developed sensitive mass spectrometry-based approach to analyse the barley anther proteome, we conducted high-resolution mass spectrometry analysis of barley anthers, collected at six time points and representing their development from pre-meiosis to metaphase. Each time point was carefully staged using immunocytology, providing a robust and accurate staging mirroring our previous BAnTr dataset. We identified >6100 non-redundant proteins including 82 known and putative meiotic proteins. Although the protein abundance was relatively stable throughout prophase I, we were able to quantify the dynamic variation of 336 proteins. We present the first quantitative comparative proteomics study of barley anther development during meiotic prophase I when the important process of homologous recombination is taking place., (© The Author(s) 2021. Published by Oxford University Press on behalf of the Society for Experimental Biology.)

Key Message: Variety age and population structure detect novel QTL for yield and adaptation in wheat and barley without the need to phenotype. The process of crop breeding over the last century has delivered new varieties with increased genetic gains, resulting in higher crop performance and yield. However, in many cases, the alleles and genomic regions underpinning this success remain unknown. This is partly due to the difficulty of generating sufficient phenotypic data on large numbers of historical varieties to enable such analyses. Here we demonstrate the ability to circumvent such bottlenecks by identifying genomic regions selected over 100 years of crop breeding using age of a variety as a surrogate for yield. Rather than collecting phenotype data, we deployed 'environmental genome-wide association scans' (EnvGWAS) based on variety age in two of the world's most important crops, wheat and barley, and detected strong signals of selection across both genomes. EnvGWAS identified 16 genomic regions in barley and 10 in wheat with contrasting patterns between spring and winter types of the two crops. To further examine changes in genome structure, we used the genomic relationship matrix of the genotypic data to derive eigenvectors for analysis in EigenGWAS. This detected seven major chromosomal introgressions that contributed to adaptation in wheat. EigenGWAS and EnvGWAS based on variety age avoid costly phenotyping and facilitate the identification of genomic tracts that have been under selection during breeding. Our results demonstrate the potential of using historical cultivar collections coupled with genomic data to identify chromosomal regions under selection and may help guide future plant breeding strategies to maximise the rate of genetic gain and adaptation., (© 2021. The Author(s).)

Determining when a barley plant starts and finishes meiosis is not trivial as when the spikelets undergo meiosis, the spike is not visible as it is still well within the leaf sheath on the developing tiller. This is a general constraint for any experiment involving meiosis, such as cytology, RNA extractions, or abiotic stress treatments aiming to target such a developmental stage. The lack of synchronicity between barley tillers within the same plant exacerbates the difficulty to determine the overall meiotic stage of a plant at a certain time.Given the lack of a nondestructive staging system for predicting the entry into meiosis and the problems of working with large pot plant systems, a modular plant growing is proposed. This system enables the growth of a high number of plants in a small surface, each producing a single tiller. The modular tray system was used to generate a nondestructive prediction tool for meiosis by using external morphological features. As an example, the system is used here for heat treating F 1 plants in early meiosis stages to modify recombination.

Wheat and barley have large genomes of 15 Gb and 5.1 Gb, respectively, which is much larger than the human genome (3.3 Gb). The release of their respective genomes has been a tremendous advance the understanding of the genome organization and the ability for deeper functional analysis in particular meiosis. Meiosis is the cell division required during sexual reproduction. One major event of meiosis is called recombination, or the formation of crossing over, a tight link between homologous chromosomes, ensuring gene exchange and faithful chromosome segregation. Recombination is a major driver of genetic diversity but in these large genome crops, the vast majority of these events is constrained at the end of their chromosomes. It is estimated that in barley, about 30% of the genes are located within the poor recombining centromeric regions, making important traits, such as resistance to pest and disease for example, difficult to access. Increasing recombination in these crops has the potential to speed up breeding program and requires a good understand of the meiotic mechanism. However, most research on recombination in plant has been carried in Arabidopsis thaliana which despite many of the advantages it brings for plant research, has a small genome and more spread out of recombination compare to barley or wheat. Advance in microscopy and cytological procedures have emerged in the last few years, allowing to follow meiotic events in these crops. This protocol provides the steps required for cytological preparation of barley and wheat pollen mother cells for light microscopy, highlighting some of the differences between the two cereals.

Recombination (crossover) drives the release of genetic diversity in plant breeding programs. However, in barley, recombination is skewed toward the telomeric ends of its seven chromosomes, restricting the re-assortment of about 30% of the genes located in the centromeric regions of its large 5.1 Gb genome. A better understanding of meiosis and recombination could provide ways of modulating crossover distribution and frequency in barley as well as in other grasses, including wheat. While most research on recombination has been carried out in the model plant Arabidopsis thaliana, recent studies in barley (Hordeum Vulgare) have provided new insights into the control of crossing over in large genome species. A major achievement in these studies has been the use of cytological procedures to follow meiotic events. This protocol provides detailed practical steps required to perform immunostaining of barley meiocytes (pollen mother cells) for confocal or structured illumination microscopy.

We carried out a genome-wide analysis of polymorphism (4,596 SNP loci across 190 elite cultivated accessions) chosen to represent the available genetic variation in current elite North West European and North American barley germplasm. Population sub-structure, patterns of diversity and linkage disequilibrium varied considerably across the seven barley chromosomes. Gene-rich and rarely recombining haplotype blocks that may represent up to 60% of the physical length of barley chromosomes extended across the 'genetic centromeres'. By positioning 2,132 bi-parentally mapped SNP markers with minimum allele frequencies higher than 0.10 by association mapping, 87.3% were located to within 5 cM of their original genetic map position. We show that at this current marker density genetically diverse populations of relatively small size are sufficient to fine map simple traits, providing they are not strongly stratified within the sample, fall outside the genetic centromeres and population sub-structure is effectively controlled in the analysis. Our results have important implications for association mapping, positional cloning, physical mapping and practical plant breeding in barley and other major world cereals including wheat and rye that exhibit comparable genome and genetic features.