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S Abbo

Publications and source records attributed to S Abbo.

18 recordsLinked to original sources
PubMed2005

Quantitative trait loci governing carotenoid concentration and weight in seeds of chickpea (Cicer arietinum L.).

Chickpea is a staple protein source in many Asian and Middle Eastern countries. The seeds contain carotenoids such as beta-carotene, cryptoxanthin, lutein and zeaxanthin in amounts above the engineered beta-carotene-containing "golden rice" level. Thus, breeding for high carotenoid concentration in seeds is of nutritional, socio-economic, and economic importance. To study the genetics governing seed carotenoids in chickpea, we studied the relationship between seed weight and concentrations of beta-carotene and lutein by means of high-performance liquid chromatography in segregating progeny from a cross between an Israeli cultivar and wild Cicer reticulatum Ladiz. Seeds of the cross progeny varied with respect to their carotenoid concentration (heritability estimates ranged from 0.5 to 0.9), and a negative genetic correlation was found between mean seed weight and carotenoid concentration in the F(3). To determine the loci responsible for the genetic variation observed, the population was genotyped using 91 sequence tagged microsatellite site markers and two CytP450 markers to generate a genetic map consisting of nine linkage groups and a total length of 344.6 cM. Using quantitative data collected for beta-carotene and lutein concentration and seed weight of the seeds of the F(2) population, we were able to identify quantitative trait loci (QTLs) by interval mapping. At a LOD score of 2, four QTLs for beta-carotene concentration, a single QTL for lutein concentration and three QTLs for seed weight were detected. The results of this investigation may assist in improving the nutritional quality of chickpea.

Carotenoids↗
PubMed2004

Cytogenetics of semi-fertile triploid and aneuploid intergeneric vine cacti hybrids.

Crosses between the diploid Hylocereus polyrhizus, as the female parent, and the tetraploid Selenicereus megalanthus, as the male parent, yielded triploid and aneuploid hybrids. The fruits of these hybrids combined the attractive appearance of Hylocereus fruits with the delicious taste of S. megalanthus fruits. The aim of this work was to assess the fertility and breeding potential of the triploid and aneuploid hybrids with a view to developing an improved vine cactus crop. Pollen mother cells at metaphase I revealed univalents, bivalents, trivalents, and occasionally quadrivalents. Chromosome distribution at anaphase I revealed different classes of chromosome segregation as well as lagging chromosomes. At metaphase II, parallel and tripolar spindles were observed. The occurrence of triads was frequent, whereas dyads were rarely observed. Pollen stainability varied among the clones studied ranging from 9.8% to 18.6%. The diameters of the stained pollen grains varied widely, probably as a result of the number of chromosomes. Despite the allotriploid origin of our hybrids, functional female and male gametes were produced in considerable proportions, most likely as a result of balanced chromosome segregation. The triploid and aneuploid clones studied yielded viable seeds whose number per fruit was strongly dependent on the pollen donor.

Breeding↗
PubMed2004

Construction of BAC and BIBAC libraries and their applications for generation of SSR markers for genome analysis of chickpea, Cicer arietinum L.

Large-insert bacterial artificial chromosome (BAC) libraries, plant-transformation-competent binary BAC (BIBAC) libraries, and simple sequence repeat (SSR) markers are essential for many aspects of genomics research. We constructed a BAC library and a BIBAC library from the nuclear DNA of chickpea, Cicer arietinum L., cv. Hadas, partially digested with HindIII and BamHI, respectively. The BAC library has 14,976 clones, with an average insert size of 121 kb, and the BIBAC library consists of 23,040 clones, with an average insert size of 145 kb. The combined libraries collectively cover ca. 7.0 x genomes of chickpea. We screened the BAC library with eight synthetic SSR oligos, (GA)10, (GAA)7, (AT)10, (TAA)7, (TGA)7, (CA)10, (CAA)7, and (CCA)7. Positive BACs were selected, subcloned, and sequenced for SSR marker development. Two hundred and thirty-three new chickpea SSR markers were developed and characterized by PCR, using chickpea DNA as template. These results have demonstrated that BACs are an excellent source for SSR marker development in chickpea. We also estimated the distribution of the SSR loci in the chickpea genome. The SSR motifs (TAA)n and (GA)n were much more abundant than the others, and the distribution of the SSR loci appeared non-random. The BAC and BIBAC libraries and new SSR markers will provide valuable resources for chickpea genomics research and breeding (the libraries and their filters are available to the public at http://hbz.tamu.edu).

