Genomic Hybridization Research Articles

Distinct genome stabilization procedures lead to phenotypic variability in newly generated interspecific yeast hybrids

Yeast cells sometimes engage in interspecific hybridization, i.e., crosses between different species. These interspecific yeast hybrids combine phenotypes of the two parental species and can therefore allow fast adaptation to new niches. This is perhaps most evident in beer yeasts, where a cross between Saccharomyces cerevisiae and Saccharomyces eubayanus led to the emergence of the lager yeast Saccharomyces pastorianus, which combines the fermentation capacity of S. cerevisiae with the cold tolerance of S. eubayanus, making the hybrid suitable for the typical cool lager beer fermentation conditions. Interestingly, however, merging two different genomes into one cell causes genomic instability and rearrangements, ultimately leading to a reorganized but more stable hybrid genome. Here, we investigate how different parameters influence this genome stabilization trajectory and ultimately can lead to variants with different industrial phenotypes. We generated seven de novo interspecific hybrids between two S. eubayanus strains and an ale S. cerevisiae strain, subsequently exposing them to three different genome stabilization procedures. Next, we analyzed the fermentation characteristics and metabolite production of selected stabilized hybrids. Our results reveal how variation in the genome stabilization procedure leads to phenotypic variability and can generate additional diversity after the initial hybridization process. Moreover, several stabilized hybrids showed phenotypes that are interesting for industrial applications.

Chromosomal rDNA Distribution Patterns in Clonal Cobitis Triploid Hybrids (Teleostei, Cobitidae): Insights into Parental Genomic Contributions.

Background: Interspecific hybridization between relative species Cobitis taenia (with a diploid genome designated as TT), Cobitis elongatoides (EE) and Cobitis tanaitica (NN) and the successive polyploidization with transitions from sexuality to asexuality experienced by triploid Cobitis hybrids likely influence their chromosomal rearrangements, including rearrangements of ribosomal DNA (rDNA) distribution patterns. Previously, we documented distinct karyotypic differences: C. elongatoides exhibited bi-armed chromosomes while C. taenia showed uni-armed chromosomes with rDNA-positive hybridization signals, respectively. Methods: In this study, fluorescence in situ hybridization (FISH) with 5S rDNA and 28S rDNA probes was used to analyze and compare chromosomal distribution patterns of rDNAs in clonally reproduced triploid Cobitis hybrids of different genomic constitutions ETT, ETN, EEN and EET (referred to using acronyms denoting the haploid genomes of their parent species), and their parental species. Results:Cobitis triploid hybrids exhibited intermediate karyotypes with ribosome synthesis sites on chromosomes inherited from both parents, showing no evidence of nucleolar dominance. The rDNA pattern derived from the C. elongatoides genome was more stable in the hybrids' karyotypes. Two and one submetacentric chromosomes with co-localized rDNAs were effective markers to ascertain C. elongatoides diploid (EE) and haploid (E) genomes within the genome of triploid hybrids, respectively. Fewer 5S rDNA loci were observed in diploid (TT) and haploid (T) chromosome sets from C. taenia in ETT and EET females. C. taenia and C. tanaitica exhibited similar rDNA distribution patterns. Conclusions: The karyotypes of triploid Cobitis hybrids reflect the genomic contributions of their parental species. Variability in rDNA distribution patterns suggests complex genomic interactions in Cobitis hybrids resulting from polyploidization and hybridization, potentially influencing their reproductive potential.

The highly allo-autopolyploid modern sugarcane genome and very recent allopolyploidization in Saccharum.

Modern sugarcane, a highly allo-autopolyploid organism, has a very complex genome. In the present study, the karyotype and genome architecture of modern sugarcane were investigated, resulting in a genome assembly of 97 chromosomes (8.84 Gb). The allopolyploid genome was divided into subgenomes from Saccharum officinarum (Soh) and S. spontaneum (Ssh), with Soh dominance in the Saccharum hybrid (S. hybrid). Genome shock affected transcriptome dynamics during allopolyploidization. Analysis of an inbreeding population with 192 individuals revealed the underlying genetic basis of transgressive segregation. Population genomics of 310 Saccharum accessions clarified the breeding history of modern sugarcane. Using the haplotype-resolved S. hybrid genome as a reference, genome-wide association studies identified a potential candidate gene for sugar content from S. spontaneum. These findings illuminate the complex genome evolution of allopolyploids, offering opportunities for genomic enhancements and innovative breeding strategies for sugarcane.

