Chromosome-level Genome Assembly Research Articles

Chromosome-scale assembly of Artemia tibetiana genome, first aquatic invertebrate genome from Tibet Plateau

Genomic-level studies on the adaptive evolution of animals in the Qinghai-Tibet Plateau have been rapidly increasing. However, most studies are concentrated on vertebrates, and there are few reports on invertebrates. Here, we report the chromosome-level genome assembly for the brine shrimp Artemia tibetiana from Kyêbxang Co, a high-altitude (4620 m above sea level) salt lake on the plateau, based on the combination of Illumina, Nanopore long-reads and Hi-C sequencing data. The assembled genome is 1.69 Gb, and 94.83% of the assembled sequences are anchored to 21 pseudo-chromosomes. Approximately 75% of the genome was identified as repetitive sequences, which is higher than most crustaceans documented so far. A total of 17,988 protein-coding genes were identified, among them 14,388 were functionally annotated. This genomic resource provides the foundation for whole-genome level investigation on the genetic adaptation of Artemia to the harsh conditions in the Qinghai-Tibet Plateau.

Chromosome-level genome assembly of the doctor fish (Garra rufa)

Garra rufa, or doctor fish, is a small cyprinid known for its high-temperature tolerance and its use in ichthyotherapy. Recently, this trait has gained interest as a model for human diseases, including infections and cancer xenografts, though limited genomic resources hinder experimental use. In this study, we have generated a high-quality, chromosome-level genome assembly of G. rufa using PacBio HiFi long-read sequencing and Hi-C technology. The genome is 1.38 Gb in size, with 25 chromosomes and a scaffold N50 of 49.3 Mb. Approximately 59% of the genome consists of repetitive elements, while 27,352 protein-coding genes were annotated, with 98.3% being functionally characterized. BUSCO analysis revealed 94.5% and 94.7% completeness for the genome assembly and annotated protein sequences, respectively. Notably, we identified two heat shock transcription factor (HSF) genes, 239 heat shock protein (HSP)-related genes, and 1,036 heat shock elements (HSEs) in regulatory regions. Phylogenetic analysis supports the placement of G. rufa within the Labeoninae subfamily. This genome assembly provides a valuable resource for advancing G. rufa as a model organism.

Chromosome-level genome assemblies of five Sinocyclocheilus species

Sinocyclocheilus, a genus of tetraploid fishes endemic to Southwest China’s karst regions, are classified as second-class nationally protected species due to their fragile habitat. Limited high-quality genomic resources have hampered studies on their phylogenetic relationships and the origin of their polyploidy. Here, we present a high-quality genome assembly of the most abundant Sinocyclocheilus species, the golden-line barbel (Sinocyclocheilus grahami), by integrating PacBio long-read and Hi-C sequencing. The resulting scaffold-level genome-assembly is 1.6 Gb long, with a scaffold N50 of up to 30.7 Mb. We annotated 42,806 protein-coding genes. Also, 93.1% of the assembled genome sequences (about 1.5 Gb) and 93.8% of the total predicted genes were successfully anchored onto 48 chromosomes. Furthermore, we obtained chromosome-level genome assemblies for four other Sinocyclocheilus species (S. anophthalmus, S. maitianheensis, S. anshuiensis, and S. rhinocerous) based on homologous comparisons. These genomic resources will enable in-depth investigations on cave adaptation, improvement of economic values, and conservation of diverse Sinocyclocheilus fishes.

Chromosome-level genome assembly and annotation of the Amur rat snake Elaphe schrenckii.

