Polyploidy and novelty: Gottlieb's legacy

Natural neopolyploids: a stimulus for novel research

Recently formed allopolyploid species offer unprecedented insights into the early stages of polyploid evolution. This review examines seven well-studied neopolyploids (we use 'neopolyploid' to refer to very recently formed polyploids, i.e. during the past 300 years), spanning different angiosperm families, exploring commonalities and differences in their evolutionary trajectories. Each neopolyploid provides a unique case study, demonstrating both shared patterns, such as rapid genomic and phenotypic changes, and unique responses to hybridization and genome doubling. While previous studies of these neopolyploids have improved our understanding of polyploidy, significant knowledge gaps remain, highlighting the need for further research into the varied impacts of whole-genome duplication on gene expression, epigenetic modifications, and ecological interactions. Notably, all of these neopolyploids have spontaneously arisen due to human activity in natural environments, underscoring the profound consequences of polyploidization in a rapidly changing world. Understanding the immediate effects of polyploidy is crucial not only for evolutionary biology but also for applied practices, as polyploidy can lead to novel traits, as well as stress tolerance and increased crop yields. Future research directions include investigating the genetic and epigenetic mechanisms underlying polyploid evolution, as well as exploring the potential of neopolyploids for crop improvement and environmental adaptation.

Differential Gene Expression and Unbalanced Homeolog Expression Bias in 4 Million-Year-Old Allopolyploids of Nicotiana Section Repandae

Allopolyploidy, a phenomenon prevalent in angiosperms involving hybridization and whole-genome duplication, results in species with multiple subgenomes, altering genome structure and gene expression, leading to novel phenotypes. Allopolyploids often experience unbalanced homeolog expression bias, the preferential expression of homeologs from one of the two progenitor genomes. To explore the consequences of allopolyploidy and unbalanced homeolog expression bias, we investigate global gene expression and the fate of homeologs in Nicotiana (Solanaceae). We focus on Nicotiana section Repandae, including three allotetraploid species, Nicotiana nudicaulis, N. repanda, and N. stocktonii, derived from diploid progenitors N. sylvestris and N. obtusifolia ∼4.3 Ma. We identify genes with differential expression and investigate expression of candidate genes for flower size variation. Our results show expression differences with the allopolyploids intermediate between the two progenitor species, with a slight bias toward N. obtusifolia. Moreover, we demonstrate unbalanced homeolog expression bias toward the N. obtusifolia subgenome across developmental stages in the allopolyploids, with a stronger bias in N. nudicaulis. In contrast, unbalanced homeolog expression bias shifts toward N. sylvestris for flower size genes in N. nudicaulis, showing that genes involved in particular phenotypes can display different patterns of unbalanced homeolog expression than the overall transcriptome. We also see differential expression of several known flower size genes across corolla developmental stages. Our results highlight the role of unbalanced homeolog expression bias in shaping the evolutionary trajectory of Nicotiana species and provide a foundation for future research into the ecological and evolutionary implications of allopolyploidy in flowering plants.

The genomic secrets of invasive plants

Genomics has revolutionised the study of invasive species, allowing evolutionary biologists to dissect mechanisms of invasion in unprecedented detail. Botanical research has played an important role in these advances, driving much of what we currently know about key determinants of invasion success (e.g. hybridisation, whole-genome duplication). Despite this, a comprehensive review of plant invasion genomics has been lacking. Here, we aim to address this gap, highlighting recent discoveries that have helped progress the field. For example, by leveraging genomics in natural and experimental populations, botanical research has confirmed the importance of large-effect standing variation during adaptation in invasive species. Further, genomic investigations of plants are increasingly revealing that large structural variants, as well as genetic changes induced by whole-genome duplication such as genomic redundancy or the breakdown of dosage-sensitive reproductive barriers, can play an important role during adaptive evolution of invaders. However, numerous questions remain, including when chromosomal inversions might help or hinder invasions, whether adaptive gene reuse is common during invasions, and whether epigenetically induced mutations can underpin the adaptive evolution of plasticity in invasive populations. We conclude by highlighting these and other outstanding questions that genomic studies of invasive plants are poised to help answer.

When Genetic Diversity Is Low: The Effects of Ploidy Level on Plant Functional Trait Expression in Spartina Under Global Change

Whole genome duplication (WGD or polyploidization) events shape plant evolution, altering ecological responses and plant traits, particularly those related to cell and tissue size. We studied genetic diversity and phenotypic plasticity in Spartina populations, focusing on hybrid (Spartina × townsendii) and allopolyploid (S. anglica) cytotypes in Wadden Sea salt marshes. Our results reveal low genetic diversity in both cytotypes and a complex response of plant traits to global change factors (drought, elevated CO2 concentration). While WGD increased stomatal length, plasticity varied between cytotypes, with allopolyploids showing higher plasticity, especially under elevated CO2. Biomass allocation patterns differed between cytotypes under global change conditions, suggesting distinct effects on ecosystem functioning, such as belowground carbon sequestration and cycling. The allopolyploid's comparatively fewer, larger-diameter stems may affect aboveground ecosystem functions differently, including sediment trapping and the slowing of tidal currents. Despite similar genetic backgrounds, allopolyploids did not consistently exhibit higher plasticity, challenging previous assumptions. Our findings highlight the complex interplay between hybridization, WGD, phenotypic plasticity, and ecosystem responses to global change, emphasizing the importance of considering polyploidization in understanding plant adaptation and evolutionary dynamics.

Every Gain Comes With Loss: Ecological and Physiological Shifts Associated With Polyploidization in a Pygmy Frog

Polyploidization plays a pivotal role in vertebrate evolution and diversification. However, the effects of polyploidization on animals across various biological levels, and how these differences drive ecological shifts, remain unclear. Through karyotype analysis and whole-genome sequencing, we identified an autotetraploid Microhyla fissipes from Hainan Island, which shows reproductive isolation and geographic differentiation from its diploid counterpart. Tetraploids exhibited larger cell size, improved tadpole growth rates, and greater whole-body size, along with reduced cell cycle activity. Rather than being simple scaled-up diploids, tetraploids showed shifts in physiological performance, organ allometry, gene expression profiles, and metabolic patterns. Tetraploid adults demonstrated superior jumping ability and increased reproductive investment (e.g. larger gonads and steeper slopes in the relationship between gonadal weight and body weight), suggesting a potential competitive advantage over diploids. However, tetraploids exhibited higher energy expenditure at elevated temperatures, reduced hepatic energy storage, and altered pulmonary regulatory metabolites at 25 °C. Males had smaller relative heart sizes, and females showed flatter slopes in the relationship between heart and lung weight and body weight, indicating reduced investment in cardiopulmonary system. These variations suggest an increased risk of metabolic constraints under heat stress, putting tetraploids at a disadvantage in warmer regions. Importantly, the physiological tradeoffs associated with polyploidization help explain the geographical differentiation between diploids and tetraploids, which reflects a climatic boundary, with tetraploids occupying cooler northeastern areas. Our findings identify an autotetraploid frog, report the first autotetraploid genome in amphibians, and demonstrate how vertebrate polyploids physiologically and ecologically diverge from their diploid counterparts.

Genomic correlates of vascular plant reproductive complexity and the uniqueness of angiosperms

Whole genome duplication (WGD) likely plays an important role in plant macroevolution, and has been implicated in diversification rate shifts, structural innovations, and increased disparity. But the general effects of WGD are challenging to evaluate, in part due to the difficulty of directly comparing morphological patterns across disparate clades. We explored relationships between WGD and the evolution of reproductive complexity across vascular plants using a metric based on the number of reproductive part types. We used multiple regression models to evaluate the relative importance of inferred WGD events, genome size, and a suite of additional variables relating to growth habit and reproductive biology in explaining part type complexity. WGD was a consistent predictor of reproductive complexity only among angiosperms. Across vascular plants generally, reproductive biology, clade identity, and the presence of bisexual strobili (those that produce microsporangiate and megasporangiate organs) were better predictors of complexity. Angiosperms are unique among vascular plants in combining frequent polyploidy with high-reproductive complexity. Whether WGD is mechanistically linked to floral complexity is unclear, but we suggest widespread polyploidy and increased complexity were ultimately facilitated by the evolution of herbaceous growth habits in early angiosperms.

