Chromosome-level Genome Assembly Research Articles

Chromosome-level genome assembly of Hippophae tibetana provides insights into high-altitude adaptation and flavonoid biosynthesis

BackgroundAs an endemic shrub of the Qinghai-Tibetan Plateau (QTP), the distribution of Hippophae tibetana Schlecht. ranges between 2800 and 5200 m above sea level. As the most basal branch of the Hippophae genus, H. tibetana has an extensive evolutionary history. The H. tibetana is a valuable tree for studying the ecological evolution of species under extreme conditions.ResultsHere, we generated a high-quality chromosome-level genome of H. tibetana. The total size of the assembly genome is 917 Mb. The phylogenomic analysis of 1064 single-copy genes showed a divergence between 3.4 and 12.8 Mya for H. tibetana. Multiple gene families associated with DNA repair and disease resistance were significantly expanded in H. tibetana. We also identified many genes related to DNA repair with signs of positive selection. These results showed expansion and positive selection likely play important roles in H. tibetana’s adaptation to comprehensive extreme environments in the QTP. A comprehensive genomic and transcriptomic analysis identified 49 genes involved in the flavonoid biosynthesis pathway in H. tibetana. We generated transgenic sea buckthorn hairy root producing high levels of flavonoid.ConclusionsTaken together, this H. tibetana high-quality genome provides insights into the plant adaptation mechanisms of plant under extreme environments and lay foundation for the functional genomic research and molecular breeding of H. tibetana.

A chromosome-level genome assembly of the Asian house martin implies potential genes associated with the feathered-foot trait.

The presence of feathers is a vital characteristic among birds, yet most modern birds had no feather on their feet. The discoveries of feathers on the hind limbs of basal birds and dinosaurs have sparked an interest in the evolutionary origin and genetic mechanism of feathered feet. However, the majority of studies investigating the genes associated with this trait focused on domestic populations. Understanding the genetic mechanism underpinned feathered-foot development in wild birds is still in its infancy. Here, we assembled a chromosome-level genome of the Asian house martin (Delichon dasypus) using the long-read HiFi sequencing approach to initiate the search for genes associated with its feathered feet. We employed the whole genome alignment of D. dasypus with other swallow species to identify high-SNP regions and chromosomal inversions in the D. dasypus genome. After filtering out variations unrelated to D. dasypus evolution, we found six genes related to feather development near the high-SNP regions. We also detected three feather development genes in chromosomal inversions between the Asian house martin and the barn swallow genomes. We discussed their association with the WNT, BMP and FGF pathways and their potential roles in feathered-foot development. Future studies are encouraged to utilize the D. dasypus genome to explore the evolutionary process of the feathered-foot trait in avian species. This endeavor will shed light on the evolutionary path of feathers in birds.

A pan-genome of 69 Arabidopsis thaliana accessions reveals a conserved genome structure throughout the global species range.

Although originally primarily a system for functional biology, Arabidopsis thaliana has, owing to its broad geographical distribution and adaptation to diverse environments, developed into a powerful model in population genomics. Here we present chromosome-level genome assemblies of 69 accessions from a global species range. We found that genomic colinearity is very conserved, even among geographically and genetically distant accessions. Along chromosome arms, megabase-scale rearrangements are rare and typically present only in a single accession. This indicates that the karyotype is quasi-fixed and that rearrangements in chromosome arms are counter-selected. Centromeric regions display higher structural dynamics, and divergences in core centromeres account for most of the genome size variations. Pan-genome analyses uncovered 32,986 distinct gene families, 60% being present in all accessions and 40% appearing to be dispensable, including 18% private to a single accession, indicating unexplored genic diversity. These 69 new Arabidopsis thaliana genome assemblies will empower future genetic research.

Chromosome-level genome assembly and characterization of the Calophaca sinica genome.

