wgd v2: a suite of tools to uncover and date ancient polyploidy and whole-genome duplication

A high-quality genome assembly of Annona squamosa (custard apple) provides functional insights into an emerging fruit crop

Annona squamosa, also known as custard apple, is an emerging fruit crop with medicinal significance. We constructed a high-quality genome of A. squamosa along with transcriptome data to gain insights into its phylogeny, evolution, and demographic history. The genome has a size of 730.4 Mb with an N50 value of 93.2 Mb assembled into seven pseudochromosomes. The demographic history showed a continuous decline in the effective population size of A. squamosa. Phylogenetic analysis revealed that magnoliids were sister to eudicots. Genome syntenic and Ks distribution analyses confirmed the absence of a recent whole-genome duplication event in the A. squamosa. Gene families related to photosynthesis, oxidative phosphorylation, and plant thermogenesis were found to be highly expanded in the genome. Comparative analysis with other magnoliids revealed the adaptive evolution in the genes of flavonoid biosynthesis pathway, amino sugar, nucleotide sugar and sucrose metabolism, conferring medicinal value, and enhanced hexose sugar accumulation. In addition, we performed genome-wide identification of SWEET genes. Our high-quality genome and evolutionary insights of this emerging fruit crop, thus, serve as a valuable resource for advancing studies in functional genomics, evolutionary biology, and crop improvement.

The expanded Bostrychia moritziana genome unveils evolution in the most diverse and complex order of red algae

Red algae are an ancient eukaryotic lineage that were among the first to evolve multicellularity. Although they share a common origin with modern-day plants and display complex multicellular development, comprehensive genome data from the most highly evolved red algal groups remain scarce. Here, we present a chromosome-level genome assembly of Bostrychia moritziana, a complex red seaweed in the Rhodomelaceae family of the Ceramiales-the largest and most diverse order of red algae. Contrary to the view that red algal genomes are typically small, we report significant genome size expansion in Bostrychia and other Ceramiales, which represents one of at least three independent expansion events in red algal evolution. Our analyses suggest that these expansions do not involve polyploidy or ancient whole-genome duplications, but in Bostrychia rather stem from the proliferation of a single lineage of giant Plavaka DNA transposons. Consistent with its enlarged genome, Bostrychia has an increased gene content shaped by de novo gene emergence and amplified gene families in common with other Ceramiales, providing insight into the genetic adaptations underpinning this successful and species-rich order. Finally, our sex-specific assemblies resolve the UV sex chromosomes in Bostrychia, which feature expanded gene-rich sex-linked regions. Notably, each sex chromosome harbors a three amino acid loop extension homeodomain (TALE-HD) transcription factor orthologous to ancient regulators of haploid-diploid transitions in other multicellular lineages. Together, our findings offer a unique perspective of the genomic adaptations driving red algal diversity and demonstrate how this red seaweed lineage can provide insight into the evolutionary origins and universal principles underpinning complex multicellularity.

The genomic insights of intertidal adaptation in Bryopsis corticulans

Many marine green algae thrive in intertidal zones, adapting to complex light environments that fluctuate between low underwater light and intense sunlight. Exploring their genomic bases could help to comprehend the diversity of adaptation strategies in response to environmental pressures. Here, we developed a novel and practical strategy to assemble high-confidence algal genomes and sequenced a high-quality genome of Bryopsis corticulans, an intertidal zone macroalga in the Bryopsidales order of Chlorophyta that originated 678 million years ago. Comparative genomic analyses revealed a previously overlooked whole genome duplication event in a closely related species, Caulerpa lentillifera. A total of 100 genes were acquired through horizontal gene transfer, including a homolog of the cryptochrome photoreceptor CRY gene. We also found that all four species studied in Bryopsidales lack key photoprotective genes (LHCSR, PsbS, CYP97A3, and VDE) involved in the xanthophyll cycle and energy-dependent quenching processes. We elucidated that the expansion of light-harvesting antenna genes and the biosynthesis pathways for siphonein and siphonaxanthin in B. corticulans likely contribute to its adaptation to intertidal light conditions. Our study unraveled the underlying special genetic basis of Bryopsis' adaptation to intertidal environments, advancing our understanding of plant adaptive evolution.

