Contig N50 Length Research Articles

Chromosome-level genome assembly of the Suminoe oyster Crassostrea ariakensis in south China

The Suminoe oyster Crassostrea ariakensis (Fujita, 1913) is one of the most important ecological and fishery bivalve mollusks with a worldwide distribution. Here, we reported an improved high-quality chromosomal-level genome assembly of C. ariakensis inhabiting the South China Sea, using Nanopore technology, Illumina sequencing, and high-throughput chromosomal conformation capture analysis. The assembled genome size is 631.73 Mb, with contig N50 length of 5.36 Mb and scaffold N50 length of 61.15 Mb, and is assigned to 10 chromosomes. A total of 29,357 protein-coding genes are predicted, 96.68% of which are functionally annotated. The genome contains 347.11 Mb (54.94%) of repetitive elements and 1130 noncoding RNAs. This improved genome assembly of south C. ariakensis is an important resource for understanding oyster diversity and evolution, and provides insights into genetic improvement, protection and management of oyster resource.

Genome assembly at chromosome scale with telomere ends for Pearlspot, Etroplus suratensis

The pearlspot, Etroplus suratensis is a climate resilient cichlid fish that exhibits unusual adaptation to salinity. The fish is able to complete full life cycle in diverse salinity habitats ranging from fresh water to marine environments. High-quality primary and phased genome assemblies were generated for pearlspot fish using PacBio HiFi and Arima HiC sequencing technologies, for the first time. The primary assembly is highly contiguous with contig N50 length of 36 Mb. The final assembly is of 1.247 Gb with N50 length of 51.57 Mb and 98% of the genome length anchored to 24 chromosomes. The genome was assessed to be 99.9% complete based on BUSCO evaluation and was predicted to contain 52.96% repeat elements. We have predicted 27,192 protein encoding genes, of which 21,580 were functionally annotated. The genome offers an invaluable resource to understand adaptation of pearlspot fish to diverse salinity habitats.

Chromosome-level genome assembly of the ivory shell Babylonia areolata

The ivory shell Babylonia areolata is an economically important marine benthic gastropod known for its rapid growth and high nutritional value. B. areolata is distributed in Southeast Asia and the southeast coastal areas of China. In this study, we constructed a high-quality genome for B. areolata using PacBio, Illumina, and Hi-C sequencing technologies. The genome assembly comprised 35 chromosomal sequences with a total length of 1.65 Gb. The scaffold and contig N50 lengths were 53.17 Mb and 2.64 Mb, respectively, with repeat sequences constituting 64.46% of the genome. Furthermore, 26,130 protein-coding genes and 96.75% of the genome’s BUSCOs were identified. This inaugural report of a B. areolata genome provides crucial foundational information for further investigations into the biology, genomics, and genetic improvement of economic traits of this species.

Clam Genome and Transcriptomes Provide Insights into Molecular Basis of Morphological Novelties and Adaptations in Mollusks.

Bivalve mollusks, comprising animals enclosed in two shell valves, are well-adapted to benthic life in many intertidal zones. Clams have evolved the buried lifestyle, which depends on their unique soft tissue structure and their wedge-shaped muscular foot and long extendible siphons. However, molecular mechanisms of adaptative phenotype evolution remain largely unknown. In the present study, we obtain the high-quality chromosome-level genome of Manila clam R. philippinarum, an economically important marine bivalve in many coastal areas. The genome is constructed by the Hi-C assisted assembly, which yields 19 chromosomes with a total of 1.17 Gb and BUSCO integrity of 92.23%. The de novo assembled genome has a contig N50 length of 307.7 kb and scaffold N50 of 59.5 Mb. Gene family expansion analysis reveals that a total of 24 single-copy gene families have undergone the significant expansion or contraction, including E3 ubiquitin ligase and dynein heavy chain. The significant expansion of transposable elements has been also identified, including long terminal repeats (LTR) and non-LTR retrotransposons. The comparative transcriptomics among different clam tissues reveals that extracellular matrix (ECM) receptors and neuroactive ligand receptors may play the important roles in tissue structural support and neurotransmission during their infaunal life. These findings of gene family expansion and tissue-specific expression may reflect the unique soft tissue structure of clams, suggesting the evolution of lineage-specific morphological novelties. The high-quality genome and transcriptome data of R. philippinarum will not only facilitate the genetic studies on clams but will also provide valuable information on morphological novelties in mollusks.

A chromosome-scale genome assembly of Timorese crabgrass (Digitaria radicosa): a useful genomic resource for the Poaceae.

