Plant pan-genomics and its applications

The near-complete genome assembly of hexaploid wild oat reveals its genome evolution and divergence with cultivated oats

Avena sterilis, the ancestral species of cultivated oats, is a valuable genetic resource for oat improvement. Here we generated a near-complete 10.99 Gb A. sterilis genome and a high-quality 10.89 Gb cultivated oat genome. Genome evolution analysis revealed the centromeres dynamic and structural variations landscape associated with domestication between wild and cultivated oats. Population genetic analysis of 117 wild and cultivated oat accessions worldwide detected many candidate genes associated with important agronomic traits for oat domestication and improvement. Remarkably, a large fragment duplication from chromosomes 4A to 4D harbouring many agronomically important genes was detected during oat domestication and was fixed in almost all cultivated oats from around the world. The genes in the duplication region from 4A showed significantly higher expression levels and lower methylation levels than the orthologous genes located on 4D in A. sterilis. This study provides valuable resources for evolutionary and functional genomics and genetic improvement of oat.

Genetic advancements and future directions in ruminant livestock breeding: from reference genomes to multiomics innovations

Ruminant livestock provide a rich source of products, such as meat, milk, and wool, and play a critical role in global food security and nutrition. Over the past few decades, genomic studies of ruminant livestock have provided valuable insights into their domestication and the genetic basis of economically important traits, facilitating the breeding of elite varieties. In this review, we summarize the main advancements for domestic ruminants in reference genome assemblies, population genomics, and the identification of functional genes or variants for phenotypic traits. These traits include meat and carcass quality, reproduction, milk production, feed efficiency, wool and cashmere yield, horn development, tail type, coat color, environmental adaptation, and disease resistance. Functional genomic research is entering a new era with the advancements of graphical pangenomics and telomere-to-telomere (T2T) gap-free genome assembly. These advancements promise to improve our understanding of domestication and the molecular mechanisms underlying economically important traits in ruminant livestock. Finally, we provide new perspectives and future directions for genomic research on ruminant genomes. We suggest how ever-increasing multiomics datasets will facilitate future studies and molecular breeding in livestock, including the potential to uncover novel genetic mechanisms underlying phenotypic traits, to enable more accurate genomic prediction models, and to accelerate genetic improvement programs.

Omics-Driven Strategies for Developing Saline-Smart Lentils: A Comprehensive Review

A number of consequences of climate change, notably salinity, put global food security at risk by impacting the development and production of lentils. Salinity-induced stress alters lentil genetics, resulting in severe developmental issues and eventual phenotypic damage. Lentils have evolved sophisticated signaling networks to combat salinity stress. Lentil genomics and transcriptomics have discovered key genes and pathways that play an important role in mitigating salinity stress. The development of saline-smart cultivars can be further revolutionized by implementing proteomics, metabolomics, miRNAomics, epigenomics, phenomics, ionomics, machine learning, and speed breeding approaches. All these cutting-edge approaches represent a viable path toward creating saline-tolerant lentil cultivars that can withstand climate change and meet the growing demand for high-quality food worldwide. The review emphasizes the gaps that must be filled for future food security in a changing climate while also highlighting the significant discoveries and insights made possible by omics and other state-of-the-art biotechnological techniques.

Biparental graph strategy to represent and analyze hybrid plant genomes

Hybrid plants are found extensively in the wild, and they often demonstrate superior performance of complex traits over their parents and other selfing plants. This phenomenon, known as heterosis, has been extensively applied in plant breeding for decades. However, the process of decoding hybrid plant genomes has seriously lagged due to the challenges associated with genome assembly and the lack of appropriate methodologies for their subsequent representation and analysis. Here, we present the assembly and analysis of 2 hybrids, an intraspecific hybrid between 2 maize (Zea mays ssp. mays) inbred lines and an interspecific hybrid between maize and its wild relative teosinte (Z. mays ssp. parviglumis), utilizing a combination of PacBio High Fidelity sequencing and chromatin conformation capture sequencing data. The haplotypic assemblies are well phased at chromosomal scale, successfully resolving the complex loci with extensive parental structural variations (SVs). By integrating into a biparental genome graph, the haplotypic assemblies can facilitate downstream short-read-based SV calling and allele-specific gene expression analysis, demonstrating outstanding advantages over a single linear genome. Our work offers a comprehensive workflow that aims to facilitate the decoding of numerous hybrid plant genomes, particularly those with unknown or inaccessible parentage, thereby enhancing our understanding of genome evolution and heterosis.

