Genome Biology and Evolution最新文献

Studying fundamental aspects of eukaryotic biology through genetic information can face numerous challenges, including contamination and intricate biotic interactions, which are particularly pronounced when working with uncultured eukaryotes. However, existing tools for predicting open reading frames (ORFs) from transcriptomes are limited in these scenarios. Here we introduce Transcript Identification and Selection (TIdeS), a framework designed to address these non-trivial challenges associated with current 'omics approaches. Using transcriptomes from 32 taxa, representing the breadth of eukaryotic diversity, TIdeS outperforms most conventional ORF-prediction methods (i.e., TransDecoder), identifying a greater proportion of complete and in-frame ORFs. Additionally, TIdeS accurately classifies ORFs using minimal input data, even in the presence of 'heavy contamination'. This built-in flexibility extends to previously unexplored biological interactions, offering a robust single-stop solution for precise ORF predictions and subsequent decontamination. Beyond applications in phylogenomic-based studies, TIdeS provides a robust means to explore biotic interactions in eukaryotes (e.g., host-symbiont, prey-predator) and for reproducible dataset curation from transcriptomes and genomes.

Sex-specific regulation of gene expression is the most plausible way for generating sexually differentiated phenotypes from an essentially shared genome. However, since genetic material is shared, sex-specific selection in one sex can have an indirect response in the other sex. From a gene expression perspective, this tethered response can move one sex away from their wildtype expression state and potentially impact many gene regulatory networks. Here, using experimental evolution in the model nematode Caenorhabditis elegans, we explore the coupling of direct sexual selection on males with the transcriptomic response in males and females over microevolutionary timescales to uncover the extent to which post-insemination reproductive traits share a genetic basis between the sexes. We find that differential gene expression evolved in a sex-specific manner in males, while in females indirect selection causes an evolved response. Almost all differentially expressed genes were downregulated in both evolved males and females. Moreover, 97% of significantly differentially expressed genes in males and 69% of significantly differentially expressed genes in females have wildtype female-biased expression profile. Changes in gene expression profiles were likely driven through trans-acting pathways that are shared between the sexes. We found no evidence that the core dosage compensation machinery was impacted by experimental evolution. Together these data suggest a de-feminization of the male transcriptome and masculinization of the female transcriptome driven by direct selection on male sperm competitive ability. Our results indicate that on short evolutionary timescales sexual selection can generate putative sexual conflict in expression space.

Genome streamlining, i.e. genome size reduction, is observed in bacteria with very different life traits, including endosymbiotic bacteria and several marine bacteria, raising the question of its evolutionary origin. None of the hypotheses proposed in the literature is firmly established, mainly due to the many confounding factors related to the diverse habitats of species with streamlined genomes. Computational models may help overcome these difficulties and rigorously test hypotheses. In this work, we used Aevol, a platform designed to study the evolution of genome architecture, to test two main hypotheses: that an increase in population size (N) or mutation rate (μ) could cause genome reduction. In our experiments, both conditions lead to streamlining but have very different resulting genome structures. Under increased population sizes, genomes lose a significant fraction of non-coding sequences but maintain their coding size, resulting in densely packed genomes (akin to streamlined marine bacteria genomes). By contrast, under an increased mutation rate, genomes lose both coding and non-coding sequences (akin to endosymbiotic bacteria genomes). Hence, both factors lead to an overall reduction in genome size, but the coding density of the genome appears to be determined by N × μ. Thus, a broad range of genome size and density can be achieved by different combinations of N and μ. Our results suggest that genome size and coding density are determined by the interplay between selection for phenotypic adaptation and selection for robustness.

