Genome Biology and Evolution最新文献

The Antarctic springtail Cryptopygus antarcticus Willem (family Isotomidae) is a representative arthropod species of the maritime Antarctic environment that could be used as an important organism for further study of animal evolution and adaptation. Despite the biological and ecological peculiarities that distinguish them from the majority of collembolan species, our understanding of the genetic background behind their success in an extreme habitat remains unclear. We present the first high-quality draft genome of C. antarcticus assembled from in-depth whole genome and transcriptome sequencing data obtained from both long-read and short-read sequencing platforms. The genome was 103.6 Mb in size with 81 scaffolds and a scaffold N50 of 3.4 Mb, appearing to have a smaller genome than that of hitherto known collembolan genomes. Following protein-coding gene prediction and annotation analyses, 19,808 non-redundant genes were identified, representing 97.0% Benchmarking Universal Single-Copy Ortholog (BUSCO) gene coverage. Subsequent Gene Ontology (GO) functional enrichment analyses revealed that significantly expanded gene families were mainly associated with cell cycle regulation and changes in cell states or activities, while contracted gene families were related to the inhibition of germ cell proliferation. Several glycoside hydrolase family genes were identified in C. antarcticus, some of which may have evolved to facilitate their survival in the extreme environment. These findings suggest that the evolution of these gene families is related to their adaptation to the habitat's extreme conditions.

The origin of meiotic sex was a key milestone in the evolution of the eukaryotic cell. The paralogous DNA recombinases Rad51 and meiosis-specific DMC1 are nearly universal among eukaryotes and have been used previously to trace the timing and origins of the meiotic machinery. Here we perform comparative genomics and phylogenetic analyses of Rad51 and DMC1 drawn from diverse eukaryotes with RadA recombinase sequences from a broad sampling of archaeal taxa, focusing on the recently sequenced diversity of Asgard archaeal taxa. We show that even with increased and new sampling, the eukaryotic Rad51 and DMC1 proteins still resolve separately from any archaeal RadA sequences. These findings suggest that the duplication of RadA into general and meiosis-specific paralogues occurred after the divergence of the eukaryotic progenitor and did not evolve at an earlier stage. These findings raise the important question of how the evolution of meiotic sex was linked to genome size expansion and the acquisition of the mitochondrial endosymbiont in early eukaryotes.

Genes that lack identifiable homologs in other species have been an intriguing and interesting topic of research for many years. These so-called orphan genes were first studied in yeast and since then, they have been found in many other species. This has fostered a whole field of research aiming at tracing back their evolutionary origin and functional significance. Orphan genes represent an important part of protein-coding genes in many species. Their presence was initially mainly hypothesized to result from high divergence from a pre-existing gene, with duplications or horizontal gene transfer facilitating their accelerated evolution. More recently, their possible de novo emergence from nongenic regions has gained particular interest. Several orphan genes are predicted to be involved in reproduction, while others are involved in specific developmental stages, in adaptation mechanisms such as freeze protection or even human disease. However, there is currently no unified resource or synthesis that brings together existing knowledge about how prevalent orphan genes are across different species and what their roles might be. In this review, we focus on orphan genes in animals and fungi. We provide a detailed summary of discoveries over time in terms of orphan gene prevalence in genomes, their origins as well as their roles in different biological contexts.

We present a chromosome-level genome assembly of the western nose-horned viper (Vipera ammodytes ammodytes), the most medically important viper in Europe. Using PacBio Sequel and Illumina HiSeq X Ten sequencing, we generated ∼270 Gb of data, achieving ∼131× coverage of the genome. The final assembly spans 1.55 Gb with a contig N50 of 45.9 Mb and a scaffold N50 of 210 Mb, anchored into 18 pseudo-chromosomes. Completeness was supported by recovery of 97.1% of Vertebrata BUSCOs. A total of 20,775 protein-coding genes were predicted, of which 96.6% were functionally annotated. Repetitive sequences accounted for 53.75% of the genome, dominated by LINEs (41.87%) and LTRs (14.35%). We identified 112 venom-related genes across 15 families, with expansions in SVMPs, Snaclecs, sPLA₂s, SPIs, and SVSPs, together comprising 62.5% of the venom repertoire. Chemosensory genes were also expanded, including 448 olfactory receptors, 72 taste receptors, and 29 vomeronasal receptors. This assembly represents the most complete genome resource for a true viper to date and provides a key resource for investigating venom evolution, chemosensory adaptation, and comparative snake genomics.

Comparative genomic analyses among closely related species provide an opportunity to assess their evolutionary history. The relatedness between species can depend on a variety of factors, including reproductive isolation, introgression, and incomplete lineage sorting, and this can impact divergence across the genome. Here, we use a combination of long- and short-read sequencing and HI-C scaffolding to assemble genomes for each of the four species in the testacea species group of Drosophila, including D. testacea, D. orientacea, D. neotestacea, and D. putrida, and its outgroup, D. bizonata. First, among species, we find many structural rearrangements across the genome as well as a large size difference in the dot chromosome that we infer is due to the expansion of repetitive elements. Second, we assess phylogenetic discordance and uncover a difference in the phylogeny inferred from genes on Muller E and the mitogenome relative to the rest of the genome, which may be due to recent hybridization. Lastly, we assess the rate of molecular evolution of genes shared across all species and identify genes evolving at different rates across the phylogeny. Our results present genomic resources for this species group and begin to probe into some of the evolutionary characteristics that contribute to variation in genome structure, while highlighting the need for high-quality genome resources to fully capture and understand the evolutionary history among closely related species.

