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Interspecific transfer of genetic information through polyploid bridges.

Hybridization blurs species boundaries and leads to intertwined lineages resulting in reticulate evolution. Polyploidy, the outcome of whole genome duplication (WGD), has more recently been implicated in promoting and facilitating hybridization between polyploid species, potentially leading to adaptive introgression. However, because polyploid lineages are usually ephemeral states in the evolutionary history of life it is unclear whether WGD-potentiated hybridization has any appreciable effect on their diploid counterparts. Here, we develop a model of cytotype dynamics within mixed-ploidy populations to demonstrate that polyploidy can in fact serve as a bridge for gene flow between diploid lineages, where introgression is fully or partially hampered by the species barrier. Polyploid bridges emerge in the presence of triploid organisms, which despite critically low levels of fitness, can still allow the transfer of alleles between diploid states of independently evolving mixed-ploidy species. Notably, while marked genetic divergence prevents polyploid-mediated interspecific gene flow, we show that increased recombination rates can offset these evolutionary constraints, allowing a more efficient sorting of alleles at higher-ploidy levels before introgression into diploid gene pools. Additionally, we derive an analytical approximation for the rate of gene flow at the tetraploid level necessary to supersede introgression between diploids with nonzero introgression rates, which is especially relevant for plant species complexes, where interspecific gene flow is ubiquitous. Altogether, our results illustrate the potential impact of polyploid bridges on the (re)distribution of genetic material across ecological communities during evolution, representing a potential force behind reticulation.

Polyploidy

Genomic resequencing unravels species differentiation and polyploid origins in the aquatic plant genus Trapa.

Trapa L. is a non-cereal aquatic crop with significant economic and ecological value. However, debates over its classification have caused uncertainties in species differentiation and the mechanisms of polyploid speciation. This study employed whole-genome resequencing together with the fruit morphology of 229 Trapa accessions (153 Asian and 76 North American samples) to elucidate species differentiation and polyploidization events in Trapa. For the species with AA genome and large fruits, clear genetic differentiation was found between two clades with different geographic origins, that is, from the Yangtze River and Amur River basins. The invasive AA species in North America (T. natans) was identified as originating from the Amur River based on genetic and morphological similarities, while all the cultivated accessions were AA species originating from the Yangtze River with severe genetic impoverishment. The separation of the two BB species with small seeds, that is, T. incisa and T. maximowiczii, was strongly supported by both morphological and genetic evidence. For the tetraploids, Asian and North American tetraploids were revealed to have distinct evolutionary origins. Asian allotetraploids (AABB) originated through hybridization between AA diploids from the Yangtze River Basin and BB diploids T. maximowiczii, supported by nuclear and chloroplast evidence. In contrast, the invasive North American tetraploids (T. bispinosa var. iinumai) exhibited an AACC-like genome, suggesting an independent polyploidization involving an unknown "CC" diploid. These findings provide critical insights into Trapa's complex evolutionary history, polyploidizations, and invasive origins, offering a genomic foundation for the conservation and sustainable utilization of the underutilized aquatic crop amid global environmental challenges.

Polyploidy

Distinct evolutionary trajectories of subgenomic centromeres in polyploid wheat.

BACKGROUND: Centromeres are crucial for precise chromosome segregation and maintaining genome stability during cell division. However, their evolutionary dynamics, particularly in polyploid organisms with complex genomic architectures, remain largely enigmatic. Allopolyploid wheat, with its well-defined hierarchical ploidy series and recent polyploidization history, serves as an excellent model to explore centromere evolution. RESULTS: In this study, we perform a systematic comparative analysis of centromeres in common wheat and its corresponding ancestral species, utilizing the latest comprehensive reference genome assembly available. Our findings reveal that wheat centromeres predominantly consist of five types of centromeric-specific retrotransposon elements (CRWs), with CRW1 and CRW2 being the most prevalent. We identify distinct evolutionary trajectories in the functional centromeres of each subgenome, characterized by variations in copy number, insertion age, and CRW composition. By utilizing CENH3-ChIP data across various ploidy levels, we uncover a series of CRW invasion events that have shaped the evolution of AA subgenome centromeres. Conversely, the evolutionary process of the DD subgenome centromeres involves their expansion from diploid to hexaploid wheat, facilitating adaptation to a larger genomic context. Integration of complete einkorn centromere assemblies and Aegilops tauschii pan-genomes further revealed subgenome-specific centromere evolutionary trajectories. By inclusion of synthetic hexaploid from S2-S3 generations, alongside 2x/6 × natural accessions, we demonstrate that DD subgenome centromere expansion represents a gradual evolutionary process rather than an immediate response to polyploidization. CONCLUSIONS: Our study provides a comprehensive landscape of centromere adaptation, evolution, and maturation, along with insights into how retrotransposon invasions drive centromere evolution in polyploid wheat.

