Fishes host a diverse microbiome in their gills, but a broad characterization of this microbiome at the metagenomic level is lacking. Here, we apply genome-resolved metagenomics to the gills of the hamlets (Hypoplectrus spp), a group of reef fishes from the Greater Caribbean. The analysis of 353 gill samples from 15 hamlet species collected at eight locations over 13 years revealed a stark contrast between the gill microbiota and reef water microbial communities, indicating a distinct and specific gill microbiome. A total of 70 gill-associated metagenome-assembled genomes (MAGs) were recovered. These MAGs belong to 17 lineages, most of which are novel. They relate to known fish gill pathogens, fish gut microbes, free-living and biofilm-associated taxa, indicating that the gill microbiome was assembled from a collection of distinct eco-evolutionary trajectories. The MAGs harbor diverse metabolic modules, involved notably in nitrogen cycling, antibiotic production and biofilm formation, revealing a highly dynamic microbial ecosystem. One lineage in the Burkholderiaceae family was outstandingly prevalent across fish host species, sampling locations and years. Its genome encoded complete metabolic modules for carbon fixation and sulfur oxidation, indicating chemosynthetic potential. To the best of our knowledge, this is the first line of evidence that fishes may host sulfur-oxidizing chemosynthetic bacteria in their gills. The functional significance of this chemosynthetic potential for the fish host or other members of the gill microbiome remains to be established. The high prevalence of this lineage allowed to build a pangenome. It revealed large-scale geographic structure (western Caribbean, eastern Caribbean and Gulf of Mexico), which parallels the phylogenomic pattern observed in the hamlets. Overall, our findings point to complex fish host-microbe and microbe-microbe eco-evolutionary interactions in the gills that may influence fish physiology, homeostasis and immune response.

The genetic dissection of complex traits remains a major challenge in basic and biomedical research, but is essential for understanding the molecular pathways that shape phenotypic variation and for developing predictive models of trait and disease susceptibility. Here, we leverage a novel multiparent mapping population of budding yeast, CYClones, comprising 9,344 haploid strains derived from eight genetically diverse founders (~270,000 SNVs, ~ 1 per 44 bp, capturing 56% of common variants and 32% of all variants with a minor allele frequency greater than 0.005 in the global population), to identify quantitative trait loci (QTL) and systematically investigate the genetic architecture of growth rates across ten environmental conditions. In total, we identified 349 QTL (ranging from 18 to 49 QTL per growth condition) that explained between 60% and 100% of narrow sense heritability across traits. The high power and resolution of CYClones revealed that growth traits exhibited distinct, condition-specific genetic architectures with extensive allelic heterogeneity, where a QTL was the result of multiple tightly linked causal variants. We also observed pleiotropy among QTL with complex, trait-dependent allele effects that are also consistent with allelic heterogeneity. Genetic complexity varied widely, with some traits showing nearly Mendelian architectures, while others were highly polygenic. Introgressed loci played a prominent role in the landscape of growth rate QTL, including a QTL localized to a 2.4 kb interval in the PCA1 cadmium transporter that explains 72% of variation in cadmium resistance and is largely driven by an introgression, and a non-additive interaction between the GAL3 regulator and introgressed GAL1/7/10 alleles, extending a previously described three-locus GAL-pathway incompatibility to a four-locus interaction. In both cadmium and galactose conditions, we show that allelic variation at a small number of loci stratifies the population into regulatory or physiological subgroups, each with distinct genetic architectures, a specific manifestation of epistasis we term allele-dependent stratification. Collectively, our results provide novel insights into the genetics of growth rates in budding yeast, the architectural features of genetic complexity, and demonstrate that CYClones is a powerful platform for revealing the molecular basis of complex trait variation.

