Automated assembly scaffolding using RagTag elevates a new tomato system for high-throughput genome editing

Increased maize chromosome number by engineered chromosome fission

Activation of synthetic centromeres on chromosome 4 in maize leads to its breakage and formation of trisomic fragments called neochromosomes. A limitation of neochromosomes is their low and unpredictable transmission rates due to trisomy. Here, we report that selecting for dicentric recombinants through male crosses uncovers stabilized chromosome 4 fission events, which split it into 4a-4b complementary chromosome pairs, where 4a carries a native centromere and 4b carries a synthetic one. The cells rapidly stabilized chromosome ends by de novo telomere formation, and the new centromeres spread among genes without altering their expression. When both 4a and 4b chromosomes were made homozygous, they segregated through meiosis indistinguishably from wild type and gave rise to healthy plants with normal seed set, indicating that the synthetic centromere was fully functional. This work leverages synthetic centromeres to engineer chromosome fission, raising the diploid chromosome number of maize from 20 to 22.

Chromosomal scale assembly and functional annotation of the apicomplexan parasite Eimeria acervulina

Apicomplexan parasites are single-celled obligate intracellular eukaryotic organisms that cause significant animal and human disease and pose a substantial health and socioeconomic burden worldwide. Eimeria acervulina is one such parasite of chickens, representative of several Eimeria species causing coccidiosis disease. A complete assembly of the E. acervulina genome may help identify markers of drug-resistance and design recombinant vaccines. We sequenced E. acervulina APU1 strain using Oxford Nanopore Sequencing and Illumina technology in combination with a Hi-C (Omni-C) proximity linkage library and achieved a chromosomal scale assembly using the MaSuRCA assembler. The final assembly was 52 Mb. with 15 chromosomes and 99% BUSCO completeness. A total of 7,621 genes were predicted using a pipeline of BRAKER3, GeneMark-ETP and AUGUSTUS, of which 4,647 (60.97%) have a predicted Pfam function and 1,962 (25.74%) have Gene Ontology (GO) terms matching molecular, biological, and functional classes. Stage-specific transcriptome analysis revealed 9,761 transcripts. This genome assembly and transcriptome analysis provides the foundation for identifying biologically important candidates for anticoccidial drug and vaccine development.

Whole genome sequencing and annotation of Pseudocercospora abelmoschi, a causal agent of black leaf mould of okra

Pseudocercospora abelmoschi causes black mould on the leaves of okra. The disease is prevalent post-rainy season when high moisture and warm temperatures prevail. Severe defoliation is observed during favourable environments, leading to a significant loss in productivity. Based on the importance of the pathogen agriculturally, the P. abelmoschi isolate Cer 86 - 18 (MCC:9491) was selected for genome sequencing. The genome assembly of P. abelmoschi resulted in a genome of 31.90 Mb with an overall GC content of 54.26%. Quantitative genome assessment using BUSCO (Benchmarking Universal Single-Copy Orthologs) identified 1,664 (97.53%) complete BUSCOs, reflecting a high representation of conserved genes with minimal duplication and strong orthologous uniqueness. Gene prediction analysis identified 11,325 protein-coding genes, of which 3,857 were annotated using the KEGG database. As per analyses, 410 genes were predicted to encode carbohydrate-active enzymes, whereas 369 genes were predicted to encode peptidases. Eighteen gene clusters involved in secondary metabolite biosynthesis were also identified. A total of 143 proteins were predicted to be effectors using the in-silico pipeline. This is the first report on the genome organisation of P. abelmoschi. This study was designed to address this gap by enhancing our understanding of the genome organisation of P. abelmoschi and gene annotation, thereby paving the way for functional genomics studies, such as identifying virulence genes to aid in resistance breeding. Also, this genome could be another addition to the available genomic resources of the genus Pseudocercospora and can provide valuable insights into host-pathogen interactions and evolutionary relationships.

Repeatome diversity in sea anemone genomics (Cnidaria: Actiniaria) based on the Actiniaria-REPlib library

BACKGROUND

Genomic repetitive DNA sequences (Repeatomes, REPs) are widespread in eukaryotes, influencing biological form and function. In Cnidaria, an early-diverging animal lineage, these sequences remain largely uncharacterized. This study investigates sea anemone REPs (Cnidaria: Actiniaria) in a phylogenetic context. We sequenced and assembled de novo the genome of Actinostella flosculifera and analyzed a total of 38 nuclear genomes to create the first ActiniariaREP library (Actiniaria-REPlib). We compared Actiniaria-REPlib with Repbase and RepeatModeler2 libraries, and used dnaPipeTE to annotate REPs from genomic short-read datasets of 36 species for divergence landscapes.

RESULTS

Our study assembled and annotated the mitochondrial genomes, including 27 newly assembled ones. We re-annotated ~92% of the unknown sequences from the initial nuclear genome library, finding that 6.4-30.6% were DNA transposons, 2.1-11.6% retrotransposons, 1-28.4% tandem repeat sequences, and 1.2-7% unclassifiable sequences. Actiniaria-REPlib recovered 9.4x more REP sequences from actiniarian genomes than Dfam and 10.4x more than Repbase. It yielded 79,903 annotated TE consensus sequences (74,643 known, 5,260 unknown), compared to Dfam with 7,697 (3,742 known, 3,944 unknown) and Repbae (763 known).

CONCLUSIONS

Our study significantly enhances the characterization of sea anemone repetitive DNA, assembling mitochondrial genomes, re-annotating nuclear sequences, and identifying diverse repeat elements. Actiniaria-REPlib vastly outperforms existing databases, recovering significantly more REP sequences and providing a comprehensive resource for future genomic and evolutionary studies in Actiniaria.

Optimizing plant size for vertical farming by editing stem length regulators

Vertical farming offers the advantage of providing a stable environment for plant cultivation, shielding them from adverse conditions such as climate change. For fruit-harvesting plants like tomato, vertical farming necessitates the optimization of plant growth and architecture. The gibberellin 3-oxidase (GA3ox) genes encode gibberellin 3-oxidases responsible for activating GA within the pathway and modulating stem length. Among the five SlGA3ox genes, we targeted the coding regions of three SlGA3ox genes (named SlGA3ox3, SlGA3ox4 and SlGA3ox5) using multiplex CRISPR genome editing. The slga3ox4 single mutants exhibited a slight reduction in primary shoot length, leading to a smaller stature. In contrast, the slga3ox3 and slga3ox5 single mutants showed subtle phenotypic changes. Notably, the slga3ox3 slga3ox4 double mutants developed a more compact shoot architecture with minor physiological differences, potentially making them suitable for vertical farming applications. We observed a correlation between total yield and plant size across all genotypes through multiple yield trials. Observations from vertical farm cultivation revealed that slga3ox3 slga3ox4 plants possess a markedly compact plant size, offering potential benefits for space-efficient cultivation. Our research suggests that targeted manipulation of hormone biosynthetic genes can effectively tailor plant architecture for vertical farming.

Osmoregulatory evolution of gills promoted salinity adaptation following the sea-land transition of crustaceans

The sea-land transition is one of the most dramatic evolutionary changes and requires an adaptive genetic response to salinity changes and osmotic stress. Here, we used multi-species genomes and multi-tissue transcriptomes of the talitrid crustaceans, a living sea-land transition model, to investigate the adaptive genetic changes and osmoregulatory organs that facilitated their salinity adaptation. Genomic analyses detected numerous osmoregulatory genes in terrestrial talitrids undergoing gene family expansions and positive selection. Gene expression comparisons among species and tissues confirmed the gill being the primary organ responsible for ion transport and identified the genetic expression variation that enable talitrids to adapt to marine and land habitats. V-type H+-ATPases related to H+ transport play a crucial role in land adaptations, while genes related to the transport of inorganic ions (Na+, K+, Cl-) are upregulated in marine habitats. Our results demonstrate that talitrids have divergent genetic responses to salinity change that led to the uptake or excretion of ions in the gills and promoted habitat adaptation. These findings suggest that detecting gene expression changes in talitrids presents promising potential as a biomarker for salinity monitoring.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-025-00298-6.

In a nutshell: pistachio genome and kernel development

Pistachio is a sustainable nut crop with exceptional climate resilience and nutritional value. However, the molecular processes underlying pistachio nut development and nutritional traits are largely unknown, compounded by limited genomic and molecular resources. To advance pistachios as a future food source and a model system for hard-shelled fruits, we generated a chromosome-scale reference genome of the most widely grown pistachio cultivar (Pistacia vera 'Kerman') and a spatiotemporal study of nut development. We integrated tissue-level physiological data from thousands of nuts over three growing seasons with transcriptomic data encompassing 14 developmental time points of the hull, shell, and kernel to assemble gene modules associated with physiological changes. Our study defined four distinct stages of pistachio nut growth and maturation. We then focused on the kernel to identify transcriptional and metabolic changes in molecular pathways governing nutritional quality, such as the accumulation of unsaturated fatty acids, which are vital for shelf life and dietary value. These findings revealed key candidate conserved regulatory genes, such as PvAP2-WRI1 and PvNFYB-LEC1, likely involved in oil accumulation in kernels. This work yields new knowledge and resources that will inform other woody crops and facilitate further improvement of pistachio as a globally significant, sustainable, and nutritious crop.