Structural variation discovery in wheat using PacBio high-fidelity sequencing

Structural variations (SVs) pervade plant genomes and contribute substantially to the phenotypic diversity. However, most SVs were ineffectively assayed due to their complex nature and the limitations of early genomic technologies. By applying the PacBio high-fidelity (HiFi) sequencing for wheat genomes, we performed a comprehensive evaluation of mainstream long-read aligners and SV callers in SV detection. The results indicated that the accuracy of deletion discovery is markedly influenced by callers, accounting for 87.73% of the variance, whereas both aligners (38.25%) and callers (49.32%) contributed substantially to the accuracy variance for insertions. Among the aligners, Winnowmap2 and NGMLR excelled in detecting deletions and insertions, respectively. For SV callers, SVIM achieved the best performance. We demonstrated that combining the aligners and callers mentioned above is optimal for SV detection. Furthermore, we evaluated the effect of sequencing depth on the accuracy of SV detection, revealing that low-coverage HiFi sequencing is sufficiently robust for high-quality SV discovery. This study thoroughly evaluated SV discovery approaches and established optimal workflows for investigating structural variations using low-coverage HiFi sequencing in the wheat genome, which will advance SV discovery and decipher the biological functions of SVs in wheat and many other plants.

Post-transfer adaptation of HGT-acquired genes and contribution to guanine metabolic diversification in land plants

Horizontal gene transfer (HGT) is a major driving force in the evolution of prokaryotic and eukaryotic genomes. Despite recent advances in distribution and ecological importance, the extensive pattern, especially in seed plants, and post-transfer adaptation of HGT-acquired genes in land plants remain elusive. We systematically identified 1150 foreign genes in 522 land plant genomes that were likely acquired via at least 322 distinct transfers from nonplant donors and confirmed that recent HGT events were unevenly distributed between seedless and seed plants. HGT-acquired genes evolved to be more similar to native genes in terms of average intron length due to intron gains, and HGT-acquired genes containing introns exhibited higher expression levels than those lacking introns, suggesting that intron gains may be involved in the post-transfer adaptation of HGT in land plants. Functional validation of bacteria-derived gene GuaD in mosses and gymnosperms revealed that the invasion of foreign genes introduced a novel bypass of guanine degradation and resulted in the loss of native pathway genes in some gymnosperms, eventually shaping three major types of guanine metabolism in land plants. We conclude that HGT has played a critical role in land plant evolution.

Multi-omics analyzes of Rosa gigantea illuminate tea scent biosynthesis and release mechanisms

Rose is an important ornamental crop cultivated globally for perfume production. However, our understanding of the mechanisms underlying scent production and molecular breeding for fragrance is hindered by the lack of a reference genome for tea roses. We present the first complete telomere-to-telomere (T2T) genome of Rosa gigantea, with high quality (QV > 60), including detailed characterization of the structural features of repetitive regions. The expansion of genes associated with phenylpropanoid biosynthesis may account for the unique tea scent. We uncover the release rhythm of aromatic volatile organic compounds and their gene regulatory networks through comparative genomics and time-ordered gene co-expression networks. Analyzes of eugenol homologs demonstrate how plants attract pollinators using specialized phenylpropanoids in specific tissues. This study highlights the conservation and utilization of genetic diversity from wild endangered species through multi-omics approaches, providing a scientific foundation for enhancing rose fragrance via de novo domestication.

