Patterns of heterochromatin distribution in plant chromosomes

Interphase nuclei, karyotypes and nuclear DNA amounts in five species of Oenocarpus (Arecaceae)

The genus Oenocarpus Martius, 1823 (Arecaceae) includes five species commonly used in Amazonia, especially for their fruits. Little is known about the cytogenetic characteristics and DNA amounts of these species, except for O.bataua (Martius, 1823). This study characterized and compared the types of interphase nuclei, the chromosome sets, and estimated the nuclear DNA amounts of Oenocarpusbacaba (Martius, 1823), O.bataua, O.distichus (Martius, 1823), O.mapora (H. Karsten, 1857) and O.minor (Martius, 1823). Standard cytogenetic analyses and estimates of the nuclear DNA amount by flow cytometry were carried out. These are the first reports of chromosome numbers and DNA amounts, except for O.bataua, as is the description of the chromatin distribution in interphase nuclei and karyotype for all species. All species presented 2n = 36, confirming the previous report for O.bataua. Differences between karyotype formulas and the positioning of secondary constrictions were observed. There were no significant differences for the nuclear DNA amounts among species. The constancy in chromosome number and variations in karyotype formulas suggest the occurrence of chromosome rearrangement as an important mechanism in Oenocarpus speciation.

Comparative Cytogenetic of the 36-Chromosomes Genera of Orchidinae Subtribe (Orchidaceae) in the Mediterranean Region: A Summary and New Data

This article provides a summary of the current knowledge on the cytogenetics of four genera, which are all composed of 36 chromosomes, within the Orchidinae subtribe (Orchidaceae). Previous classical studies have revealed differences in karyomorphology among these genera, indicating genomic diversity. The current study includes an analysis of the current knowledge with an update of the karyotype of 47 species with 36 chromosomes from the genera Anacamptis, Serapias, Himantoglossum, and Ophrys. The study discusses comparisons of karyotypes among these genera that used traditional techniques as well as karyotype asymmetry relationships with various asymmetry indices. Additionally, the study reports new findings on polyploidy in Anacamptis pyramidalis and Serapias lingua, which were observed through karyotype and meiotic metaphase analyses in EMC. Moreover, the study detected B chromosomes for the first time in A. papilionacea and A. palustris. The article also describes the use of fluorescent in situ hybridization in some specimens of A. papilionacea and A. collina to locate different sites of the 18S-5.8S-25S rDNA and 5S rDNA ribosomal complexes on chromosomes. The information derived from these cytogenetic analyses was used to refine the classification of these orchids and identify evolutionary relationships among different species and genera.

Comparative Cytogenetics and Fluorescent Chromosome Banding in Five Indian Species of Dipcadi Medik

The genus Dipcadi Medik. (Subfamily: Scilloideae) has a narrow distribution in India and several overlapping morphological traits make the genus taxonomically challenging at the species level. Cytogenetic characterization can provide additional taxonomic data and can be used to evaluate genetic diversity at the species level. We have accomplished comparative karyotype analysis and fluorescence banding patterns using 4'-6-Diamidino-2-phenylindole (DAPI) and Chromomycin A₃ (CMA) in five Indian species for the first time. The karyotypes of D. concanense and D. goaense exhibited similar fluorochrome banding profiles. However, D. montanum, D. ursulae and D. erythraeum differ distinctly in their karyotypes. In all taxa, CMA^+ve/DAPI^-ve or DAPI⁰ (GC-rich) constitutive heterochromatin was located at the constriction region or terminal satellite of the nucleolar chromosome. DAPI^+ve/CMA^-ve or CMA⁰ (AT-rich) heterochromatin dominates in D. montanum, D. ursulae and D. erythraeum. However, D. erythraeum shows a distinct variation in fluorochrome banding pattern from all other species. The distribution of CMA and DAPI bands is a reflection of heterochromatin composition and variations acquired by different species. This characterization can be used to assess phylogenetic relationships in the understudied genus Dipcadi and may serve as a basis for other genomic analyses and evolutionary studies.

Critical review on karyotype diversity in lentil based on classical and molecular cytogenetics

Lentil is an annual protein rich valuable edible crop with only one cultivated and six wild taxa. Keeping in mind its narrow gene pool, the genus deserves critical assessment of genomic diversity at the chromosomal level. Genetic diversity represents the heritable variation within and between populations of organisms. Over the decades classical and molecular cytogenetics have played an immense role in the field of crop improvement. Lentil, though grown in different countries, country-wise chromosomal information is inadequate. Critical evaluation of more than seven decades chromosomal information has revealed unique karyotype diversity within the landraces of different countries. Application of fluorescent banding and fluorescent in situ hybridization (FISH) has helped to segregate cultivars based on cultivar specific chromosomal markers and landmarks. Selection of cultivated and wild cultivars based on qualitative and diseases related morpho-traits and new information from this critical review especially on molecular cytogenetics may provide more options for crop improvement. More research in the field of molecular cytogenetics from country specific species and cultivars are needed to enrich the repository of gene pool. Alien gene introgression from extended gene pool through the advanced genomics and biotechnological tools could facilitate the path of sustainable improvement of this crop.

The Genomics of Plant Satellite DNA

The twenty-first century began with a certain indifference to the research of satellite DNA (satDNA). Neither genome sequencing projects were able to accurately encompass the study of satDNA nor classic methodologies were able to go further in undertaking a better comprehensive study of the whole set of satDNA sequences of a genome. Nonetheless, knowledge of satDNA has progressively advanced during this century with the advent of new analytical techniques. The enormous advantages that genome-wide approaches have brought to its analysis have now stimulated a renewed interest in the study of satDNA. At this point, we can look back and try to assess more accurately many of the key questions that were left unsolved in the past about this enigmatic and important component of the genome. I review here the understanding gathered on plant satDNAs over the last few decades with an eye on the near future.

Variations in heterochromatin content reveal important polymorphisms for studies of genetic improvement in garlic (Allium sativum L.)

