Genetic diversity of ribosomal loci (5S and 45S rDNA) and pSc119.2 repetitive DNA sequence among four species of Aegilops (Poaceae) from Algeria

In continuation of our previous research we carried out the karyological investigation of 53 populations of four Aegilops species (A. geniculata, A. triuncialis, A. ventricosa, and A. neglecta) sampled in different eco-geographical habitats in Algeria. The genetic variability of the chromosomal DNA loci of the same collection of Aegilops is highlighted by the Fluorescence In Situ Hybridization technique (FISH) using three probes: 5S rDNA, 45S rDNA, and repetitive DNA (pSc119.2). We found that the two rDNA loci (5S and 45S) hybridized with some chromosomes and showed a large genetic polymorphism within and between the four Aegilops species, while the repetitive DNA sequences (pSc119.2) hybridized with all chromosomes and differentiated the populations of the mountains with a humid bioclimate from the populations of the steppe regions with an arid bioclimate. However, the transposition of the physical maps of the studied loci (5S rDNA, 45S rDNA, and pSc119.2) with those of other collections revealed the existence of new loci in Aegilops from Algeria.

FISH-Based Karyotype Analyses of Four Dracaena Species

The genus <i>Dracaena</i> is the main source of dragon’s blood, which is a plant resin and has been used as traditional medicine since ancient times in different civilizations. However, the chromosome numbers and karyotypes present in this genus remain poorly understood. In this study, fluorescence in situ hybridization (FISH) using oligonucleotide probes for ribosomal DNAs (5S and 45S rDNA) and telomeric repeats (TTTAGGG)₃ was applied to analyze 4 related species: <i>Dracaena terniflora</i> Roxb., <i>Dracaena cambodiana</i> Pierre ex Gagnep., Aizong (<i>Dracaena</i> sp.), and <i>Dracaena cochinchinensis</i> (Lour.) S.C. Chen. In all 4 species, both 5S and 45S rDNA showed hybridization signals in the paracentromeric region of a pair of chromosomes; the sizes of the 45S rDNA signals were larger than those of the 5S rDNA. Importantly, the telomeric repeat signals were located in the telomeric regions of almost all chromosomes. The results indicated that the chromosome number of all 4 <i>Dracaena</i> species is 2n = 40, and the lengths of the mitotic metaphase chromosomes range from 0.99 to 2.98 μm. Our results provide useful cytogenetic information, which will be beneficial to future studies in genome structure of the genus <i>Dracaena</i>.

Phylogenetic study of Ipomoeeae (Convolvulaceae) based on chromosome painting

Background: The phylogenetic relationships for Ipomoeeae species are incongruence in previous studies. Comparative chromosome painting (CCP) can provide valuable information for phylogenetic relationships among species. Results: In this study, 31 Ipomoea species were analyzed by oligo-based chromosome painting (CP) technique to better understand their phylogenetic relationships. The results indicated that the distribution patterns of oligo probes in three species with 28 chromosomes were significantly different from the other species with 30 chromosomes. Therefore, we proposed that the difference of chromosome number should be foremost factor in determining the phylogenetic relationships among species and the previous division of two large clades in Ipomoeeae wasn’t supported. The division of smaller clades within the Astripomoeinae in Ipomoeeae was generally supported with a few exceptions, whereas the division of smaller clades within Argyreiinae wasn’t resolved by our CP results. In addition, species relationship for the species belonging to same smaller clade with same CP pattern was further resolved by physical mapping of the 5S and 45S rDNA using fluorescence in situ hybridization (FISH) technique. Conclusions: This study is the first phylogenetic analysis of Ipomoea species based on CP technique. Our results provide intuitive and reliable resolution of phylogenetic relationships for 31 Ipomoea species and demonstrate the validity of oligo-based CCP analysis in phylogenetic study.

Comparative analysis of rDNA distribution in 29 species of Begonia sect. Coelocentrum Irmsch.

The rDNA sites are useful chromosome landmarks and can provide valuable information for species identification and species relationships. In this study, we investigated the distribution of 5S and 45S rDNA sites in 29 species of Begonia sect. Coelocentrum Irmsch. using a two-colour fluorescence in situ hybridization (FISH) technique. This is the first report of chromosomal rDNA mapping in Begonia species. The analyzed species showed considerable diversity in rDNA distribution patterns. The 45S rDNA signals are always located in terminal regions on 1−4 chromosomes, while 5S rDNA signals are mainly located at proximal regions on 2−8 chromosomes, varying from specific major signals to highly dispersed minor signals. Based on rDNA FISH patterns, most of the investigated species could be distinguished from each other and species relationships were identified. In addition, the results provided clear proof that B. huangii is of hybrid origin and the triploid B. longgangensis was allotriploid rather than autotriploid as suggested before. The data will provide a useful reference for evaluation, conservation and utilization of the natural resources of the mega-diverse genus Begonia.