Phylogenetic trends and environmental correlates of nuclear genome size variation in Helianthus sunflowers

Environmental impacts on intraspecific variation in Ambrosia artemisiifolia genome size in Slovakia, Central Europe

The quantity of DNA in angiosperms exhibits variation attributed to many external influences, such as environmental factors, geographical features, or stress factors, which exert constant selection pressure on organisms. Since invasive species possess adaptive capabilities to acclimate to novel environmental conditions, ragweed (Ambrosia artemisiifolia L.) was chosen as a subject for investigating their influence on genome size variation. Slovakia has diverse climatic conditions, suitable for testing the hypothesis that air temperature and precipitation, the main limiting factors of ragweed occurrence, would also have an impact on its genome size. Our results using flow cytometry confirmed this hypothesis and also found a significant association with geographical features such as latitude, altitude, and longitude. We can conclude that plants growing in colder environments farther from oceanic influences exhibit smaller DNA amounts, while optimal growth conditions result in a greater variability in genome size, reflecting the diminished effect of selection pressure.

Haplotype-resolved chromosome-level genome of hexaploid Jerusalem artichoke provides insights into its origin, evolution, and inulin metabolism

Jerusalem artichoke (Helianthus tuberosus) is a global multifunctional crop. It has wide applications in the food, health, feed, and biofuel industries and in ecological protection; it also serves as a germplasm pool for breeding of the global oil crop common sunflower (Helianthus annuus). However, biological studies of Jerusalem artichoke have been hindered by a lack of genome sequences, and its high polyploidy and large genome size have posed challenges to genome assembly. Here, we report a 21-Gb chromosome-level assembly of the hexaploid Jerusalem artichoke genome, which comprises 17 homologous groups, each with 6 pseudochromosomes. We found multiple large-scale chromosome rearrangements between Jerusalem artichoke and common sunflower, and our results show that the hexaploid genome of Jerusalem artichoke was formed by a hybridization event between a tetraploid and a diploid Helianthus species, followed by chromosome doubling of the hybrid, which occurred approximately 2 million years ago. Moreover, we identified more copies of actively expressed genes involved in inulin metabolism and showed that these genes may still be undergoing loss of function or sub- or neofunctionalization. These genomic resources will promote further biological studies, breeding improvement, and industrial utilization of Helianthus crops.

Testing the large genome constraint hypothesis in tropical rhizomatous herbs: life strategies, plant traits and habitat preferences in gingers

Plant species with large genomes tend to be excluded from climatically more extreme environments with a shorter growing season. Species that occupy such environments are assumed to be under natural selection for more rapid growth and smaller genome size (GS). However, evidence for this is available only for temperate organisms. Here, we study the evolution of GS in two subfamilies of the tropical family Zingiberaceae to find out whether species with larger genomes are confined to environments where the vegetative season is longer. We tested our hypothesis on 337 ginger species from regions with contrasting climates by correlating their GS with an array of plant traits and environmental variables. We revealed 16-fold variation in GS which was tightly related to shoot seasonality. Negative correlations of GS with latitude, temperature and precipitation emerged in the subfamily Zingiberoidae, demonstrating that species with larger GS are excluded from areas with a shorter growing season. In the subfamily Alpinioideae, GS turned out to be correlated with the type of stem and light requirements and its members cope with seasonality mainly by adaptation to shady and moist habitats. The Ornstein-Uhlenbeck models suggested that evolution in regions with humid climates favoured larger GS than in drier regions. Our results indicate that climate seasonality exerts an upper constraint on GS not only in temperate regions but also in the tropics, unless species with large genomes find alternative ways to escape from that constraint.

Cytomolecular trends in Chamaecrista Moench (Caesalpinioideae, Leguminosae) diversification

Chamaecrista is a Pantropical legume genus of the tribe Cassieae, which includes six other genera. In contrast to most of the other Cassieae genera, Chamaecrista shows significant variability in chromosome number (from 2n = 14 to 2n = 56), with small and morphologically similar chromosomes. Here, we performed a new cytomolecular analysis on chromosome number, genome size, and rDNA site distribution in a molecular phylogenetic perspective to interpret the karyotype trends of Chamaecrista and other two genera of Cassieae, seeking to understand their systematics and evolution. Our phylogenetic analysis revealed that Chamaecrista is monophyletic and can be divided into four major clades corresponding to the four sections of the genus. Chromosome numbers ranged from 2n = 14, 16 (section Chamaecrista) to 2n = 28 (sections Absus, Apoucouita, and Baseophyllum). The number of 5S and 35S rDNA sites varied between one and three pairs per karyotype, distributed on different chromosomes or in synteny, with no obvious phylogenetic significance. Our data allowed us to propose x = 7 as the basic chromosome number of Cassieae, which was changed by polyploidy generating x = 14 (sections Absus, Apoucouita, and Baseophyllum) and by ascending dysploidy to x = 8 (section Chamaecrista). The DNA content values supported this hypothesis, with the genomes of the putative tetraploids being larger than those of the putative diploids. We hypothesized that ascending dysploidy, polyploidy, and rDNA amplification/deamplification are the major events in the karyotypic diversification of Chamaecrista. The chromosomal marks characterized here may have cytotaxonomic potential in future studies.