Accurate Inference of the Polyploid Continuum Using Forward-Time Simulations

Multiple rounds of whole-genome duplication (WGD) followed by diploidization have occurred throughout the evolutionary history of angiosperms. Much work has been done to model the genomic consequences and evolutionary significance of WGD. While researchers have historically modeled polyploids as either allopolyploids or autopolyploids, the variety of natural polyploids span a continuum of differentiation across multiple parameters, such as the extent of polysomic versus disomic inheritance, and the degree of genetic differentiation between the ancestral lineages. Here we present a forward-time polyploid genome evolution simulator called SpecKS. SpecKS models polyploid speciation as originating from a 2D continuum, whose dimensions account for both the level of genetic differentiation between the ancestral parental genomes, as well the time lag between ancestral speciation and their subsequent reunion in the derived polyploid. Using extensive simulations, we demonstrate that changes in initial conditions along either dimension of the 2D continuum deterministically affect the shape of the Ks histogram. Our findings indicate that the error in the common method of estimating WGD time from the Ks histogram peak scales with the degree of allopolyploidy, and we present an alternative, accurate estimation method that is independent of the degree of allopolyploidy. Lastly, we use SpecKS to derive tests that infer both the lag time between parental divergence and WGD time, and the diversity of the ancestral species, from an input Ks histogram. We apply the latter test to transcriptomic data from over 200 species across the plant kingdom, the results of which are concordant with the prevailing theory that the majority of angiosperm lineages are derived from diverse parental genomes and may be of allopolyploid origin.

Chromosome-scale and haplotype-resolved genome assembly of the autotetraploid Misgurnus anguillicaudatus

In nature, diploids and tetraploids are two common types of polyploid evolution. Misgurnus anguillicaudatus (mud loach) is a remarkable fish species that exhibits both diploid and tetraploid forms. However, reconstructing the four haplotypes of its autotetraploid genome remains unresolved. Here, we generated the first haplotype-resolved, chromosome-level genome of autotetraploid M. anguillicaudatus with a size of 4.76 Gb, contig N50 of 6.78 Mb, and scaffold N50 of 44.11 Mb. We identified approximately 2.9 Gb (61.03% of genome) of repetitive sequences and predicted 91,485 protein-coding genes. Moreover, allelic gene expression levels indicated the absence of significant dominant haplotypes within the autotetraploid loach genome. This genome will provide a valuable biological model for unraveling the mechanisms of polyploid formation and evolution, adaptation to environmental changes, and benefit for aquaculture applications and biodiversity conservation.

Ploidy variation induces butterfly effect on chromatin topology in wheat

Polyploidy is a prominent driver of plant diversification, accompanied with dramatic chromosomal rearrangement and epigenetic changes that affect gene expression. How chromatin interactions within and between subgenomes adapt to ploidy transition remains poorly understood. We generate open chromatin interaction maps for natural hexaploid wheat (AABBDD), extracted tetraploid wheat (AABB), diploid wheat progenitor Aegilops tauschii (DD) and resynthesized hexaploid wheat (RHW, AABBDD). Thousands of intra- and interchromosomal loops are de novo established or disappeared in AB subgenomes after separation of D subgenome, in which 37-95% of novel loops are lost again in RHW after merger of D genome. Interestingly, more than half of novel loops are formed by cascade reactions that are triggered by disruption of chromatin interaction between AB and D subgenomes. The interaction repressed genes in RHW relative to DD are expression suppressed, resulting in more balanced expression of the three homoeologs in RHW. The interaction levels of cascade anchors are decreased step-by-step. Leading single nucleotide polymorphisms of yield- and plant architecture-related quantitative trait locus are significantly enriched in cascade anchors. The expression of 116 genes interacted with these anchors are significantly correlated with the corresponding traits. Our findings reveal trans-regulation of intrachromosomal loops by interchromosomal interactions during genome merger and separation in polyploid species.

Genome-wide DNA methylation dynamics following recent polyploidy in the allotetraploid Tragopogon miscellus (Asteraceae)

Polyploidy is an important evolutionary force, yet epigenetic mechanisms, such as DNA methylation, that regulate genome-wide expression of duplicated genes remain largely unknown. Here, we use Tragopogon (Asteraceae) as a model system to discover patterns and temporal dynamics of DNA methylation in recently formed polyploids. The naturally occurring allotetraploid Tragopogon miscellus formed in the last 95-100 yr from parental diploids Tragopogon dubius and T. pratensis. We profiled the DNA methylomes of these three species using whole-genome bisulfite sequencing. Genome-wide methylation levels in T. miscellus were intermediate between its diploid parents. However, nonadditive CG and CHG methylation occurred in transposable elements (TEs), with variation among TE types. Most differentially methylated regions (DMRs) showed parental legacy, but some novel DMRs were detected in the polyploid. Differentially methylated genes (DMGs) were also identified and characterized. This study provides the first assessment of both overall and locus-specific patterns of DNA methylation in a recent natural allopolyploid and shows that novel methylation variants can be generated rapidly after polyploid formation. Together, these results demonstrate that mechanisms to regulate duplicate gene expression may arise soon after allopolyploid formation and that these mechanisms vary among genes.

Remarkable chromosomes and karyotypes: A top 10 list

Chromosomes and karyotypes are particularly rich in oddities and extremes. Described below are 10 remarkable chromosomes and karyotypes sprinkled throughout the tree of life. These include variants in chromosome number, structure, and dynamics both natural and engineered. This versatility highlights the robustness and tolerance of the mitotic and meiotic machinery to dramatic changes in chromosome and karyotype architecture. These examples also illustrate that the robustness comes at a cost, enabling the evolution of chromosomes that subvert mitosis and meiosis.

Formation of Different Polyploids Through Disrupting Meiotic Crossover Frequencies Based on cntd1 Knockout in Zebrafish

Polyploidy, a significant catalyst for speciation and evolutionary processes in both plant and animal kingdoms, has been recognized for a long time. However, the exact molecular mechanism that leads to polyploid formation, especially in vertebrates, is not fully understood. Our study aimed to elucidate this phenomenon using the zebrafish model. We successfully achieved an effective knockout of the cyclin N-terminal domain containing 1 (cntd1) using CRISPR/Cas9 technology. This resulted in impaired formation of meiotic crossovers, leading to cell-cycle arrest during meiotic metaphase and triggering apoptosis of spermatocytes in the testes. Despite these defects, the mutant (cntd1-/-) males were still able to produce a limited amount of sperm with normal ploidy and function. Interestingly, in the mutant females, it was the ploidy not the capacity of egg production that was altered. This resulted in the production of haploid, aneuploid, and unreduced gametes. This alteration enabled us to successfully obtain triploid and tetraploid zebrafish from cntd1-/- and cntd1-/-/- females, respectively. Furthermore, the tetraploid-heterozygous zebrafish produced reduced-diploid gametes and yielded all-triploid or all-tetraploid offspring when crossed with wild-type (WT) or tetraploid zebrafish, respectively. Collectively, our findings provide direct evidence supporting the crucial role of meiotic crossover defects in the process of polyploidization. This is particularly evident in the generation of unreduced eggs in fish and, potentially, other vertebrate species.

Investigation of regulatory divergence between homoeologs in the recently formed allopolyploids, Tragopogon mirus and T. miscellus (Asteraceae)

Polyploidy is an important evolutionary process throughout eukaryotes, particularly in flowering plants. Duplicated gene pairs (homoeologs) in allopolyploids provide additional genetic resources for changes in molecular, biochemical, and physiological mechanisms that result in evolutionary novelty. Therefore, understanding how divergent genomes and their regulatory networks reconcile is vital for unraveling the role of polyploidy in plant evolution. Here, we compared the leaf transcriptomes of recently formed natural allotetraploids (Tragopogon mirus and T. miscellus) and their diploid parents (T. porrifolius X T. dubius and T. pratensis X T. dubius, respectively). Analysis of 35 400 expressed loci showed a significantly higher level of transcriptomic additivity compared to old polyploids; only 22% were non-additively expressed in the polyploids, with 5.9% exhibiting transgressive expression (lower or higher expression in the polyploids than in the diploid parents). Among approximately 7400 common orthologous regions (COREs), most loci in both allopolyploids exhibited expression patterns that were vertically inherited from their diploid parents. However, 18% and 20.3% of the loci showed novel expression bias patterns in T. mirus and T. miscellus, respectively. The expression changes of 1500 COREs were explained by cis-regulatory divergence (the condition in which the two parental subgenomes do not interact) between the diploid parents, whereas only about 423 and 461 of the gene expression changes represent trans-effects (the two parental subgenomes interact) in T. mirus and T. miscellus, respectively. The low degree of both non-additivity and trans-effects on gene expression may present the ongoing evolutionary processes of the newly formed Tragopogon polyploids (~80-90 years).