Exocytotic sperm remodeling is essential for fertilization, yet whether conserved molecular mechanisms underlie this process across species remains unclear. In Caenorhabditis elegans, membranous organelle fusion (MOF), an exocytotic event cytologically analogous to the mammalian acrosome reaction (ASR), occurs during spermiogenesis and likely contributes to the acquisition of fertilization competence. Here, we identify DDI-4, a benzylamine analog as a small-molecule inducer of both MOF and ASR, revealing a shared sensitivity between these evolutionarily distant systems. DDI-4-induced MOF was selectively impaired in spermatids from males raised at elevated temperatures, whereas conventional protease-induced MOF remained unaffected. Through forward genetics, we isolated the nyg20 mutant, which was specifically defective in DDI-4 responsiveness. Complementation and genetic analyses suggested that the nyg20 phenotype is associated with impaired function of nsun-2, encoding a tRNA methyltransferase, despite the absence of detectable mutations in the nsun-2 coding, intronic, and flanking regions. Consistent with this, an nsun-2 deletion mutant exhibited defects in temperature-sensitive MOF and meiosis. In silico docking analysis further implicated sphingosine kinases (SPHKs) as candidate targets of DDI-4; indeed, loss of sphk-1 phenocopied the nsun-2 mutant. Moreover, we tested sphingosine (SPH) and its analog FTY720 as MOF activators, using mutants lacking sphk-1 or spin-4, which encodes a transporter of phosphorylated SPH. Intriguingly, DDI-4 and SPH activated MOF in an SPHK-1-dependent but SPIN-4-independent manner, whereas FTY720 required both SPHK-1 and SPIN-4 for MOF activation. Because DDI-4 lacks hydroxyl groups that SPHKs typically phosphorylate, these findings suggest that SPHK-1 may function not only as a kinase but also as a scaffold for downstream signaling. Together, our results reveal a temperature-sensitive, NSUN-2-dependent SPH-mediated signaling axis that regulates organelle exocytosis during spermiogenesis and suggest an evolutionarily conserved mechanism underlying fertilization competence.

Alpharetroviruses are an important group of pathogens that are known for causing leukemias and tumors and were historically considered to be restricted to avian hosts. The identification of alpharetrovirus-like envelopes in bat genomes has hinted at a potentially wider host range, although their relations to modern alpharetroviruses and distribution remains unclear. Through a paleovirological screening of 818 vertebrate genomes we identified CHIRalphaEnv, a lineage that belongs firmly within alpharetroviruses, and emerged from a cross-class transmission from saurian hosts. We determine that CHIRalphaEnv envelope genes have been co-opted across bats on eight separate occasions between 43.8 and 18.9 million years ago and are preserved in most bat genomes screened. CHIRalphaEnv elements encode full-length envelope proteins and have been maintained under purifying selection, demonstrating multiple instances of exaptation by their bat hosts and a likely ubiquitous function. We observe high expression levels of CHIRalphaEnv envelopes in endometrium tissue from Carollia perspicillata, suggesting an involvement in reproductive function. We find CHIRalphaEnv sequence relatives in multiple mammalian clades (Afrotherians, rodents and bats), expanding the host range and extending origins of alpharetroviruses beyond 43 million years. We also propose the first mammalian co-opted Endogenous retrovirus (ERV) derived from an Alpharetrovirus envelope and explore the convergent functional recruitment of CHIRalphaEnv in hemochorial placentation in bats, elephant shrews and spiny mice. These findings highlight alpharetroviruses as a previously underappreciated source of functional exaptation in mammals.

[This corrects the article DOI: 10.1371/journal.pgen.1006505.].

Gene length is a peculiar genomic feature that exhibits minimal variation within domains of life, suggesting universal underlying constraints. The length of a gene is primarily influenced by its function, expression level, and mutation risk. Interestingly, many of these factors vary depending on whether the gene is located on the leading or lagging strand of DNA replication. Studies in bacterial species E. coli and B. subtilis have shown that genes tend to be shorter on the lagging strand, potentially reflecting selection to minimize head-on encounters between the replication and transcription machinery. However, the universality of strand-specific constraints on gene length and the evolutionary basis remain unexplored. Here, using comparative genomics, we analyzed gene lengths in the bacterial domain and revealed a non-neutral distribution of gene lengths across leading and lagging strands. Genes and operons are consistently shorter on the lagging strand, irrespective of essentiality or functionality. The length restriction was more pronounced in bacterial species with a dual DNA polymerase mode of replication, which may experience severe head-on collisions between replication and transcription. Remarkably, we found that with increasing length of transcription units, substitution rates increased in the promoters on the lagging strand rather than the coding sequences, revealing a length-dependent and lagging strand-specific cis-regulatory mutational susceptibility. Together, we uncovered a pervasive selection pressure that optimizes gene lengths in a DNA strand-specific manner across bacteria to preserve the genetic integrity of promoters.

