Gene Family Contractions Research Articles

Chromosome-level genome provides insights into evolution and diving adaptability in the vulnerable common pochard (Aythya ferina)

The common pochard (Aythya ferina) is a freshwater diving duck found in the Palearctic region that has been classified as vulnerable by the IUCN due to continuous and rapid population declines across their distribution. To gain a better understanding of its genetic mechanism of adaptive evolution, we successfully sequenced and assembled the first high-quality chromosome-level genome of A. ferina using Illumina, Nanopore and Hi-C sequencing technologies. A total assembly length of 1,130.78 Mbp was obtained, with over 98.81% (1,117.37Mbp) of sequence anchored to 35 pseudo-chromosomes. We predicted 17,232 protein-coding genes, 95.9% of which were functionally annotated. We identified 339 expanded and 937 contracted gene families in the genome of A. ferina, and detected 95 genes that have been positively selected. The significantly enriched Gene Ontology and enriched pathways were related to energy metabolism, immune, nervous, and sensory systems, suggests that these factors likely played an important role in its evolution. Importantly, we recovered signatures of positive selection on genes related to vasoconstriction that may be associated with thermoregulatory adaptations of A. ferina for underwater diving. Overall, the high-quality genome assembly and annotation in this study provides valuable genomic resources for ecological and evolutionary studies, as well as toward the conservation of A. ferina.

Annotation and Characterization of the Zacco platypus Genome

The pale chub Zacco platypus (Cypriniformes; Xenocyprididae; Jordan & Evermann, 1902) is widely distributed across freshwater ecosystems in East Asia and has been recognized as a potential model fish species for ecotoxicology and environmental monitoring. Here, a high-quality de novo genome assembly of Z. platypus was constructed through the integration of a combination of long-read Pacific Bioscience (PacBio) sequencing, short-read Illumina sequencing, and Hi-C sequencing technologies. Z. platypus has the smallest genome size compared to other species belonging to the order Cypriniformes. The assembled genome encompasses 41.45% repeat sequences. As shown in other fish, a positive correlation was observed between genome size and the composition of transposable elements (TE) in the genome. Among TEs, a relatively higher rate of DNA transposon was observed, which is a common pattern in the members of the order Cypriniformes. Functional annotation was processed using four representative databases, identifying a core set of 12,907 genes shared among them. Orthologous gene family analysis revealed that Z. platypus has experienced more gene family contraction rather than expansion compared to other Cypriniformes species. Among the uniquely expanded gene families in Z. platypus, detoxification and stress-related gene families were identified, suggesting that this species could represent a promising model for ecotoxicology and environmental monitoring. Taken together, the Z. platypus genome assembly will provide valuable data for omics-based health assessments in aquatic ecosystems, offering further insights into the environmental and ecological facets within this species.

Sexual size dimorphism in mammals is associated with changes in the size of gene families related to brain development

In mammals, sexual size dimorphism often reflects the intensity of sexual selection, yet its connection to genomic evolution remains unexplored. Gene family size evolution can reflect shifts in the relative importance of different molecular functions. Here, we investigate the associate between brain development gene repertoire to sexual size dimorphism using 124 mammalian species. We reveal significant changes in gene family size associations with sexual size dimorphism. High levels of dimorphism correlate with an expansion of gene families enriched in olfactory sensory perception and a contraction of gene families associated with brain development functions, many of which exhibited particularly high expression in the human adult brain. These findings suggest a relationship between intense sexual selection and alterations in gene family size. These insights illustrate the complex interplay between sexual dimorphism, gene family size evolution, and their roles in mammalian brain development and function, offering a valuable understanding of mammalian genome evolution.

