Smallest angiosperm genomes found in lentibulariaceae, with chromosomes of bacterial size

The smallest angiosperm genomes may be the price for effective traps of bladderworts

BACKGROUND

Species of the carnivorous family Lentibulariaceae exhibit the smallest genomes in flowering plants. We explored the hypothesis that their minute genomes result from the unique mitochondrial cytochrome c oxidase (COX) mutation. The mutation may boost mitochondrial efficiency, which is especially useful for suction-bladder traps of Utricularia, but also increase DNA-damaging reactive oxygen species, leading to genome shrinkage through deletion-biased DNA repair. We aimed to explore the impact of this mutation on genome size, providing insights into genetic mutation roles in plant genome evolution under environmental pressures.

METHODS

We compiled and measured genome and mean chromosome sizes for 127 and 67 species, respectively, representing all three genera (Genlisea, Pinguicula and Utricularia) of Lentibulariaceae. We also isolated and analysed COX sequences to detect the mutation. Through phylogenetic regressions and Ornstein-Uhlenbeck models of trait evolution, we assessed the impact of the COX mutation on the genome and chromosome sizes across the family.

RESULTS

Our findings reveal significant correlations between the COX mutation and smaller genome and chromosome sizes. Specifically, species carrying the ancestral COX sequence exhibited larger genomes and chromosomes than those with the novel mutation. This evidence supports the notion that the COX mutation contributes to genome downsizing, with statistical analyses confirming a directional evolution towards smaller genomes in species harbouring these mutations.

CONCLUSIONS

Our study confirms that the COX mutation in Lentibulariaceae is associated with genome downsizing, probably driven by increased reactive oxygen species production and subsequent DNA damage requiring deletion-biased repair mechanisms. While boosting mitochondrial energy output, this genetic mutation compromises genome integrity and may potentially affect recombination rates, illustrating a complex trade-off between evolutionary advantages and disadvantages. Our results highlight the intricate processes by which genetic mutations and environmental pressures shape genome size evolution in carnivorous plants.

Molecular Phylogenomics Reveals the Deep Evolutionary History of Carnivory across Land Plants

Plastid molecular phylogenies that broadly sampled angiosperm lineages imply that carnivorous plants evolved at least 11 times independently in 13 families and 6 orders. Within and between these clades, the different prey capture strategies involving flypaper and pitfall structures arose in parallel with the subsequent evolution of snap traps and suction bladders. Attempts to discern the deep ontological history of carnivorous structures using multigene phylogenies have provided a plastid-level picture of sister relationships at the family level. Here, we present a molecular phylogeny of the angiosperms based on nuclear target sequence capture data (Angiosperms-353 probe set), assembled by the Kew Plant Trees of Life initiative, which aims to complete the tree of life for plants. This phylogeny encompasses all carnivorous and protocarnivorous families, although certain genera such as Philcoxia (Plantaginaceae) are excluded. This study offers a novel nuclear gene-based overview of relationships within and between carnivorous families and genera. Consistent with previous broadly sampled studies, we found that most carnivorous families are not affiliated with any single family. Instead, they emerge as sister groups to large clades comprising multiple non-carnivorous families. Additionally, we explore recent genomic studies across various carnivorous clades that examine the evolution of the carnivorous syndrome in relation to whole-genome duplication, subgenome dominance, small-scale gene duplication, and convergent evolution. Furthermore, we discuss insights into genome size evolution through the lens of carnivorous plant genomes.

The phylogenomics and evolutionary dynamics of the organellar genomes in carnivorous Utricularia and Genlisea species (Lentibulariaceae)

Utricularia and Genlisea are highly specialized carnivorous plants whose phylogenetic history has been poorly explored using phylogenomic methods. Additional sampling and genomic data are needed to advance our phylogenetic and taxonomic knowledge of this group of plants. Within a comparative framework, we present a characterization of plastome (PT) and mitochondrial (MT) genes of 26 Utricularia and six Genlisea species, with representatives of all subgenera and growth habits. All PT genomes maintain similar gene content, showing minor variation across the genes located between the PT junctions. One exception is a major variation related to different patterns in the presence and absence of ndh genes in the small single copy region, which appears to follow the phylogenetic history of the species rather than their lifestyle. All MT genomes exhibit similar gene content, with most differences related to a lineage-specific pseudogenes. We find evidence for episodic positive diversifying selection in PT and for most of the Utricularia MT genes that may be related to the current hypothesis that bladderworts' nuclear DNA is under constant ROS oxidative DNA damage and unusual DNA repair mechanisms, or even low fidelity polymerase that bypass lesions which could also be affecting the organellar genomes. Finally, both PT and MT phylogenetic trees were well resolved and highly supported, providing a congruent phylogenomic hypothesis for Utricularia and Genlisea clade given the study sampling.

Omics Approaches in Uncovering Molecular Evolution and Physiology of Botanical Carnivory

Systems biology has been increasingly applied with multiple omics for a holistic comprehension of complex biological systems beyond the reductionist approach that focuses on individual molecules. Different high-throughput omics approaches, including genomics, transcriptomics, metagenomics, proteomics, and metabolomics have been implemented to study the molecular mechanisms of botanical carnivory. This covers almost all orders of carnivorous plants, namely Caryophyllales, Ericales, Lamiales, and Oxalidales, except Poales. Studies using single-omics or integrated multi-omics elucidate the compositional changes in nucleic acids, proteins, and metabolites. The omics studies on carnivorous plants have led to insights into the carnivory origin and evolution, such as prey capture and digestion as well as the physiological adaptations of trap organ formation. Our understandings of botanical carnivory are further enhanced by the discoveries of digestive enzymes and transporter proteins that aid in efficient nutrient sequestration alongside dynamic molecular responses to prey. Metagenomics studies revealed the mutualistic relationships between microbes and carnivorous plants. Lastly, in silico analysis accelerated the functional characterization of new molecules from carnivorous plants. These studies have provided invaluable molecular data for systems understanding of carnivorous plants. More studies are needed to cover the diverse species with convergent evolution of botanical carnivory.

Subgenome dominance and its evolutionary implications in crop domestication and breeding

Polyploidization or whole-genome duplication (WGD) is a well-known speciation and adaptation mechanism in angiosperms, while subgenome dominance is a crucial phenomenon in allopolyploids, established following polyploidization. The dominant subgenomes contribute more to genome evolution and homoeolog expression bias, both of which confer advantages for short-term phenotypic adaptation and long-term domestication. In this review, we firstly summarize the probable mechanistic basis for subgenome dominance, including the effects of genetic [transposon, genetic incompatibility, and homoeologous exchange (HE)], epigenetic (DNA methylation and histone modification), and developmental and environmental factors on this evolutionary process. We then move to Brassica rapa, a typical allopolyploid with subgenome dominance. Polyploidization provides the B. rapa genome not only with the genomic plasticity for adapting to changeable environments, but also an abundant genetic basis for morphological variation, making it a representative species for subgenome dominance studies. According to the 'two-step theory', B. rapa experienced genome fractionation twice during WGD, in which most of the genes responding to the environmental cues and phytohormones were over-retained, enhancing subgenome dominance and consequent adaption. More than this, the pangenome of 18 B. rapa accessions with different morphotypes recently constructed provides further evidence to reveal the impacts of polyploidization and subgenome dominance on intraspecific diversification in B. rapa. Above and beyond the fundamental understanding of WGD and subgenome dominance in B. rapa and other plants, however, it remains elusive why subgenome dominance has tissue- and spatiotemporal-specific features and could shuffle between homoeologous regions of different subgenomes by environments in allopolyploids. We lastly propose acceleration of the combined application of resynthesized allopolyploids, omics technology, and genome editing tools to deepen mechanistic investigations of subgenome dominance, both genetic and epigenetic, in a variety of species and environments. We believe that the implications of genomic and genetic basis of a variety of ecologically, evolutionarily, and agriculturally interesting traits coupled with subgenome dominance will be uncovered and aid in making new discoveries and crop breeding.