Genomic insights into the domestication and genetic basis of yield in papaya

Papaya (Carica papaya L.) is an important tropical and subtropical fruit crop, and understanding its genome is essential for breeding. In this study, we assembled a high-quality genome of 344.17 Mb for the newly cultivated papaya 'Zihui', which contains 22 250 protein-coding genes. By integrating 201 resequenced papaya genomes, we identified four distinct papaya groups and a 34 Mb genomic region with strong domestication selection signals. Within these regions, two key genes associated with papaya yield were discovered: Cp_zihui06549, encoding a leucine-rich receptor-like protein kinase, and Cp_zihui06768, encoding the accumulation of photosystem one 1 (APO1) protein. Heterologous expression of Cp_zihui06549 in tomato confirmed that the total number of fruits in transgenic lines more than doubled compared to wild-type plants, resulting in a significant yield increase. Furthermore, we constructed a pan-genome of papaya and obtained a 77.41 Mb nonreference sequence containing 1543 genes. Within this pan-genome, 2483 variable genes, we detected, including four genes annotated as the 'terpene synthase activity' Gene Ontology term, which were lost in cultivars during domestication. Finally, gene retention analyses were performed using gene presence and absence variation data and differentially expressed genes across various tissues and organs. This study provides valuable insights into the genes and loci associated with phenotypes and domestication processes, laying a solid foundation for future papaya breeding efforts.

The Genome of Lolium multiflorum Reveals the Genetic Architecture of Paraquat Resistance

Herbicide resistance in agricultural weeds has become one of the greatest challenges for sustainable crop production. The repeated evolution of herbicide resistance provides an excellent opportunity to study the genetic and physiological basis of the resistance phenotype and the evolutionary responses to human-mediated selection pressures. Lolium multiflorum is a ubiquitous weed that has evolved herbicide resistance repeatedly around the world in various cropping systems. We assembled and annotated a chromosome-scale genome for L. multiflorum and elucidated the genetic architecture of paraquat resistance by performing quantitative trait locus analysis, genome-wide association studies, genetic divergence analysis and transcriptome analyses from paraquat-resistant and -susceptible L. multiflorum plants. We identified two regions on chromosome 5 that were associated with paraquat resistance. These regions both showed evidence for positive selection among the resistant populations we sampled, but the effects of this selection on the genome differed, implying a complex evolutionary history. In addition, these regions contained candidate genes that encoded cellular transport functions, including a novel multidrug and toxin extrusion (MATE) protein and a cation transporter previously shown to interact with polyamines. Given that L. multiflorum is a weed and a cultivated crop species, the genomic resources generated will prove valuable to a wide spectrum of the plant science community. Our work contributes to a growing body of knowledge on the underlying evolutionary and ecological dynamics of rapid adaptation to strong anthropogenic selection pressure that could help initiate efforts to improve weed management practices in the long term for a more sustainable agriculture.

Pan-genomic analysis highlights genes associated with agronomic traits and enhances genomics-assisted breeding in alfalfa

Alfalfa (Medicago sativa L.), a globally important forage crop, is valued for its high nutritional quality and nitrogen-fixing capacity. Here, we present a high-quality pan-genome constructed from 24 diverse alfalfa accessions, encompassing a wide range of genetic backgrounds. This comprehensive analysis identified 433,765 structural variations and characterized 54,002 pan-gene families, highlighting the pivotal role of genomic diversity in alfalfa domestication and adaptation. Key structural variations associated with salt tolerance and quality traits were discovered, with functional analysis implicating genes such as MsMAP65 and MsGA3ox1. Notably, overexpression of MsGA3ox1 led to a reduced stem-leaf ratio and enhanced forage quality. The integration of genomic selection and marker-assisted breeding strategies improved genomic estimated breeding values across multiple traits, offering valuable genomic resources for advancing alfalfa breeding. These findings provide insights into the genetic basis of important agronomic traits and establish a solid foundation for future crop improvement.

Genome-Wide Demographic Analyses of Balaenid Whales Revealed Complex History of Gene Flow Associated with Past Climate Oscillation

The balaenid whale, comprising three species of right whales and the bowhead whale, represents an ancient and highly endangered lineage of marine mammals. To unravel the evolutionary history of balaenid whales with respect to gene flow, a comprehensive analysis based on whole-genome data was conducted for all species within this group. Employing population genomic methodologies, we revealed that extant right whales form an unresolved branching pattern, identified evidence of historical transequatorial migration, and provided estimates of the age of the group. Furthermore, we investigated the impact of glacial cycles on the connectivity of bowhead whale populations. By employing multiple complementary approaches to detect gene flow, we identified and characterized gene flow events from bowhead whales to North Atlantic right whales, offering detailed insights into the process. Lastly, we assessed the phenotypic consequences of interspecies gene flow. Our study sheds light on the intricate evolutionary history of modern balaenid whales, which have been profoundly shaped by ancient climate events.

Pan-Genome Analysis Reveals Local Adaptation to Climate Driven by Introgression in Oak Species

The genetic base of local adaptation has been extensively studied in natural populations. However, a comprehensive genome-wide perspective on the contribution of structural variants (SVs) and adaptive introgression to local adaptation remains limited. In this study, we performed de novo assembly and annotation of 22 representative accessions of Quercus variabilis, identifying a total of 543,372 SVs. These SVs play crucial roles in shaping genomic structure and influencing gene expression. By analyzing range-wide genomic data, we identified both SNPs and SVs associated with local adaptation in Q. variabilis and Quercus acutissima. Notably, SV-outliers exhibit selection signals that did not overlap with SNP-outliers, indicating that SNP-based analyses may not detect the same candidate genes associated with SV-outliers. Remarkably, 29%-37% of candidate SNPs were located in a 250 kb region on chromosome 9, referred to as Chr9-ERF. This region contains 8 duplicated ethylene-responsive factor (ERF) genes, which may have contributed to local adaptation of Q. variabilis and Q. acutissima. We also found that a considerable number of candidate SNPs were shared between Q. variabilis and Q. acutissima in the Chr9-ERF region, suggesting a pattern of repeated selection. We further demonstrated that advantageous variants in this region were introgressed from western populations of Q. acutissima into Q. variabilis, providing compelling evidence that introgression facilitates local adaptation. This study offers a valuable genomic resource for future studies on oak species and highlights the importance of pan-genome analysis in understating mechanism driving adaptation and evolution.

Phylogenomic associations among methicillin-resistant Staphylococcus aureus isolates derived from pets, dairies, and humans

Methicillin resistance in Staphylococcus aureus is conferred by the mobile genetic element, staphylococcal cassette chromosome mec (SCCmec). Methicillin-resistant Staphylococcus aureus (MRSA) can transmit among animals and humans, leading to persistence and back transmission events. The current study tested the hypothesis that companion animal and livestock-associated (LA) MRSA isolates share genomic similarity, suggesting shared ancestry with hospital-associated (HA) or community-associated (CA) MRSA. Eight S. aureus isolates from therapy dogs (n = 5) and bulk tank milk (n = 3) were genome sequenced, and 71,721 genome-wide single nucleotide polymorphism (SNP) locations were extracted and phylogenetically compared against methicillin-sensitive Staphylococcus aureus (MSSA) and MRSA genomes of isolates from a variety of species and time frames, available in the National Center for Biotechnology Information (NCBI) database. A maximum likelihood phylogenetic tree was constructed to define S. aureus lineages across isolates from animals and humans. Four isolates from companion animals and three bulk tank milk isolates clustered with human isolates, while one companion animal isolate clustered with genomes of MRSA isolated from swine. Four therapy dog isolates had CA-MRSA SCCmec types IVa, IVc, and V/VII, respectively, while one therapy dog and one bulk tank milk isolate shared SCCmec type (IIa) that is commonly seen in HA-MRSA. Two isolates from bulk tank milk were methicillin sensitive and did not carry mecA.

IMPORTANCE

Methicillin-resistant Staphylococcus aureus (MRSA) infections are a major medical concern, causing a range of conditions from skin infections and invasive disease to death. MRSA was discovered as a nosocomial infection; however, it has since been isolated in communities and animals worldwide. This research was significant because canine and bulk tank milk isolates were found to have genomic relatedness to human and domestic animal S. aureus isolates. This genetic relatedness implies either a parallel evolution within hosts converging to successful genotypes or real interspecies transmission events among animals and humans.