The Amur rat snake (Elaphe schrenckii), a widely distributed colubrid species in Northeast Asia, plays a critical role in controlling rodent and mouse populations in the wild. Despite its ecological and evolutionary significance, genomic resources for this non-venomous species have been limited. In this study, we present a high-quality, chromosome-level genome assembly of E. schrenckii, generated by PacBio HiFi long-read sequencing and Hi-C chromatin interaction mapping. The assembled genome size comprises 1.69 Gb, with a scaffold N50 length of 215 Mb. Hi-C scaffolding anchored the genome into 18 chromosomes, including one that represents the conserved Z chromosome of snakes, consistent with karyotypic observations. This assembly enables further gene annotation and analysis of chromosomal synteny patterns. Repetitive elements account for 53.2% of the genome, with LINE retrotransposons being the predominant class (23.2%). We identified 18,529 protein-coding genes, with 90.6% functionally annotated through homology-based methods. The genome assembly is highly complete, with a BUSCO score of 97.4% (tetrapoda_odb10). This resource provides a foundation for comparative studies of colubrid genome evolution, which also serves as a crucial reference for conservation genomics, particularly for Asian snake populations facing habitat fragmentation.

Chromosome-level genome assembly of Parotis chlorochroalis (Lepidoptera: Crambidae: Spilomelinae)

Parotis Hübner, 1831 is a genus within the family Crambidae, which is recognized as one of the most diverse families of Lepidoptera. Species within the genus Parotis can be readily distinguished from other closely related genera by their distinctive green or yellow-green body coloration. However, the genus Parotis has received relatively limited research attention, and the scarcity of genome-wide molecular resources has impeded a more comprehensive understanding of its evolution, adaptation, and phylogenetic relationships. This study reports the first genome assembly for Parotis chlorochroalis (Hampson, 1912), generated through PacBio Hi-Fi and Hi-C sequencing technologies. The assembled genome has a size of 456.23 Mb, comprising 31 chromosomes. Approximately 181.82 Mb, which constitutes 39.85% of the genome, has been identified as repetitive sequences. The genome assembly includes 16,299 protein-coding genes, of which 94.82% have been functionally annotated. This chromosome-level genome assembly not only advance understanding of P. chlorochroalis but also has the potential to facilitate genomic studies of other lepidopteran species.

Where did the Y chromosome in the spiny rat go, and how did it get there?

The XX/XY sex chromosome system is highly conserved across mammals, with rare exceptions where males lack a Y chromosome. Among these is the genus Tokudaia, a group of spiny rats comprising three species with unique sex chromosome systems deviating from the typical XX/XY pattern. While T. osimensis and T. tokunoshimensis have completely lost the Y chromosome, they retain some Y-linked genes on the X chromosome. In contrast, T. muenninki retains large sex chromosomes where both the X and Y chromosomes have fused with an autosome pair, carrying multi-copied Y-linked genes, including Sry. In this study, we generated chromosome-level genome assemblies for male individuals of all three Tokudaia species. By investigating loci typically associated with rodent Y-linked genes, we characterized sequences derived from the Tokudaia Y-chromosomal most recent common ancestor (Tokudaia Y-MRCA) and traced their evolutionary trajectories. Our analyses revealed that an initial X-to-Y translocation of a sequence containing the Boundary-Associated Segmental Duplication (BASD) in a common ancestor of Tokudaia marked the beginning of their unique sex chromosome evolution. The BASD, uniquely multi-copied in Tokudaia, facilitated further rearrangements through non-allelic homologous recombination and duplications. These processes culminated in subsequent Y-to-X translocations and duplications, leading to the complete loss of the Y chromosome as a distinct entity while preserving Y-linked genes in a multicopy state on the X chromosome. These findings highlight Tokudaia's rapid sex chromosome evolution within three million years and provide insights into the mechanisms underlying Y chromosome loss, contributing to a broader understanding of sex chromosome evolution in rodents.