Hybrid Origin of ×Leymotrigia bergrothii (Poaceae) as Revealed by Analysis of the Internal Transcribed Spacer ITS1 and trnL Sequences.

×Leymotrigia bergrothii is a presumed hybrid of Leymus arenarius and Elytrigia repens. This article investigates the hybrid origin and genome composition of this species. These plants are sterile, do not undergo pollination, and do not produce seeds; occasionally, underdeveloped stamens containing abortive pollen grains form in individual spikelets. The karyotype analysis of root meristem cells revealed a diploid chromosome number of 49 in ×L. bergrothii, reported here for the first time. Subsequently, we examined the intragenomic polymorphism of the transcribed spacer ITS1 in several species of Elytrigia, Elymus, Leymus, Hordeum, and Psathyrostachys, and compared the ribotype patterns of these species with those of ×L. bergrothii. It is shown that the St-ribotype variants found in Elytrigia repens and Elytrigia pseudocaesia, as well as the ribotypes of the La family, which dominate in the genome of Leymus arenarius, correspond to major ribotypes in ×L. bergrothii. The ribotypes of the St and La families are present in the nuclear genome of ×L. bergrothii in almost equal proportions. A comparison of intron and exon sequences of the trnL gene in the chloroplast DNA of Leymus arenarius, Elytrigia repens, and ×L. bergrothii showed that this region in ×L. bergrothii is identical or very close to that of Elytrigia repens, suggesting that Elytrigia repens was the cytoplasmic donor to ×L. bergrothii. Thus, our study confirms the hypothesis that this species represents a sterile first-generation hybrid of Leymus arenarius and Elytrigia repens, reproducing vegetatively.

Uncovering the fungus responsible for stem and root rot of false indigo: pathogen identification, new disease description, and genome analyses.

Calonectria spp. can cause destructive diseases on forestry crops, legumes like soybean and peanut, and ornamentals. Species of Calonectria affecting ornamental plants are not well characterized or understood, though they have been widely documented as an issue in the ornamental industry. This research focused on the molecular identification, pathogenicity validation, and genome analysis of a Calonectria sp. isolate recovered from ornamental blue false indigo (Baptisia australis) plants showing disease symptoms of crown and root rot in a commercial nursery in Virginia. The fungus on B. australis was identified as C. fujianensis (Nectriaceae, Hypocreales), a member of the C. colhuonii species complex using multilocus sequencing. Pathogenicity tests were fulfilled by inoculating C. fujianensis conidia on B. australis seedlings, confirming a causal relationship between this pathogen and the disease symptoms observed. A 62.7 Mb high-quality hybrid genome assembly generated using Illumina and Nanopore data was obtained, contained in 16 contigs, four of which were complete chromosomes. A total of 750 effectors were found in the genome, similar to cutinase and pectinase virulence factors described from other Calonectria species' genomes. Characterization of this novel disease of B. australis advances our understanding of Calonectria as an important but poorly studied group of plant pathogens.

Hybridization has localized effect on genetic variation in closely related pine species

BackgroundHybridization is a known phenomenon in nature but its genetic impact on populations of parental species remains less understood. We investigated the evolutionary consequences of the interspecific gene flow in several contact zones of closely related pine species. Using a set of genetic markers from both nuclear and organellar genomes, we analyzed four hybrid zones (384 individuals) and a large panel of reference allopatric populations of parental taxa (2104 individuals from 96 stands).ResultsWe observed reduced genetic diversity in maternally transmitted mitochondrial genomes of pure pine species and hybrids from contact zones compared to reference allopatric populations. The distribution of mtDNA haplotypes followed geographic rather than species boundaries. Additionally, no new haplotypes emerged in the contact zones, instead these zones contained the most common local variants. However, species diverged significantly at nuclear genomes and populations in contact zones exhibited similar or higher genetic diversity compared to the reference stands. There were no signs of admixture in any allopatric population, while clear admixture was evident in the contact zones, indicating that hybridization has a geographically localized effect on the genetic variation of the analyzed pine species.ConclusionsOur results suggest that hybrid zones act as sinks rather than melting pots of genetic diversity. Hybridization influences sympatric populations but is confined to contact zones. The spectrum of parental species ancestry in hybrids reflects the old evolutionary history of the sympatric populations. These findings also imply that introgression may play a crucial role in the adaptation of hybrids to specific environments.