Pigmentation plays multiple important roles in development, physiology and evolution. Melanization of the insect cuticle requires dopamine as a precursor of melanin and involves key enzymes in dopamine biosynthesis including Tyrosine hydroxylase (TH) and Dopa decarboxylase (Ddc). Some studies have hinted that disruption of the evolutionarily conserved Hippo signaling pathway, which has been primarily studied in the context of tissue growth, may lead to changes in cuticle pigmentation in the fruit fly Drosophila melanogaster. However, to our knowledge, there have not been any systematic investigations into their potential mechanistic links. In this study, we identified that all genes that comprise the canonical Hippo signaling pathway [hippo (hpo), salvador (sav), mats, warts (wts), yorkie (yki) and scalloped (sd)] are involved in cuticle pigmentation in the fly notum based on tissue-specific gene knock-down/out experiments and epistatic analysis. Despite the notable divergence of pigmentation mechanisms between invertebrates and vertebrates, these phenotypes can often be rescued by the human orthologs of corresponding fly genes. While we find that manipulation of Hippo signaling in dopaminergic neurons does not affect global dopamine levels in the fly brain, developmental inhibition of this pathway can increase dopamine levels in the fly head, indicating that the mechanism by which dopamine levels are regulated in the nervous system is distinct from that in epithelial cells. Through single nuclei RNA sequencing of the developing fly nota and subsequent functional studies of differentially expressed genes that are altered upon inhibition of Hippo signaling, we found many genes that contribute to cuticle pigmentation downstream of Hippo signaling. We conclude that regulation of cuticle pigmentation by canonical Hippo signaling acts through multiple downstream genes rather than directly through TH and Ddc. We also propose that the Drosophila melanogaster cuticle may serve as a useful platform to identify previously uncharacterized mediators of Hippo signaling as well as an in vivo experimental system to test the functionality of rare genetic variants found in human Hippo signaling orthologs associated with a variety of diseases.

Gene amplification is a potent driver of evolution and is thought to contribute to genetic diseases, including cancer. The yeast Saccharomyces cerevisiae is a powerful organism for understanding amplification mechanisms. When yeast is grown long term in sulfate-limiting chemostats, amplification of the gene that encodes the primary sulfate transporter, SUL1, is a common outcome. Here we describe a form of SUL1 amplification in which multiple copies of the right terminal region of chromosome II are appended in tandem to a native telomere. We find this form of amplicon when we delete the origin of replication next to SUL1 or delete a variety of genes involved in DNA metabolism. It is the only form of amplification found in a yku70Δ mutant suggesting that telomeres are involved. We propose that these terminal addition events occur when a destabilized 3' G1-3T telomeric sequence invades a short (~7 bp) internal telomere sequence (ITS) to begin a form of microhomology-mediated break-induced replication (mmBIR) that has been documented in type-I survivors of telomerase mutants. In addition to amplification of the right end of chromosome II we also find that telomeres containing the sub-telomeric repeat Y' experience similar tandem amplification events and show that their formation is reduced in a pol32Δ mutant, a gene involved in mmBIR. Within individual amplicons the expanded ITSs and Y's are nearly identical, suggesting that the multiple copies of the amplified region are generated in a single mmBIR event that we describe as pseudo-rolling circle mmBIR. A similar amplification event at the P-telomere of human chromosome 18 has four copies of a ~ 54 kb region separated by ITSs of nearly identical size. This finding suggests that these additional copies of the terminal fragment of human chromosome 18 arose by the same pseudo-rolling circle mechanism, perhaps during a period of telomeric stress.

The SKN-1/Nrf transcription factor family is integral to metabolic homeostasis. There are three SKN-1 isoforms in Caenorhabditis elegans, each with different functions. One of these, SKN-1B, is expressed specifically in neurons and controls hermaphrodite behaviour in response to food. In a laboratory environment C. elegans hermaphrodites must allocate energy efficiently between exploratory food-seeking behaviour, reproduction, and survival, whereas males have to balance both food-seeking with mate-seeking exploratory behaviours. Here, we evaluate the role of SKN-1B in male behaviour and show that SKN-1B acts in a sexually dimorphic manner to control exploratory behaviour, mitochondrial morphology, and mitochondrial function. Moreover, we show that SKN-1B is expressed in a sexually dimorphic pattern, and that SKN-1B influences gene expression on a much broader scale in males compared to hermaphrodites. This analysis identified a neuronal signalling pathway, specifically in males between SKN-1B, the TGF-β ligand DAF-7 and the chemosensory regulator ODR-10, and that this pathway contributes to increased exploratory behaviour in skn-1b mutant males. Taken together our findings identify SKN-1B as a sex-specific neuronal switch to control food searching and mating behaviours. Sexual dimorphism is essential for optimizing survival and reproductive success and our findings establish SKN-1B as a regulator of sex-specific behavioural and metabolic traits. This work provides new insights into neuronal regulation of metabolism and behaviour, with implications for sex-specific physiological adaptations in other species.