Genome size variation and evolution during invasive range expansion in an introduced plant

Plants demonstrate exceptional variation in genome size across species, and their genome sizes can also vary dramatically across individuals and populations within species. This aspect of genetic variation can have consequences for traits and fitness, but few studies attributed genome size differentiation to ecological and evolutionary processes. Biological invasions present particularly useful natural laboratories to infer selective agents that might drive genome size shifts across environments and population histories. Here, we test hypotheses for the evolutionary causes of genome size variation across 14 invading populations of yellow starthistle, Centaurea solstitialis, in California, United States. We use a survey of genome sizes and trait variation to ask: (1) Is variation in genome size associated with developmental trait variation? (2) Are genome sizes smaller toward the leading edge of the expansion, consistent with selection for "colonizer" traits? Or alternatively, does genome size increase toward the leading edge of the expansion, consistent with predicted consequences of founder effects and drift? (3) Finally, are genome sizes smaller at higher elevations, consistent with selection for shorter development times? We found that 2C DNA content varied 1.21-fold among all samples, and was associated with flowering time variation, such that plants with larger genomes reproduced later, with lower lifetime capitula production. Genome sizes increased toward the leading edge of the invasion, but tended to decrease at higher elevations, consistent with genetic drift during range expansion but potentially strong selection for smaller genomes and faster development time at higher elevations. These results demonstrate how genome size variation can contribute to traits directly tied to reproductive success, and how selection and drift can shape that variation. We highlight the influence of genome size on dynamics underlying a rapid range expansion in a highly problematic invasive plant.

Genome-material costs and functional trade-offs in the autopolyploid Solidago gigantea (giant goldenrod) series

PREMISE

Increased genome-material costs of N and P atoms inherent to organisms with larger genomes have been proposed to limit growth under nutrient scarcities and to promote growth under nutrient enrichments. Such responsiveness may reflect a nutrient-dependent diploid versus polyploid advantage that could have vast ecological and evolutionary implications, but direct evidence that material costs increase with ploidy level and/or influence cytotype-dependent growth, metabolic, and/or resource-use trade-offs is limited.

METHODS

We grew diploid, autotetraploid, and autohexaploid Solidago gigantea plants with one of four ambient or enriched N:P ratios and measured traits related to material costs, primary and secondary metabolism, and resource-use.

RESULTS

Relative to diploids, polyploids invested more N and P into cells, and tetraploids grew more with N enrichments, suggesting that material costs increase with ploidy level. Polyploids also generally exhibited strategies that could minimize material-cost constraints over both long (reduced monoploid genome size) and short (more extreme transcriptome downsizing, reduced photosynthesis rates and terpene concentrations, enhanced N-use efficiencies) evolutionary time periods. Furthermore, polyploids had lower transpiration rates but higher water-use efficiencies than diploids, both of which were more pronounced under nutrient-limiting conditions.

CONCLUSIONS

N and P material costs increase with ploidy level, but material-cost constraints might be lessened by resource allocation/investment mechanisms that can also alter ecological dynamics and selection. Our results enhance mechanistic understanding of how global increases in nutrients might provide a release from material-cost constraints in polyploids that could impact ploidy (or genome-size)-specific performances, cytogeographic patterning, and multispecies community structuring.

Genetic basis of genome size variation of wheat

Research on various species has revealed a connection between genome size variation and the physiological and ecological characteristics of the species, suggesting that it could be a crucial factor influencing a species' adaptability to different environments. Wheat, being one of the world's three primary grains, holds significance in this regard. Investigating the genome size of wheat and analyzing the genetic factors contributing to its variation could offer valuable insights for enhancing wheat agronomic traits. This project has developed a conservative site ratio calculation approach to determine the size of the wheat genome. Additionally, it employs flow cytometry and k-mer distribution analysis to validate this method. Furthermore, the researchers use re-sequencing data to investigate the impact of environmental selection pressure and transposon dynamics on the variation in the size of the wheat genome. The findings from this study demonstrate a strong relationship between the size of the wheat genome and several environmental factors. These results serve as a valuable reference for understanding the development of variation in the size of the hetero-hexaploid wheat genome. Moreover, they contribute to advancing fundamental research on the genetic mechanisms underlying wheat characteristics. Additionally, the study paves the way for exploring new research directions in wheat breeding, which holds promise for future advancements in this field.