Molecular evidence that GBS early neonatal sepsis results from ascending infection: comparative hybrid genomics analyses show that microorganisms in the vaginal ecosystem, amniotic fluid, chorioamniotic membranes, and neonatal blood are the same.

Streptococcus agalactiae, or Group B Streptococcus (GBS), is a leading cause of neonatal sepsis. Materno-fetal transmission of the microorganisms present in the lower genital tract/perineum is considered to be the most frequent mode for acquisition of infection. It has also been proposed that, in a subset of cases, GBS causes acute chorioamnionitis, intraamniotic infection, and fetal/neonatal sepsis. However, the evidence to support this ascending pathway is derived from microbiologic studies that rely on cultivation methods, which do not have the resolution to determine if the microorganisms causing neonatal sepsis are the same as those found in the amniotic fluid and the vaginal ecosystem. We used whole genome sequencing of the microorganisms isolated from the vagina, amniotic fluid, chorioamniotic membranes, and neonatal blood (four isolates) in a case of early neonatal sepsis. Using hybrid genome assembly, we characterized the genomic features including virulence factors and antimicrobial resistance in four isolates from the same mother, placenta, and newborn. Whole genome sequencing revealed that the microorganisms in the four clinical isolates corresponded to S. agalactiae sequence type 1, clonal complexes 1, and serotype Ib. Comparative genomic analysis illustrated similar DNA sequences of the four genomes. This study presents the first evidence of the genomic similarity of microorganisms in the vaginal ecosystem, the space between the chorioamniotic membranes of the placenta, amniotic fluid, and neonatal blood.

Draft hybrid genome sequence of phytopathogen Marasmius tenuissimus strain MS-2, isolated from cacao in Ghana.

Here, we report a hybrid genome of Marasmius tenuissimus strain MS-2, a cacao thread blight disease causing isolate that was collected from cacao leaves in Tafo, Eastern region, Ghana. The final assembly consists of 2,083 contigs spanning 69,843,039 bp, with 49.21% GC content, 92.6% BUSCO completeness, and scaffold N50 186,871.

Karyotype's Rearrangement in Some Hybrids of the Orchidinae Subtribe.

Based on our karyological findings in the Anacamptis Rich., Ophrys L., and Serapias L. genera, we have identified chromosomal markers within some hybrids and elucidated their interrelationships. Mitotic chromosomes of fifteen taxa were analyzed using the conventional Feulgen staining method. Only for Anacamptis ×gennarii (Rchb. f.) H.Kretzschmar, Eccarius & Dietr. [A. morio (L.) R.M.Bateman, Pridgeon & M.W.Chase × A. papilionacea (L.) R.M.Bateman, Pridgeon & M.W.Chase] and its parental species were some data obtained and reported with the banding method with Giemsa, Hoechst 33258 fluorochrome, and the FISH techniques. Our research involved new chromosomal measurements of fifteen taxa, including six hybrids, along with schematic representations. Morphometric parameters, i.e., MCA and CVCL, were used to evaluate karyotype asymmetry. Of meaning were the analyses performed on chromosomal complements of selected hybrids, which distinctly revealed marker chromosomes present in one or both putative parental species. Among the parents identified in some hybrids, Ophrys tenthredinifera Willd. has shown some interest due to the presence in its karyotype of a pair of chromosomes (n.1) showing a notable secondary constriction on the long arm. Indeed, one of the homologs is clearly distinguishable in the analyzed hybrids, where it clearly emerges as one of the putative parents. Given the challenges in detecting certain karyomorphological features within the Orchidinae subtribe using alternative methods, such as Giemsa C-banding or fluorescence banding, the Feulgen method remains valuable for cytogenetic characterization. It helps us to understand the genomes of hybrids and parental species, thus contributing to a deeper understanding of their genetic composition.

Whole-genome sequence and annotation of Diaporthe australafricana strain CBS 118571.