Recombination and transposition drive genomic structural variation potentially impacting life history traits in a host-generalist fungal plant pathogen

BACKGROUND

An understanding of plant pathogen evolution is important for sustainable management of crop diseases. Plant pathogen populations must maintain adequate heritable phenotypic variability to survive. Polymorphisms ≥ 50 bp, known as structural variants (SVs), could contribute strongly to this variability by disrupting gene activities. SV acquisition is largely driven by mobile genetic elements called transposons, though a less appreciated source of SVs is erroneous meiotic double-strand break repair. The relative impacts of transposons and recombination on SV diversity and the overall contribution of SVs to phenotypic variability is elusive, especially in host generalists.

RESULTS

We use 25 high-quality genomes to create a graphical pan-genome of the globally distributed host-generalist crop pathogen Sclerotinia sclerotiorum. Outcrossing and recombination rates in this self-fertile species have been debated. Using bisulfite sequencing and short-read data from 190 strains, we show that S. sclerotiorum has many hallmarks of eukaryotic meiosis, including recombination hot and cold spots, centromeric and genic recombination suppression, and rapid linkage disequilibrium decay. Using a new statistic that captures average pairwise structural variation, we show that recombination and transposons make distinct contributions to SV diversity. Furthermore, despite only 5% of genes being dispensable, SVs often had a stronger impact than other variants across 14 life history traits measured in 103 distinct strains.

CONCLUSIONS

Transposons and recombination make distinct contributions to SV diversity in S. sclerotiorum. Despite limited gene content diversity, SVs may strongly impact phenotypic variability. This sheds light on the genomic forces shaping adaptive flexibility in host generalists.

Characterisation of the Gillenia S-locus provides insight into evolution of the nonself-recognition self-incompatibility system in apple

Self-incompatibility (SI) in plants has evolved independently multiple times and S-RNase-based gametophytic self-incompatibility (GSI) is most common. The Rosaceae family possesses both self-recognition (Prunus) and nonself-recognition (Malus) GSI systems, and the latter is widespread in flowering plants. Gillenia trifoliata is a Rosaceae species related to Prunus and Malus, providing utility for understanding SI evolution. Gillenia is sister taxon to Malus, but unlike Malus, has not undergone polyploidisation. In addition, the common ancestor of Gillenia and Prunus is close to the origin of the subfamily. Using a highly contiguous Gillenia genome, orthologous regions to both Malus and Prunus S-loci were identified. Only the Prunus-like S-locus was highly polymorphic and had signatures of a functional S-locus including positive selection of the S-RNase. This suggests a self-recognition system controls SI in Gillenia, and the common ancestors of Gillenia and Prunus, and Gillenia and the apple tribe, likely had a self-recognition SI system. Comparative genomics between Gillenia and Malus suggest apple lost the self-recognition mechanism, and a nonself-recognition mechanism evolved independently from a rudimentary locus with at least one male S-determinant. Repetitive sequences in the Malus-like S-locus in Gillenia may facilitate illegitimate recombination, suggesting putative mechanisms of evolution of nonself-recognition S-loci.

Duckweed genomes and epigenomes underlie triploid hybridization and clonal reproduction

The Lemnaceae (duckweeds) are the world's smallest but fastest-growing flowering plants. Prolific clonal propagation facilitates continuous micro-cropping for plant-based protein and starch production and holds tremendous promise for sequestration of atmospheric CO2. Here, we present chromosomal assemblies, annotations, and phylogenomic analysis of Lemna genomes that uncover candidate genes responsible for the unique metabolic and developmental traits of the family, such as anatomical reduction, adaxial stomata, lack of stomatal closure, and carbon sequestration via crystalline calcium oxalate. Lemnaceae have selectively lost genes required for RNA interference, including Argonaute genes required for reproductive isolation (the triploid block) and haploid gamete formation. Triploid hybrids arise commonly among Lemna, and we have found mutations in highly conserved meiotic crossover genes that could support polyploid meiosis. Further, mapping centromeres by chromatin immunoprecipitation suggests their epigenetic origin despite divergence of underlying tandem repeats and centromeric retrotransposons. Syntenic comparisons with Wolffia and Spirodela reveal that diversification of these genera coincided with the "Azolla event" in the mid-Eocene, during which aquatic macrophytes reduced high atmospheric CO2 levels to those of the current ice age. Facile regeneration of transgenic fronds from tissue culture, aided by reduced epigenetic silencing, makes Lemna a powerful biotechnological platform, as exemplified by recent engineering of high-oil Lemna that outperforms oil-seed crops.

Robust sex determination in the Caenorhabditis nigoni germ line

Sexual characteristics and reproductive systems are dynamic traits in many taxa, but the developmental modifications that allow change and innovation are largely unknown. A leading model for this process is the evolution of self-fertile hermaphrodites from male/female ancestors. However, these studies require direct analysis of sex determination in male/female species, as well as in the hermaphroditic species that are related to them. In Caenorhabditis nematodes, this has only become possible recently, with the discovery of new species. Here, we use gene editing to characterize major sex determination genes in Caenorhabditis nigoni, a sister to the widely studied hermaphroditic species Caenorhabditis briggsae. These 2 species are close enough to mate and form partially fertile hybrids. First, we find that tra-1 functions as the master regulator of sex in C. nigoni, in both the soma and the germ line. Surprisingly, these mutants make only sperm, in contrast to tra-1 mutants in related hermaphroditic species. Moreover, the XX mutants display a unique defect in somatic gonad development that is not seen elsewhere in the genus. Second, the fem-3 gene acts upstream of tra-1 in C. nigoni, and the mutants are females, unlike in the sister species C. briggsae, where they develop as hermaphrodites. This result points to a divergence in the role of fem-3 in the germ line of these species. Third, tra-2 encodes a transmembrane receptor that acts upstream of fem-3 in C. nigoni. Outside of the germ line, tra-2 mutations in all species cause a similar pattern of partial masculinization. However, heterozygosity for tra-2 does not alter germ cell fates in C. nigoni, as it can in sensitized backgrounds of 2 hermaphroditic species of Caenorhabditis. Finally, the epistatic relationships point to a simple, linear germline pathway in which tra-2 regulates fem-3 which regulates tra-1, unlike the more complex relationships seen in hermaphrodite germ cell development. Taking these results together, the regulation of sex determination is more robust and streamlined in the male/female species C. nigoni than in related species that make self-fertile hermaphrodites, a conclusion supported by studies of interspecies hybrids using sex determination mutations. Thus, we infer that the origin of self-fertility not only required mutations that activated the spermatogenesis program in XX germ lines, but prior to these there must have been mutations that decanalized the sex determination process, allowing for subsequent changes to germ cell fates.

A chromosome-level genome assembly of the varied leaved jewelflower, Streptanthus diversifolius, reveals a recent whole genome duplication

The Streptanthoid complex, a clade of primarily Streptanthus and Caulanthus species in the Thelypodieae (Brassicaceae) is an emerging model system for ecological and evolutionary studies. This complex spans the full range of the California Floristic Province including desert, foothill, and mountain environments. The ability of these related species to radiate into dramatically different environments makes them a desirable study subject for exploring how plant species expand their ranges and adapt to new environments over time. Ecological and evolutionary studies for this complex have revealed fascinating variation in serpentine soil adaptation, defense compounds, germination, flowering, and life history strategies. Until now a lack of publicly available genome assemblies has hindered the ability to relate these phenotypic observations to their underlying genetic and molecular mechanisms. To help remedy this situation, we present here a chromosome-level genome assembly and annotation of Streptanthus diversifolius, a member of the Streptanthoid Complex, developed using Illumina, Hi-C, and HiFi sequencing technologies. Construction of this assembly also provides further evidence to support the previously reported recent whole genome duplication unique to the Thelypodieae. This whole genome duplication may have provided individuals in the Streptanthoid Complex the genetic arsenal to rapidly radiate throughout the California Floristic Province and to occupy commonly inhospitable environments including serpentine soils.

Taurine pangenome uncovers a segmental duplication upstream of KIT associated with depigmentation in white-headed cattle

Cattle have been selectively bred for coat color, spotting, and depigmentation patterns. The assumed autosomal dominant inherited genetic variants underlying the characteristic white head of Fleckvieh, Simmental, and Hereford cattle have not been identified yet, although the contribution of structural variation upstream of the KIT gene has been proposed. Here, we construct a graph pangenome from 24 haplotype assemblies representing seven taurine cattle breeds to identify and characterize the white-head-associated locus for the first time based on long-read sequencing data and pangenome analyses. We introduce a pangenome-wide association mapping approach that examines assembly path similarities within the graph to reveal an association between two most likely serial alleles of a complex structural variant (SV) 66 kb upstream of KIT and facial depigmentation. The complex SV contains a variable number of tandemly duplicated 14.3 kb repeats, consisting of LTRs, LINEs, and other repetitive elements, leading to misleading alignments of short and long reads when using a linear reference. We align 250 short-read sequencing samples spanning 15 cattle breeds to the pangenome graph, further validating that the alleles of the SV segregate with head depigmentation. We estimate an increased count of repeats in Hereford relative to Simmental and other white-headed cattle breeds from the graph alignment coverage, suggesting a large under-assembly in the current Hereford-based cattle reference genome, which had fewer copies. Our work shows that exploiting assembly path similarities within graph pangenomes can reveal trait-associated complex SVs.

