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Polyploidization drives regulatory and phenotypic innovation. How the merger of different genomes contributes to polyploid development is a fundamental issue in evolutionary developmental biology and breeding research. Clarifying this issue is challenging because of genome complexity and the difficulty in tracking stochastic subgenome divergence during development. Recent single-cell sequencing techniques enabled probing subgenome-divergent regulation in the context of cellular differentiation. However, analyzing single-cell data suffers from high error rates due to high dimensionality, noise, and sparsity, and the errors stack up in polyploid analysis due to the increased dimensionality of comparisons between subgenomes of each cell, hindering deeper mechanistic understandings. In this study, we develop a quantitative computational framework, called "pseudo-genome divergence quantification" (pgDQ), for quantifying and tracking subgenome divergence directly at the cellular level. Further comparing with cellular differentiation trajectories derived from single-cell RNA sequencing data allows for an examination of the relationship between subgenome divergence and the progression of development. pgDQ produces robust results and is insensitive to data dropout and noise, avoiding high error rates due to multiple comparisons of genes, cells, and subgenomes. A statistical diagnostic approach is proposed to identify genes that are central to subgenome divergence during development, which facilitates the integration of different data modalities, enabling the identification of factors and pathways that mediate subgenome-divergent activity during development. Case studies have demonstrated that applying pgDQ to single-cell and bulk tissue transcriptomic data promotes a systematic and deeper understanding of how dynamic subgenome divergence contributes to developmental trajectories in polyploid evolution. [ABSTRACT FROM AUTHOR]

Background: White clover (Trifolium repens) is a globally important perennial forage legume. This species also serves as an eco-evolutionary model system for studying within-species chemical defense variation; it features a well-studied polymorphism for cyanogenesis (HCN release following tissue damage), with higher frequencies of cyanogenic plants favored in warmer locations worldwide. Using a newly generated haplotype-resolved genome and two other long-read assemblies, we tested the hypothesis that copy number variants (CNVs) at cyanogenesis genes play a role in the ability of white clover to rapidly adapt to local environments. We also examined questions on subgenome evolution in this recently evolved allotetraploid species and on chromosomal rearrangements in the broader IRLC legume clade. Results: Integration of PacBio HiFi, Omni-C, Illumina, and linkage map data yielded a completely de novo genome assembly for white clover (created without a priori sequence assignment to subgenomes). We find that white clover has undergone extensive transposon diversification since its origin but otherwise shows highly conserved genome organization and composition with its diploid progenitors. Unlike some other clover species, its chromosomal structure is conserved with other IRLC legumes. We further find extensive evidence of CNVs at the major cyanogenesis loci; these contribute to quantitative variation in the cyanogenic phenotype and to local adaptation across wild North American populations. Conclusions: This work provides a case study documenting the role of CNVs in local adaptation in a plant species, and it highlights the value of pan-genome data for identifying contributions of structural variants to adaptation in nature. [ABSTRACT FROM AUTHOR]

All flowering plants are now recognized as diploidized paleopolyploids (Jiao et al., 2011; One Thousand Plant Transcriptomes Initiative, 2019), and polyploid species comprise approximately 30% of contemporary plant species (Wood et al., 2009; Barker et al., 2016a). A major implication of these discoveries is that, to appreciate the evolution of plant diversity, we need to understand the fundamental biology of polyploids and diploidization. This need is broadly recognized by our community as there is a continued, growing interest in polyploidy as a research topic. Over the past 25 years, the sequencing and analysis of plant genomes has revolutionized our understanding of the importance of polyploid speciation to the evolution of land plants. [ABSTRACT FROM AUTHOR]

Premise: A complicating factor in analyzing allopolyploid genomes is the possibility of physical interactions between homoeologous chromosomes during meiosis, resulting in either crossover (homoeologous exchanges) or non‐crossover products (homoeologous gene conversion). Homoeologous gene conversion was first described in cotton by comparing SNP patterns in sequences from two diploid progenitors with those from the allopolyploid subgenomes. These analyses, however, did not explicitly consider other evolutionary scenarios that may give rise to similar SNP patterns as homoeologous gene conversion, creating uncertainties about the reality of the inferred gene conversion events. Methods: Here, we use an expanded phylogenetic sampling of high‐quality genome assemblies from seven allopolyploid Gossypium species (all derived from the same polyploidy event), four diploid species (two closely related to each subgenome), and a diploid outgroup to derive a robust method for identifying potential genomic regions of gene conversion and homoeologous exchange. Results: We found little evidence for homoeologous gene conversion in allopolyploid cottons, and that only two of the 40 best‐supported events were shared by more than one species. We did, however, reveal a single, shared homoeologous exchange event at one end of chromosome 1, which occurred shortly after allopolyploidization but prior to divergence of the descendant species. Conclusions: Overall, our analyses demonstrated that homoeologous gene conversion and homoeologous exchanges are uncommon in Gossypium, affecting between zero and 24 genes per subgenome (0.0–0.065%) across the seven species. More generally, we highlighted the potential problems of using simple four‐taxon tests to investigate patterns of homoeologous gene conversion in established allopolyploids. [ABSTRACT FROM AUTHOR]

Abstract Background White clover (Trifolium repens) is a globally important perennial forage legume. This species also serves as an eco-evolutionary model system for studying within-species chemical defense variation; it features a well-studied polymorphism for cyanogenesis (HCN release following tissue damage), with higher frequencies of cyanogenic plants favored in warmer locations worldwide. Using a newly generated haplotype-resolved genome and two other long-read assemblies, we tested the hypothesis that copy number variants (CNVs) at cyanogenesis genes play a role in the ability of white clover to rapidly adapt to local environments. We also examined questions on subgenome evolution in this recently evolved allotetraploid species and on chromosomal rearrangements in the broader IRLC legume clade. Results Integration of PacBio HiFi, Omni-C, Illumina, and linkage map data yielded a completely de novo genome assembly for white clover (created without a priori sequence assignment to subgenomes). We find that white clover has undergone extensive transposon diversification since its origin but otherwise shows highly conserved genome organization and composition with its diploid progenitors. Unlike some other clover species, its chromosomal structure is conserved with other IRLC legumes. We further find extensive evidence of CNVs at the major cyanogenesis loci; these contribute to quantitative variation in the cyanogenic phenotype and to local adaptation across wild North American populations. Conclusions This work provides a case study documenting the role of CNVs in local adaptation in a plant species, and it highlights the value of pan-genome data for identifying contributions of structural variants to adaptation in nature.

Polyploidy is a major factor in the evolution of plants, yet we know little about the origin and evolution of polyploidy in intertidal species. This study aimed to identify the evolutionary transitions in three true-mangrove species of the genus Acanthus distributed in the Indo–West Pacific region. For this purpose, we took an integrative approach that combined data on morphology, cytology, climatic niche, phylogeny, and biogeography of 493 samples from 42 geographic sites. Our results show that the Acanthus ilicifolius lineage distributed east of the Thai–Malay Peninsula possesses a tetraploid karyotype, which is morphologically distinct from that of the lineage on the west side. The haplotype networks and phylogenetic trees for the chloroplast genome and eight nuclear genes reveal that the tetraploid species has two sub-genomes, one each from A. ilicifolius and A. ebracteatus, the paternal and maternal parents, respectively. Population structure analysis also supports the hybrid speciation history of the new tetraploid species. The two sub-genomes of the tetraploid species diverged from their diploid progenitors during the Pleistocene. Environmental niche models revealed that the tetraploid species not only occupied the near-entire niche space of the diploids, but also expanded into novel environments. Our findings suggest that A. ilicifolius species distributed on the east side of the Thai–Malay Peninsula should be regarded as a new species, A. tetraploideus, which originated from hybridization between A. ilicifolius and A. ebracteatus, followed by chromosome doubling. This is the first report of a true-mangrove allopolyploid species that can reproduce sexually and clonally reproduction, which explains the long-term adaptive potential of the species.