Allium sativum L. is an herb of the Alliaceae family with a specific taste and aroma and medicinal and nutraceutical properties that are widely marketed in several countries. Brazil is one of the largest importers of garlic in the world, despite of its production is restricted and limited to internal consumption. Thus, explore the genetic diversity of commercial garlic conserved at germplasm banks is essential to generate additional genetic information about its economically important crop. A suitable tool for this purpose is the cytogenetic characterisation of these accessions. This study aimed to characterise the cytogenetic diversity among seven accessions of garlic from a Germplasm Bank in Brazil. The karyotypes were obtained by conventional staining and with chromomycin A3 (CMA) and 4,6-diamidino-2-phenylindole (DAPI) fluorochromes. All accessions analysed showed chromosome number 2n = 16, karyotype formula 6M+2SM, symmetrical karyotypes, reticulate interphase nuclei, and chromosomes with uniform chromatin condensation from prophase to metaphase. The fluorochromes staining showed differences in the amount and distribution of heterochromatin along the chromosomes and between accessions studied. Based on the distribution pattern of these small polymorphisms, it was possible to separate the seven accessions into three groups. It was also possible to differentiate some of the accessions individually. One of the results obtained showed a heteromorphic distension of the nucleolar organiser region observed on the chromosome pairs 6 or 7 with peculiar characteristics. It was suggested for example, that the heteromorphic block of heterochromatin (CMA+++/DAPI-) on chromosome 6 of the "Branco Mineiro Piauí" accession can be used as a marker to identify this genotype or may be associated with some character of economic interest.

Genetic Diversity Analysis of Tomato (Solanum lycopersicum L.) with Morphological, Cytological, and Molecular Markers under Heat Stress

Tomatoes are usually consumed daily in the human diet. High temperatures reduce the number of tomato yields per year. Heat stress has been considered one of the most prominent causes of alterations in morphological and molecular characteristics in crops that decrease normal growth, production, and yield in diverse plants, including tomatoes (Solanum lycopersicum L.). In this study, we evaluated six tomato lines, namely G1, G2, G3, G4, G5, and G6, at morphological, molecular, and cytological levels under heat stress. The average results of two seasons (2018 and 2019) clarified that the G6, G1, and G2 lines recorded the highest flowering values, as well as some fruit and vegetative growth traits. Furthermore, G6 and G2 had the maximum number of fruits/plant, whereas G2 and G1 produced the highest yield/plant under high temperatures. The number of chromosomes in all lines was 2n = 24, except for G5, in which the number was 2n = 26, whereas chromosome sizes were small, ranging from 323.08 to 464.48 µm. The G1 cultivar was a symmetrical cultivar (primitive), having the highest total form percentage (TF%) and symmetry index (Syi) values and the minimum karyotype asymmetry index (ASK) value, whereas G4 was asymmetrical (advanced). Molecular marker analysis demonstrated that intersimple sequence repeat (ISSR) primers 49A, HB-14, 49A, 49B, and 89B presented the highest values for polymorphism percentage P%, marker index (MI), effective multiplex ratio (EMR), and polymorphism information content (PIC), respectively. In contrast, OP-A3, OP-B3, SCoT 2, and SCoT 12 primers showed the highest PIC, EMR, MI, P%, and resolving power (Rp) values across the studied random amplified polymorphic DNA (RAPD) and start codon-targeted (SCoT) primers. Moreover, ISSR revealed the highest number of unique specific markers (6), followed by RAPD (4) and SCoT (3) markers. Cluster analysis of combined cytological data and data relating to molecular marker attributes separated the G1, G2, and G3 lines into one group, whereas the other lines were clustered in another group. On the whole, the application of combined analysis using morphological, cytological, and molecular genetics techniques could be considered to provide suitable parameters for studying the evolution of the genetic divergence between the studied tomato lines.

A reference chromosomal map of the hot chili pepper Capsicum pubescens cv. “locoto” (Solanaceae)

Abstract Capsicum pubescens is a cultivated hot chili pepper, consumed in Latin American cuisine as a distinctive ingredient, and popularly known as “locoto” or “rocoto”. This taxon is also an outstanding source of resistance to biotic and abiotic stresses as well as other valuable fruit traits for breeding of the worldwidely cultivated C. annuum and related species. In this study, the chromosome complement of C. pubescens cv. “locoto” (2n = 24) was deeply characterized through a sequential combination of conventional and molecular cytogenetics approaches comprising: Ag-NOR staining, heterochromatic fluorescent C-DAPI, DAPI/AMD-CMA/DA bandings, fluorescence in situ hybridization (FISH) of Capsicum-derived probes of the 5S and 18S-25S rRNA genes and different regions of spacers of the ribosomal unit, as well as telomeric probe. The markers identified were systematically combined with morphological karyotype parameters - number, size, centromeres, satellites - to produce a physical map which allowed the identification of several landmarks in each individual chromosome. The reference chromosomal map of C. pubescens here presented is the most comprehensively developed in Capsicum so far. It is envisioned that this chromosomal map will serve as a reference framework for the upcoming sequencing projects and as starting point to assist future genetic mapping of important agronomic traits.

Brazilian Kayabi Indian accessions of peanut, Arachis hypogaea (Fabales, Fabaceae): origin, diversity and evolution

Peanut is a crop of the Kayabi tribe, inhabiting the Xingu Indigenous Park, Brazil. Morphological analysis of Xingu accessions showed variation exceeding that described for cultivated peanuts. This raised questions as to the origin of the Xingu accessions: are they derived from different species, or is their diversity a result of different evolutionary and selection processes? To answer these questions, cytogenetic and genotyping analyses were conducted. The karyotypes of Xingu accessions analyzed are very similar to each other, to an A. hypogaea subsp. fastigiata accession and to the wild allotetraploid A. monticola. The accessions share the number and general morphology of the chromosomes; DAPI+ bands; 5S and 45S rDNA loci distribution and a high genomic affinity with A. duranensis and A. ipaënsis genomic probes. However, the number of CMA3+ bands differs from those determined for A. hypogaea and A. monticola, which are also different from each other. SNP genotyping grouped all Arachis allotetraploids into four taxonomic groups: Xingu accessions were closer to A. monticola and A. hypogaea subsp. hypogaea. Our data suggests that the morphological diversity within these accessions is not associated with a different origin and can be attributed to morphological plasticity and different selection by the Indian tribes.

Chromosome diversity in species of the genus Arachis, revealed by FISH and CMA/DAPI banding, and inferences about their karyotype differentiation

The species of the genus Arachis (Leguminosae) are ordered into nine sections. The assignment of genome types in this genus has been based on cross-compatibility analysis and molecular cytogenetic studies. The latter has also allowed karyotypically establishing well-defined genomes and reassigning the genome of several species. However, most of these studies have been focused mainly on the sections Arachis and Rhizomatosae. To increase the knowledge about the chromosome diversity of the whole genus, here we performed a detailed karyotype characterization of representative species of most of the sections and genomes of Arachis. This characterization included chromosome morphology, CMA/DAPI chromosome banding, and chromosome marker localization (rDNAloci and one satDNA sequence) by fluorescent in situ hybridization (FISH). Based on the data obtained and other previously published data, we established the karyotype similarities by cluster analysis and defined eleven karyotype groups. The grouping was partly coincident with the traditional genome assignment, except for some groups and some individual species. Karyotype similarities among some genomes were also found. The main characteristics of each karyotype group of Arachis were summarized. Together, our results provide information that may be beneficial for future cytogenetic and evolutionary studies, and also contribute to the identification of interspecific hybrids.