Genomic data reveal a north-south split and introgression history of blood fluke populations across Africa

The human parasitic fluke, Schistosoma haematobium hybridizes with the livestock parasite S. bovis in the laboratory, but the frequency of hybridization in nature is unclear. Here, we analyze 34.6 million single nucleotide variants in 162 samples from 18 African countries, revealing a sharp genetic discontinuity between northern and southern S. haematobium. We find no evidence for recent hybridization. Instead the data reveal admixture events that occurred 257-879 generations ago in northern S. haematobium populations. Fifteen introgressed S. bovis genes are approaching fixation in northern S. haematobium with four genes potentially driving adaptation. Further, we identify 19 regions that are resistant to introgression; these are enriched on the sex chromosomes. These results (i) suggest strong barriers to gene flow between these species, (ii) indicate that hybridization may be less common than currently envisaged, but (iii) reveal profound genomic consequences of rare interspecific hybridization between schistosomes of medical and veterinary importance.

Draft genome sequence of Bacillus anthracis strains, isolated from soil samples from a historic tannery site in Upper Austria

In this announcement, we present the draft genomes of four Bacillus anthracis isolates, MH-MFM, MH-VW, MH-PR, and MH-JJ, originating from soil samples retrieved from a sludge disposal site of a historic tannery site in Upper Austria.

Centromeric transposable elements and epigenetic status drive karyotypic variation in the eastern hoolock gibbon

Great apes have maintained a stable karyotype with few large-scale rearrangements; in contrast, gibbons have undergone a high rate of chromosomal rearrangements coincident with rapid centromere turnover. Here, we characterize fully assembled centromeres in the eastern hoolock gibbon, Hoolock leuconedys (HLE), finding a diverse group of transposable elements (TEs) that differ from the canonical alpha-satellites found across centromeres of other apes. We find that HLE centromeres contain a CpG methylation centromere dip region, providing evidence that this epigenetic feature is conserved in the absence of satellite arrays. We uncovered a variety of atypical centromeric features, including protein-coding genes and mismatched replication timing. Further, we identify duplications and deletions in HLE centromeres that distinguish them from other gibbons. Finally, we observed differentially methylated TEs, topologically associated domain boundaries, and segmental duplications at chromosomal breakpoints, and thus propose that a combination of multiple genomic attributes with propensities for chromosome instability shaped gibbon centromere evolution.

Graph-based pangenome provides insights into structural variations and genetic basis of metabolic traits in potato

Potato is the world's most important nongrain crop. In this study, to assess genetic diversity within the Petota section, 29 genomes from Petota and Etuberosum sections were newly de novo assembled and 248 accessions of wild potatoes, landraces, and modern cultivars were re-sequenced at >25× depth. Subsequently, a graph-based pangenome was constructed using DM8.1 as the backbone, integrating194,330 nonredundant structural variants. To characterize the metabolome of tubers and illuminate the genomic basis of metabolic traits, LC-MS/MS was employed to obtain the metabolome of 157 accessions, and 9,321 structural variants (SVs) were detected to be significantly associated with 1,258 distinct metabolites via PAV (presence and absence variations)-based metabolomics-GWAS analysis, including metabolites of flavonoids, phenolic acids, and phospholipids. To facilitate the utilization of pangenome resources, a comprehensive platform, the Potato Pangenome Database (PPDB), was developed. Our study provides a comprehensive genomic resource for dissecting the genomic basis of agronomic and metabolic traits in potato, which will accelerate functional genomics studies and genetic improvements in potato.

Structural variation-based and gene-based pangenome construction reveals untapped diversity of hexaploid wheat

Increasing number of structural variations (SVs) have been identified as causative mutations for diverse agronomic traits. However, the systematic exploration of SVs quantity, distribution, and contribution in wheat was lacking. Here, we report high-quality gene-based and SV-based pangenomes comprising 22 hexaploid wheat assemblies showing a wide range of chromosome size, gene number, and TE component, which indicates their representativeness of wheat genetic diversity. Pan-gene analyses uncover 140,261 distinct gene families, of which only 23.2 % are shared in all accessions. Moreover, we build a ∼16.15 Gb graph pangenome containing 695,897 bubbles, intersecting 5132 genes and 230,307 cis-regulatory regions. Pairwise genome comparisons identify ∼1,978,221 non-redundant SVs and 497 SV hotspots. Notably, the density of bubbles as well as SVs show remarkable aggregation in centromeres, which probably play an important role in chromosome plasticity and stability. As for functional SVs exploration, we identify 2769 SVs with absolute relative frequency differences exceeding 0.7 between spring and winter growth habit groups. Additionally, several reported functional genes in wheat display complex structural graphs, for example, PPD-A1, VRT-A2, and TaNAAT2-A. These findings deepen our understanding of wheat genetic diversity, providing valuable graphical pangenome and variation resources to improve the efficiency of genome-wide association mapping in wheat.

A rearranged Amaranthus palmeri extrachromosomal circular DNA confers resistance to glyphosate and glufosinate

Some herbicide-resistant weeds become resistant by generating additional copies of specific loci. For example, amplification of the locus encoding chloroplastic glutamine synthetase (GS2) produces herbicide resistance in the glufosinate-resistant Palmer amaranth (Amaranthus palmeri) accession MSR2. Previously, overamplification of the glyphosate-resistant gene encoding 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) in Palmer amaranth was determined to be driven by an extrachromosomal circular DNA (eccDNA). Here, we describe a rearranged eccDNA that confers resistance to both glyphosate and glufosinate ammonium due to the coduplication of the native chromosomal regions that contain the genes that encode for these herbicides target proteins. In addition to EPSPS, the replicon carries 2 GS2 isoforms (GS2.1 and GS2.2) and other genes. MSR2 samples harbored eccDNA carrying only EPSPS coexisting with eccDNAs harboring both EPSPS and GS2. A second glufosinate-resistant Palmer amaranth accession (MSR1) showed distinct GS2.1 and GS2.2 amplification patterns from MSR2, suggesting the existence of diverse replicons in Palmer amaranth. EPSPS copy number was correlated with both GS2 isoforms copy number in MSR2, further supporting the coexistence of these genes in the same replicon. These findings shed light on the complexity of eccDNA formation in plant systems, with the collection and accumulation of extra pieces of DNA.

Comprehensive Genomic Dataset of Chinese Lizardtail Herb and Comparative Genomic Analysis Provide Insights Into Its Paleo-Polyploidization Event

The Chinese lizardtail herb, Saururus chinensis, holds a prominent position in traditional Chinese medicine. In this study, we present a comprehensive genomic dataset for S. chinensis. Furthermore, comparative genomic analysis indicates that the extant genome of S. chinensis retains extensive traces of a paleo-tetraploidization event. These traces are observable at both the macroscopic level of chromosomes and the microscopic level within specific gene families, such as the PEL (pseudo-etiolation in light) gene family. Additionally, our findings further suggest that this paleo-tetraploidization event drives an expansion of the PEL gene family in the S. chinensis genome, potentially facilitating its neo- and sub-functionalization, and thereby contributing to the evolutionary adaptability of this species.

The Eastern Fox Squirrel (Sciurus niger) exhibits minimal patterns of phylogeography across native and introduced sites

Introduced species are one of the leading causes of declining global biodiversity and result in many billions of dollars of losses to the bioeconomy worldwide. Introduced species have become increasingly common due to globalization and climate change, and population genetics is a useful tool for the management of such species. The Eastern Fox Squirrel (Sciurus niger) is a highly successful invader that was introduced to many states in western North America throughout the 20th century. We used low-pass whole genome sequencing to evaluate phylogeographic structure across native and introduced ranges of this species and identify the putative number and geographic sources of introductions in California and Utah. We found minimal patterns of phylogeographic structure, consistent with recent range and population expansion since the Last Glacial Maximum. Additionally, we found evidence for multiple mitochondrial haplotypes in California and only 1 haplotype in Utah, which suggests that fox squirrels in California were sourced from multiple introduction events while those in Utah were likely sourced from a single event. Genomic resources generated in this study will be useful for future conservation efforts in this species and will assist with the ongoing management of its introductions across western North America.

