The Chromosome Number and rDNA Loci Evolution in Onobrychis (Fabaceae).

The evolution of chromosome number and ribosomal DNA (rDNA) loci number and localisation were studied in Onobrychis Mill. Diploid and tetraploid species, as well as two basic chromosome numbers, x = 7 and x = 8, were observed among analysed taxa. The chromosomal distribution of rDNA loci was presented here for the first time using fluorescence in situ hybridisation (FISH) with 5S and 35S rDNA probes. Onobrychis species showed a high polymorphism in the number and localisation of rDNA loci among diploids, whereas the rDNA loci pattern was very similar in polyploids. Phylogenetic relationships among the species, inferred from nrITS sequences, were used as a framework to reconstruct the patterns of basic chromosome number and rDNA loci evolution. Analysis of the evolution of the basic chromosome numbers allowed the inference of x = 8 as the ancestral number and the descending dysploidy and polyploidisation as the major mechanisms of the chromosome number evolution. Analyses of chromosomal patterns of rRNA gene loci in a phylogenetic context resulted in the reconstruction of one locus of 5S rDNA and one locus of 35S rDNA in the interstitial chromosomal position as the ancestral state in this genus.

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

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

Descending Dysploidy and Bidirectional Changes in Genome Size Accompanied Crepis (Asteraceae) Evolution.

The evolution of the karyotype and genome size was examined in species of Crepis sensu lato. The phylogenetic relationships, inferred from the plastid and nrITS DNA sequences, were used as a framework to infer the patterns of karyotype evolution. Five different base chromosome numbers (x = 3, 4, 5, 6, and 11) were observed. A phylogenetic analysis of the evolution of the chromosome numbers allowed the inference of x = 6 as the ancestral state and the descending dysploidy as the major direction of the chromosome base number evolution. The derived base chromosome numbers (x = 5, 4, and 3) were found to have originated independently and recurrently in the different lineages of the genus. A few independent events of increases in karyotype asymmetry were inferred to have accompanied the karyotype evolution in Crepis. The genome sizes of 33 Crepis species differed seven-fold and the ancestral genome size was reconstructed to be 1C = 3.44 pg. Both decreases and increases in the genome size were inferred to have occurred within and between the lineages. The data suggest that, in addition to dysploidy, the amplification/elimination of various repetitive DNAs was likely involved in the genome and taxa differentiation in the genus.

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.

Organization and evolution of two repetitive sequences, 18-24J and 12-13P, in the genome of Chenopodium (Amaranthaceae).

The abundance and chromosomal organization of two repetitive sequences named 12-13P and 18-24J were analyzed in 24 diploid and nine polyploid species of Chenopodium s.l., with special attention to Chenopodium s.s. Both sequences were predominantly present in species of Chenopodium s.s.; however, differences in the amplification levels were observed among the species. The 12-13P repeat was highly amplified in all of the analyzed Eurasian species, whereas the American diploids showed a marked variation in the amplification levels. The 12-13P repeat contains a tandemly arranged 40 bp minisatellite element forming a large proportion of the genome of Chenopodium (up to 3.5%). FISH revealed its localization to the pericentromeric regions of the chromosomes. The chromosomal distribution of 12-13P delivered additional chromosomal marker for B-genome diploids. The 18-24J repeat showed a dispersed organization in all of the chromosomes of the analyzed diploid species and the Eurasian tetraploids. In the American allotetraploids (C. quinoa, C. berlandieri) and Eurasian allohexaploids (e.g., C. album) very intense hybridization signals of 18-24J were observed only on 18 chromosomes that belong to the B subgenome of these polyploids. Combined cytogenetic and molecular analyses suggests that reorganization of these two repeats accompanied the diversification and speciation of diploid (especially A genome) and polyploid species of Chenopodium s.s.

Molecular and cytogenetic evidence for an allotetraploid origin of Chenopodium quinoa and C. berlandieri (Amaranthaceae).

Most of the cultivated chenopods are polyploids, but their origin and evolutionary history are still poorly understood. Phylogenetic analyses of DNA sequences of four plastid regions, nrITS and nuclear 5S rDNA spacer region (NTS) of two tetraploid chenopods (2n=4x=36), Andean C. quinoa and North American C. berlandieri, and their diploid relatives allowed inferences of their origin. The phylogenetic analyses confirmed allotetraploid origin of both tetraploids involving diploids of two different genomic groups (genomes A and B) and suggested that these two might share very similar parentage. The hypotheses on the origin of the two allopolyploid species were further tested using genomic in situ hybridization (GISH). Several diploid Chenopodium species belonging to the two lineages, genome A and B, suggested by phylogenetic analyses, were tested as putative parental taxa. GISH differentiated two sets of parental chromosomes in both tetraploids and further corroborated their allotetraploid origin. Putative diploid parental taxa have been suggested by GISH for C. quinoa and C. berlandieri. Genome sizes of the analyzed allotetraploids fit nearly perfectly the expected additive values of the putative parental taxa. Directional and uniparental loss of rDNA loci of the maternal A-subgenome was revealed for both C. berlandieri and C. quinoa.

High ploidy diversity and distinct patterns of cytotype distribution in a widespread species of Oxalis in the Greater Cape Floristic Region.

BACKGROUND AND AIMS: Genome duplication is widely acknowledged as a major force in the evolution of angiosperms, although the incidence of polyploidy in different floras may differ dramatically. The Greater Cape Floristic Region of southern Africa is one of the world's biodiversity hotspots and is considered depauperate in polyploids. To test this assumption, ploidy variation was assessed in a widespread member of the largest geophytic genus in the Cape flora: Oxalis obtusa. METHODS: DNA flow cytometry complemented by confirmatory chromosome counts was used to determine ploidy levels in 355 populations of O. obtusa (1014 individuals) across its entire distribution range. Ecological differentiation among cytotypes was tested by comparing sets of vegetation and climatic variables extracted for each locality. KEY RESULTS: Three majority (2x, 4x, 6x) and three minority (3x, 5x, 8x) cytotypes were detected in situ, in addition to a heptaploid individual originating from a botanical garden. While single-cytotype populations predominate, 12 mixed-ploidy populations were also found. The overall pattern of ploidy level distribution is quite complex, but some ecological segregation was observed. Hexaploids are the most common cytotype and prevail in the Fynbos biome. In contrast, tetraploids dominate in the Succulent Karoo biome. Precipitation parameters were identified as the most important climatic variables associated with cytotype distribution. CONCLUSIONS: Although it would be premature to make generalizations regarding the role of genome duplication in the genesis of hyperdiversity of the Cape flora, the substantial and unexpected ploidy diversity in Oxalis obtusa is unparalleled in comparison with any other cytologically known native Cape plant species. The results suggest that ploidy variation in the Greater Cape Floristic Region may be much greater than currently assumed, which, given the documented role of polyploidy in speciation, has direct implications for radiation hypotheses in this biodiversity hotspot.