Calophaca sinica is a rare plant endemic to northern China which belongs to the Fabaceae family and possesses rich nutritional value. To support the preservation of the genetic resources of this plant, we have successfully generated a high-quality genome of C. sinica (1.06 Gb). Notably, transposable elements (TEs) constituted ~73% of the genome, with long terminal repeat retrotransposons (LTR-RTs) dominating this group of elements (~54% of the genome). The average intron length of the C. sinica genome was noticeably longer than what has been observed for closely-related species. The expansion of LTR-RTs and elongated introns emerged had the largest influence on the enlarged genome size of C. sinica in comparison to other Fabaceae species. The proliferation of TEs could be explained by certain modes of gene duplication, namely, whole genome duplication (WGD) and dispersed duplication (DSD). Gene family expansion, which was found to enhance genes associated with metabolism, genetic maintenance, and environmental stress resistance, was a result of transposed duplicated genes (TRD) and WGD. The presented genomic analysis sheds light on the genetic architecture of C. sinica, as well as provides a starting point for future evolutionary biology, ecology, and functional genomics studies centered around C. sinica and closely-related species.

A chromosome-level genome assembly of the soybean pod borer: insights into larval transcriptional response to transgenic soybean expressing the pesticidal Cry1Ac protein

BackgroundGenetically modified (GM) crop plants with transgenic expression of Bacillus thuringiensis (Bt) pesticidal proteins are used to manage feeding damage by pest insects. The durability of this technology is threatened by the selection for resistance in pest populations. The molecular mechanism(s) involved in insect physiological response or evolution of resistance to Bt is not fully understood.ResultsTo investigate the response of a susceptible target insect to Bt, the soybean pod borer, Leguminivora glycinivorella (Lepidoptera: Tortricidae), was exposed to soybean, Glycine max, expressing Cry1Ac pesticidal protein or the non-transgenic parental cultivar. Assessment of larval changes in gene expression was facilitated by a third-generation sequenced and scaffolded chromosome-level assembly of the L. glycinivorella genome (657.4 Mb; 27 autosomes + Z chromosome), and subsequent structural annotation of 18,197 RefSeq gene models encoding 23,735 putative mRNA transcripts. Exposure of L. glycinivorella larvae to transgenic Cry1Ac G. max resulted in prediction of significant differential gene expression for 204 gene models (64 up- and 140 down-regulated) and differential splicing among isoforms for 10 genes compared to unexposed cohorts. Differentially expressed genes (DEGs) included putative peritrophic membrane constituents, orthologs of Bt receptor-encoding genes previously linked or associated with Bt resistance, and those involved in stress responses. Putative functional Gene Ontology (GO) annotations assigned to DEGs were significantly enriched for 36 categories at GO level 2, respectively. Most significantly enriched cellular component (CC), biological process (BP), and molecular function (MF) categories corresponded to vacuolar and microbody, transport and metabolic processes, and binding and reductase activities. The DEGs in enriched GO categories were biased for those that were down-regulated (≥ 0.783), with only MF categories GTPase and iron binding activities were bias for up-regulation genes.ConclusionsThis study provides insights into pathways and processes involved larval response to Bt intoxication, which may inform future unbiased investigations into mechanisms of resistance that show no evidence of alteration in midgut receptors.

The genetic regulatory architecture and epigenomic basis for age-related changes in rattlesnake venom

Developmental phenotypic changes can evolve under selection imposed by age- and size-related ecological differences. Many of these changes occur through programmed alterations to gene expression patterns, but the molecular mechanisms and gene-regulatory networks underlying these adaptive changes remain poorly understood. Many venomous snakes, including the eastern diamondback rattlesnake (Crotalus adamanteus), undergo correlated changes in diet and venom expression as snakes grow larger with age, providing models for identifying mechanisms of timed expression changes that underlie adaptive life history traits. By combining a highly contiguous, chromosome-level genome assembly with measures of expression, chromatin accessibility, and histone modifications, we identified cis-regulatory elements and trans-regulatory factors controlling venom ontogeny in the venom glands of C. adamanteus. Ontogenetic expression changes were significantly correlated with epigenomic changes within genes, immediately adjacent to genes (e.g., promoters), and more distant from genes (e.g., enhancers). We identified 37 candidate transcription factors (TFs), with the vast majority being up-regulated in adults. The ontogenetic change is largely driven by an increase in the expression of TFs associated with growth signaling, transcriptional activation, and circadian rhythm/biological timing systems in adults with corresponding epigenomic changes near the differentially expressed venom genes. However, both expression activation and repression contributed to the composition of both adult and juvenile venoms, demonstrating the complexity and potential evolvability of gene regulation for this trait. Overall, given that age-based trait variation is common across the tree of life, we provide a framework for understanding gene-regulatory-network-driven life-history evolution more broadly.