Base Sequence↗
PubMed2000

A new hyperrecombinogenic mutant of Nicotiana tabacum.

We have isolated a hyperrecombinogenic Nicotiana tabacum mutant. The mutation, Hyrec, is dominant and segregates in a Mendelian fashion. In the mutant, the level of mitotic recombination between homologous chromosomes is increased by more than three orders of magnitude. Recombination between extrachromosomal substrates is increased six- to ninefold, and intrachromosomal recombination is not affected. Hyrec plants were found to perform non-homologous end joining as efficiently as the wild type, ruling out the possibility that the increase in homologous recombination is due to a defect in end joining. In addition, Hyrec plants show significant resistance to gamma-irradiation, whereas UV resistance is not different from the wild type. This suggests that homologous recombination can be strongly up-regulated in plants. Moreover, Hyrec constitutes a novel type of mutation: no similar mutant was reported in plants and hyperrecombinogenic mutants from other organisms usually show sensitivity to DNA damaging agents. We discuss the insight that this mutant provides into understanding the mechanisms of recombination plus the potential application for gene targeting in plants.

DNA Damage↗
PubMed2000

Cytology and mating systems in the climbing cacti Hylocereus and Selenicereus.

Chromosome numbers and meiotic behavior are reported for the climbing cacti species Hylocereus undatus, Hylocereus polyrhizus, and Selenicereus megalanthus. The Hylocereus spp. are diploid (2n = 22), while S. megalanthus is a tetraploid (2n = 44). Irregular chromosome disjunction at anaphase I in pollen mother cells of S. megalanthus is probably the major cause of its reduced pollen viability and may contribute to low seed set, low number of viable seeds and, consequently, low fruit mass. A pollination study confirmed self-incompatibility in H. polyrhizus and a weakened incompatibility reaction in H. undatus and S. megalanthus. Major crossability barriers do not exist between the Hylocereus spp. investigated. Reciprocal intergeneric crosses were successful between Hylocereus spp. and S. megalanthus, suggesting that an Hylocereus sp. might be one of the diploid progenitors of the tetraploid S. megalanthus. The implications of the results on cacti nomenclature and systematics are briefly discussed.

Journal Article↗
PubMed1997

Rapid elimination of low-copy DNA sequences in polyploid wheat: a possible mechanism for differentiation of homoeologous chromosomes.

To study genome evolution in allopolyploid plants, we analyzed polyploid wheats and their diploid progenitors for the occurrence of 16 low-copy chromosome- or genome-specific sequences isolated from hexaploid wheat. Based on their occurrence in the diploid species, we classified the sequences into two groups: group I, found in only one of the three diploid progenitors of hexaploid wheat, and group II, found in all three diploid progenitors. The absence of group II sequences from one genome of tetraploid wheat and from two genomes of hexaploid wheat indicates their specific elimination from these genomes at the polyploid level. Analysis of a newly synthesized amphiploid, having a genomic constitution analogous to that of hexaploid wheat, revealed a pattern of sequence elimination similar to the one found in hexaploid wheat. Apparently, speciation through allopolyploidy is accompanied by a rapid, nonrandom elimination of specific, low-copy, probably noncoding DNA sequences at the early stages of allopolyploidization, resulting in further divergence of homoeologous chromosomes (partially homologous chromosomes of different genomes carrying the same order of gene loci). We suggest that such genomic changes may provide the physical basis for the diploid-like meiotic behavior of polyploid wheat.

Chromosomes↗
PubMed1996

Characterization of the calmodulin gene family in wheat: structure, chromosomal location, and evolutionary aspects.