Chromosome-level genome sequencing and multi-omics of the Hungarian White Goose (Anser anser domesticus) reveals novel miRNA-mRNA regulation mechanism of waterfowl feather follicle development

The Hungarian White Goose (Anser anser domesticus) is an excellent European goose breed, with high feather and meat production. Despite its importance in the poultry industry, no available genome assembly information has been published. This study aimed to present Chromosome-level and functional genome sequencing of the Hungarian White Goose. The results showed that the genome assembly has a total length of 1115.82 Mb, 39 pairs of chromosomes, 92.98% of the BUSCO index, and contig N50 and scaffold N50 were up to 2.32 Mb and 60.69 Mb, respectively. Annotation of the genome assembly revealed 19550 genes, 286 miRNAs, etc. We identified 235 expanded and 1,167 contracted gene families in this breed compared with the other 16 species. We performed a positive selection analysis between this breed and four species of Anatidae to uncover the genetic information underlying feather follicle development. Further, we detected the function of miR-199-x, miR-143-y, and miR-23-z on goose embryonic skin fibroblast. In summary, we have successfully generated a highly complete genome sequence of the Hungarian white goose, which will provide a great resource to improve our understanding of gene functions and enhance the studies on feather follicle development at the genomic level.

Chromosome-level genome assembly of the freshwater mussel Sinosolenaia oleivora (Heude, 1877)

Sinosolenaia oleivora (Bivalve, Unionida, Unionidae), is a near-endangered edible mussel. In 2022, it was selected by the Ministry of Agriculture and Rural Affairs as a top-ten aquatic germplasm resource, with potential for industrial development. Using Illumina, PacBio, and Hi-C technology, a high-quality chromosome-level genome of S. oleivora was assembled. The assembled S. oleivora genome spanned 2052.29 Mb with a contig N50 size of 20.36 Mb and a scaffold N50 size of 103.57 Mb. The 302 contigs, accounting for 98.41% of the total assembled genome, were anchored into 19 chromosomes using Hi-C scaffolding. A total of 1171.78 Mb repeat sequences were annotated and 22,971 protein-coding genes were predicted. Compared with the nearest ancestor, a total of 603 expanded and 1767 contracted gene families were found. This study provides important genomic resources for conservation, evolutionary research, and genetic improvements of many economic traits like growth performance.

Chromosome-Level Genome Assembly of Apoderus dimidiatus Voss (Coleoptera: Attelabidae): Insights into Evolution and Behavior.

Attelabidae insects have attracted much attention due to their unique leaf rolling behavior before oviposition. However, the lack of genomic data makes it difficult to understand the molecular mechanism behind their behavior and their evolutionary relationship with other species. To address this gap, we utilized Illumina and Nanopore sequencing platforms along with Hi-C technology to establish a highly accurate whole genome of A. dimidiatus at the chromosome level. The resulting genome size was determined to be 619.26 Mb, with a contig N50 of 50.89 Mb and GC content of 33.89%. Moreover, a total of 12,572 genes were identified, with 82.59% being functionally annotated, and 64.78% designated as repeat sequences. Our subsequent phylogenetic tree analysis revealed that Attelabidae's divergence from Curculionidae occurred approximately 161.52 million years ago. Furthermore, the genome of A. dimidiatus contained 334 expanded gene families and 1718 contracted gene families. In addition, using Phylogenetic Analysis by Maximum Likelihood (PAML), we identified 106 rapidly evolved genes exhibiting significant signals and 540 positively selected genes. Our research endeavors to serve as an invaluable genomic data resource for the study of Attelabidae, offering fresh perspectives for the exploration of its leaf rolling behavior.

Unique trajectory of gene family evolution from genomic analysis of nearly all known species in an ancient yeast lineage.

Gene gains and losses are a major driver of genome evolution; their precise characterization can provide insights into the origin and diversification of major lineages. Here, we examined gene family evolution of 1,154 genomes from nearly all known species in the medically and technologically important yeast subphylum Saccharomycotina. We found that yeast gene family and genome evolution are distinct from plants, animals, and filamentous ascomycetes and are characterized by small genome sizes and smaller gene numbers but larger gene family sizes. Faster-evolving lineages (FELs) in yeasts experienced significantly higher rates of gene losses-commensurate with a narrowing of metabolic niche breadth-but higher speciation rates than their slower-evolving sister lineages (SELs). Gene families most often lost are those involved in mRNA splicing, carbohydrate metabolism, and cell division and are likely associated with intron loss, metabolic breadth, and non-canonical cell cycle processes. Our results highlight the significant role of gene family contractions in the evolution of yeast metabolism, genome function, and speciation, and suggest that gene family evolutionary trajectories have differed markedly across major eukaryotic lineages.