Subgenome-aware analyses reveal the genomic consequences of ancient allopolyploid hybridizations throughout the cotton family

Malvaceae comprise some 4,225 species in 243 genera and nine subfamilies and include economically important species, such as cacao, cotton, durian, and jute, with cotton an important model system for studying the domestication of polyploids. Here, we use chromosome-level genome assemblies from representatives of five or six subfamilies (depending on the placement of Ochroma) to differentiate coexisting subgenomes and their evolution during the family's deep history. The results reveal that the allohexaploid Helicteroideae partially derive from an allotetraploid Sterculioideae and also form a component of the allodecaploid Bombacoideae and Malvoideae. The ancestral Malvaceae karyotype consists of 11 protochromosomes. Four subfamilies share a unique reciprocal chromosome translocation, and two other subfamilies share a chromosome fusion. DNA alignments of single-copy nuclear genes do not yield the same relationships as inferred from chromosome structural traits, probably because of genes originating from different ancestral subgenomes. These results illustrate how chromosome-structural data can unravel the evolutionary history of groups with ancient hybrid genomes.

Genome comparisons reveal accessory genes crucial for the evolution of apple Glomerella leaf spot pathogenicity in Colletotrichum fungi.

Apple Glomerella leaf spot (GLS) is an emerging fungal disease caused by Colletotrichum fructicola and other Colletotrichum species. These species are polyphyletic and it is currently unknown how these pathogens convergently evolved to infect apple. We generated chromosome-level genome assemblies of a GLS-adapted isolate and a non-adapted isolate in C. fructicola using long-read sequencing. Additionally, we resequenced 17 C. fructicola and C. aenigma isolates varying in GLS pathogenicity using short-read sequencing. Genome comparisons revealed a conserved bipartite genome architecture involving minichromosomes (accessory chromosomes) shared by C.fructicola and other closely related species within the C. gloeosporioides species complex. Moreover, two repeat-rich genomic regions (1.61 Mb in total) were specifically conserved among GLS-pathogenic isolates in C. fructicola and C. aenigma. Single-gene deletion of 10 accessory genes within the GLS-specific regions of C. fructicola identified three that were essential for GLS pathogenicity. These genes encoded a putative non-ribosomal peptide synthetase, a flavin-binding monooxygenase and a small protein with unknown function. These results highlight the crucial role accessory genes play in the evolution of Colletotrichum pathogenicity and imply the significance of an unidentified secondary metabolite in GLS pathogenesis.

The chromosome-scale assembly of the Notopterygium incisum genome provides insight into the structural diversity of coumarins

Coumarins, derived from the phenylpropanoid pathway, represent one of the primary metabolites found in angiosperms. The alignment of the tetrahydropyran (THP) and tetrahydrofuran (THF) rings with the lactone structure results in the formation of at least four types of complex coumarins. However, the mechanisms underlying the structural diversity of coumarin remain poorly understood. Here, we report the chromosome-level genome assembly of Notopterygium incisum, spanning 1.64 Gb, with a contig N50 value of 22.7 Mb and 60,021 annotated protein-coding genes. Additionally, we identified the key enzymes responsible for shaping the structural diversity of coumarins, including two p-coumaroyl CoA 2′-hydroxylases crucial for simple coumarins basic skeleton architecture, two UbiA prenyltransferases responsible for angular or linear coumarins biosynthesis, and five CYP736 cyclases involved in THP and THF ring formation. Notably, two bifunctional enzymes capable of catalyzing both demethylsuberosin and osthenol were identified for the first time. Evolutionary analysis implies that tandem and ectopic duplications of the CYP736 subfamily, specifically arising in the Apiaceae, contributed to the structural diversity of coumarins in N. incisum. Conclusively, this study proposes a parallel evolution scenario for the complex coumarin biosynthetic pathway among different angiosperms and provides essential synthetic biology elements for the heterologous industrial production of coumarins.

