A high-quality de novo genome assembly based on nanopore sequencing of a wild-caught coconut rhinoceros beetle (Oryctes rhinoceros)

PacBio-based de novo transcriptomics of the coconut rhinoceros beetle Oryctes rhinoceros identifies physiologically important full-length genes and sheds insights into the molecular relationship (chitin synthase) between Scarabaeidae (Coleoptera) and Hymenoptera

The sparser molecular data in non-model insects such as Oryctes rhinoceros prompted us to investigate and identify its physiologically important genes using the novel PacBio Iso-Seq Sequel II platform with single-molecule real-time (SMRT) technology. SMRT library was prepared from various tissues and sequenced. In total, 16,916,297 subreads clustered into 17,547 contigs which collapsed to form 8708 full-length sequences out of which 4352 functionally annotated transcripts were identified. Genes involved in innate immunity, growth and development, hormonal regulation, cellular process, peritrophic membrane, melanogenesis, integument, circulation, cuticle formation, glycan metabolism, etc., were identified. The transcripts' orthologues were identified predominantly in Coleoptera and Hymenoptera in which chitin synthase (CHS), toll, haemocytin, serine protease/limulus clotting factor c, vitellogenin and trehalose transporter exhibited significant molecular relationships between these two insect orders. Chitin synthase 8 (CHS-8) found in ant has been identified for the first time in the order Coleoptera. (O. rhinoceros) at the translational level and projected a potential to explore evolution (horizontal gene transfer) of CHS in insects. The findings will bridge the molecular data between the genome and transcriptome of O. rhinoceros, thus helping develop molecular targets for its control and management.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-025-04348-9.

Apicortin, a Putative Apicomplexan-Specific Protein, Is Present in Deep-Branching Opisthokonts

Apicortin, a tubulin/microtubule-binding protein, was first described in 2009 as a protein characteristic of apicomplexans; it was found to be present in all Apicomplexa genomes already sequenced. Apart from these, it was found only in Trichoplax adhaerens, the only known representative of Placozoa at the time. Subsequent analyses revealed that it is present in both closely and distantly related taxa of Apicomplexa (Chrompodellids, Squirmids, Dinoflagellates, and Perkinsids, i.e., in Myzozoa). On the other hand, it turned out that it is also present in early-branching fungi that reproduce by zoospores. Now, we have shown that apicortin is found in many deep-branching opisthokonts. In addition to these fungi and T. adhaerens, it is also present in other simple animals, including further Placozoa and Ctenophora, and another opisthokont clade, choanoflagellates. However, apicortin-homologous sequences detected in the genomes/transcriptomes of bilaterian animals are the result of contamination.

Diverse viral communities inhabit the guts of date palm rhinoceros beetles (Oryctes spp.)

Two species of palm tree pests, Oryctes elegans and Oryctes agamemnon (Coleoptera: Scarabaeidae), cause significant damage to date palm trees (Phoenix dactylifera) in many countries in the Middle East. Despite several decades of research and the implementation of numerous control strategies, including mechanical, chemical, regulatory, and biosecurity measures, managing these pests remains challenging. Control of O. rhinoceros in the Pacific using an entomopathogenic virus is a landmark of classical biological control. In this study, we used a transcriptomic approach to examine the virome of populations of two Oryctes species across various regions in southern Iran, with the hope of discovering natural viral pathogens as potential biocontrol agents. Total RNA was extracted from a pool of larval gut samples and sequenced using the Illumina NovaSeq 6000. After analysing the RNA-Seq data, 28 novel virus sequences, including a diverse range of RNA and DNA viruses, were identified. Phylogenetic analyses revealed that these newly discovered viruses are evolutionarily linked with other closely related members in several families, including Partitiviridae, Picobirnaviridae, Totiviridae, Dicistroviridae, Tombusviridae, Nodaviridae, Potyviridae, Endornaviridae, Circoviridae and some unassigned viruses such as Negevirus and Jivivirus. Given the similarity of some of these viruses to plant viruses, and viruses reported from fungi and protists and their unclear host association, we have tentatively named them "Oryctes-associated viruses." This study uncovers the great diversity of viruses in Oryctes species; however, further studies are necessary to determine their natural incidence, geographical distribution, impact on their hosts, and their potential as biological control agents for these significant date palm pests.