Phylogenetic inference of polyploid species is the first step towards understanding their patterns of diversification. In this paper, we review the challenges and limitations of inferring species relationships of polyploid plants using traditional phylogenetic sequencing approaches, as well as the mischaracterization of the species tree from single or multiple gene trees. We provide a roadmap to infer interspecific relationships among polyploid lineages by comparing and evaluating the application of current phylogenetic, phylogenomic, transcriptomic, and whole‐genome approaches using different sequencing platforms. For polyploid species tree reconstruction, we assess the following criteria: (1) the amount of prior information or tools required to capture the genetic region(s) of interest; (2) the probability of recovering homeologs for polyploid species; and (3) the time efficiency of downstream data analysis. Moreover, we discuss bioinformatic pipelines that can reconstruct networks of polyploid species relationships. In summary, although current phylogenomic approaches have improved our understanding of reticulate species relationships in polyploid‐rich genera, the difficulties of recovering reliable orthologous genes and sorting all homeologous copies for allopolyploids remain a challenge. In the future, assembled long‐read sequencing data will assist the recovery and identification of multiple gene copies, which can be particularly useful for reconstructing the multiple independent origins of polyploids. [ABSTRACT FROM AUTHOR]

Allopolyploids are individuals that have two or more complete sets of chromosomes derived from different species. The number of chromosome-scaled allopolyploid genomes assembled has increased as genome sequencing has become cheaper, longer, and more accurate. Several computational tools have been developed to leverage differences in biology between progenitor species to identify subgenomes of allopolyploids. Whole-genome duplications (WGDs) are widespread genomic events in eukaryotes that are hypothesized to contribute to the evolutionary success of many lineages, including flowering plants, Saccharomyces yeast, and vertebrates. WGDs generally can be classified into autopolyploids (ploidy increase descended from one species) or allopolyploids (ploidy increase descended from multiple species). Assignment of allopolyploid progenitor species (called subgenomes in the polyploid) is important to understanding the biology and evolution of polyploids, including the asymmetric subgenome evolution following hybridization (biased fractionation). Here, I review the different methodologies used to identify the ancestors of allopolyploid subgenomes, discuss the advantages and disadvantages of these methods, and outline the implications of how these methods affect the subsequent evolutionary analysis of these genomes. [ABSTRACT FROM AUTHOR]

“Synthetic” allopolyploids recreated by interspecific hybridization play an important role in providing novel genomic variation for crop improvement. Such synthetic allopolyploids often undergo rapid genomic structural variation (SV). However, how such SV arises, is inherited and fixed, and how it affects important traits, has rarely been comprehensively and quantitively studied in advanced generation synthetic lines. A better understanding of these processes will aid breeders in knowing how to best utilize synthetic allopolyploids in breeding programs. Here, we analyzed three genetic mapping populations (735 DH lines) derived from crosses between advanced synthetic and conventional Brassica napus (rapeseed) lines, using whole-genome sequencing to determine genome composition. We observed high tolerance of large structural variants, particularly toward the telomeres, and preferential selection for balanced homoeologous exchanges (duplication/deletion events between the A and C genomes resulting in retention of gene/chromosome dosage between homoeologous chromosome pairs), including stable events involving whole chromosomes (“pseudoeuploidy”). Given the experimental design (all three populations shared a common parent), we were able to observe that parental SV was regularly inherited, showed genetic hitchhiking effects on segregation, and was one of the major factors inducing adjacent novel and larger SV. Surprisingly, novel SV occurred at low frequencies with no significant impacts on observed fertility and yield-related traits in the advanced generation synthetic lines. However, incorporating genome-wide SV in linkage mapping explained significantly more genetic variance for traits. Our results provide a framework for detecting and understanding the occurrence and inheritance of genomic SV in breeding programs, and support the use of synthetic parents as an important source of novel trait variation.

Abstract Background Capsella bursa-pastoris, a cosmopolitan weed of hybrid origin, is an emerging model object for the study of early consequences of polyploidy, being a fast growing annual and a close relative of Arabidopsis thaliana. The development of this model is hampered by the absence of a reference genome sequence. Results We present here a subgenome-resolved chromosome-scale assembly and a genetic map of the genome of Capsella bursa-pastoris. It shows that the subgenomes are mostly colinear, with no massive deletions, insertions, or rearrangements in any of them. A subgenome-aware annotation reveals the lack of genome dominance—both subgenomes carry similar number of genes. While most chromosomes can be unambiguously recognized as derived from either paternal or maternal parent, we also found homeologous exchange between two chromosomes. It led to an emergence of two hybrid chromosomes; this event is shared between distant populations of C. bursa-pastoris. The whole-genome analysis of 119 samples belonging to C. bursa-pastoris and its parental species C. grandiflora/rubella and C. orientalis reveals introgression from C. orientalis but not from C. grandiflora/rubella. Conclusions C. bursa-pastoris does not show genome dominance. In the earliest stages of evolution of this species, a homeologous exchange occurred; its presence in all present-day populations of C. bursa-pastoris indicates on a single origin of this species. The evidence coming from whole-genome analysis challenges the current view that C. grandiflora/rubella was a direct progenitor of C. bursa-pastoris; we hypothesize that it was an extinct (or undiscovered) species sister to C. grandiflora/rubella.

Homeologue expression bias occurs when one progenitor copy of a gene is expressed at a higher level than the other in allopolyploids. Morphological variation, including differences in flower colour, exists between natural and synthetic allopolyploids of Nicotiana tabacum and their progenitors. In this study, we use a comparative transcriptomic approach to investigate gene expression differences as well as homeologue bias in the flavonoid biosynthetic pathway (FBP) in these accessions. We do not observe reciprocal homeologue bias between dark and light pink allopolyploids, but the production of light pink flowers is correlated with high FLAVONOL SYNTHASE:DIHYDROFLAVONOL-4-REDUCTASE (FLS:DFR) ratio at 60% of anthesis length due to delayed activation of DFR in these accessions. We do find that natural allopolyploids have stronger homeologue bias than synthetic allopolyploids in both FBP genes and across the transcriptome. While there is no overall subgenome dominance, there is a bias towards expression of N. tomentosiformis homeologues in FBP genes; however, the magnitude of this bias is reduced in allopolyploids compared to the progenitors, suggesting that N. sylvestris homeologues play an active role in the development of flower colour in N. tabacum allopolyploids. In addition, synthetic allopolyploids tend to exhibit trans regulation of homeologues whereas natural allopolyploids often have evolved cis -regulatory differences between homeologues since their origin. [ABSTRACT FROM AUTHOR]