Mitogenomic Research of Silverleaf Sunflower (Helianthus argophyllus) and Its Interspecific Hybrids

Interspecific hybridization is widespread for sunflowers, both in wild populations and commercial breeding. One of the most common species that can efficiently cross with Helianthus annuus is the Silverleaf sunflower-Helianthus argophyllus. The current study carried out structural and functional organization analyses of mitochondrial DNA in H. argophyllus and the interspecific hybrid, H. annuus (VIR114A line) × H. argophyllus. The complete mitogenome of H. argophyllus counts 300,843 bp, has a similar organization to the mitogenome of cultivated sunflower, and holds SNPs typical for wild sunflowers. RNA editing analysis predicted 484 sites in H. argophyllus mitochondrial CDS. The mitochondrial genome of the H. annuus × H. argophyllus hybrid is identical to the maternal line (VIR114A). We expected that significant rearrangements in the mitochondrial DNA of the hybrid would occur, due to the frequent recombination. However, the hybrid mitogenome lacks rearrangements, presumably due to the preservation of nuclear-cytoplasmic interaction paths.

Fewer chromosomes, more co-occurring species within plant lineages: A likely effect of local survival and colonization

PREMISE

Plant lineages differ markedly in species richness globally, regionally, and locally. Differences in whole-genome characteristics (WGCs) such as monoploid chromosome number, genome size, and ploidy level may explain differences in global species richness through speciation or global extinction. However, it is unknown whether WGCs drive species richness within lineages also in a recent, postglacial regional flora or in local plant communities through local extinction or colonization and regional species turnover.

METHODS

We tested for relationships between WGCs and richness of angiosperm families across the Netherlands/Germany/Czechia as a region, and within 193,449 local vegetation plots.

RESULTS

Families that are species-rich across the region have lower ploidy levels and small monoploid chromosomes numbers or both (interaction terms), but the relationships disappear after accounting for continental and local richness of families. Families that are species-rich within occupied localities have small numbers of polyploidy and monoploid chromosome numbers or both, independent of their own regional richness and the local richness of all other locally co-occurring species in the plots. Relationships between WGCs and family species-richness persisted after accounting for niche characteristics and life histories.

CONCLUSIONS

Families that have few chromosomes, either monoploid or holoploid, succeed in maintaining many species in local communities and across a continent and, as indirect consequence of both, across a region. We suggest evolutionary mechanisms to explain how small chromosome numbers and ploidy levels might decrease rates of local extinction and increase rates of colonization. The genome of a macroevolutionary lineage may ultimately control whether its species can ecologically coexist.

Genome size variation and polyploidy prevalence in the genus Eragrostis are associated with the global dispersal in arid area

BACKGROUND

Biologists have long debated the drivers of the genome size evolution and variation ever since Darwin. Assumptions for the adaptive or maladaptive consequences of the associations between genome sizes and environmental factors have been proposed, but the significance of these hypotheses remains controversial. Eragrostis is a large genus in the grass family and is often used as crop or forage during the dry seasons. The wide range and complex ploidy levels make Eragrostis an excellent model for investigating how the genome size variation and evolution is associated with environmental factors and how these changes can ben interpreted.

METHODS

We reconstructed the Eragrostis phylogeny and estimated genome sizes through flow cytometric analyses. Phylogenetic comparative analyses were performed to explore how genome size variation and evolution is related to their climatic niches and geographical ranges. The genome size evolution and environmental factors were examined using different models to study the phylogenetic signal, mode and tempo throughout evolutionary history.

RESULTS

Our results support the monophyly of Eragrostis. The genome sizes in Eragrostis ranged from ~0.66 pg to ~3.80 pg. We found that a moderate phylogenetic conservatism existed in terms of the genome sizes but was absent from environmental factors. In addition, phylogeny-based associations revealed close correlations between genome sizes and precipitation-related variables, indicating that the genome size variation mainly caused by polyploidization may have evolved as an adaptation to various environments in the genus Eragrostis.

CONCLUSION

This is the first study to take a global perspective on the genome size variation and evolution in the genus Eragrostis. Our results suggest that the adaptation and conservatism are manifested in the genome size variation, allowing the arid species of Eragrostis to spread the xeric area throughout the world.

