SOI: robust identification of orthologous synteny with the Orthology Index and broad applications in evolutionary genomics

With the explosive growth of whole-genome datasets, accurate detection of orthologous synteny has become crucial for reconstructing evolutionary history. However, current methods for identifying orthologous synteny face great limitations, particularly in scaling with varied polyploidy histories and accurately removing out-paralogous synteny. In this study, we developed a scalable and robust approach, based on the Orthology Index (OI), to effectively identify orthologous synteny. Our evaluation across a large-scale empirical dataset with diverse polyploidization events demonstrated the high reliability and robustness of the OI method. Simulation-based benchmarks further validated the accuracy of our method, showing its superior performance against existing methods across a wide range of scenarios. Additionally, we explored its broad applications in reconstructing the evolutionary histories of plant genomes, including the inference of polyploidy, identification of reticulation, and phylogenomics. In conclusion, OI offers a robust, interpretable, and scalable approach for identifying orthologous synteny, facilitating more accurate and efficient analyses in plant evolutionary genomics.

Accurate Inference of the Polyploid Continuum Using Forward-Time Simulations

Multiple rounds of whole-genome duplication (WGD) followed by diploidization have occurred throughout the evolutionary history of angiosperms. Much work has been done to model the genomic consequences and evolutionary significance of WGD. While researchers have historically modeled polyploids as either allopolyploids or autopolyploids, the variety of natural polyploids span a continuum of differentiation across multiple parameters, such as the extent of polysomic versus disomic inheritance, and the degree of genetic differentiation between the ancestral lineages. Here we present a forward-time polyploid genome evolution simulator called SpecKS. SpecKS models polyploid speciation as originating from a 2D continuum, whose dimensions account for both the level of genetic differentiation between the ancestral parental genomes, as well the time lag between ancestral speciation and their subsequent reunion in the derived polyploid. Using extensive simulations, we demonstrate that changes in initial conditions along either dimension of the 2D continuum deterministically affect the shape of the Ks histogram. Our findings indicate that the error in the common method of estimating WGD time from the Ks histogram peak scales with the degree of allopolyploidy, and we present an alternative, accurate estimation method that is independent of the degree of allopolyploidy. Lastly, we use SpecKS to derive tests that infer both the lag time between parental divergence and WGD time, and the diversity of the ancestral species, from an input Ks histogram. We apply the latter test to transcriptomic data from over 200 species across the plant kingdom, the results of which are concordant with the prevailing theory that the majority of angiosperm lineages are derived from diverse parental genomes and may be of allopolyploid origin.

Genomic evidence for the widespread presence of GH45 cellulases among soil invertebrates

Lignocellulose is a major component of vascular plant biomass. Its decomposition is crucial for the terrestrial carbon cycle. Microorganisms are considered primary decomposers, but evidence increases that some invertebrates may also decompose lignocellulose. We investigated the taxonomic distribution and evolutionary origins of GH45 hydrolases, important enzymes for the decomposition of cellulose and hemicellulose, in a collection of soil invertebrate genomes. We found that these genes are common in springtails and oribatid mites. Phylogenetic analysis revealed that cellulase genes were acquired early in the evolutionary history of these groups. Domain architectures and predicted 3D enzyme structures indicate that these cellulases are functional. Patterns of presence and absence of these genes across different lineages prompt further investigation into their evolutionary and ecological benefits. The ubiquity of cellulase genes suggests that soil invertebrates may play a role in lignocellulose decomposition, independently or in synergy with microorganisms. Understanding the ecological and evolutionary implications might be crucial for understanding soil food webs and the carbon cycle.

Species-tree topology impacts the inference of ancient whole-genome duplications across the angiosperm phylogeny

PREMISE

The history of angiosperms is marked by repeated rounds of ancient whole-genome duplications (WGDs). Here we used state-of-the-art methods to provide an up-to-date view of the distribution of WGDs in the history of angiosperms that considers both uncertainty introduced by different WGD inference methods and different underlying species-tree hypotheses.