SUMMARY: The allopolyploid okra (Abelmoschus esculentus) unveiled telomeric repeats flanking distal gene‐rich regions and short interstitial TTTAGGG telomeric repeats, possibly representing hallmarks of chromosomal speciation. Ribosomal RNA (rRNA) genes organize into 5S clusters, distinct from the 18S–5.8S–28S units, indicating an S‐type rRNA gene arrangement. The assembly, in line with cytogenetic and cytometry observations, identifies 65 chromosomes and a 1.45 Gb genome size estimate in a haploid sibling. The lack of aberrant meiotic configurations implies limited to no recombination among sub‐genomes. k‐mer distribution analysis reveals 75% has a diploid nature and 15% heterozygosity. The configurations of Benchmarking Universal Single‐Copy Ortholog (BUSCO), k‐mer, and repeat clustering point to the presence of at least two sub‐genomes one with 30 and the other with 35 chromosomes, indicating the allopolyploid nature of the okra genome. Over 130 000 putative genes, derived from mapped IsoSeq data and transcriptome data from public okra accessions, exhibit a low genetic diversity of one single nucleotide polymorphisms per 2.1 kbp. The genes are predominantly located at the distal chromosome ends, declining toward central scaffold domains. Long terminal repeat retrotransposons prevail in central domains, consistent with the observed pericentromeric heterochromatin and distal euchromatin. Disparities in paralogous gene counts suggest potential sub‐genome differentiation implying possible sub‐genome dominance. Amino acid query sequences of putative genes facilitated phenol biosynthesis pathway annotation. Comparison with manually curated reference KEGG pathways from related Malvaceae species reveals the genetic basis for putative enzyme coding genes that likely enable metabolic reactions involved in the biosynthesis of dietary and therapeutic compounds in okra. Significance Statement: Our study delves into the genetic composition of allopolyploid okra and provides insight into the evolutionary dynamics of its sub‐genomes. Augmented by a comprehensive structural and functional genome annotation, our findings establish a robust foundation for advancing okra breeding practices. [ABSTRACT FROM AUTHOR]

Background: Capsella bursa-pastoris, a cosmopolitan weed of hybrid origin, is an emerging model object for the study of early consequences of polyploidy, being a fast growing annual and a close relative of Arabidopsis thaliana. The development of this model is hampered by the absence of a reference genome sequence. Results: We present here a subgenome-resolved chromosome-scale assembly and a genetic map of the genome of Capsella bursa-pastoris. It shows that the subgenomes are mostly colinear, with no massive deletions, insertions, or rearrangements in any of them. A subgenome-aware annotation reveals the lack of genome dominance—both subgenomes carry similar number of genes. While most chromosomes can be unambiguously recognized as derived from either paternal or maternal parent, we also found homeologous exchange between two chromosomes. It led to an emergence of two hybrid chromosomes; this event is shared between distant populations of C. bursa-pastoris. The whole-genome analysis of 119 samples belonging to C. bursa-pastoris and its parental species C. grandiflora/rubella and C. orientalis reveals introgression from C. orientalis but not from C. grandiflora/rubella. Conclusions: C. bursa-pastoris does not show genome dominance. In the earliest stages of evolution of this species, a homeologous exchange occurred; its presence in all present-day populations of C. bursa-pastoris indicates on a single origin of this species. The evidence coming from whole-genome analysis challenges the current view that C. grandiflora/rubella was a direct progenitor of C. bursa-pastoris; we hypothesize that it was an extinct (or undiscovered) species sister to C. grandiflora/rubella. [ABSTRACT FROM AUTHOR]

Summary: Combining two or more related homoeologous genomes in a single nucleus, newly formed allopolyploids must rapidly adapt meiosis to restore balanced chromosome segregation, production of euploid gametes and fertility. The poor fertility of such neo‐allopolyploids thus strongly selects for the limitation or avoidance of genetic crossover formation between homoeologous chromosomes.In this study, we have reproduced the interspecific hybridization between Arabidopsis thaliana and Arabidopsis arenosa leading to the allotetraploid Arabidopsis suecica and have characterized the first allopolyploid meioses.First‐generation neo‐allopolyploid siblings vary considerably in fertility, meiotic behavior and levels of homoeologous recombination. We show that centromere dynamics at early meiosis is altered in synthetic neo‐allopolyploids compared with evolved A. suecica, with a significant increase in homoeologous centromere interactions at zygotene. At metaphase I, the presence of multivalents involving homoeologous chromosomes confirms that homoeologous recombination occurs in the first‐generation synthetic allopolyploid plants and this is associated with a significant reduction in homologous recombination, compared to evolved A. suecica.Together, these data strongly suggest that the fidelity of recombination partner choice, likely during the DNA invasion step, is strongly impaired during the first meiosis of neo‐allopolyploids and requires subsequent adaptation. [ABSTRACT FROM AUTHOR]

Premise: Cultivation and naturalization of plants beyond their natural range can bring previously geographically isolated taxa together, increasing the opportunity for hybridization, the outcomes of which are not predictable. Here, we explored the phenotypic and genomic effects of interspecific gene flow following the widespread cultivation of Mentha spicata (spearmint), M. longifolia, and M. suaveolens. Methods: We morphologically evaluated 155 herbarium specimens of three Mentha species and sequenced the genomes of a subset of 93 specimens. We analyzed the whole genomes in a population and the phylogenetic framework and associated genomic classifications in conjunction with the morphological assessments. Results: The allopolyploid M. spicata, which likely evolved in cultivation, had altered trichome characters, that is possibly a product of human selection for a more palatable plant or a byproduct of selection for essential oils. There were signs of genetic admixture between mints, including allopolyploids, indicating that the reproductive barriers between Mentha species with differences in ploidy are likely incomplete. Still, despite gene flow between species, we found that genetic variants associated with the cultivated trichome morphology continue to segregate. Conclusions: Although hybridization, allopolyploidization, and human selection during cultivation can increase species richness (e.g., by forming hybrid taxa), we showed that unless reproductive barriers are strong, these processes can also result in mixing of genes between species and the potential loss of natural biodiversity. [ABSTRACT FROM AUTHOR]

Abstract Phylogenetic inference of polyploid species is the first step towards understanding their patterns of diversification. In this paper, we review the challenges and limitations of inferring species relationships of polyploid plants using traditional phylogenetic sequencing approaches, as well as the mischaracterization of the species tree from single or multiple gene trees. We provide a roadmap to infer interspecific relationships among polyploid lineages by comparing and evaluating the application of current phylogenetic, phylogenomic, transcriptomic, and whole‐genome approaches using different sequencing platforms. For polyploid species tree reconstruction, we assess the following criteria: (1) the amount of prior information or tools required to capture the genetic region(s) of interest; (2) the probability of recovering homeologs for polyploid species; and (3) the time efficiency of downstream data analysis. Moreover, we discuss bioinformatic pipelines that can reconstruct networks of polyploid species relationships. In summary, although current phylogenomic approaches have improved our understanding of reticulate species relationships in polyploid‐rich genera, the difficulties of recovering reliable orthologous genes and sorting all homeologous copies for allopolyploids remain a challenge. In the future, assembled long‐read sequencing data will assist the recovery and identification of multiple gene copies, which can be particularly useful for reconstructing the multiple independent origins of polyploids.

Sour cherry (Prunus cerasus L.) is an agriculturally valuable tree that produces fruits used in a range of culinary dishes, beverages, and other products. The progenitor species and number of origins of sour cherry remain unresolved. Here, we performed phylogenetic analyses of plastid genomes and nuclear genes from nine wild species and three historically important sour cherry cultivars. Our analyses identified Prunus fruticosa and Prunus avium as the closest extant relatives of the progenitor species of tetraploid sour cherry. Furthermore, our analyses revealed P. fruticosa as the likely maternal contributor. These findings and transcriptomic datasets should serve as valuable new resources to guide future breeding efforts in sour cherry.