Timorese crabgrass (Digitaria radicosa) is a grass species commonly found in Southeast Asia and Oceania. Digitaria species have high intraspecific and interspecific genetic and phenotypic diversity, suggesting their potential usefulness as a genetic resource. However, as the only high-quality reference genome available is for a tetraploid Digitaria species, a reference genome of the diploid species D. radicosa would be a useful resource for genomic studies of Digitaria and Poaceae plants. Here, we present a chromosome-level genome assembly of D. radicosa and describe its genetic characteristics; we also illustrate its usefulness as a genomic resource for Poaceae. We constructed a 441.6 Mb draft assembly consisting of 61 contigs with an N50 contig length of 41.5 Mb, using PacBio HiFi long reads. We predicted 26,577 protein-coding genes, reaching a BUSCO score of 96.5%. To demonstrate the usefulness of the D. radicosa reference genome, we investigated the evolution of Digitaria species and the genetic diversity of Japanese Digitaria plants based on our new reference genome. We also defined the syntenic blocks between D. radicosa and 2 Poaceae crops, fonio and rice, and the diverse distribution of representative resistance genes in D. radicosa. The D. radicosa reference genome presented here should help elucidate the genetic relatedness of Digitaria species and the genetic diversity of Digitaria plants. In addition, the D. radicosa genome will be an important genomic resource for Poaceae genomics and crop breeding.

A chromosome-level genome assembly of Cape hare (Lepus capensis)

The Cape hare (Lepus capensis) is among the most widely distributed hare species globally, inhabiting extensive regions across Africa, the Middle East, and Central Asia. However, evolutionary and genetic research on L. capensis was seriously impeded by the absence of a reference genome. Here, we assembled and constructed a chromosome-level genome of L. capensis (with scaffolds anchored to 25 chromosomes and a total assembled length of 2.9 Gb, achieving a contig N50 length of 124.44 Mb) using PacBio HiFi sequencing and Hi-C assembly technology. Evaluation using BUSCO indicated the genome assembly to be 98.2% complete. The de novo prediction revealed that repetitive sequences constitute 46.13% of the entire genome, and long interspersed nuclear elements (LINEs) constituted the largest portion. We annotated a total of 13, 868 protein-coding genes using transcriptomes from two tissues (muscle and skin). This high-quality reference genome serves as a valuable genomic resource for advancing genetic studies in this species.

Chromosome-level genome assembly and annotation of Clanis bilineata tsingtauica Mell (Lepidoptera: Sphingidae).

The soybean hawkmoth Clanis bilineata tsingtauica Mell (Lepidoptera, Sphingidae; CBT), as one of the main leaf-chewing pests of soybeans, has gained popularity as an edible insect in China recently due to its high nutritional value. However, high-quality genome of CBT remains unclear, which greatly limits further research. In the present study, we assembled a high-quality chromosome-level genome of CBT using PacBio HiFi reads and Hi-C technologies for the first time. The size of the assembled genome is 477.45 Mb with a contig N50 length of 17.43 Mb. After Hi-C scaffolding, the contigs were anchored to 29 chromosomes with a mapping rate of 99.61%. Benchmarking Universal Single-Copy Orthologues (BUSCO) completeness value is 99.49%. The genome contains 252.16 Mb of repeat elements and 14,214 protein-coding genes. In addition, chromosomal synteny analysis showed that the genome of CBT has a strong synteny with that of Manduca sexta. In conclusion, this high-quality genome provides an important resource for future studies of CBT and contributes to the development of integrated pest management strategies.

De novo genome of thick-tailed pygmy jerboa Salpingotus crassicauda, Cardiocraniinae, Dipodidae

Pygmy jerboas are one of the smallest taxa of rodents. They exhibit distinctly different morphological and biological characteristics from other subfamilies, such as more restricted distribution, species richness, reproductive ability, and population size. Agricultural expansion and the development of new energy projects in recent years lead to sharp decline of their natural populations. Here, we assembled and annotated the first reference genome for the subfamily Cardiocraniinae using Illunima and Nanopore sequencing from the thick-tailed pygmy jerboa, Salpingotus crassicauda. The final genome is 2.44 Gb in size, with a contig N50 length of 13.71 Mb and a BUSCO completeness of 96.35%. A total of 23,344 protein-coding genes were annotated in the final genome. We also determined the mitochondrial genome of this species and annotated 13 protein-coding genes, 22 tRNAs, and 2 rRNA. These genomic assemblies provide resources in studying phylogeny and adaptive evolution of Dipodidae, as well as implementing conservation management of jerboas.

