A high-quality chromosome-scale genome assembly of the Swiss L. multiflorum ecotype Tremona is presented and ParaLies, a post-assembly tool that identifies and removes artefactual duplications based on sequence divergence while preserving true paralogous gene copies, is developed.
Abstract
Italian ryegrass (Lolium multiflorum) is a key temperate forage species underpinning livestock production in Europe. Genomic resources remain limited by its large (2.2 Gb), repetitive, and highly heterozygous genome. Here, we present a high-quality chromosome-scale genome assembly of the Swiss L. multiflorum ecotype Tremona, collected in 2008 in Ticino, Switzerland, and subsequently incorporated into recurrent breeding cycles in the Swiss breeding program. To address systematic assembly artefacts caused by unresolved haplotypes in our initial PacBio HiFi assembly, we developed ParaLies, a post-assembly tool that identifies and removes artefactual duplications based on sequence divergence while preserving true paralogous gene copies. ParaLies reduced the duplicated BUSCO rate from 16.91% to 6.72% without loss of bona fide genomic content. The resulting assembly has a contig N50 of 15.69 Mb and captures 94% of the expected 2.2-Gb genome size. We further analyzed whole-genome resequencing data from Tremona, additional Swiss ecotypes, and publicly available North American germplasm. Tremona was genetically homogeneous, with no evidence of pronounced recent bottlenecks or substantial within-population structure, and was genetically distinct from the other Swiss ecotypes analyzed. Together, the Tremona genome and ParaLies provide valuable resources for L. multiflorum genomics and breeding and demonstrate a scalable approach for reducing haplotype-induced redundancy in highly heterozygous genomes.
Conifers, which comprise nearly two-thirds of extant gymnosperm species, are ecologically and economically important but remain genomically understudied because of their exceptionally large, repeat-rich genomes. Here, we report a chromosome-level assembly of the haploid genome of Cupressus sempervirens generated using PacBio HiFi reads and scaffolded with optical and genetic maps. The 10 Gb assembly shows exceptional contiguity for a conifer genome (contig N50 = 29.8 Mb) and was organized into 11 pseudomolecules. Iso-Seq-supported annotation identified 42,980 protein-coding genes. Repetitive elements account for over 80% of the genome, with LTR retrotransposons alone representing 52.5%. Transposable elements (TE) are pervasive in both intergenic and genic regions and have a major impact on gene architecture: TE insertions within introns generate ultra-long introns, often exceeding 100 kb, and drive gene size expansion. Analyses of LTR retrotransposon dynamics indicate that genome enlargement in C. sempervirens was driven not by recent transpositional bursts, but by the long-term accumulation and incomplete removal of ancient LTR retrotransposons. Consistent with this pattern, paleogenomic reconstruction across representative gymnosperms found no evidence of whole-genome duplication in the Cupressus lineage. This reference genome provides a valuable resource for studying conifer genome evolution, gene structure, and traits of agronomic and ecological interest, including cypress pollinosis.
Cravero Charlotte, L. Isabelle, Choisne Nathalie et al.· bioRxiv· 0 citations
Bitterlings (Acheilognathidae) exhibit a unique reproductive strategy characterized by symbiotic embryonic development inside the gill cavities of freshwater unionid mussels. Despite extensive ecological and physiological research on this system, genomic resources for bitterlings have remained limited, hindering comparative and evolutionary studies. Here, we present a high-quality, chromosome-level genome assembly for Rhodeus sinensis, a widely distributed bitterling species in the Korean Peninsula. By combining PacBio Continuous Long Read (CLR) sequencing, Illumina short reads, and Hi-C scaffolding, we generated a 0.77 Gb genome assembly with a scaffold N50 of 30.06 Mb. The final assembly comprises 24 chromosome-scale scaffolds, accounting for 98.3% of the assembled genome, with a BUSCO completeness score of 96.3% against the Actinopterygii_odb10. Comparative genomic analyses identified prominent expansions in gene families associated with alcohol metabolism, lipid catabolism, and oxidative stress responses. These genomic signatures of metabolic rewiring suggest a potential fuel flexibility, which may serve as a critical adaptive mechanism to mitigate the severe hypoxic stress encountered within the host mussel's gill environment. Ultimately, our chromosome-level genome assembly and findings provide a robust genomic foundation, contributing to a deeper understanding of the extreme physiological adaptations and unique life-history evolution within the Acheilognathidae.