A trait-based approach to determining principles of plant biogeography

Lineage-specific traits determine how plants interact with their surrounding environment. Unrelated species may evolve similar phenotypic characteristics to tolerate, persist in, and invade environments with certain characteristics, resulting in some traits becoming relatively more common in certain types of habitats. Analyses of these general patterns of geographical trait distribution have led to the proposal of general principles to explain how plants diversify in space over time. Trait-environment correlation analyses quantify to what extent unrelated lineages have similar evolutionary responses to a given type of habitat. In this synthesis, I give a short historical overview on trait-environment correlation analyses, from some key observations from classic naturalists to modern approaches using trait evolution models, large phylogenies, and massive data sets of traits and distributions. I discuss some limitations of modern approaches, including the need for more realistic models, the lack of data from tropical areas, and the necessary focus on trait scoring that goes beyond macromorphology. Overcoming these limitations will allow the field to explore new questions related to trait lability and niche evolution and to better identify generalities and exceptions in how plants diversify in space over time.

Intraspecific variation in genome size in Artemisia argyi determined using flow cytometry and a genome survey

Different collections and accessions of Artemisia argyi (Chinese mugwort) harbour considerable diversity in morphology and bioactive compounds, but no mechanisms have been reported that explain these variations. We studied genome size in A. argyi accessions from different regions of China by flow cytometry. Genome size was significantly distinct among origins of these 42 Chinese mugwort accessions, ranging from 8.428 to 11.717 pg. There were no significant intraspecific differences among the 42 accessions from the five regions of China. The clustering analysis showed that these 42 A. argyi accessions could be divided into three groups, which had no significant relationship with geographical location. In a genome survey, the total genome size of A. argyi (A15) was estimated to be 7.852 Gb (or 8.029 pg) by K-mer analysis. This indicated that the results from the two independent methods are consistent, and that the genome survey can be used as an adjunct to flow cytometry to compensate for its deficiencies. In addition, genome survey can provide the information about heterozygosity, repeat sequences, GC content and ploidy of A. argyi genome. The nuclear DNA contents determined here provide a new reference for intraspecific variation in genome size in A. argyi, and may also be a potential resource for the study of genetic diversity and for breeding new cultivar.

Broad diversity in monoterpene-sesquiterpene balance across wild sunflowers: Implications of leaf and floral volatiles for biotic interactions

PREMISE

As plant lineages diversify across environmental gradients, species are predicted to encounter divergent biotic pressures. This study investigated the evolution of volatile secondary metabolism across species of Helianthus.

METHODS

Leaves and petals of 40 species of wild Helianthus were analyzed via gas chromatography-mass spectrometry to determine volatile secondary metabolite profiles.

RESULTS

Across all species, 500 compounds were identified; 40% were sesquiterpenes, 18% monoterpenes, 3% diterpenes, 4% fatty acid derivatives, and 35% other compounds such as phenolics and small organic molecules. Qualitatively, annuals and species from more arid western climates had leaf compositions with a higher proportion of total monoterpenes, while erect perennials and species from more mesic eastern habitats contained a higher proportion of total sesquiterpenes. Among species, mass-based leaf monoterpene and sesquiterpene abundance were identified as largely orthogonal axes of variation by principal component analysis. Profiles for leaves were not strongly correlated with those of petals.

CONCLUSIONS

Volatile metabolites were highly diverse among wild Helianthus, indicating the value of this genus as a model system and rich genetic resource. The independence of leaf and petal volatile profiles indicates a low level of phenotypic integration between vegetative and reproductive structures, implying vegetative defense and reproductive defense or pollinator attraction functions mediated by terpene profiles in these two organs can evolve without major trade-offs. The major biosynthetic pathways for the major terpenes in wild Helianthus are already well described, providing a road map to deeper inquiry into the drivers of this diversity.

Genome Size Variation in Dianthus sylvestris Wulfen sensu lato (Caryophyllaceae)

Genome size (GS) is an important characteristic that may be helpful in delimitation of taxa, and multiple studies have shown correlations between intraspecific GS variation and morphological or environmental factors, as well as its geographical segregation. We estimated a relative GS (RGS) of 707 individuals from 162 populations of Dianthus sylvestris with a geographic focus on the Balkan Peninsula, but also including several populations from the European Alps. Dianthus sylvestris is morphologically variable species thriving in various habitats and six subspecies have been recognized from the Balkan Peninsula. Our RGS data backed-up with chromosome counts revealed that the majority of populations were diploid (2n = 30), but ten tetraploid populations have been recorded in D. sylvestris subsp. sylvestris from Istria (Croatia, Italy). Their monoploid RGS is significantly lower than that of the diploids, indicating genome downsizing. In addition, the tetraploids significantly differ from their diploid counterparts in an array of morphological and environmental characteristics. Within the diploid populations, the RGS is geographically and only partly taxonomically correlated, with the highest RGS inferred in the southern Balkan Peninsula and the Alps. We demonstrate greater RGS variation among the Balkan populations compared to the Alps, which is likely a result of more pronounced evolutionary differentiation within the Balkan Peninsula. In addition, a deep RGS divergence within the Alps likely points to persistence of the alpine populations in different Pleistocene refugia.