A high-quality chromosome-level genome assembly of the Chinese medaka Oryzias sinensis

Oryzias sinensis, also known as Chinese medaka or Chinese ricefish, is a commonly used animal model for aquatic environmental assessment in the wild as well as gene function validation or toxicology research in the lab. Here, a high-quality chromosome-level genome assembly of O. sinensis was generated using single-tube long fragment read (stLFR) reads, Nanopore long-reads, and Hi-C sequencing data. The genome is 796.58 Mb, and a total of 712.17 Mb of the assembled sequences were anchored to 23 pseudo-chromosomes. A final set of 22,461 genes were annotated, with 98.67% being functionally annotated. The Benchmarking Universal Single-Copy Orthologs (BUSCO) benchmark of genome assembly and gene annotation reached 95.1% (93.3% single-copy) and 94.6% (91.7% single-copy), respectively. Furthermore, we also use ATAC-seq to uncover chromosome transposase-accessibility as well as related genome area function enrichment for Oryzias sinensis. This study offers a new improved foundation for future genomics research in Chinese medaka.

A chromosome-level genome assembly of East Asia endemic minnow Zacco platypus

Zacco platypus is an endemic colorful freshwater minnow that is intensively distributed in East Asia. In this study, two adult female individuals collected from Haihe River basin were used for karyotypic study and genome sequencing, respectively. The karyotype formula of Z. platypus is 2N = 48 = 18 M + 24SM/ST + 6 T. We used PacBio long-read sequencing and Hi-C technology to assemble a chromosome-level genome of Z. platypus. As a result, an 814.87 Mb genome was assembled with the PacBio long reads. Subsequently, 98.64% assembled sequences were anchored into 24 chromosomes based on the Hi-C data. The chromosome-level assembly contained 54 scaffolds with a N50 length of 32.32 Mb. Repeat elements accounted for 52.35% in genome, and 24,779 protein-coding genes were predicted, with 92.11% were functionally annotated with the public databases. BUSCO analysis yielded a completeness score of 96.5%. This high-quality genome assembly provides valuable resources for future functional genomic research, comparative genomics, and evolutionary studies of genus Zacco.

Development of NBS-LRR gene-specific microsatellite markers for passion fruit Passiflora edulis Sims

The chromosome-level genome assembly of passion fruit (Passiflora edulis Sims) has facilitated computational analyses in developing novel informative SSR markers for genetics and breeding research. In this study, in-silico analysis was conducted to discover potential microsatellite loci and to design specific primers from the sequences of the characterised nucleotide-binding site - leucine-rich repeats (NBS-LRR) gene family of passion fruit, and a genotyping experiment was performed to validate the novel simple sequence repeat (SSR) markers.In total, 497 microsatellite loci were detected from 161 passion fruit NBS-LRR genes, of which 383 loci were qualified for primer generation. Forty-six SSR markers were selected for polymorphism verification, targeting 35 NBS-LRR genes that showed potential gene expression in response to biotic and abiotic stresses. From that, 25 SSR markers showed consistent polymorphic alleles among different passion fruit genotypes via PCR-PAGE analysis. These novel NBS-LRR-specific SSR markers might provide valuable tools for fortifying research on germplasm evaluation, genetic mapping, and molecular breeding for disease-resistant passion fruit varieties.

Selection of Catechin Biosynthesis-Related Genes and Functional Analysis from Chromosome-Level Genome Assembly in C. sinensis L. Variety 'Sangmok'.

