Comparative cytogenetics of three economically important Piper L. species from the Brazilian Amazon

The species Piper hispidinervum, Piper aduncum, and Piper affinis hispidinervum have essential oils with high levels of safrole, dillapiole, and sarisan, respectively. Safrole is important for pharmaceutical and chemical industries, while dillapiole and sarisan are promising compounds to control insects and fungi. These species are very similar morphologically and their taxonomy is controversial. Divergent hypotheses consider P. aduncum and P. hispidinervum either as a single species or as distinct taxa, while P. affinis hispidinervum is inferred to be a natural hybrid or a chemotype of P. hispidinervum. Delimiting the taxonomic boundaries would be helpful for germplasm conservation and breeding programs. This study aimed to undertake a detailed analysis of P. aduncum, P. hispidinervum, and P. affinis hispidinervum karyotype and rDNA sites. Genomic in situ hybridization (GISH) was used to establish genomic homology among species and to test the natural hybridization hypothesis for origin of P. affinis hispidinervum. Karyotype traits were similar for all three species: 2n = 26 small chromosomes, predominantly metacentric. All three species exhibited CMA+ bands on the secondary constriction of chromosome pair 4. A size-heteromorphic 35S rDNA site was co-localized with the CMA+ band. A 5S rDNA site was located in the proximal region of chromosome pair 7. The patterns of genomic hybridization revealed that the repetitive DNA fraction of the species is highly similar in terms of proportion of genome, sequence type, and distribution. Our findings did not allow us to differentiate the three species and point to the importance of deeper genomic studies to elucidate the taxonomic controversy.

     

Abnormalities induced by agricultural pesticides in the microsporogenesis of olive tree (Olea europaea L.) cultivars

The study evaluated the microsporogenesis of olive trees subjected to different agricultural pesticide applications during flowering. Inflorescences of cultivars Arbequina and MGS GRAP541 were subjected to agricultural pesticides: mineral oil, neem oil, dimethoate and deltamethrin. The floral buds were fixed in Carnoy for the microsporogenesis analysis and in Karnovsky for scanning electron microscopy. The slides were prepared by squash technique and staining with propionic carmine. The pollen viability was determined by Alexander’s stain and in vitro germination. Results show that the quantification of abnormalities in meiosis in the two cultivars caused significant effect among the treatments, being that all differed statistically from the control group. Both methods showed a higher percentage of viable pollens in the control treatment and lower percentage of viability with the agricultural pesticides. The method of pollen viability by staining presented the highest averages of viable pollens, but when compared together, both methods presented a strongly related positive linear correlation. It was concluded that the used chemical products increased the percentage of chromosomal abnormalities during microsporogenesis, which interfered in the pollen viability of the two analyzed cultivars. The product deltamethrin caused the strongest effect on meiosis and on pollen viability.     

Meiotic irregularities in diploid and tetraploid plants of <Emphasis Type="Italic">Lolium multiflorum</Emphasis> Lam.

The genus Lolium comprises several species of economical importance in temperate countries, mostly due to their high nutritional value and adaptability to cold environments, including southern regions of Brazil. Recently, several diploid cultivars and populations, as well as synthetic tetraploid cultivars have been explored. In order to viabilize or to direct crossings, it is important that the accessions present regular meiosis, thus, producing viable pollen grains. In this way, this study aimed at investigating the meiosis of nine accessions of Lolium multiflorum used in breeding programs, seeking to evaluate its viability in future crossings. The meiosis of diploid plants (2n?=?2×?=?14) is more regular than the artificially tetraploidized genotypes (2n?=?4×?=?28). In the tetraploids, univalent, bivalent, and multivalent configurations were observed. The irregularities were associated to mixoploidy, irregular segregation of chromosomes, spindle disorders, asynchrony, micronuclei, and cellular fusion and formation of syncyte. The abnormalities affected the meiotic index of tetraploid cultivars, characterizing them as unstable. Nevertheless, both diploid and tetraploid genotypes are considered able to participate in crossings because, although there are abnormalities, they do not occur at levels that could affect the production of viable pollen grains.     

Epigenetic Marks Associated to the Study of Nucleolar Dominance in Urochloa P. Beauv.

The genus Urochloa P. Beauv. presents a prominent role in the tropical agricultural scenario being composed of species with different ploidy levels. Studies on the genomic relationship within this genus as well as specific analysis involving epigenetic marks are limited. The aim of the present study was to identify the cytosine methylation (5-mCyt) and histone H3 lysine 9 dimethylation (H3k9me2) in the different modulations of 45S ribosomal DNA (rDNA) sites in interphase nuclei and to associate these results with gene expression analysis in Urochloa ruziziensis (2n = 4x = 36), Urochloa brizantha cv. Marandu (2n = 4x = 36), and their respective interspecific hybrid H1863 (2n = 4x = 36). Immunolocalization techniques were performed in combination with Fluorescence in situ hybridization (FISH) for the location of the 45S rDNA sites. Predominantly, we observed intra- and perinucleolar sites, mostly hypomethylated and/or hyper/hypomethylated, decondensed or partially condensed. The gene expression analysis was performed qualitatively through the conventional PCR using complementary DNA and confirmed by the RT-qPCR technique and primers designed for the ITS-1 region of U. brizantha and U. ruziziensis. The molecular analyses performed on leaves showed that there is dominance of U. brizantha 45S rDNA gene expression on U. ruziziensis in the H1863 hybrid. In roots, the analyses showed that the 45S rDNA genes of the two parents are expressed in the hybrid genome. Thus, it is plausible to infer a tissue-specific nuclear dominance model in which the pattern of hypermethylated cytosine sites with heterochromatic marks and, therefore, silenced were mostly inherited from U. ruziziensis, whereas the rDNA originated from U. brizantha was characterized by cytosine and H3k9 hypomethylation.

     

Heterochromatin Bands and rDNA Sites Evolution in Polyploidization Events in Cynodon Rich. (Poaceae)

Plant Molecular Biology Reporter - Cynodon is a genus with a wide distribution in tropical and subtropical areas. Ploidy levels in Cynodon range from diploid to hexaploid; hence, polyploidy is the...     

Fragile sites of 45S rDNA of <Emphasis Type="Italic">Lolium multiflorum</Emphasis> are not hotspots for chromosomal breakages induced by X-ray

Sites of 45S rDNA of Lolium are regions denominated fragile sites (FSs), constituting regions slightly stained with DAPI due to increased DNA unpacking in metaphasic chromosomes. Considered to be fragile regions in the genome, the FSs might be more responsive to induced breaks and result in chromosomal fragments and rearrangements, unless repairing mechanisms such as recombination or de novo telomere formation play a role at the break site of the DNA. Thus, this study aimed at investigating if SFs from Lolium are hotspots for the occurrence of breakages induced by X-ray and if they are regions favorable to synthesize new telomeres, using Hordeum vulgare as a comparative model. Lolium multiflorum and H. vulgare seedlings were irradiated with 20 and 50 Gy X-ray and evaluated one day following the irradiation and at 7-days intervals for a 28-days period, using FISH technique with 45S rDNA and Arabidopsis-type telomere probes in order to investigate the presence of chromosomal breakages and new telomere formation. H. vulgare did not survive after a few days of irradiation due to the increased rate of abnormalities. L. multiflorum also exhibited chromosomal abnormalities following the exposure, yet over the 28-days trial it had a decrease in the chromosomal damage rate and formation of de novo telomere has not been detected along this time. Despite being considered to be fragile regions in the genome, the 45S rDNA sites of Lolium are not hotspots to chromosomal breakages after the induction of breakages.