Abstract Background The common carp (Cyprinus carpio) might best represent the domesticated allopolyploid animals. Although subgenome divergence which is well-known to be a key to allopolyploid domestication has been comprehensively characterized in common carps, the link between genetic architecture underlying agronomic traits and subgenome divergence is unknown in the selective breeding of common carps globally. Results We utilized a comprehensive SNP dataset in 13 representative common carp strains worldwide to detect genome-wide genetic variations associated with scale reduction, vibrant skin color, and high growth rate in common carp domestication. We identified numerous novel candidate genes underlie the three agronomically most desirable traits in domesticated common carps, providing potential molecular targets for future genetic improvement in the selective breeding of common carps. We found that independently selective breeding of the same agronomic trait (e.g., fast growing) in common carp domestication could result from completely different genetic variations, indicating the potential advantage of allopolyploid in domestication. We observed that candidate genes associated with scale reduction, vibrant skin color, and/or high growth rate are repeatedly enriched in the immune system, suggesting that domestication of common carps was often accompanied by the disease resistance improvement. Conclusions In common carp domestication, asymmetric subgenome selection is prevalent, while parallel subgenome selection occurs in selective breeding of common carps. This observation is not due to asymmetric gene retention/loss between subgenomes but might be better explained by reduced pleiotropy through transposable element-mediated expression divergence between ohnologs. Our results demonstrate that domestication benefits from polyploidy not only in plants but also in animals.

Allopolyploidization often leads to disruptive conflicts among more than two sets of subgenomes, leading to genomic modifications and changes in gene expression. Although the evolutionary trajectories of subgenomes in allopolyploids have been studied intensely in angiosperms, the dynamics of subgenome evolution remain poorly understood in ferns, despite the prevalence of allopolyploidization. In this study, we have focused on an allotetraploid fern--Phegopteris decursivepinnata--and its diploid parental species, P. koreana (K) and P. taiwaniana (T). Using RNA-seq analyses, we have compared the gene expression profiles for 9,540 genes among parental species, synthetic F1 hybrids, and natural allotetraploids. The changes in gene expression patterns were traced from the F1 hybrids to the natural allopolyploids. This study has revealed that the expression patterns observed in most genes in the F1 hybrids are largely conserved in the allopolyploids; however, there were substantial differences in certain genes between these groups. In the allopolyploids compared with the F1 hybrids, the number of genes showing a transgressive pattern in total expression levels was increased. There was a slight reduction in T-dominance and a slight increase in K-dominance, in terms of expression level dominance. Interestingly, there is no obvious bias toward the Tor K-subgenomes in the number and expression levels overall, showing the absence of subgenome dominance. These findings demonstrated the impacts of the substantial transcriptome change after hybridization and the moderate modification during allopolyploid establishment on gene expression in ferns and provided important insights into subgenome evolution in polyploid ferns. [ABSTRACT FROM AUTHOR]

Background: The common carp (Cyprinus carpio) might best represent the domesticated allopolyploid animals. Although subgenome divergence which is well-known to be a key to allopolyploid domestication has been comprehensively characterized in common carps, the link between genetic architecture underlying agronomic traits and subgenome divergence is unknown in the selective breeding of common carps globally. Results: We utilized a comprehensive SNP dataset in 13 representative common carp strains worldwide to detect genome-wide genetic variations associated with scale reduction, vibrant skin color, and high growth rate in common carp domestication. We identified numerous novel candidate genes underlie the three agronomically most desirable traits in domesticated common carps, providing potential molecular targets for future genetic improvement in the selective breeding of common carps. We found that independently selective breeding of the same agronomic trait (e.g., fast growing) in common carp domestication could result from completely different genetic variations, indicating the potential advantage of allopolyploid in domestication. We observed that candidate genes associated with scale reduction, vibrant skin color, and/or high growth rate are repeatedly enriched in the immune system, suggesting that domestication of common carps was often accompanied by the disease resistance improvement. Conclusions: In common carp domestication, asymmetric subgenome selection is prevalent, while parallel subgenome selection occurs in selective breeding of common carps. This observation is not due to asymmetric gene retention/loss between subgenomes but might be better explained by reduced pleiotropy through transposable element-mediated expression divergence between ohnologs. Our results demonstrate that domestication benefits from polyploidy not only in plants but also in animals. [ABSTRACT FROM AUTHOR]

Abstract Background Poa annua (annual bluegrass) is an allotetraploid turfgrass, an agronomically significant weed, and one of the most widely dispersed plant species on earth. Here, we report the chromosome-scale genome assemblies of P. annua’s diploid progenitors, P. infirma and P. supina, and use multi-omic analyses spanning all three species to better understand P. annua’s evolutionary novelty. Results We find that the diploids diverged from their common ancestor 5.5 – 6.3 million years ago and hybridized to form P. annua ≤ 50,000 years ago. The diploid genomes are similar in chromosome structure and most notably distinguished by the divergent evolutionary histories of their transposable elements, leading to a 1.7 × difference in genome size. In allotetraploid P. annua, we find biased movement of retrotransposons from the larger (A) subgenome to the smaller (B) subgenome. We show that P. annua’s B subgenome is preferentially accumulating genes and that its genes are more highly expressed. Whole-genome resequencing of several additional P. annua accessions revealed large-scale chromosomal rearrangements characterized by extensive TE-downsizing and evidence to support the Genome Balance Hypothesis. Conclusions The divergent evolutions of the diploid progenitors played a central role in conferring onto P. annua its remarkable phenotypic plasticity. We find that plant genes (guided by selection and drift) and transposable elements (mostly guided by host immunity) each respond to polyploidy in unique ways and that P. annua uses whole-genome duplication to purge highly parasitized heterochromatic sequences. The findings and genomic resources presented here will enable the development of homoeolog-specific markers for accelerated weed science and turfgrass breeding.

Variation in patterns of recombination in plant genomes provides information about species evolution, genetic diversity and crop improvement. We investigated meiotic crossovers generated in biparental segregating and reciprocal backcross populations of the allopolyploid genome of rapeseed (Brassica napus) (AACC, 2n = 38). A structured set of 1445 intercrossed lines was derived from two homozygous de novo genome-assembled parents that represented the major genetic clusters of semi-winter Chinese and winter European rapeseeds, and was used to increase QTL resolution and achieve genomic reciprocal introgression. A high-density genetic map constructed with 6161 genetic bins and anchored centromere regions was used to establish the pattern of recombination variation in each chromosome. Around 93% of the genome contained crossovers at a mean rate of 3.8 cM Mb−1, with the remaining 7% attributed to centromeres or low marker density. Recombination hotspots predominated in the A genome, including two-thirds of those associated with breeding introgression from B. rapa. Genetic background might affect recombination variation. Introgression of genetic diversity from European winter to Chinese semi-winter rapeseed showed an increase in crossover rate under the semi-winter environment. Evidence for an elevated recombination rate having historically contributed to selective trait improvement includes accumulation of favorable alleles for seed oil content on hotspots of chromosome A10. Conversely, strong artificial selection may affect recombination rate variation, as appears to be the case with a coldspot resulting from strong selection for glucosinolate alleles on A09. But the cold region would be promptly reactivated by crossing design indicated by the pedigree analysis. Knowledge of recombination hotspots and coldspots associated with QTL for 22 traits can guide selection strategies for introgression breeding between the two gene pools. These results and rich genomic resources broaden our understanding of recombination behavior in allopolyploids and may advance rapeseed genetic improvement.