Gene cluster from plant to microbes: Their role in genome architecture, organism's development, specialized metabolism and drug discovery

Plants and microbes fulfil our daily requirements through different high-value chemicals, e.g., nutraceuticals, pharmaceuticals, cosmetics, and through varieties of fruits, crops, vegetables, and many more. Utmost care would therefore be taken for growth, development and sustainability of these important crops and medicinal plants and microbes. Homeobox genes and HOX clusters and their recently characterized expanded family members, including newly discovered homeobox, WOX gene from medicinal herb, Panax ginseng, significantly contributes in the growth and development of these organisms. On the other hand, secondary metabolites produced through secondary metabolism of plants and microbes are used as organisms defense as well as drugs/drug-like molecules for humans. Both the developmental HOX cluster and the biosynthetic gene-cluster (BGC) for secondary metabolites are organised in organisms genome. Genome mining and genomewide analysis of these clusters will definitely identify and characterize many more important molecules from unexplored plants and microbes and underexplored human microbiota and the evolution studies of these clusters will indicate their source of origin. Although genomics revolution now continues at a pace, till date only few hundred plant genome sequences are available. However, next-generation sequencing (NGS) technology now in market and may be applied even for plants with recalcitrant genomes, eventually may discover genomic potential towards production of secondary metabolites of diverse plants and micro-organisms present in the environment and microbiota. Additionally, the development of tools for genome mining e.g., antiSMASH, plantiSMASH, and more and more computational approaches that predicts hundreds of secondary metabolite BGCs will be discussed.

Chromosome Number, Ploidy Level, and Nuclear DNA Content in 23 Species of Echeveria (Crassulaceae)

Echeveria is a polyploid genus with a wide diversity of species and morphologies. The number of species registered for Echeveria is approximately 170; many of them are native to Mexico. This genus is of special interest in cytogenetic research because it has a variety of chromosome numbers and ploidy levels. Additionally, there are no studies concerning nuclear DNA content and the extent of endopolyploidy. This work aims to investigate the cytogenetic characteristics of 23 species of Echeveria collected in 9 states of Mexico, analyzing 2n chromosome numbers, ploidy level, nuclear DNA content, and endopolyploidy levels. Chromosome numbers were obtained from root tips. DNA content was obtained from the leaf parenchyma, which was processed according to the two-step protocol with Otto solutions and propidium iodide as fluorochrome, and then analyzed by flow cytometry. From the 23 species of Echeveria analyzed, 16 species lacked previous reports of 2n chromosome numbers. The 2n chromosome numbers found and analyzed in this research for Echeveria species ranged from 24 to 270. The range of 2C nuclear DNA amounts ranged from 1.26 pg in E. catorce to 7.70 pg in E. roseiflora, while the 1C values were 616 Mbp and 753 Mbp, respectively, for the same species. However, differences in the level of endopolyploidy nuclei were found, corresponding to 4 endocycles (8C, 16C, 32C and 64C) in E. olivacea, E. catorce, E. juarezensis and E. perezcalixii. In contrast, E. longiflora presented 3 endocycles (8C, 16C and 32C) and E. roseiflora presented 2 endocycles (8C and 16C). It has been suggested that polyploidization and diploidization processes, together with the presence of endopolyploidy, allowed Echeveria species to adapt and colonize new adverse environments.

A Historical Perspective of Bladderworts (Utricularia): Traps, Carnivory and Body Architecture

The genus Utricularia includes around 250 species of carnivorous plants, commonly known as bladderworts. The generic name Utricularia was coined by Carolus Linnaeus in reference to the carnivorous organs (Utriculus in Latin) present in all species of the genus. Since the formal proposition by Linnaeus, many species of Utricularia were described, but only scarce information about the biology for most species is known. All Utricularia species are herbs with vegetative organs that do not follow traditional models of morphological classification. Since the formal description of Utricularia in the 18th century, the trap function has intrigued naturalists. Historically, the traps were regarded as floating organs, a common hypothesis that was maintained by different botanists. However, Charles Darwin was most likely the first naturalist to refute this idea, since even with the removal of all traps, the plants continued to float. More recently, due mainly to methodological advances, detailed studies on the trap function and mechanisms could be investigated. This review shows a historical perspective on Utricularia studies which focuses on the traps and body organization.

Recent ecophysiological, biochemical and evolutional insights into plant carnivory

BACKGROUND

Carnivorous plants are an ecological group of approx. 810 vascular species which capture and digest animal prey, absorb prey-derived nutrients and utilize them to enhance their growth and development. Extant carnivorous plants have evolved in at least ten independent lineages, and their adaptive traits represent an example of structural and functional convergence. Plant carnivory is a result of complex adaptations to mostly nutrient-poor, wet and sunny habitats when the benefits of carnivory exceed the costs. With a boost in interest and extensive research in recent years, many aspects of these adaptations have been clarified (at least partly), but many remain unknown.

SCOPE

We provide some of the most recent insights into substantial ecophysiological, biochemical and evolutional particulars of plant carnivory from the functional viewpoint. We focus on those processes and traits in carnivorous plants associated with their ecological characterization, mineral nutrition, cost-benefit relationships, functioning of digestive enzymes and regulation of the hunting cycle in traps. We elucidate mechanisms by which uptake of prey-derived nutrients leads to stimulation of photosynthesis and root nutrient uptake.

CONCLUSIONS

Utilization of prey-derived mineral (mainly N and P) and organic nutrients is highly beneficial for plants and increases the photosynthetic rate in leaves as a prerequisite for faster plant growth. Whole-genome and tandem gene duplications brought gene material for diversification into carnivorous functions and enabled recruitment of defence-related genes. Possible mechanisms for the evolution of digestive enzymes are summarized, and a comprehensive picture on the biochemistry and regulation of prey decomposition and prey-derived nutrient uptake is provided.

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.

Is the evolution of carnivory connected with genome size reduction?

PREMISE

As repeatedly shown, the remarkable variation in the genome size of angiosperms can be shaped by extrinsic selective pressures, including nutrient availability. Carnivory has evolved independently in 10 angiosperm clades, but all carnivorous plants share a common affinity to nutrient-poor habitats. As such, carnivory and genome reduction could be responses to the same environmental pressure. Indeed, the smallest genomes among flowering plants are found in the carnivorous family Lentibulariaceae, where a unique mutation in cytochrome c oxidase (COX) is suspected to promote genome miniaturization. Despite these hypotheses, a phylogenetically informed test of genome size and nutrient availability across carnivorous clades has so far been missing.