Identification of non-model mammal species using the MinION DNA sequencer from Oxford Nanopore

Background

The Neotropics harbors the largest species richness of the planet; however, even in well-studied groups, there are potentially hundreds of species that lack a formal description, and likewise, many already described taxa are difficult to identify using morphology. Specifically in small mammals, complex morphological diagnoses have been facilitated by the use of molecular data, particularly from mitochondrial sequences, to obtain accurate species identifications. Obtaining mitochondrial markers implies the use of PCR and specific primers, which are largely absent for non-model organisms. Oxford Nanopore Technologies (ONT) is a new alternative for sequencing the entire mitochondrial genome without the need for specific primers. Only a limited number of studies have employed exclusively ONT long-reads to assemble mitochondrial genomes, and few studies have yet evaluated the usefulness of such reads in multiple non-model organisms.

Methods

We implemented fieldwork to collect small mammals, including rodents, bats, and marsupials, in five localities in the northern extreme of the Cordillera Central of Colombia. DNA samples were sequenced using the MinION device and Flongle flow cells. Shotgun-sequenced data was used to reconstruct the mitochondrial genome of all the samples. In parallel, using a customized computational pipeline, species-level identifications were obtained based on sequencing raw reads (Whole Genome Sequencing). ONT-based identifications were corroborated using traditional morphological characters and phylogenetic analyses.

Results

A total of 24 individuals from 18 species were collected, morphologically identified, and deposited in the biological collection of Universidad EAFIT. Our different computational pipelines were able to reconstruct mitochondrial genomes from exclusively ONT reads. We obtained three new mitochondrial genomes and eight new molecular mitochondrial sequences for six species. Our species identification pipeline was able to obtain accurate species identifications for up to 75% of the individuals in as little as 5 s. Finally, our phylogenetic analyses corroborated the identifications from our automated species identification pipeline and revealed important contributions to the knowledge of the diversity of Neotropical small mammals.

Discussion

This study was able to evaluate different pipelines to reconstruct mitochondrial genomes from non-model organisms, using exclusively ONT reads, benchmarking these protocols on a multi-species dataset. The proposed methodology can be applied by non-expert taxonomists and has the potential to be implemented in real-time, without the need to euthanize the organisms and under field conditions. Therefore, it stands as a relevant tool to help increase the available data for non-model organisms, and the rate at which researchers can characterize life specially in highly biodiverse places as the Neotropics.

Low-input PacBio sequencing generates high-quality individual fly genomes and characterizes mutational processes

Long-read sequencing, exemplified by PacBio, revolutionizes genomics, overcoming challenges like repetitive sequences. However, the high DNA requirement ( > 1 µg) is prohibitive for small organisms. We develop a low-input (100 ng), low-cost, and amplification-free library-generation method for PacBio sequencing (LILAP) using Tn5-based tagmentation and DNA circularization within one tube. We test LILAP with two Drosophila melanogaster individuals, and generate near-complete genomes, surpassing preexisting single-fly genomes. By analyzing variations in these two genomes, we characterize mutational processes: complex transpositions (transposon insertions together with extra duplications and/or deletions) prefer regions characterized by non-B DNA structures, and gene conversion of transposons occurs on both DNA and RNA levels. Concurrently, we generate two complete assemblies for the endosymbiotic bacterium Wolbachia in these flies and similarly detect transposon conversion. Thus, LILAP promises a broad PacBio sequencing adoption for not only mutational studies of flies and their symbionts but also explorations of other small organisms or precious samples.