Many recent studies have provided significant insights into polyploid breeding, but limited research has been carried out on trees. The genomic information needed to understand growth and response to abiotic stress in polyploidy trees is largely unknown, but has become critical due to the threats to forests imposed by climate change. Populus alba 'Berolinensis,' also known "Yinzhong poplar," is a triploid poplar from northeast China. This hybrid triploid poplar is widely used as a landscape ornamental and in urban forestry owing to its adaptation to adverse environments and faster growth than its parental diploid. It is an artificially synthesized male allotriploid hybrid, with three haploid genomes of P. alba 'Berolinensis' originating from different poplar species, so it is attractive for studying polyploidy genomic mechanisms in heterosis. In this study, we focused on the allelic genomic interactions in P. alba 'Berolinensis,' and generated a high‐quality chromosome‐level genome assembly consisting of 19 allelic chromosomes. Its three haploid chromosome sets are polymorphic with an average of 25.73 nucleotide polymorphism sites per kilobase. We found that some stress‐related genes such as RD22 and LEA7 exhibited sequence differences between different haploid genomes. The genome assembly has been deposited in our polyploid genome online analysis website TreeGenomes (https://www.treegenomes.com). These polyploid genome‐related resources will provide a critical foundation for the molecular breeding of P. alba 'Berolinensis' and help us uncover the allopolyploidization effects of heterosis and abiotic stress resistance and traits of polyploidy species in the future. [ABSTRACT FROM AUTHOR]

Premise: Recently formed allopolyploids Tragopogon mirus and T. miscellus and their diploid parental species, T. dubius, T. porrifolius, and T. pratensis, offer a rare opportunity to study the earliest stages of allopolyploidy. The allopolyploid species have also been resynthesized, allowing comparisons between the youngest possible allopolyploid lineages and their natural, established counterparts. For the first time, we compared phenotypic traits on a large scale in Tragopogon diploids, natural allopolyploids, and three generations of synthetic allopolyploids. Methods: Our large common‐garden experiment measured traits in growth, development, physiology, and reproductive fitness. We analyzed trait differences between allopolyploids and their parental species, and between synthetic and natural allopolyploids. Results: As in many polyploids, the allopolyploid species had some larger physical traits and a higher capacity for photosynthesis than diploid species. Reproductive fitness traits were variable and inconsistent. Allopolyploids had intermediate phenotypes compared to their diploid parents in several traits, but patterns of variation often varied between allopolyploid complexes. Resynthesized and natural allopolyploid lines generally showed minor to nonexistent trait differences. Conclusions: In Tragopogon, allopolyploidy results in some typical phenotypic changes, including gigas effects and increased photosynthetic capacity. Being polyploid did not produce a significant reproductive advantage. Comparisons between natural and synthetic T. mirus and T. miscellus are consistent with very limited, idiosyncratic phenotypic evolution following allopolyploidization. [ABSTRACT FROM AUTHOR]

Background: Poa annua (annual bluegrass) is an allotetraploid turfgrass, an agronomically significant weed, and one of the most widely dispersed plant species on earth. Here, we report the chromosome-scale genome assemblies of P. annua's diploid progenitors, P. infirma and P. supina, and use multi-omic analyses spanning all three species to better understand P. annua's evolutionary novelty. Results: We find that the diploids diverged from their common ancestor 5.5 – 6.3 million years ago and hybridized to form P. annua ≤ 50,000 years ago. The diploid genomes are similar in chromosome structure and most notably distinguished by the divergent evolutionary histories of their transposable elements, leading to a 1.7 × difference in genome size. In allotetraploid P. annua, we find biased movement of retrotransposons from the larger (A) subgenome to the smaller (B) subgenome. We show that P. annua's B subgenome is preferentially accumulating genes and that its genes are more highly expressed. Whole-genome resequencing of several additional P. annua accessions revealed large-scale chromosomal rearrangements characterized by extensive TE-downsizing and evidence to support the Genome Balance Hypothesis. Conclusions: The divergent evolutions of the diploid progenitors played a central role in conferring onto P. annua its remarkable phenotypic plasticity. We find that plant genes (guided by selection and drift) and transposable elements (mostly guided by host immunity) each respond to polyploidy in unique ways and that P. annua uses whole-genome duplication to purge highly parasitized heterochromatic sequences. The findings and genomic resources presented here will enable the development of homoeolog-specific markers for accelerated weed science and turfgrass breeding. [ABSTRACT FROM AUTHOR]

Polyploidy after hybridization between species can lead to immediate post-zygotic isolation, causing saltatory origin of new species. Although the incidence of polyploidization in plants is high, it is thought that a new polyploid lineage can succeed only if it establishes a new ecological niche divergent from its progenitor lineages. We tested the hypothesis that Rhodiola integrifolia from North America is an allopolyploid produced by R. rhodantha and R. rosea and determined whether its survival can be explained by the niche divergence hypothesis. To this end, we sequenced two low-copy nuclear genes (ncpGS and rpb2) in a phylogenetic analysis of 42 Rhodiola species and tested for niche equivalency and similarity using Schoener’s D as the index of niche overlap. Our phylogeny-based approach showed that R. integrifolia possesses alleles from both R. rhodantha and R. rosea. Dating analysis showed that the hybridization event that led to R. integrifolia occurred ca. 1.67 Mya and niche modeling analysis showed that at this time, both R. rosea and R. rhodantha may have been present in Beringia, providing the opportunity for the hybridization event. We also found that the niche of R. integrifolia differs from that of its progenitors in both niche breadth and optimum. Taken together, these results confirm the hybrid origin of R. integrifolia and support the niche divergence hypothesis for this tetraploid species. Our results underscore the fact that lineages with no current overlapping distribution could produce hybrid descendants in the past, when climate oscillations made their distributions overlap.

BackgroundOur understanding of polyploid genomes is limited by our inability to definitively assign sequences to a specific subgenome without extensive prior knowledge like high resolution genetic maps or genome sequences of diploid progenitors. In theory, existing methods for assigning sequences to individual species from metagenome samples could be used to separate subgenomes in polyploid organisms, however, these methods rely on differences in coarse genome properties like GC content or sequences from related species. Thus, these approaches do not work for subgenomes where gross features are indistinguishable and related genomes are lacking. Here we describe a method that uses rapidly evolving repetitive DNA to circumvent these limitations.ResultsBy using short, repetitive, DNA sequences as species-specific signals we separated closely related genomes from test datasets and subgenomes from two polyploid plants, tobacco and wheat, without any prior knowledge.ConclusionThis approach is ideal for separating the subgenomes of polyploid species with unsequenced or unknown progenitor genomes.

Societal impact statement Sour cherry (Prunus cerasus L.) is an agriculturally valuable tree that produces fruits used in a range of culinary dishes, beverages, and other products. The progenitor species and number of origins of sour cherry remain unresolved. Here, we performed phylogenetic analyses of plastid genomes and nuclear genes from nine wild species and three historically important sour cherry cultivars. Our analyses identified Prunus fruticosa and Prunus avium as the closest extant relatives of the progenitor species of tetraploid sour cherry. Furthermore, our analyses revealed P. fruticosa as the likely maternal contributor. These findings and transcriptomic datasets should serve as valuable new resources to guide future breeding efforts in sour cherry.