Chromosome-level genome assembly of Protandrena (Anthemurgus) passiflorae (Hymenoptera: Andrenidae), a host-plant specialist bee

Abstract The passion flower bee, Protandrena (Anthemurgus) passiflorae (Robertson) is a monolectic, host-plant specialist of the passionflower plant Passiflora lutea L. Using a single adult male individual, we generated long-read PacBio HiFi, HiC, and short-read RNA sequencing data to build a well-annotated, chromosome-level genome assembly for this species. The final nuclear genome is 249 Mb with 150x coverage and with most of the genome scaffolding into 12 chromosomes. The scaffold N50 is 21.4 Mb and the genome has a Benchmarking Universal Single-Copy Ortholog (BUSCO) score of 97.2% for 5991 hymenopteran genes. BRAKER3 annotation of the genome identified 12,098 genes and 15,353 total transcripts and found that 20.27% of the genome is made up of repetitive elements. We resolved a mitochondrial genome of 12.7 kb. The P. passiflorae genome represents one of only a few published andrenid bee genomes and one of the first monolectic bees. This new high-quality genome will serve as a valuable resource for investigating the genomic basis of specialization and for providing a useful resource for studying pollinator health and conservation.

Gap-free genome assembly and comparative analysis reveal the evolution and lignin degradation mechanisms of Cylindrobasidium torrendii.

Gap-free genome assembly and comparative analysis reveal the evolution and lignin degradation mechanisms of Cylindrobasidium torrendii.

The expanded Bostrychia moritziana genome unveils evolution in the most diverse and complex order of red algae.

The expanded Bostrychia moritziana genome unveils evolution in the most diverse and complex order of red algae.

A chromosome-level reference genome for the critically endangered Southern Corroboree frog (Pseudophryne corroboree)

The Southern Corroboree frog (Pseudophryne corroboree; Anura; Myobatrachidae) is a Critically Endangered amphibian, according to the IUCN, and is endemic to the Snowy Mountains region of Kosciuszko National Park in New South Wales, Australia. This species has been driven to functional extinction by the introduction of the fungal disease, chytridiomycosis. Here we provide the first reference genome for P. corroboree. Using PacBio HiFi sequencing, Arima Hi-C, and Bionano optical mapping, we produced a chromosome-level genome assembly. Additionally, we generated a reference transcriptome based on multiple tissues from both male and female individuals to support genome annotation. The resulting genome spans 8.87 Gb across 12 chromosomes, with a contig N50 of 6.8 Mb. This research provides a phased, annotated genome assembly along with transcriptomic resources to facilitate future conservation genomic studies of P. corroboree. Furthermore, the genome offers an invaluable resource for taxonomic and evolutionary research, particularly given the nearest available chromosome-level reference genome is from Mixophyes fleayi, a species that last shared a common ancestor with P. corroboree 80 million years ago.

Chromosome-level genome assembly of Dendrothrips minowai and genomic analysis highlights distinct adaptations to high polyphenols in tea plants.

Dendrothrips minowai Priesner, a significant pest in tea-producing regions of Asia, particularly China, damages tea plants (Camellia sinensis) by feeding on their tender leaves rich in polyphenols. Seven assembled genomes from the order Thysanoptera are currently available. This study presents the first chromosome-level genome assembly of D. minowai generated by PacBio Revio, Oxford Nanopore Technologies, MGI, and Hi-C technology. The assembled genome measures 350.11 Mb with 1269 contigs with a contig N50 of 536.34 Kb and a scaffold N50 of 16.86 Mb, organized across 19 chromosomes. A total of 16 730 protein-coding genes were identified, with 92.28% functionally annotated. The phylogenetic analysis reveals that D. minowai diverged approximately 103.2 million years ago, preceding all reported genomes of Thripidae species. Comparative genomic analysis identified 12 expanded and 172 contracted gene families of D. minowai, with expanded gene families linked to host plant metabolite processing and detoxification enzymes. Additionally, oligophagous thrips, D. minowai and Stenchaetothrips biformis, possess fewer chemosensory genes (gustatory receptors, odorant receptors, ionotropic receptors, chemosensory proteins, and odorant binding proteins) and detoxification genes (P450s, carboxyl/cholinesterases, UDP-glycosyltransferases) than polyphagous species (Frankliniella occidentalis and Thrips palmi). Interestingly, D. minowai exhibits an expansion in ABC transporter families, especially ABCG and ABCC, which is likely essential for detoxifying the high polyphenol content in tea plants. This study provides another genome sequence for oligophagous thrips species, which enriches the genomic data for further studies on the evolution, host adaptation, and novel control strategies of thrips. © 2025 Society of Chemical Industry.