METHODS

We used the distribution synonymous divergences (Ks) of paralogs and orthologs from transcriptomic and genomic data to infer and place WGDs across two hypothesized angiosperm phylogenies. We further tested these WGD hypotheses with syntenic inferences and Bayesian models of duplicate gene gain and loss.

RESULTS

The predicted number of WGDs in the history of angiosperms (~170) based on the current taxon sampling is largely similar across different inference methods, but varies in the precise placement of WGDs on the phylogeny. Ks-based methods often yield alternative hypothesized WGD placements due to variation in substitution rates among lineages. Phylogenetic models of duplicate gene gain and loss are more robust to topological variation. However, errors in species-tree inference can still produce spurious WGD hypotheses, regardless of method used.

CONCLUSIONS

Here we showed that different WGD inference methods largely agree on an average of 3.5 WGD in the history of individual angiosperm species. However, the precise placement of WGDs on the phylogeny is subject to the WGD inference method and tree topology. As researchers continue to test hypotheses regarding the impacts ancient WGDs have on angiosperm evolution, it is important to consider the uncertainty of the phylogeny as well as WGD inference methods.

FEVER: an interactive web-based resource for evolutionary transcriptomics across fishes

Teleost fish represent one of the largest and most diverse clades of vertebrates, which makes them great models in various research areas such as ecology and evolution. Recent sequencing endeavors provided high-quality genomes for species covering the main fish evolutionary lineages, opening up large-scale comparative genomics studies. However, transcriptomic data across fish species and organs are heterogenous and have not been integrated with newly sequenced genomes making gene expression quantification and comparative analyses particularly challenging. Thus, resources integrating genomic and transcriptomic data across fish species and organs are still lacking. Here, we present FEVER, a web-based resource allowing evolutionary transcriptomics across species and tissues. First, based on query genes FEVER reconstructs gene trees providing orthologous and paralogous relationships as well as their evolutionary dynamics across 13 species covering the major fish lineages, and 4 model species as evolutionary outgroups. Second, it provides unbiased gene expression across 11 tissues using up-to-date fish genomes. Finally, genomic and transcriptomic data are combined together allowing the exploration of gene expression evolution following speciation and duplication events. FEVER is freely accessible at https://fever.sk8.inrae.fr/.

Molecular Dating of the Teleost Whole Genome Duplication (3R) Is Compatible With the Expectations of Delayed Rediploidization

Vertebrate evolution has been punctuated by three whole genome duplication events that have been implicated causally in phenotypic evolution, from the origin of phenotypic novelties to explosive diversification. Arguably, the most dramatic of these is the 3R whole genome duplication event associated with the origin of teleost fishes which comprise more than half of all living vertebrate species. However, tests of a causal relationship between whole genome duplication and teleost diversification have proven difficult due to the challenge of establishing the timing of these phenomena. Here we show, based on molecular clock dating of concatenated gene alignments, that the 3R whole genome duplication event occurred in the early-middle Permian (286.18 to 267.20 million years ago; Ma), 52.02 to 12.84 million years (Myr) before the divergence of crown-teleosts in the latest Permian-earliest Late Triassic (254.36 to 234.16 Ma) and long before the major pulses of teleost diversification in Ostariophysi and Percomorpha (56.37 to 100.17 Myr and at least 139.24 to 183.29 Myr later, respectively). The extent of this temporal gap between putative cause and effect precludes 3R as a deterministic driver of teleost diversification. However, these age constraints remain compatible with the expectations of a prolonged rediploidization process following whole genome duplication which, through the effects of chromosome rearrangement and gene loss, remains a viable mechanism to explain the evolution of teleost novelties and diversification.

Genome-wide patterns of homoeologous gene flow in allotetraploid coffee

Premise

Allopolyploidy-a hybridization-induced whole-genome duplication event-has been a major driver of plant diversification. The extent to which chromosomes pair with their proper homolog vs. with their homoeolog in allopolyploids varies across taxa, and methods to detect homoeologous gene flow (HGF) are needed to understand how HGF has shaped polyploid lineages.