Haplotype-resolved genome assembly of the upas tree (Antiaris toxicaria)

The upas tree (Antiaris toxicaria Lesch.) is a medically important plant that contains various specialized metabolites with significant bioactivity. The lack of a reference genome hinders the in-depth study as well as rational exploitation and conservation of this plant. Here, we present the first holotype-resolved chromosome-scale genome of the upas tree. The assembled genome consisted of 26 chromosomes that contain 1.34 Gb of sequencing data with a contig N50 length of 60 Mb. Genome annotation identified 43,500 protein-coding genes in the upas tree genome, of which 98.75% were functionally annotated. This high-quality reference genome will lay the foundation for further studies on the evolution and functional genomics of the upas tree.

Haplotype-resolved genome and mapping of freezing tolerance in the wild potato Solanum commersonii.

Solanum commersonii (2n = 2x = 24, 1EBN, Endosperm Balance Number), native to the southern regions of Brazil, Uruguay, and northeastern Argentina, is the first wild potato germplasm collected by botanists and exhibits a remarkable array of traits related to disease resistance and stress tolerance. In this study, we present a high-quality haplotype-resolved genome of S. commersonii. The two identified haplotypes demonstrate chromosome sizes of 706.48 and 711.55Mb, respectively, with corresponding chromosome anchoring rates of 94.2 and 96.9%. Additionally, the contig N50 lengths are documented at 50.87 and 45.16Mb. The gene annotation outcomes indicate that the haplotypes encompasses a gene count of 39 799 and 40 078, respectively. The genome contiguity, completeness, and accuracy assessments collectively indicate that the current assembly has produced a high-quality genome of S. commersonii. Evolutionary analysis revealed significant positive selection acting on certain disease resistance genes, stress response genes, and environmentally adaptive genes during the evolutionary process of S. commersonii. These genes may be related to the formation of diverse and superior germplasm resources in the wild potato species S. commersonii. Furthermore, we utilized a hybrid population of S. commersonii and S. verrucosum to conduct the mapping of potato freezing tolerance genes. By combining BSA-seq analysis with traditional QTL mapping, we successfully mapped the potato freezing tolerance genes to a specific region on Chr07, spanning 1.25Mb, with a phenotypic contribution rate of 18.81%. In short, current research provides a haplotype-resolved reference genome of the diploid wild potato species S. commersonii and establishes a foundation for further cloning and unraveling the mechanisms underlying cold tolerance in potatoes.

A high-quality genome assembly of the shrubby cinquefoil (Dasiphora fruticosa)

Dasiphora fruticosa (Rosaceae), commonly known as shrubby cinquefoil, is a flowering shrub of high ornamental value yet underutilized in East Asian landscapes. Given its broad elevational distribution range, D. fruticosa serves as an ideal model for studying genetic adaptations and speciation along elevation gradients. Here, we present a high-quality chromosome-scale assembly of D. fruticosa with a genome size of 249.23 Mb and a contig N50 length of 14.01 Mb. The genome sequence contains 32,613 protein-coding genes, of which 30,643 (93.96%) were functionally annotated. Compared to the published D. fruticosa genome sequence, our assembly demonstrates higher completeness and continuity. Furthermore, comparative genomic analyses provide insights into the phylogenetic relationship and high-altitude adaptation of D. fruticosa. Overall, our study offers a valuable genetic resource for both molecular and evolutionary research on shrubby cinquefoil.

Chromosome-level genome assembly and annotation of the Spinibarbus caldwelli

Spinibarbus caldwelli is an important freshwater economic fish in China. Owing to uncontrolled fishing, wild resources of S. caldwelli have decreased rapidly and may be on the verge of extinction. In this study, utilizing single-molecule real-time (SMRT) sequencing technology and chromatin interaction mapping (Hi-C) technologies, we assembled the first chromosome-scale genome for S. caldwelli about 1.77 Gb in size, with a contig N50 length of 11.83 Mb and scaffold N50 length of 33.91 Mb. In total 1.72 Gb (97.01%) of the contig sequences were anchored onto fifty chromosomes with the longest scaffold being 56.20 Mb. Furthermore, proximately 49.41% of the genome was composed of repetitive elements. In total, 49,377 protein-coding genes were predicted, of which 47,724 (96.65%) genes have been functionally annotated. The high-quality chromosome-level reference genome and annotation are vital for supporting basic genetic studies and will be contribute to genetic structure, functional elucidation, evolutionary inquiry, and germplasm conservation for S. caldwelli.