METHODS

Using linear mixed models, we compared genome sizes of 127 carnivorous plants from 7 diverse angiosperm clades with 1072 of their noncarnivorous relatives. We also tested whether genome size in Lentibulariaceae reflects the presence of the COX mutation.

RESULTS

The genome sizes of carnivorous plants do not differ significantly from those of their noncarnivorous relatives. Based on available data, no significant association between the COX mutation and genome miniaturization could be confirmed, not even when considering polyploidy.

CONCLUSIONS

Carnivory alone does not seem to significantly affect genome size decrease. Plausibly, it might actually counterbalance the effect of nutrient limitation on genome size evolution. The role of the COX mutation in genome miniaturization needs to be evaluated by analysis of a broader data set because current knowledge of its presence across Lentibulariaceae covers less than 10% of the species diversity in this family.

Cross-Species Annotation of Expressed Genes and Detection of Different Functional Gene Modules Between 10 Cold- and 10 Hot-Propertied Chinese Herbal Medicines

According to the traditional Chinese medicine (TCM) system, Chinese herbal medicines (HMs) can be divided into four categories: hot, warm, cold, and cool. A cool nature usually is categorized as a cold nature, and a warm nature is classified as a hot nature. However, the detectable characteristics of the gene expression profile associated with the cold and hot properties have not been studied. To address this question, a strategy for the cross-species annotation of conserved genes was established in the present study by using transcriptome data of 20 HMs with cold and hot properties. Functional enrichment analysis was performed on group-specific expressed genes inferred from the functional genome of the reference species (i.e., Arabidopsis). Results showed that metabolic pathways relevant to chrysoeriol, luteolin, paniculatin, and wogonin were enriched for cold-specific genes, and pathways of inositol, heptadecane, lauric acid, octanoic acid, hexadecanoic acid, and pentadecanoic acid were enriched for hot-specific genes. Six functional modules were identified in the HMs with the cold property: nucleotide biosynthetic process, peptidy-L-cysteine S-palmitoylation, lipid modification, base-excision repair, dipeptide transport, and response to endoplasmic reticulum stress. For the hot HMs, another six functional modules were identified: embryonic meristem development, embryonic pattern specification, axis specification, regulation of RNA polymerase II transcriptional preinitiation complex assembly, mitochondrial RNA modification, and cell redox homeostasis. The research provided a new insight into HMs’ cold and hot properties from the perspective of the gene expression profile of plants.

Intense proliferation of rDNA sites and heterochromatic bands in two distantly related Cuscuta species (Convolvulaceae) with very large genomes and symmetric karyotypes

The genome size varies widely among angiosperms but only a few clades present huge variation at a low phylogenetic level. Among diploid species of the genus Cuscuta the genome size increased enormously in at least two independent lineages: in species of subgenus Monogynella and in at least one species (C. indecora) of the subgenus Grammica. Curiously, the independent events lead to similar karyotypes, with 2n = 30 mostly metacentric chromosomes. In this paper we compared the patterns of heterochromatic bands and rDNA sites of C. indecora and C. monogyna, aiming to evaluate the role of these repetitive fractions in these karyotypes. We found out that the large genomes of these species were incremented by a huge number of small heterochromatic CMA+ and DAPI+ bands and 5S and 35 rDNA sites, most of them clearly colocalized with CMA+ bands. Silver nitrate impregnation revealed that the maximum number of nucleoli per nucleus was low in both species, suggesting that some of these sites may be inactive. Noteworthy, the tandem repeats did not generate large bands or sites but rather dozens of small blocks dispersed throughout the chromosomes, apparently contributing to conserve the original karyotype symmetry.

Agrobacterium tumefaciens mediated transformation of the aquatic carnivorous plant Utricularia gibba

BACKGROUND

The genus Utricularia belongs to Lentibulariaceae, the largest family of carnivorous plants, which includes terrestrial, epiphytic and aquatic species. The development of specialized structures that evolved for carnivory is a feature of this genus that has been of great interest to biologists since Darwin's early studies. Utricularia gibba is itself an aquatic plant with sophisticated bladder traps having one of the most complex suction mechanisms for trapping prey. However, the molecular characterization of the mechanisms that regulate trap development and the biophysical processes involved in prey trapping are still largely unknown due to the lack of a simple and reproducible gene transfer system.

RESULTS

Here, we report the establishment of a simple, fast and reproducible protocol for genetic transformation of U. gibba based on the T-DNA of Agrobacterium tumefaciens. An in vitro selection system using Phosphinotricin as a selective agent was established for U. gibba. Plant transformation was confirmed by histochemical GUS assays and PCR and qRT-PCR analyses. We report on the expression pattern of the 35S promoter and of the promoter of a trap-specific ribonuclease gene in transgenic U. gibba plants.

CONCLUSIONS

The genetic transformation protocol reported here is an effective method for studying developmental biology and functional genomics of this genus of carnivorous plants and advances the utility of U. gibba as a model system to study developmental processes involved in trap formation.

Charting the path to fully synthetic plant chromosomes

The concepts of synthetic biology have the potential to transform plant genetics, both in how we analyze genetic pathways and how we transfer that knowledge into useful applications. While synthetic biology can be applied at the level of the single gene or small groups of genes, this commentary focuses on the ultimate challenge of designing fully synthetic plant chromosomes. Engineering at this scale will allow us to manipulate whole genome architecture and to modify multiple pathways and traits simultaneously. Advances in genome synthesis make it likely that the initial phases of plant chromosome construction will occur in bacteria and yeast. Here I discuss the next steps, including specific ways of overcoming technical barriers associated with plant transformation, functional centromere design, and ensuring accurate meiotic transmission.

The Terrestrial Carnivorous Plant Utricularia reniformis Sheds Light on Environmental and Life-Form Genome Plasticity

Utricularia belongs to Lentibulariaceae, a widespread family of carnivorous plants that possess ultra-small and highly dynamic nuclear genomes. It has been shown that the Lentibulariaceae genomes have been shaped by transposable elements expansion and loss, and multiple rounds of whole-genome duplications (WGD), making the family a platform for evolutionary and comparative genomics studies. To explore the evolution of Utricularia, we estimated the chromosome number and genome size, as well as sequenced the terrestrial bladderwort Utricularia reniformis (2n = 40, 1C = 317.1-Mpb). Here, we report a high quality 304 Mb draft genome, with a scaffold NG50 of 466-Kb, a BUSCO completeness of 87.8%, and 42,582 predicted genes. Compared to the smaller and aquatic U. gibba genome (101 Mb) that has a 32% repetitive sequence, the U. reniformis genome is highly repetitive (56%). The structural differences between the two genomes are the result of distinct fractionation and rearrangements after WGD, and massive proliferation of LTR-retrotransposons. Moreover, GO enrichment analyses suggest an ongoing gene birth-death-innovation process occurring among the tandem duplicated genes, shaping the evolution of carnivory-associated functions. We also identified unique patterns of developmentally related genes that support the terrestrial life-form and body plan of U. reniformis. Collectively, our results provided additional insights into the evolution of the plastic and specialized Lentibulariaceae genomes.