Two CENH3 paralogs in the green alga Chlamydomonas reinhardtii have a redundantly essential function and associate with ZeppL-LINE1 elements

Centromeres in eukaryotes are defined by the presence of histone H3 variant CENP-A/CENH3. Chlamydomonas encodes two predicted CENH3 paralogs, CENH3.1 and CENH3.2, that have not been previously characterized. We generated peptide antibodies to unique N-terminal epitopes for each of the two predicted Chlamydomonas CENH3 paralogs as well as an antibody against a shared CENH3 epitope. All three CENH3 antibodies recognized proteins of the expected size on immunoblots and had punctate nuclear immunofluorescence staining patterns. These results are consistent with both paralogs being expressed and localized to centromeres. CRISPR-Cas9-mediated insertional mutagenesis was used to generate predicted null mutations in either CENH3.1 or CENH3.2. Single mutants were viable but cenh3.1 cenh3.2 double mutants were not recovered, confirming that the function of CENH3 is essential. We sequenced and assembled two chromosome-scale Chlamydomonas genomes from strains CC-400 and UL-1690 (a derivative of CC-1690) with complete centromere sequences for 17/17 and 14/17 chromosomes respectively, enabling us to compare centromere evolution across four isolates with near complete assemblies. These data revealed significant changes across isolates between homologous centromeres including mobility and degeneration of ZeppL-LINE1 (ZeppL) transposons that comprise the major centromere repeat sequence in Chlamydomonas. We used cleavage under targets and tagmentation (CUT&Tag) to purify and map CENH3-bound genomic sequences and found enrichment of CENH3-binding almost exclusively at predicted centromere regions. An interesting exception was chromosome 2 in UL-1690, which had enrichment at its genetically mapped centromere repeat region as well as a second, distal location, centered around a single recently acquired ZeppL insertion. The CENH3-bound regions of the 17 Chlamydomonas centromeres ranged from 63.5 kb (average lower estimate) to 175 kb (average upper estimate). The relatively small size of its centromeres suggests that Chlamydomonas may be a useful organism for testing and deploying artificial chromosome technologies.

Jan and mini-Jan, a model system for potato functional genomics

Potato (Solanum tuberosum) is the third-most important food crop in the world. Although the potato genome has been fully sequenced, functional genomics research of potato lags behind that of other major food crops, largely due to the lack of a model experimental potato line. Here, we present a diploid potato line, 'Jan,' which possesses all essential characteristics for facile functional genomics studies. Jan exhibits a high level of homozygosity after seven generations of self-pollination. Jan is vigorous, highly fertile and produces tubers with outstanding traits. Additionally, it demonstrates high regeneration rates and excellent transformation efficiencies. We generated a chromosome-scale genome assembly for Jan, annotated its genes and identified syntelogs relative to the potato reference genome assembly DMv6.1 to facilitate functional genomics. To miniaturize plant architecture, we developed two 'mini-Jan' lines with compact and dwarf plant stature through CRISPR/Cas9-mediated mutagenesis targeting the Dwarf and Erecta genes involved in growth. One mini-Jan mutant, mini-JanE, is fully fertile and will permit higher-throughput studies in limited growth chamber and greenhouse space. Thus, Jan and mini-Jan offer a robust model system that can be leveraged for gene editing and functional genomics research in potato.

Solanum pan-genetics reveals paralogues as contingencies in crop engineering

Pan-genomics and genome-editing technologies are revolutionizing breeding of global crops1,2. A transformative opportunity lies in exchanging genotype-to-phenotype knowledge between major crops (that is, those cultivated globally) and indigenous crops (that is, those locally cultivated within a circumscribed area)3-5 to enhance our food system. However, species-specific genetic variants and their interactions with desirable natural or engineered mutations pose barriers to achieving predictable phenotypic effects, even between related crops6,7. Here, by establishing a pan-genome of the crop-rich genus Solanum8 and integrating functional genomics and pan-genetics, we show that gene duplication and subsequent paralogue diversification are major obstacles to genotype-to-phenotype predictability. Despite broad conservation of gene macrosynteny among chromosome-scale references for 22 species, including 13 indigenous crops, thousands of gene duplications, particularly within key domestication gene families, exhibited dynamic trajectories in sequence, expression and function. By augmenting our pan-genome with African eggplant cultivars9 and applying quantitative genetics and genome editing, we dissected an intricate history of paralogue evolution affecting fruit size. The loss of a redundant paralogue of the classical fruit size regulator CLAVATA3 (CLV3)10,11 was compensated by a lineage-specific tandem duplication. Subsequent pseudogenization of the derived copy, followed by a large cultivar-specific deletion, created a single fused CLV3 allele that modulates fruit organ number alongside an enzymatic gene controlling the same trait. Our findings demonstrate that paralogue diversifications over short timescales are underexplored contingencies in trait evolvability. Exposing and navigating these contingencies is crucial for translating genotype-to-phenotype relationships across species.

The genomic landscape of gene-level structural variations in Japanese and global soybean Glycine max cultivars

Japanese soybeans are traditionally bred to produce soy foods such as tofu, miso and boiled soybeans. Here, to investigate their distinctive genomic features, including genomic structural variations (SVs), we constructed 11 nanopore-based genome references for Japanese and other soybean lines. Our assembly-based comparative method, designated 'Asm2sv', identified gene-level SVs comprehensively, enabling pangenome analysis of 462 worldwide cultivars and varieties. Based on these, we identified selective sweeps between Japanese and US soybeans, one of which was the pod-shattering resistance gene PDH1. Genome-wide association studies further identified several quantitative trait loci that accounted for large-seed phenotypes of Japanese soybean lines, some of which were also close to regions of the selective sweeps, including PDH1. Notably, specific combinations of alleles, including SVs, were found to increase the seed size of some Japanese landraces. In addition to the differences in cultivation environments, distinct food processing usages might result in changes in Japanese soybean genomes.

Developmental innovation of inferior ovaries and flower sex orchestrated by KNOX1 in cucurbits

In flowering plants, inferior ovaries are key morphological innovations that evolved multiple times from superior ovaries to protect female parts of the flower. However, the developmental mechanisms underlying inferior ovary formation remain largely unknown. Comparative spatial transcriptome mapping and cell lineage reconstructions in developing floral buds of cucumber and tomato, which have inferior and superior ovaries, respectively, revealed that inferior ovaries develop from accelerated receptacle growth resulting from the continuous activity of meristematic stems cells at the base of the cucumber floral organs. Genetic knockout of a receptacle-specific KNOX1 transcription factor in cucumber caused arrest in receptacle growth and yielded bisexual flowers with superior ovaries similar to those of tomato. Here we provide developmental and mechanistic insights into inferior ovary formation and sex determination in cucurbits.

Identification of quantitative trait loci (QTLs) for key cheese making phenotypes in the blue-cheese mold Penicillium roqueforti

Elucidating the genomic architecture of quantitative traits is essential for our understanding of adaptation and for breeding in domesticated organisms. Penicillium roqueforti is the mold used worldwide for the blue cheese maturation, contributing to flavors through proteolytic and lipolytic activities. The two domesticated cheese populations display very little genetic diversity, but are differentiated and carry opposite mating types. We produced haploid F1 progenies from five crosses, using parents belonging to cheese and non-cheese populations. Analyses of high-quality genome assemblies of the parental strains revealed five large translocations, two having occurred via a circular intermediate, one with footprints of Starship giant mobile elements. Offspring genotyping with genotype-by-sequencing (GBS) revealed several genomic regions with segregation distortion, possibly linked to degeneration in cheese lineages. We found transgressions for several traits relevant for cheese making, with offspring having more extreme trait values than parental strains. We identified quantitative trait loci (QTLs) for colony color, lipolysis, proteolysis, extrolite production, including mycotoxins, but not for growth rates. Some genomic regions appeared rich in QTLs for both lipid and protein metabolism, and other regions for the production of multiple extrolites, indicating that QTLs have pleiotropic effects. Some QTLs corresponded to known biosynthetic gene clusters, e.g., for the production of melanin or extrolites. F1 hybrids constitute valuable strains for cheese producers, with new traits and new allelic combinations, and allowed identifying target genomic regions for traits important in cheese making, paving the way for strain improvement. The findings further contribute to our understanding of the genetic mechanisms underlying rapid adaptation, revealing convergent adaptation targeting major gene regulators.

Examining the potential of plastic-fed black soldier fly larvae (Hermetia illucens) as "bioincubators" of plastic-degrading bacteria

AIMS

Larvae of the black soldier fly (BSFL), Hermetia illucens, are recognized for their remarkable feeding flexibility and ability to convert a variety of organic waste streams into useful end products. Their ability to feed on both harmful and recalcitrant waste streams is thought to be due in part to plasticity in their gut microbiota, which shifts rapidly to select for taxa better suited to the incoming diet. Here, we aimed to exploit this feeding plasticity by using BSFL as "bioincubators," to grow and isolate plastic-degrading bacteria.