Pan-genome analyses of 11 Fraxinus species provide insights into salt adaptation in ash trees

Ash trees (Fraxinus) exhibit rich genetic diversity and wide adaptation to various ecological environments, and several species are highly salt tolerant. Dissecting the genomic basis of salt adaptation in Fraxinus is vital for its resistance breeding. Here, we present 11 high-quality chromosome-level genome assemblies for Fraxinus species, which reveal two unequal subgenome compositions and two recent whole-genome triplication events in their evolutionary history. A Fraxinus pan-genome was constructed on the basis of structural variations and revealed that presence-absence variations (PAVs) of transmembrane transport genes have likely contributed to salt adaptation in Fraxinus. Through whole-genome resequencing of an F1 population from an interspecies cross of F. velutina 'Lula 3' (salt tolerant) with F. pennsylvanica 'Lula 5' (salt sensitive), we mapped salt-tolerance PAV-based quantitative trait loci (QTLs) and pinpointed two PAV-QTLs and candidate genes associated with Fraxinus salt tolerance. Mechanistically, FvbHLH85 enhances salt tolerance by mediating reactive oxygen species and Na+/K+ homeostasis, whereas FvSWEET5 enhances salt tolerance by mediating osmotic homeostasis. Collectively, these findings provide valuable genomic resources for Fraxinus salt-resistance breeding and the research community.

Retrospect and prospect of Nicotiana tabacum genome sequencing

Investigating plant genomes offers crucial foundational resources for exploring various aspects of plant biology and applications, such as functional genomics and breeding practices. With the development in sequencing and assembly technology, several Nicotiana tabacum genomes have been published. In this paper, we reviewed the progress on N. tabacum genome assembly and quality, from the initial draft genomes to the recent high-quality chromosome-level assemblies. The application of long-read sequencing, optical mapping, and Hi-C technologies has significantly improved the contiguity and completeness of N. tabacum genome assemblies, with the latest assemblies having a contig N50 size over 50 Mb. Despite these advancements, further improvements are still required and possible, particularly on the development of pan-genome and telomere-to-telomere (T2T) genomes. These new genomes will capture the genomic diversity and variations among different N. tabacum cultivars and species, and provide a comprehensive view of the N. tabacum genome structure and gene content, so to deepen our understanding of the N. tabacum genome and facilitate precise breeding and functional genomics.

Omics approaches to unravel insecticide resistance mechanism in Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae)

Bemisia tabaci (Gennadius) whitefly (BtWf) is an invasive pest that has already spread worldwide and caused major crop losses. Numerous strategies have been implemented to control their infestation, including the use of insecticides. However, prolonged insecticide exposures have evolved BtWf to resist these chemicals. Such resistance mechanism is known to be regulated at the molecular level and systems biology omics approaches could shed some light on understanding this regulation wholistically. In this review, we discuss the use of various omics techniques (genomics, transcriptomics, proteomics, and metabolomics) to unravel the mechanism of insecticide resistance in BtWf. We summarize key genes, enzymes, and metabolic regulation that are associated with the resistance mechanism and review their impact on BtWf resistance. Evidently, key enzymes involved in the detoxification system such as cytochrome P450 (CYP), glutathione S-transferases (GST), carboxylesterases (COE), UDP-glucuronosyltransferases (UGT), and ATP binding cassette transporters (ABC) family played key roles in the resistance. These genes/proteins can then serve as the foundation for other targeted techniques, such as gene silencing techniques using RNA interference and CRISPR. In the future, such techniques will be useful to knock down detoxifying genes and crucial neutralizing enzymes involved in the resistance mechanism, which could lead to solutions for coping against BtWf infestation.

Revealing the Genetic Diversity and Population Structure of Garlic Resource Cultivars and Screening of Core Cultivars Based on Specific Length Amplified Fragment Sequencing (SLAF-Seq)