Rawon Jeong, Jeonghun Kim, Young-Suk Ho· G3· 0 citations
The European leaf-toed gecko (Euleptes europaea) is a small, nocturnal gecko endemic to the western Mediterranean. As a phylogenetically distinctive member of the Gondwanan family Sphaerodactylidae, it represents an important species for studying Mediterranean island biogeography, adaptation, and reptile genome evolution. The species also occupies a key position for investigating the evolution of sex chromosomes, as geckos exhibit remarkable diversity and frequent transitions in sex-determination systems. We present a chromosome-level genome assembly of Euleptes europaea generated as part of the Vertebrate Genomes Project. The 1.8 Gb assembly has a scaffold N50 of 102.3 Mb (contig N50 27 Mb), with 21 chromosome-scale scaffolds corresponding to the known karyotype (2n = 42). The primary assembly has a BUSCO completeness of 97.80% (95.60% as single-copy), a k-mer completeness of 96.00%, and a k-mer quality value (QV) of 61.20. Repetitive elements account for 53.20% of the genome and genome annotation identified 18,633 protein-coding genes. This high-quality reference genome will facilitate studies of genome evolution, island adaptation, and sex chromosome evolution across geckos and other reptiles.
J. Paris, L. Abueg, S. Pelan et al.· bioRxiv· 0 citations
An improved rye genome assembly is presented and unique retrotransposon organizations within its centromeres are uncovered, revealing RLG_Abia and RLG_Abigail as abundant, recently active elements, unlike in wheat.
Erwang Chen, Carlotta Marie Wehrkamp, Srijan Jhingan et al.· Nature Communications· 0 citations
The Malabar red snapper (Lutjanus malabaricus) is a high-value marine food fish of growing economic and aquaculture importance across the Indo-Pacific. Despite its significance, genomic resources for this species have remained scarce, hindering the application of genomic tools for selective breeding. Here, we present the first chromosome-level genome assemblies and full-length transcriptome of L. malabaricus. Using PacBio HiFi long-read sequencing and Hi-C scaffolding, we generated high-quality assemblies for unsexed, male, and female individuals, each approximately 1.0 Gb in size and anchored to 24 chromosomes. The assemblies exhibited exceptional contiguity (N50 ≈ 42 Mb) and completeness (BUSCO > 99%), with karyotyping confirming 2n = 48 telocentric chromosomes. Genome annotation identified ~25,000 protein-coding genes, and repeat sequences accounted for almost half of the genome, comparable to other reef-associated teleosts. Comparative analyses of the male and female assemblies revealed strong chromosomal synteny and localized sex-associated regions, suggesting a polygenic or complex mechanism of sex determination. The accompanying multi-tissue full-length transcriptome supports functional and developmental studies. Together, these genomic and transcriptomic datasets provide a comprehensive molecular foundation for population genetics, comparative genomics, and selective breeding in L. malabaricus.
Shubha Vij, V. Nguyen, Kathiresan Purushothaman et al.· Scientific Data· 0 citations
Background/Objectives: The long-spined sea urchin Diadema antillarum is a keystone herbivore whose grazing maintains Caribbean coral reefs; basin-wide mass mortalities in 1983–1984 and 2022 have made genomic resources a conservation priority, yet no nuclear genome existed for the species. We aimed to generate the first nuclear reference and to resolve the high heterozygosity that complicates genome assembly in broadcast-spawning marine invertebrates. Methods: For the assembly, we combined PacBio HiFi, Oxford Nanopore, and Illumina sequencing. Genome size and heterozygosity were estimated by k-mer profiling. We compared standard and haplotype-aware assembly strategies (hifiasm), evaluated completeness with BUSCO, and annotated repeats using a species-specific RepeatModeler library. Results: k-mer profiling estimated a haploid genome of ~703 Mb with 2.52% heterozygosity. Standard assembly then produced an inflated 1.75 Gb assembly (98.4% BUSCO-complete but 84.4% duplicated), indicating retention of both haplotypes. Haplotype-aware reassembly separated this into a collapsed primary assembly (1.03 Gb) and two phased haplotypes (0.95 and 0.89 Gb), each comparable in size to the chromosome-level congener D. antillarum (886 Mb). BUSCO completeness reached 99.0%, with single-copy orthologs rising to 85–90%, and reference-free consensus quality reached QV 44.5 (Merqury; initial assembly). This genome is repeat-rich (42.84% repetitive; 29.96% unclassified). Conclusions: We provide the collapsed primary assembly together with both phased haplotypes as a haplotype-resolved reference for D. antillarum, establishing a foundation for immunogenomic, comparative, and population-genetic studies and for monitoring and restoration of this ecologically critical species. More broadly, the study shows that haplotype-aware assembly is essential for resolving such highly heterozygous genomes and delivers the genomic foundation needed to guide the conservation of this keystone Caribbean reef species.
Audrey J. Majeske, Juliet M. Wong, Carlos A. Farkas Pool et al.· Genes· 0 citations
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