Methods

The ABBA-BABA test represents a classic method for detecting introgression between closely related species, but here we developed a modified use of the ABBA-BABA test to characterize the extent and direction of HGF in allotetraploid Coffea arabica.

Results

We found that HGF is abundant in the C. arabica genome, with both subgenomes serving as donors and recipients of variation. We also found that HGF is highly maternally biased in plastid-targeted-but not mitochondrial-targeted-genes, as would be expected if plastid-nuclear incompatibilities exist between the two parent species.

Discussion

Together, our analyses provide a simple framework for detecting HGF and new evidence consistent with selection favoring overwriting of paternally derived alleles by maternally derived alleles to ameliorate plastid-nuclear incompatibilities. Natural selection therefore appears to shape the direction and intensity of HGF in allopolyploid coffee, indicating that cytoplasmic inheritance has long-term consequences for polyploid lineages.

Solving an enigma in the tree of life, at the origins of teleost fishes

Tracing the phylogenetic relationships between species is one of the fundamental objectives of evolutionary biology. Since Charles Darwin's seminal work in the 19th century, considerable progress has been made towards establishing a tree of life that summarises the evolutionary history of species. Nevertheless, substantial uncertainties still remain. Specifically, the relationships at the origins of teleost fishes have been the subject of extensive debate over the last 50 years. This question has major implications for various research fields: there are almost 30,000 species in the teleost group, which includes invaluable model organisms for biomedical, evolutionary and ecological studies. Here, we present the work in which we solved this enigma. We demonstrated that eels are more closely related to bony-tongued fishes than to the rest of teleost fishes. We achieved this by taking advantage of new genomic data and leveraging innovative phylogenetic markers. Notably, in addition to traditional molecular phylogeny methods based on the evolution of gene sequences, we also considered the evolution of gene order along the DNA molecule. We discuss the challenges and opportunities that these new markers represent for the field of molecular phylogeny, and in particular the possibilities they offer for re-examining other controversial branches in the tree of life.

Genome-wide identification and transcriptome profiling expression analysis of the U-box E3 ubiquitin ligase gene family related to abiotic stress in maize (Zea mays L.)

BACKGROUND

The U-box gene family encodes E3 ubiquitin ligases involved in plant hormone signaling pathways and abiotic stress responses. However, there has yet to be a comprehensive analysis of the U-box gene family in maize (Zea mays L.) and its responses to abiotic stress.

RESULTS

In this study, 85 U-box family proteins were identified in maize and were classified into four subfamilies based on phylogenetic analysis. In addition to the conserved U-box domain, we identified additional functional domains, including Pkinase, ARM, KAP and Tyr domains, by analyzing the conserved motifs and gene structures. Chromosomal localization and collinearity analysis revealed that gene duplications may have contributed to the expansion and evolution of the U-box gene family. GO annotation and KEGG pathway enrichment analysis identified a total of 105 GO terms and 21 KEGG pathways that were notably enriched, including ubiquitin-protein transferase activity, ubiquitin conjugating enzyme activity and ubiquitin-mediated proteolysis pathway. Tissue expression analysis showed that some ZmPUB genes were specifically expressed in certain tissues and that this could be due to their functions. In addition, RNA-seq data for maize seedlings under salt stress revealed 16 stress-inducible plant U-box genes, of which 10 genes were upregulated and 6 genes were downregulated. The qRT-PCR results for genes responding to abiotic stress were consistent with the transcriptome analysis. Among them, ZmPUB13, ZmPUB18, ZmPUB19 and ZmPUB68 were upregulated under all three abiotic stress conditions. Subcellular localization analysis showed that ZmPUB19 and ZmPUB59 were located in the nucleus.

CONCLUSIONS

Overall, our study provides a comprehensive analysis of the U-box gene family in maize and its responses to abiotic stress, suggesting that U-box genes play an important role in the stress response and providing insights into the regulatory mechanisms underlying the response to abiotic stress in maize.