Honey bee survival mechanisms against the parasite Varroa destructor: a systematic review of phenotypic and genomic research efforts

The ectoparasitic mite Varroa destructor is the most significant pathological threat to the western honey bee, Apis mellifera, leading to the death of most colonies if left untreated. An alternative approach to chemical treatments is to selectively enhance heritable honey bee traits of resistance or tolerance to the mite through breeding programs, or select for naturally surviving untreated colonies. We conducted a literature review of all studies documenting traits of A. mellifera populations either selectively bred or naturally selected for resistance and tolerance to mite parasitism. This allowed us to conduct an analysis of the diversity, distribution and importance of the traits in different honey bee populations that can survive V. destructor globally. In a second analysis, we investigated the genetic bases of these different phenotypes by comparing 'omics studies (genomics, transcriptomics, and proteomics) of A. mellifera resistance and tolerance to the parasite. Altogether, this review provides a detailed overview of the current state of the research projects and breeding efforts against the most devastating parasite of A. mellifera. By highlighting the most promising traits of Varroa-surviving bees and our current knowledge on their genetic bases, this work will help direct future research efforts and selection programs to control this pest. Additionally, by comparing the diverse populations of honey bees that exhibit those traits, this review highlights the consequences of anthropogenic and natural selection in the interactions between hosts and parasites.

Heterochromatin and numeric chromosome evolution in Bignoniaceae, with emphasis on the Neotropical clade Tabebuia alliance

Bignoniaceae is a diverse family composed of 840 species with Pantropical distribution. The chromosome number 2n = 40 is predominant in most species of the family, with n = 20 formerly being considered the haploid base number. We discuss here the haploid base number of Bignoniaceae and examine heterochromatin distributions revealed by CMA/DAPI fluorochromes in the Tabebuia alliance, as well as in some species of the Bignonieae, Tecomeae, and Jacarandeae tribes. When comparing the chromosome records and the phylogenies of Bignoniaceae it can be deduced that the base number of Bignoniaceae is probably n = 18, followed by an ascendant dysploidy (n = 18 → n = 20) in the most derived and diverse clades. The predominant heterochromatin banding patterns in the Tabebuia alliance were found to be two terminal CMA⁺ bands or two terminal and two proximal CMA⁺ bands. The banding pattern in the Tabebuia alliance clade was more variable than seen in Jacarandeae, but less variable than Bignonieae. Despite the intermediate level of variation observed, heterochromatin banding patterns offer a promising tool for distinguishing species, especially in the morphologically complex genus Handroanthus.

Chromosomal variability in Brazilian species of Anthurium Schott (Araceae): Heterochromatin, polyploidy, and B chromosomes

The genus Anthurium has a Neotropical distribution, with karyotype predominance of x = 15, although some species show disploidy or polyploid variations. The karyotypes of seven species and different populations of Anthurium were analyzed using fluorochrome CMA and DAPI staining. The karyotypes were composed of meta- and submetacentric chromosomes, with numbers varying from 2n = 30 to 2n = 60. Supernumerary euchromatic chromosomes were observed in A. affine, and supernumerary heterochromatic chromosomes were observed in A. gladiifolium and A. petrophilum. Polyploidy was recurrent in the Anthurium species analyzed, with records of 2n = 30 and 60 in different A. pentaphyllum populations. Fluorochrome staining revealed different CMA⁺ banding distributions between diploid and polyploid cytotypes of A. pentaphyllum, suggesting structural alteration events. Anthurium petrophilum, on the other hand, showed a more consistent banding profile, with 10 to 12 proximal CMA bands in the three populations analyzed. DAPI⁺/CMA⁰ regions occurred exclusively in populations of A. gracile and A. pentaphyllum. The heterochromatic fraction in Anthurium was found to be quantitatively variable among species and populations, which may be related with adaptive aspects, different environmental conditions, or phylogenetic position.

Comparative karyotype analysis among cytotypes of Cynodon dactylon (L.) Pers. (Poaceae)

Cynodon dactylon is characterized by taxonomic and systematic complexity, and polyploidy is one of the factors responsible for its genetic and morphological diversity. The aim of the present study was to compare karyotypes of C. dactylon cytotypes based on fluorescent banding and nuclear DNA content. The nine C. dactylon accessions evaluated were obtained from the Active Germplasm Bank (BAG) of the United States Department of Agriculture (USDA). Roots were pretreated with cycloheximide, fixed in Carnoy's solution and subjected to enzymatic digestion. Slides were prepared by the dissociation and air-drying technique. The fluorescent banding pattern was obtained using chromomycin A3 (CMA)/4,6-dimidino-2-phenylindole (DAPI) staining and DNA content was estimated by flow cytometry. The chromosome number of the accessions ranged from 2n = 2x = 18 to 2n = 5x = 45. Chromosomal polymorphism was observed based on the distribution and number of heterochromatic bands, with CMA⁺ bands located in the pericentromeric position and DAPI⁺ bands mainly in the terminal position. PI477004-26 (2n = 3x = 27) and PI291966-27 (2n = 4x = 36) had the highest and lowest number of DAPI⁺ bands, respectively. The number of CMA⁺ bands was stable, as only PI477004-26, PI291966-27 and PI289750-10 (2n = 5x = 45) showed variation. There was no direct correlation between an increase in the ploidy level and an increase in the percentage of heterochromatic regions, mainly in relation to A-T-rich blocks. The chromosomal banding variation found reinforces the notion of allopolyploidy occurrence in C. dactylon and demonstrates the genomic complexity of this species regard to repetitive DNA content.

Phenotypic and molecular cytogenetic variability in calendula (Calendula officinalis L.) cultivars and mutant lines obtained via chemical mutagenesis

The morphological, meiotic and chromosomal variability were studied in two cultivars of Calendula officinalis L. and their mutant lines obtained though chemical mutagenesis using diethyl sulphate (DES) (0.04%, 0.08%) and dimethyl sulphate (DMS) (0.025%, 0.05%). The studied cultivars displayed different sensitivity to DMS and DES mutagens. More M1 plants with morphological changes were observed in C. officinalis cv. ‘Zolotoe more’ than in cv. ‘Rajskij sad’. DMS and DES at low concentrations had positive effects on main agro-metrical traits in both cultivars including plant height, inflorescence diameter and number of inflorescences per plant. Dose-dependent increase in number of various meiotic abnormalities was revealed in both mutant lines. Comparative karyotype analysis and FISH-based visualization of 45S and 5S rDNA indicated a high level of karyotype stability in M1 and M2 plants. Seed treatments with DMS and DES at certain concentrations resulted in higher yields of inflorescences in M1 plants compared to the control. In M2 generation, dose-dependent reduction in the yields of inflorescences was observed. Our findings demonstrate that DMS and DES at low concentrations have great potential in calendula mutation breeding.