Calmodulin is a ubiquitous transducer of calcium signals in eukaryotes. In diploid plant species, several isoforms of calmodulin have been described. Here, we report on the isolation and characterization of calmodulin cDNAs corresponding to 10 genes from hexaploid (bread) wheat (Triticum aestivum). These genes encode three distinct calmodulin isoforms; one isoform is novel in that it lacks a conserved calcium binding site. Based on their nucleotide sequences, the 10 cDNAs were classified into four subfamilies. Using subfamily-specific DNA probes, calmodulin genes were identified and the chromosomal location of each subfamily was determined by Southern analysis of selected aneuploid lines. The data suggest that hexaploid wheat possesses at least 13 calmodulin-related genes. Subfamilies 1 and 2 were both localized to the short arms of homoeologous-group 3 chromosomes; subfamily 2 is located on all three homoeologous short arms (3AS, 3BS and 3DS), whereas subfamily 1 is located only on 3AS and 3BS but not on 3DS. Further analysis revealed that Aegilops tauschii, the presumed diploid donor of the D-genome of hexaploid wheat, lacks a subfamily-1 calmodulin gene homologue, whereas diploid species related to the progenitors of the A and B genomes do contain such genes. Subfamily 3 was localized to the short arm of homoeologous chromosomes 2A, 2B and 2D, and subfamily 4 was mapped to the proximal regions of 4AS, 4BL and 4DL. These findings suggest that the calmodulin genes within each subfamily in hexaploid wheat represent homoeoallelic loci. Furthermore, they also suggest that calmodulin genes diversified into subfamilies before speciation of Triticum and Aegilops diploid species.

Amino Acid Sequence↗
PubMed1996

Isolation of two differentially expressed wheat ACC synthase cDNAs and the characterization of one of their genes with root-predominant expression.

Two partial 1-aminocyclopropane-1-carboxylic acid (ACC) synthase cDNA clones (pWAS1, 1089 bp; and pWAS3, 779 bp) were isolated by polymerase chain reaction (PCR) using cDNA to total mRNA purified from etiolated wheat seedlings as template and degenerate oligonucleotides synthesized based on the regions of the ACC synthase amino acid sequence that are highly conserved among different plants. Northern analysis showed that the expression of the corresponding genes are differentially regulated. While the transcripts of pWAS1 were found in all the tissues of wheat that were tested with a maximum level at the early stages of spike development, pWAS3 mRNA was present almost exclusively in the root. A 5590 bp genomic clone, TA-ACS2, corresponding to pWAS3 cDNA has been isolated. The TA-ACS2 sequence consists of a 589-bp 5'-upstream region, 2743 bp of transcribed region with four exons and three introns and a 3'-downstream region of 2257 bp. Expression in Escherichia coli confirmed the ACC synthase activity of TA-ACS2 polypeptide. Sequence comparisons show that the two wheat ACC synthases are more similar to each other and to the rice ACC synthase, OS-ACS1, at the nucleotide level than at the amino acid level. The amino acid sequence of TA-ACS2 is most similar (66.1% identity) to that of broccoli. The chromosomal location of both wheat ACC synthase genes have been determined by aneuploid analysis. TA-ACS1 is located on the short arm of chromosomes 7A and 7D and on the long arm of chromosome 4A. TA-ACS2 is located on the long arm of homoeologous group 2 chromosomes.

Amino Acid Sequence↗
PubMed1995

Organization of retro-element and stem-loop repeat families in the genomes and nuclei of cereals.

Sequences homologous to the retro-element BIS-1 and the stem-loop repeat Hi-10 are present in the genomes of a number of cereal species. A detailed characterization of these elements indicated that they are non-randomly organized in the genomes of at least two of these species, namely barley and rye. In contrast to the BIS-1 retro-elements, the stem-loop repeats are also non-randomly organized into discrete domains in interphase nuclei from barley and rye. Features of the organization of these repeats along chromosomes and within interphase nuclei of rye, barley and rice are discussed.

Base Sequence↗
PubMed1994

Chromosome painting in plants: in situ hybridization with a DNA probe from a specific microdissected chromosome arm of common wheat.