Genome-wide identification of the Medicago sativa L. MYB family and its transcriptional dynamics during pollen development

BACKGROUND

The myeloblastosis (MYB) gene family plays crucial roles in the development of anthers and the establishment of pollen morphology during plant growth. However, little is known about the role of MYB transcription factors in pollen development in alfalfa (Medicago sativa L.).

RESULTS

In this study, we identified 161 MsMYBs in the alfalfa genome, including 34 1R-MYBs, 123 R2R3-MYBs, 3 3R-MYBs, and 1 4R-MYBs (categorized by the number of repeats). These were classified into six subfamilies based on the phylogenetic analysis, conserved structural domains, and gene structures. All MsMYBs were predicted to be hydrophilic and localized in the cell nucleus. The promoter regions contained three classes of cis-regulatory elements related to pollen development, as well as a variable set of functionally diverse elements, including hormone responsiveness, growth and development, and stress responsiveness elements. A transcriptome and qRT-PCR analysis revealed 12 MsMYBs with anther-specific expression and exhibited distinct expression patterns. Some MsMYBs showed a close phylogenetic relationship with Arabidopsis MYBs related to pollen development, such as MsMYB49 and MsMYB100, were found to be localized in the nucleus upon subcellular localization analysis. This genetic proximity suggests a potential role for these MsMYBs in the developmental processes of pollen.

CONCLUSIONS

This study provides a comprehensive understanding of MsMYBs in alfalfa and elucidates their potential roles and expression patterns in pollen development.

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.

Lineage-Specific Class-A GPCR Dynamics Reflect Diverse Chemosensory Adaptations in Lophotrochozoa

Sensing external chemosensory cues via Class-A G protein-coupled receptors (GPCRs) is crucial for a multitude of behavioral and biological functions, influencing animal evolution and ecological adaptations. While extensively studied in vertebrates and echinoderms, the role of GPCR-mediated chemoreception in major protostome clades like Lophotrochozoa remains obscure despite their remarkable ecological adaptations across diverse aquatic and terrestrial environments. Utilizing 238 lophotrochozoan genomes across eight phyla, we conducted a large-scale comparative genomics analysis to identify lineage-specific expansions of Class-A GPCR subsets that are likely adapted for chemoreception. Using phylogeny and orthology-inference-based clustering, we distinguished these expansions from conserved orthogroups of prospective endogenous ligand-binding Class-A GPCR subsets. Across phyla, lineage-specific expansions correlated with adaptations to various habitats, ecological niches, and lifestyles, while the influence of whole-genome duplications in driving these lineage-specific expansions appeared to be less significant. Species adapted to various coastal, freshwater, and terrestrial habitats across several classes of Mollusca, Annelida, and other analyzed phyla exhibit large and diverse lineage-specific expansions, while adaptations to extreme deep-sea environments, parasitic lifestyles, sessile behaviors, or alternative chemosensory mechanisms consistently exhibit reductions. Sequence heterogeneity, signatures of positive selection, and conformational flexibility in ligand-binding pockets further highlighted adaptations to environmental signals. In summary, the evolutionary dynamics of Class-A GPCRs in lophotrochozoans reveal a widespread pattern of lineage-specific expansions driven by adaptations for chemoreception across diverse environmental niches, mirroring the trends and prominent roles seen in deuterostome lineages. The comprehensive datasets spanning numerous genomes offer a valuable foundation for advancing GPCR-mediated chemoreception studies in Lophotrochozoa.