Conserved and divergent arms of the antiviral response in the duplicated genomes of salmonid fishes

Antiviral innate immunity is orchestrated by the interferon system, which appeared in ancestors of jawed vertebrates. Interferon upregulation induces hundreds of interferon-stimulated-genes (ISGs) with effector or regulatory functions. Here we investigated the evolutionary diversification of ISG responses through comparison of two salmonid fishes, accounting for the impact of sequential whole genome duplications ancestral to teleosts and salmonids. We analysed the transcriptomic response of the IFN pathway in the head kidney of rainbow trout and Atlantic salmon, which separated 25-30 Mya. We identified a large set of ISGs conserved in both species and cross-referenced them with zebrafish and human ISGs. In contrast, around one-third of salmonid ISG lacked orthologs in human, mouse, chicken or frog, and often between rainbow trout and Atlantic salmon, revealing a fast-evolving, lineage-specific arm of the antiviral response. This study also provides a key resource for in-depth functional analysis of ISGs in salmonids of commercial significance.

Phylogeny and expression of tetraspanin CD9 paralogues in rainbow trout (Oncorhynchus mykiss)

CD9 is a member of the tetraspanin family, which is characterised by a unique domain structure and conserved motifs. In mammals, CD9 is found in tetraspanin-enriched microdomains (TEMs) on the surface of virtually every cell type. CD9 has a wide variety of roles, including functions within the immune system. Here we show the first in-depth analysis of the cd9 gene family in salmonids, showing that this gene has expanded to six paralogues in three groups (cd9a, cd9b, cd9c) through whole genome duplication events. We suggest that through genome duplications, cd9 has undergone subfunctionalisation in the paralogues and that cd9c1 and cd9c2 in particular are involved in antiviral responses in salmonid fish. We show that these paralogues are significantly upregulated in parallel to classic interferon-stimulated genes (ISGs) active in the antiviral response. Expression analysis of cd9 may therefore become an interesting target to assess teleost responses to viruses.

Reconstruction of hundreds of reference ancestral genomes across the eukaryotic kingdom

Ancestral sequence reconstruction is a fundamental aspect of molecular evolution studies and can trace small-scale sequence modifications through the evolution of genomes and species. In contrast, fine-grained reconstructions of ancestral genome organizations are still in their infancy, limiting our ability to draw comprehensive views of genome and karyotype evolution. Here we reconstruct the detailed gene contents and organizations of 624 ancestral vertebrate, plant, fungi, metazoan and protist genomes, 183 of which are near-complete chromosomal gene order reconstructions. Reconstructed ancestral genomes are similar to their descendants in terms of gene content as expected and agree precisely with reference cytogenetic and in silico reconstructions when available. By comparing successive ancestral genomes along the phylogenetic tree, we estimate the intra- and interchromosomal rearrangement history of all major vertebrate clades at high resolution. This freely available resource introduces the possibility to follow evolutionary processes at genomic scales in chronological order, across multiple clades and without relying on a single extant species as reference.

SCORPiOs, a Novel Method to Reconstruct Gene Phylogenies in the Context of a Known WGD Event

Phylogenetic gene trees recapitulate the evolutionary history of genes across species, forming an essential framework for comparative genomic studies. In particular, within the context of whole-genome duplications (WGDs), they serve as a basis to investigate patterns of duplicate gene retention and loss, timing of genome rediploidization, and, more generally, to explore the functional consequences of the duplication in descending species. Yet, despite ever more sophisticated models to describe the evolution of gene sequences, building accurate gene trees remains a challenge in ancient polyploid taxons. WGDs generate complex gene families with many duplicated copies and recurrent gene losses, which complicate this task even more. Here, we describe how to use SCORPiOs, a novel method that leverages synteny conservation to provide more accurate phylogenies in the presence of a known WGD event.