We report the whole-genome sequence of Diaporthe australafricana Crous & J.M. van Niekerkusing using Oxford Nanopore long-read sequencing and Illumina short-read sequencing. The hybrid genome consists of 11 contigs with a total length of 53.509 Mb, and a GC content of 52.40%.

Complete genome sequences of sucrose non-fermenting non-O1/non-O139 Vibrio cholerae isolated from human soft tissue infection.

This paper describes the hybrid genome assembly of sucrose non-fermenting non-O1/non-O139 Vibrio cholerae isolated from human soft tissue infection. The hybrid assembled genome comprises two circular chromosomes with lengths of 3,001,999 bp and 1,264,051 bp, respectively, with a G + C content of 47.38%.

Improved draft genome of Ignatzschineria larvae DSM 13226 via hybrid assembly.

Ignatzschineria larvae is studied for its role in decomposition and disease ecology; however, the type strain reference genome remains fragmented. The current reference genome consists of 61 contigs calculated at 82.18% complete with 10.98% contamination. Here, we announce the hybrid genome assembly as an improved single contig.

Genome sequence of the New Zealand cheese isolate and candidate probiotic strain Lactiplantibacillus plantarum FNZ042.

The complete genome sequence of the candidate probiotic strain Lactiplantibacillus plantarum FNZ042 was determined using a hybrid genome assembly comprising data from Illumina and PacBio sequencing platforms. The genome assembly comprised 3,265,637 bp, including the complete circular chromosome and three circular plasmids.

Genome sequence of the New Zealand raw milk isolate and candidate probiotic strain Lactococcus lactis FNZ339.

The complete genome sequence of the candidate probiotic strain Lactococcus lactis FNZ339 was determined using a hybrid genome assembly comprising data from Illumina and Oxford Nanopore Technologies sequencing platforms. The genome assembly comprised 2,673,297 bp, including the complete circular chromosome and four circular plasmids.

Chromosome-level subgenome-aware de novo assembly provides insight into Saccharomyces bayanus genome divergence after hybridization.

Interspecies hybridization is prevalent in various eukaryotic lineages and plays important roles in phenotypic diversification, adaptation, and speciation. To better understand the changes that occurred in the different subgenomes of a hybrid species and how they facilitate adaptation, we have completed chromosome-level de novo assemblies of all chromosomes for a recently formed hybrid yeast, Saccharomyces bayanus strain CBS380, using Oxford Nanopore Technologies' MinION long-read sequencing. We characterize the S. bayanus genome and compare it with its parent species, Saccharomyces uvarum and Saccharomyces eubayanus, and other S. bayanus genomes to better understand genome evolution after a relatively recent hybridization event. We observe multiple recombination events between the subgenomes in each chromosome, followed by loss of heterozygosity (LOH) in nine chromosome pairs. In addition to maintaining nearly all gene content and synteny from its parental genomes, S. bayanus has acquired many genes from other yeast species, primarily through the introgression of Saccharomyces cerevisiae, such as those involved in the maltose metabolism. Finally, the patterns of recombination and LOH suggest an allotetraploid origin of S. bayanus The gene acquisition and rapid LOH in the hybrid genome probably facilitated its adaptation to maltose brewing environments and mitigated the maladaptive effect of hybridization. This paper describes the first in-depth study using long-read sequencing technology of an S. bayanus hybrid genome, which may serve as an excellent reference for future studies of this important yeast and other yeast strains.