Camellia is an important plant genus that includes well-known species such as C. sinensis, C. oleifera, and C. japonica. The C. sinensis cultivar 'Sangmok', one of Korea's standard types of tea landraces, is a small evergreen tree or shrub. Genome annotation has shown that Korean tea plants have special and unique benefits and superior components, such as catechin. The genome of Camellia sinensis cultivar 'Sangmok' was assembled on the chromosome level, with a length of 2678.62 Mbp and GC content of 38.16%. Further, 15 chromosome-scale scaffolds comprising 82.43% of the assembly (BUSCO completeness, 94.3%) were identified. Analysis of 68,151 protein-coding genes showed an average of 5.003 exons per gene. Among 82,481 coding sequences, the majority (99.06%) were annotated by Uniprot/Swiss-Prot. Further analysis revealed that 'Sangmok' is closely related to C. sinensis, with a divergence time of 60 million years ago. A total of 3336 exclusive gene families in 'Sangmok' were revealed by gene ontology analysis to play roles in auxin transport and cellular response mechanisms. By comparing these exclusive genes with 551 similar catechin genes, 17 'Sangmok'-specific catechin genes were identified by qRT-PCR, including those involved in phytoalexin biosynthesis and related to cytochrome P450. The 'Sangmok' genome exhibited distinctive genes compared to those of related species. This comprehensive genomic investigation enhances our understanding of the genetic architecture of 'Sangmok' and its specialized functions. The findings contribute valuable insights into the evolutionary and functional aspects of this plant species.

Genomic Features of the Host-Specific Fungal Biocontrol Agent Ramularia crupinae Approved for the Management of the Federally Noxious Weed Crupina vulgaris

Ramularia crupinae is a novel host-specific fungal pathogen of the invasive rangeland weed common crupina ( Crupina vulgaris). The foliar and stem blighting pathogen was originally identified in France and has been approved by the United States Department of Agriculture–Animal and Plant Health Inspection Service as the first biological control agent for the management of common crupina in the western United States. In this study, a chromosome-level genome assembly of R. crupinae 00-010 was performed using PacBio sequencing technology. The assembly had a total size of 37.9 Mb distributed across 14 (telomere to telomere) chromosomes, with a GC content of 47.6%. The genome encoded 10,159 protein-coding genes with 890 predicted secreted proteins that comprised both unique and conserved canonical pathogen effectors. Genome comparisons with closely related pathogen species in the family Mycosphaerellaceae demonstrated family-wide orthologous effector groups and Ramularia-specific orthogroups. This new reference sequence is a valuable genomic tool that will assist in characterizing Ramularia–Crupina interactions and increase our understanding of Ramularia pathogenicity on both crops and weeds. [Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 “No Rights Reserved” license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2024.

Identification and characterization of structural variants related to meat quality in pigs using chromosome-level genome assemblies

BackgroundMany studies have been performed to identify various genomic loci and genes associated with the meat quality in pigs. However, the full genetic architecture of the trait still remains unclear in part because of the lack of accurate identification of related structural variations (SVs) which resulted from the shortage of target breeds, the limitations of sequencing data, and the incompleteness of genome assemblies. The recent generation of a new pig breed with superior meat quality, called Nanchukmacdon, and its chromosome-level genome assembly (the NCMD assembly) has provided new opportunities.ResultsBy applying assembly-based SV calling approaches to various genome assemblies of pigs including Nanchukmacdon, the impact of SVs on meat quality was investigated. Especially, by checking the commonality of SVs with other pig breeds, a total of 13,819 Nanchukmacdon-specific SVs (NSVs) were identified, which have a potential effect on the unique meat quality of Nanchukmacdon. The regulatory potentials of NSVs for the expression of nearby genes were further examined using transcriptome- and epigenome-based analyses in different tissues.ConclusionsWhole-genome comparisons based on chromosome-level genome assemblies have led to the discovery of SVs affecting meat quality in pigs, and their regulatory potentials were analyzed. The identified NSVs will provide new insights regarding genetic architectures underlying the meat quality in pigs. Finally, this study confirms the utility of chromosome-level genome assemblies and multi-omics analysis to enhance the understanding of unique phenotypes.