The transition from small genetic to genome-scale datasets for studying biodiversity has revealed that genetic exchange through introgressive hybridization is a widespread phenomenon in nature. Despite this, a lack of high-quality reference genomes for most non-model species limits our understanding of the impact of this process for many taxonomic groups. This restricts the range of insights that genomic tools can provide for conservation biologists, who often hope to employ genomic datasets to accurately identify historically isolated lineages to protect and to predict their evolutionary fate in the face of environmental change. Tiger whiptail lizards (Aspidoscelis tigris complex) are an abundant and important ecological component of ecosystems across the southwestern United States. In this study, we assembled and annotated a chromosome-level reference genome for A. t. stejnegeri from coastal California. We then used this reference genome to reconstruct patterns of speciation and admixture within the larger species complex, finding evidence that gene flow is widespread both geographically and across the genome.

Clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated (Cas) systems of bacteria and archaea provide immunities against mobile genetic elements, like viruses. In addition, protospacer analyses revealed a very specific acquisition of CRISPR spacers derived from genomes of related species or from closely interacting episymbiont genomes as recently shown for subsurface archaea. However, the origin of most of the spacers that can be found in CRISPR-Cas systems from natural environments has not been deciphered. Here, by analyzing CRISPR-Cas systems of metagenome-assembled genomes (MAGs) from two subsurface environments spanning more than 1 Tb of sequencing data, we show that a substantial proportion of CRISPR spacers are acquired from DNA of other prokaryotes inhabiting the same environment. As such, we found that the number of respective spacers can be up to three times higher than the number of self-targeting spacers. Statistical analyses demonstrated that the acquisition of CRISPR spacers from other prokaryotic genomes is partly explained by the relative abundance of the MAG containing the protospacer, as well as by other factors, such as the total number of CRISPR arrays present in a MAG with the respective spacers. Further, we found that spacer acquisition from foreign prokaryotic DNA occurs in almost all types of CRISPR-Cas systems, but shows preferences for subtypes of CRISPR-Cas systems that differ across the investigated ecosystems. Taken together, our results shed new light on the diversity of CRISPR spacers in natural microbial communities and provide an explanation for some of the many unmatched spacers in public databases.

Genomic diversity within species encompasses a range of sequence-related, structural, and regulatory features. To illustrate their complexity, we invoke the analogy of a kaleidoscope: while the DNA sequence represents its core, the genome has a dynamic, multidimensional configuration shaped by interactions across these features, generating an array of dimensions of genomic variation. In this perspective, we highlight underexplored dimensions of genomic variation that contribute to phenotypic diversity. We begin by revisiting the existence of noncanonical chromosomes and by emphasizing the role of large-scale structural changes and the 3D genome architecture in modulating genomic function. We then examine the regulatory mechanisms shaping transcriptional activity and genetic variation that, instead of regulating mean trait values, defines the degree of trait variability. Finally, we discuss the influence of sequence composition on its mutational potential. These dimensions, though rooted in sequence, are context dependent, interconnected, and often difficult to disentangle, reflecting a level of structural and regulatory complexity that challenges traditional genotype-phenotype models. By synthesizing recent findings across these dimensions, we argue for a broader framework for studying within-species genomic diversity: one that accounts for the diverse molecular architectures underlying phenotypic output. This expanded view not only deepens our knowledge of the genome itself but also contributes to our understanding of genome evolution and within-species phenotypic variation.

The prevalence and evolutionary importance of inversion polymorphisms in natural populations is poorly known because of limited genome-wide sequence data availability for most species. Inversion studies in wild populations usually target rare cases of major trait polymorphisms or local adaptation whose genetic basis involves inversions, creating a strong impression that inversions in nature are generally maintained by natural selection through links to ecologically relevant phenotypes. By contrast, genome-wide studies in humans and model organisms suggest that inversion polymorphisms are common, subject to highly complex evolutionary processes, and generally difficult to link with clearly observable cases of phenotypic variation. Using a large comparative population genomic dataset generated from 35 codistributed species of birds, we tested the hypothesis that inversions are common even within populations that lack known phenotypic polymorphisms. We leveraged analytical methods suitable for low-coverage whole genome sequencing to reveal evidence for over 170 putative inversion polymorphisms within 28 species. We find that many polymorphisms are large and present at balanced frequencies, and some are shared across species boundaries. Yet, most polymorphisms do not deviate significantly from Hardy-Weinberg Equilibrium, raising the possibility that many of these massive haploblocks could be segregating neutrally. Our results thereby reveal evidence that inversions show a variety of complex yet largely hidden patterns in natural populations, beyond cases where they contribute to known variation in ecologically relevant traits.

NUPTs are DNA sequences of plastid origin that are present in plant nuclear genomes in varying, though typically low, amounts. It is assumed that they are continuously formed and, due to their potentially mutagenic effect, they are removed at a constant turnover rate, which should result in an exponential decay of their age distributions and a negative correlation between age and size. However, these assumptions are based on analyses from a limited number of species and have never been explicitly tested. To gain insight into the mechanisms driving the origin and evolution of NUPTs, here we surveyed the plastid and nuclear genomes of 30 species representing the main angiosperm (flowering plants) lineages. By modeling the distribution of ages and sizes, examining their linear arrangement across the plastid genome, and statistically assessing spatial biases with respect to other genomic features, we showed that NUPTs are: (i) formed by both continuous and episodic mechanisms; (ii) unevenly represented across the plastid genome; (iii) consistently associated with certain classes of RNA genes, in particular rRNA, tRNA, and regulatory RNA genes; (iv) differentially contributing to structural genes; and (v) closer than expected to different superfamilies of transposons in a species-specific manner. Our results reveal the unexpected complexity in the mechanisms driving the origin of NUPTs, which not only involve their continuous formation but also episodic events, highlight their role as a major source of noncoding RNA genes and other genomic features, and provide a more complete picture of the different drivers of evolutionary change at the genome level.