Chromosome-level genome assembly and annotation of Flueggea virosa (Phyllanthaceae)

Flueggea virosa (Roxb. ex Willd.) Royle, an evergreen shrub and small tree in the Phyllanthaceae family, holds significant potential in garden landscaping and pharmacological applications. However, the lack of genomic data has hindered further scientific understanding of its horticultural and medicinal values. In this study, we have assembled a haplotype-resolved genome of F. virosa for the first time. The two haploid genomes, named haplotype A genome and haplotype B genome, are 487.33 Mb and 477.53 Mb in size, respectively, with contig N50 lengths of 31.45 Mb and 32.81 Mb. More than 99% of the assembled sequences were anchored to 13 pairs of pseudo-chromosomes. Furthermore, 21,587 and 21,533 protein-coding genes were predicted in haplotype A and haplotype B genomes, respectively. The availability of this chromosome-level genome fills the gap in genomic data for F. virosa and provides valuable resources for molecular studies of this species, supporting future research on speciation, functional genomics, and comparative genomics within the Phyllanthaceae family.

A chromosome-level genome assembly and evolutionary analysis of Coregonus ussuriensis Berg

Coregonus ussuriensis Berg, distributed widely in cold waters above 45° N latitude, is a savored freshwater whitefish that has been included in the list of endangered animals as a consequence of overfishing. Lack of genomic information seriously hampers evolutionary and genetic research on C. ussuriensis warranting the need to assemble a high-quality reference genome to promote its genetic breeding. We assembled and constructed a reference chromosome-level C. ussuriensis genome (sequence length, 2.51 Gb; contig N50 length, 4.27 Mb) using PacBio sequencing and Hi-C assembly technology, 3,109 contigs were assembled into scaffolds, resulting in a genome assembly with 40 chromosomes and a scaffold N50 length of 62.20 Mb. In addition, 43,320 protein-coding genes were annotated. The peak Ks position in the species comparison reflects the whole-genome replication event of C. ussuriensis. This chromosome-level genome provides reference data for further studies on the molecular breeding of C. ussuriensis.

Whole-genome sequencing of 13 Arctic plants and draft genomes of Oxyria digyna and Cochlearia groenlandica

To understand the genomic characteristics of Arctic plants, we generated 28–44 Gb of short-read sequencing data from 13 Arctic plants collected from the High Arctic Svalbard. We successfully estimated the genome sizes of eight species by using the k-mer-based method (180–894 Mb). Among these plants, the mountain sorrel (Oxyria digyna) and Greenland scurvy grass (Cochlearia groenlandica) had relatively small genome sizes and chromosome numbers. We obtained 45 × and 121 × high-fidelity long-read sequencing data. We assembled their reads into high-quality draft genomes (genome size: 561 and 250 Mb; contig N50 length: 36.9 and 14.8 Mb, respectively), and correspondingly annotated 43,105 and 29,675 genes using ~46 and ~85 million RNA sequencing reads. We identified 765,012 and 88,959 single-nucleotide variants, and 18,082 and 7,698 structural variants (variant size ≥ 50 bp). This study provided high-quality genome assemblies of O. digyna and C. groenlandica, which are valuable resources for the population and molecular genetic studies of these plants.

A near complete genome assembly of the East Friesian sheep genome

Advancements in sequencing have enabled the assembly of numerous sheep genomes, significantly advancing our understanding of the link between genetic variation and phenotypic traits. However, the genome of East Friesian sheep (Ostfriesisches Milchschaf), a key high-yield milk breed, remains to be fully assembled. Here, we constructed a near-complete and gap-free East Friesian genome assembly using PacBio HiFi, ultra-long ONT and Hi-C sequencing. The resulting genome assembly spans approximately 2.96 Gb, with a contig N50 length of 104.1 Mb and only 164 unplaced sequences. Remarkably, our assembly has captured 41 telomeres and 24 centromeres. The assembled sequence is of high quality on completeness (BUSCO score: 97.1%) and correctness (QV: 69.1). In addition, a total of 24,580 protein-coding genes were predicted, of which 97.2% (23,891) carried at least one conserved functional domain. Collectively, this assembly provides not only a near T2T gap-free genome, but also provides a valuable genetic resource for comparative genome studies of sheep and will serve as an important tool for the sheep research community.