Fungi have been found to be associated with many insect species, with some species transitioning to reside within insects as symbionts. However, the evolutionary pressures and genomic consequences associated with this transition are not well understood. Pathogenic fungi of the genus Ophiocordyceps have undergone multiple, independent transitions from pathogen to endosymbiont lifestyles, where they reside within the fatty tissues of infected soft-scale insects trans-generationally without killing their hosts. To gain an understanding of the genomic adaptations underlying this life history shift, long-read sequencing was utilized to assemble the genomes of both the soft scale insect Parthenolecanium corni and its Ophiocordyceps endosymbiont from a single insect. Assembly and metagenomic-based binning produced a highly contiguous genome for Part. corni and a chromosome-level assembly for the Ophiocordyceps endosymbiont. The endosymbiont genome was characterized by 524 gene loss events compared to free-living pathogenic Ophiocordyceps relatives, with predicted roles in hyphal growth, cell wall integrity, metabolism, gene regulation and toxin production. Contrasting patterns of selection were observed between the nuclear and mitochondrial genomes specific to the endosymbiont lineage. Intensified selection was most frequently observed across orthologs in the nuclear genome, whereas selection on most mitochondrial genes was found to be relaxed. Scans for positive selection were enriched within the fatty acid metabolism pathway with associate specific selection within three adjacent enzymes catalyzing the conversion of acetoacetate to acetyl-COA, suggesting that the endosymbiont lineage is under selective pressure to effectively exploit the lipid rich environment of the insect fat bodies in which it is found.

The giant ground beetle genus Calosoma (Coleoptera, Carabidae) comprises ca. 120 species distributed worldwide. About half of the species in this genus are flightless due to a process of wing reduction likely resulting from the colonization of remote habitats such as oceanic islands, highlands and deserts. This clade is emerging as a new model to study the genomic basis of wing evolution in insects. In this framework, we present the de novo assemblies and annotations of two Calosoma species genomes from British Columbia, Calosoma tepidum and Calosoma wilkesii. Combining PacBio HiFi and Hi-C sequencing, we produce high-quality reference genomes for these two species. Our annotation using long-read RNAseq and existing Coleoptera protein evidence, identified a total of 21,976 genes for C. tepidum and 26,814 genes for C. wilkesii. Using synteny analyses, we provide an in-depth comparison of genomic architectures in these two species. We infer an overall pattern of chromosome-scale conservation between the two species, with only minor rearrangements within chromosomes. These new reference genomes represent a major step forward in the study of this group, providing high-quality references that open the door to different approaches such as comparative genomics or population scale resequencing to study the implications of flight evolution.

Mitochondrial DNA (mtDNA) has been widely used in genetics research for decades. Contamination from nuclear DNA of mitochondrial origin (NUMT) can confound studies of phylogenetic relationships and mtDNA heteroplasmy. Homology searches with mtDNA are widely used to detect NUMTs in the nuclear genome. Nevertheless, false positive detection of NUMTs is common when handling repeat-rich sequences, whilst fragmented genomes might result in missing true NUMTs. In this study, we investigated different NUMT detection methods and how the quality of the genome assembly affects them. We presented an improved nuclear genome assembly (aRhiMar1.3) of the invasive cane toad (Rhinella marina) with additional long-read Nanopore and 10x linked-read sequencing. The final assembly was 3.47 Gb in length with 91.3% of tetrapod universal single-copy orthologs (n=5,310), indicating the gene-containing regions were well assembled. We used three complementary methods (NUMTFinder, dinumt and PALMER) to study the NUMT landscape of the cane toad genome. All three methods yielded consistent results, showing very few NUMTs in the cane toad genome. Furthermore, we expanded NUMT detection analyses to other amphibians and confirmed a weak relationship between genome size and the number of NUMTs present in the nuclear genome. Amphibians are repeat-rich, and we show that the number of NUMTs found in highly repetitive genomes is prone to inflation when using homology-based detection without filters. Together, this study provides an exemplar of how to robustly identify NUMTs in complex genomes when confounding effects on mtDNA analyses are a concern.

The earlier vertion of AncestryPainter is a Perl program to display the ancestry composition of numerous individuals using a rounded graph. Motivated by the requests of users in practical applications, we updated AncestryPainter to version 2.0 by coding in an R package and improving the layout, providing more options and compatible statistical functions for graphing. Apart from improving visualization functions per se in this update, we added an extra graphing module to visualize genetic distance through radial bars of varying lengths surrounding a core. Notably, AncestryPainter 2.0 implements a method admixture history graph (AHG) to infer the admixture sequence of multiple ancestry populations, and allows for multiple pie charts at the center of the graph to display the ancestry composition of more than one target population. We validated the six AHG metrics using both simulated and real data and implemented a Pearson coefficient-based metric with the best performance in AncestryPainter 2.0. Furthermore, a statistical module to merge ancestry proportion matrices. AncestryPainter 2.0 is freely available at https://github.com/Shuhua-Group/AncestryPainterV2 and https://pog.fudan.edu.cn/#/Software.