Subgenomic Stability of Progenitor Genomes During Repeated Allotetraploid Origins of the Same Grass Brachypodium hybridum

Both homeologous exchanges and homeologous expression bias are generally found in most allopolyploid species. Whether homeologous exchanges and homeologous expression bias differ between repeated allopolyploid speciation events from the same progenitor species remains unknown. Here, we detected a third independent and recent allotetraploid origin for the model grass Brachypodium hybridum. Our homeologous exchange with replacement analyses indicated the absence of significant homeologous exchanges in any of the three types of wild allotetraploids, supporting the integrity of their progenitor subgenomes and the immediate creation of the amphidiploids. Further homeologous expression bias tests did not uncover significant subgenomic dominance in different tissues and conditions of the allotetraploids. This suggests a balanced expression of homeologs under similar or dissimilar ecological conditions in their natural habitats. We observed that the density of transposons around genes was not associated with the initial establishment of subgenome dominance; rather, this feature is inherited from the progenitor genome. We found that drought response genes were highly induced in the two subgenomes, likely contributing to the local adaptation of this species to arid habitats in the third allotetraploid event. These findings provide evidence for the consistency of subgenomic stability of parental genomes across multiple allopolyploidization events that led to the same species at different periods. Our study emphasizes the importance of selecting closely related progenitor species genomes to accurately assess homeologous exchange with replacement in allopolyploids, thereby avoiding the detection of false homeologous exchanges when using less related progenitor species genomes.

Induction of tetraploids in Paper Mulberry (Broussonetia papyrifera (L.) L'Hér. ex Vent.) by colchicine

BACKGROUND

Broussonetia papyrifera (L.) L'Hér. ex Vent. has the characteristics of strong stress resistance, high crude protein content, and pruning tolerance. It is an ecological, economic, and medicinal plant. Polyploid plants usually perform better than their corresponding diploid plants in terms of nutrients, active substances, and stress resistance.

RESULTS

In this study, the leaves, calli, and seeds of diploid B. papyrifera were used for tetraploid induction by colchicine. The induction effect of colchicine on B. papyrifera was summarized through the early morphology, chromosome count and flow cytometry. It was concluded that the best induction effect (18.6%) was obtained when the leaves of B. papyrifera were treated in liquid MS (Murashige and Skoog) medium containing 450 mg·L-1 colchicine for 3 d. The comparative analysis of the growth characteristics of diploid and tetraploid B. papyrifera showed that tetraploid B. papyrifera has larger ground diameter, larger stomata, thicker palisade tissue and thicker sponge tissue than diploid B. papyrifera. In addition, the measurement of photosynthetic features also showed that tetraploids had higher chlorophyll content and higher photosynthetic rates.

CONCLUSION

This study showed that tetraploid B. papyrifera could be obtained by treating leaves, callus and seeds with liquid and solid colchicine, but the induction efficiency was different. Moreover, there were differences in stomata, leaf cell structure and photosynthetic features between tetraploid B. papyrifera and its corresponding diploid. The induced tetraploid B. papyrifera can provide a technical basis and breeding material for the creation of B. papyrifera germplasm resources in the future.

The duplication of genomes and genetic networks and its potential for evolutionary adaptation and survival during environmental turmoil

The importance of whole-genome duplication (WGD) for evolution is controversial. Whereas some view WGD mainly as detrimental and an evolutionary dead end, there is growing evidence that polyploidization can help overcome environmental change, stressful conditions, or periods of extinction. However, despite much research, the mechanistic underpinnings of why and how polyploids might be able to outcompete or outlive nonpolyploids at times of environmental upheaval remain elusive, especially for autopolyploids, in which heterosis effects are limited. On the longer term, WGD might increase both mutational and environmental robustness due to redundancy and increased genetic variation, but on the short-or even immediate-term, selective advantages of WGDs are harder to explain. Here, by duplicating artificially generated Gene Regulatory Networks (GRNs), we show that duplicated GRNs-and thus duplicated genomes-show higher signal output variation than nonduplicated GRNs. This increased variation leads to niche expansion and can provide polyploid populations with substantial advantages to survive environmental turmoil. In contrast, under stable environments, GRNs might be maladaptive to changes, a phenomenon that is exacerbated in duplicated GRNs. We believe that these results provide insights into how genome duplication and (auto)polyploidy might help organisms to adapt quickly to novel conditions and to survive ecological uproar or even cataclysmic events.

Leaf structure and water relations of an allotetraploid Mediterranean fern and its diploid parents

Allopolyploidy is a common speciation mechanism in plants; however, its physiological and ecological consequences in niche partitioning have been scarcely studied. In this sense, leaf traits are good proxies to study the adaptive capacity of allopolyploids and diploid parents to their respective environmental conditions. In the present work, leaf water relations (assessed through pressure-volume curves) and structural and anatomical traits of the allotetraploid fern Oeosporangium tinaei and its diploid parents, Oeosporangium hispanicum and Oeosporangium pteridioides, were studied under controlled conditions in response to a water stress (WS) cycle. O. hispanicum showed the lowest osmotic potential at turgor loss point (πtlp ) and leaf capacitance, together with higher leaf mass per area (LMA), leaf thickness (LT), leaf density (LD), and leaf dry matter content (LDMC), whereas O. pteridioides presented the opposite set of traits (high πtlp and capacitance, and low LMA, LT, LD, and LDMC). O. tinaei showed an intermediate position for most of the studied traits. The responsiveness (osmotic and elastic adjustments) to WS was low, although most of the traits explained the segregation of the three species across a range of drought tolerance according to the rank: O. hispanicum > O. tinaei > O. pteridioides. These trait differences may underlie the niche segregation among coexisting populations of the three species in the Mediterranean basin.

First insight into the phylogeny of fine-leaved Festuca in the Altai Mountain Country based on genome-wide genotyping

Festuca is one of the largest genera within the Poaceae family. Molecular phylogenies demonstrate that Festuca s.l. comprises two groups: broad- and fine-leaved species. The latter is the species-richest and taxonomically complicated group due to being paraphyletic. Here, we provide the first insight into the phylogeny of 17 fine-leaved species of Altai fescues. Based on genome-wide genotyping, the examined taxa were divided into three markedly differentiated clusters. The first cluster comprises species from the F. rubra complex, the second cluster includes the F. brachyphylla complex, and the third cluster contains taxa from the groups F. ovina, F. valesiaca, and F. kryloviana. Importantly, we detected a complex genetic pattern within the groups of F. valesiaca and F. kryloviana. Moreover, our findings underline a discrepancy between morphological and molecular data for some species distributed within the Altai Mountain Country. We suggest that in order to validate the current findings on the fine-leaved fescues, additional comprehensive research including morphological, karyological, and molecular methods is required. Nonetheless, our work provides a baseline for further investigations on the genus and studies on the floral diversity of Asia.

Ecophysiological Differentiation among Two Resurrection Ferns and Their Allopolyploid Derivative

Theoretically, the coexistence of diploids and related polyploids is constrained by reproductive and competitive mechanisms. Although niche differentiation can explain the commonly observed co-occurrence of cytotypes, the underlying ecophysiological differentiation among cytotypes has hardly been studied. We compared the leaf functional traits of the allotetraploid resurrection fern Oeosporangium tinaei (HHPP) and its diploid parents, O. hispanicum (HH) and O. pteridioides (PP), coexisting in the same location. Our experimental results showed that all three species can recover physiological status after severe leaf dehydration, which confirms their 'resurrection' ability. However, compared with PP, HH had much higher investment per unit area of light-capturing surface, lower carbon assimilation rate per unit mass for the same midday water potential, higher non-enzymatic antioxidant capacity, higher carbon content, and lower contents of nitrogen, phosphorus, and other macronutrients. These traits allow HH to live in microhabitats with less availability of water and nutrients (rock crevices) and to have a greater capacity for resurrection. The higher assimilation capacity and lower antioxidant capacity of PP explain its more humid and nutrient-rich microhabitats (shallow soils). HHPP traits were mostly intermediate between those of HH and PP, and they allow the allotetraploid to occupy the free niche space left by the diploids.

Infrared spectroscopy for ploidy estimation: An example in two species of Veronica using fresh and herbarium specimens

Premise

Polyploidy has become a central factor in plant evolutionary biological research in recent decades. Methods such as flow cytometry have revealed the widespread occurrence of polyploidy; however, its inference relies on expensive lab equipment and is largely restricted to fresh or recently dried material.

Methods

Here, we assess the applicability of infrared spectroscopy to infer ploidy in two related species of Veronica (Plantaginaceae). Infrared spectroscopy relies on differences in the absorbance of tissues, which could be affected by primary and secondary metabolites related to polyploidy. We sampled 33 living plants from the greenhouse and 74 herbarium specimens with ploidy known through flow cytometrical measurements and analyzed the resulting spectra using discriminant analysis of principal components (DAPC) and neural network (NNET) classifiers.

Results

Living material of both species combined was classified with 70% (DAPC) to 75% (NNET) accuracy, whereas herbarium material was classified with 84% (DAPC) to 85% (NNET) accuracy. Analyzing both species separately resulted in less clear results.