Polyploidy, which arises from genome duplication, has occurred throughout the history of eukaryotes, though it is especially common in plants. The resulting increased size, heterozygosity, and complexity of the genome can be an evolutionary opportunity, facilitating diversification, adaptation and the evolution of functional novelty. On the other hand, when they first arise, polyploids face a number of challenges, one of the biggest being the meiotic pairing, recombination and segregation of the suddenly more than two copies of each chromosome, which can limit their fertility. Both for developing polyploidy as a crop improvement tool (which holds great promise due to the high and lasting multi-stress resilience of polyploids), as well as for our basic understanding of meiosis and plant evolution, we need to know both the specific nature of the challenges polyploids face, as well as how they can be overcome in evolution. In recent years there has been a dramatic uptick in our understanding of the molecular basis of polyploid adaptations to meiotic challenges, and that is the focus of this review. [ABSTRACT FROM AUTHOR]

Dalbergioid is a large group within the family Fabaceae that consists of diverse plant species distributed in distinct biogeographic realms. Here, we have performed a comprehensive study to understand the evolution of the nucleotide-binding leucine-rich repeats (NLRs) gene family in Dalbergioids. The evolution of gene families in this group is affected by a common whole genome duplication that occurred approximately 58 million years ago, followed by diploidization that often leads to contraction. Our study suggests that since diploidization, the NLRome of all groups of Dalbergioids is expanding in a clade-specific manner with fewer exceptions. Phylogenetic analysis and classification of NLRs revealed that they belong to seven subgroups. Specific subgroups have expanded in a species-specific manner, leading to divergent evolution. Among the Dalbergia clade, the expansion of NLRome in six species of the genus Dalbergia was observed, with the exception of Dalbergia odorifera, where a recent contraction of NLRome occurred. Similarly, members of the Pterocarpus clade genus Arachis revealed a large-scale expansion in the diploid species. In addition, the asymmetric expansion of NLRome was observed in wild and domesticated tetraploids after recent duplications in the genus Arachis. Our analysis strongly suggests that whole genome duplication followed by tandem duplication after divergence from a common ancestor of Dalbergioids is the major cause of NLRome expansion. To the best of our knowledge, this is the first ever study to provide insight toward the evolution of NLR genes in this important tribe. In addition, accurate identification and characterization of NLR genes is a substantial contribution to the repertoire of resistances among members of the Dalbergioids species. [ABSTRACT FROM AUTHOR]

Allopolyploids are believed to inherit the genetic characteristics of its progenitors and exhibit stronger adaptability and vigor. The allotetraploid Isoetes sinensis was formed by the natural hybridization and polyploidization of two diploid progenitors, Isoetes taiwanensis and Isoetes yunguiensis, and was believed to have the potential to adapt to plateau environments. To explore the expression pattern of homoeologous genes and their contributions to altitude adaptation, we transplanted natural allotetraploid I. sinensis (TnTnYnYn) along the altitude gradient for a long‐term, and harvested them in summer and winter, respectively. One year after transplanting, it still lived well, even in the extreme environment of the Qinghai‐Tibet Plateau. Then, we performed high‐throughput RNA sequencing to measure their gene expression level. A total of 7801 homoeologous genes were expressed, among which 5786 were identified as shared expression in different altitudes and seasons. We further found that altitude variations could change the subgenome bias trend of I. sinensis, but season could not. Moreover, the functions of uniquely expressed genes indicated that temperature might be an important restrictive factor during the adaptation process. Through the analysis of DEGs and uniquely expressed genes, we found that Y subgenome provided more contributions to high altitude adaptation than T subgenome. These adaptive traits to high altitude may be inherited from its plateau progenitor I. yunguiensis. Through weighted gene co‐expression network analysis, pentatricopeptide repeats gene family and glycerophospholipid metabolism pathway were considered to play important roles in high‐altitude adaptation. Totally, this study will enrich our understanding of allopolyploid in environmental adaptation. [ABSTRACT FROM AUTHOR]

Hybridization is common and considered as an important evolutionary force to increase intraspecific genetic diversity. Detecting hybridization events is crucial for understanding the evolutionary history of species and further improving molecular breeding. The studies on identifying hybridization events through the phylogenomic approach are still limited. We proposed the conception and method of identifying allopolyploidy events by phylogenomics. The reconciliation and summary of nuclear multi-labeled gene family trees were adopted to untangle hybridization events from next-generation data in our novel phylogenomic approach. Given horticulturalists' relatively clear cultivated crossbreeding history, the water lily family is a suitable case for examining recent allopolyploidy events. Here, we reconstructed and confirmed the well- resolved nuclear phylogeny for the Nymphaeales family in the context of geological time as a framework for identifying hybridization signals. We successfully identified two possible allopolyploidy events with the parental lineages for the hybrids in the family Nymphaeaceae based on summarization from multi-labeled gene family trees of Nymphaeales. The lineages where species Nymphaea colorata and Nymphaea caerulea are located may be the progenitors of horticultural cultivated species Nymphaea 'midnight' and Nymphaea 'Woods blue goddess'. The proposed hybridization hypothesis is also supported by horticultural breeding records. Our methodology can be widely applied to identify hybridization events and theoretically facilitate the genome breeding design of hybrid plants. [ABSTRACT FROM AUTHOR]

There is a relatively long history of plant hybridization traced back to ancient time, both from theoretical as well as practical perspectives. At first considered as an evolutionary dead-end, it was soon recognized to have important role in plant speciation. Beside his work on pea, G.J. Mendel also conducted interspecific hybridization using several species including Hieracium. Current knowledge shows that the frequent occurrence of wide hybridization in nature is often connected with polyploidy. Interspecific hybridization has played a role in plant domestication and numerous crops are allopolyploids, sometimes of complex hybrid origin. This has been also used in practical breeding, extending even to intergeneric crosses which benefit from heterosis, transgressive segregation and introgression phenomenon. This review aims to provide a a historical retrospective and summarize both current knowledge and the usage of interspecific hybridization in crop breeding.

The Adriatic sturgeon, Acipenser naccarii (Bonaparte, 1836), is a critically endangered tetraploid endemism of the Adriatic region; it has been targeted, over the last 20 years, by different conservation programs based on controlled reproduction of captive breeders followed by the release of their juvenile offspring; its preservation would greatly benefit from the correct and coordinated management of the residual genetic variability available in the different captive stocks. In this sense, the setup of an efficient parental allocation procedure would allow identifying familiar groups and establishing informed breeding plans, effectively preserving genetic variation. However, being the species tetraploid, the analyses often deal with complex genome architecture and a preliminary evaluation of allele segregation patterns at different chromosomes is necessary to assess whether the species can be considered a pure tetraploid, as previously observed at some loci, or if a more complex situation is present. Here we study the segregation at 14 microsatellites loci in 12 familiar groups. Results support in different families the tetrasomic segregation pattern at 11 markers and the disomic segregation at three markers. The Adriatic sturgeon thus shows a mixed inheritance modality. In this species, and likely in other sturgeons, accurate knowledge of the loci used for paternity analysis is therefore required. [ABSTRACT FROM AUTHOR]

Polyploidization in plants often leads to increased cell size and grain size, which may be affected by the increased genome dosage and transcription abundance. The synthesized Triticum durum (AABB)-Haynaldia villosa (VV) amphiploid (AABBVV) has significantly increased grain size, especially grain length, than the tetraploid and diploid parents. To investigate how polyploidization affects grain development at the transcriptional level, we perform transcriptome analysis using the immature seeds of T. durum, H. villosa, and the amphiploid. The dosage effect genes are contributed more by differentially expressed genes from genome V of H. villosa. The dosage effect genes overrepresent grain development-related genes. Interestingly, the vernalization gene TaVRN1 is among the positive dosage effect genes in the T. durum‒H. villosa and T. turgidum‒Ae. tauschii amphiploids. The expression levels of TaVRN1 homologs are positively correlated with the grain size and weight. The TaVRN1-B1 or TaVRN1-D1 mutation shows delayed florescence, decreased cell size, grain size, and grain yield. These data indicate that dosage effect genes could be one of the important explanations for increased grain size by regulating grain development. The identification and functional validation of dosage effect genes may facilitate the finding of valuable genes for improving wheat yield., Competing Interests: Conflict of interest The authors declare no competing interests., (Copyright © 2024 Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, and Genetics Society of China. Published by Elsevier Ltd. All rights reserved.)