Heterochromatin evolution in Arachis investigated through genome-wide analysis of repetitive DNA

The most conspicuous difference among chromosomes and genomes in Arachis species, the patterns of heterochromatin, was mainly modeled by differential amplification of different members of one superfamily of satellite DNAs. Divergence in repetitive DNA is a primary driving force for genome and chromosome evolution. Section Arachis is karyotypically diverse and has six different genomes. Arachis glandulifera (D genome) has the most asymmetric karyotype and the highest reproductive isolation compared to the well-known A and B genome species. These features make A. glandulifera an interesting model species for studying the main repetitive components that accompanied the genome and chromosome diversification in the section. Here, we performed a genome-wide analysis of repetitive sequences in A. glandulifera and investigated the chromosome distribution of the identified satellite DNA sequences (satDNAs). LTR retroelements, mainly the Ty3-gypsy families "Fidel/Feral" and "Pipoka/Pipa", were the most represented. Comparative analyses with the A and B genomes showed that many of the previously described transposable elements (TEs) were differently represented in the D genome, and that this variation accompanied changes in DNA content. In addition, four major satDNAs were characterized. Agla_CL8sat was the major component of pericentromeric heterochromatin, while Agla_CL39sat, Agla_CL69sat, and Agla_CL122sat were found in heterochromatic and/or euchromatic regions. Even though Agla_CL8sat belong to a different family than that of the major satDNA (ATR-2) found in the heterochromatin of the A, K, and F genomes, both satDNAs are members of the same superfamily. This finding suggests that closely related satDNAs of an ancestral library were differentially amplified leading to the major changes in the heterochromatin patterns that accompanied the karyotype and genome differentiation in Arachis.

Characterization of aneuploidy in interspecific hybrid between Urochloa ruziziensis (R. Germ. & Evrard) Crins and Urochloa decumbens (Stapf) R. D. Webster

The aim of the study was to characterize the type of aneuploidy present in the hybrid Urochloa ruziziensis × Urochloa decumbens and to confirm the origin of the additional chromosomes through comparative analysis of the hybrid and parental karyotypes. C and CMA banding techniques were used for chromosome differentiation. The parental genotypes showed 36 chromosomes. The hybrid presented plants with 36 + 2 chromosomes and plants with 36 + 1 chromosomes. Urochloa ruziziensis (4x) presented four chromosomes with CMA and C bands co-located in the terminal position. In U. decumbens, four chromosomes presented terminal CMA bands, eight chromosomes were distinguished by C banding with pericentromeric and terminal bands, one chromosome with terminal band at both ends and one chromosome presented one C terminal band. For the hybrid, CMA bands were found on five chromosomes and C bands on seven chromosomes, all in terminal position. Aneuploidy was identified in pairs 3' and 4' in the hybrid plants with 36 + 2 chromosomes, characterizing it as double trisomy. The karyotype of hybrid plants with 36 + 1 chromosomes indicated elimination of the additional chromosome identified in pair 4' and maintenance of trisomy on pair 3'. The comparative analysis of karyotypes indicates that the additional chromosomes that characterize the trisomy were inherited from U. ruziziensis (artificial tetraploid).

Cytogenetic studies in three diploid species of Andropogon (Andropogoneae), section Leptopogon

Abstract Karyotypes can provide a relevant information about relationships and evolutionary origin among species of the Andropogon genus. This paper presents the karyotype, C+ and DAPI/CMA3 banding and DNA content of three diploid (2n=20) species belonging to section Leptopogon: A. selloanus, A. macrothrix and A. gyrans. Karyotypes of the three diploid species are symmetrical. We propose a karyotype formulae (18m + 2sm) for each of them. The three species show a pair of metacentric chromosomes with a terminal secondary constriction on short arms. Fluorochrome banding revealed different constitutive heterochromatin patterns and CMA3+/DAPI¬ terminal bands related to the nucleolar organizer region in each species. Nuclear DNA content was estimated by flow cytometry ranged from 2.22 to 2.61 pg. FISH technique revealed that these three species have two 45S rDNA loci at the distal ends of the short arms of two metacentric chromosomes. We compare the genomes of the diploids A. selloanus, A. macrothrix and A. gyrans, and the triploid A. ternatus using GISH. These technique allowed us to confirm the hypotheses that the A. selloanus, A. macrothrix and A. gyrans constitute a homogeneous group that share a common S genome that comprises just one of the genomes in the triploid A. ternatus.

Karyotype analysis of eight cultivated Allium species

The karyotypes of Allium, a genus that comprises many crops and ornamental plants, are relatively poorly studied. To extend our knowledge on karyotype structure of the genus, the chromosomal organization of rRNA genes and CMA/DAPI bands was studied. Fluorescence in situ hybridization using 5S and 35S rDNA probes and banding methods (silver staining and CMA₃/DAPI staining) were used to analyze the karyotypes of eight cultivated Allium L. species. Analyzed Allium taxa revealed three different basic chromosome numbers (x = 7, 8, 9) and three different ploidy levels (diploid, triploid, and tetraploid). The rDNA sites chromosomal organization is reported the first time for the six species (A. moly, A. oreophilum, A. karataviense, A. nigrum, A. sphaerocephalon, A. porrum). The Allium species that were analyzed showed a high level of interspecies polymorphism in the number and localization of the rDNA sites. The fluorescence in situ hybridization patterns of 35S rDNA sites were more polymorphic than those of the 5S rDNA in the diploid species. Several groups of similar chromosomes could be distinguished among the chromosomes that had rDNA sites in the polyploid species. Each of the groups had three chromosomes (triploid A. sphaerocephalon L.) or four chromosomes (tetraploid A. porrum L.) suggesting their autopolyploid origin. In the genomes of four of the analyzed species, only some of the 35S rDNA sites were transcriptionally active. Fluorochrome banding revealed that the CMA₃⁺ bands were associated with the 35S rDNA sites in all of the species that were analyzed, except A. fistulosum L. in which positive CMA₃⁺ bands were detected in the terminal position of all of the chromosome arms. The rDNA sequences, nucleolar organizer regions (NORs), and CMA/DAPI bands are very good chromosome markers that allowed to distinguished from two to five pairs of homologous chromosomes in analyzed Allium species. The karyotypes of the studied species could be clearly distinguished by the number and position of the rDNA sites, NORs, and CMA/DAPI bands, which revealed high interspecific differentiation among the taxa.