Diversity of telomeric sequences in true bugs (Heteroptera): new data on the infraorders Pentatomomorpha and Cimicomorpha.

Telomeric sequences are stable parts of the genome and are widely conserved among higher-level taxa (e.g., TTAGG in insects and other arthropods), although exceptions are known and their numbers are increasing with research. The true bug suborder Heteroptera (Hemiptera) includes more than 40,000 species in about 100 families, classified into seven infraorders. Four different telomeric motifs are currently known in Heteroptera, including (TTAGG)n, (TTAGGGATGG)n, (TTAGGGGTGG)n, and (TTAGGGTGGT)n. The canonical "insect" motif (TTAGG)n was found in representatives of two infraorders, Nepomorpha and Cimicomorpha. Derived motifs were found in a few species previously known as TTAGG-negative in the evolutionarily advanced sister infraorders Cimicomorpha and Pentatomomorpha (= Terheteroptera). Here, we studied telomeric motifs in 20 species of true bugs belonging to 10 families of Terheteroptera. We used fluorescence in situ hybridization (FISH) with the "insect" telomeric probe (TTAGG)n and an alternative probe (TTAGGGATGG)n to map the distribution of telomeric sequences in the chromosomes of 8 species of Pentatomomorpha (from the families Pentatomidae, Rhopalidae, Lygaeidae, Geocoridae, and Blissidae). We also analyzed chromosome-level genome assemblies available in the NCBI database for another 4 species of Pentatomomorpha (from Alydidae, Coreidae, and Pentatomidae) and 8 species of Cimicomorpha (from Reduviidae, Miridae, and Anthocoridae). Overall, we identified telomeric sequences in all but one (Geocoris dispar; Geocoridae) species. The telomeric motif (TTAGGGATGG)n was detected in both Cimicomorpha (in the families Anthocoridae and Miridae) and Pentatomomorpha (in Blissidae, Lygaeidae, Pentatomidae, and Rhopalidae); the motif (TTAGGGGTGG)n was found only in Pentatomomorpha (in Alydidae, Coreidae, and Pentatomidae); and the canonical "insect" motif (TTAGG)n was found in the family Reduviidae (Cimicomorpha). With our new data, telomeric motifs are now known for 40 species of true bugs from 30 genera, 13 families and 3 infraorders, including Nepomorpha, Cimicomorpha, and Pentatomomorpha. Non-canonical motifs are found so far only in the Terheteroptera clade and are dominant in this group, with (TTAGGGATGG)n leading. Our new data have expanded the understanding of telomere composition and evolution in Cimicomorpha and Pentatomomorpha and suggested that (TTAGGGATGG)n telomeric sequences can be considered ancestral for the entire clade Terheteroptera.

A chromosome-level genome assembly of the polyembryonic endoparasitoid Macrocentrus cingulum

Polyembryony is a unique reproductive pattern, where multiple genetically identical offspring develop from a single egg. Macrocentrus cingulum, a polyembryonic endoparasitoid, is one of the dominant parasitoids of the globally agricultural pest, Ostrinia furnacalis, and it can serve as a valuable model for investigating the mechanisms of polyembryony. However, the previously published genome of M. cingulum remains highly fragmented, limiting comprehensive studies of its biological characteristics. Here, we present a chromosome-level genome assembly of M. cingulum using PacBio HiFi and Hi-C sequencing. This genome assembly is approximately 151.93 Mb with a contig N50 of 8.42 Mb and a scaffold N50 of 16.93 Mb, organized into 9 chromosomes. The repeat sequences constitute 25.52% of the genome assembly. A total of 14,471 protein-coding genes with 98.2% BUSCO completeness were predicted, of which 12,500 genes have been annotated in public biological databases. In conclusion, this reported genome should be a valuable genomic resource for exploring macroevolutionary mechanisms underlying polyembryony, and the molecular mechanisms of polyembryony in M. cingulum.