Centromere

RHAMM drives formation of polyploid cancer cells and confers resistance to ER-targeted therapy in breast cancer.

Endocrine resistance in ER+ breast cancer remains a major clinical challenge. Here, we identify RHAMM as a key driver of resistance by orchestrating polyploid cancer cell (PCC) formation. Single-cell transcriptomics uncovered a G2/M-enriched, RHAMM+ subpopulation in endocrine-resistant tumors. Mechanistically, RHAMM binds Septin9/10 to promote aberrant cytoskeleton polymerization, activating YAP independent of Hippo signaling, which induces cytokinesis failure and facilitates PCC generation. Concurrently, RHAMM destabilizes p21 mRNA, enabling cell cycle progression despite genomic instability. The RHAMM-p21 axis serves as a bypass mechanism supporting polyploidization. Upon endocrine treatment, RHAMM is transcriptionally up-regulated by Slug. Clinically, RHAMMhigh signatures are enriched in metastatic and recurrent ER+ tumors and correlate with poor prognosis, highlighting its therapeutic relevance. Importantly, targeting RHAMM or YAP abrogates PCC formation and restores fulvestrant sensitivity. These findings reveal RHAMM-mediated polyploidization as an adaptive mechanism underlying endocrine resistance, suggesting the therapeutic potential of targeting the RHAMM-YAP axis.

Humans

Unraveling evolutionary pathways: allopolyploidization and introgression in polyploid Prunus (Rosaceae).

Allopolyploidization, resulting from hybridization and subsequent whole-genome duplication (WGD), is a fundamental mechanism driving evolutionary diversification across various lineages within the Tree of Life. The polyploid Prunus (Rosaceae), significant for its economic and agricultural value, provides an ideal model for investigating the evolutionary dynamics associated with allopolyploidy. In this study, we utilized deep genome skimming (DGS) data to demonstrate a comprehensive analytical framework for elucidating the underlying allopolyploidy that includes a newly adapted tool (DGS-Tree2GD) tailored explicitly for accurately detecting WGD events. Additionally, we introduced two methods to evaluate the contribution of incomplete lineage sorting (ILS) to lineage diversification. Phylogenomic discordance analyses revealed that allopolyploidization, rather than ILS, played a dominant role in the origin and dynamics of polyploid Prunus. Moreover, we inferred that the uplift of the Himalayas from the Middle to Late Miocene was a key driver in the rapid diversification of the Maddenia clade, an endemic group in East Asia. This geological event facilitated extensive hybridization and allopolyploidization, particularly the introgression between the Himalayas-Hengduan and Central-Eastern China clades. This case study demonstrates the robustness and efficacy of our analytical approach in precisely identifying WGD events and elucidating the evolutionary mechanisms underlying allopolyploidization in polyploid Prunus.

Polyploidy

Deciphering the mosaic genome of sugarcane cultivars through polyploid admixture inference with AdmixPoly.