FISH-aimed karyotype analysis in Aconitum subgen. Aconitum reveals excessive rDNA sites in tetraploid taxa

The location of 5S and 35S rDNA sequences in chromosomes of four Aconitum subsp. Aconitum species was analyzed after fluorescence in situ hybridization (FISH). Both in diploids (2n = 2x = 16; Aconitum variegatum, A. degenii) and tetraploids (2n = 4× = 32; A. firmum, A. plicatum), rDNA repeats were localized exclusively on the shorter arms of chromosomes, in subterminal or pericentromeric sites. All analyzed species showed similar basal genome size (Cx = 5.31-5.71 pg). The most striking features of tetraploid karyotypes were the conservation of diploid rDNA loci and emergence of many additional 5S rDNA clusters. Chromosomal distribution of excessive ribosomal sites suggests their role in the secondary diploidization of tetraploid karyotypes.

Karyotype analysis in Bignonieae (Bignoniaceae): chromosome numbers and heterochromatin

Chromosome numbers and heterochromatin banding pattern variability have been shown to be useful for taxonomic and evolutionary studies of different plant taxa. Bignonieae is the largest tribe of Bignoniaceae, composed mostly by woody climber species whose taxonomies are quite complicated. We reviewed and added new data concerning chromosome numbers in Bignonieae and performed the first analyses of heterochromatin banding patterns in that tribe based on the fluorochromes chromomycin A3 (CMA) and 4'-6-diamidino-2-phenylindole (DAPI). We confirmed the predominant diploid number 2n = 40, as well as variations reported in the literature (dysploidy in Mansoa [2n = 38] and polyploidy in Dolichandra ungis-cati [2n = 80] and Pyrostegia venusta [2n = 80]). We also found a new cytotype for the genus Anemopaegma (Anemopaegma citrinum, 2n = 60) and provide the first chromosome counts for five species (Adenocalymma divaricatum, Amphilophium scabriusculum, Fridericia limae, F. subverticillata, and Xylophragma myrianthum). Heterochromatin analyses revealed only GC-rich regions, with six different arrangements of those bands. The A-type (one large and distal telomeric band) were the most common, although the presence and combinations of the other types appear to be the most promising for taxonomic studies.

Intrachromosomal karyotype asymmetry in Orchidaceae

The asymmetry indexes have helped cytotaxonomists to interpret and classify plant karyotypes for species delimitation efforts. However, there is no consensus about the best method to calculate the intrachromosomal asymmetry. The present study aimed to compare different intrachromosomal asymmetry indexes in order to indicate which are more efficient for the estimation of asymmetry in different groups of orchids. Besides, we aimed to compare our results with the Orchidaceae phylogenetic proposal to test the hypothesis of Stebbins (1971). Through a literature review, karyotypes were selected and analyzed comparatively with ideal karyotypes in a cluster analysis. All karyotypes showed some level of interchromosomal asymmetry, ranging from slightly asymmetric to moderately asymmetric. The five tested intrachromosomal asymmetry indexes indicated Sarcoglottis grandiflora as the species with the most symmetrical karyotype and Christensonella pachyphylla with the most asymmetrical karyotype. In the cluster analysis, the largest number of species were grouped with the intermediary ideal karyotypes B or C. Considering our results, we recommend the combined use of at least two indexes, especially Ask% or A1 with Syi, for cytotaxonomic analysis in groups of orchids. In an evolutionary perspective, our results support Stebbins’ hypothesis that asymmetric karyotypes derive from a symmetric karyotypes.

The Cerrado (Brazil) plant cytogenetics database

Cerrado is a biodiversity hotspot that has lost ca. 50% of its original vegetation cover and hosts ca. 11,000 species belonging to 1,423 genera of phanerogams. For a fraction of those species some cytogenetic characteristics like chromosome numbers and C-value were available in databases, while other valuable information such as karyotype formula and banding patterns are missing. In order to integrate and share all cytogenetic information published for Cerrado species, including frequency of cytogenetic attributes and scientometrics aspects, Cerrado plant species were searched in bibliographic sources, including the 50 richest genera (with more than 45 taxa) and 273 genera with only one species in Cerrado. Determination of frequencies and the database website (http://cyto.shinyapps.io/cerrado) were developed in R. Studies were pooled by employed technique and decade, showing a rise in non-conventional cytogenetics since 2000. However, C-value estimation, heterochromatin staining and molecular cytogenetics are still not common for any family. For the richest and best sampled families, the following modal 2n counts were observed: Oxalidaceae 2n = 12, Lythraceae 2n = 30, Sapindaceae 2n = 24, Solanaceae 2n = 24, Cyperaceae 2n = 10, Poaceae 2n = 20, Asteraceae 2n = 18 and Fabaceae 2n = 26. Chromosome number information is available for only 16.1% of species, while there are genome size data for only 1.25%, being lower than the global percentages. In general, genome sizes were small, ranging from 2C = ca. 1.5 to ca. 3.5 pg. Intra-specific 2n number variation and higher 2n counts were mainly related to polyploidy, which relates to the prevalence of even haploid numbers above the mode of 2n in most major plant clades. Several orphan genera with almost no cytogenetic studies for Cerrado were identified. This effort represents a complete diagnosis for cytogenetic attributes of plants of Cerrado.

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.

Using chromosomal data in the phylogenetic and molecular dating framework: karyotype evolution and diversification in Nierembergia (Solanaceae) influenced by historical changes in sea level

Karyotype data within a phylogenetic framework and molecular dating were used to examine chromosome evolution in Nierembergia and to infer how geological or climatic processes have influenced in the diversification of this solanaceous genus native to South America and Mexico. Despite the numerous studies comparing karyotype features across species, including the use of molecular phylogenies, to date relatively few studies have used formal comparative methods to elucidate chromosomal evolution, especially to reconstruct the whole ancestral karyotypes. Here, we mapped on the Nierembergia phylogeny one complete set of chromosomal data obtained by conventional staining, AgNOR-, C- and fluorescent chromosome banding, and fluorescent in situ hybridisation. In addition, we used a Bayesian molecular relaxed clock to estimate divergence times between species. Nierembergia showed two major divergent clades: a mountainous species group with symmetrical karyotypes, large chromosomes, only one nucleolar organising region (NOR) and without centromeric heterochromatin, and a lowland species group with asymmetrical karyotypes, small chromosomes, two chromosomes pairs with NORs and centromeric heterochromatin bands. Molecular dating on the DNA phylogeny revealed that both groups diverged during Late Miocene, when Atlantic marine ingressions, called the 'Paranense Sea', probably forced the ancestors of these species to find refuge in unflooded areas for about 2 Myr. This split agrees with an increased asymmetry and heterochromatin amount, and decrease in karyotype length and chromosome size. Thus, when the two Nierembergia ancestral lineages were isolated, major divergences occurred in chromosomal evolution, and then each lineage underwent speciation separately, with relatively minor changes in chromosomal characteristics.