Chromosomal-level genome assembly of Trichogramma dendrolimi (Trichogrammatidae: Hymenoptera)

Trichogramma dendrolimi is an essential egg parasitic wasp with a broad host range and has been widely used for controlling agricultural and forestry pests. Despite the availability of fragmented genomes of Trichogramma, a high-quality, chromosome-level genome reference is not yet available for this diverse genus. In this study, we assembled a high-quality chromosome-level genome of T. dendrolimi using PacBio CLR long sequencing and further scaffolded it with Hi-C technologies. The genome size was 216.24 Mb, featuring a N50 of 39.07 Mb, and 98.79% of scaffolds were anchored to five chromosomes. In addition, we annotated 12,902 protein-coding genes and 60.74 Mb repeat sequences for this genome assembly. In conclusion, our chromosome-level genome assembly provided important genomic resources that benefit the utilization of Trichogramma parasitoids in pest control.

Deep Insight into the genome of a major rice pest, Scripophaga incertulas

The yellow stem borer, Scripophaga incertulas (Crambidae, Lepidoptera), is a highly destructive pest damaging rice crops. Here, we combined Illumina, PacBio sequencing and Hi-C scaffolding to generate a high-quality chromosome-level genome assembly of S. incertulas. We initially obtained an 839.78 Mb assembly with scoffold N50 of 1.13 Mb. Benchmarking Universal Single-Copy Orthologs (BUSCO) analysis demonstrated that this genome assembly has a high-level completeness of 97.5% gene coverage. The assembly contained 45.67% repetitive sequences (383.50 Mb), and has been annotated with 19,874 protein-coding genes. Next, 3,369 scaffolds were anchored to 26 chromosomes, resulting in an increase of the N50 to 32.16 Mb. Our research provides insights into the evolution and ecology of S. incertulas, offering valuable resources for future pest management.

High-quality chromosome-level genome assembly of the whitespotted conger (Conger myriaster)

The whitespotted conger (Conger myriaster) is an ecologically and economically significant benthic marine species widely distributed across East Asia’s coastal waters. Despite this importance, the genomic resources for this species remain limited, hindering evolutionary and aquaculture research. Here, we present the first high-quality chromosome-level genome assembly of C. myriaster using PacBio CLR, WGS, 10X Genomics and Hi-C data. The resulting 1.09 Gb genome assembly exhibits excellent contiguity, with 97.49% of sequences anchored onto 19 chromosomes. The assembled genome achieved a BUSCO completeness stands at 98.00%, containing 34.80% repetitive sequences and 24,063 predicted protein-coding genes. This foundational genomic resource overcomes a major limitation, providing the essential framework for future investigations into the evolutionary adaptations and for the genetic improvement of C. myriaster in aquaculture.

The chromosomal-level genome assembly and annotation of pen shell Atrina pectinata

The pen shell Atrina pectinata is a bivalve recognized for its outstanding large adductor muscle and developed byssus. Now, it becomes threatened in East Asia, requiring special attention for artificial breeding to boost yield. However, the lack of high-quality genomes hinders our understanding of its reproductive biology, which resulting in the artificial breeding in pen shell is still a scientific technological problem. Here, we produced a high-quality chromosome-level genome assembly of A. pectinata combing the PacBio, Illumina, and high-resolution chromosome conformation capture sequencing. The final assembly has a size of 951.01 Mb with a scaffold N50 of 52.64 Mb, 98.87% of sequence was anchored onto 17 chromosomes, with a BUSCO evaluation integrity score of 98.8%. We successfully identified 29,326 protein-coding genes and 24,708 genes (84.25%) were functionally annotated. The BUSCO evaluation integrity score for the predicted protein-coding genes was 97.7%. This work promotes the applicability of the A. pectinata genome, laying a solid foundation for future investigations into genomics and biology within this species.

High-quality genome of allotetraploid Avena barbata provides insights into the origin and evolution of B subgenome in Avena.