Ongoing climate change is driving unprecedented environmental fluctuations, with extreme events predicted to increase in frequency, intensity and duration. Among climatic parameters, temperature is expected to fluctuate the most by the end of the century and its elevation has already demonstrated to pose a major challenge to plant health. In this context, understanding how temperature modulates plant-pathogen interactions and their underlying genetic architecture is critical. Bacterial wilt, caused by strains of the Ralstonia solanacearum species complex, is a devastating disease affecting many plant species. Genetic resistance remains the most effective control strategy. In tomato, resistance is quantitative and mostly relies on quantitative trait loci (QTLs) bwr-6 and bwr-12. However, as in other crops, high temperature and humidity can compromise this resistance in commercial tomato cultivars. We investigated temperature-dependent quantitative disease resistance (QDR) using a panel of 189 wild tomato accessions, predominantly Solanum pimpinellifolium, representing genetic diversity from contrasting ecological conditions. Disease progression was monitored from three to ten days post-inoculation at 28 °C and 32 °C, using a time-course phenotyping approach. Genome-wide association (GWA) analyses were performed, based on daily symptom scores and two reference genomes, to account for structural variations and improve QTL detection. This strategy identified 44 candidate genes and revealed a temporally dynamic genetic architecture of the plant response. Strikingly, no candidate genes were shared between temperatures, supporting distinct genetic determinants under different temperature conditions. Many candidate genes were expressed in roots and belong to gene families involved in plant immunity, with two candidates co-localizing with bwr-6 and bwr-12, whose causal genes remain unknown. Altogether, our findings demonstrate that resistance to bacterial wilt in wild tomato is flexible, environment-dependent, and temporally dynamic, highlighting the importance of integrating environmental context and genomic diversity to better understand plant-pathogen interactions.

Tetraploid potato is the most important vegetable food crop in the world. However, genetic gains from modern breeding efforts have been limited due to tetrasomic inheritance, the accumulation of deleterious mutations during domestication, and subsequent clonal propagation during modern breeding. In this study, we analyzed previously identified evolutionarily constrained genomic regions in the potato genome relative to a breeding panel of tetraploid potato clones derived from elite cultivars (the MASPOT panel). We demonstrate a significant association between derived allele frequency (DAF) and both positive (constrained) and negative (excess of substitutions relative to neutrality, i.e., hypervariable) nucleotide conservation scores (GERP scores) in the breeding panel, indicating that negative GERP scores can annotate sites affected by positive selection or other non-neutral processes affecting population allele frequency. The deep phylogeny approach can be leveraged to alleviate inbreeding in potatoes through the qualification of causative alleles in tetraploids, offering a valuable resource for potato genetic improvement by molecular breeding. Estimates of genetic load within the tetraploid clones reveal that heterozygous loads vastly exceed homozygous loads for deleterious alleles, consistent with masking of recessive mutations. Deleterious load was significantly correlated with several trait phenotypes but did not improve prediction accuracy of any traits in the tetraploid panel. This could be due to the increased complexity of tetrasomic inheritance, including more effective load complementation, and/or a higher proportion of heterozygosity in tetraploid compared to diploid potato. Intriguingly, the hypervariable load correlated significantly with several phenotypes and improved genomic prediction accuracy of yield by 5% relative to a negative control (permuted loads). This indicates that the inferred hypervariable sites from Solanaceae evolutionary information may contain genetic information relevant for breeding, and that, in contrast to current practice, it is relevant to include and further explore sites with negative GERP scores in general.

The ubiquitin proteasome system (UPS) is the primary mechanism for targeted protein degradation in eukaryotic cells. Dysfunction of this system is a driver of human disease and a hallmark of aging and late-onset neurodegenerative disorders. Understanding the mechanisms that ensure robust protein turnover may provide new avenues for treatment in these contexts. E3 ubiquitin ligases play critical roles in supplying ubiquitinated substrates to the proteasome, with HUWE1 being an enormous, versatile, and highly conserved member of this family. Here, we show that the C. elegans HUWE1 ortholog EEL-1 contributes to robust protein turnover, particularly during conditions that challenge the proteolytic capacity of the proteasome. We demonstrate that the ability of EEL-1/HUWE1 to safeguard protein turnover requires the HECT-type ubiquitin ligase activity, supporting a model in which EEL-1 ensures degradation via substrate ubiquitination. EEL-1 contains extensive lysine-deficient regions, found at conserved locations in its substrate-binding arena. Through unbiased mutagenesis screening and precise engineering of the EEL-1 protein, we uncover that introducing lysine residues into these regions is detrimental to UPS function and to animal physiology. Together, our findings indicate a central and evolutionarily ancient role for EEL-1/HUWE1 in maintaining optimal UPS function and support targeting this E3 for therapeutic manipulation.