Garlic is an important vegetable and condiment that has good medical and health care effects. At present, the origin of Chinese garlic and its association with other types of quality are limited to the molecular marker level, and there are few reports at the genome level. Therefore, this study is based on the specific length amplified fragment sequencing (SLAF-seq) of 102 copies of garlic germplasm resources, the group structure, and further screening of the core germplasm. SLAF-seq of 102 garlic cultivars yielded 1949.85 Mb of clean data and 526,432,275 SNPs. Through principal component analysis, evolutionary tree, population structure, and genetic relationship analysis, all garlic cultivars were divided into 3 groups. Among them, Group 1 contains 45 Chinese cultivars and 1 Egyptian cultivar, which are distributed mainly in the coastal and central areas of China. Group 2 contains 36 Chinese cultivars and 1 U.S. cultivar, which are distributed mainly in Northwest China. Group 3 contains 19 Chinese cultivars, which are distributed mainly in Xinjiang, China. The genetic diversity results indicate that the fixation index (Fst) values of Group 1 and Group 2 are lower than those of Group 1 and Group 3 and that the diversity of nucleotides (π) of Group 3 is greater than those of Group 2 and Group 1. Finally, the 30 parts of the cultivars were used as the core germplasms, and there was no difference between the two cultivars in terms of core quality. In summary, this study provides tags for the determination of garlic molecular markers and genotypes and provides a theoretical basis for subsequent resource protection and utilization, genetic positioning of important agronomic traits, and molecular marking agglomeration breeding.

Triumphs of genomic-assisted breeding in crop improvement

Conventional breeding approaches have played a significant role in meeting the food demand remarkably well until now. However, the increasing population, yield plateaus in certain crops, and limited recombination necessitate using genomic resources for genomics-assisted crop improvement programs. As a result of advancements in the next-generation sequence technology, GABs have developed dramatically to characterize allelic variants and facilitate their rapid and efficient incorporation in crop improvement programs. Genomics-assisted breeding (GAB) has played an important role in harnessing the potential of modern genomic tools, exploiting allelic variation from genetic resources and developing cultivars over the past decade. The availability of pangenomes for major crops has been a significant development, albeit with varying degrees of completeness. Even though adopting these technologies is essentially determined on economic grounds and cost-effective assays, which create a wealth of information that can be successfully used to exploit the latent potential of crops. GAB has been instrumental in harnessing the potential of modern genomic resources and exploiting allelic variation for genetic enhancement and cultivar development. GAB strategies will be indispensable for designing future crops and are expected to play a crucial role in breeding climate-smart crop cultivars with higher nutritional value.

Engineering the future cereal crops with big biological data: toward intelligence-driven breeding by design

How to feed 10 billion human populations is one of the challenges that need to be addressed in the following decades, especially under an unpredicted climate change. Crop breeding, initiating from the phenotype-based selection by local farmers and developing into current biotechnology-based breeding, has played a critical role in securing the global food supply. However, regarding the changing environment and ever-increasing human population, can we breed outstanding crop varieties fast enough to achieve high productivity, good quality, and widespread adaptability? This review outlines the recent achievements in understanding cereal crop breeding, including the current knowledge about crop agronomic traits, newly developed techniques, crop big biological data research, and the possibility of integrating them for intelligence-driven breeding by design, which ushers in a new era of crop breeding practice and shapes the novel architecture of future crops. This review focuses on the major cereal crops, including rice, maize, and wheat, to explain how intelligence-driven breeding by design is becoming a reality.

Evolutionary insights into the organization of chromatin structure and landscape of transcriptional regulation in plants

Development of complex traits necessitates the functioning and coordination of intricate regulatory networks involving multiple genes. Understanding 3D chromatin structure can facilitate insight into the regulation of gene expression by regulatory elements. This potential, of visualizing the role of chromatin organization in the evolution and function of regulatory elements, remains largely unexplored. Here, we describe new perspectives that arise from the dual considerations of sequence variation of regulatory elements and chromatin structure, with a special focus on whole-genome doubling or polyploidy. We underscore the significance of hierarchical chromatin organization in gene regulation during evolution. In addition, we describe strategies for exploring chromatin organization in future investigations of regulatory evolution in plants, enabling insights into the evolutionary influence of regulatory elements on gene expression and, hence, phenotypes.