Discussion

Infrared spectroscopy is quite reliable but is not a certain method for assessing intraspecific ploidy level differences in two species of Veronica. More accurate inferences rely on large training data sets and herbarium material. This study demonstrates an important way to expand the field of polyploid research to herbaria.

Polyploidy on islands - concerted evolution and gene loss amid chromosomal stasis

BACKGROUND AND AIMS

Polyploidy is an important process that often generates genomic diversity within lineages, but it can also cause changes that result in loss of genomic material. Island lineages, while often polyploid, typically show chromosomal stasis but have not been investigated in detail regarding smaller-scale gene loss. Our aim was to investigate post-polyploidization genome dynamics in a chromosomally stable lineage of Malvaceae endemic to New Zealand.

METHODS

We determined chromosome numbers and used fluorescence in situ hybridization to localize 18S and 5S rDNA. Gene sequencing of 18S rDNA, the internal transcribed spacers (ITS) with intervening 5.8S rDNA, and a low-copy nuclear gene, GBSSI-1, was undertaken to determine if gene loss occurred in the New Zealand lineage following polyploidy.

KEY RESULTS

The chromosome number for all species investigated was 2n = 42, with the first published report for the monotypic Australian genus Asterotrichion. The five species investigated all had two 5S rDNA signals localized interstitially on the long arm of one of the largest chromosome pairs. All species, except Plagianthus regius, had two 18S rDNA signals localized proximally on the short arm of one of the smallest chromosome pairs. Plagianthus regius had two additional 18S rDNA signals on a separate chromosome, giving a total of four. Sequencing of nuclear ribosomal 18S rDNA and the ITS cistron indicated loss of historical ribosomal repeats. Phylogenetic analysis of a low-copy nuclear gene, GBSSI-1, indicated that some lineages maintained three copies of the locus, while others have lost one or two copies.

CONCLUSIONS

Although island endemic lineages show chromosomal stasis, with no additional changes in chromosome number, they may undergo smaller-scale processes of gene loss and concerted evolution ultimately leading to further genome restructuring and downsizing.

Does one subgenome become dominant in the formation and evolution of a polyploid?

BACKGROUND

Polyploids are common in flowering plants and they tend to have more expanded ranges of distributions than their diploid progenitors. Possible mechanisms underlying polyploid success have been intensively investigated. Previous studies showed that polyploidy generates novel changes and that subgenomes in allopolyploid species often differ in gene number, gene expression levels and levels of epigenetic alteration. It is widely believed that such differences are the results of conflicts among the subgenomes. These differences have been treated by some as subgenome dominance, and it is claimed that the magnitude of subgenome dominance increases in polyploid evolution.

SCOPE

In addition to changes which occurred during evolution, differences between subgenomes of a polyploid species may also be affected by differences between the diploid donors and changes which occurred during polyploidization. The variable genome components in many plant species are extensive, which would result in exaggerated differences between a subgenome and its progenitor when a single genotype or a small number of genotypes are used to represent a polyploid or its donors. When artificially resynthesized polyploids are used as surrogates for newly formed genotypes which have not been exposed to evolutionary selection, differences between diploid genotypes available today and those involved in the formation of the natural polyploid genotypes must also be considered.

CONCLUSIONS

Contrary to the now widely held views that subgenome biases in polyploids are the results of conflicts among the subgenomes and that one of the parental subgenomes generally retains more genes which are more highly expressed, available results show that subgenome biases mainly reflect legacy from the progenitors and that they can be detected before the completion of polyploidization events. Further, there is no convincing evidence that the magnitudes of subgenome biases have significantly changed during evolution for any of the allopolyploid species assessed.

Genetic characteristics influence the phenotype of marine macroalga Fucus vesiculosus (Phaeophyceae)

Intraspecific variation is an important component of heterogeneity in biological systems that can manifest at the genotypic and phenotypic level. This study investigates the influence of genetic characteristics on the phenotype of free-living Fucus vesiculosus using traditional morphological measures and microsatellite genotyping. Two sympatric morphotypes were observed to be significantly genetically and morphologically differentiated despite experiencing analogous local environmental conditions; indicating a genetic element to F. vesiculosus morphology. Additionally, the observed intraclonal variation established divergent morphology within some genets. This demonstrated that clonal lineages have the ability to alter morphological traits by either a plastic response or somatic mutations. We provide support for the potential occurrence of the Gigas effect (cellular/organ enlargement through genome duplication) in the Fucus genus, with polyploidization appearing to correlate with a general increase in the size of morphological features. Phenotypic traits, as designated by morphology within the study, of F. vesiculosus are partially controlled by the genetic characteristics of the thalli. This study suggests that largely asexually reproducing algal populations may have the potential to adapt to changing environmental conditions through genome changes or phenotypic plasticity.

Convergence without divergence in North American red-flowering Silene

Combinations of correlated floral traits have arisen repeatedly across angiosperms through convergent evolution in response to pollinator selection to optimize reproduction. While some plant groups exhibit very distinct combinations of traits adapted to specific pollinators (so-called pollination syndromes), others do not. Determining how floral traits diverge across clades and whether floral traits show predictable correlations in diverse groups of flowering plants is key to determining the extent to which pollinator-mediated selection drives diversification. The North American Silene section Physolychnis is an ideal group to investigate patterns of floral evolution because it is characterized by the evolution of novel red floral color, extensive floral morphological variation, polyploidy, and exposure to a novel group of pollinators (hummingbirds). We test for correlated patterns of trait evolution that would be consistent with convergent responses to selection in the key floral traits of color and morphology. We also consider both the role of phylogenic distance and geographic overlap in explaining patterns of floral trait variation. Inconsistent with phenotypically divergent pollination syndromes, we find very little clustering of North American Silene into distinct floral morphospace. We also find little evidence that phylogenetic history or geographic overlap explains patterns of floral diversity in this group. White- and pink-flowering species show extensive phenotypic diversity but are entirely overlapping in morphological variation. However, red-flowering species have much less phenotypic disparity and cluster tightly in floral morphospace. We find that red-flowering species have evolved floral traits that align with a traditional hummingbird syndrome, but that these trait values overlap with several white and pink species as well. Our findings support the hypothesis that convergent evolution does not always proceed through comparative phenotypic divergence, but possibly through sorting of standing ancestral variation.

Polyploidization: Consequences of genome doubling on the evolutionary potential of populations

Whole-genome duplication is common in plants and is considered to have a broad range of effects on individuals' phenotypes and genomes and to be an important driver of plant adaptation and speciation. Despite their increased capacity to cope with challenging environments, polyploid lineages are generally as prone to extinction, and sometimes more prone, than their diploid progenitors. Although several explanations have been proposed to explain the short- and long-term disadvantages of polyploidy on the survival probability of populations, the consequences of whole-genome doubling on the heritable variance remain poorly studied. Whole-genome doubling can have major effects not only on the genetics, but also on the ecology and life history of the populations. Modifications of other properties of populations can reverse the effects of polyploidization per se on heritable variance. In this synthesis, I summarize the empirical and theoretical knowledge about the multifarious consequences of genome doubling on the heritable variance of quantitative traits and on the evolutionary potential of polyploid populations compared to their diploid progenitors. I propose several ways to decipher the consequences of whole-genome doubling on survival probability and to study the further consequences of shifting the ecological niche and life-history traits of a population. I also highlight some practical considerations for comparing the heritable variance of a trait among different cytotypes. Such investigations appear to be timely and necessary to understand more about the paradoxical aspects of polyploidization and to understand the evolutionary potential of polyploid lineages in a global warming context.

Evolvability and Macroevolution: Overview and Synthesis

Evolvability is best addressed from a multi-level, macroevolutionary perspective through a comparative approach that tests for among-clade differences in phenotypic diversification in response to an opportunity, such as encountered after a mass extinction, entering a new adaptive zone, or entering a new geographic area. Analyzing the dynamics of clades under similar environmental conditions can (partially) factor out shared external drivers to recognize intrinsic differences in evolvability, aiming for a macroevolutionary analog of a common-garden experiment. Analyses will be most powerful when integrating neontological and paleontological data: determining differences among extant populations that can be hypothesized to generate large-scale, long-term contrasts in evolvability among clades; or observing large-scale differences among clade histories that can by hypothesized to reflect contrasts in genetics and development observed directly in extant populations. However, many comparative analyses can be informative on their own, as explored in this overview. Differences in clade-level evolvability can be visualized in diversity-disparity plots, which can quantify positive and negative departures of phenotypic productivity from stochastic expectations scaled to taxonomic diversification. Factors that evidently can promote evolvability include modularity—when selection aligns with modular structure or with morphological integration patterns; pronounced ontogenetic changes in morphology, as in allometry or multiphase life cycles; genome size; and a variety of evolutionary novelties, which can also be evaluated using macroevolutionary lags between the acquisition of a trait and phenotypic diversification, and dead-clade-walking patterns that may signal a loss of evolvability when extrinsic factors can be excluded. High speciation rates may indirectly foster phenotypic evolvability, and vice versa. Mechanisms are controversial, but clade evolvability may be higher in the Cambrian, and possibly early in the history of clades at other times; in the tropics; and, for marine organisms, in shallow-water disturbed habitats.