Advancing Eucalyptus Genomics: Cytogenomics Reveals Conservation of Eucalyptus Genomes

The genus Eucalyptus encloses several species with high ecological and economic value, being the subgenus Symphyomyrtus one of the most important. Species such as E. grandis and E. globulus are well characterized at the molecular level but knowledge regarding genome and chromosome organization is very scarce. Here we characterized and compared the karyotypes of three economically important species, E. grandis, E. globulus, and E. calmadulensis, and three with ecological relevance, E. pulverulenta, E. cornuta, and E. occidentalis, through an integrative approach including genome size estimation, fluorochrome banding, rDNA FISH, and BAC landing comprising genes involved in lignin biosynthesis. All karyotypes show a high degree of conservation with pericentromeric 35S and 5S rDNA loci in the first and third pairs, respectively. GC-rich heterochromatin was restricted to the 35S rDNA locus while the AT-rich heterochromatin pattern was species-specific. The slight differences in karyotype formulas and distribution of AT-rich heterochromatin, along with genome sizes estimations, support the idea of Eucalyptus genome evolution by local expansions of heterochromatin clusters. The unusual co-localization of both rDNA with AT-rich heterochromatin was attributed mainly to the presence of silent transposable elements in those loci. The cinnamoyl CoA reductase gene (CCR1) previously assessed to linkage group 10 (LG10) was clearly localized distally at the long arm of chromosome 9 establishing an unexpected correlation between the cytogenetic chromosome 9 and the LG10. Our work is novel and contributes to the understanding of Eucalyptus genome organization which is essential to develop successful advanced breeding strategies for this genus.

Evidence of the occurrence of structural chromosome changes at the initial diploid diversification of the autopolyploid Turnera sidoides L. (Passifloraceae) complex

Turnera sidoides is an autopolyploid complex of obligate outcrossing perennial herbs. It includes five subspecies and five morphotypes in which diploid to octoploid cytotypes were found. Based on phenetic analyses of the complex and karyotype data of polyploid cytotypes, it has been hypothesized that morphological and chromosome differentiation of T. sidoides occurred at the diploid level. To test this hypothesis, we present the first detailed chromosome analysis of diploid populations of three subspecies and four morphotypes. CMA(+)/DAPI(-) bands were restricted to secondary constrictions (except in the andino morphotype) and varied in number and position among taxa. By contrast, DAPI staining was uniform in all the materials investigated. The number and position of 45S rDNA loci were coincident with the CMA(+)/DAPI(-) bands associated with secondary constrictions. Only one pair of 5S rDNA loci was detected in all the taxa (except in subsp. holosericea), but its position was variable. The identified chromosome markers varied among the three subspecies analyzed, but they were more conserved among the morphotypes of subsp. pinnatifida. Cluster analysis of these chromosome markers supports the current taxonomic arrangement of diploids and demonstrates that structural chromosome changes would have led or accompanied the initial differentiation of T. sidoides at the diploid level.

Unraveling the karyotype structure of the spurges Euphorbia hirta Linnaeus, 1753 and E. hyssopifolia Linnaeus, 1753 (Euphorbiaceae) using genome size estimation and heterochromatin differentiation

Euphorbia Linnaeus, 1753 (Euphorbiaceae) is one of the most diverse and complex genera among the angiosperms, showing a huge diversity in morphologic traits and ecologic patterns. In order to improve the knowledge of the karyotype organization of Euphorbia hirta (2n = 18) and Euphorbia hyssopifolia (2n = 12), cytogenetic studies were performed by means of conventional staining with Giemsa, genome size estimations with flow cytometry, heterochromatin differentiation with chromomycin A₃ (CMA) and 4',6-diamidino-2-phenylindole (DAPI) and Giemsa C-banding, fluorescent in situ hybridization (FISH) with 45S and 5S rDNA probes, and impregnation with silver nitrate (AgNO₃). Our results revealed small metacentric chromosomes, CMA⁺/DAPI⁰ heterochromatin in the pericentromeric regions of all chromosomes and CMA⁺/DAPI^- in the distal part of chromosome arms carriers of nucleolar organizing regions (NORs). The DNA content measurements revealed small genomes for both species: Euphorbia hirta with 2C = 0.77 pg and Euphorbia hyssopifolia with 2C = 1.41 pg. After FISH procedures, Euphorbia hirta, and Euphorbia hyssopifolia presented three and four pairs of terminal 45S rDNA sites, respectively, colocalizing with CMA⁺ heterochromatic blocks, besides only one interstitial pair of 5S rDNA signals. Additionally, the maximum number of active NORs agreed with the total number of observed 45S rDNA sites. This work represents the first analysis using FISH in the subfamily Euphorbioideae, revealing a significant number of chromosomal markers, which may be very helpful to understand evolutionary patterns among Euphorbia species.

Karyotype characterization and evolution in South American species of Lathyrus (Notolathyrus, Leguminosae) evidenced by heterochromatin and rDNA mapping

Notolathyrus is a section of South American endemic species of the genus Lathyrus. The origin, phylogenetic relationship and delimitation of some species are still controversial. The present study provides an exhaustive analysis of the karyotypes of approximately half (10) of the species recognized for section Notolathyrus and four outgroups (sections Lathyrus and Orobus) by cytogenetic mapping of heterochromatic bands and 45S and 5S rDNA loci. The bulk of the parameters analyzed here generated markers to identify most of the chromosomes in the complements of the analyzed species. Chromosome banding showed interspecific variation in the amount and distribution of heterochromatin, and together with the distribution of rDNA loci, allowed the characterization of all the species studied here. Additionally, some of the chromosome parameters described (st chromosomes and the 45S rDNA loci) constitute the first diagnostic characters for the Notolathyrus section. Evolutionary, chromosome data revealed that the South American species are a homogeneous group supporting the monophyly of the section. Variation in the amount of heterochromatin was not directly related to the variation in DNA content of the Notolathyrus species. However, the correlation observed between the amount of heterochromatin and some geographical and bioclimatic variables suggest that the variation in the heterochromatic fraction should have an adaptive value.