Maptcha: an efficient parallel workflow for hybrid genome scaffolding

BackgroundGenome assembly, which involves reconstructing a target genome, relies on scaffolding methods to organize and link partially assembled fragments. The rapid evolution of long read sequencing technologies toward more accurate long reads, coupled with the continued use of short read technologies, has created a unique need for hybrid assembly workflows. The construction of accurate genomic scaffolds in hybrid workflows is complicated due to scale, sequencing technology diversity (e.g., short vs. long reads, contigs or partial assemblies), and repetitive regions within a target genome.ResultsIn this paper, we present a new parallel workflow for hybrid genome scaffolding that would allow combining pre-constructed partial assemblies with newly sequenced long reads toward an improved assembly. More specifically, the workflow, called Maptcha, is aimed at generating long scaffolds of a target genome, from two sets of input sequences—an already constructed partial assembly of contigs, and a set of newly sequenced long reads. Our scaffolding approach internally uses an alignment-free mapping step to build a ⟨contig,contig⟩ graph using long reads as linking information. Subsequently, this graph is used to generate scaffolds. We present and evaluate a graph-theoretic “wiring” heuristic to perform this scaffolding step. To enable efficient workload management in a parallel setting, we use a batching technique that partitions the scaffolding tasks so that the more expensive alignment-based assembly step at the end can be efficiently parallelized. This step also allows the use of any standalone assembler for generating the final scaffolds.ConclusionsOur experiments with Maptcha on a variety of input genomes, and comparison against two state-of-the-art hybrid scaffolders demonstrate that Maptcha is able to generate longer and more accurate scaffolds substantially faster. In almost all cases, the scaffolds produced by Maptcha are at least an order of magnitude longer (in some cases two orders) than the scaffolds produced by state-of-the-art tools. Maptcha runs significantly faster too, reducing time-to-solution from hours to minutes for most input cases. We also performed a coverage experiment by varying the sequencing coverage depth for long reads, which demonstrated the potential of Maptcha to generate significantly longer scaffolds in low coverage settings (1×–10×).

Engineering a Sinorhizobium meliloti Chassis with Monopartite, Single Replicon Genome Configuration.

Multipartite bacterial genomes pose challenges for genome engineering and the establishment of additional replicons. We simplified the tripartite genome structure (3.65 Mbp chromosome, 1.35 Mbp megaplasmid pSymA, 1.68 Mbp chromid pSymB) of the nitrogen-fixing plant symbiont Sinorhizobium meliloti. Strains with bi- and monopartite genome configurations were generated by targeted replicon fusions. Our design preserved key genomic features such as replichore ratios, GC skew, KOPS, and coding sequence distribution. Under standard culture conditions, the growth rates of these strains and the wild type were nearly comparable, and the ability for symbiotic nitrogen fixation was maintained. Spatiotemporal replicon organization and segregation were maintained in the triple replicon fusion strain. Deletion of the replication initiator-encoding genes, including the oriVs of pSymA and pSymB from this strain, resulted in a monopartite genome with oriC as the sole origin of replication, a strongly unbalanced replichore ratio, slow growth, aberrant cellular localization of oriC, and deficiency in symbiosis. Suppressor mutation R436H in the cell cycle histidine kinase CckA and a 3.2 Mbp inversion, both individually, largely restored growth, but only the genomic rearrangement recovered the symbiotic capacity. These strains will facilitate the integration of secondary replicons in S. meliloti and thus be useful for genome engineering applications, such as generating hybrid genomes.

Single-fly genome assemblies fill major phylogenomic gaps across the Drosophilidae Tree of Life.

Long-read sequencing is driving rapid progress in genome assembly across all major groups of life, including species of the family Drosophilidae, a longtime model system for genetics, genomics, and evolution. We previously developed a cost-effective hybrid Oxford Nanopore (ONT) long-read and Illumina short-read sequencing approach and used it to assemble 101 drosophilid genomes from laboratory cultures, greatly increasing the number of genome assemblies for this taxonomic group. The next major challenge is to address the laboratory culture bias in taxon sampling by sequencing genomes of species that cannot easily be reared in the lab. Here, we build upon our previous methods to perform amplification-free ONT sequencing of single wild flies obtained either directly from the field or from ethanol-preserved specimens in museum collections, greatly improving the representation of lesser studied drosophilid taxa in whole-genome data. Using Illumina Novaseq X Plus and ONT P2 sequencers with R10.4.1 chemistry, we set a new benchmark for inexpensive hybrid genome assembly at US $150 per genome while assembling genomes from as little as 35 ng of genomic DNA from a single fly. We present 183 new genome assemblies for 179 species as a resource for drosophilid systematics, phylogenetics, and comparative genomics. Of these genomes, 62 are from pooled lab strains and 121 from single adult flies. Despite the sample limitations of working with small insects, most single-fly diploid assemblies are comparable in contiguity (>1 Mb contig N50), completeness (>98% complete dipteran BUSCOs), and accuracy (>QV40 genome-wide with ONT R10.4.1) to assemblies from inbred lines. We present a well-resolved multi-locus phylogeny for 360 drosophilid and 4 outgroup species encompassing all publicly available (as of August 2023) genomes for this group. Finally, we present a Progressive Cactus whole-genome, reference-free alignment built from a subset of 298 suitably high-quality drosophilid genomes. The new assemblies and alignment, along with updated laboratory protocols and computational pipelines, are released as an open resource and as a tool for studying evolution at the scale of an entire insect family.