Resurrection of Stipatremula and taxonomy of the high-alpine species from the Stipapurpurea complex (Poaceae, Pooideae)

Stipapurpurea is a high-alpine species that occurs in cryophilous steppes, semi-deserts and stony slopes, from the Tian Shan and Pamirian Plateau through Qinghai-Xizang Plateau to the Himalayas and is characterised by a great morphological variability. During the revision of specimens of the taxon, we observed that the pattern of this variability is linked to the geographical distribution of the specimens. Numerical analyses (PCA and UPGMA) revealed three groups of OTUs corresponding to three morphotypes within the S.purpurea complex. A set of macro- and micromorphological characters, supported by a map of general distributional ranges, are presented to distinguish each of the three taxa within the complex and we reassess the status of Lasiagrostistremula described by Ruprecht in 1869. As a result, Stipatremula, S.purpurea and S.arenosa were distinguished within the complex. The intermediate characters of S.arenosa may suggest its putative hybrid origin (S.tremula × S.purpurea), whereas the presence of extremely long florets may be an expression of the gigas effect. We propose two new combinations (S.tremula and S.arenosa), describe a new nothospecies (S.×ladakhensis) that originated from hybridisation between S.klimesii and S.purpurea s.l. and designate the lectotype for Ptilagrostissemenovii. An identification key and detailed morphological description of species from the S.purpurea complex are also presented.

The evolution of the additive variance of a trait under stabilizing selection after autopolyploidization

Whole‐genome duplication is a common mutation in eukaryotes with far‐reaching phenotypic effects. The resulting morphological, physiological and fitness consequences and how they affect the survival probability of polyploid lineages are intensively studied, but little is known about the effect of genome doubling on the evolutionary potential of populations. Historically, it has been argued polyploids should be less able to adapt because gene duplication dilutes the effects of alleles, such that polyploids are less likely to evolve new adaptive gene complexes compared with diploids. In this paper, I investigate the short‐ and long‐term consequences of genome doubling on the additive genetic variance of populations. To do so, I extended the classical models of quantitative traits under stabilizing selection to study the evolution of the additive variance of the trait under study after a shift from diploidy to tetraploidy. I found that, for realistic allele‐dosage effects, polyploidization is associated with an initial decrease in adaptive potential. In the long term, the better masking of recessive deleterious mutations associated with polyploidy compensates for the initial decrease in additive variance. The time for the tetraploid populations to reach or exceed the additive variance of their diploid progenitors is generally lower than 200 generations. These results highlight that polyploidization per se has a negligible negative effect on the adaptive potential of populations in the short term, and a substantial positive effect in the long term.

Tracing the Evolution of the Angiosperm Genome from the Cytogenetic Point of View

Cytogenetics constitutes a branch of genetics that is focused on the cellular components, especially chromosomes, in relation to heredity and genome structure, function and evolution. The use of modern cytogenetic approaches and the latest microscopes with image acquisition and processing systems enables the simultaneous two- or three-dimensional, multicolour visualisation of both single-copy and highly-repetitive sequences in the plant genome. The data that is gathered using the cytogenetic methods in the phylogenetic background enable tracing the evolution of the plant genome that involve changes in: (i) genome sizes; (ii) chromosome numbers and morphology; (iii) the content of repetitive sequences and (iv) ploidy level. Modern cytogenetic approaches such as FISH using chromosome- and genome-specific probes have been widely used in studies of the evolution of diploids and the consequences of polyploidy. Nowadays, modern cytogenetics complements analyses in other fields of cell biology and constitutes the linkage between genetics, molecular biology and genomics.

BnaA03.MKK5-BnaA06.MPK3/BnaC03.MPK3 Module Positively Contributes to Sclerotinia sclerotiorum Resistance in Brassica napus

Brassica napus (oilseed rape) is one of the most important oil crops worldwide, but its growth is seriously threatened by Sclerotinia sclerotiorum. The mechanism of oilseed rape response to this pathogen has rarely been studied. Here, it was identified that BnaA03.MKK5 whose expression was induced by S. sclerotiorum infection was involved in plant immunity. BnaA03.MKK5 overexpression lines exhibited decreased disease symptoms compared to wild-type plants, accompanied by the increased expression of camalexin-biosynthesis-related genes, including BnPAD3 and BnCYP71A13. In addition, two copies of BnMPK3 (BnA06.MPK3 and BnC03.MPK3) were induced by Sclerotinia incubation, and BnaA03.MKK5 interacted with BnaA06.MPK3/BnaC03.MPK3 in yeast. These interactions were confirmed using in vivo co-immunoprecipitation assays. In vitro phosphorylation assays showed that BnaA06.MPK3 and BnaC03.MPK3 were the direct phosphorylation substrates of BnaA03.MKK5. The transgenic oilseed rape plants including BnaA06.MPK3 and BnaC03.MPK3 overexpression lines and BnMPK3 gene editing lines mediated by CRISPR/Cas9 were generated; the results of the genetic transformation of BnaA06.MPK3/BnaC03.MPK3 indicate that BnMPK3 also has a positive role in Sclerotinia resistance. This study provides information about the potential mechanism of B. napus defense against S. Sclerotiorum mediated by a detailed BnaA03.MKK5-BnaA06.MPK3/BnaC03.MPK3 module.

Evolution of crossover interference enables stable autopolyploidy by ensuring pairwise partner connections in Arabidopsis arenosa

Polyploidy is a major driver of evolutionary change. Autopolyploids, which arise by within-species whole-genome duplication, carry multiple nearly identical copies of each chromosome. This presents an existential challenge to sexual reproduction. Meiotic chromosome segregation requires formation of DNA crossovers (COs) between two homologous chromosomes. How can this outcome be achieved when more than two essentially equivalent partners are available? We addressed this question by comparing diploid, neo-autotetraploid, and established autotetraploid Arabidopsis arenosa using new approaches for analysis of meiotic CO patterns in polyploids. We discover that crossover interference, the classical process responsible for patterning of COs in diploid meiosis, is defective in the neo-autotetraploid but robust in the established autotetraploid. The presented findings suggest that, initially, diploid-like interference fails to act effectively on multivalent pairing and accompanying pre-CO recombination interactions and that stable autopolyploid meiosis can emerge by evolution of a “supercharged” interference process, which can now act effectively on such configurations. Thus, the basic interference mechanism responsible for simplifying CO patterns along chromosomes in diploid meiosis has evolved the capability to also simplify CO patterns among chromosomes in autopolyploids, thereby promoting bivalent formation. We further show that evolution of stable autotetraploidy preadapts meiosis to higher ploidy, which in turn has interesting mechanistic and evolutionary implications.

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In a neo-autotetraploid, aberrant crossover interference confers aberrant meiosis

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In a stable autotetraploid, regular crossover interference confers regular meiosis

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Crossover and synaptic patterns point to evolution of “supercharged” interference

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Accordingly, evolution of stable autotetraploidy preadapts to higher ploidies

Dual-species origin of an adaptive chemical defense polymorphism

Allopolyploid speciation and chemical defense diversification are two of the most characteristic features of plant evolution; although the former has likely shaped the latter, this has rarely been documented. Here we document allopolyploidy-mediated chemical defense evolution in the origin of cyanogenesis (HCN release upon tissue damage) in white clover (Trifolium repens). We combined linkage mapping of the loci that control cyanogenesis (Ac, controlling production of cyanogenic glucosides; and Li, controlling production of their hydrolyzing enzyme linamarase) with genome sequence comparisons between white clover, a recently evolved allotetraploid, and its diploid progenitors (Trifolium pallescens, Trifolium occidentale). The Ac locus (a three-gene cluster comprising the cyanogenic glucoside pathway) is derived from T. occidentale; it maps to linkage group 2O (occidentale subgenome) and is orthologous to a highly similar cluster in the T. occidentale reference genome. By contrast, Li maps to linkage group 4P (pallescens subgenome), indicating an origin in the other progenitor species. These results indicate that cyanogenesis evolved in white clover as a product of the interspecific hybridization that created the species. This allopolyploidization-derived chemical defense, together with subsequent selection on intraspecific cyanogenesis variation, appears to have contributed to white clover's ecological success as a globally distributed weed species.

