Genomic DNA base composition (GC content) is predicted to significantly affect genome functioning and species ecology. Although several hypotheses have been put forward to address the biological impact of GC content variation in microbial and vertebrate organisms, the biological significance of GC content diversity in plants remains unclear because of a lack of sufficiently robust genomic data. Using flow cytometry, we report genomic GC contents for 239 species representing 70 of 78 monocot families and compare them with genomic characters, a suite of life history traits and climatic niche data using phylogeny-based statistics. GC content of monocots varied between 33.6% and 48.9%, with several groups exceeding the GC content known for any other vascular plant group, highlighting their unusual genome architecture and organization. GC content showed a quadratic relationship with genome size, with the decreases in GC content in larger genomes possibly being a consequence of the higher biochemical costs of GC base synthesis. Dramatic decreases in GC content were observed in species with holocentric chromosomes, whereas increased GC content was documented in species able to grow in seasonally cold and/or dry climates, possibly indicating an advantage of GC-rich DNA during cell freezing and desiccation. We also show that genomic adaptations associated with changing GC content might have played a significant role in the evolution of the Earth's contemporary biota, such as the rise of grass-dominated biomes during the mid-Tertiary. One of the major selective advantages of GC-rich DNA is hypothesized to be facilitating more complex gene regulation.plant genome | genome size evolution | Poaceae | phylogenetic regression | geographical stratification D eep insights into the genomic architecture of model plants are rapidly accumulating, especially because of advances being made in high-throughput next generation and third generation sequencing techniques (1). However, the genomic constitution of the vast majority of nonmodel plants still remains unknown (2), impeding our understanding of the relationship between particular genomic architectures and evolutionary fitness in various environments. One of the important qualitative aspects of genomic architecture is the genomic nucleotide composition, which is usually expressed as the proportion of guanine and cytosine bases in the DNA molecule (GC content). In prokaryotes, the GC content is a well-studied and widely used character in taxonomy (3), and numerous studies have shown both the impact of GC content on microbial ecology and the influence of the environment in shaping the DNA base composition of microbial communities (4-7). The DNA base composition is also frequently discussed in relation to the evolution of the isochore structure in humans and other homeothermic (warm-blooded) vertebrates (i.e., birds and mammals) (8-10). In contrast, considerably less attention has been paid to the biological relevance of genomic GC content variation in plants (11), with genomic GC co...

SummaryPolyploidy and increased genome size are hypothesized to increase organismal nutrient demands, namely of phosphorus (P), which is an essential and abundant component of nucleic acids. Therefore, polyploids and plants with larger genomes are expected to be selectively disadvantaged in P-limited environments. However, this hypothesis has yet to be experimentally tested.We measured the somatic DNA content and ploidy level in 74 vascular plant species in a long-term fertilization experiment. The differences between the fertilizer treatments regarding the DNA content and ploidy level of the established species were tested using phylogenybased statistics.The percentage and biomass of polyploid species clearly increased with soil P in particular fertilizer treatments, and a similar but weaker trend was observed for the DNA content. These increases were associated with the dominance of competitive life strategy (particularly advantageous in the P-treated plots) in polyploids and the enhanced competitive ability of dominant polyploid grasses at high soil P concentrations, indicating their increased P limitation.Our results verify the hypothesized effect of P availability on the selection of polyploids and plants with increased genome sizes, although the relative contribution of increased P demands vs increased competitiveness as causes of the observed pattern requires further evaluation.

The present study indicates the high potential of general quantitative characters of the genome for understanding the long-term processes of genome evolution, testing evolutionary hypotheses and their usefulness for large-scale genomic projects. Taken together, the results suggest that there is an evolutionary advantage for small genomes in Festuca.

Considerable differences in nuclear DNA content exist among Central European species of Cirsium on the diploid level. Perennial soft spiny Cirsium species of wet habitats and continental distributions generally have smaller genomes. The hybrids of diploid species remain diploid, and their DNA content is smaller than the mean of the parents. Species with smaller genomes produce interspecific hybrids more frequently.

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Genomes of Carex are relatively small and very GC-poor compared with other angiosperms. We conclude that the evolution of genome and karyotype in Carex is promoted by frequent chromosomal fissions/fusions, rare polyploidy and common repetitive DNA proliferation/removal.

Genome sizes and genomic guanine+cytosine (GC) contents of the Czech vascular flora with new estimates for 1700 species.-Preslia 91: 117-142. The content of DNA in the somatic, unreplicated cell nuclei (genome size) and DNA base composition (GC content) are the basic genomic parameters that can be measured by flow cytometry. Genome size, or ploidy level, can affect many plant properties and are therefore included as important features in modern biological floras and plant trait databases. However, genomic data are still largely measured mainly for taxonomic and biosystematic purposes, and despite the popularity of flow cytometry in the Czech Republic, this information is still missing for many of the vascular plants in the Czech flora. The biological significance of the GC content is less clear compared to the genome size, which, along with the greater difficulty in measuring it, results in the absence of such information for the vast majority of species. Here, we measure these two genomic parameters for 1908 samples of 1700 species in the Czech vascular flora. Here for the first time are reported the genome sizes of more than 1000 species and GC contents of more than 1500 species, which more than doubles the amount of information on the GC content of vascular plants. Together with the published data obtained in our laboratory using the same methods and flow cytometers, this information is now available for 1910 species that occur in the Czech Republic (~83% of this country's permanent flora, excluding apomicts). They are summarized in a table, accompanied by information about assumed chromosome number, ploidy level and an estimate of the monoploid genome size. We further provide a descriptive analysis of this dataset, list extreme values and comment on some cytogeographically interesting findings. This dataset is the largest and most comprehensive set of genomic data covering almost the entire flora of a country. It will serve as the basis of the karyological traits section of the Czech plant trait database Pladias (www.pladias.cz) and for testing of hypotheses about the evolution and biological relevance of these genomic parameters.

Flow cytometry (FCM) is currently the most widely‐used method to establish nuclear DNA content in plants. Since simple, 1‐3‐parameter, flow cytometers, which are sufficient for most plant applications, are commercially available at a reasonable price, the number of laboratories equipped with these instruments, and consequently new FCM users, has greatly increased over the last decade. This paper meets an urgent need for comprehensive recommendations for best practices in FCM for different plant science applications. We discuss advantages and limitations of establishing plant ploidy, genome size, DNA base composition, cell cycle activity, and level of endoreduplication. Applications of such measurements in plant systematics, ecology, molecular biology research, reproduction biology, tissue cultures, plant breeding, and seed sciences are described. Advice is included on how to obtain accurate and reliable results, as well as how to manage troubleshooting that may occur during sample preparation, cytometric measurements, and data handling. Each section is followed by best practice recommendations; tips as to what specific information should be provided in FCM papers are also provided.