BACKGROUND: Characterizing population structure and admixture events between ancestral groups plays a key role in understanding the evolutionary history of species and crops. Most tools for inferring admixture have been developed for diploids and are not suitable for polyploids, in particular those with high and mixed ploidy such as Saccharum. RESULTS: Here we present AdmixPoly, an R-package designed to infer admixture in polyploid species both at the genome-wide scale and locally along chromosomes. We compare AdmixPoly with state-of-the-art methods using simulations, demonstrating its precision and computational efficiency. Notably, local admixture inference in complex scenarios, such as high ploidy levels, large numbers of ancestral groups and alleles per marker is enabled through efficient approximations of emission and transition probabilities within a hidden Markov model framework. We apply this approach to characterize the contributions of wild Saccharum species to the complex polyploid genome of modern sugarcane cultivars. A panel of wild and cultivated Saccharum accessions is genotyped for 80K genomic regions, each revealing approximately 50 read-scale haplotypes. CONCLUSIONS: The results reveal that most of the approximately 12 copies of each basic chromosome in modern cultivars are derived from the domesticated species Saccharum officinarum, with one to four copies typically contributed by distinct subgroups of the wild species Saccharum spontaneum. In addition, contributions from an unknown wild Saccharum group originating from the Pacific were identified in most cultivars. The conserved pattern of these introgressions suggests that they can be traced back to the early stages of sugarcane breeding approximately a century ago.

Saccharum

Genomic analyses of three Acanthus L. species provide insight into polyploidization-driven speciation and evolution.

Allopolyploidy fundamentally influences plant evolution, yet the genomic dynamics of allotetraploidization remain incompletely understood. We investigated Acanthus tetraploideus (2n = 4x = 96), an ecologically significant allotetraploid true mangrove from Indo-West Pacific intertidal zones. Our prior integrative investigations indicate that A. tetraploideus originated through hybridization of the diploid species A. ilicifolius and A. ebracteatus with subsequent chromosome doubling. Here, we present complete chromosome-scale genome assemblies for all three species, representing the first genomic resources for true mangrove polyploid research. Our analysis reveals that the three species have experienced at least four rounds of polyploidization events, with the most recent, approximately 53 mya, possibly an Acanthus-specific event. The allotetraploid A. tetraploideus, which emerged between 1.5 and 2.2 mya, has A. ebracteatus as its maternal progenitor and A. ilicifolius as its paternal one. Through a comprehensive genomic comparison and analysis of homoeologous gene expression, we propose a gradual evolutionary trajectory for allotetraploidy in A. tetraploideus. Despite the allotetraploidization event dating back to around 2 mya, A. tetraploideus retains a high degree of colinearity with its ancestral genomes, with the majority (76.2%) of duplicated genes retained and no significant sub-genome bias in gene expression. Furthermore, we have identified positive selection in specific genes that may facilitate the adaptation of Acanthus mangrove species to their intertidal habitats. These findings establish A. tetraploideus as a model for studying allopolyploid evolution while providing new insights into mangrove speciation processes.

Genome, Plant

Adaptive evolution of polyploid crops.

Crop evolution represents a fundamental biological process through which plants respond to selection in different environments. This encompasses mechanisms operating at multiple scales of biological organization, including genetic and epigenetic regulation and higher-order interactions among molecular complexes. This Review synthesizes how polyploidy shapes crop evolution by generating duplicated genes, driving genome reorganization, altering dosage relationships and promoting regulatory divergence, which together influence crop metabolism, physiology, development and environmental responses. We focus mainly on the mechanisms underlying adaptation in polyploid crops, including the consequences of gene and genome duplication, genome reorganization and subfunctionalization. We also examine how hybridization, phenotypic plasticity and crop-microbiome interactions intersect with polyploidy to expand or constrain adaptive potential. Together, these processes affect crop survival, fitness and breeding value under changing environments. We suggest that future research connect polyploid genome architecture with experimentally validated signatures of selection and field performance to make better use of polyploidy-derived variation in crop improvement.

Polyploidy

Diploids derived from polyploids: genetic characteristics of four novel interspecific Sorghum populations.