Genome Assembly of a Living Fossil, the Atlantic Horseshoe Crab Limulus polyphemus, Reveals Lineage-Specific Whole-Genome Duplications, Transposable Element-Based Centromeres, and a ZW Sex Chromosome System

Horseshoe crabs, considered living fossils with a stable morphotype spanning ∼445 million years, are evolutionarily, ecologically, and biomedically important species experiencing rapid population decline. Of the four extant species of horseshoe crabs, the Atlantic horseshoe crab, Limulus polyphemus, has become an essential component of the modern medicine toolkit. Here, we present the first chromosome-level genome assembly, and the most contiguous and complete assembly to date, for L. polyphemus using nanopore long-read sequencing and chromatin conformation analysis. We find support for three horseshoe crab-specific whole-genome duplications, but none shared with Arachnopulmonata (spiders and scorpions). Moreover, we discovered tandem duplicates of endotoxin detection pathway components Factors C and G, identify candidate centromeres consisting of Gypsy retroelements, and classify the ZW sex chromosome system for this species and a sister taxon, Carcinoscorpius rotundicauda. Finally, we revealed this species has been experiencing a steep population decline over the last 5 million years, highlighting the need for international conservation interventions and fisheries-based management for this critical species.

Fusion, fission, and scrambling of the bilaterian genome in Bryozoa

Groups of orthologous genes are commonly found together on the same chromosome over vast evolutionary distances. This extensive physical gene linkage, known as macrosynteny, is seen between bilaterian phyla as divergent as Chordata, Echinodermata, Mollusca, and Nemertea. Here, we report a unique pattern of genome evolution in Bryozoa, an understudied phylum of colonial invertebrates. Using comparative genomics, we reconstruct the chromosomal evolutionary history of five bryozoans. Multiple ancient chromosome fusions followed by gene mixing led to the near-complete loss of bilaterian linkage groups in the ancestor of extant bryozoans. A second wave of rearrangements, including chromosome fission, then occurred independently in two bryozoan classes, further scrambling bryozoan genomes. We also discover at least five derived chromosomal fusion events shared between bryozoans and brachiopods, supporting the traditional but highly debated Lophophorata hypothesis and suggesting macrosynteny to be a potentially powerful source of phylogenetic information. Finally, we show that genome rearrangements led to the dispersion of genes from bryozoan Hox clusters onto multiple chromosomes. Our findings demonstrate that the canonical bilaterian genome structure has been lost across all studied representatives of an entire phylum, and reveal that linkage group fission can occur very frequently in specific lineages.

Phylogenomic analysis of target enrichment and transcriptome data uncovers rapid radiation and extensive hybridization in the slipper orchid genus Cypripedium

BACKGROUND AND AIMS

Cypripedium is the most widespread and morphologically diverse genus of slipper orchids. Despite several published phylogenies, the topology and monophyly of its infrageneric taxa remained uncertain. Here, we aimed to reconstruct a robust section-level phylogeny of Cypripedium and explore its evolutionary history using target capture data for the first time.

METHODS

We used the orchid-specific bait set Orchidaceae963 in combination with transcriptomic data to reconstruct the phylogeny of Cypripedium based on 913 nuclear loci, covering all 13 sections. Subsequently, we investigated discordance among nuclear and chloroplast trees, estimated divergence times and ancestral ranges, searched for anomaly zones, polytomies and diversification rate shifts, and identified potential gene (genome) duplication and hybridization events.

KEY RESULTS

All sections were recovered as monophyletic, contrary to the two subsections within sect. Cypripedium. The two subclades within this section did not correspond to its subsections but matched the geographical distribution of their species. Additionally, we discovered high levels of discordance in the short backbone branches of the genus and within sect. Cypripedium, which can be attributed to hybridization events detected based on phylogenetic network analyses, and incomplete lineage sorting caused by rapid radiation. Our biogeographical analysis suggested a Neotropical origin of the genus during the Oligocene (~30 Ma), with a lineage of potentially hybrid origin spreading to the Old World in the Early Miocene (~22 Ma). The rapid radiation at the backbone probably occurred in Southeast Asia around the Middle Miocene Climatic Transition (~15-13 Ma), followed by several independent dispersals back to the New World. Moreover, the glacial cycles of the Pliocene-Quaternary may have contributed to further speciation and reticulate evolution within Cypripedium.

CONCLUSIONS

Our study provides novel insights into the evolutionary history of Cypripedium based on high-throughput molecular data, shedding light on the dynamics of its distribution and diversity patterns from its origin to the present.

