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Comparative cytogenetic mapping between the lima bean (Phaseolus lunatus L.) and the common bean (P. vulgaris L.)

The common bean (Phaseolus vulgaris) and lima bean (P. lunatus) are among the most important legumes in terms of direct human consumption. The present work establishes a comparative cytogenetic map of P. lunatus, using previously mapped markers from P. vulgaris, in association with analyses of heterochromatin distribution using the fluorochromes chromomycin A3 (CMA) and 4′,6-diamidino-2-phenylindole (DAPI) and localization of the 5S and 45S ribosomal DNA (rDNA) probes. Seven BACs selected from different common bean chromosomes demonstrated a repetitive pericentromeric pattern corresponding to the heterochromatic regions revealed by CMA/DAPI and could not be mapped. The subtelomeric repetitive pattern observed for BAC 63H6 in most of the chromosome ends of common bean was not detected in lima bean, indicating lack of conservation of this subtelomeric repeat. All chromosomes could be identified and 16 single-copy clones were mapped. These results showed a significant conservation of synteny between species, although change in centromere position suggested the occurrence of pericentric inversions on chromosomes 2, 9 and 10. The low number of structural rearrangements reflects the karyotypic stability of the genus.

Genetic similarity among genotypes of sugarcane estimated by SSR and coefficient of parentage

The aim of this study was to analyze the genetic similarity in commercial cultivars of sugarcane from the breeding program cultivars RB (Republic of Brazil), using SSR markers and coefficient of parentage. Eighteen microsatellite markers were used to estimate genetic similarity in 30 genotypes and coefficient of parentage was estimated in 28 accessions. Eighteen primer pairs produced an average of 3.2 alleles, the level of polymorphism (PIC value) ranged from 0.34 to 0.78 in SMC248CG and SCC2 primers, respectively. The parentage coefficient was high among cultivars, with a mean of 0.14, suggesting high relationship among the cultivars. The results here suggest that to analyzed accessions, there is a high genetic similarity which could reduce the genetic gain in breeding. However, crosses among genotypes of sugarcane produce a high variability in the progenies, suggesting a combination between the genomes of species that originated the current cultivars.

Contrasting rDNA Evolution in Lima Bean (Phaseolus lunatus L.) and Common Bean (P. vulgaris L., Fabaceae)

Phaseolus vulgaris has two 5S rDNA sites in chromosomes 6 and 10 and from two up to nine 45S rDNA sites depending on the accession. The presence of three 45S rDNA sites, in chromosomes 6, 9 and 10, is considered the ancestral state for the species. For P. lunatus, only one 5S and one 45S rDNA sites in distinct chromosomes were known. In order to investigate the homeologies among these rDNA-bearing chromosomes and the stability of the rDNA sites in P. lunatus, rDNA and P. vulgaris chromosome-specific probes were hybridized in situ to P. lunatus. The chromosomes bearing the 5S and the 45S rDNA of P. lunatus are homeologous to chromosomes 10 and 6 of P. vulgaris, respectively. In contrast to the common bean, no variation in the number of rDNA loci was detected, except for a duplication of the 5S rDNA in the same chromosome in a small group of cultivars. These results suggest that the 5S rDNA site in chromosome 10 and the 45S rDNA site in chromosome 6 represent the ancestral loci in the genus. The 5S rDNA site in chromosome 10 of P. vulgaris is located in the long arm, while in P. lunatus it is present in the short arm, suggesting the occurrence of a transposition or a pericentric inversion after separation of both lineages.

Karyotype of Araucaria angustifolia and the decondensation/ activation mode of its nucleolus organiser region

The chromosomes of the gymnosperm Araucaria angustifolia (Bertol.) Kuntze were analysed with the fluorochromes chromomycin A3 (CMA) and 4′,6-diamidino-2-phenylindole (DAPI) and with C-banding. This species contains a diploid complement made of 26 chromosomes, with 18 larger metacentric, four smaller metacentric and four submetacentric chromosomes. The only CMA+/DAPI– region observed corresponded to the nucleolus organiser region (NOR) localised at the proximal portion of a large metacentric chromosome pair. C-banding marked the NOR as well as a terminal region of another chromosome pair. In addition, small C-bands were occasionally seen interspersed in many chromosomes. The NOR appeared to condense at approximately the same rate as the rest of the chromosome from prophase throughout metaphase. In interphase nuclei, NOR decondensation and activation was characterised by the formation of CMA+ blocks that resembled a string of beads inside the nucleolus. The number and size of beads was inversely proportional to the size of the nucleolus, suggesting that transcriptional activation of the nucleolar cistrons starts simultaneously at several points of the NOR. The mode of NOR activation in A. angustifolia differs from that observed in most species, providing a unique opportunity to study activation and transcriptional control of rRNA genes.

Genetic variability in populations of sweet corn, common corn and teosinte

The maize (Zea mays L. ssp. mays) has several related species, called teosinte, which are distributed in various subspecies of Zea and other genera. Among the different types of corn, sweet corn shows a great potential for human food. This type was originated from mutations, which increased the amount of polysaccharide in the endosperm. In Brazil there are populations of sweet corn, common maize and teosinte, however, little is known about their genetic variability. Hence, the aim of this present paper was to analyze the genetic variability in two populations of sweet corn (BR 400 and BR 402), two common corn (Pampa and Suwan) and teosinte, using microsatellite markers. The results showed a low intra-population genetic variability in populations of maize, and high variability for the population of teosinte, suggesting that the maize populations may have limitations in future cycles of breeding.