Polyploidy has repeatedly shaped grass evolution, yet direct observations of how polyploid-derived chromosomes behave when returned to diploidy remain rare. Interspecific crosses between diploid Sorghum bicolor and tetraploid hybrids derived from Sorghum halepense generate mixed-ploidy progeny, providing an opportunity to examine chromosome transmission during the early stages of diploidization. Using genome-wide SNP markers, we characterized chromosomal inheritance patterns in 2 diploid and 2 tetraploid families derived from these crosses. Genotype-dosage profiles alone distinguished diploids from tetraploids with complete accuracy, reflecting strong ploidy-dependent differences in dosage-class distributions. Although diploid progeny retained much of the halepense-derived genomic background, several genomic intervals exhibited extended, nonrandom runs of S. bicolor homozygosity that remained polymorphic in corresponding tetraploid populations. These patterns, together with recurrent segregation distortion across independent families, suggest that the transition from tetraploidy to diploidy can expose allelic combinations that differ in transmission or viability. Analyses of flowering time further indicated that diploid and tetraploid derivatives possess distinct genomic architectures, with major association peaks occurring in different chromosomal regions across ploidy levels. Collectively, these results indicate that early diploidization involves nonrandom retention and loss of parental haplotypes shaped by both selective and structural constraints. The diploid extractions characterized here provide a rare empirical system for investigating the early stages of diploidization and a practical framework for studying and eventually mobilizing polyploid-derived variation for sorghum germplasm development. However, broader integration into elite breeding programs will require additional evaluation of cross-fertility, meiotic behavior, and chromosomal stability across diverse breeding backgrounds.

Sorghum

Genome-wide cyclin gene evolution in Arabidopsis and Brassica reveals polyploidization-driven duplication and flowering-time associations.

Cyclin genes are plant cell cycle regulators that play essential roles in growth, development, and reproduction. However, the evolutionary dynamics and genomic organization of cyclin genes across the Brassicaceae family remain poorly understood, particularly in the context of allotetraploid genome evolution. Here, we investigated the diversity, expansion mechanisms, and potential functional diversification of cyclin genes across ten Brassicaceae genomes, including four Arabidopsis and six Brassica species. A total of 1087 cyclin genes representing 23 cyclin types were identified. Comparative genomic analyses revealed that cyclin gene expansion was strongly influenced by polyploidization in Brassica species, with 1845 duplication events involving 1063 genes. Whole-genome duplication was the predominant mechanism driving expansion, while both inter- and intra-genomic duplications contributed to gene retention in tetraploid Brassica species, with the highest duplication frequency observed in Brassica juncea. Across genomes, 120 physical gene clusters were identified, including homogeneous and heterogeneous types. Ortholog analysis between progenitor and allotetraploid species identified 852 orthologous pairs involving 366 genes, indicating extensive conservation following allotetraploid formation. Phylogenetic analysis resolved cyclins into three major clades, while expression-based clustering in Brassica napus grouped genes into four major clusters, suggesting functional diversification. Integration of pan-genomic and flowering-time QTL analyses further identified two cyclin genes, Bna21cycA2 and Bna113cycD4, which contain amino acid polymorphisms and represent putative candidate variations potentially associated with flowering-time variation across multiple genomes. These findings provide new insights into the evolutionary expansion, retention, and potential functional divergence of cyclin genes in Brassicaceae and highlight candidate loci for future functional studies and crop improvement.

Evolution, Molecular

Transposable element-driven expansion of enhancer RNA repertoires underlies regulatory innovation and polyploid adaptation in cereal crops.

Cereal genomes have undergone repeated polyploidization and transposable element (TE) proliferation, collectively generating complex regulatory landscapes. However, the evolutionary trajectories and functional implications of these landscapes remain largely unexplored. Using chromatin-bound RNA sequencing across seven cereal species, we systematically mapped 45,952 regulatory element transcripts (RETs), including 32,867 distal RETs corresponding to enhancer RNAs (eRNAs). Our analysis revealed that 56% of lineage-specific eRNAs originated from TE expansions, indicating that TEs serve as major reservoirs of species-specific regulatory innovation in cereals. Notably, we identified remarkable conservation in defense-related functions, root-specific expression, and TE-derived origins of eRNAs across both ancient and recent evolutionary layers of Triticeae, suggesting recurrent recruitment of TE-derived, root-associated regulatory elements throughout Triticeae evolution. Furthermore, we found that young eRNA pairs in hexaploid wheat with high sequence similarity, many originating from RLG_famc8.3 and DTC_famc4.3, exhibited pronounced root specificity and coordinated expression, suggesting targeted amplification and refinement of successful ancestral regulatory strategies established after Triticeae divergence. To facilitate community access, we developed Cereal-eRNAdb (http://bioinfo.cemps.ac.cn/Cereal-eRNAdb/), a comprehensive database integrating 69,426 eRNAs with functional annotations across 296 samples. Our findings suggest that TE-mediated innovation of root-specific eRNAs may contribute to Triticeae adaptation and provide a foundational resource for exploiting regulatory variation in cereal crop breeding.