Genome assembly of Melilotus officinalis provides a new reference genome for functional genomics

BackgroundSweet yellow clover (Melilotus officinalis) is a diploid plant (2n = 16) that is native to Europe. It is an excellent legume forage. It can both fix nitrogen and serve as a medicine. A genome assembly of Melilotus officinalis that was collected from Best corporation in Beijing is available based on Nanopore sequencing. The genome of Melilotus officinalis was sequenced, assembled, and annotated.ResultsThe latest PacBio third generation HiFi assembly and sequencing strategies were used to produce a Melilotus officinalis genome assembly size of 1,066 Mbp, contig N50 = 5 Mbp, scaffold N50 = 130 Mbp, and complete benchmarking universal single-copy orthologs (BUSCOs) = 96.4%. This annotation produced 47,873 high-confidence gene models, which will substantially aid in our research on molecular breeding. A collinear analysis showed that Melilotus officinalis and Medicago truncatula shared conserved synteny. The expansion and contraction of gene families showed that Melilotus officinalis expanded by 565 gene families and shrank by 56 gene families. The contacted gene families were associated with response to stimulus, nucleotide binding, and small molecule binding. Thus, it is related to a family of genes associated with peptidase activity, which could lead to better stress tolerance in plants.ConclusionsIn this study, the latest PacBio technology was used to assemble and sequence the genome of the Melilotus officinalis and annotate its protein-coding genes. These results will expand the genomic resources available for Melilotus officinalis and should assist in subsequent research on sweet yellow clover plants.

Whole-Genome Sequencing Analyses Reveal the Evolution Mechanisms of Typical Biological Features of Decapterus maruadsi.

Decapterus maruadsi is a typical representative of small pelagic fish characterized by fast growth rate, small body size, and high fecundity. It is a high-quality marine commercial fish with high nutritional value. However, the underlying genetics and genomics research focused on D. maruadsi is not comprehensive. Herein, a high-quality chromosome-level genome of a male D. maruadsi was assembled. The assembled genome length was 716.13 Mb with contig N50 of 19.70 Mb. Notably, we successfully anchored 95.73% contig sequences into 23 chromosomes with a total length of 685.54 Mb and a scaffold N50 of 30.77 Mb. A total of 22,716 protein-coding genes, 274.90 Mb repeat sequences, and 10,060 ncRNAs were predicted, among which 22,037 (97%) genes were successfully functionally annotated. The comparative genome analysis identified 459 unique, 73 expanded, and 52 contracted gene families. Moreover, 2804 genes were identified as candidates for positive selection, of which some that were related to the growth and development of bone, muscle, cardioid, and ovaries, such as some members of the TGF-β superfamily, were likely involved in the evolution of typical biological features in D. maruadsi. The study provides an accurate and complete chromosome-level reference genome for further genetic conservation, genomic-assisted breeding, and adaptive evolution research for D. maruadsi.

Chromosome-level genome provides insights into environmental adaptability and innate immunity in the common dolphin (Delphinus delphis)