The important contribution of transposable elements to phenotypic variation and evolution

Transposable elements (TEs) are responsible for significant genomic variation in plants. Our understanding of the evolutionary forces shaping TE polymorphism has lagged behind other mutations because of the difficulty of accurately identifying TE polymorphism in short-read population genomic data. However, new approaches allow us to quantify TE polymorphisms in population datasets and address fundamental questions about the evolution of these polymorphisms. Here, we discuss how insertional biases shape where, when, and how often TEs insert throughout the genome. Next, we examine mechanisms by which TEs can affect phenotype. Finally, we evaluate current evidence for selection on TE polymorphisms. All together, it is clear that TEs are important, but underappreciated, contributors to intraspecific phenotypic variation, and that understanding the dynamics governing TE polymorphism is crucial for evolutionary biologists interested in the maintenance of variation.

Image analysis for the automatic phenotyping of Orobanche cumana tubercles on sunflower roots

BACKGROUND

The parasitic plant Orobanche cumana is one of the most important threats to sunflower crops in Europe. Resistant sunflower varieties have been developed, but new O. cumana races have evolved and have overcome introgressed resistance genes, leading to the recurrent need for new resistance methods. Screening for resistance requires the phenotyping of thousands of sunflower plants to various O. cumana races. Most phenotyping experiments have been performed in fields at the later stage of the interaction, requiring time and space. A rapid phenotyping screening method under controlled conditions would need less space and would allow screening for resistance of many sunflower genotypes. Our study proposes a phenotyping tool for the sunflower/O. cumana interaction under controlled conditions through image analysis for broomrape tubercle analysis at early stages of the interaction.

RESULTS

We optimized the phenotyping of sunflower/O. cumana interactions by using rhizotrons (transparent Plexiglas boxes) in a growth chamber to control culture conditions and Orobanche inoculum. We used a Raspberry Pi computer with a picamera for acquiring images of inoculated sunflower roots 3 weeks post inoculation. We set up a macro using ImageJ free software for the automatic counting of the number of tubercles. This phenotyping tool was named RhizOSun. We evaluated five sunflower genotypes inoculated with two O. cumana races and showed that automatic counting of the number of tubercles using RhizOSun was highly correlated with manual time-consuming counting and could be efficiently used for screening sunflower genotypes at the tubercle stage.

CONCLUSION

This method is rapid, accurate and low-cost. It allows rapid imaging of numerous rhizotrons over time, and it enables image tracking of all the data with time kinetics. This paves the way toward automatization of phenotyping in rhizotrons that could be used for other root phenotyping, such as symbiotic nodules on legumes.

Repeat proliferation and partial endoreplication jointly shape the patterns of genome size evolution in orchids

Although the evolutionary drivers of genome size change are known, the general patterns and mechanisms of plant genome size evolution are yet to be established. Here we aim to assess the relative importance of proliferation of repetitive DNA, chromosomal variation (including polyploidy), and the type of endoreplication for genome size evolution of the Pleurothallidinae, the most species-rich orchid lineage. Phylogenetic relationships between 341 Pleurothallidinae representatives were refined using a target enrichment hybrid capture combined with high-throughput sequencing approach. Genome size and the type of endoreplication were assessed using flow cytometry supplemented with karyological analysis and low-coverage Illumina sequencing for repeatome analysis on a subset of samples. Data were analyzed using phylogeny-based models. Genome size diversity (0.2-5.1 Gbp) was mostly independent of profound chromosome count variation (2n = 12-90) but tightly linked with the overall content of repetitive DNA elements. Species with partial endoreplication (PE) had significantly greater genome sizes, and genomic repeat content was tightly correlated with the size of the non-endoreplicated part of the genome. In PE species, repetitive DNA is preferentially accumulated in the non-endoreplicated parts of their genomes. Our results demonstrate that proliferation of repetitive DNA elements and PE together shape the patterns of genome size diversity in orchids.

Genome size evolution is associated with climate seasonality and glucosinolates, but not life history, soil nutrients or range size, across a clade of mustards

BACKGROUND AND AIMS

We investigate patterns of evolution of genome size across a morphologically and ecologically diverse clade of Brassicaceae, in relation to ecological and life history traits. While numerous hypotheses have been put forward regarding autecological and environmental factors that could favour small vs. large genomes, a challenge in understanding genome size evolution in plants is that many hypothesized selective agents are intercorrelated.