Incongruent phylogenies and their implications for the study of diversification, taxonomy, and genome size evolution of Rhododendron

PREMISE

Classification of taxa depends on the quality of inferred phylogenies. Rhododendron, a highly species-rich genus (>1156 species) of woody plants, has a highly debated infrageneric classification, due to its huge diversity, homoplasy in key characters, and incongruence among data sets. We provide a broad coverage of representative species to resolve Rhododendron infrageneric phylogeny and highlight the areas of incongruence. We further investigate the effect of polyploidy and genome size evolution on diversification of Rhododendron.

METHODS

We generated two plastid and two nuclear loci for 260 Rhododendron species. We analyzed the loci separately as well as concatenated, utilizing both likelihood and Bayesian methods. We tested incongruence both among the data sets and with previous studies. We estimated genome sizes for 125 species through flow cytometry.

RESULTS

Our results suggest stronger support for larger subgenera; however, the smaller subgenera pose several problems; for example, R. tomentosum (former genus Ledum) occupies incongruent positions based on different DNA regions. The main shift to higher diversification in the genus occurs in the Himalayan/Southeast Asian clade of R. subg. Hymenanthes. We found that polyploidy occurs in almost all subgenera but most frequently within R. subg. Rhododendron sections Rhododendron and Schistanthe.

CONCLUSIONS

We endorse the recognition of five major clades at the subgeneric level, but a number of species cannot be confidently assigned to these clades due to incongruency. With regard to genome size evolution, results support previous reports that genome sizes of tropical plants are lower than those of colder and temperate regions and that genome downsizing promotes diversification.

Phenotypic diploidization in plant functional traits uncovered by synthetic neopolyploids in Dianthus broteri

Whole-genome duplication and post-polyploidization genome downsizing play key roles in the evolution of land plants; however, the impact of genomic diploidization on functional traits still remains poorly understood. Using Dianthus broteri as a model, we compared the ecophysiological behaviour of colchicine-induced neotetraploids (4xNeo) to diploids (2x) and naturally occurring tetraploids (4xNat). Leaf gas-exchange and chlorophyll fluorescence analyses were performed in order to asses to what extent post-polyploidization evolutionary processes have affected 4xNat. Genomic diploidization and phenotypic novelty were evident. Distinct patterns of variation revealed that post-polyploidization processes altered the phenotypic shifts directly mediated by genome doubling. The photosynthetic phenotype was affected in several ways but the main effect was phenotypic diploidization (i.e. 2x and 4xNat were closer to each other than to 4xNeo). Overall, our results show the potential benefits of considering experimentally synthetized versus naturally established polyploids when exploring the role of polyploidization in promoting functional divergence.

Functional Divergence of Multiple Duplicated Foxl2 Homeologs and Alleles in a Recurrent Polyploid Fish

Evolutionary fates of duplicated genes have been widely investigated in many polyploid plants and animals, but research is scarce in recurrent polyploids. In this study, we focused on foxl2, a central player in ovary, and elaborated the functional divergence in gibel carp (Carassius gibelio), a recurrent auto-allo-hexaploid fish. First, we identified three divergent foxl2 homeologs (Cgfoxl2a-B, Cgfoxl2b-A, and Cgfoxl2b-B), each of them possessing three highly conserved alleles and revealed their biased retention/loss. Then, their abundant sexual dimorphism and biased expression were uncovered in hypothalamic-pituitary-gonadal axis. Significantly, granulosa cells and three subpopulations of thecal cells were distinguished by cellular localization of CgFoxl2a and CgFoxl2b, and the functional roles and the involved process were traced in folliculogenesis. Finally, we successfully edited multiple foxl2 homeologs and/or alleles by using CRISPR/Cas9. Cgfoxl2a-B deficiency led to ovary development arrest or complete sex reversal, whereas complete disruption of Cgfoxl2b-A and Cgfoxl2b-B resulted in the depletion of germ cells. Taken together, the detailed cellular localization and functional differences indicate that Cgfoxl2a and Cgfoxl2b have subfunctionalized and cooperated to regulate folliculogenesis and gonad differentiation, and Cgfoxl2b has evolved a new function in oogenesis. Therefore, the current study provides a typical case of homeolog/allele diversification, retention/loss, biased expression, and sub-/neofunctionalization in the evolution of duplicated genes driven by polyploidy and subsequent diploidization from the recurrent polyploid fish.

Hybridization, ecogeographical displacement and the emergence of new lineages - A genotyping-by-sequencing and ecological niche and species distribution modelling study of Sempervivum tectorum L. (Houseleek)

Ecogeographical displacement of homoploid hybrid lineages from their parents is well documented and considered an important mechanism to achieve reproductive isolation. In this study, we investigated the origin of the flowering plant species Sempervivum tectorum in the Massif Central (France) through homoploid hybridization between lineages of the species from the Rhine Gorge area (Germany) and the Pyrenees (France). We used genotyping-by-sequencing genetic data as evidence for the hybrid origin of the Massif Central lineage, and WorldClim climatic data and soil pH and soil temperature data collected by us for ecological niche and species distribution modelling. We could show that the Massif Central lineage shows hybrid admixture and that the niche of this lineage is significantly different from those of the parental lineages. In comparison with the parental niches, different variables of the niche of the hybrid lineage are intermediate, parental-combined or extreme. The different niche of the Massif Central populations thus can plausibly be interpreted as hybridization-derived. Our species distribution modelling for the Last Glacial Maximum and Mid-Holocene showed that the potential distribution of the hybrid lineage at the likely time of its origin in the Quaternary possibly was parapatric in relation to the largely sympatric distributions of the parental lineages. We hypothesize that reproductive isolation of the hybrid lineage from the parental lineages resulted from the segregation of distribution ranges by a differential response of the three lineages to a warming climate.

Polyploidy: an evolutionary and ecological force in stressful times

Polyploidy has been hypothesized to be both an evolutionary dead-end and a source for evolutionary innovation and species diversification. Although polyploid organisms, especially plants, abound, the apparent nonrandom long-term establishment of genome duplications suggests a link with environmental conditions. Whole-genome duplications seem to correlate with periods of extinction or global change, while polyploids often thrive in harsh or disturbed environments. Evidence is also accumulating that biotic interactions, for instance, with pathogens or mutualists, affect polyploids differently than nonpolyploids. Here, we review recent findings and insights on the effect of both abiotic and biotic stress on polyploids versus nonpolyploids and propose that stress response in general is an important and even determining factor in the establishment and success of polyploidy.

Polyploidy on Islands: Its Emergence and Importance for Diversification

Whole genome duplication or polyploidy is widespread among floras globally, but traditionally has been thought to have played a minor role in the evolution of island biodiversity, based on the low proportion of polyploid taxa present. We investigate five island systems (Juan Fernández, Galápagos, Canary Islands, Hawaiian Islands, and New Zealand) to test whether polyploidy (i) enhances or hinders diversification on islands and (ii) is an intrinsic feature of a lineage or an attribute that emerges in island environments. These island systems are diverse in their origins, geographic and latitudinal distributions, levels of plant species endemism (37% in the Galapagos to 88% in the Hawaiian Islands), and ploidy levels, and taken together are representative of islands more generally. We compiled data for vascular plants and summarized information for each genus on each island system, including the total number of species (native and endemic), generic endemicity, chromosome numbers, genome size, and ploidy levels. Dated phylogenies were used to infer lineage age, number of colonization events, and change in ploidy level relative to the non-island sister lineage. Using phylogenetic path analysis, we then tested how the diversification of endemic lineages varied with the direct and indirect effects of polyploidy (presence of polyploidy, time on island, polyploidization near colonization, colonizer pool size) and other lineage traits not associated with polyploidy (time on island, colonizer pool size, repeat colonization). Diploid and tetraploid were the most common ploidy levels across all islands, with the highest ploidy levels (>8x) recorded for the Canary Islands (12x) and New Zealand (20x). Overall, we found that endemic diversification of our focal island floras was shaped by polyploidy in many cases and certainly others still to be detected considering the lack of data in many lineages. Polyploid speciation on the islands was enhanced by a larger source of potential congeneric colonists and a change in ploidy level compared to overseas sister taxa.