METHODS AND RESULTS

We fed larvae wheat bran containing a mix of microplastic (polyethylene terephthalate, polylactic acid, and polyhydroxybutyrate) and determined the community composition of plastic-degrading microorganisms using a combination of culturing techniques and next-generation sequencing. On average, more than a third of the gut microbiome was made up of genera that have previously demonstrated plastic degradation capabilities. To confirm this assessment, we isolated seven bacterial strains from plastic-fed BSFL that were positively identified as polyhydroxybutyrate-degraders in vitro.

CONCLUSIONS

Our results provide proof of concept that plastic-fed H. illucens could be used as bioincubators to grow plastic-degrading bacteria. We believe our methodology provides a simple model for verifying in silico results with in vitro tests and should be used to enhance the future isolation and characterization of novel plastic-degrading taxa.

A Segregating Structural Variant Defines Novel Venom Phenotypes in the Eastern Diamondback Rattlesnake

Of all mutational mechanisms contributing to phenotypic variation, structural variants are both among the most capable of causing major effects as well as the most technically challenging to identify. Intraspecific variation in snake venoms is widely reported, and one of the most dramatic patterns described is the parallel evolution of streamlined neurotoxic rattlesnake venoms from hemorrhagic ancestors by means of deletion of snake venom metalloproteinase (SVMP) toxins and recruitment of neurotoxic dimeric phospholipase A2 (PLA2) toxins. While generating a haplotype-resolved, chromosome-level genome assembly for the eastern diamondback rattlesnake (Crotalus adamanteus), we discovered that our genome animal was heterozygous for a ∼225 Kb deletion containing six SVMP genes, paralleling one of the two steps involved in the origin of neurotoxic rattlesnake venoms. Range-wide population-genomic analysis revealed that, although this deletion is rare overall, it is the dominant homozygous genotype near the northwestern periphery of the species' range, where this species is vulnerable to extirpation. Although major SVMP deletions have been described in at least five other rattlesnake species, C. adamanteus is unique in not additionally gaining neurotoxic PLA2s. Previous work established a superficially complementary north-south gradient in myotoxin (MYO) expression based on copy number variation with high expression in the north and low in the south, yet we found that the SVMP and MYO genotypes vary independently, giving rise to an array of diverse, novel venom phenotypes across the range. Structural variation, therefore, forms the basis for the major axes of geographic venom variation for C. adamanteus.

Synteny Enabled Upgrade of the Galapagos Giant Tortoise Genome Improves Inferences of Runs of Homozygosity

The utility and importance of whole-genome sequences are recognized across various fields, including evolution and conservation. However, for some taxa, like extinct species, using methods to generate contiguous genomes that rely on high-quality DNA is impossible. In such cases, an alternative may be to employ synteny-based methods using a genome from a closely related taxon to generate more complete genomes. Here we update the reference genome for the Pinta Island Galapagos giant tortoise (Chelonoidis abingdonii) without conducting additional sequencing through rescaffolding against the most closely related chromosome-level genome assembly, the Aldabra giant tortoise (Aldabrachelys gigantea). This effort resulted in a much more contiguous genome, CheloAbing_2.0, with an N50 that is two orders of magnitude longer and large reductions in L50 and the number of gaps. We then examined the impact of the CheloAbing_2.0 genome on estimates of runs of homozygosity (ROH) using genome resequencing data from 37 individual Galapagos giant tortoises from the 13 extant lineages to test the mechanisms by which a fragmented assembly may over- or underestimate the number and extent of ROH. The use of CheloAbing_2.0 resulted in individual estimates of inbreeding, including ROH proportion (FROH), number (NROH), and cumulative length (SROH), that were statistically different from those derived from the earlier genome assembly. This improved genome will serve as a resource for future efforts focusing on the ecology, evolution, and conservation of this species group. More broadly, our results highlight that synteny-based scaffolding is promising for generating contiguous genomes without needing additional data types.

A wheat tandem kinase activates an NLR to trigger immunity

The role of nucleotide-binding leucine-rich repeat (NLR) receptors in plant immunity is well studied, but the function of a class of tandem kinases (TKs) that confer disease resistance in wheat and barley remains unclear. In this study, we show that the SR62 locus is a digenic module encoding the Sr62TK TK and an NLR (Sr62NLR), and we identify the corresponding AvrSr62 effector. AvrSr62 binds to the N-terminal kinase 1 of Sr62TK, triggering displacement of kinase 2, which activates Sr62NLR. Modeling and mutation analysis indicated that this is mediated by overlapping binding sites (i) on kinase 1 for binding AvrSr62 and kinase 2 and (ii) on kinase 2 for binding kinase 1 and Sr62NLR. Understanding this two-component resistance complex may help engineering and breeding plants for durable resistance.

Persistence in time: the hunt for Bacillus anthracis at a historic tannery site in Austria reveals genetic diversity thought extinct

Identifying and analyzing historic anthrax loci may provide a treasure trove to fill in the gaps of persistence in time and genetic diversity of Bacillus anthracis. In countries where anthrax has become a disease of the past, detailed knowledge of the exact location and stability of spores in soil reservoirs is limited. Reviewing archival records may provide valuable clues to unearthing such forgotten sites. Knowledge of anthrax diversity in Austria is scarce, as the only available isolates-originating from the last outbreak in Austria in 1988-cluster in the B.Br.004 (CNEVA) canonical single-nucleotide polymorphism (canSNP) group. Thus, we analyzed archival records on anthrax incidents in Austria to locate historic B. anthracis soil reservoirs. In parallel, we tested the performance of different soil processing protocols for the isolation of B. anthracis spores to establish a suitable workflow for screening historical anthrax loci. Using an optimized workflow, we were able to isolate viable B. anthracis spores 80 years after the last occurrence of anthrax at an abandoned tannery identified through our archival work. Genome analysis of the isolated strains allowed to improve the phylogeographic resolution within the hitherto poorly covered A.Br.064 (V770) canSNP group by linking historical records to genetic information. Furthermore, our results re-emphasize that B. anthracis can survive for decades at historic sites and may pose a health threat when such sites are eventually reactivated by climatic factors or human intervention.

IMPORTANCE

Bacillus anthracis is a continuing threat from a One Health perspective since it leads to severe infections in animals and humans. Ongoing climate change or human activities can reactivate historical B. anthracis loci, previously considered inactive or forgotten. Therefore, knowledge of historic anthrax incidents at abandoned animal processing facilities, such as tanneries or farmyards, along with robust detection protocols, is of prime interest when monitoring this important zoonosis. As shown here, archival records of possible origins of anthrax-contaminated goods received at tanneries are valuable sources and support these efforts. Investigation for viable spores at such historical sites could not only provide new insights into the past genetic diversity and population structure of B. anthracis but also provide important information for taking appropriate measures to prevent future outbreaks originating from these sites.

Identification of the male-specific region on the guppy Y Chromosome from a haplotype-resolved assembly

The guppy Y Chromosome has been a paradigmatic model for studying the genetics of sex-linked traits and Y Chromosome-driven evolution for more than a century. Despite strong efforts, knowledge on genomic organization and molecular differentiation of the sex chromosome pair remains unsatisfactory and partly contradictory with respect to regions of reduced recombination. Especially the border between pseudoautosomal and male-specific regions of the Y has not been defined so far. To circumvent the problems in assigning the repeat-rich differentiated hemizygous or heterozygous sequences of the sex chromosome pair, we sequenced a YY male generated by a cross of a sex-reversed Maculatus strain XY female to a normal XY male from the inbred Guanapo population. High-molecular-weight genomic DNA from the YY male was sequenced on the Pacific Biosciences platform, and both Y haplotypes were reconstructed by Trio binning. By mapping of male specific SNPs and RADseq sequences, we identify a single male specific-region of ∼5 Mb length at the distal end of the Y (MSY). Sequence divergence between X and Y in the segment is on average five times higher than in the proximal part in agreement with reduced recombination. The MSY is enriched for repeats and transposons but does not differ in the content of coding genes from the X, indicating that genic degeneration has not progressed to a measurable degree.

Individual leaf microbiota tunes a genetic regulatory network to promote leaf growth

In natural ecosystems, microbes have the ability to stably colonize plant leaves, overcoming the fluctuating environmental conditions that the leaves represent. How the phyllosphere microbiota influences the growth of individual leaves remains poorly understood. Here, we investigate the growth of Zea mays (maize/corn) leaves in plants grown in three soils with differing amounts of nutrients and water and identify a leaf-growth-promoting effect driven by the leaf microbiota, which we also validate in field studies. We built and used a bacterial strain collection for recolonization experiments to study the microbiota-mediated mechanisms involved in leaf growth promotion. We demonstrate that prevalent bacteria inhabiting young leaves promote individual leaf growth. Using transcriptomic analyses, we reveal a defense-related genetic network that integrates the beneficial effect of the phyllosphere microbiota into the leaf development program. We demonstrate that the individual leaf microbiota differentially represses this genetic network to modulate the growth-defense trade-off at single-leaf resolution.