The C-Fern (Ceratopteris richardii) genome: insights into plant genome evolution with the first partial homosporous fern genome assembly

Ferns are notorious for possessing large genomes and numerous chromosomes. Despite decades of speculation, the processes underlying the expansive genomes of ferns are unclear, largely due to the absence of a sequenced homosporous fern genome. The lack of this crucial resource has not only hindered investigations of evolutionary processes responsible for the unusual genome characteristics of homosporous ferns, but also impeded synthesis of genome evolution across land plants. Here, we used the model fern species Ceratopteris richardii to address the processes (e.g., polyploidy, spread of repeat elements) by which the large genomes and high chromosome numbers typical of homosporous ferns may have evolved and have been maintained. We directly compared repeat compositions in species spanning the green plant tree of life and a diversity of genome sizes, as well as both short- and long-read-based assemblies of Ceratopteris. We found evidence consistent with a single ancient polyploidy event in the evolutionary history of Ceratopteris based on both genomic and cytogenetic data, and on repeat proportions similar to those found in large flowering plant genomes. This study provides a major stepping-stone in the understanding of land plant evolutionary genomics by providing the first homosporous fern reference genome, as well as insights into the processes underlying the formation of these massive genomes.

Shaping of a three-dimensional carnivorous trap through modulation of a planar growth mechanism

Leaves display a remarkable range of forms, from flat sheets with simple outlines to cup-shaped traps. Although much progress has been made in understanding the mechanisms of planar leaf development, it is unclear whether similar or distinctive mechanisms underlie shape transformations during development of more complex curved forms. Here, we use 3D imaging and cellular and clonal analysis, combined with computational modelling, to analyse the development of cup-shaped traps of the carnivorous plant Utricularia gibba. We show that the transformation from a near-spherical form at early developmental stages to an oblate spheroid with a straightened ventral midline in the mature form can be accounted for by spatial variations in rates and orientations of growth. Different hypotheses regarding spatiotemporal control predict distinct patterns of cell shape and size, which were tested experimentally by quantifying cellular and clonal anisotropy. We propose that orientations of growth are specified by a proximodistal polarity field, similar to that hypothesised to account for Arabidopsis leaf development, except that in Utricularia, the field propagates through a highly curved tissue sheet. Independent evidence for the polarity field is provided by the orientation of glandular hairs on the inner surface of the trap. Taken together, our results show that morphogenesis of complex 3D leaf shapes can be accounted for by similar mechanisms to those for planar leaves, suggesting that simple modulations of a common growth framework underlie the shaping of a diverse range of morphologies.

Many plant and animal organs derive from tissue sheets, but how are they shaped to create the diversity of forms observed in nature? This study uses a combination of imaging and mathematical modelling to show how carnivorous plant traps shape themselves in 3D by a growth framework oriented by tissue polarity, similar to that found in planar leaves.

The large genome size variation in the Hesperis clade was shaped by the prevalent proliferation of DNA repeats and rarer genome downsizing

BACKGROUND AND AIMS

Most crucifer species (Brassicaceae) have small nuclear genomes (mean 1C-value 617 Mb). The species with the largest genomes occur within the monophyletic Hesperis clade (Mandáková et al., Plant Physiology174: 2062-2071; also known as Clade E or Lineage III). Whereas most chromosome numbers in the clade are 6 or 7, monoploid genome sizes vary 16-fold (256-4264 Mb). To get an insight into genome size evolution in the Hesperis clade (~350 species in ~48 genera), we aimed to identify, quantify and localize in situ the repeats from which these genomes are built. We analysed nuclear repeatomes in seven species, covering the phylogenetic and genome size breadth of the clade, by low-pass whole-genome sequencing.

METHODS

Genome size was estimated by flow cytometry. Genomic DNA was sequenced on an Illumina sequencer and DNA repeats were identified and quantified using RepeatExplorer; the most abundant repeats were localized on chromosomes by fluorescence in situ hybridization. To evaluate the feasibility of bacterial artificial chromosome (BAC)-based comparative chromosome painting in Hesperis-clade species, BACs of arabidopsis were used as painting probes.

KEY RESULTS

Most biennial and perennial species of the Hesperis clade possess unusually large nuclear genomes due to the proliferation of long terminal repeat retrotransposons. The prevalent genome expansion was rarely, but repeatedly, counteracted by purging of transposable elements in ephemeral and annual species.

CONCLUSIONS

The most common ancestor of the Hesperis clade has experienced genome upsizing due to transposable element amplification. Further genome size increases, dominating diversification of all Hesperis-clade tribes, contrast with the overall stability of chromosome numbers. In some subclades and species genome downsizing occurred, presumably as an adaptive transition to an annual life cycle. The amplification versus purging of transposable elements and tandem repeats impacted the chromosomal architecture of the Hesperis-clade species.

Genotyping-by-sequencing through transcriptomics: implementation in a range of crop species with varying reproductive habits and ploidy levels

The application of genomics in crops has the ability to significantly improve genetic gain for agriculture. Many marker-dense tools have been developed, but few have seen broad adoption in plant genomics due to issues of significant variations of genome size, levels of ploidy, single nucleotide polymorphism (SNP) frequency and reproductive habit. When combined with limited breeding activities, small research communities and scant sequence resources, the suitability of popular systems is often suboptimal and routinely fails to effectively balance cost-effectiveness and sample throughput. Genotyping-by-sequencing (GBS) encompasses a range of protocols including resequencing of the transcriptome. This study describes a skim GBS-transcriptomics (GBS-t) approach developed to be broadly applicable, cost-effective and high-throughput while still assaying a significant number of SNP loci. A range of crop species with differing levels of ploidy and degree of inbreeding/outbreeding were chosen, including perennial ryegrass, a diploid outbreeding forage grass; phalaris, a putative segmental allotetraploid outbreeding forage grass; lentil, a diploid inbreeding grain legume; and canola, an allotetraploid partially outbreeding oilseed. GBS-t was validated as a simple and largely automated, cost-effective method which generates sufficient SNPs (from 89 738 to 231 977) with acceptable levels of missing data and even genome coverage from c. 3 million sequence reads per sample. GBS-t is therefore a broadly applicable system suitable for many crops, offering advantages over other systems. The correct choice of subsequent sequence analysis software is important, and the bioinformatics process should be iterative and tailored to the specific challenges posed by ploidy variation and extent of heterozygosity.

A guide to sequence your favorite plant genomes

With the rapid development of sequencing technology and the plummeting cost, assembling whole genomes from non-model plants will soon become routine for plant systematists and evolutionary biologists. Here we summarize and compare several of the latest genome sequencing and assembly approaches, offering a practical guide on how to approach a genome project. We also highlight certain precautions that need to be taken before investing time and money into a genome project.

Comparative genomic analysis of Genlisea (corkscrew plants-Lentibulariaceae) chloroplast genomes reveals an increasing loss of the ndh genes

In the carnivorous plant family Lentibulariaceae, all three genome compartments (nuclear, chloroplast, and mitochondria) have some of the highest rates of nucleotide substitutions across angiosperms. While the genera Genlisea and Utricularia have the smallest known flowering plant nuclear genomes, the chloroplast genomes (cpDNA) are mostly structurally conserved except for deletion and/or pseudogenization of the NAD(P)H-dehydrogenase complex (ndh) genes known to be involved in stress conditions of low light or CO2 concentrations. In order to determine how the cpDNA are changing, and to better understand the evolutionary history within the Genlisea genus, we sequenced, assembled and analyzed complete cpDNA from six species (G. aurea, G. filiformis, G. pygmaea, G. repens, G. tuberosa and G. violacea) together with the publicly available G. margaretae cpDNA. In general, the cpDNA structure among the analyzed Genlisea species is highly similar. However, we found that the plastidial ndh genes underwent a progressive process of degradation similar to the other terrestrial Lentibulariaceae cpDNA analyzed to date, but in contrast to the aquatic species. Contrary to current thinking that the terrestrial environment is a more stressful environment and thus requiring the ndh genes, we provide evidence that in the Lentibulariaceae the terrestrial forms have progressive loss while the aquatic forms have the eleven plastidial ndh genes intact. Therefore, the Lentibulariaceae system provides an important opportunity to understand the evolutionary forces that govern the transition to an aquatic environment and may provide insight into how plants manage water stress at a genome scale.