There is a relatively long history of plant hybridization traced back to ancient time, both from theoretical as well as practical perspectives. At first considered as an evolutionary dead-end, it was soon recognized to have important role in plant speciation. Beside his work on pea, G.J. Mendel also conducted interspecific hybridization using several species including Hieracium. Current knowledge shows that the frequent occurrence of wide hybridization in nature is often connected with polyploidy. Interspecific hybridization has played a role in plant domestication and numerous crops are allopolyploids, sometimes of complex hybrid origin. This has been also used in practical breeding, extending even to intergeneric crosses which benefit from heterosis, transgressive segregation and introgression phenomenon. This review aims to provide a a historical retrospective and summarize both current knowledge and the usage of interspecific hybridization in crop breeding. [ABSTRACT FROM AUTHOR]

Premise: Camelina (gold‐of‐pleasure or false flax) is an ancient oilseed crop with emerging applications in the production of sustainable, low‐input biofuels. Previous domestication hypotheses suggested a European or western Asian origin, yet little genetic evidence has existed to assess the geographical origin for this crop, and archaeological data have not been systematically surveyed. Methods: We utilized genotyping‐by‐sequencing of 185 accessions of C. sativa and its wild relatives to examine population structure within the crop species and its relationship to populations of its wild progenitor, C. microcarpa; cytotype variation was also assessed in both species. In a complementary analysis, we surveyed the archaeological literature to identify sites with archaeobotanical camelina remains and assess the timing and prevalence of usage across Europe and western Asia. Results: The majority of C. microcarpa sampled in Europe and the United States belongs to a variant cytotype (2n = 38) with a distinct evolutionary origin from that of the crop lineage (2n = 40). Populations of C. microcarpa from Transcaucasia (South Caucasus) are most closely related to C. sativa based on cytotype and population structure; in combination with archaeological insights, these data refute prior hypotheses of a European domestication origin. Conclusions: Our findings support a Caucasus, potentially Armenian, origin of C. sativa domestication. We cannot definitively determine whether C. sativa was intentionally targeted for domestication in its own right or instead arose secondarily through selection for agricultural traits in weedy C. sativa, as originally proposed by Vavilov for this species. [ABSTRACT FROM AUTHOR]

Distant hybridization is an effective strategy for creating polyploids in fish genetic breeding. In this study, the cross of common carp (Cyprinus carpio , 2n = 100, COC, ♀) and topmouth culter (Culter alburnus , 2n = 48, TC, ♂), which belonged to different subfamilies, was conducted and obtained surviving hybrid offspring (CT hybrids). Based on the measurement of DNA content and chromosomal numbers, three ploidy levels of CT hybrids were identified: diploid hybrids (2n = 74, 2nCT), triploid hybrids (3n = 124, 3nCT), and tetraploid hybrids (4n = 148, 4nCT). Analyses of countable traits and measurable traits indicated a significant similarity between CT hybrids and COC in comparison to TC. The genetic variation analysis of 5S rDNA and HoxD10a gene in CT hybrids revealed the retention of all COC genotypes and the partial elimination of TC genotypes, as well as the generation of novel variant genotypes (derived from TC genotypes) and recombinant genotypes (derived from parental genotypes), which suggested that in CT hybrids, the paternal subgenome exhibited greater instability than the maternal subgenome. In addition, the droplet digital PCR (ddPCR) method, combining allele-specific probes targeting the EPHX2 gene, was employed for the first time to investigate the genome composition of hybrids. The results showed that the ratios of COC-allele number to TC-allele number were approximately 1 in 2nCT, 2 in 3nCT, and 1.5 in 4nCT, respectively, which confirmed the hybridization origins for each type and effectively distinguished between the three CT hybrids. The obtainment of CT hybrids harbors potential benefits and application in aquaculture and provides an ideal model for understanding the influence of hybridization and polyploidization on the genomic composition of fish species. • 2nCT, 3nCT, and 4nCT hybrids were obtained from the cross of female COC × male TC. • The appearance of CT hybrids resembled COC more than TC. • The paternal subgenome exhibited greater instability than the maternal subgenome. • Three CT hybrids could be effectively distinguished by ddPCR with specific probes. [ABSTRACT FROM AUTHOR]

Summary: Humans have domesticated diverse species from across the plant kingdom; however, our current understanding of plant domestication is largely founded on major cereal crops. Here, we examine the evolutionary processes and genetic basis underlying the domestication of water caltrop (Trapa spp., Lythraceae), a traditional, yet presently underutilized non‐cereal crop that sustained early Chinese agriculturalists. We generated a chromosome‐level genome assembly of tetraploid T. natans, and then divided the allotetraploid genome into two subgenomes. Based on resequencing data from 57 accessions, representing cultivated diploid T. natans, wild T. natans (2x and 4x) and diploid T. incisa, we showed that water caltrop was likely first domesticated in the Yangtze River Valley as early as 6300 yr BP, and experienced a second improvement c. 800 years ago. We also provided strong support for an allotetraploid origin of T. natans within the past 230 000–310 000 years. By integrating selective sweep and transcriptome profiling analyses, we identified a number of genes potentially selected and/or differentially expressed during domestication, some of which likely contributed not only to larger fruit sizes but also to a more vigorous root system, facilitating nutrient uptake, environmental stress response and underwater photosynthesis. Our results shed light on the evolutionary and domestication history of water caltrop, one of the earliest domesticated crops in China. This study has implications for genomic‐assisted breeding of this presently underutilized aquatic plant, and improves our general understanding of plant domestication. [ABSTRACT FROM AUTHOR]

Allopolyploid Brassica juncea is particularly enriched in sinigrin, a kind of 3C aliphatic glucosinolates (GSLs), giving rise to characteristic taste after picking. However, the molecular mechanism underlying 3C aliphatic GSLs biosynthesis in this species remains unknown. In this study, we genome-widely identified GSLs metabolic genes, indicating different evolutionary rate of GSLs metabolic genes between subgenomes of B. juncea. Eight methythioalkylmalate synthase (MAMs) homologs were identified from B. juncea, in which six MAM1s were located in chloroplast and the other two were not detected with any expression. Furthermore, BjMAM1-4, BjMAM1-5, and BjMAM1-6 displayed higher expression levels in leaves than other tissues. Silenced expression analysis revealed that BjMAM1-4 and BjMAM1-6 function in 3C and 4C aliphatic GSLs accumulation. The specificity of the substrate selection for the second cycle reaction is much lower than that of the first cycle, suggesting these genes may preferentially catalyze 3C aliphatic GSLs biosynthesis. Our study provides insights into the molecular mechanism underlying the accumulation of 3C aliphatic GSLs, thereby facilitating the manipulation of aliphatic GSLs content in B. juncea.

It has recently become clear that many invasive species have evolved in situ via hybridization or polyploidy from progenitors which themselves are introduced species. For species formed by hybridization or polyploidy, genetic diversity within the newly formed species is influenced by the number of independent evolutionary origins of the species. For recently formed species, an analysis of genetic structure can provide insight into the number of independent origin events involved in the formation of the species. For a putative invasive allopolyploid species, the number of origins involved in the species formation, the genetic diversity present within these origins, and the level of gene flow between independent origins determines the genetic composition of the neospecies. Here we analyze the genetic structure of the newly formed allopolyploid species, Salsola ryanii, a tumbleweed which evolved within the last 20-100 years in California. We utilize the genetic structure analysis to determine that this new species is the result of at least three independent allopolyplodization events followed by gene flow between the descendants of independent origins.