Unraveling the pathogenomics of Rhizoctonia solani infecting proso millet (Panicum miliaceum L.): genomic perspective on ruthless virulence and adaptive evolution

Introduction

Banded sheath blight (Bsb), caused by Rhizoctonia solani, is an emerging threat to proso millet cultivation, significantly impacting yield and grain quality. This study on the pathogenomics of R. solani seeks to unravel its genetic mechanisms, identify key virulence factors, decode host-pathogen interactions, and pinpoint molecular targets for effective control strategies.

Methods

R. solani isolates were collected from various regions across India, resulting in six distinct isolates. These isolates were comprehensively characterized through morphological observations, molecular analyses, and virulence assessments to gain comprehensive insights into their diversity and pathogenic potential. The most virulent strain, designated VAP-1, infecting proso millet, was sequenced using the Illumina platform and de novo assembled using the SPAdes assembler, resulting in a highly complete genome. Functional regions of the genome were predicted and annotated using Funannotate. A subsequent comparative genomics study and secretome analysis were conducted to support functional genomic investigations.

Results

The VAP-1 genome assembly resulted in a total size of 47.12 Mb, with approximately 17.62% of the genome consisting of repetitive sequences, predominantly dominated by interspersed elements (around 97.8%). These interspersed elements were primarily classified as retrotransposons (72%), with DNA transposons comprising a smaller proportion (5%), while the remaining interspersed sequences were not fully annotated. Functional analysis of the genome revealed significant enrichment in KEGG pathways, including "Carbohydrate metabolism," "Translation," "Signal transduction," and "Transport and catabolism." In addition, Gene Ontology (GO) terms such as "Proteolysis," "Membrane," and "ATP binding" were notably enriched. The secretory protein profile of the VAP-1 genome from R. solani features key proteins from the major facilitator superfamily (MFS) transporters, (Trans) glycosidases, P-loop containing nucleoside triphosphate hydrolases, and galactose oxidase, all within the central domain superfamily. Glycoside hydrolases represent the largest class of CAZymes in the VAP-1 genome. Comparative genomic analysis of VAP-1 with other R. solani strains infecting Poaceae (e.g., rice) and non-Poaceae (e.g., sugar beet and tobacco) hosts showed that VAP-1 clusters closely with rice-infecting strains at the species level, yet exhibits a greater divergence in genomic similarity from strains infecting sugar beet and tobacco. Notably, variations were observed in important secretory proteins, such as multiple base deletions in MFS proteins across strains infecting proso millet, rice, and sugar beet.

Discussion

Functional analysis of the VAP-1 genome has unveiled a wealth of insights, though we have only begun to scratch the surface. KEGG and GO annotations point to critical proteins that are essential for host infection, providing the pathogen with a potent arsenal for successful penetration, survival, and dissemination within the host. The secretory proteins encoded in the VAP-1 genome play a pivotal role in equipping the pathogen with the necessary tools to degrade plant cell wall polymers, release cell wall-bound saccharides, and break down polysaccharides for energy utilization and host colonization. Notable variations were observed in several secretome superfamily proteins within the VAP-1 strain. These findings underscore the genomic diversity present within R. solani strains and suggest possible adaptations that may contribute to host specificity.

Genetic Mechanisms and Adaptive Benefits of Anthocyanin Red Stigmas in a Wind-Pollinated Tree

Anthocyanin accumulation in leaves or flowers mitigates photooxidation damage from reactive oxygen species (ROS) and functions in plant/animal interactions. Among the most conspicuously anthocyanin-accumulating tissues are stigmas, especially in wind-pollinated trees. In the walnut genus (Juglans), yellow stigmas are ancestral, but a few species have dark red stigmas. We have used a natural F1 hybrid resulting from crosses between yellow stigma and red stigma species to investigate the genetic basis of the red stigmas. We found that a Copia transposable element (TE) insertion in the ubiquitin-protein ligase gene MIEL1 suppresses its expression in stigmas through RNA-directed DNA methylation and has gone to fixation in red stigma species. A younger Gypsy TE insertion fully inhibits MIEL1 expression, but is not fixed, explaining the color segregation in hybrid populations. Based on reference genomes and whole-genome sequencing data representing 20 of the 22 species of Juglans, we traced the evolution of MIEL1, finding the insertions in all consistently red stigma species. Red stigmas had lower levels of ROS than yellow stigmas, and population genetic data reveal strong positive selection on the TE-bearing MIEL1 allele. In combination, these results suggest that anthocyanin-accumulating stigma tissues support pollen germination and growth by protecting cells from ROS.

Isolation, Identification, and Characteristics of Aeromonas salmonicida subsp. masoucida from Diseased Starry Flounder (Platichthys stellatus)

Aeromonas salmonicida is a predominant pathogen that infects fish. The pathogen A. salmonicida subsp. masoucida (ASM) was isolated for the first time from diseased starry flounders (Platichthys stellatus). Our study aimed to isolate, characterize, and investigate the pathogenicity of ASM. Bacterial species were identified using 16s rRNA, gyrB, dnaJ, and vapA analyses. Phylogenetic tree analysis revealed that the ASM strains were clustered with the ASM ATCC strain and other strains isolated from black rockfish. In the antimicrobial susceptibility test, the three ASM strains were considered non-wild types for enrofloxacin, florfenicol, flumequine, oxolinic acid, and oxytetracycline susceptibility. Histopathological analysis revealed bacterial colonies in the secondary lamella and heart, indicating that ASM strains are highly virulent in fish. Comparative analysis and annotation via genome sequencing revealed that, among the 1156 factors, adherence factors were the most prevalent putative virulence determinants, followed by the effector delivery system and adherence. ASM was found to possess 43 type III secretion systems, 22 type VI secretion systems, 11 antimicrobial resistance genes, 3 stress genes, and prophage regions. These findings provide new insights into the virulence profile of ASM and highlight the risk posed by emerging pathogenic strains to starry flounders.

Evaluating long-read assemblers to assemble several aphididae genomes

Aphids are a speciose family of the Hemiptera compromising >5500 species. They have adapted to feed off multiple plant species and occur on every continent on Earth. Although economically devastating, very few aphid genomes have been sequenced and assembled, and those that have suffer low contiguity due to repeat-rich and AT-rich genomes. With third-generation sequencing becoming more affordable and approaching quality levels to that of second-generation sequencing, the ability to produce more contiguous aphid genome assemblies is becoming a reality. With a growing list of long-read assemblers becoming available, the choice of which assembly tool to use becomes more complicated. In this study, six recently released long-read assemblers (Canu, Flye, Hifiasm, Mecat2, Raven, and Wtdbg2) were evaluated on several quality and contiguity metrics after assembling four populations (or biotypes) of the same species (Russian wheat aphid, Diuraphis noxia) and two unrelated aphid species that have publicly available long-read sequences. All assemblers did not fare equally well between the different read sets, but, overall, the Hifiasm and Canu assemblers performed the best. Merging of the best assemblies for each read set was also performed using quickmerge, where, in some cases, it resulted in superior assemblies and, in others, introduced more errors. Ab initio gene calling between assemblies of the same read set also showed surprisingly less similarity than expected. Overall, the quality control pipeline followed during the assembly resulted in chromosome-level assemblies with minimal structural or quality artefacts.

Transposon insertion causes ctnnb2 transcript instability that results in the maternal effect zebrafish ichabod (ich) mutation

The maternal-effect mutation ichabod (ich) results in ventralized zebrafish embryos due to impaired induction of the dorsal canonical Wnt-signaling pathway. While previous studies linked the phenotype to reduced ctnnb2 transcript levels, the causative mutation remained unidentified. Using long-read sequencing, we discovered that the ich phenotype stems from the insertion of a non-autonomous CMC-Enhancer/Suppressor-mutator (CMC-EnSpm) transposon in the 3'UTR of the gene. Through reporter assays, we demonstrate that while wild type ctnnb2 mRNAs exhibit remarkably high stability throughout the early stages of development, the insertion of the transposon dramatically reduces transcript stability. Genome-wide mapping of the CMC-EnSpm transposons across multiple zebrafish strains also indicated ongoing transposition activity in the zebrafish genome. Our findings not only resolve the molecular basis of the ich mutation but also highlight the continuing mutagenic potential of endogenous transposons and reveal unexpected aspects of maternal transcript regulation during early zebrafish development.