Development of microsatellite markers for the carnivorous plant Genlisea aurea (Lentibulariaceae) using genomics data of NGS

Genlisea aurea A.St.-Hil. is a carnivorous plant endemic species to Brazil in the Lentibulariaceae family. Very few studies have addressed the genetic structure and conservation status of G. aurea and the Lentibulariaceae. Microsatellites markers are advantageous tools that can be employed to predict the vulnerability of Lentibulariaceae species. Therefore, the development of molecular markers focusing the population analyses of Genlisea for future genetic studies and conservation actions are essential. Thus, we developed simple sequence repeats (SSRs) based on in silico analyses of G. aurea draft genome assembly. We characterized 40 individuals from several populations and identified 12 loci that were polymorphic, with heterozygosity between 0.123 and 0.650. We demonstrated that the G. aurea SSR markers work cross-species in Genlisea filiformis, G. repens, G. tuberosa and G. violacea. These markers will be important for future population, phylogeographic and conservation studies in G. aurea and other Genlisea species.

Trap diversity and character evolution in carnivorous bladderworts (Utricularia, Lentibulariaceae)

Bladderworts (Utricularia, Lentibulariaceae, Lamiales) constitute the largest genus of carnivorous plants but only aquatic species (about one fifth of the genus) have so far been thoroughly studied as to their suction trap functioning. In this study, we comparatively investigated trap biomechanics in 19 Utricularia species to examine correlations between life-forms, trapping mechanisms, and functional-morphological traits. Our investigations show the existence of two functional trap principles (passive trap in U. multifida vs. active suction traps), and - in active suction traps - three main trapdoor movement types (with several subtypes). The trapdoor movement types and their corresponding functional-morphological features most presumably represent adaptations to the respective habitat. We furthermore give insights into fluid dynamics during suction in three representatives of the main types of trapdoor movement. The results on functional morphology and trapdoor movement were mapped onto a new phylogenetic reconstruction of the genus, derived from the rapidly evolving chloroplast regions trnK, rps16 and trnQ-rps16 and a sampling of 105 Utricularia species in total. We discuss potential scenarios of trap character evolution and species radiation, highlighting possible key innovations that enable such a unique carnivorous lifestyle in different habitats.

Deletion-bias in DNA double-strand break repair differentially contributes to plant genome shrinkage

In order to prevent genome instability, cells need to be protected by a number of repair mechanisms, including DNA double-strand break (DSB) repair. The extent to which DSB repair, biased towards deletions or insertions, contributes to evolutionary diversification of genome size is still under debate. We analyzed mutation spectra in Arabidopsis thaliana and in barley (Hordeum vulgare) by PacBio sequencing of three DSB-targeted loci each, uncovering repair via gene conversion, single strand annealing (SSA) or nonhomologous end-joining (NHEJ). Furthermore, phylogenomic comparisons between A. thaliana and two related species were used to detect naturally occurring deletions during Arabidopsis evolution. Arabidopsis thaliana revealed significantly more and larger deletions after DSB repair than barley, and barley displayed more and larger insertions. Arabidopsis displayed a clear net loss of DNA after DSB repair, mainly via SSA and NHEJ. Barley revealed a very weak net loss of DNA, apparently due to less active break-end resection and easier copying of template sequences into breaks. Comparative phylogenomics revealed several footprints of SSA in the A. thaliana genome. Quantitative assessment of DNA gain and loss through DSB repair processes suggests deletion-biased DSB repair causing ongoing genome shrinking in A. thaliana, whereas genome size in barley remains nearly constant.

Genome size, cytogenetic data and transferability of EST-SSRs markers in wild and cultivated species of the genus Theobroma L. (Byttnerioideae, Malvaceae)

The genus Theobroma comprises several trees species native to the Amazon. Theobroma cacao L. plays a key economic role mainly in the chocolate industry. Both cultivated and wild forms are described within the genus. Variations in genome size and chromosome number have been used for prediction purposes including the frequency of interspecific hybridization or inference about evolutionary relationships. In this study, the nuclear DNA content, karyotype and genetic diversity using functional microsatellites (EST-SSR) of seven Theobroma species were characterized. The nuclear content of DNA for all analyzed Theobroma species was 1C = ~ 0.46 pg. These species presented 2n = 20 with small chromosomes and only one pair of terminal heterochromatic bands positively stained (CMA⁺/DAPI⁻ bands). The small size of Theobroma ssp. genomes was equivalent to other Byttnerioideae species, suggesting that the basal lineage of Malvaceae have smaller genomes and that there was an expansion of 2C values in the more specialized family clades. A set of 20 EST-SSR primers were characterized for related species of Theobroma, in which 12 loci were polymorphic. The polymorphism information content (PIC) ranged from 0.23 to 0.65, indicating a high level of information per locus. Combined results of flow cytometry, cytogenetic data and EST-SSRs markers will contribute to better describe the species and infer about the evolutionary relationships among Theobroma species. In addition, the importance of a core collection for conservation purposes is highlighted.

Evolution of genome size and genomic GC content in carnivorous holokinetics (Droseraceae)

BACKGROUND AND AIMS

Studies in the carnivorous family Lentibulariaceae in the last years resulted in the discovery of the smallest plant genomes and an unusual pattern of genomic GC content evolution. However, scarcity of genomic data in other carnivorous clades still prevents a generalization of the observed patterns. Here the aim was to fill this gap by mapping genome evolution in the second largest carnivorous family, Droseraceae, where this evolution may be affected by chromosomal holokinetism in Drosera METHODS: The genome size and genomic GC content of 71 Droseraceae species were measured by flow cytometry. A dated phylogeny was constructed, and the evolution of both genomic parameters and their relationship to species climatic niches were tested using phylogeny-based statistics.

KEY RESULTS

The 2C genome size of Droseraceae varied between 488 and 10 927 Mbp, and the GC content ranged between 37·1 and 44·7 %. The genome sizes and genomic GC content of carnivorous and holocentric species did not differ from those of their non-carnivorous and monocentric relatives. The genomic GC content positively correlated with genome size and annual temperature fluctuations. The genome size and chromosome numbers were inversely correlated in the Australian clade of Drosera CONCLUSIONS: Our results indicate that neither carnivory (nutrient scarcity) nor the holokinetism have a prominent effect on size and DNA base composition of Droseraceae genomes. However, the holokinetic drive seems to affect karyotype evolution in one of the major clades of Drosera Our survey confirmed that the evolution of GC content is tightly connected with the evolution of genome size and also with environmental conditions.