METHODS

We contribute genome size estimates for 47 species of Streptanthus Nutt. and close relatives, and take advantage of many data collections for this group to assemble data on climate, life history, soil affinity and composition, geographic range and plant secondary chemistry to identify simultaneous correlates of variation in genome size in an evolutionary framework. We assess models of evolution across clades and use phylogenetically informed analyses as well as model selection and information criteria approaches to identify variables that can best explain genome size variation in this clade.

KEY RESULTS

We find differences in genome size and heterogeneity in its rate of evolution across subclades of Streptanthus and close relatives. We show that clade-wide genome size is positively associated with climate seasonality and glucosinolate compounds. Model selection and information criteria approaches identify a best model that includes temperature seasonality and fraction of aliphatic glucosinolates, suggesting a possible role for genome size in climatic adaptation or a role for biotic interactions in shaping the evolution of genome size. We find no evidence supporting hypotheses of life history, range size or soil nutrients as forces shaping genome size in this system.

CONCLUSIONS

Our findings suggest climate seasonality and biotic interactions as potential forces shaping the evolution of genome size and highlight the importance of evaluating multiple factors in the context of phylogeny to understand the effect of possible selective agents on genome size.

Primeras medidas del tamaño del genoma en Carduncellusy los géneros afines Femeniasia y Phonus (Asteraceae, Cardueae), con datos para 21 táxones

El tamaño del genoma de 18 especies del género Carduncellus, dos especies de los géneros relacionados, Phonus y el género monotípico Femeniasia (F. balearica) ha sido medido por primera vez mediante citometría de flujo. Los niveles de ploidía se asignaron utilizando datos de tamaño del genoma junto con los recuentos de cromosomas previamente reportados. Se construyó un marco filogenético para visualizar la distribución de las características citogenéticas de los táxones. Los resultados confirmaron tres niveles de ploidía (2x, 4x y 6x), con un predominio de los táxones diploides. Los valores de 2C oscilaron entre 3,24 pg en Carduncellus calvus y 11,16 pg en C. eriocephalus, mientras que el tamaño del genoma monoploide (1Cx) osciló entre 1,29 pg en C. duvauxii (4x) y 2,30 pg en Phonus rhiphaeus (2x). La media de los valores 1Cx para los tetraploides fue menor que para los diploides. Los valores de tamaño del genoma de Carduncellus, Femeniasia y Phonus fueron más elevados que los de Carthamus dentro del mismo nivel de ploidía. Este resultado concuerda con una tendencia frecuentemente observada en plantas en la que los táxones con ciclos de vida largos presentan tamaños del genoma más elevados que los táxones relacionados que poseen ciclos de vida cortos.

Diversification of Aeonium Species Across Macaronesian Archipelagos: Correlations Between Genome-Size Variation and Their Conservation Status

The rich endemic flora of the Macaronesian Islands places these oceanic archipelagos among the top biodiversity hotspots worldwide. The radiations that have determined the evolution of many of these insular lineages resulted in a wealth of endemic species, many of which occur in a wide range of ecological niches, but show small distribution areas in each of them. Aeonium (Crassulaceae) is the most speciose lineage in the Canary Islands (ca. 40 taxa), and as such can be considered a good model system to understand the diversification dynamics of oceanic endemic floras. The present study aims to assess the genome size variation within Aeonium distribution, i.e., the Macaronesian archipelagos of Madeira, Canaries and Cabo Verde, and analyse it together with information on distribution (i.e., geography and conservation status), taxonomy (i.e., sections), morphological traits (i.e., growth-form), geological data (i.e., island's geological age), and environmental variables (i.e., altitude, annual mean temperature, and precipitation). Based on extensive fieldwork, a cytogeographic screening of 24 Aeonium species was performed. The conservation status of these species was assessed based on IUCN criteria. 61% of the taxa were found to be threatened (4% Endangered and 57% Vulnerable). For the first time, the genome size of a comprehensive sample of Aeonium across the Macaronesian archipelagos was estimated, and considerable differences in Cx-values were found, ranging from 0.984 pg (A. dodrantale) to 2.768 pg (A. gorgoneum). An overall positive correlation between genome size and conservation status was found, with the more endangered species having the larger genomes on average. However, only slight relationships were found between genome size, morphological traits, and environmental variables. These results underscore the importance of characterizing the cytogenomic diversity and conservation status of endemic plants found in Macaronesian Islands, providing, therefore, new data to establish conservation priorities.