Chromosome-level genome assembly of Helwingia omeiensis: the first genome in the family Helwingiaceae

Helwingia, a shrub of the monotypic cosmopolitan family Helwingiaceae, is distinguished by its inflorescence, in which flowers are borne on the midrib of the leaf—a trait not commonly observed in related plant families. Previous studies have investigated the development of this unusual structure using comparative anatomical methods. However, the scarcity of genomic data has hindered our understanding of the origins and evolutionary history of this uncommon trait at the molecular level. Here, we report the first high-quality genome of the family Helwingiaceae. Assembled using HiFi sequencing and Hi-C technologies, the genome of H. omeiensis is anchored to 19 chromosomes, with a total length of 2.75 Gb and a contig N50 length of 6.78 Mb. The BUSCO completeness score of the assembled genome was 98.2%. 53,951 genes were identified, of which 99.7% were annotated in at least one protein database. The high-quality reference genome of H. omeiensis provides an essential genetic resource and sheds light on the phylogeny and evolution of specific traits in the family Helwingiaceae.

Chromosome-level assembly of the synthetic hexaploid wheat-derived cultivar Chuanmai 104

Synthetic hexaploid wheats (SHWs) are effective genetic resources for transferring agronomically important genes from wild relatives to common wheat (Triticum aestivum L.). Dozens of reference-quality pseudomolecule assemblies of hexaploid wheat have been generated, but none is reported for SHW-derived cultivars. Here, we generated a chromosome-scale assembly for the SHW-derived cultivar ‘Chuanmai 104’ based on PacBio HiFi reads and chromosome conformation capture sequencing. The total assembly size was 14.81 Gb with a contig N50 length of 58.25 Mb. A BUSCO analysis yielded a completeness score of 99.30%. In total, repetitive elements comprised 81.36% of the genome and 122,554 high-confidence protein-coding gene models were predicted. In summary, the first chromosome-level assembly for a SHW-derived cultivar presents a promising outlook for the study and utilization of SHWs in wheat improvement, which is essential to meet the global food demand.

An improved genome assembly of Chrysanthemum nankingense reveals expansion and functional diversification of terpene synthase gene family

BackgroundTerpenes are important components of plant aromas, and terpene synthases (TPSs) are the key enzymes driving terpene diversification. In this study, we characterized the volatile terpenes in five different Chrysanthemum nankingense tissues. In addition, genome-wide identification and expression analysis of TPS genes was conducted utilizing an improved chromosome-scale genome assembly and tissue-specific transcriptomes. The biochemical functions of three representative TPSs were also investigated.ResultsWe identified tissue-specific volatile organic compound (VOC) and volatile terpene profiles. The improved Chrysanthemum nankingense genome assembly was high-quality, including a larger assembled size (3.26 Gb) and a better contig N50 length (3.18 Mb) compared to the old version. A total of 140 CnTPS genes were identified, with the majority representing the TPS-a and TPS-b subfamilies. The chromosomal distribution of these TPS genes was uneven, and 26 genes were included in biosynthetic gene clusters. Closely-related Chrysanthemum taxa were also found to contain diverse TPS genes, and the expression profiles of most CnTPSs were tissue-specific. The three investigated CnTPS enzymes exhibited versatile activities, suggesting multifunctionality.ConclusionsWe systematically characterized the structure and diversity of TPS genes across the Chrysanthemum nankingense genome, as well as the potential biochemical functions of representative genes. Our results provide a basis for future studies of terpene biosynthesis in chrysanthemums, as well as for the breeding of improved chrysanthemum varieties.

Haplotype-resolved chromosome-level genome assembly of Ehretia macrophylla

Ehretia macrophylla Wall, known as wild loquat, is an ecologically, economically, and medicinally significant tree species widely grown in China, Japan, Vietnam, and Nepal. In this study, we have successfully generated a haplotype-resolved chromosome-scale genome assembly of E. macrophylla by integrating PacBio HiFi long-reads, Illumina short-reads, and Hi-C data. The genome assembly consists of two haplotypes, with sizes of 1.82 Gb and 1.58 Gb respectively, and contig N50 lengths of 28.11 Mb and 21.57 Mb correspondingly. Additionally, 99.41% of the assembly was successfully anchored into 40 pseudo-chromosomes. We predicted 58,886 protein-coding genes, of which 99.60% were functionally annotated from databases. We furthermore detected 2.65 Gb repeat sequences, 659,290 rRNAs, 4,931 tRNAs and 4,688 other ncRNAs. The high-quality assembly of the genome offers a solid basis for furthering the fields of molecular breeding and functional genomics of E. macrophylla.