Phylogenomics and the flowering plant tree of life

The advances accelerated by next-generation sequencing and long-read sequencing technologies continue to provide an impetus for plant phylogenetic study. In the past decade, a large number of phylogenetic studies adopting hundreds to thousands of genes across a wealth of clades have emerged and ushered plant phylogenetics and evolution into a new era. In the meantime, a roadmap for researchers when making decisions across different approaches for their phylogenomic research design is imminent. This review focuses on the utility of genomic data (from organelle genomes, to both reduced representation sequencing and whole-genome sequencing) in phylogenetic and evolutionary investigations, describes the baseline methodology of experimental and analytical procedures, and summarizes recent progress in flowering plant phylogenomics at the ordinal, familial, tribal, and lower levels. We also discuss the challenges, such as the adverse impact on orthology inference and phylogenetic reconstruction raised from systematic errors, and underlying biological factors, such as whole-genome duplication, hybridization/introgression, and incomplete lineage sorting, together suggesting that a bifurcating tree may not be the best model for the tree of life. Finally, we discuss promising avenues for future plant phylogenomic studies.

Genomic analysis of hypoxia inducible factor alpha in ray-finned fishes reveals missing Ohnologs and evidence of widespread positive selection

As aquatic hypoxia worsens on a global scale, fishes will become increasingly challenged by low oxygen, and understanding the molecular basis of their response to hypoxia may help to better define the capacity of fishes to cope with this challenge. The hypoxia inducible factor (HIF) plays a critical role in the molecular response to hypoxia by activating the transcription of genes that serve to improve oxygen delivery to the tissues or enhance the capacity of tissues to function at low oxygen. The current study examines the molecular evolution of genes encoding the oxygen-dependent HIFα subunit (HIFA) in the ray-finned fishes (Actinopterygii). Genomic analyses demonstrate that several lineages retain four paralogs of HIFA predicted from two rounds of genome duplication at the base of vertebrate evolution, broaden the known distribution of teleost-specific HIFA paralogs, and provide evidence for salmonid-specific HIFA duplicates. Evolution of the HIFA gene family is characterized by widespread episodic positive selection at amino acid sites that potentially mediate protein stability, protein-protein interactions, and transcriptional regulation. HIFA transcript abundance depends upon paralog, tissue, and fish lineage. A phylogenetically-informed gene nomenclature is proposed along with avenues for future research on this critical family of transcription factors.

Salmonidae Genome: Features, Evolutionary and Phylogenetic Characteristics

The salmon family is one of the most iconic and economically important fish families, primarily possessing meat of excellent taste as well as irreplaceable nutritional and biological value. One of the most common and, therefore, highly significant members of this family, the Atlantic salmon (Salmo salar L.), was not without reason one of the first fish species for which a high-quality reference genome assembly was produced and published. Genomic advancements are becoming increasingly essential in both the genetic enhancement of farmed salmon and the conservation of wild salmon stocks. The salmon genome has also played a significant role in influencing our comprehension of the evolutionary and functional ramifications of the ancestral whole-genome duplication event shared by all Salmonidae species. Here we provide an overview of the current state of research on the genomics and phylogeny of the various most studied subfamilies, genera, and individual salmonid species, focusing on those studies that aim to advance our understanding of salmonid ecology, physiology, and evolution, particularly for the purpose of improving aquaculture production. This review should make potential researchers pay attention to the current state of research on the salmonid genome, which should potentially attract interest in this important problem, and hence the application of new technologies (such as genome editing) in uncovering the genetic and evolutionary features of salmoniforms that underlie functional variation in traits of commercial and scientific importance.

WGDTree: a phylogenetic software tool to examine conditional probabilities of retention following whole genome duplication events

BACKGROUND

Multiple processes impact the probability of retention of individual genes following whole genome duplication (WGD) events. In analyzing two consecutive whole genome duplication events that occurred in the lineage leading to Atlantic salmon, a new phylogenetic statistical analysis was developed to examine the contingency of retention in one event based upon retention in a previous event. This analysis is intended to evaluate mechanisms of duplicate gene retention and to provide software to generate the test statistic for any genome with pairs of WGDs in its history.

RESULTS

Here a software package written in Python, 'WGDTree' for the analysis of duplicate gene retention following whole genome duplication events is presented. Using gene tree-species tree reconciliation to label gene duplicate nodes and differentiate between WGD and SSD duplicates, the tool calculates a statistic based upon the conditional probability of a gene duplicate being retained after a second whole genome duplication dependent upon the retention status after the first event. The package also contains methods for the simulation of gene trees with WGD events. After running simulations, the accuracy of the placement of events has been determined to be high. The conditional probability statistic has been calculated for Phalaenopsis equestris on a monocot species tree with a pair of consecutive WGD events on its lineage, showing the applicability of the method.