Caused by both eukaryotic dinoflagellates and prokaryotic cyanobacteria, harmful algal blooms (HABs) are events of severe ecological, economic, and public health consequence, and their incidence has become more common of late. Despite coordinated research efforts to identify and characterize the genomes of HAB-causing organisms, the genomic basis and evolutionary origins of paralytic shellfish toxins (PSTs) produced by HABs remain at best incomplete. The PST saxitoxin has an especially complex genomic architecture and enigmatic phylogenetic distribution, spanning dinoflagellates and multiple cyanobacterial genera. Using filtration and extraction techniques to target the desired cyanobacteria from non-axenic culture, coupled with a combination of short and long read sequencing, we generated a reference-quality hybrid genome assembly for Heteroscytonema crispum UTEX LB 1556, a freshwater, PST-producing cyanobacterium thought to have the largest known genome in its phylum. We report a complete, novel biosynthetic gene cluster for the PST saxitoxin. Leveraging this biosynthetic gene cluster, we find support for the hypothesis that PST production has appeared in divergent Cyanobacteria lineages through widespread and repeated horizontal gene transfer. This work demonstrates the utility of long-read sequencing and metagenomic assembly toward advancing our understanding of PST biosynthetic gene cluster diversity and suggests a mechanism for the origin of PST biosynthetic genes.

Nuclear Matrix Constituent Proteins (NMCPs) in plants function like animal lamins, providing the structural foundation of the nuclear lamina and regulating nuclear organization and morphology. Although they are well-characterized in angiosperms, the presence and structure of NMCPs in more distantly related species, such as streptophytic algae, are relatively unknown. The rapid evolution of NMCPs throughout the plant lineage has caused a divergence in protein sequence that makes similarity-based searches less effective. Structural features are more likely to be conserved compared to primary amino acid sequence; therefore, we developed a filtration protocol to search for diverged NMCPs based on four physical characteristics: intrinsically disordered content, isoelectric point, number of amino acids, and the presence of a central coiled-coil domain. By setting parameters to recognize the properties of bona fide NMCP proteins in angiosperms, we filtered eight complete proteomes from streptophytic algae species and identified strong NMCP candidates in six taxa in the Classes Zygnematophyceae, Charophyceae, and Klebsormidophyceae. Through analysis of these proteins, we observed structural variance in domain size between NMCPs in algae and land plants, as well as a single block of amino acid conservation. Our analysis indicates that NMCPs are absent in the Mesostigmatophyceae. The presence versus absence of NMCP proteins does not correlate with the distribution of different forms of mitosis (e.g., closed/semi-closed/open) but does correspond to the transition from unicellularity to multicellularity in the streptophytic algae, suggesting that an NMCP-based nucleoskeleton plays important roles in supporting cell-to-cell interactions.

In contrast to the typified view of genomes cycling only between haploidy and diploidy, there is evidence from across the tree of life of genome dynamics that alter both copy number (i.e. ploidy) and chromosome complements. Here we highlight examples of such processes, including endoreplication, aneuploidy, inheritance of extrachromosomal DNA, and chromatin extrusion. Synthesizing data on eukaryotic genome dynamics in diverse extant lineages suggests the possibility that such processes were present before the last eukaryotic common ancestor (LECA). While present in some prokaryotes, these features appear exaggerated in eukaryotes where they are regulated by eukaryote-specific innovations including the nucleus, complex cytoskeleton, and synaptonemal complex. Based on these observations, we propose a model by which genome conflict drove the transformation of genomes during eukaryogenesis: from the origin of eukaryotes (i.e. FECA) through the evolution of LECA.