The common dolphin (Delphinus delphis) is widely distributed worldwide and well adapted to various habitats. Animal genomes store clues about their pasts, and can reveal the genes underlying their evolutionary success. Here, we report the first high-quality chromosome-level genome of D. delphis. The assembled genome size was 2.56 Gb with a contig N50 of 63.85 Mb. Phylogenetically, D. delphis was close to Tursiops truncatus and T. aduncus. The genome of D. delphis exhibited 428 expanded and 1,885 contracted gene families, and 120 genes were identified as positively selected. The expansion of the HSP70 gene family suggested that D. delphis has a powerful system for buffering stress, which might be associated with its broad adaptability, longevity, and detoxification capacity. The expanded IFN-α and IFN-ω gene families, as well as the positively selected genes encoding tripartite motif-containing protein 25, peptidyl-prolyl cis-trans isomerase NIMA-interacting 1, and p38 MAP kinase, were all involved in pathways for antiviral, anti-inflammatory, and antineoplastic mechanisms. The genome data also revealed dramatic fluctuations in the effective population size during the Pleistocene. Overall, the high-quality genome assembly and annotation represent significant molecular resources for ecological and evolutionary studies of Delphinus and help support their sustainable treatment and conservation.

Chromosome-level genome assembly of Oncomelania hupensis: the intermediate snail host of Schistosoma japonicum

BackgroundSchistosoma japonicum is a parasitic flatworm that causes human schistosomiasis, which is a significant cause of morbidity in China, the Philippines and Indonesia. Oncomelania hupensis (Gastropoda: Pomatiopsidae) is the unique intermediate host of S. japonicum. A complete genome sequence of O. hupensis will enable the fundamental understanding of snail biology as well as its co-evolution with the S. japonicum parasite. Assembling a high-quality reference genome of O. hupehensis will provide data for further research on the snail biology and controlling the spread of S. japonicum.MethodsThe draft genome was de novo assembly using the long-read sequencing technology (PacBio Sequel II) and corrected with Illumina sequencing data. Then, using Hi-C sequencing data, the genome was assembled at the chromosomal level. CAFE was used to do analysis of contraction and expansion of the gene family and CodeML module in PAML was used for positive selection analysis in protein coding sequences.ResultsA total length of 1.46 Gb high-quality O. hupensis genome with 17 unique full-length chromosomes (2n = 34) of the individual including a contig N50 of 1.35 Mb and a scaffold N50 of 75.08 Mb. Additionally, 95.03% of these contig sequences were anchored in 17 chromosomes. After scanning the assembled genome, a total of 30,604 protein-coding genes were predicted. Among them, 86.67% were functionally annotated. Further phylogenetic analysis revealed that O. hupensis was separated from a common ancestor of Pomacea canaliculata and Bellamya purificata approximately 170 million years ago. Comparing the genome of O. hupensis with its most recent common ancestor, it showed 266 significantly expanded and 58 significantly contracted gene families (P < 0.05). Functional enrichment of the expanded gene families indicated that they were mainly involved with intracellular, DNA-mediated transposition, DNA integration and transposase activity.ConclusionsIntegrated use of multiple sequencing technologies, we have successfully constructed the genome at the chromosomal-level of O. hupensis. These data will not only provide the compressive genomic information, but also benefit future work on population genetics of this snail as well as evolutional studies between S. japonicum and the snail host.Graphical

An Antarctic lichen isolate (Cladonia borealis) genome reveals potential adaptation to extreme environments

Cladonia borealis is a lichen that inhabits Antarctica’s harsh environment. We sequenced the whole genome of a C. borealis culture isolated from a specimen collected in Antarctica using long-read sequencing technology to identify specific genetic elements related to its potential environmental adaptation. The final genome assembly produced 48 scaffolds, the longest being 2.2 Mbp, a 1.6 Mbp N50 contig length, and a 36 Mbp total length. A total of 10,749 protein-coding genes were annotated, containing 33 biosynthetic gene clusters and 102 carbohydrate-active enzymes. A comparative genomics analysis was conducted on six Cladonia species, and the genome of C. borealis exhibited 45 expanded and 50 contracted gene families. We identified that C. borealis has more Copia transposable elements and expanded transporters (ABC transporters and magnesium transporters) compared to other Cladonia species. Our results suggest that these differences contribute to C. borealis’ remarkable adaptability in the Antarctic environment. This study also provides a useful resource for the genomic analysis of lichens and genetic insights into the survival of species isolated from Antarctica.

The reference genome sequence of Artemisia argyi provides insights into secondary metabolism biosynthesis.