CONCLUSIONS

A new software tool has been created for the analysis of duplicate genes in examination of retention mechanisms. The software tool has been made available on the Python package index and the source code can be found on GitHub here: https://github.com/cnickh/wgdtree .

An atlas of fish genome evolution reveals delayed rediploidization following the teleost whole-genome duplication

Teleost fishes are ancient tetraploids descended from an ancestral whole-genome duplication that may have contributed to the impressive diversification of this clade. Whole-genome duplications can occur via self-doubling (autopolyploidy) or via hybridization between different species (allopolyploidy). The mode of tetraploidization conditions evolutionary processes by which duplicated genomes return to diploid meiotic pairing, and subsequent genetic divergence of duplicated genes (cytological and genetic rediploidization). How teleosts became tetraploid remains unresolved, leaving a fundamental gap in the interpretation of their functional evolution. As a result of the whole-genome duplication, identifying orthologous and paralogous genomic regions across teleosts is challenging, hindering genome-wide investigations into their polyploid history. Here, we combine tailored gene phylogeny methodology together with a state-of-the-art ancestral karyotype reconstruction to establish the first high-resolution comparative atlas of paleopolyploid regions across 74 teleost genomes. We then leverage this atlas to investigate how rediploidization occurred in teleosts at the genome-wide level. We uncover that some duplicated regions maintained tetraploidy for more than 60 million years, with three chromosome pairs diverging genetically only after the separation of major teleost families. This evidence suggests that the teleost ancestor was an autopolyploid. Further, we find evidence for biased gene retention along several duplicated chromosomes, contradicting current paradigms that asymmetrical evolution is specific to allopolyploids. Altogether, our results offer novel insights into genome evolutionary dynamics following ancient polyploidizations in vertebrates.

DupScan: predicting and visualizing vertebrate genome duplication database

Duplicated genes prevail in vertebrates and are important in the acquisition of new genes and novelties. Whole genome duplication (WGD) is one of the sources of duplicated genes. It can provide raw materials for natural selection by increasing the flexibility and complexity of the genome. WGDs are the driving force for the evolution of vertebrates and contribute greatly to their species diversity, especially in fish species with complicated WGD patterns. Here, we constructed the DupScan database (https://dupscan.sysumeg.com/) by integrating 106 chromosomal-level genomes, which can analyze and visualize synteny at both the gene and genome scales, visualize the Ka, Ks, and 4DTV values, and browse genomes. DupScan was used to perform functional adaptation for the intricate WGD investigation based on synteny matching. DupScan supports the analysis of five WGD rounds (R): VGD2 (vertebrate genome duplication 2), Ars3R (Acipenser-ruthenus-specific 3R), Pss3R (Polyodon-spathula-specific 3R), Ts3R (teleost-specific duplication 3R), Ss4R (salmonid-specific 4R), and Cs4R (carp-specific 4R). DupScan serves as one-stop analysis platform for synteny and WGD research in which users can analyze and predict synteny and WGD patterns across 106 species of whole genome sequences. This further aided us in elucidating genome evolutionary patterns across over 60,000 vertebrate species with synteny and WGD events.

Genome-Wide Reconstruction of Rediploidization Following Autopolyploidization across One Hundred Million Years of Salmonid Evolution