Finding divergent sequences of homomorphic sex chromosomes via diploidized nanopore-based assembly from a single male

Although homomorphic sex chromosomes can have non-recombining regions with elevated sequence divergence between its complements, such divergence signals can be difficult to detect bioinformatically. If found in genomes of e.g. insect pests, these sequences could be targeted by the engineered genetic sexing and control systems. Here, we report an approach that can leverage long-read nanopore sequencing of a single XY male to identify divergent regions of homomorphic sex chromosomes. Long-read data are used for de novo genome assembly that is diploidized in a way that maximizes sex-specific differences between its haploid complements. We show that the correct assembly phasing is supported by the mapping of nanopore reads from the male's haploid Y-bearing sperm cells. The approach revealed a highly divergent region (HDR) near the centromere of the homomorphic sex chromosome of Aedes aegypti, the most important arboviral vector, for which there is a great interest in creating new genetic control tools. HDR is located ~5Mb downstream of the known male-determining locus on chromosome 1 and is significantly enriched for ovary-biased genes. While recombination in HDR ceased relatively recently (~1.4 MYA), HDR gametologs have divergent exons and introns of protein coding genes, and most lncRNA genes became X-specific. Megabases of previously invisible sex-linked sequences provide new putative targets for engineering the genetic systems to control this deadly mosquito. Broadly, our approach expands the toolbox for studying cryptic structure of sex chromosomes.

Highly-multiplexed and efficient long-amplicon PacBio and Nanopore sequencing of hundreds of full mitochondrial genomes

BACKGROUND

Mitochondrial genome sequences have become critical to the study of biodiversity. Genome skimming and other short-read based methods are the most common approaches, but they are not well-suited to scale up to multiplexing hundreds of samples. Here, we report on a new approach to sequence hundreds to thousands of complete mitochondrial genomes in parallel using long-amplicon sequencing. We amplified the mitochondrial genome of 677 specimens in two partially overlapping amplicons and implemented an asymmetric PCR-based indexing approach to multiplex 1,159 long amplicons together on a single PacBio SMRT Sequel II cell. We also tested this method on Oxford Nanopore Technologies (ONT) MinION R9.4 to assess if this method could be applied to other long-read technologies. We implemented several optimizations that make this method significantly more efficient than alternative mitochondrial genome sequencing methods.

RESULTS

With the PacBio sequencing data we recovered at least one of the two fragments for 96% of samples (~ 80-90%) with mean coverage ~ 1,500x. The ONT data recovered less than 50% of input fragments likely due to low throughput and the design of the Barcoded Universal Primers which were optimized for PacBio sequencing. We compared a single mitochondrial gene alignment to half and full mitochondrial genomes and found, as expected, increased tree support with longer alignments, though whole mitochondrial genomes were not significantly better than half mitochondrial genomes.

CONCLUSIONS

This method can effectively capture thousands of long amplicons in a single run and be used to build more robust phylogenies quickly and effectively. We provide several recommendations for future users depending on the evolutionary scale of their system. A natural extension of this method is to collect multi-locus datasets consisting of mitochondrial genomes and several long nuclear loci at once.

Tracking Adaptive Pathways of Invasive Insects: Novel Insight from Genomics

Despite the huge human and economic costs of invasive insects, which are the main group of invasive species, their environmental impacts through various mechanisms remain inadequately explained in databases and much of the invasion biology literature. High-throughput sequencing technology, especially whole-genome sequencing, has been used as a powerful method to study the mechanisms through which insects achieve invasion. In this study, we reviewed whole-genome sequencing-based advances in revealing several important invasion mechanisms of invasive insects, including (1) the rapid genetic variation and evolution of invasive populations, (2) invasion history and dispersal paths, (3) rapid adaptation to different host plant ranges, (4) strong environmental adaptation, (5) the development of insecticide resistance, and (6) the synergistic damage caused by invasive insects and endosymbiotic bacteria. We also discussed prevention and control technologies based on whole-genome sequencing and their prospects.

The genome of the soybean gall midge (Resseliella maxima)