Genetic variability in maize and teosinte populations estimated by microsatellites markers

Wild species are important sources of genetic variability and may be exploited by breeding programs. Crosses between teosinte and maize occur freely and teosinte serves as genetic source of agronomic traits for introduction in maize. The objective of this study was to estimate genetic variability among and within maize and teosinte populations (Zea mays mexicana). Two sweet maize populations (BR400 and BR402), two common maize populations (Suwan and Pampa) and one teosinte population were analyzed using microsatellites markers. Results indicated that 64,5% of the variation was detected within the populations, suggesting the possibility of obtaining genetic progress by selection within each population. The analysis with 25 microsatellites loci enabled the identification of 92 alleles with a mean of 3.7 alleles per locus. The average Polymorphism Information Content (PIC) was 0.52. The percentage of polymorphic loci varied from 64% in the BR400 and Pampa populations to 80% in the teosinte population. The estimated genetic distance confirmed the genomic similarity of maize and teosinte.

Expression profiles of sugarcane under drought conditions: Variation in gene regulation

Abstract Drought is a major factor in decreased sugarcane productivity because of the resulting morphophysiological effects that it causes. Gene expression studies that have examined the influence of water stress in sugarcane have yielded divergent results, indicating the absence of a fixed pattern of changes in gene expression. In this work, we investigated the expression profiles of 12 genes in the leaves of a drought-tolerant genotype (RB72910) of sugarcane and compared the results with those of other studies. The genotype was subjected to 80–100% water availability (control condition) and 0–20% water availability (simulated drought). To analyze the physiological status, the SPAD index, Fv/Fm ratio, net photosynthesis (A), stomatal conductance (g s) and stomatal transpiration (E) were measured. Total RNA was extracted from leaves and the expression of SAMDC, ZmPIP2-1 protein, ZmTIP4-2 protein, WIP protein, LTP protein, histone H3, DNAj, ferredoxin I, β-tubulin, photosystem I, gene 1 and gene 2 was analyzed by quantitative real-time PCR (RT-PCR). Important differences in the expression profiles of these genes were observed when compared with other genotypes, suggesting that complex defense mechanisms are activated in response to water stress. However, there was no recognizable pattern for the changes in expression of the different proteins associated with tolerance to drought stress.

New Polymorphic EST-SSR Markers in Sugarcane

New polymorphic SSR markers in sugarcane has potential usefulness to studies genetic diversity, genetic mapping, DNA fingerprinting and determination offspring as true hybrids, selfing or contaminant in germplasm from breeding program. SSR markers can be obtained in several ways, and the search for SSR-EST sequences an alternative with significant results. The aim of this study was to develop highly polymorphic SSR markers for germplasm studies in sugarcane. Di- tri- and tetra-nucleotide sequences were mined in the TGI bank and 53 EST-SSR markers developed. These markers were analyzed in five genotypes and showed to be highly polymorphic, with the PIC ranging between 0.48 and 0.95 with a mean of 0.86. The discriminatory power ranged from 0.35 to 0.94 with a mean of 0.82 and the genetic similarity was high in the accessions evaluated.

Conservação e germinação in vitro de pólen de milho (Zea mays subsp. mays)

The storage of pollen can be considered an important tool for maize breeding programs, allowing to preserve, under artificial conditions, the viability of male gametes and extend the possibilities of crossings regardless of flowering time of parental varieties. This study aimed to evaluate the culture media for in vitro germination of corn pollen and analyze storage conditions. To examine viability, six different culture media containing sucrose, boric acid, calcium chloride and agar were evaluated. For pollen preservation, two temperatures (4 oC and -20 oC) and two agents of pollen dehydration (silica gel and hydrated calcium chloride) were evaluated. The high values of pollen viability up to 30 days of storage indicate that dehydration in silica gel and storage at 4 oC preserve the viability of corn pollen. The culture medium that provided the highest germination rate in vitro was the composition of 0.7% agar, 17% sucrose, 0.01% boric acid and 0.03% calcium chloride hydrate.

Differential detection of transposable elements between Saccharum species

Cultivars of sugarcane (Saccharum) are hybrids between species S. officinarum (x = 10, 2n = 8x = 80) and S. spontaneum (x = 8, 2n = 5 – 16x = 40 – 128). These accessions have 100 to 130 chromosomes, 80–85% of which are derived from S. officinarum, 10–15% from S. spontaneum, and 5–10% are possible recombinants between the two genomes. The aim of this study was to analyze the repetition of DNA sequences in S. officinarum and S. spontaneum. For this purpose, genomic DNA from S. officinarum was digested with restriction enzymes and the fragments cloned. Sixty-eight fragments, approximately 500 bp, were cloned, sequenced and had their identity analyzed in NCBI, and in the rice, maize, and sorghum genome databases using BLAST. Twelve clones containing partial transposable elements, one single-copy control, one DNA repetitive clone control and two genome controls were analyzed by DNA hybridization on membrane, using genomic probes from S. officinarum and S. spontaneum. The hybridization experiment revealed that six TEs had a similar repetitive DNA pattern in the genomes of S. officinarum and S. spontaneum, while six TEs were more abundant in the genome of S. officinarum. We concluded that the species S. officinarum and S. spontaneum have differential accumulation LTR retrotransposon families, suggesting distinct insertion or modification patterns.