Artemisia argyi, a perennial herb of the genus Artemisia in the family Asteraceae, holds significant importance in Chinese traditional medicine, referred to as "Aicao". Here, we report a high-quality reference genome of Artemisia argyi L. cv. beiai, with a genome size up to 4.15 Gb and a contig N50 of 508.96 Kb, produced with third-generation Nanopore sequencing technology. We predicted 147,248 protein-coding genes, with approximately 68.86% of the assembled sequences comprising repetitive elements, primarily long terminal repeat retrotransposons(LTRs). Comparative genomics analysis shows that A. argyi has the highest number of specific gene families with 5121, and much more families with four or more members than the other 6 plant species, which is consistent with its more expanded gene families and fewer contracted gene families. Furthermore, through transcriptome sequencing of A. argyi in response to exogenous MeJA treatment, we have elucidated acquired regulatory insights into MeJA's impact on the phenylpropanoid, flavonoid, and terpenoid biosynthesis pathways of A. argyi. The whole-genome information obtained in this study serves as a valuable resource for delving deeper into the cultivation and molecular breeding of A. argyi. Moreover, it holds promise for enhancing genome assemblies across other members of the Asteraceae family. The identification of key genes establishes a solid groundwork for developing new varieties of Artemisia with elevated concentrations of active compounds.

The first chromosome-level genome assembly and transcriptome sequencing provide insights into cantharidin production of the blister beetles.

Blister beetles (Coleoptera: Meloidae) produce a natural defensive toxin cantharidin (CTD), which has been used for various cancer treatments and other diseases. Currently, the lack of chromosome-level reference genomes in Meloidae limits further understanding of the mechanism of CTD biosynthesis and environmental adaptation. In this study, the chromosome-level genome assembly of Mylabris phalerata was generated based on PacBio and Hi-C sequencing. This reference genome was about 136.68 Mb in size with contig N50 of 9.17 Mb and composed of 12 chromosomes. In comparison to six other Coleoptera insects, M. phalerata exhibited multiple expanded gene families enriched in juvenile hormone (JH) biosynthetic process pathway, farnesol dehydrogenase activity, and cytochrome P450, which may be related to CTD biosynthesis. Consistently, the transcriptomic analysis suggested the "terpenoid backbone biosynthesis" pathway and "the juvenile hormone" as putative core pathways of CTD biosynthesis and presented eight up-regulated differential expression genes in male adults as candidate genes. It is possible that the restricted feeding niche and lifestyle of M. phalerata were the cause of the gene family's contraction of odorant binding proteins. The ABC transporters (ABCs) related to exporting bound toxins out of the cell and the resistance to the self-secreted toxins (e.g. CTD) were also contracted, possibly due to other self-protection strategies in M. phalerata. A foundation of understanding CTD biosynthesis and environmental adaptation of blister beetles will be established by our reference genome and discoveries.

Comparative transcriptomics reveals divergence in pathogen response gene families amongst 20 forest tree species.

Forest trees provide critical ecosystem services for humanity that are under threat due to ongoing global change. Measuring and characterizing genetic diversity are key to understanding adaptive potential and developing strategies to mitigate negative consequences arising from climate change. In the area of forest genetic diversity, genetic divergence caused by large-scale changes at the chromosomal level has been largely understudied. In this study, we used the RNA-seq data of 20 co-occurring forest trees species from genera including Acer, Alnus, Amelanchier, Betula, Cornus, Corylus, Dirca, Fraxinus, Ostrya, Populus, Prunus, Quercus, Ribes, Tilia, and Ulmus sampled from Upper Peninsula of Michigan. These data were used to infer the origin and maintenance of gene family variation, species divergence time, as well as gene family expansion and contraction. We identified a signal of common whole genome duplication events shared by core eudicots. We also found rapid evolution, namely fast expansion or fast contraction of gene families, in plant-pathogen interaction genes amongst the studied diploid species. Finally, the results lay the foundation for further research on the genetic diversity and adaptive capacity of forest trees, which will inform forest management and conservation policies.