Summary: Allopolyploid Brassica juncea crops in Brassicaceae are becoming increasingly revitalized as vegetables and oilseeds owing to wide adaptability and significant economic values. However, the genomic differentiation of diversified vegetables and oilseed B. juncea and the genetic basis underlying glucosinolates accumulation have yet to be elucidated. To address this knowledge gap, we report the sequencing of pairwise genomes of vegetable and oilseed B. juncea at chromosome scale. Comparative genomics analysis unveils panoramic structural variation footprints, particularly the genetic loci of HSP20 and TGA1 associated with abiotic and biotic stresses responses between oilseed and vegetable subgroups. We anchored two major loci of MYB28 (HAG1) orthologues caused by copy number variations on A02 and A09 chromosomes using scored genomic SNPs‐based GWAS that are responsible for seed oil quality‐determining glucosinolates biosynthesis. These findings will provide valuable repertories of polyploidy genomic information enabling polyploidy genome evolution studies and precise genomic selections for crucial traits like functional components of glucosinolates in B. juncea crops and beyond. [ABSTRACT FROM AUTHOR]

Whole genome duplications (WGDs) have played a major role in angiosperm species evolution. Polyploid plants have undergone multiple cycles of ancient WGD events during their evolutionary history. However, little attention has been paid to the additional WGD of the existing allopolyploids. In this study, we explored the influences of additional WGD on the allopolyploid Brassica napus. Compared to tetraploid B. napus, octoploid B. napus (AAAACCCC, 2n = 8x =76) showed significant differences in phenotype, reproductive ability and the ploidy of self-pollinated progeny. Genome duplication also altered a key reproductive organ feature in B. napus, that is, increased the number of pollen apertures. Unlike autopolyploids produced from the diploid Brassica species, the octoploid B. napus produced from allotetraploid B. napus had a relatively stable meiotic process, high pollen viability and moderate fertility under self-pollination conditions, indicating that sub-genomic interactions may be important for the successful establishment of higher-order polyploids. Doubling the genome of B. napus provided us with an opportunity to gain insight into the flexibility of the Brassica genomes. The genome size of self-pollinated progeny of octoploid B. napus varied greatly, and was accompanied by extensive genomic instability, such as aneuploidy, mixed-ploidy and mitotic abnormality. The octoploid B. napus could go through any of genome reduction, equilibrium or expansion in the short-term, thus providing a novel karyotype library for the Brassica genus. Our results reveal the short-term evolutionary consequences of recurrent polyploidization events, and help to deepen our understanding of polyploid plant evolution.

Abstract Background The Chinese Isoetes L. are distributed in a stairway pattern: diploids in the high altitude and polyploids in the low altitude. The allopolyploid I. sinensis and its diploid parents I. yunguiensis and I. taiwanensis is an ideal system with which to investigate the relationships between polyploid speciation and the ecological niches preferences. Results There were two major clades in the nuclear phylogenetic tree, all of the populations of polyploid were simultaneously located in both clades. The chloroplast phylogenetic tree included two clades with different populations of the polyploid clustered with the diploids separately: I. yunguiensis with partial populations of the I. sinensis and I. taiwanensis with the rest populations of the I. sinensis. The crow node of the I. sinensis allopolyploid system was 4.43 Ma (95% HPD: 2.77–6.97 Ma). The divergence time between I. sinensis and I. taiwanensis was estimated to 0.65 Ma (95% HPD: 0.26–1.91 Ma). The narrower niche breadth in I.sinensis than those of its diploid progenitors and less niche overlap in the pairwise comparisons between the polyploid and its progenitors. Conclusions Our results elucidate that I. yunguinensis and I. taiwanensis contribute to the speciation of I. sinensis, the diploid parents are the female parents of different populations. The change of altitude might have played an important role in allopolyploid speciation and the pattern of distribution of I. sinensis. Additionally, niche novelty of the allopolyploid population of I. sinensis has been detected, in accordance with the hypothesis that niche shift between the polyploids and its diploid progenitors is important for the establishment and persistence of the polyploids.

Abstract Background Meiosis of newly formed allopolyploids frequently encounter perturbations induced by the merging of divergent and hybridizable genomes. However, to date, the meiotic properties of allopolyploids with dysploid parental karyotypes have not been studied in detail. The allotetraploid Cucumis ×hytivus (HHCC, 2n = 38) was obtained from interspecific hybridization between C. sativus (CC, 2n = 14) and C. hystrix (HH, 2n = 24) followed by chromosome doubling. The results of this study thus offer an excellent opportunity to explore the meiotic properties of allopolyploids with dysploid parental karyotypes. Results In this report, we describe the meiotic properties of five chromosomes (C5, C7, H1, H9 and H10) and two genomes in interspecific hybrids and C. ×hytivus (the 4th and 14th inbred family) through oligo-painting and genomic in situ hybridization (GISH). We show that 1) only two translocations carrying C5-oligo signals were detected on the chromosomes C2 and C4 of one 14th individual by the karyotyping of eight 4th and 36 14th plants based on C5- and C7-oligo painting, and possible cytological evidence was observed in meiosis of the 4th generation; 2) individual chromosome have biases for homoeologous pairing and univalent formation in F1 hybrids and allotetraploids; 3) extensive H-chromosome autosyndetic pairings (e.g., H-H, 25.5% PMCs) were observed in interspecific F1 hybrid, whereas no C-chromosome autosyndetic pairings were observed (e.g. C-C); 4) the meiotic properties of two subgenomes have significant biases in allotetraploids: H-subgenome exhibits higher univalent and chromosome lagging frequencies than C-subgenome; and 5) increased meiotic stability in the S14 generation compared with the S4 generation, including synchronous meiosis behavior, reduced incidents of univalent and chromosome lagging. Conclusions These results suggest that the meiotic behavior of two subgenomes has dramatic biases in response to interspecific hybridization and allopolyploidization, and the meiotic behavior harmony of subgenomes is a key subject of meiosis evolution in C. ×hytivus. This study helps to elucidate the meiotic properties and evolution of nascent allopolyploids with the dysploid parental karyotypes.

The Adriatic sturgeon, Acipenser naccarii (Bonaparte, 1836), is a critically endangered tetraploid endemism of the Adriatic region; it has been targeted, over the last 20 years, by different conservation programs based on controlled reproduction of captive breeders followed by the release of their juvenile offspring; its preservation would greatly benefit from the correct and coordinated management of the residual genetic variability available in the different captive stocks. In this sense, the setup of an efficient parental allocation procedure would allow identifying familiar groups and establishing informed breeding plans, effectively preserving genetic variation. However, being the species tetraploid, the analyses often deal with complex genome architecture and a preliminary evaluation of allele segregation patterns at different chromosomes is necessary to assess whether the species can be considered a pure tetraploid, as previously observed at some loci, or if a more complex situation is present. Here we study the segregation at 14 microsatellites loci in 12 familiar groups. Results support in different families the tetrasomic segregation pattern at 11 markers and the disomic segregation at three markers. The Adriatic sturgeon thus shows a mixed inheritance modality. In this species, and likely in other sturgeons, accurate knowledge of the loci used for paternity analysis is therefore required.