The Evolution of Haploid Chromosome Numbers in the Sunflower Family

Chromosome number changes during the evolution of angiosperms are likely to have played a major role in speciation. Their study is of utmost importance, especially now, as a probabilistic model is available to study chromosome evolution within a phylogenetic framework. In the present study, likelihood models of chromosome number evolution were fitted to the largest family of flowering plants, the Asteraceae. Specifically, a phylogenetic supertree of this family was used to reconstruct the ancestral chromosome number and infer genomic events. Our approach inferred that the ancestral chromosome number of the family is n = 9. Also, according to the model that best explained our data, the evolution of haploid chromosome numbers in Asteraceae was a very dynamic process, with genome duplications and descending dysploidy being the most frequent genomic events in the evolution of this family. This model inferred more than one hundred whole genome duplication events; however, it did not find evidence for a paleopolyploidization at the base of this family, which has previously been hypothesized on the basis of sequence data from a limited number of species. The obtained results and potential causes of these discrepancies are discussed.

From Mendel's discovery on pea to today's plant genetics and breeding : Commemorating the 150th anniversary of the reading of Mendel's discovery

KEY MESSAGE

This work discusses several selected topics of plant genetics and breeding in relation to the 150th anniversary of the seminal work of Gregor Johann Mendel. In 2015, we celebrated the 150th anniversary of the presentation of the seminal work of Gregor Johann Mendel. While Darwin's theory of evolution was based on differential survival and differential reproductive success, Mendel's theory of heredity relies on equality and stability throughout all stages of the life cycle. Darwin's concepts were continuous variation and "soft" heredity; Mendel espoused discontinuous variation and "hard" heredity. Thus, the combination of Mendelian genetics with Darwin's theory of natural selection was the process that resulted in the modern synthesis of evolutionary biology. Although biology, genetics, and genomics have been revolutionized in recent years, modern genetics will forever rely on simple principles founded on pea breeding using seven single gene characters. Purposeful use of mutants to study gene function is one of the essential tools of modern genetics. Today, over 100 plant species genomes have been sequenced. Mapping populations and their use in segregation of molecular markers and marker-trait association to map and isolate genes, were developed on the basis of Mendel's work. Genome-wide or genomic selection is a recent approach for the development of improved breeding lines. The analysis of complex traits has been enhanced by high-throughput phenotyping and developments in statistical and modeling methods for the analysis of phenotypic data. Introgression of novel alleles from landraces and wild relatives widens genetic diversity and improves traits; transgenic methodologies allow for the introduction of novel genes from diverse sources, and gene editing approaches offer possibilities to manipulate gene in a precise manner.

The Chloroplast Genome of Utricularia reniformis Sheds Light on the Evolution of the ndh Gene Complex of Terrestrial Carnivorous Plants from the Lentibulariaceae Family

Lentibulariaceae is the richest family of carnivorous plants spanning three genera including Pinguicula, Genlisea, and Utricularia. Utricularia is globally distributed, and, unlike Pinguicula and Genlisea, has both aquatic and terrestrial forms. In this study we present the analysis of the chloroplast (cp) genome of the terrestrial Utricularia reniformis. U. reniformis has a standard cp genome of 139,725bp, encoding a gene repertoire similar to essentially all photosynthetic organisms. However, an exclusive combination of losses and pseudogenization of the plastid NAD(P)H-dehydrogenase (ndh) gene complex were observed. Comparisons among aquatic and terrestrial forms of Pinguicula, Genlisea, and Utricularia indicate that, whereas the aquatic forms retained functional copies of the eleven ndh genes, these have been lost or truncated in terrestrial forms, suggesting that the ndh function may be dispensable in terrestrial Lentibulariaceae. Phylogenetic scenarios of the ndh gene loss and recovery among Pinguicula, Genlisea, and Utricularia to the ancestral Lentibulariaceae cladeare proposed. Interestingly, RNAseq analysis evidenced that U. reniformis cp genes are transcribed, including the truncated ndh genes, suggesting that these are not completely inactivated. In addition, potential novel RNA-editing sites were identified in at least six U. reniformis cp genes, while none were identified in the truncated ndh genes. Moreover, phylogenomic analyses support that Lentibulariaceae is monophyletic, belonging to the higher core Lamiales clade, corroborating the hypothesis that the first Utricularia lineage emerged in terrestrial habitats and then evolved to epiphytic and aquatic forms. Furthermore, several truncated cp genes were found interspersed with U. reniformis mitochondrial and nuclear genome scaffolds, indicating that as observed in other smaller plant genomes, such as Arabidopsis thaliana, and the related and carnivorous Genlisea nigrocaulis and G. hispidula, the endosymbiotic gene transfer may also shape the U. reniformis genome in a similar fashion. Overall the comparative analysis of the U. reniformis cp genome provides new insight into the ndh genes and cp genome evolution of carnivorous plants from Lentibulariaceae family.

Chromosomal distribution and evolution of abundant retrotransposons in plants: gypsy elements in diploid and polyploid Brachiaria forage grasses

Like other eukaryotes, the nuclear genome of plants consists of DNA with a small proportion of low-copy DNA (genes and regulatory sequences) and very abundant DNA sequence motifs that are repeated thousands up to millions of times in the genomes including transposable elements (TEs) and satellite DNA. Retrotransposons, one class of TEs, are sequences that amplify via an RNA intermediate and reinsert into the genome, are often the major fraction of a genome. Here, we put research on retrotransposons into the larger context of plant repetitive DNA and genome behaviour, showing features of genome evolution in a grass genus, Brachiaria, in relation to other plant species. We show the contrasting amplification of different retroelement fractions across the genome with characteristics for various families and domains. The genus Brachiaria includes both diploid and polyploid species, with similar chromosome types and chromosome basic numbers x = 6, 7, 8 and 9. The polyploids reproduce asexually and are apomictic, but there are also sexual species. Cytogenetic studies and flow cytometry indicate a large variation in DNA content (C-value), chromosome sizes and genome organization. In order to evaluate the role of transposable elements in the genome and karyotype organization of species of Brachiaria, we searched for sequences similar to conserved regions of TEs in RNAseq reads library produced in Brachiaria decumbens. Of the 9649 TE-like contigs, 4454 corresponded to LTR-retrotransposons, and of these, 79.5 % were similar to members of the gypsy superfamily. Sequences of conserved protein domains of gypsy were used to design primers for producing the probes. The probes were used in FISH against chromosomes of accesses of B. decumbens, Brachiaria brizantha, Brachiaria ruziziensis and Brachiaria humidicola. Probes showed hybridization signals predominantly in proximal regions, especially those for retrotransposons of the clades CRM and Athila, while elements of Del and Tat exhibited dispersed signals, in addition to those proximal signals. These results show that the proximal region of Brachiaria chromosomes is a hotspot for retrotransposon insertion, particularly for the gypsy family. The combination of high-throughput sequencing and a chromosome-centric cytogenetic approach allows the abundance, organization and nature of transposable elements to be characterized in unprecedented detail. By their amplification and dispersal, retrotransposons can affect gene expression; they can lead to rapid diversification of chromosomes between species and, hence, are useful for studies of genome evolution and speciation in the Brachiaria genus. Centromeric regions can be identified and mapped, and retrotransposon markers can also assisting breeders in the developing and exploiting interspecific hybrids.