Fine-scale empirical data on niche divergence and homeolog expression patterns in an allopolyploid and its diploid progenitor species

Polyploidization is pervasive in plants, but little is known about the niche divergence of wild allopolyploids (species that harbor polyploid genomes originating from different diploid species) relative to their diploid progenitor species and the gene expression patterns that may underlie such ecological divergence. We conducted a fine-scale empirical study on habitat and gene expression of an allopolyploid and its diploid progenitors. We quantified soil properties and light availability of habitats of an allotetraploid Cardamine flexuosa and its diploid progenitors Cardamine amara and Cardamine hirsuta in two seasons. We analyzed expression patterns of genes and homeologs (homeologous gene copies in allopolyploids) using RNA sequencing. We detected niche divergence between the allopolyploid and its diploid progenitors along water availability gradient at a fine scale: the diploids in opposite extremes and the allopolyploid in a broader range between diploids, with limited overlap with diploids at both ends. Most of the genes whose homeolog expression ratio changed among habitats in C. flexuosa varied spatially and temporally. These findings provide empirical evidence for niche divergence between an allopolyploid and its diploid progenitor species at a fine scale and suggest that divergent expression patterns of homeologs in an allopolyploid may underlie its persistence in diverse habitats.

Apple Autotetraploids with Enhanced Resistance to Apple Scab (Venturia inaequalis) Due to Genome Duplication-Phenotypic and Genetic Evaluation

Among the fungal diseases of apple trees, serious yield losses are due to an apple scab caused by Venturia inaequalis. Protection against this disease is based mainly on chemical treatments, which are currently very limited. Therefore, it is extremely important to introduce cultivars with reduced susceptibility to this pathogen. One of the important sources of variability for breeding is the process of polyploidization. Newly obtained polyploids may acquire new features, including increased resistance to diseases. In our earlier studies, numerous tetraploids have been obtained for several apple cultivars with 'Free Redstar' tetraploids manifesting enhanced resistance to apple scab. In the present study, tetraploids of 'Free Redstar' were assessed in terms of phenotype and genotype with particular emphasis on the genetic background of their increased resistance to apple scab. Compared to diploid plants, tetraploids (own-rooted plants) were characterized with poor growth, especially during first growing season. They had considerably shorter shoots, fewer branches, smaller stem diameter, and reshaped leaves. In contrast to own-rooted plants, in M9-grafted three-year old trees, no significant differences between diplo- and tetraploids were observed, either in morphological or physiological parameters, with the exceptions of the increased leaf thickness and chlorophyll content recorded in tetraploids. Significant differences between sibling tetraploid clones were recorded, particularly in leaf shape and some physiological parameters. The amplified fragment length polymorphism (AFLP) analysis confirmed genetic polymorphism of tetraploid clones. Methylation-sensitive amplification polymorphism (MSAP) analysis showed that the level of DNA methylation was twice as high in young tetraploid plants as in a diploid donor tree, which may explain the weaker vigour of neotetraploids in the early period of their growth in the juvenile phase. Molecular analysis showed that 'Free Redstar' cultivar and their tetraploids bear six Rvi genes (Rvi5, Rvi6, Rvi8, Rvi11, Rvi14 and Rvi17). Transcriptome analysis confirmed enhanced resistance to apple scab of 'Free Redstar' tetraploids since the expression levels of genes related to resistance were strongly enhanced in tetraploids compared to their diploid counterparts.

Multiple Drivers of High Species Diversity and Endemism Among Alyssum Annuals in the Mediterranean: The Evolutionary Significance of the Aegean Hotspot

The Mediterranean Basin is a significant hotspot of species diversity and endemism, with various distribution patterns and speciation mechanisms observed in its flora. High species diversity in the Mediterranean is also manifested in the monophyletic lineage of Alyssum annuals (Brassicaceae), but little is known about its origin. These species include both diploids and polyploids that grow mainly in open and disturbed sites across a wide elevational span and show contrasting distribution patterns, ranging from broadly distributed Eurasian species to narrow island endemics. Here, we investigated the evolution of European representatives of this lineage, and aimed to reconstruct their phylogeny, polyploid and genome size evolution using flow cytometric analyses, chloroplast and nuclear high- and low-copy DNA markers. The origin and early diversification of the studied Alyssum lineage could be dated back to the Late Miocene/Pliocene and were likely promoted by the onset of the Mediterranean climate, whereas most of the extant species originated during the Pleistocene. The Aegean region represents a significant diversity center, as it hosts 12 out of 16 recognized European species and comprises several (sub)endemics placed in distinct phylogenetic clades. Because several species, including the closest relatives, occur here sympatrically without apparent niche differences, we can reject simple allopatric speciation via vicariance as well as ecological speciation for most cases. Instead, we suggest scenarios of more complex speciation processes that involved repeated range shifts in response to sea-level changes and recurrent land connections and disconnections since the Pliocene. In addition, multiple polyploidization events significantly contributed to species diversity across the entire distribution range. All seven polyploids, representing both widespread species and endemics to the western or eastern Mediterranean, were inferred to be allopolyploids. Finally, the current distribution patterns have likely been affected also by the human factor (farming and grazing). This study illustrates the complexity of evolutionary and speciation processes in the Mediterranean flora.

When everything changes at once: finding a new normal after genome duplication

Whole-genome duplication (WGD), which leads to polyploidy, is implicated in adaptation and speciation. But what are the immediate effects of WGD and how do newly polyploid lineages adapt to them? With many studies of new and evolved polyploids now available, along with studies of genes under selection in polyploids, we are in an increasingly good position to understand how polyploidy generates novelty. Here, I will review consistent effects of WGD on the biology of plants, such as an increase in cell size, increased stress tolerance and more. I will discuss how a change in something as fundamental as cell size can challenge the function of some cell types in particular. I will also discuss what we have learned about the short- to medium-term evolutionary response to WGD. It is now clear that some of this evolutionary response may 'lock in' traits that happen to be beneficial, while in other cases, it might be more of an 'emergency response' to work around physiological changes that are either deleterious, or cannot be undone in the polyploid context. Yet, other traits may return rapidly to a diploid-like state. Polyploids may, by re-jigging many inter-related processes, find a new, conditionally adaptive, normal.

Effect of Whole-Genome Duplication on the Evolutionary Rescue of Sterile Hybrid Monkeyflowers

Hybridization is a creative evolutionary force, increasing genomic diversity and facilitating adaptation and even speciation. Hybrids often face significant challenges to establishment, including reduced fertility that arises from genomic incompatibilities between their parents. Whole-genome duplication in hybrids (allopolyploidy) can restore fertility, cause immediate phenotypic changes, and generate reproductive isolation. Yet the survival of polyploid lineages is uncertain, and few studies have compared the performance of recently formed allopolyploids and their parents under field conditions. Here, we use natural and synthetically produced hybrid and polyploid monkeyflowers (Mimulus spp.) to study how polyploidy contributes to the fertility, reproductive isolation, phenotype, and performance of hybrids in the field. We find that polyploidization restores fertility and that allopolyploids are reproductively isolated from their parents. The phenotype of allopolyploids displays the classic gigas effect of whole-genome duplication, in which plants have larger organs and are slower to flower. Field experiments indicate that survival of synthetic hybrids before and after polyploidization is intermediate between that of the parents, whereas natural hybrids have higher survival than all other taxa. We conclude that hybridization and polyploidy can act as sources of genomic novelty, but adaptive evolution is key in mediating the establishment of young allopolyploid lineages.

Genetic similarities versus morphological resemblance: Unraveling a polyploid complex in a Mediterranean biodiversity hotspot

The Balkan Peninsula is recognized as one of the hotspots of biodiversity in Europe. This area has shown since the Last Glacial Maximum appropriate conditions for species diversification and hybridization, which has led to the existence of numerous taxonomically unresolved entities. Here, we focus on the Western Balkans and explore the genetic structure and relationships among species belonging to the V. austriaca - V. orbiculata diploid-polyploid complex, including populations showing intermediate morphologies. A combination of nuclear markers (microsatellites), plastid DNA regions (trnH-psbA, ycf6-psbM) and ploidy level estimations using flow cytometry are employed to assess the genetic structure and evolutionary dynamics of this polyploid complex. To reconstruct the evolutionary history, an approximate Bayesian computation approach is combined with projections of the species distribution models onto the climatic scenarios of the Mid-Holocene (6 ka BP) and Last Glacial Maximum (22 ka BP). Four main groups were found: one well-established entity within the diploid level, V. dalmatica, a second diploid-tetraploid group which corresponds to V. orbiculata, a hexaploid cluster harboring V. austriaca subsp. jacquinii individuals, and an enigmatic tetraploid group. According to the molecular data obtained, this latter cluster represents an allopolyploid cryptic lineage −with V. orbiculata and V. dalmatica as putative parents− morphologically similar to V. orbiculata, but genetically more related to V. austriaca subsp. jacquinii. Veronica dalmatica and this “uncertain tetraploid” group are involved in the formation of the hexaploid taxon V. austriaca subsp. jacquinii, with the possibility of recent gene flow among different cytotypes. The present study supports a scenario of diversification from a diploid common ancestor leading to two different but interrelated lineages. The first one would correspond with the diploid V. orbiculata plus tetraploid individuals of this species arising through allo- and autopolyploidization, and the second one would involve all ploidy levels with allopolyploidization being prevalent.