Chromosome level genome assembly and transcriptome analysis of E11 cells infected by tilapia lake virus

The E11 cell line, derived from striped snakehead fish (Channa striata), possesses a distinctive feature: it is persistently infected with a C-type retrovirus. Notably, it exhibits high permissiveness to piscine nodavirus and the emerging tilapia lake virus (TiLV). Despite its popularity in TiLV research, the absence of genome assembly for the E11 cell line and Channa striata has constrained research on host-virus interactions. This study aimed to fill this gap by sequencing, assembling, and annotating the E11 cell line genome. Our efforts yielded a 600.5 Mb genome including 24 chromosomes with a BUSCO score of 98.8%. In addition, the complete proviral DNA sequence of snakehead retrovirus (SnRV) was identified in the E11 cell genome. Comparative genomic analysis between the E11 cell line and another snakehead species Channa argus revealed the loss of many immune-related gene families in the E11 cell genome, indicating a compromised immune response. We also conducted transcriptome analysis of mock- and TiLV-infected E11 cells, unveiling new perspectives on virus-virus and host-virus interactions. The TiLV infection suppressed the high expression of SnRV in E11 cells, and activated some other endogenous retroviruses. The protein-coding gene comparison revealed a pronounced up-regulation of genes involved in immune response, alongside a down-regulation of genes associated with specific metabolic processes.In summary, the genome assembly and annotation of the E11 cell line provide valuable resources to understand the SnRV and facilitate further studies on nodavirus and TiLV. The RNA-seq profiles shed light on the cellular mechanisms employed by fish cells in response to viral challenges, potentially guiding the development of therapeutic strategies against TiLV in aquaculture. This study also provides the first insights into the viral transcriptome profiles of endogenous SnRV and evading TiLV, enhancing our understanding of host-virus interactions in fish.

Insight into the adaptive role of arachnid genome-wide duplication through chromosome-level genome assembly of the Western black widow spider.

Although spiders are one of the most diverse groups of arthropods, the genetic architecture of their evolutionary adaptations is largely unknown. Specifically, ancient genome-wide duplication occurring during arachnid evolution ~450 mya resulted in a vast assembly of gene families, yet the extent to which selection has shaped this variation is understudied. To aid in comparative genome sequence analyses, we provide a chromosome-level genome of the Western black widow spider (Latrodectus hesperus)-a focus due to its silk properties, venom applications, and as a model for urban adaptation. We used long-read and Hi-C sequencing data, combined with transcriptomes, to assemble 14 chromosomes in a 1.46 Gb genome, with 38,393 genes annotated, and a BUSCO score of 95.3%. Our analyses identified high repetitive gene content and heterozygosity, consistent with other spider genomes, whichhas led to challenges in genome characterization. Our comparative evolutionary analyses of eight genomes available for species within the Araneoidea group (orb weavers and their descendants) identified 1,827 single-copy orthologs. Of these, 155 exhibit significant positive selection primarily associated with developmental genes, and with traits linked to sensory perception. These results support the hypothesis that several traits unique to spiders emerged from the adaptive evolution of ohnologs-or retained ancestrally duplicated genes-from ancient genome-wide duplication. These comparative spider genome analyses can serve as a model to understand how positive selection continually shapes ancestral duplications in generating novel traits today within and between diverse taxonomic groups.

Chromosome-level genome assembly provides insights into the genome evolution and functional importance of the phenylpropanoid–flavonoid pathway in Thymus mongolicus