Genome Stability and Evolution: Attempting a Holistic View

The reason why the DNA content, chromosome number and shape, and gene content of eukaryotic genomes vary independently remains a matter of speculation. The same is true for the questions of whether there is a general tendency for increase or decrease of genome size and chromosome number and whether genome size and/or chromosome number have an adaptive value and, if so, what this value is. Here we assume that three strategies of genome evolution (shrinkage, expansion, and equilibrium) have developed to find the optimal balance between genomic stability and plasticity. We suggest various modes of DNA double-strand break (DSB) repair in combination with whole-genome duplication (WGD) and dysploid chromosome number alteration to explain the different strategies of genome size and karyotype evolution.

Chromosome identification for the carnivorous plant Genlisea margaretae

Genlisea margaretae, subgenus Genlisea, section Recurvatae (184 Mbp/1C), belongs to a plant genus with a 25-fold genome size difference and an extreme genome plasticity. Its 19 chromosome pairs could be distinguished individually by an approach combining optimized probe pooling and consecutive rounds of multicolor fluorescence in situ hybridization (mcFISH) with bacterial artificial chromosomes (BACs) selected for repeat-free inserts. Fifty-one BACs were assigned to 18 chromosome pairs. They provide a tool for future assignment of genomic sequence contigs to distinct chromosomes as well as for identification of homeologous chromosome regions in other species of the carnivorous Lentibulariaceae family, and potentially of chromosome rearrangements, in cases where more than one BAC per chromosome pair was identified.

Ploidy Level and DNA Content of Erianthus arundinaceus as Determined by Flow Cytometry and the Association with Biological Characteristics

Erianthus arundinaceus is not only an important germplasm resource for sugarcane breeding but also a potential bioenergy plant. Making clear the distribution of the chromosome ploidy of wild E. arundinaceus in china is the premise of the research and utilization of this species. Therefore, the objectives of this study were to determine the ploidy level and DNA content of the 55 E. arundinaceus accessions using flow cytometry and to identify the correlation between ploidy and phenotypic traits. Among the 55 accessions, four tetraploids and 51 hexaploids were identified. The four tetraploids originated from Mengma Yunnan, Shuangjiang Yunnan, Gaozhou Guangdong and Chengle Sichuan. The mean DNA content was 4.82 pg/2C for the tetraploid and 7.30 pg/2C for the hexaploid plants. The ploidy was negatively correlated with cellulose content and positively correlated (P<0.05) with plant height, stem diameter, leaf width, dry weight per plant, fresh weight per plant and hemicellulose content. However, ploidy was not correlated with leaf length, tiller number and the ratio of dry weight and fresh weight. This study will be useful for revealing the distribution of the ploidy of wild E. arundinaceus in Chin, traits markers analysis, and utilization of this species, such as cultivar improvement and sugarcane breeding in the future.

Identification and characterization of abundant repetitive sequences in Eragrostis tef cv. Enatite genome

BACKGROUND

Eragrostis tef is an allotetraploid (2n = 4 × = 40) annual, C4 grass with an estimated nuclear genome size of 730 Mbp. It is widely grown in Ethiopia, where it provides basic nutrition for more than half of the population. Although a draft assembly of the E. tef genome was made available in 2014, characterization of the repetitive portion of the E. tef genome has not been a subject of a detailed analysis. Repetitive sequences constitute most of the DNA in eukaryotic genomes. Transposable elements are usually the most abundant repetitive component in plant genomes. They contribute to genome size variation, cause mutations, can result in chromosomal rearrangements, and influence gene regulation. An extensive and in depth characterization of the repetitive component is essential in understanding the evolution and function of the genome.

RESULTS

Using new paired-end sequence data and a de novo repeat identification strategy, we identified the most repetitive elements in the E. tef genome. Putative repeat sequences were annotated based on similarity to known repeat groups in other grasses. Altogether we identified 1,389 medium/highly repetitive sequences that collectively represent about 27% of the teff genome. Phylogenetic analyses of the most important classes of TEs were carried out in a comparative framework including paralog elements from rice and maize. Finally, an abundant tandem repeat accounting for more than 4% of the whole genome was identified and partially characterized.

CONCLUSIONS

Analyzing a large sample of randomly sheared reads we obtained a library of the repetitive sequences of E. tef. The approach we used was designed to avoid underestimation of repeat contribution; such underestimation is characteristic of whole genome assembly projects. The data collected represent a valuable resource for further analysis of the genome of this important orphan crop.

Genome size variation in the genus Avena

Genome size is an indicator of evolutionary distance and a metric for genome characterization. Here, we report accurate estimates of genome size in 99 accessions from 26 species of Avena. We demonstrate that the average genome size of C genome diploid species (2C = 10.26 pg) is 15% larger than that of A genome species (2C = 8.95 pg), and that this difference likely accounts for a progression of size among tetraploid species, where AB < AC < CC (average 2C = 16.76, 18.60, and 21.78 pg, respectively). All accessions from three hexaploid species with the ACD genome configuration had similar genome sizes (average 2C = 25.74 pg). Genome size was mostly consistent within species and in general agreement with current information about evolutionary distance among species. Results also suggest that most of the polyploid species in Avena have experienced genome downsizing in relation to their diploid progenitors. Genome size measurements could provide additional quality control for species identification in germplasm collections, especially in cases where diploid and polyploid species have similar morphology.

Centromere and telomere sequence alterations reflect the rapid genome evolution within the carnivorous plant genus Genlisea

Linear chromosomes of eukaryotic organisms invariably possess centromeres and telomeres to ensure proper chromosome segregation during nuclear divisions and to protect the chromosome ends from deterioration and fusion, respectively. While centromeric sequences may differ between species, with arrays of tandemly repeated sequences and retrotransposons being the most abundant sequence types in plant centromeres, telomeric sequences are usually highly conserved among plants and other organisms. The genome size of the carnivorous genus Genlisea (Lentibulariaceae) is highly variable. Here we study evolutionary sequence plasticity of these chromosomal domains at an intrageneric level. We show that Genlisea nigrocaulis (1C = 86 Mbp; 2n = 40) and G. hispidula (1C = 1550 Mbp; 2n = 40) differ as to their DNA composition at centromeres and telomeres. G. nigrocaulis and its close relative G. pygmaea revealed mainly 161 bp tandem repeats, while G. hispidula and its close relative G. subglabra displayed a combination of four retroelements at centromeric positions. G. nigrocaulis and G. pygmaea chromosome ends are characterized by the Arabidopsis-type telomeric repeats (TTTAGGG); G. hispidula and G. subglabra instead revealed two intermingled sequence variants (TTCAGG and TTTCAGG). These differences in centromeric and, surprisingly, also in telomeric DNA sequences, uncovered between groups with on average a > 9-fold genome size difference, emphasize the fast genome evolution within this genus. Such intrageneric evolutionary alteration of telomeric repeats with cytosine in the guanine-rich strand, not yet known for plants, might impact the epigenetic telomere chromatin modification.