Molecular regulatory mechanisms underlying the adaptability of polyploid plants

Polyploidization influences the genetic composition and gene expression of an organism. This multi-level genetic change allows the formation of new regulatory pathways leading to increased adaptability. Although both forms of polyploidization provide advantages, autopolyploids were long thought to have little impact on plant divergence compared to allopolyploids due to their formation through genome duplication only, rather than in combination with hybridization. Recent advances have begun to clarify the molecular regulatory mechanisms such as microRNAs, alternative splicing, RNA-binding proteins, histone modifications, chromatin remodelling, DNA methylation, and N⁶ -methyladenosine (m6A) RNA methylation underlying the evolutionary success of polyploids. Such research is expanding our understanding of the evolutionary adaptability of polyploids and the regulatory pathways that allow adaptive plasticity in a variety of plant species. Herein we review the roles of individual molecular regulatory mechanisms and their potential synergistic pathways underlying plant evolution and adaptation. Notably, increasing interest in m6A methylation has provided a new component in potential mechanistic coordination that is still predominantly unexplored. Future research should attempt to identify and functionally characterize the evolutionary impact of both individual and synergistic pathways in polyploid plant species.

Impact of genome duplication on secondary metabolite composition in non-cultivated species: a systematic meta-analysis

BACKGROUND AND AIMS

Whole-genome duplication is known to influence ecological interactions and plant physiology; however, despite abundant case studies, much is still unknown about the typical impact of genome duplication on plant secondary metabolites (PSMs). In this study, we assessed the impact of polyploidy events on PSM characteristics in non-cultivated plants.

METHODS

We conducted a systematic review and meta-analysis to compare composition and concentration of PSMs among closely related plant species or species complexes differing in ploidy level.

KEY RESULTS

We assessed 53 studies that focus on PSMs among multiple cytotypes, of which only 14 studies compared concentration quantitatively among cytotypes. We found that whole-genome duplication can have a significant effect on PSM concentration; however, these effects are highly inconsistent.

CONCLUSION

Overall, there was no consistent effect of whole-genome duplication on PSM concentrations or profiles.

Conservation and Divergence in Duplicated Fiber Coexpression Networks Accompanying Domestication of the Polyploid Gossypium hirsutum L

Gossypium hirsutum L. (Upland cotton) has an evolutionary history involving inter-genomic hybridization, polyploidization, and subsequent domestication. We analyzed the developmental dynamics of the cotton fiber transcriptome accompanying domestication using gene coexpression networks for both joint and homoeologous networks. Remarkably, most genes exhibited expression for at least one homoeolog, confirming previous reports of widespread gene usage in cotton fibers. Most coexpression modules comprising the joint network are preserved in each subgenomic network and are enriched for similar biological processes, showing a general preservation of network modular structure for the two co-resident genomes in the polyploid. Interestingly, only one fifth of homoeologs co-occur in the same module when separated, despite similar modular structures between the joint and homoeologous networks. These results suggest that the genome-wide divergence between homoeologous genes is sufficient to separate their co-expression profiles at the intermodular level, despite conservation of intramodular relationships within each subgenome. Most modules exhibit D-homoeolog expression bias, although specific modules do exhibit A-homoeolog bias. Comparisons between wild and domesticated coexpression networks revealed a much tighter and denser network structure in domesticated fiber, as evidenced by its fewer modules, 13-fold increase in the number of development-related module member genes, and the poor preservation of the wild network topology. These results demonstrate the amazing complexity that underlies the domestication of cotton fiber.

Genomics of Evolutionary Novelty in Hybrids and Polyploids

It has long been recognized that hybridization and polyploidy are prominent processes in plant evolution. Although classically recognized as significant in speciation and adaptation, recognition of the importance of interspecific gene flow has dramatically increased during the genomics era, concomitant with an unending flood of empirical examples, with or without genome doubling. Interspecific gene flow is thus increasingly thought to lead to evolutionary innovation and diversification, via adaptive introgression, homoploid hybrid speciation and allopolyploid speciation. Less well understood, however, are the suite of genetic and genomic mechanisms set in motion by the merger of differentiated genomes, and the temporal scale over which recombinational complexity mediated by gene flow might be expressed and exposed to natural selection. We focus on these issues here, considering the types of molecular genetic and genomic processes that might be set in motion by the saltational event of genome merger between two diverged species, either with or without genome doubling, and how these various processes can contribute to novel phenotypes. Genetic mechanisms include the infusion of new alleles and the genesis of novel structural variation including translocations and inversions, homoeologous exchanges, transposable element mobilization and novel insertional effects, presence-absence variation and copy number variation. Polyploidy generates massive transcriptomic and regulatory alteration, presumably set in motion by disrupted stoichiometries of regulatory factors, small RNAs and other genome interactions that cascade from single-gene expression change up through entire networks of transformed regulatory modules. We highlight both these novel combinatorial possibilities and the range of temporal scales over which such complexity might be generated, and thus exposed to natural selection and drift.

In Support of Winge's Theory of "Hybridization Followed by Chromosome Doubling"

Polyploidy-or chromosome doubling-plays a significant role in plant speciation and evolution. Much of the existing evidence indicates that fusion of unreduced (or 2n) gametes is the major pathway responsible for polyploid formation. In the early 1900s, a theory was put forward that the mechanism of "hybridization followed by chromosome doubling" would enable the survival and development of the hybrid zygote by providing each chromosome with a homolog with which to pair. However, to date there is only scant empirical evidence supporting this theory. In our previous study, interspecific-interploid crosses between the tetraploid Hylocereus megalanthus, as the female parent, and the diploid H. undatus, as the male parent, yielded only allopentaploids, allohexaploids, and 5x-and 6x-aneuploids instead of the expected allotriploids. No viable hybrids were obtained from the reciprocal cross. Since H. undatus underwent normal meiosis with regular pairing in the pollen mother cells and only reduced pollen grains were observed, the allohexaploids obtained supported the concept of "chromosome doubling." In this work, we report ploidy level, fruit morphology, and pollen viability and diameter in a group of putative hybrids obtained from an embryo rescue procedure following controlled H. megalanthus × H. undatus crosses, with the aim to elucidate, for the first time, the timing and developmental stage of the chromosome doubling. As in our previous report, no triploids were obtained, but tetraploids, pentaploids, hexaploids, and 5x- and 6x-aneuploids were found in the regenerated plants. The tetraploids exhibited the morphological features of the maternal parent and could not be considered true hybrids. Based on our previous studies, we can assume that the pentaploids were a result of a fertilization event between one unreduced (2n) female gamete from the tetraploid H. megalanthus and a normal (n) haploid male gamete from H. undatus. All the allohexaploids obtained from the embryo rescue technique where those that regenerated from fertilized ovules 10 days after pollination (at the pro-embryo stage), showing that the chromosome doubling event occurred at a very early development stage, i.e., at the zygote stage or shortly after zygote formation. These allohexaploids thus constitute empirical evidence of "hybridization followed by chromosome doubling."

Phylotranscriptomic Analyses Reveal Asymmetrical Gene Duplication Dynamics and Signatures of Ancient Polyploidy in Mints

Ancient duplication events and retained gene duplicates have contributed to the evolution of many novel plant traits and, consequently, to the diversity and complexity within and across plant lineages. Although mounting evidence highlights the importance of whole-genome duplication (WGD; polyploidy) and its key role as an evolutionary driver, gene duplication dynamics and mechanisms, both of which are fundamental to our understanding of evolutionary process and patterns of plant diversity, remain poorly characterized in many clades. We use newly available transcriptomic data and a robust phylogeny to investigate the prevalence, occurrence, and timing of gene duplications in Lamiaceae (mints), a species-rich and chemically diverse clade with many ecologically, economically, and culturally important species. We also infer putative WGDs—an extreme mechanism of gene duplication—using large-scale data sets from synonymous divergence (K_S), phylotranscriptomic, and divergence time analyses. We find evidence for widespread but asymmetrical levels of gene duplication and ancient polyploidy in Lamiaceae that correlate with species richness, including pronounced levels of gene duplication and putative ancient WGDs (7–18 events) within the large subclade Nepetoideae and up to 10 additional WGD events in other subclades. Our results help disentangle WGD-derived gene duplicates from those produced by other mechanisms and illustrate the nonuniformity of duplication dynamics in mints, setting the stage for future investigations that explore their impacts on trait diversity and species diversification. Our results also provide a practical context for evaluating the benefits and limitations of transcriptome-based approaches to inferring WGD, and we offer recommendations for researchers interested in investigating ancient WGDs in other plant groups.