Enhancer RNAs

Comparative transmission genetics of introgressed chromatin in reciprocal advanced backcross populations in Gossypium (cotton) polyploids.

Introgression is a potential source of valuable genetic variation and interspecific introgression lines are important resources for plant breeders to access novel alleles. Experimental advanced-generation backcross populations contain individuals with genomic compositions similar to those resulting from natural interspecific hybridization and provide opportunities to study the nature and transmission pattern of donor chromatin in recipient genomes. Here, we analyze transmission of donor chromatin in reciprocal backcrosses between G. hirsutum and G. barbadense. Across the genome, recurrent backcrossing in both backgrounds yielded donor chromatin at slightly higher frequencies than the Mendelian expectation in BC5F1 plants, while the average frequency of donor alleles in BC5F2 segregating families was less than expected. In the two subgenomes of polyploid cotton, the rate of donor chromatin introgression was similar. Although donor chromatin was tolerated over much of the recipient genomes, 21 regions recalcitrant to donor alleles were identified. Only limited correspondence is observed between the recalcitrant regions in the two backgrounds, suggesting the effect of species background on introgression of donor segments. Genetic breakdown was progressive, with floral abscission and seed inviability ongoing during backcrossing cycles. Regions of either high or low introgression tended to be in terminal chromosomal regions that are generally rich in both genes and crossover events, with long stretches around the centromere having limited crossover activity resulting in relatively constant low introgression frequencies. Constraints on fixation and selection of donor alleles highlights the challenges of utilizing introgression breeding in crop improvement.

Humans

A high-quality draft genome assembly of Johnsongrass illuminates relationships between polyploidization, crop-wild hybridization, and reproductive biology.

Johnsongrass [Sorghum halepense (L.) Pers.] is an allopolyploid, rhizomatous, perennial grass species and one of the most troublesome weeds in global agriculture. We assembled the first Johnsongrass genome to clarify poorly understood genetic factors influencing variable rates of crop-wild hybridization with cultivated sorghum [S. bicolor (L.) Moench]. The draft genome assembly has a total size of 3.26 Gb and BUSCO completeness of 95.3%. We also report the first evolutionary analysis of INHIBITION OF ALIEN POLLEN (IAP), the only known cross-(in)compatibility locus in the genus. Our results reveal an evolutionary history of genome instability, including the loss of distinct parental subgenomes, and suggest that Nebraska accession 'J-37,' the genome donor, is a segmental allotetraploid that may function as a diploid or aneuploid during meiosis. Genome instability could explain observations of variable ploidies in Johnsongrass and facilitate ongoing hybridization with sorghum where gamete ploidies and IAP alleles match. Given this information, we provide a suggested research framework for studying evolution and gene expression in the Sorghum genus where crop-wild hybridization occurs and for predicting the potential for hybridization between specific crossing partners. Collectively, this work will bolster efforts to study and manage reproductive biology in other crop-wild polyploid complexes.

Sorghum

Ancient polyploidization waves as evolutionary shields for angiosperms.

Chen et al. identified 132 whole-genome duplications (WGDs) clustered around environmental crises. We highlight how, over longer evolutionary timescales, ancient WGDs convergently retained MADS-box, MYB, WRKY and HSF transcription factors, building stress-adaptation networks. These insights guide climate-resilient crop improvement through comparative genomics and CRISPR engineering.

MADS-box

Genome diversity and evolution of the duckweed section Alatae comprising diploids, polyploids, and interspecific hybrids.

The section Alatae of genus Lemna of the monocotyledonous aquatic duckweed family (Lemnaceae) consists of rather diverse accessions with unknown phylogeny and unclear taxonomic assignment. In contrast to other duckweeds, some Alatae accessions, in addition to mainly vegetative propagation, produce readily flowers and viable seeds. We analyzed the genomic diversity and phylogenetic relationship of 52 Alatae accessions. For this purpose, we applied multiple molecular and cytogenetic approaches, including plastid and nuclear sequence polymorphisms, chromosome counting, genome size determination, and genomic in situ hybridization in combination with geographic distribution. We uncovered ploidy variation, recurrent hybridization, and backcrosses between species and their hybrids. The latter successfully spread over three continents. The results elucidate the evolution of Alatae accessions and explain the difficult taxonomic assignment of distinct accessions. Our study might be an example for analogous studies to resolve the hitherto unclear relationships among accessions of the duckweed genera Wolffiella and Wolffia.