2-Furoic acid associated with the infection of nematodes by Dactylellina haptotyla and its biocontrol potential on plant root-knot nematodes.

Dactylellina haptotyla is a typical nematode-trapping fungus that has garnered the attention of many scholars for its highly effective lethal potential for nematodes. Secondary metabolites play an important role in D. haptotyla-nematode interactions, but which metabolites perform which function remains unclear. We report the metabolic functions based on high-quality, chromosome-level genome assembly of wild D. haptotyla YMF1.03409. The results indicate that a large variety of secondary metabolites and their biosynthetic genes were significantly upregulated during the nematode-trapping stage. In parallel, we identified that 2-furoic acid was specifically produced during nematode trapping by D. haptotyla YMF1.03409 and isolated it from fermentation production. 2-Furoic acid demonstrated strong nematicidal activity with an LD50 value of 55.05 µg/mL against Meloidogyne incognita at 48 h. Furthermore, the pot experiment showed that the number of galls of tomato root was significantly reduced in the experimental group treated with 2-furoic acid. The considerable increase in the 2-furoic acid content during the infection process and its virulent nematicidal activity revealed an essential synergistic effect during the process of nematode-trapping fungal infection. IMPORTANCE Dactylellina haptotyla have significant application potential in nematode biocontrol. In this study, we determined the chromosome-level genome sequence of D. haptotyla YMF1.03409 by long-read sequencing technology. Comparative genomic analysis identified a series of pathogenesis-related genes and revealed significant gene family contraction events during the evolution of D. haptotyla YMF1.03409. Combining transcriptomic and metabolomic data as well as in vitro activity test results, a compound with important application potential in nematode biocontrol, 2-furoic acid, was identified. Our result expanded the genetic resource of D. haptotyla and identified a previously unreported nematicidal small molecule, which provides new options for the development of plant biocontrol agents.

A telomere-to-telomere reference genome provides genetic insight into the pentacyclic triterpenoid biosynthesis in Chaenomeles speciosa.

Chaenomeles speciosa (2n = 34), a medicinal and edible plant in the Rosaceae, is commonly used in traditional Chinese medicine. To date, the lack of genomic sequence and genetic studies has impeded efforts to improve its medicinal value. Herein, we report the use of an integrative approach involving PacBio HiFi (third-generation) sequencing and Hi-C scaffolding to assemble a high-quality telomere-to-telomere genome of C. speciosa. The genome comprised 650.4Mb with a contig N50 of 35.5Mb. Of these, 632.3Mb were anchored to 17 pseudo-chromosomes, in which 12, 4, and 1 pseudo-chromosomes were represented by a single contig, two contigs, and four contigs, respectively. Eleven pseudo-chromosomes had telomere repeats at both ends, and four had telomere repeats at a single end. Repetitive sequences accounted for 49.5% of the genome, while a total of 45 515 protein-coding genes have been annotated. The genome size of C. speciosa was relatively similar to that of Malus domestica. Expanded or contracted gene families were identified and investigated for their association with different plant metabolisms or biological processes. In particular, functional annotation characterized gene families that were associated with the biosynthetic pathway of oleanolic and ursolic acids, two abundant pentacyclic triterpenoids in the fruits of C. speciosa. Taken together, this telomere-to-telomere and chromosome-level genome of C. speciosa not only provides a valuable resource to enhance understanding of the biosynthesis of medicinal compounds in tissues, but also promotes understanding of the evolution of the Rosaceae.