Specific anti-SVCV antibodies in hybrids of common carp (Cyprinus carpio) and gibel carp (Carassius gibelio) reflect heterosis advantage and genetic breakdown

Spring viraemia of carp virus (SVCV) is a disease with a serious economic impact on the farming of cyprinid fish. High susceptibility to SVCV has been documented mostly in common carp (Cyprinus carpio), whilst gibel carp (Carassius gibelio) is a weakly susceptible species. Specific anti-SVCV antibodies were analyzed in pure lines of common carp and gibel carp, and various generations of F1 and post-F1 hybrids. Specifically, we focused on anti-SVCV antibodies in weakly susceptible F1 hybrids and highly infected backcross and F2 hybrids, hypothesizing that the level of anti-SVCV antibodies will reflect heterosis advantage in F1 generations and hybrid breakdown in post-F1 generations.Backcross generations with common carp exhibited the most frequently symptomatic infections, followed by pure common carp. The high capacity of susceptible common carp to produce anti-SVCV antibodies was reported, whilst gibel carp expressed almost undetectable levels of anti-SVCV antibodies. We found the very good capacity of F1 hybrids to produce anti-SVCV antibodies, suggesting heterosis advantage. In contrast, we revealed different patterns of anti-SVCV antibodies production between maternal backcrosses (having parents with the same mtDNA – here, gibel carp) and paternal backcrosses (having parents with different mtDNA, i.e., resulting from reciprocal crosses of F1 hybrids with gibel carp mtDNA and pure common carp). Whilst both maternal backcross generations and the F2 generation of hybrids tended to produce low anti-SVCV antibodies, both paternal backcross generations expressed levels of anti SVCV-antibodies similar to those of highly susceptible common carp. The low capacity to produce anti-SVCV antibodies in F2 hybrids may be interpreted as a potential consequence of genetic disruption. However, the different capacity to induce an adaptive response in paternal hybrids and maternal hybrids (with mtDNA C. gibelio) may be interpreted as potential compensation for the cyto-nuclear breakdown hypothesized for paternal hybrids when coping with viral infection. Alternatively, the genetic background of hybrid fish, i.e. a combination of the genes of highly susceptible common carp and of less susceptible gibel carp in the hybrid genome may be responsible for this pattern.

Multiple hybridization events and repeated evolution of homoeologue expression bias in parthenogenetic, polyploid New Zealand stick insects.

During hybrid speciation, homoeologues combine in a single genome. Homoeologue expression bias (HEB) occurs when one homoeologue has higher gene expression than another. HEB has been well characterized in plants but rarely investigated in animals, especially invertebrates. Consequently, we have little idea as to the role that HEB plays in allopolyploid invertebrate genomes. If HEB is constrained by features of the parental genomes, then we predict repeated evolution of similar HEB patterns among hybrid genomes formed from the same parental lineages. To address this, we reconstructed the history of hybridization between the New Zealand stick insect genera Acanthoxyla and Clitarchus using a high-quality genome assembly from Clitarchus hookeri to call variants and phase alleles. These analyses revealed the formation of three independent diploid and triploid hybrid lineages between these genera. RNA sequencing revealed a similar magnitude and direction of HEB among these hybrid lineages, and we observed that many enriched functions and pathways were also shared among lineages, consistent with repeated evolution due to parental genome constraints. In most hybrid lineages, a slight majority of the genes involved in mitochondrial function showed HEB towards the maternal homoeologues, consistent with only weak effects of mitonuclear incompatibility. We also observed a proteasome functional enrichment in most lineages and hypothesize this may result from the need to maintain proteostasis in hybrid genomes. Reference bias was a pervasive problem, and we caution against relying on HEB estimates from a single parental reference genome.