Sympatric genome size variation and hybridization of four oak species as determined by flow cytometry genome size variation and hybridization

The Quercus species serve as a powerful model for studying introgression in relation to species boundaries and adaptive processes. Coexistence of distant relatives, or lack of coexistence of closely relative oak species, introgression may play a role. In the current study, four closely related oak species were found in Zijinshan, China. We generated a comprehensive genome size (GS) database for 120 individuals of four species using flow cytometry-based approaches. We examined GS variability within and among the species and hybridization events among the four species. The mean GSs of Q. acutissima, Q. variabilis, Q. fabri, and Q. serrata var. brevipetiolata were estimated to be 1.87, 1.92, 1.97, and 1.97 pg, respectively. The intraspecific and interspecific variations of GS observed among the four oak species indicated adaptation to the environment. Hybridization occurred both within and between the sections. A hybrid offspring was produced from Q. fabri and Q. variabilis, which belonged to different sections. The GS evolutionary pattern for hybrid species was expansion. Hybridization between the sections may be affected by habitat disturbance. This study increases our understanding of the evolution of GS in Quercus and will help establish guidelines for the ecological protection of oak trees.

Evolution of Disease Severity and Susceptibility in the Asteraceae to the Powdery Mildew Golovinomyces latisporus: Major Phylogenetic Structure Coupled With Highly Variable Disease Severity at Fine Scales

Pathogen host range and pathogen severity are dependent on interactions with their hosts and are hypothesized to have evolved as products of a coevolutionary arms race. An understanding of the factors that affect host range and pathogen severity is especially crucial in introduced pathogens that infect evolutionarily naïve hosts and cause substantial damage to ecosystems. Powdery mildews are detrimental pathogens found worldwide in managed and natural systems. Golovinomyces latisporus is a powdery mildew species that is especially damaging to plants within Asteraceae and to plants within the genus Helianthus in particular. In this study, we evaluated 126 species within Asteraceae to measure the role of host plant morphophysiological traits and evolutionary history on susceptibility to G. latisporus and disease severity. We observed phylogenetic signal in both susceptibility and severity within and among major clades of the Asteraceae. In general, there was a major phylogenetic structure of host severity to G. latisporus; however, there was some fine-scale phylogenetic variability. Phylogenetic statistical methods showed that chlorophyll content, biomass, stomatal index, and trichome density were not associated with disease severity, thus providing evidence that phylogenetic structure, rather than observed plant morphophysiological traits, is the most reliable predictor of pathogen severity. This work sheds light on the role that evolutionary history plays in plant susceptibility and severity to disease and underscores the relative unimportance of commonly assessed host plant traits in powdery mildew severity.

Evolutionary dynamics of genome size in a radiation of woody plants

PREMISE

Plant genome size ranges widely, providing many opportunities to examine how genome size variation affects plant form and function. We analyzed trends in chromosome number, genome size, and leaf traits for the woody angiosperm clade Viburnum to examine the evolutionary associations, functional implications, and possible drivers of genome size.

METHODS

Chromosome counts and genome size estimates were mapped onto a Viburnum phylogeny to infer the location and frequency of polyploidization events and trends in genome size evolution. Genome size was analyzed with leaf anatomical and physiological data to evaluate the influence of genome size on plant function.

RESULTS

We discovered nine independent polyploidization events, two reductions in base chromosome number, and substantial variation in genome size with a slight trend toward genome size reduction in polyploids. We did not find strong relationships between genome size and the functional and morphological traits that have been highlighted at broader phylogenetic scales.

CONCLUSIONS

Polyploidization events were sometimes associated with rapid radiations, demonstrating that polyploid lineages can be highly successful. Relationships between genome size and plant physiological function observed at broad phylogenetic scales may be largely irrelevant to the evolutionary dynamics of genome size at smaller scales. The view that plants readily tolerate changes in ploidy and genome size, and often do so, appears to apply to Viburnum.

The Investigation of Perennial Sunflower Species (Helianthus L.) Mitochondrial Genomes

The genus Helianthus is a diverse taxonomic group with approximately 50 species. Most sunflower genomic investigations are devoted to economically valuable species, e.g., H. annuus, while other Helianthus species, especially perennial, are predominantly a blind spot. In the current study, we have assembled the complete mitogenomes of two perennial species: H. grosseserratus (273,543 bp) and H. strumosus (281,055 bp). We analyzed their sequences and gene profiles in comparison to the available complete mitogenomes of H. annuus. Except for sdh4 and trnA-UGC, both perennial sunflower species had the same gene content and almost identical protein-coding sequences when compared with each other and with annual sunflowers (H. annuus). Common mitochondrial open reading frames (ORFs) (orf117, orf139, and orf334) in sunflowers and unique ORFs for H. grosseserratus (orf633) and H. strumosus (orf126, orf184, orf207) were identified. The maintenance of plastid-derived coding sequences in the mitogenomes of both annual and perennial sunflowers and the low frequency of nonsynonymous mutations point at an extremely low variability of mitochondrial DNA (mtDNA) coding sequences in the Helianthus genus.