Avena barbata, a wild oat species within the genus Avena, is a widely used model for studying plant ecological adaptation due to its strong environmental adaptability and disease resistance, serving as a valuable genetic resource for oat improvement. Here, we phased the high-quality chromosome-level genome assembly of A. barbata (6.88 Gb, contig N50 = 53.74 Mb) into A (3.57 Gb with 47,687 genes) and B (3.31 Gb with 46,029 genes) subgenomes. Comparative genomics and phylogenomic analyses clarified the evolutionary relationships and trajectories of A, B, C and D subgenomes in Avena. We inferred that the A subgenome donor of A. barbata was Avena hirtula, while the B subgenome donor was probably an extinct diploid species closely related to Avena wiestii. Genome evolution analysis revealed the dynamic transposable element (TE) content and subgenome divergence, as well as extensive structure variations across A, B, C, and D subgenomes in Avena. Population genetic analysis of 211 A. barbata accessions from distinct ecotypes identified several candidate genes related to environmental adaptability and drought resistance. Our study provides a comprehensive genetic resource for exploring the genetic basis underlying the strong environmental adaptability of A. barbata and the molecular identification of important agronomic traits for oat breeding.

Chromosome-Level Genome Assembly of the Asian Tramp Snail Bradybaena similaris (Stylommatophora: Camaenidae).

While terrestrial land snails have long been used for evolutionary research, a lack of high-quality genomic resources has impeded recent progress. Bradybaena snails in particular have numerous intriguing traits that make them a good model for studying evolution, including shell pattern polymorphism and convergent evolution. They are also introduced and invasive across the world. In this study, we present a chromosome-level genome assembly of the Asian tramp snail Bradybaena similaris, utilizing 88-fold Illumina short-read sequences, 125-fold Nanopore long-read sequences, 63-fold PacBio HiFi sequences, and 47-fold Hi-C sequences. The assembled genome of 2.18 Gb is anchored to 28 chromosomes and exhibits high completeness (single copy, 91.7%; duplicates, 7.1%) and contiguity (N50 of 75.6 Mb). Additionally, we also obtained a high-quality transcriptome for annotation. This resource represents the first chromosome-level assembly for snails in the superfamily Helicoidea, which includes more than 5,000 species of terrestrial snails, and will facilitate genomic study in Bradybaena and, more broadly, in the superfamily Helicoidea.

Cytogenetics of insects in the era of chromosome-level genome assemblies.

Over the past few years, a revolution has occurred in cytogenetics, driven by the emergence and spread of methods for obtaining high-quality chromosome-level genome assemblies. In fact, this has led to a new tool for studying chromosomes and chromosomal rearrangements, and this tool is thousands of times more powerful than light microscopy. This tool has revolutionized the cytogenetics of many groups of insects for which previously karyotype information, if available at all, was limited to the chromosome number. Even more impressive are the achievements of the genomic approach for studying the general patterns of chromosome organization and evolution in insects. Thus, it has been shown that rapid transformations of chromosomal numbers, which are often found in the order Lepidoptera, are most often carried out in the most parsimonious way, as a result of simple fusions and fissions of chromosomes. It has been established that these fusions and fissions are not random and occur independently in different phylogenetic lineages due to the reuse of the same ancestral chromosomal breakpoints. It has been shown that the tendency for chromosome fissions is correlated with the presence in chromosomes of the so-called interstitial telomeres, i. e. telomere-like structures located not at the ends of chromosomes, but inside them. It has been revealed that, in most insects, telomeric DNA is not just a set of short repeats, but a very long sequence consisting of (TTAGG)n (or other telomeric motifs), regularly and specifically interrupted by retrotransposons, and the telomeric motifs are diverse in terms of their length and nucleotide composition. The number of high-quality chromosome-level genome assemblies available for insects in the GenBank database is growing exponentially and now exceeds a thousand species. Therefore, the exceptional prospects for using genomic data for karyotype analysis are beyond doubt.