Two major duplication events shaped the transcription factor repertoires in Solanaceae species

Solanaceae is a significant plant family widely dispersed in the world, and most of them are important vegetable resources. Transcription factors (TFs) play critical roles in regulating plant growth and various stresses. However, there was no comprehensive and systematic analysis of TFs in all released Solanaceae genomes. In this study, 51,169 TFs were identified and systematically analyzed from 18 Solanaceae and 10 non-Solanaceae species. In some Solanaceae species, whole-genome duplication/triplication (WGD/T) and tandem duplication (TD) were the main duplicated types leading to the TF expansion. We further divided all TF families into 1,209 orthogroups (OGs), of which 298 were unique to Solanaceae. Despite all Solanaceae species shared the recent WGT event, 10 species had more gene family contractions than expansions among the 18 Solanaceae species. Functional enrichment analysis showed that 6 gene families (AP2, ARF, ARR-B, BBB-BPC, NF-YB, and NF-YC) showed different contraction and expansion trends in Solanaceae species, indicating that these Solanaceae species have different selection requirements for these gene families during evolution. In conclusion, our study provides an understanding between the evolution of the TFs family and the gene duplications of other plants. Meanwhile, this study also provides rich genetic resources for gene function research and molecular breeding of Solanaceae in the future.

Comparative analyses reveal potential genetic mechanisms for high-altitude adaptation of Schizopygopsis fishes based on chromosome-level genomes.

The schizothoracine fishes, widely distributed in the Qinghai-Tibetan Plateau and its adjacent areas, are considered as ideal models for investigation of high-altitude adaptation. Schizophygopsis are one group of the highly specialized schizothoracine fishes, and the genetic basis for their high-altitude adaptation is poorly understood. In this study, we performed comparative genomics analyses to investigate the potential genetic mechanisms for high-altitude adaptation of Schizopygopsis malacanthus and Schizopygopsis pylzovi based on the chromosome-level genomes. Functional enrichment analysis revealed that many expanded gene families in Schizopygopsis were associated with immune response while many contracted gene families were functionally associated with olfaction. Among the 123 positively selected genes (PSGs), angpt2a was detected in HIF-1 signaling pathway and possibly related to the hypoxia adaptation of Schizopygopsis. Furthermore, two PSGs cox15 and ndufb10 were distributed in thermogenesis, and there was a Schizopygopsis-specific missense mutation in cox15 (Gln115Glu), which possibly contributed to the cold temperature adaptation of the Schizopygopsis. Kyoto Encyclopedia of Genes and Genomes enrichment of the PSGs revealed three significant pathways including metabolic pathways, cell cycle, and homologous recombination and Gene Ontology enrichment analysis of the PSGs revealed several categories associated with DNA repair, cellular response to DNA damage stimulus, and metabolic process. Chromosome-scale characterization of olfactory receptor (OR) repertoires indicated that Schizopygopsis had the least number of OR genes, and the OR gene contraction was possibly caused by the limited food variety and the environmental factors such as lower air pressure, lower humidity, and lower temperature. Our study will help expand our understanding of the potential adaptive mechanism of Schizopygopsis to cope with the high-altitude conditions.

A High-Quality Chromosome-Level Genome Assembly of a Snail Cipangopaludina cathayensis (Gastropoda: Viviparidae).

Cipangopaludina cathayensis (Gastropoda: Prosobranchia; Mesogastropoda; Viviparidae) is widely distributed in the freshwater habitats of China. It is an economically important snail with high edible and medicinal value. However, the genomic resources and the reference genome of this snail are lacking. In this study, we assembled the first chromosome-level genome of C. cathayensis. The preliminary assembly genome was 1.48 Gb in size, with a contig N50 size of 93.49 Mb. The assembled sequences were anchored to nine pseudochromosomes using Hi-C data. The final genome after Hi-C correction was 1.48 Gb, with a contig N50 of 98.49 Mb and scaffold N50 of 195.21 Mb. The anchored rate of the chromosome was 99.99%. A total of 22,702 protein-coding genes were predicted. Phylogenetic analyses indicated that C. cathayensis diverged with Bellamya purificata approximately 158.10 million years ago. There were 268 expanded and 505 contracted gene families in C. cathayensis when compared with its most recent common ancestor. Five putative genes under positive selection in C. cathayensis were identified (false discovery rate <0.05). These genome data provide a valuable resource for evolutionary studies of the family Viviparidae, and for the genetic improvement of C. cathayensis.