Harnessing the predicted maize pan-interactome for putative gene function prediction and prioritization of candidate genes for important traits

The recent assembly and annotation of the 26 maize nested association mapping population founder inbreds have enabled large-scale pan-genomic comparative studies. These studies have expanded our understanding of agronomically important traits by integrating pan-transcriptomic data with trait-specific gene candidates from previous association mapping results. In contrast to the availability of pan-transcriptomic data, obtaining reliable protein-protein interaction (PPI) data has remained a challenge due to its high cost and complexity. We generated predicted PPI networks for each of the 26 genomes using the established STRING database. The individual genome-interactomes were then integrated to generate core- and pan-interactomes. We deployed the PPI clustering algorithm ClusterONE to identify numerous PPI clusters that were functionally annotated using gene ontology (GO) functional enrichment, demonstrating a diverse range of enriched GO terms across different clusters. Additional cluster annotations were generated by integrating gene coexpression data and gene description annotations, providing additional useful information. We show that the functionally annotated PPI clusters establish a useful framework for protein function prediction and prioritization of candidate genes of interest. Our study not only provides a comprehensive resource of predicted PPI networks for 26 maize genomes but also offers annotated interactome clusters for predicting protein functions and prioritizing gene candidates. The source code for the Python implementation of the analysis workflow and a standalone web application for accessing the analysis results are available at https://github.com/eporetsky/PanPPI.

Identification of allelic relationship and translocation region among chromosomal translocation lines that leads to less-seed watermelon

Less-seed and seedless traits are desirable characteristics in watermelon (Citrullus lanatus). Hybridization between watermelon chromosomal translocated lines and wild lines significantly reduced seed counts in the hybrid fruits, approaching even seedless. However, the allelic relationships and the chromosomal translocation breakpoints from different sources are unclear, which limits their utility in breeding practices. This study focused on three groups of chromosomal translocation materials from different sources and conducted inheritance and allelic relationship analysis of translocation points. The results from third-generation genome sequencing and fluorescence in situ hybridization (FISH) revealed that the specific translocations in the naturally mutated material MT-a involved reciprocal translocations between Chr6 and Chr10. The Co60γ radiation-induced mutant material MT-b involved reciprocal translocations between Chr1 and Chr5, Chr4 and Chr8. The Co60γ radiation-induced mutant material MT-c involved complex translocations among Chr1, Chr5, and Chr11. Cytological observation showed that heterozygous translocation hybrids showed chromosomal synapsis abnormalities during meiotic diakinesis. Further, dominant and codominant molecular markers were developed on both sides of the translocation breakpoints, which could facilitate rapid and efficient identification of chromosome translocation lines. This study provides technical guidance for utilizing chromosomal translocation materials in the development of less-seed watermelon varieties.

HEMU: An integrated comparative genomics database and analysis platform for Andropogoneae grasses

This study reports an online database and analysis platform HEMU, which integrates 75 genome assemblies from 20 unique species, large amounts of multi-omics data, and six sophisticated analysis toolkits. HEMU will facilitate comparative genomics analysis within the tribe Andropogoneae.

Technology-enabled great leap in deciphering plant genomes

Plant genomes provide essential and vital basic resources for studying many aspects of plant biology and applications (for example, breeding). From 2000 to 2020, 1,144 genomes of 782 plant species were sequenced. In the past three years (2021-2023), 2,373 genomes of 1,031 plant species, including 793 newly sequenced species, have been assembled, representing a great leap. The 2,373 newly assembled genomes, of which 63 are telomere-to-telomere assemblies and 921 have been generated in pan-genome projects, cover the major phylogenetic clades. Substantial advances in read length, throughput, accuracy and cost-effectiveness have notably simplified the achievement of high-quality assemblies. Moreover, the development of multiple software tools using different algorithms offers the opportunity to generate more complete and complex assemblies. A database named N3: plants, genomes, technologies has been developed to accommodate the metadata associated with the 3,517 genomes that have been sequenced from 1,575 plant species since 2000. We also provide an outlook for emerging opportunities in plant genome sequencing.

Functional genomics of Brassica napus: Progresses, challenges, and perspectives

Brassica napus, commonly known as rapeseed or canola, is a major oil crop contributing over 13% to the stable supply of edible vegetable oil worldwide. Identification and understanding the gene functions in the B. napus genome is crucial for genomic breeding. A group of genes controlling agronomic traits have been successfully cloned through functional genomics studies in B. napus. In this review, we present an overview of the progress made in the functional genomics of B. napus, including the availability of germplasm resources, omics databases and cloned functional genes. Based on the current progress, we also highlight the main challenges and perspectives in this field. The advances in the functional genomics of B. napus contribute to a better understanding of the genetic basis underlying the complex agronomic traits in B. napus and will expedite the breeding of high quality, high resistance and high yield in B. napus varieties.