Chromosome scale genome assembly and annotation of coconut cultivar Chowghat Green Dwarf

The high-quality genome of coconut (Cocos nucifera L.) is a crucial resource for enhancing agronomic traits and studying genome evolution within the Arecaceae family. We sequenced the Chowghat Green Dwarf cultivar, which is resistant to the root (wilt) disease, utilizing Illumina, PacBio, ONT, and Hi-C technologies to produce a chromosome-level genome of ~ 2.68 Gb with a scaffold N50 of 174 Mb; approximately 97% of the genome could be anchored to 16 pseudo-molecules (2.62 Gb). In total, 34,483 protein-coding genes were annotated; the BUSCO completeness score was 96.80%, while the k-mer completeness was ~ 87%. The assembled genome includes 2.19 Gb (81.64%) of repetitive sequences, with long terminal repeats (LTRs) constituting the most abundant class at 53.76%. Additionally, our analysis confirms two whole-genome duplication (WGD) events in the C. nucifera lineage. A genome-wide analysis of LTR insertion time revealed ancient divergence and proliferation of copia and gypsy elements. In addition, 1368 RGAs were discovered in the CGD genome. We also developed a web server 'Kalpa Genome Resource' ( http://210.89.54.198:3000/ ), to manage and store a comprehensive array of genomic data, including genome sequences, genetic markers, structural and functional annotations like metabolic pathways, and transcriptomic profiles. The web server has an embedded genome browser to analyze and visualize the genome, its genomics elements, and transcriptome data. The in-built BLAST server allows sequence homology searches against genome, annotated transcriptome & proteome sequences. The genomic dataset and the database will support comparative genome analysis and can expedite genome-driven breeding and enhancement efforts for tapping genetic gains in coconut.

Genome of the most noxious weed water hyacinth (Eichhornia crassipes) provides insights into plant invasiveness and its translational potential

The invasive character of Eichhornia crassipes (water hyacinth) is a major threat to global biodiversity and ecosystems. To investigate the genomic basis of invasiveness, we performed the genome and transcriptome sequencing of E. crassipes and reported the genome of 1.11 Gbp size with 63,299 coding genes and N50 of 1.98 Mb. We confirmed a recent whole genome duplication event in E. crassipes that resulted in high intraspecific collinearity and significant expansion in gene families. Further, the orthologs gene clustering analysis and comparative evolutionary analysis with 14 other aquatic invasive and non-invasive angiosperm species revealed adaptive evolution in genes associated with plant-pathogen interaction, hormone signaling, abiotic stress tolerance, heavy metals sequestration, photosynthesis, and cell wall biosynthesis with highly expanded gene families, which contributes toward invasive characteristics of the water hyacinth. However, these characteristics also make water hyacinth an excellent candidate for biofuel production, phytoremediation, and other translational applications.

Crossroads of assembling a moss genome: navigating contaminants and horizontal gene transfer in the moss Physcomitrellopsis africana

The first chromosome-scale reference genome of the rare narrow-endemic African moss Physcomitrellopsis africana (P. africana) is presented here. Assembled from 73 × Oxford Nanopore Technologies (ONT) long reads and 163 × Beijing Genomics Institute (BGI)-seq short reads, the 414 Mb reference comprises 26 chromosomes and 22,925 protein-coding genes [Benchmarking Universal Single-Copy Ortholog (BUSCO) scores: C:94.8% (D:13.9%)]. This genome holds 2 genes that withstood rigorous filtration of microbial contaminants, have no homolog in other land plants, and are thus interpreted as resulting from 2 unique horizontal gene transfers (HGTs) from microbes. Further, P. africana shares 176 of the 273 published HGT candidates identified in Physcomitrium patens (P. patens), but lacks 98 of these, highlighting that perhaps as many as 91 genes were acquired in P. patens in the last 40 million years following its divergence from its common ancestor with P. africana. These observations suggest rather continuous gene gains via HGT followed by potential losses during the diversification of the Funariaceae. Our findings showcase both dynamic flux in plant HGTs over evolutionarily "short" timescales, alongside enduring impacts of successful integrations, like those still functionally maintained in extant P. africana. Furthermore, this study describes the informatic processes employed to distinguish contaminants from candidate HGT events.