We report here on the successful painting of a specific plant chromosome within its own genome. Isochromosomes for the long arm of chromosome 5 of the wheat B genome (5BL) were microdissected from first meiotic metaphase spreads of a monoisosomic 5BL line of the common wheat Triticum aestivum cv. Chinese Spring. The dissected isochromosomes were amplified by degenerate oligonucleotide-primed PCR in a single tube reaction. The amplified DNA was used as a complex probe mixture for fluorescent in situ hybridization on first meiotic metaphase spreads of lines carrying 5BL as a distinctive marker. Hybridization signals were observed, specifically, along the entire 5BL. In some of the cells, labeling was also detected in two bivalents, presumably those of the 5B "homoeologues" (partial homologues) found in common wheat (5A and 5D). The probe also revealed discrete domains in tapetal nuclei at interphase, further supporting the probe's high specificity. These data suggest that chromosome and homoeologous group-specific sequences are more abundant in 5BL than genome-specific sequences. Chromosome-painting probes, such as the one described here for 5BL, can facilitate the study of chromosome evolution in polyploid wheat.

Base Sequence↗
PubMed1994

A family of related sequences associated with (TTTAGGG)n repeats are located in the interstitial regions of wheat chromosomes.

A family of related sequences associated with (TTTAGGG)n repeats has been cloned from the wheat cultivar Chinese Spring. These sequences reveal a high level of polymorphism between wheat varieties when used as restriction fragment length polymorphism (RFLP) probes. Although this family of sequences contains motifs homologous to the repeats in the telomeres of wheat, they are located at interstitial sites on wheat chromosomes.

Blotting, Southern↗
PubMed1993

Primer-mediated in situ detection of the B-hordein gene cluster on barley chromosome 1H.

In situ hybridization methods allow the detection of specific DNA sequences on whole chromosomes. The technique has been widely used as a diagnostic and research tool by animal cytogeneticists, for whom detection of unique sequences on mammalian chromosomes is routinely achieved. However, detection of unique sequences on plant chromosomes is less reliable. The recently developed primer-induced in situ hybridization (PRINS) technique allows rapid and reliable in situ detection by the hybridization of primers to denatured target DNA, followed by extension with DNA polymerase in the presence of a labeled nucleotide. The use of short oligonucleotide primers could allow improved penetration of debris and highly condensed chromatin common in preparations of plant chromosomes, thus increasing the sensitivity of in situ detection. The feasibility of this approach is demonstrated by the oligonucleotide primer-mediated detection of the B-hordein gene cluster on a barley chromosome. Applications of the PRINS technique for plant cytogeneticists are discussed.

Journal Article↗
PubMed1993

Key features of cereal genome organization as revealed by the use of cytosine methylation-sensitive restriction endonucleases.

Unlike mammalian genomes, cereal (Gramineae) genomes exhibit little suppression of CpG dinucleotides. In cereal genomes, however, most of the numerous potential recognition sites for CpG methylation-sensitive restriction enzymes are methylated. Analysis of cereal genomic libraries and of regions flanking genes indicates that unmethylated NotI sites are useful landmarks for regions containing genes/single-copy sequences. Studies of a rye chromosome arm indicate that its pericentromeric region has a reduced density of unmethylated NotI (and MluI) sites and therefore of genes. Unmethylated MluI and NruI sites are distributed nonrandomly in the genomes of wheat, barley, and rice. Analysis of the genomic blocks defined by these sites in wheat and barley indicates that they are most likely to have arisen by amplification. These observations form the basis of a proposed model for the organization and evolution of the wheat, barley, and rice genomes.

Bacterial Proteins↗
PubMedDate not supplied

Chromosome doubling in vine cacti hybrids.

We performed reciprocal crosses between the tetraploid Selenicereus megalanthus and the diploid Hylocereus species, H. undatus and H. polyrhizus. S. megalanthus x H. undatus gave rise to viable hexaploids and 6x-aneuploid hybrids rather than to the expected triploids. No genuine hybrids were obtained in the reciprocal cross. The pollen diameter of the tetraploid S. megalanthus varied widely, indicating the occurrence of unreduced gametes, while that of H. undatus pollen was very uniform, indicating an extremely low frequency of unreduced gametes. This finding suggests that the hexaploids were formed by chromosome doubling after the formation of the hybrid triploid zygote rather than by fusion of unreduced gametes of the two species.

Cactaceae↗