Gapless genome assembly and epigenetic profiles reveal gene regulation of whole-genome triplication in lettuce

BACKGROUND

Lettuce, an important member of the Asteraceae family, is a globally cultivated cash vegetable crop. With a highly complex genome (∼2.5 Gb; 2n = 18) rich in repeat sequences, current lettuce reference genomes exhibit thousands of gaps, impeding a comprehensive understanding of the lettuce genome.

FINDINGS

Here, we present a near-complete gapless reference genome for cutting lettuce with high transformability, using long-read PacBio HiFi and Nanopore sequencing data. In comparison to stem lettuce genome, we identify 127,681 structural variations (SVs, present in 0.41 Gb of sequence), reflecting the divergence of leafy and stem lettuce. Interestingly, these SVs are related to transposons and DNA methylation states. Furthermore, we identify 4,612 whole-genome triplication genes exhibiting high expression levels associated with low DNA methylation levels and high N6-methyladenosine RNA modifications. DNA methylation changes are also associated with activation of genes involved in callus formation.

CONCLUSIONS

Our gapless lettuce genome assembly, an unprecedented achievement in the Asteraceae family, establishes a solid foundation for functional genomics, epigenomics, and crop breeding and sheds new light on understanding the complexity of gene regulation associated with the dynamics of DNA and RNA epigenetics in genome evolution.

Genotype and phenotype data standardization, utilization and integration in the big data era for agricultural sciences

Large-scale genotype and phenotype data have been increasingly generated to identify genetic markers, understand gene function and evolution and facilitate genomic selection. These datasets hold immense value for both current and future studies, as they are vital for crop breeding, yield improvement and overall agricultural sustainability. However, integrating these datasets from heterogeneous sources presents significant challenges and hinders their effective utilization. We established the Genotype-Phenotype Working Group in November 2021 as a part of the AgBioData Consortium (https://www.agbiodata.org) to review current data types and resources that support archiving, analysis and visualization of genotype and phenotype data to understand the needs and challenges of the plant genomic research community. For 2021-22, we identified different types of datasets and examined metadata annotations related to experimental design/methods/sample collection, etc. Furthermore, we thoroughly reviewed publicly funded repositories for raw and processed data as well as secondary databases and knowledgebases that enable the integration of heterogeneous data in the context of the genome browser, pathway networks and tissue-specific gene expression. Based on our survey, we recommend a need for (i) additional infrastructural support for archiving many new data types, (ii) development of community standards for data annotation and formatting, (iii) resources for biocuration and (iv) analysis and visualization tools to connect genotype data with phenotype data to enhance knowledge synthesis and to foster translational research. Although this paper only covers the data and resources relevant to the plant research community, we expect that similar issues and needs are shared by researchers working on animals. Database URL: https://www.agbiodata.org.

Selection of Flax Genotypes for Pan-Genomic Studies by Sequencing Tagmentation-Based Transcriptome Libraries

Flax (Linum usitatissimum L.) products are used in the food, pharmaceutical, textile, polymer, medical, and other industries. The creation of a pan-genome will be an important advance in flax research and breeding. The selection of flax genotypes that sufficiently cover the species diversity is a crucial step for the pan-genomic study. For this purpose, we have adapted a method based on Illumina sequencing of transcriptome libraries prepared using the Tn5 transposase (tagmentase). This approach reduces the cost of sample preparation compared to commercial kits and allows the generation of a large number of cDNA libraries in a short time. RNA-seq data were obtained for 192 flax plants (3-6 individual plants from 44 flax accessions of different morphology and geographical origin). Evaluation of the genetic relationship between flax plants based on the sequencing data revealed incorrect species identification for five accessions. Therefore, these accessions were excluded from the sample set for the pan-genomic study. For the remaining samples, typical genotypes were selected to provide the most comprehensive genetic diversity of flax for pan-genome construction. Thus, high-throughput sequencing of tagmentation-based transcriptome libraries showed high efficiency in assessing the genetic relationship of flax samples and allowed us to select genotypes for the flax pan-genomic analysis.