Acting as the central endocrine hub, the pituitary gland is closely related to the mechanism of adaptation to high-altitude hypoxia. Here, by integratively combining long-read (Oxford Nanopore) and short-read (Illumina) single-cell sequencing approaches, we profiled pituitaries from Diqing Tibetan pigs, inhabiting high-altitude environments (3,200 m) and Diannan small-ear pigs from low-altitude regions (500 m), thereby generating a full-length single-cell atlas, which in turn enabled the identification of molecular mechanisms potentially underlying adaptation to high-altitude hypoxia stress. Systematically delineating pituitary structure and transcriptional dynamics, we profiled 27,339 single cells encompassing 28,932 expressed genes. Leveraging unsupervised clustering coupled with marker-based annotation, we identified ten major cell types. Expression profiling of 20 canonical marker genes revealed pronounced cell-type-specific expression patterns, ten of which were independently validated by immunofluorescence, thus substantiating the accuracy of cell-type annotation. Gene-ontology enrichment analysis further suggested that upregulated genes were predominantly involved in oxidative metabolism and energy production, whereas downregulated genes were significantly associated with protein biosynthesis and translation processes, indicating a functional reprogramming of metabolic pathways. Moreover, comparative analyses between breeds and cell-cell communication analyses highlighted pathway shifts, including broad upregulation of the collagen family and four ligand-receptor pairs that may mediate pituitary intercellular coordination. In parallel, transcription-factor activity analysis nominated several regulators, including EBF3, DBX2, and TCF21, which may collectively contribute to altitude-associated adaptation. Finally, integrating long-read sequencing data revealed widespread transcript isoform diversity, with ~28% novel annotations, indicating considerable isoform complexity in pigs. Our findings delineate cellular heterogeneity, inferred intercellular communication networks, and transcript-isoform diversity in the porcine pituitary, thereby providing a cell-resolved resource for understanding pituitary features associated with high-altitude environments.

Previous research suggests that social isolation induces changes in gene expression that encode a starvation-like brain state and reduce sleep. However, the extent to which social isolation alters behaviors via sex-specific brain changes is unclear. Here, we use Drosophila melanogaster to explore sex differences in isolation-induced behavioral and transcriptomic changes. Male and female adult flies were isolated for seven days, and multiple behavioral sex-based differences were identified through tests of activity, motivation, aggression, and sugar preference. RNA-seq analysis also identified several candidate genes that were associated with sex differences in isolation-induced behavioral changes. Takeout (to) expression and sucrose selection were upregulated exclusively in females following social isolation. Following to knockdown in to-expressing cells, sucrose preference decreased in socially isolated females but increased in males. Overall, our results suggest that manipulating to expression influences sucrose choice in opposite directions between females and males following social isolation. It is possible that isolation-induced to overexpression in non-neuronal cells in the female head could contribute to sex differences in this behavior.

Abscisic acid (ABA) acts as a key signalling molecule that mediates plant responses to environmental cues as well as plant growth and development. Stress-induced and developmental changes in ABA content trigger a myriad of post-transcriptional and transcriptional events. Yet, ABA-dependent transcriptional responses are context dependent, and their temporal dynamics in roots under non-stress conditions remain poorly resolved. In this study, we characterised the hallmarks of ABA signalling and responses in the poplar root transcriptome (Populus nigra L.). We disturbed ABA homeostasis by exogenous ABA treatments, and we combined time-resolved transcriptomics with unsupervised gene network analysis to identify ABA-activated and ABA-inactivated gene co-expression modules. Considering the temporal dynamics of transcriptional events, we predicted the primary targets of the ABA signal, characterised early responding ABA-dependent processes, identified hub genes and revealed their putative functional links. We demonstrated that the properties of a master ABA-activated module induced by exogenous treatments were preserved in the transcriptome response to osmotic stress, revealing a core gene set of ABA-dependent stress responses. Our work sheds light on ABA repression of gene expression, the reprogramming of metabolism and the leaf-senescence pathway. Based on current functional knowledge and phylogenetic information, including poplar-specific features, we proposed a working model of ABA action on root transcriptome in poplar that integrates master genes, key responsive processes, and their putative regulatory architecture.