Massive haplotypes underlie ecotypic differentiation in sunflowers

Species often include multiple ecotypes that are adapted to different environments¹. However, it is unclear how ecotypes arise and how their distinctive combinations of adaptive alleles are maintained despite hybridization with non-adapted populations^2-4. Here, by resequencing 1,506 wild sunflowers from 3 species (Helianthus annuus, Helianthus petiolaris and Helianthus argophyllus), we identify 37 large (1-100 Mbp in size), non-recombining haplotype blocks that are associated with numerous ecologically relevant traits, as well as soil and climate characteristics. Limited recombination in these haplotype blocks keeps adaptive alleles together, and these regions differentiate sunflower ecotypes. For example, haplotype blocks control a 77-day difference in flowering between ecotypes of the silverleaf sunflower H. argophyllus (probably through deletion of a homologue of FLOWERING LOCUS T (FT)), and are associated with seed size, flowering time and soil fertility in dune-adapted sunflowers. These haplotypes are highly divergent, frequently associated with structural variants and often appear to represent introgressions from other-possibly now-extinct-congeners. These results highlight a pervasive role of structural variation in ecotypic adaptation.

Skim-Sequencing Reveals the Likely Origin of the Enigmatic Endangered Sunflower Helianthus schweinitzii

Resolving the origin of endangered taxa is an essential component of conservation. This information can be used to guide efforts of bolstering genetic diversity, and also enables species recovery and future evolutionary studies. Here, we used low-coverage whole genome sequencing to clarify the origin of Helianthus schweinitzii, an endangered tetraploid sunflower that is endemic to the Piedmont Plateau in the eastern United States. We surveyed four accessions representing four populations of H. schweinitzii and 38 accessions of six purported parental species. Using de novo approaches, we assembled 87,004 bp of the chloroplast genome and 6770 bp of the nuclear 35S rDNA. Phylogenetic reconstructions based on the chloroplast genome revealed no reciprocal monophyly of taxa. In contrast, nuclear rDNA data strongly supported the currently accepted sections of the genus Helianthus. Information from combined cpDNA and rDNA provided evidence that H. schweinitzii is likely an allo-tetraploid that formed as a result of hybridization between the diploids Helianthus giganteus and Helianthus microcephalus.

Intraspecific genetic divergence within Helianthus niveus and the status of two new morphotypes from Mexico

PREMISE

Collecting and characterizing the genetic diversity of wild relatives of crops can contribute importantly to sustainable crop production and food security. Wild sunflower, Helianthus niveus, occurs in arid regions in western North America and is partially cross-compatible with the cultivated sunflower (H. annuus). We assessed phylogenetic relationships and patterns of genetic divergence among three previously described subspecies (subsp. niveus, subsp. canescens, and subsp. tephrodes) as well as two new morphotypes of H. niveus recently discovered in extreme drought and dune habitats in Baja California, Mexico.

METHODS

We measured 50 plants growing in a common garden for 27 morphological traits and conducted principal component analysis to assess patterns of phenotypic variation. Genome size of each accession was determined using flow cytometry. Pollen viability of first generation hybrids between taxa was tested to infer the strength of intrinsic postzygotic reproductive barriers. Finally, genotyping-by-sequencing data were used to investigate the genetic structure and phylogenetic relationships among the previously described subspecies and new morphotypes.

RESULTS

The intraspecific genetic and phenotypic divergence of H. niveus populations closely tracks their geographical distribution. Subspecies niveus is phenotypically, genetically, and reproductively distinct from the other two subspecies and has a larger genome. Therefore, H. niveus as currently circumscribed should be considered to contain two distinct species, H. niveus and H. tephrodes. ABBA-BABA tests revealed substantial introgression between subsp. canescens and its sympatric congener H. petiolaris, which might contribute to their morphological similarities. The two new morphotypes collected in Mexico represent local ecotypes of subsp. niveus that occur in extreme drought and dune environments. Mantel tests showed a strong positive correlation between genetic and geographic distances.

CONCLUSIONS

We conclude that geographic isolation is primarily responsible for intraspecific genomic divergence within H. niveus, while patterns of phenotypic variation appear to have been shaped by ecological selection and interspecific introgression.