Fastest predators in the plant kingdom: functional morphology and biomechanics of suction traps found in the largest genus of carnivorous plants

Understanding the physics of plant movements, which describe the interplay between plant architecture, movement speed and actuation principles, is essential for the comprehension of important processes like plant morphogenesis. Recent investigations especially on rapid plant movements at the interface of biology, physics and engineering sciences highlight how such fast motions can be achieved without the presence of muscles, nerves and technical hinge analogies. The suction traps (bladders) of carnivorous bladderworts (Utricularia spp., Lentibulariaceae, Lamiales) are considered as some of the most elaborate moving structures in the plant kingdom. A complex interplay of morphological and physiological adaptations allows the traps to pump water out of their body and to store elastic energy in the deformed bladder walls. Mechanical stimulation by prey entails opening of the otherwise watertight trapdoor, followed by trap wall relaxation, sucking in of water and prey, and consecutive trapdoor closure. Suction can also occur spontaneously in non-stimulated traps. We review the current state of knowledge about the suction trap mechanism with a focus on architectonically homogeneous traps of aquatic bladderwort species from section Utricularia (the so-called 'Utricularia vulgaris trap type'). The functional morphology and biomechanics of the traps are described in detail. We discuss open questions and propose promising aspects for future studies on these sophisticated ultra-fast trapping devices.

Analysis of the giant genomes of Fritillaria (Liliaceae) indicates that a lack of DNA removal characterizes extreme expansions in genome size

Plants exhibit an extraordinary range of genome sizes, varying by > 2000-fold between the smallest and largest recorded values. In the absence of polyploidy, changes in the amount of repetitive DNA (transposable elements and tandem repeats) are primarily responsible for genome size differences between species. However, there is ongoing debate regarding the relative importance of amplification of repetitive DNA versus its deletion in governing genome size. Using data from 454 sequencing, we analysed the most repetitive fraction of some of the largest known genomes for diploid plant species, from members of Fritillaria. We revealed that genomic expansion has not resulted from the recent massive amplification of just a handful of repeat families, as shown in species with smaller genomes. Instead, the bulk of these immense genomes is composed of highly heterogeneous, relatively low-abundance repeat-derived DNA, supporting a scenario where amplified repeats continually accumulate due to infrequent DNA removal. Our results indicate that a lack of deletion and low turnover of repetitive DNA are major contributors to the evolution of extremely large genomes and show that their size cannot simply be accounted for by the activity of a small number of high-abundance repeat families.

How to Isolate a Plant's Hypomethylome in One Shot

Genome assembly remains a challenge for large and/or complex plant genomes due to their abundant repetitive regions resulting in studies focusing on gene space instead of the whole genome. Thus, DNA enrichment strategies facilitate the assembly by increasing the coverage and simultaneously reducing the complexity of the whole genome. In this paper we provide an easy, fast, and cost-effective variant of MRE-seq to obtain a plant's hypomethylome by an optimized methyl filtration protocol followed by next generation sequencing. The method is demonstrated on three plant species with knowingly large and/or complex (polyploid) genomes: Oryza sativa, Picea abies, and Crocus sativus. The identified hypomethylomes show clear enrichment for genes and their flanking regions and clear reduction of transposable elements. Additionally, genomic sequences around genes are captured including regulatory elements in introns and up- and downstream flanks. High similarity of the results obtained by a de novo assembly approach with a reference based mapping in rice supports the applicability for studying and understanding the genomes of nonmodel organisms. Hence we show the high potential of MRE-seq in a wide range of scenarios for the direct analysis of methylation differences, for example, between ecotypes, individuals, within or across species harbouring large, and complex genomes.

Chromatin organization and cytological features of carnivorous Genlisea species with large genome size differences

The monophyletic carnivorous genus Genlisea (Lentibulariaceae) is characterized by a bi-directional genome size evolution resulting in a 25-fold difference in nuclear DNA content. This is one of the largest ranges found within a genus so far and makes Genlisea an interesting subject to study mechanisms of genome and karyotype evolution. Genlisea nigrocaulis, with 86 Mbp one of the smallest plant genomes, and the 18-fold larger genome of G. hispidula (1,550 Mbp) possess identical chromosome numbers (2n = 40) but differ considerably in chromatin organization, nuclear and cell size. Interphase nuclei of G. nigrocaulis and of related species with small genomes, G. aurea (133 Mbp, 2n ≈ 104) and G. pygmaea (179 Mbp, 2n = 80), are hallmarked by intensely DAPI-stained chromocenters, carrying typical heterochromatin-associated methylation marks (5-methylcytosine, H3K9me2), while in G. hispidula and surprisingly also in the small genome of G. margaretae (184 Mbp, 2n = 38) the heterochromatin marks are more evenly distributed. Probes of tandem repetitive sequences together with rDNA allow the unequivocal discrimination of 13 out of 20 chromosome pairs of G. hispidula. One of the repetitive sequences labeled half of the chromosome set almost homogenously supporting an allopolyploid status of G. hispidula and its close relative G. subglabra (1,622 Mbp, 2n = 40). In G. nigrocaulis 11 chromosome pairs could be individualized using a combination of rDNA and unique genomic probes. The presented data provide a basis for future studies of karyotype evolution within the genus Genlisea.

Genome sizes of 227 accessions of Gagea (Liliaceae) discriminate between the species from the Netherlands and reveal new ploidies in Gagea

Nuclear genome size, as measured by flow cytometry with propidium iodide, was used to investigate the relationships within the genus Gagea (Liliaceae), mainly from the Netherlands. The basic chromosome number for Gagea is x = 12. The inferred ploidy in the Dutch and German accessions varies from diploid to decaploid. Consequently there is a large range of genome sizes (DNA 2C-values) from 14.9 to 75.1 pg. Genome sizes are evaluated here in combination with the results of morphological observations. Five species and the hybrid G. × megapolitana are reported. Apart from 14 diploid G. villosa, six plants of G. villosa with an inferred tetraploidy were found. For the 186 Dutch accessions investigated 85 turned out to be the largely sterile G. pratensis (inferred to be pentaploid). Inferred tetraploid and hexaploid G. pratensis were found in 30 and 20 localities, respectively. In one locality an inferred decaploid (10×) plant was found that could represent a doubled pentaploid G. pratensis. An inferred decaploid G. pratensis was never reported before. The genome size of Gagea × megapolitana from Germany fitted with its origin as a cross between the two hexaploids G. pratensis and G. lutea. Gagea spathacea from the Netherlands was inferred to be nonaploid as was recorded from plants across Europe. The aim of the study was to use flow cytometry as a tool to elucidate the taxonomic position of the Dutch Gagea.

Potential for chromium (VI) bioremediation by the aquatic carnivorous plant Utricularia gibba L. (Lentibulariaceae)

The aquatic carnivorous plant Utricularia gibba has one of the smallest known genomes among flowering plants, and therefore, it is an excellent model organism for physiological and developmental studies. The main aim of our work was to check whether the ubiquitous U. gibba might be useful for the phytoremediation of the highly toxic and mobile hexavalent chromium in waters. Plants were incubated for 1 week in a 50 μM (2.6 mg dm(-3)) Cr(VI) solution in laboratory conditions. Our results revealed that the plant exhibits a very high accumulation capacity for Cr. The accumulation level was higher than 780 mg kg(-1) and a bioconcentration factor >300. On the other hand, the plants showed a low tolerance to the elevated Cr concentration, which was expressed in a significant decrease of the photosystem II activity. However, the most pronounced negative influence of chromate was found on the morphology and activity of the traps. Due to its high accumulation capacity, we suggest that U. gibba may be efficient in the removal of chromate over a short time scale. It can also provide a new molecular resource for studying the mechanisms of Cr(VI) detoxification.