The cecidomyiid fly, soybean gall midge, Resseliella maxima Gagné, is a recently discovered insect that feeds on soybean plants in the Midwestern United States. R. maxima larvae feed on soybean stems that may induce plant death and can cause considerable yield losses, making it an important agricultural pest. From three pools of 50 adults each, we used long-read nanopore sequencing to assemble a R. maxima reference genome. The final genome assembly is 206 Mb with 64.88× coverage, consisting of 1,009 contigs with an N50 size of 714 kb. The assembly is high quality with a Benchmarking Universal Single-Copy Ortholog (BUSCO) score of 87.8%. Genome-wide GC level is 31.60%, and DNA methylation was measured at 1.07%. The R. maxima genome is comprised of 21.73% repetitive DNA, which is in line with other cecidomyiids. Protein prediction annotated 14,798 coding genes with 89.9% protein BUSCO score. Mitogenome analysis indicated that R. maxima assembly is a single circular contig of 15,301 bp and shares highest identity to the mitogenome of the Asian rice gall midge, Orseolia oryzae Wood-Mason. The R. maxima genome has one of the highest completeness levels for a cecidomyiid and will provide a resource for research focused on the biology, genetics, and evolution of cecidomyiids, as well as plant-insect interactions in this important agricultural pest.

Genomic resources for population analyses of an invasive insect pest Oryctes rhinoceros

Over the last few years, various types of NGS data have been accumulating for the coconut rhinoceros beetle (CRB, Oryctes rhinoceros), reflecting the growing interest in curtailing this invasive pest of palm trees. Whilst reference-free analyses of RNA-seq and RAD-seq datasets have been done for different CRB collections, recent availability of the CRB's genome assembly provides an opportunity to collate diverse data and create a reference-based population dataset. Here, I release such a dataset containing 6,725,935 SNPs and genotypes called across 393 individual samples from 16 populations, using the previously published raw sequences generated in 9 different experiments (RAD-Seq, RNA-Seq, WGS). I also provide reference-based datasets for the CRB's mitochondrial variants and for variants of its viral biocontrol agent Oryctes rhinoceros nudivirus. SNP data provide high resolution for determining the geographic origin of invasive CRB. With these genomic resources, new data can be analysed without re-processing the published samples and then integrated to expand the reference datasets.

Omics in the Red Palm Weevil Rhynchophorus ferrugineus (Olivier) (Coleoptera: Curculionidae): A Bridge to the Pest

The red palm weevil (RPW), Rhynchophorus ferrugineus (Coleoptera: Curculionidae), is the most devastating pest of palm trees worldwide. Mitigation of the economic and biodiversity impact it causes is an international priority that could be greatly aided by a better understanding of its biology and genetics. Despite its relevance, the biology of the RPW remains poorly understood, and research on management strategies often focuses on outdated empirical methods that produce sub-optimal results. With the development of omics approaches in genetic research, new avenues for pest control are becoming increasingly feasible. For example, genetic engineering approaches become available once a species's target genes are well characterized in terms of their sequence, but also population variability, epistatic interactions, and more. In the last few years alone, there have been major advances in omics studies of the RPW. Multiple draft genomes are currently available, along with short and long-read transcriptomes, and metagenomes, which have facilitated the identification of genes of interest to the RPW scientific community. This review describes omics approaches previously applied to RPW research, highlights findings that could be impactful for pest management, and emphasizes future opportunities and challenges in this area of research.

The Genome of the Soybean Gall Midge ( Resseliella maxima )

The cecidomyiid fly, soybean gall midge, Resseliella maxima Gagné, is a recently discovered insect that feeds on soybean plants in the Midwest US. Resseliella maxima larvae feed on soybean stems which may induce plant death and can cause considerable yield losses, making it an important agricultural pest. From three pools of 50 adults each, we used long-read nanopore sequencing to assemble a R. maxima reference genome. The final genome assembly is 206 Mb with 64.88X coverage, consisting of 1009 contigs with an N50 size of 714 kb. The assembly is high quality with a BUSCO score of 87.8%. Genome-wide GC level is 31.60% and DNA methylation was measured at 1.07%. The R. maxima genome is comprised of 21.73% repetitive DNA, which is in line with other cecidomyiids. Protein prediction annotated 14,798 coding genes with 89.9% protein BUSCO score. Mitogenome analysis indicated that R. maxima assembly is a single circular contig of 15,301 bp and shares highest identity to the mitogenome of the Asian rice gall midge, Orseolia oryzae (Wood-Mason). The R. maxima genome has one of the highest completeness levels for a cecidomyiid and will provide a resource for research focused on the biology, genetics, and evolution of cecidomyiids, as well as plant-insect interactions in this important agricultural pest.