Whole-genome automated assembly pipeline for Chlamydia trachomatis strains from reference, in vitro and clinical samples using the integrated CtGAP pipeline

Whole genome sequencing (WGS) is pivotal for the molecular characterization of Chlamydia trachomatis (Ct)-the leading bacterial cause of sexually transmitted infections and infectious blindness worldwide. Ct WGS can inform epidemiologic, public health and outbreak investigations of these human-restricted pathogens. However, challenges persist in generating high-quality genomes for downstream analyses given its obligate intracellular nature and difficulty with in vitro propagation. No single tool exists for the entirety of Ct genome assembly, necessitating the adaptation of multiple programs with varying success. Compounding this issue is the absence of reliable Ct reference strain genomes. We, therefore, developed CtGAP-Chlamydia trachomatisGenome Assembly Pipeline-as an integrated 'one-stop-shop' pipeline for assembly and characterization of Ct genome sequencing data from various sources including isolates, in vitro samples, clinical swabs and urine. CtGAP, written in Snakemake, enables read quality statistics output, adapter and quality trimming, host read removal, de novo and reference-guided assembly, contig scaffolding, selective ompA, multi-locus-sequence and plasmid typing, phylogenetic tree construction, and recombinant genome identification. Twenty Ct reference genomes were also generated. Successfully validated on a diverse collection of 363 samples containing Ct, CtGAP represents a novel pipeline requiring minimal bioinformatics expertise with easy adaptation for use with other bacterial species.

Comparative genomic analysis of Fusarium oxysporum f. sp. lycopersici reveals telomeric duplications of a lineage-specific region carrying SIX8 and PSL1 and genome-wide expansion of Foxy transposable elements

Fusarium oxysporum f. sp. lycopersici (Fol), the causal agent of tomato wilt disease, is a soil-borne, vascular-colonizing fungal pathogen that severely impacts tomato production in most growing regions worldwide. Despite the availability of over thirty Fol genome sequences in public databases, only one chromosome-scale assembly exists, comprising the low sequence-coverage Fol4287 reference genome generated using Sanger sequencing. Thus, genome structural variation and comparative genomics analyses of Fol remain largely unexplored. Here, using third generation Nanopore long-read sequencing in combination with high-throughput chromosome conformation capture (Hi-C) data, we have independently constructed a high-quality assembly and annotation of the Fol007 race 2 genome that consists of 15 pseudochromosomes with 25 telomeres, including 10 telomere-to-telomere chromosomes. The Fol007 genome is predicted to contain 29,148 protein-encoding genes, including all known SIX genes except for SIX4, which is absent in Fol race 2. Compared to the genome of Fusarium verticillioides, the Fol007 genome contains four complete lineage-specific (LS) chromosomes, including chromosome 5 (Chr5), chromosome 13 (Chr13), and two small chromosomes, Chr14 and Chr15. Comparative genomic analysis between the newly assembled Fol007 genome and Fol4287_2010 deposited in the GenBank database reveals that the completely assembled Chr13 of Fol007 carrying all known SIX genes (except SIX4 and SIX8) and three novel candidate effector genes is relatively stable and corresponds to pathogenicity chromosome Chr14 in Fol4287_2010. It also reveals a telomeric duplication of an LS region carrying SIX8 and PSL1 on core chromosomes Chr6, Chr7 and Chr11, and LS chromosome Chr15, as well as the absence of segmental duplications on LS chromosomes of the Fol007 genome. Furthermore, compared to the genomes of Fol race 1 and non-pathogenic Fo strains, an active and specific Foxy transposable element, responsible for the inactivation of a second copy of SIX13, was identified and found to have expanded in the genomes of Fol race 2 and 3 strains. This element may contribute to Fusarium oxysporum genome evolution and has potential as a genetic marker for studying phylogenetic relationships among formae speciales of Fusarium oxysporum. These findings provide a basis for further genetic and genomic understanding of Fol evolution and virulence mechanisms employed by Fol and contribute another reference genome for Fusarium study more broadly.

Rapid Evolution in Action: Environmental Filtering Supports Coral Adaptation to a Hot, Acidic, and Deoxygenated Extreme Habitat

The semienclosed Bouraké lagoon in New Caledonia is a natural system that enables observation of evolution in action with respect to stress tolerance in marine organisms, a topic directly relevant to understanding the consequences of global climate change. Corals inhabiting the Bouraké lagoon endure extreme conditions of elevated temperature (> 33°C), acidification (7.2 pH units), and deoxygenation (2.28 mg O2 L-1), which fluctuate with the tide due to the lagoon's geomorphology. To investigate the underlying bases of the apparent stress tolerance of these corals, we combined whole genome resequencing of the coral host and ITS2 metabarcoding of the photosymbionts from 90 Acropora tenuis colonies from three localities along the steep environmental gradient from Bouraké to two nearby control reefs. Our results highlight the importance of coral flexibility to associate with different photosymbionts in facilitating stress tolerance of the holobiont; but, perhaps more significantly, strong selective effects were detected at specific loci in the host genome. Fifty-seven genes contained SNPs highly associated with the extreme environment of Bouraké and were enriched in functions related to sphingolipid metabolism. Within these genes, the conserved sensor of noxious stimuli TRPA1 and the ABCC4 transporter stood out due to the high number of environmentally selected SNPs that they contained. Protein 3D structure predictions suggest that a single-point mutation causes the rotation of the main regulatory domain of TRPA1, which may be behind this case of natural selection through environmental filtering. While the corals of the Bouraké lagoon provide a striking example of rapid adaptation to extreme conditions, overall, our results highlight the need to preserve the current standing genetic variation of coral populations to safeguard their adaptive potential to ongoing rapid environmental change.

The Marchantia polymorpha pangenome reveals ancient mechanisms of plant adaptation to the environment

Plant adaptation to terrestrial life started 450 million years ago and has played a major role in the evolution of life on Earth. The genetic mechanisms allowing this adaptation to a diversity of terrestrial constraints have been mostly studied by focusing on flowering plants. Here, we gathered a collection of 133 accessions of the model bryophyte Marchantia polymorpha and studied its intraspecific diversity using selection signature analyses, a genome-environment association study and a pangenome. We identified adaptive features, such as peroxidases or nucleotide-binding and leucine-rich repeats (NLRs), also observed in flowering plants, likely inherited from the first land plants. The M. polymorpha pangenome also harbors lineage-specific accessory genes absent from seed plants. We conclude that different land plant lineages still share many elements from the genetic toolkit evolved by their most recent common ancestor to adapt to the terrestrial habitat, refined by lineage-specific polymorphisms and gene family evolution.

Quasi-species prevalence and clinical impact of evolving SARS-CoV-2 lineages in European COVID-19 cohorts, January 2020 to February 2022

BackgroundEvolution of SARS-CoV-2 is continuous.AimBetween 01/2020 and 02/2022, we studied SARS-CoV-2 variant epidemiology, evolution and association with COVID-19 severity.MethodsIn nasopharyngeal swabs of COVID-19 patients (n = 1,762) from France, Italy, Spain, and the Netherlands, SARS-CoV-2 was investigated by reverse transcription-quantitative PCR and whole-genome sequencing, and the virus variant/lineage (NextStrain/Pangolin) was determined. Patients' demographic and clinical details were recorded. Associations between mild/moderate or severe COVID-19 and SARS-CoV-2 variants and patient characteristics were assessed by logistic regression. Rates and genomic locations of mutations, as well as quasi-species distribution (≥ 2 heterogeneous positions, ≥ 50× coverage) were estimated based on 1,332 high-quality sequences.ResultsOverall, 11 SARS-CoV-2 clades infected 1,762 study patients of median age 59 years (interquartile range (IQR): 45-73), with 52.5% (n = 925) being male. In total, 101 non-synonymous substitutions/insertions correlated with disease prognosis (severe, n = 27; mild-to-moderate, n = 74). Several hotspots (mutation rates ≥ 85%) occurred in Alpha, Delta, and Omicron variants of concern (VOCs) but none in pre-Alpha strains. Four hotspots were retained across all study variants, including spike:D614G. Average number of mutations per open-reading-frame (ORF) increased in the spike gene (average < 5 per genome in January 2020 to > 15 in 2022), but remained stable in ORF1ab, membrane, and nucleocapsid genes. Quasi-species were most prevalent in 20A/EU2 (48.9%), 20E/EU1 (48.6%), 20A (38.8%), and 21K/Omicron (36.1%) infections. Immunocompromised status and age (≥ 60 years), while associated with severe COVID-19 or death irrespective of variant (odds ratio (OR): 1.60-2.25; p ≤ 0.014), did not affect quasi-species' prevalence (p > 0.05).ConclusionSpecific mutations correlate with COVID-19 severity. Quasi-species potentially shaping VOCs' emergence are relevant to consider.