Application of Multi-Perspectives in Tea Breeding and the Main Directions

Tea plants are an economically important crop and conducting research on tea breeding contributes to enhancing the yield and quality of tea leaves as well as breeding traits that satisfy the requirements of the public. This study reviews the current status of tea plants germplasm resources and their utilization, which has provided genetic material for the application of multi-omics, including genomics and transcriptomics in breeding. Various molecular markers for breeding were designed based on multi-omics, and available approaches in the direction of high yield, quality and resistance in tea plants breeding are proposed. Additionally, future breeding of tea plants based on single-cellomics, pangenomics, plant-microbe interactions and epigenetics are proposed and provided as references. This study aims to provide inspiration and guidance for advancing the development of genetic breeding in tea plants, as well as providing implications for breeding research in other crops.

Pan-genome for pearl millet that beats the heat

A better understanding of crop genomes reveals that structural variations (SVs) are crucial for genetic improvement. A graph-based pan-genome by Yan et al. uncovered 424 085 genomic SVs and provided novel insights into heat tolerance of pearl millet. We discuss how these SVs can fast-track pearl millet breeding under harsh environments.

k-mer-Based Genome-Wide Association Studies in Plants: Advances, Challenges, and Perspectives

Genome-wide association studies (GWAS) have allowed the discovery of marker-trait associations in crops over recent decades. However, their power is hampered by a number of limitations, with the key one among them being an overreliance on single-nucleotide polymorphisms (SNPs) as molecular markers. Indeed, SNPs represent only one type of genetic variation and are usually derived from alignment to a single genome assembly that may be poorly representative of the population under study. To overcome this, k-mer-based GWAS approaches have recently been developed. k-mer-based GWAS provide a universal way to assess variation due to SNPs, insertions/deletions, and structural variations without having to specifically detect and genotype these variants. In addition, k-mer-based analyses can be used in species that lack a reference genome. However, the use of k-mers for GWAS presents challenges such as data size and complexity, lack of standard tools, and potential detection of false associations. Nevertheless, efforts are being made to overcome these challenges and a general analysis workflow has started to emerge. We identify the priorities for k-mer-based GWAS in years to come, notably in the development of user-friendly programs for their analysis and approaches for linking significant k-mers to sequence variation.

Combination of Hairy Root and Whole-Plant Transformation Protocols to Achieve Efficient CRISPR/Cas9 Genome Editing in Soybean

The new gene-editing technology CRISPR/Cas system has been widely used for genome engineering in various organisms. Since the CRISPR/Cas gene-editing system has a certain possibility of low efficiency and the whole plant transformation of soybean is time-consuming and laborious, it is important to evaluate the editing efficiency of designed CRISPR constructs before the stable whole plant transformation process starts. Here, we provide a modified protocol for generating transgenic hairy soybean roots to assess the efficiency of guide RNA (gRNA) sequences of the CRISPR/Cas constructs within 14 days. The cost- and space-effective protocol was first tested in transgenic soybean harboring the GUS reporter gene for the efficiency of different gRNA sequences. Targeted DNA mutations were detected in 71.43-97.62% of the transgenic hairy roots analyzed as evident by GUS staining and DNA sequencing of the target region. Among the four designed gene-editing sites, the highest editing efficiency occurred at the 3' terminal of the GUS gene. In addition to the reporter gene, the protocol was tested for the gene-editing of 26 soybean genes. Among the gRNAs selected for stable transformation, the editing efficiency of hairy root transformation and stable transformation ranged from 5% to 88.8% and 2.7% to 80%, respectively. The editing efficiencies of stable transformation were positively correlated with those of hairy root transformation with a Pearson correlation coefficient (r) of 0.83. Our results demonstrated that soybean hairy root transformation could rapidly assess the efficiency of designed gRNA sequences on genome editing. This method can not only be directly applied to the functional study of root-specific genes, but more importantly, it can be applied to the pre-screening of gRNA in CRISPR/Cas gene editing.