Araceae

Periplasmic SacB as a robust counter-selection tool for genome engineering in the polyploid bacterium Zymomonas mobilis.

UNLABELLED: The alpha-proteobacterium Zymomonas mobilis exhibits exceptional ethanologenic physiology, which makes it a traditional alcoholic beverage producer and a promising chassis for biofuel production. Although genetic tools for this organism have expanded in recent years, a fundamental aspect of its chromosome organization remains to be understood. In particular, Z. mobilis has been suggested to exhibit polyploidy, but this feature is not fully confirmed because of discrepancies among studies reporting the copy number of chromosomes. Here, we tagged the chromosome-partitioning protein ParB with a fluorescent marker to visualize its cellular localization and estimate chromosome copy number in individual cells. Imaging showed that Z. mobilis exhibits several distinctive ParB foci throughout the cytoplasm and an accumulated focus at the pole, indicating that a single Z. mobilis cell contains >5 copies of the chromosome at the oriC regions. We then sought to establish an efficient counter-selection system, which is crucial for engineering multiple copies of the chromosome. We assessed the efficacy of levan-sucrase (SacB) toxicity in Z. mobilis. We found that, despite Z. mobilis secreting a native extracellular sucrase SacB, heterologous periplasmically localized Bacillus subtilis SacB rendered Z. mobilis cells sensitive to sucrose. We successfully used this effect for counter-selection when deleting and inserting targeted DNA sequences into the Z. mobilis genome. Together, this work provides important insights and tools for advancing Z. mobilis genetics and its biotechnological applications. IMPORTANCE: Zymomonas mobilis is a promising industrial bacterium with the capacity to convert sugars into ethanol at nearly maximum theoretical yield. With its expanding use in industrial applications, it is crucial to clarify if individual Z. mobilis cells carry multiple copies of the chromosome, as this has important implications for genome engineering. Two previous studies have used quantitative PCR to address this question, but their reported chromosome copy numbers varied widely from 20 to 100. Here, we used a cell biological approach to estimate the copy number and confirmed that a single Z. mobilis cell possesses multiple copies. In addition, we show that a SacB-based counter-selection works in Z. mobilis, enabling efficient and complete mutation of all chromosome copies.

Zymomonas

Unscheduled polyploidy synergizes with oncogenic mutations to enhance genome instability and tumorigenesis.

Polyploid Giant Cancer Cells (PGCCs) occur across multiple cancer types and are associated with therapy resistance, genome instability, disease progression, and metastasis. PGCCs can grow through endocycles, a variant cell cycle of alternating Growth (G) and DNA Synthesis (S) phases without cell division. Unlike programmed endocycles that occur during normal tissue development, PGCCs switch from mitotic cycles to unscheduled endocycles in response to stress. PGCCs can subsequently return to error-prone divisions which generate aneuploid daughter cells that contribute to disease progression. However, the regulation of PGCC cell cycles and contributions to cancer are still being defined. Filling this knowledge gap will lead to the development of improved cancer therapies. In this study, we used a molecular-genetic system in the model organism Drosophila melanogaster to examine how oncogenes interact with unscheduled endocycles in vivo. We found that several oncogenes promote bypass of an endocycle arrest, resulting in increased polyploid cell size and DNA content. The extent of this increased growth was dependent on the type of oncogenic mutation. When these polyploid cells returned to division, RasG12V promoted continued divisions of polyploid daughter cells with elevated genome instability. RasG12V expression during transient endocycles and subsequent divisions also induced expression of a matrix metalloprotease and a Wnt pathway ligand. Importantly, RasG12V with transient endocycles enhanced the growth of large, neoplastic tumors. These findings indicate that oncogenic mutations can synergize with transient, unscheduled endocycles to promote tumorigenesis with important broader implications for cancer prognosis and therapies.

Animals