The long-term evolutionary impacts of whole-genome duplication (WGD) are strongly influenced by the ensuing rediploidization process. Following autopolyploidization, rediploidization involves a transition from tetraploid to diploid meiotic pairing, allowing duplicated genes (ohnologs) to diverge genetically and functionally. Our understanding of autopolyploid rediploidization has been informed by a WGD event ancestral to salmonid fishes, where large genomic regions are characterized by temporally delayed rediploidization, allowing lineage-specific ohnolog sequence divergence in the major salmonid clades. Here, we investigate the long-term outcomes of autopolyploid rediploidization at genome-wide resolution, exploiting a recent "explosion" of salmonid genome assemblies, including a new genome sequence for the huchen (Hucho hucho). We developed a genome alignment approach to capture duplicated regions across multiple species, allowing us to create 121,864 phylogenetic trees describing genome-wide ohnolog divergence across salmonid evolution. Using molecular clock analysis, we show that 61% of the ancestral salmonid genome experienced an initial "wave" of rediploidization in the late Cretaceous (85-106 Ma). This was followed by a period of relative genomic stasis lasting 17-39 My, where much of the genome remained tetraploid. A second rediploidization wave began in the early Eocene and proceeded alongside species diversification, generating predictable patterns of lineage-specific ohnolog divergence, scaling in complexity with the number of speciation events. Using gene set enrichment, gene expression, and codon-based selection analyses, we provide insights into potential functional outcomes of delayed rediploidization. This study enhances our understanding of delayed autopolyploid rediploidization and has broad implications for future studies of WGD events.

Applying Synteny Networks (SynNet) to Study Genomic Arrangements of Protein-Coding Genes in Plants

In comparative genomics, the study of synteny can be a powerful method for exploring genome rearrangements, inferring genomic ancestry, defining orthology relationships, determining gene and genome duplications, and inferring gene positional conservation patterns across taxa. In this chapter, we present a step-by-step protocol for microsynteny network (SynNet) analysis, as an alternative to traditional methods of synteny comparison, where nodes in the network represent protein-coding genes and edges represent the pairwise syntenic relationships. The SynNet pipeline consists of six main steps: (1) pairwise genome comparisons between all the genomes being analyzed, (2) detection of inter- and intrasynteny blocks, (3) generation of an entire synteny database (i.e., edgelist), (4) network clustering, (5) phylogenomic profiling of the gene family of interest, and (6) evolutionary inference. The SynNet approach facilitates the rapid analysis and visualization of synteny relationships (from specific genes, specific gene families up to all genes) across a large number of genomes.

A supernumerary "B-sex" chromosome drives male sex determination in the Pachón cavefish, Astyanax mexicanus

Sex chromosomes are generally derived from a pair of classical type-A chromosomes, and relatively few alternative models have been proposed up to now.^1,2 B chromosomes (Bs) are supernumerary and dispensable chromosomes with non-Mendelian inheritance found in many plant and animal species^3,4 that have often been considered as selfish genetic elements that behave as genome parasites.^5,6 The observation that in some species Bs can be either restricted or predominant in one sex^7-14 raised the interesting hypothesis that Bs could play a role in sex determination.¹⁵ The characterization of putative B master sex-determining (MSD) genes, however, has not yet been provided to support this hypothesis. Here, in Astyanax mexicanus cavefish originating from Pachón cave, we show that Bs are strongly male predominant. Based on a high-quality genome assembly of a B-carrying male, we characterized the Pachón cavefish B sequence and found that it contains two duplicated loci of the putative MSD gene growth differentiation factor 6b (gdf6b). Supporting its role as an MSD gene, we found that the Pachón cavefish gdf6b gene is expressed specifically in differentiating male gonads, and that its knockout induces male-to-female sex reversal in B-carrying males. This demonstrates that gdf6b is necessary for triggering male sex determination in Pachón cavefish. Altogether these results bring multiple and independent lines of evidence supporting the conclusion that the Pachón cavefish B is a "B-sex" chromosome that contains duplicated copies of the gdf6b gene, which can promote male sex determination in this species.