Non-Random Distribution of 5S rDNA Sites and Its Association with 45S rDNA in Plant Chromosomes

5S and 45S rDNA sites are the best mapped chromosome regions in eukaryotic chromosomes. In this work, a database was built gathering information about the position and number of 5S rDNA sites in 784 plant species, aiming to identify patterns of distribution along the chromosomes and its correlation with the position of 45S rDNA sites. Data revealed that in most karyotypes (54.5%, including polyploids) two 5S rDNA sites (a single pair) are present, with 58.7% of all sites occurring in the short arm, mainly in the proximal region. In karyotypes of angiosperms with only 1 pair of sites (single sites) they are mostly found in the proximal region (52.0%), whereas in karyotypes with multiple sites the location varies according to the average chromosome size. Karyotypes with multiple sites and small chromosomes (<3 µm) often display proximal sites, while medium-sized (between 3 and 6 µm) and large chromosomes (>6 µm) more commonly show terminal or interstitial sites. In species with holokinetic chromosomes, the modal value of sites per karyotype was also 2, but they were found mainly in a terminal position. Adjacent 5S and 45S rDNA sites were often found in the short arm, reflecting the preferential distribution of both sites in this arm. The high frequency of genera with at least 1 species with adjacent 5S and 45S sites reveals that this association appeared several times during angiosperm evolution, but it has been maintained only rarely as the dominant array in plant genera.

The diversity of karyotypes and genomes within section Syllinum of the Genus Linum (Linaceae) revealed by molecular cytogenetic markers and RAPD analysis

The wide variation in chromosome number found in species of the genus Linum (2n = 16, 18, 20, 26, 28, 30, 32, 36, 42, 72, 84) indicates that chromosomal mutations have played an important role in the speciation of this taxon. To contribute to a better understanding of the genetic diversity and species relationships in this genus, comparative studies of karyotypes and genomes of species within section Syllinum Griseb. (2n = 26, 28) were carried out. Elongated with 9-aminoacridine chromosomes of 10 species of section Syllinum were investigated by C- and DAPI/С-banding, CMA and Ag-NOR-staining, FISH with probes of rDNA and of telomere repeats. RAPD analysis was also performed. All the chromosome pairs in karyotypes of the studied species were identified. Chromosome DAPI/C-banding patterns of 28-chromosomal species were highly similar. Two of the species differed from the others in chromosomal location of rDNA sites. B chromosomes were revealed in all the 28-chromosomal species. Chromosomes of Linum nodiflorum L. (2n = 26) and the 28-chromosomal species were similar in DAPI/C-banding pattern and localization of several rDNA sites, but they differed in chromosomal size and number. The karyotype of L. nodiflorum was characterized by an intercalary site of telomere repeat, one additional 26S rDNA site and also by the absence of B chromosomes. Structural similarities between different chromosome pairs in karyotypes of the studied species were found indicating their tetraploid origin. RAPD analysis did not distinguish the species except L. nodiflorum. The species of section Syllinum probably originated from a common tetraploid ancestor. The 28-chromosomal species were closely related, but L. nodiflorum diverged significantly from the rest of the species probably due to chromosomal rearrangements occurring during evolution.

Heterochromatin characterization through differential fluorophore binding pattern in some species of Vigna Savi

Heterochromatin regions are the most intensively studied and best known chromosome markers in plants. In Vigna species, blocks of constitutive heterochromatin were found either in the terminal or interstitial region of the chromosomes. The number and distribution of CMA(+) and DAPI(+) binding sites exhibit high chromosomal variability with characteristic unique banding patterns in all the eight taxa. A predominant feature was observed, i.e., most of the CMA(+) binding sites were in the terminal region of the short arm of some chromosomes while DAPI(+) binding sites were found mostly in the intercalary region of the chromosomes. The higher divergence in the heterochromatin blocks, as revealed by chromomycin A3 (CMA) binding pattern, in a few taxa, viz. Vigna glabrescens, Vigna khandalensis, and Vigna mungo, suggests that the processes of divergent evolution of repetitive sequences in genomic DNA involve a guanine-cytosine (GC)-rich region. On the contrary, Vigna dalzelliana had shown a prominent adenine-thymine (AT)-rich repetitive DNA sequence in terminal regions in the short arm of chromosomes while Vigna umbellata had shown in interstitial regions. The presence of prominent heterochromatic-rich regions, either GC- or AT-rich regions, does facilitate the rate of chromosomal rearrangements leading to restructuring of the karyotypes and thereby helping the species to attempt structural alterations as means of speciation.

Comparative analysis of heterochromatin distribution in wild and cultivated Abelmoschus species based on fluorescent staining methods

A comparative analysis of fluorochrome-binding pattern in nine taxa of Abelmoschus had shown that the type, amount and distribution pattern of heterochromatin were characteristic for each taxa. The fluorescent chromosome-binding sites obtained by chromomycin A3 (CMA) and 4',6-diamidino-2-phenylindole (DAPI) staining in all the nine species showed constitutive heterochromatin CMA(+), DAPI(+) and CMA(+)/DAPI(+). Large amount of heterozygosity was observed with regard to heterochromatin distribution pattern in all the taxa studied. The CMA(+)-binding sites are comparatively less than DAPI(+)-binding sites which is clearly evident as AT-rich regions are more than GC-rich regions in all the nine taxa analysed in Abelmoschus. These CMA(+) and DAPI(+)-binding sites apparently rise with the increased in chromosome numbers of the different species. This pattern of heterochromatin heterogeneity seems to be a general characteristic feature. Therefore, the differential pattern of distribution of GC- and AT-rich sequences might have played an important role in diversification of the genus Abelmoschus. Polyploidy is an important factor in the evolution of Abelmoschus and the sole reason for range in chromosome numbers in this genus. It may be noted that, though often, but not always, the increase of DNA is caused by an increase in the amount of heterochromatin, i.e. increase of non-coding sections indicating restructuring of the heterochromatin. Thus, cumulative small and direct numerical changes might have played a role in the speciation of Abelmoschus.