BackgroundThymus mongolicus (family Lamiaceae) is a Thyme subshrub with strong aroma and remarkable environmental adaptability. Limited genomic information limits the use of this plant.ResultsChromosome-level 605.2 Mb genome of T. mongolicus was generated, with 96.28% anchored to 12 pseudochromosomes. The repetitive sequences were dominant, accounting for 70.98%, and 32,593 protein-coding genes were predicted. Synteny analysis revealed that Lamiaceae species generally underwent two rounds of whole genome duplication; moreover, species-specific genome duplication was identified. A recent LTR retrotransposon burst and tandem duplication might play important roles in the formation of the Thymus genome. Using comparative genomic analysis, phylogenetic tree of seven Lamiaceae species was constructed, which revealed that Thyme plants evolved recently in the family. Under the phylogenetic framework, we performed functional enrichment analysis of the genes on nodes that contained the most gene duplication events (> 50% support) and of relevant significant expanded gene families. These genes were highly associated with environmental adaptation and biosynthesis of secondary metabolites. Combined transcriptome and metabolome analyses revealed that Peroxidases, Hydroxycinnamoyl-CoA shikimate/quinate hydroxycinnamoyl transferases, and 4-coumarate-CoA ligases genes were the essential regulators of the phenylpropanoid–flavonoid pathway. Their catalytic products (e.g., apigenin, naringenin chalcone, and several apigenin-related compounds) might be responsible for the environmental tolerance and aromatic properties of T. mongolicus.ConclusionThis study enhanced the understanding of the genomic evolution of T. mongolicus, enabling further exploration of its unique traits and applications, and contributed to the understanding of Lamiaceae genomics and evolutionary biology.

Evolution of alternative reproductive systems in Bacillus stick insects.

Reproduction is a key feature of all organisms, yet the way in which it is achieved varies greatly across the tree of life. One striking example of this variation is the stick insect genus Bacillus, in which five different reproductive modes have been described: sex, facultative and obligate parthenogenesis, and two highly unusual reproductive modes: hybridogenesis and androgenesis. Under hybridogenesis, the entire genome from the paternal species is eliminated, and replaced each generation by mating with the corresponding species. Under androgenesis, an egg is fertilized but the developing diploid offspring bear two paternal genomes, and no maternal genome, as a consequence of unknown mechanisms. Here, we re-evaluate previous descriptions of Bacillus lineages and the proposed F1 hybrid ancestries of the hybridogenetic and obligately parthenogenetic lineages (based on allozymes and karyotypes) from Sicily, where all these reproductive modes are found. We generate a chromosome-level genome assembly for a facultative parthenogenetic species (B. rossius) and combine extensive field sampling with RADseq and mtDNA data. We identify and genetically corroborate all previously described species and confirm the ancestry of hybrid lineages. All hybrid lineages have fully retained their F1 hybrid constitution throughout the genome, indicating that the elimination of the paternal genome in hybridogens is always complete and that obligate parthenogenesis in Bacillus hybrid species is not associated with an erosion of heterozygosity as known in other hybrid asexuals. Our results provide a stepping stone towards understanding the transitions between reproductive modes and the proximate mechanisms of genome elimination.

Updated single cell reference atlas for the starlet anemone Nematostella vectensis.

The recent combination of genomics and single cell transcriptomics has allowed to assess a variety of non-conventional model organisms in much more depth. Single cell transcriptomes can uncover hidden cellular complexity and cell lineage relationships within organisms. The recent developmental cell atlases of the sea anemone Nematostella vectensis, a representative of the basally branching Cnidaria, has provided new insights into the development of all cell types (Steger et al Cell Rep 40(12):111370, 2022; Sebé-Pedrós et al. Cell 173(6):1520-1534.e20). However, the mapping of the single cell reads still suffers from relatively poor gene annotations and a draft genome consisting of many scaffolds. Here we present a new wildtype resource of the developmental single cell atlas, by re-mapping of sequence data first published in Steger et al. (2022) and Cole et al. (Nat Commun 14(1):1747, 2023), to the new chromosome-level genome assembly and corresponding gene models in Zimmermann et al. (Nat Commun 14, 8270 (2023). https://doi.org/10.1038/s41467-023-44080-7 ). We expand the pre-existing dataset through the incorporation of additional sequence data derived from the capture and sequencing of cell suspensions from four additional samples: 24h gastrula, 2d planula, an inter-parietal region of the bodywall from a young unsexed animal, and another adult mesentery from a mature male animal. Our analyses of the full cell-state inventory provide transcriptomic signatures for 127 distinct cell states, of which 47 correspond to neuroglandular subtypes. We also identify two distinct putatively immune-related transcriptomic profiles that segregate between the inner and outer cell layers. Furthermore, the new gene annotation Nv2 has markedly improved the mapping on the single cell transcriptome data and will therefore be of great value for the community and anyone using the dataset.