Reconstructing the evolutionary history of the oxytocin and vasotocin receptor gene family: Insights on whole genome duplication scenarios

Vertebrate genome evolution remains a hotly debated topic, specifically as regards the number and the timing of putative rounds of whole genome duplication events. In this study, I sought to shed light to this conundrum through assessing the evolutionary history of the oxytocin/vasotocin receptor family. I performed ancestral analyses of the genomic segments containing oxytocin and vasotocin receptors (OTR-VTRs) by mapping them back to the reconstructed ancestral vertebrate/chordate karyotypes reported in five independent studies (Nakatani et al., 2007; Putnam et al., 2008; Smith and Keinath, 2015; Smith et al., 2018; Simakov et al., 2020) and found that two alternative scenarios can account for their evolution: one consistent with one round of whole genome duplication in the common ancestor of lampreys and gnathostomes, followed by segmental duplications in both lineages, and another consistent with two rounds of whole genome duplication, with the first occurring in the gnathostome-lamprey ancestor and the second in the jawed vertebrate ancestor. Combining the data reported here with synteny and phylogeny data reported in our previous study (Theofanopoulou et al., 2021), I put forward that a single round of whole genome duplication scenario is more consistent with the synteny and evolution of chromosomes where OTR-VTRs are encountered, without excluding the possibility of a scenario including two rounds of whole genome duplication. Although the analysis of one gene family is not able to capture the full complexity of vertebrate genome evolution, this study can provide solid insight, since the gene family used here has been meticulously analyzed for its genes' orthologous and paralogous relationships across species using high quality genomes.

A prescient evolutionary model for genesis, duplication and differentiation of MIR160 homologs in Brassicaceae

MicroRNA160 is a class of nitrogen-starvation responsive genes which governs establishment of root system architecture by down-regulating AUXIN RESPONSE FACTOR genes (ARF10, ARF16 and ARF17) in plants. The high copy number of MIR160 variants discovered by us from land plants, especially polyploid crop Brassicas, posed questions regarding genesis, duplication, evolution and function. Absence of studies on impact of whole genome and segmental duplication on retention and evolution of MIR160 homologs in descendent plant lineages prompted us to undertake the current study. Herein, we describe ancestry and fate of MIR160 homologs in Brassicaceae in context of polyploidy driven genome re-organization, copy number and differentiation. Paralogy amongst Brassicaceae MIR160a, MIR160b and MIR160c was inferred using phylogenetic analysis of 468 MIR160 homologs from land plants. The evolutionarily distinct MIR160a was found to represent ancestral form and progenitor of MIR160b and MIR160c. Chronology of evolutionary events resulting in origin and diversification of genomic loci containing MIR160 homologs was delineated using derivatives of comparative synteny. A prescient model for causality of segmental duplications in establishment of paralogy in Brassicaceae MIR160, with whole genome duplication accentuating the copy number increase, is being posited in which post-segmental duplication events viz. differential gene fractionation, gene duplications and inversions are shown to drive divergence of chromosome segments. While mutations caused the diversification of MIR160a, MIR160b and MIR160c, duplicated segments containing these diversified genes suffered gene rearrangements via gene loss, duplications and inversions. Yet the topology of phylogenetic and phenetic trees were found congruent suggesting similar evolutionary trajectory. Over 80% of Brassicaceae genomes and subgenomes showed a preferential retention of single copy each of MIR160a, MIR160b and MIR160c suggesting functional relevance. Thus, our study provides a blue-print for reconstructing ancestry and phylogeny of MIRNA gene families at genomics level and analyzing the impact of polyploidy on organismal complexity. Such studies are critical for understanding the molecular basis of agronomic traits and deploying appropriate candidates for crop improvement.

Evolutionary context can clarify gene names: Teleosts as a case study

We developed an ex silico evolutionary-based systematic synteny approach to define and name the duplicated genes in vertebrates. The first convention for the naming of genes relied on historical precedent, the order in the human genome, and mutant phenotypes in model systems. However, total-genome duplication that resulted in teleost genomes required the naming of duplicated orthologous genes (ohnologs) in a specific manner. Unfortunately, as we review here, such naming has no defined criteria, and some ohnologs and their orthologs have suffered from incorrect nomenclature, thus creating confusion in comparative genetics and disease modeling. We sought to overcome this barrier by establishing an ex silico evolutionary-based systematic approach to naming ohnologs in teleosts. We developed software and compared gene synteny in zebrafish using the spotted gar genome as a reference, representing the unduplicated ancestral state. Using new criteria, we identified several hundred potentially misnamed ohnologs and validated the principle manually. Also see the video abstract here: https://youtu.be/UKNLa_TvSgY.