Karyotype structure and chromosome fragility in the grass Phleum echinatum Host

Phleum echinatum Host (2n = 2x = 10) is an annual Mediterranean species which differs from other representatives of the genus Phleum by reduced chromosome number, asymmetric karyotype and unusually high amount of DNA in the genome. Chromosomes of this plant were studied using conventional acetic-orcein staining and fluorescence in situ hybridization (FISH). FISH showed the major 35S ribosomal DNA (rDNA) site at the secondary constriction of satellite chromosome (3) and the minor 35S rDNA site near 5S rDNA cluster in the monobrachial chromosome 5. Telomeric repeats were detected at all chromosome ends within secondary constriction in satellited chromosome 3 and at the centromeric regions of chromosomes 1 and 2. Intrachromosomally located telomeric repeats are probably traces of chromosomal rearrangements that have shaped P.echinatum genome; they were prone to breakage which was manifested in chromosome fragmentation. The most distinct telomeric signals, suggesting massive amplification of interstitial telomeric sequences (ITRs), were observed at the nucleolar organizer region (NOR) of the third chromosome pair. Double FISH confirmed co-localization of telomeric and 35S rDNA repeats in this locus characterized by the biggest fragility in the karyotype. Fragile sites of P.echinatum, composed of amplified telomeric repeats, may bear a resemblance to metazoan rare fragile sites enriched in microsatellite repeats.

Chiasmatic and achiasmatic inverted meiosis of plants with holocentric chromosomes

Meiosis is a specialized cell division in sexually reproducing organisms before gamete formation. Following DNA replication, the canonical sequence in species with monocentric chromosomes is characterized by reductional segregation of homologous chromosomes during the first and equational segregation of sister chromatids during the second meiotic division. Species with holocentric chromosomes employ specific adaptations to ensure regular disjunction during meiosis. Here we present the analysis of two closely related plant species with holocentric chromosomes that display an inversion of the canonical meiotic sequence, with the equational division preceding the reductional. In-depth analysis of the meiotic divisions of Rhynchospora pubera and R. tenuis reveals that during meiosis I sister chromatids are bi-oriented, display amphitelic attachment to the spindle and are subsequently separated. During prophase II, chromatids are connected by thin chromatin threads that appear instrumental for the regular disjunction of homologous non-sister chromatids in meiosis II.

The absence of a defined centromere in organisms with holocentric chromosomes presents particular problems for the control of chromosome segregation during meiosis. Cabral et al. present evidence that two plant species overcome this challenge by inverting the conventional sequence of meiotic divisions.

Molecular organization of the 25S-18S rDNA IGS of Fagus sylvatica and Quercus suber: a comparative analysis

The 35S ribosomal DNA (rDNA) units, repeated in tandem at one or more chromosomal loci, are separated by an intergenic spacer (IGS) containing functional elements involved in the regulation of transcription of downstream rRNA genes. In the present work, we have compared the IGS molecular organizations in two divergent species of Fagaceae, Fagus sylvatica and Quercus suber, aiming to comprehend the evolution of the IGS sequences within the family. Self- and cross-hybridization FISH was done on representative species of the Fagaceae. The IGS length variability and the methylation level of 18 and 25S rRNA genes were assessed in representatives of three genera of this family: Fagus, Quercus and Castanea. The intergenic spacers in Beech and Cork Oak showed similar overall organizations comprising putative functional elements needed for rRNA gene activity and containing a non-transcribed spacer (NTS), a promoter region, and a 5′-external transcribed spacer. In the NTS: the sub-repeats structure in Beech is more organized than in Cork Oak, sharing some short motifs which results in the lowest sequence similarity of the entire IGS; the AT-rich region differed in both spacers by a GC-rich block inserted in Cork Oak. The 5′-ETS is the region with the higher similarity, having nonetheless different lengths. FISH with the NTS-5′-ETS revealed fainter signals in cross-hybridization in agreement with the divergence between genera. The diversity of IGS lengths revealed variants from ∼2 kb in Fagus, and Quercus up to 5.3 kb in Castanea, and a lack of correlation between the number of variants and the number of rDNA loci in several species. Methylation of 25S Bam HI site was confirmed in all species and detected for the first time in the 18S of Q. suber and Q. faginea. These results provide important clues for the evolutionary trends of the rDNA 25S-18S IGS in the Fagaceae family.

Intraspecific chromosomal and genetic polymorphism in Brassica napus L. detected by cytogenetic and molecular markers

The application of DNA intercalator 9-aminoacridine allowed us to increase the resolution of chromosome C-banding and DAPI-banding patterns and to investigate chromosomal polymorphism in karyotypes of seven spring and six winter rape varieties. It was shown that the pericentromeric and intercalary C-bands of most of the chromosomes in spring rape were smaller in size and less polymorphic than those of winter rape. More 26S and 5S rDNA sites were found in the winter rape karyotypes than the spring varieties. Separate or colocalized 26S and 5S rDNA sites were revealed on chromosomes 4, 5, 6, 8, 10, 14, 15, 16 and 18. Intervarietal and intravarietal polymorphism of the number and chromosomal localization of rDNA sites were detected. The generalized idiogram of chromosomes of 13 Brassica napus varieties with account of all possibilities of C-banding patterns as well as localization of 26S and 5S rDNA sites were constructed. Polymorphism of the examined molecular and cytogenetic markers as well as the heterozygosis level of FAE1.1 gene controlling erucic acid synthesis in rapeseed was higher in the winter varieties than in the spring ones. The obtained data were in a atisfactory agreement with increased tolerance to environmental stress conditions of winter rape.

Karyotype evolution and phylogenetic analyses in the genus Cardiospermum L. (Paullinieae, Sapindaceae)

Cardiospermum L. belongs to the Paullinieae tribe (Sapindaceae) and comprises 16 species. Of these, 12 species are present in South America and all occur in Brazil. Cardiospermum shows the most variable chromosome number of the tribe. Phylogenetic relationships within the genus Cardiospermum, especially with other species of the tribe, are poorly understood. This research focuses on characterisation of the karyotypic features of Cardiospermum using conventional cytogenetic methods, CMA/DAPI chromosome banding and fluorescence in situ hybridisation (FISH). To elucidate the phylogeny of the genus, the nuclear markers ITS1 and ITS2 were sequenced and analysed using maximum parsimony and Bayesian inference. Cardiospermum shows important diversity in basic numbers, with x = 7, 9, 10, 11 and 12. All species studied have metacentric and submetacentric chromosomes, some species have subtelocentric chromosomes, while telocentric chromosomes are absent. The interphase nuclei differentiate the Cardiospermum species into two groups. The CMA(3) /DAPI chromosome banding revealed the presence of an AT-rich terminal region in C. corindum, C. grandiflorum and C. urvilleoides, whereas GC-rich regions were found in C. grandiflorum, C. halicacabum var. halicacabum, C. halicacabum var. microcarpum, C. heringeri and C. integerrimum. FISH revealed syntenic and non-syntenic distribution of the 18-5.8-26S and 5S rDNA. The syntenic distribution always occurred in the short arms of the same chromosome in all of the species. The phylogenetic relationships reveal, in part, the taxonomic arrangement of the genus Cardiospermum.