Pepper (<Emphasis Type="Italic">capsicum annuum</Emphasis> L.) regenerants obtained by direct somatic embryogenesis fail to develop a shoot

Summary Three auxin-type herbicides, namely 2.4-dichlorophenoxyacetic acid (2,4-D), (4-chlorophenoxy)acetic acid 2-(dimethylamino)ethyl ester (centrophenoxine), and quinolinecarboxylic acid (quinclorac) induced direct somatic embryogenesis in seed-derived zygotic embryo explants of sweet pepper (Capsicum annuum L.) when added to Murashige and Skoog medium with 200 mM sucrose. Optimum concentrations for embryogenesis induction were 0.40–0.45 mM and 1.15–1.30 μM for 2.4-D and centrophenoxine, respectively (in the presence of 5.0 gl⁻¹ activated charcoal), or 40 μM for quinclorac (in medium without activated charcoal). Somatic embryos emerged from the epidermal and subepidermal tissues and developed on the surface of the explant. Centrophenoxine- or 2.4-D-mediated embryogenesis was accomplished from 95% of the explants in about 3 wk and, on average, six embryos were formed per explant. Induction efficieney was lower for quinelorac. Centrophenoxine-mediated embryognesis was possible in 10 pepper cultivars, the extent of the reponse-being genotype-dependent. embryos detached from the explant and transplanted onto a growth regulator-free medium germinated; however, the recovered regenerants were without a shoot, and some of them bore a single deformed cotyledon while others had no cotyledons. Regenerants lacking a shoot were generated irrespective of the auxin type applied and across all responsive genotypes investigated. Absence of a shoot, resulting from a failure in the establishment of a normal functioning apical shoot meristem, was the principal developmental disorder that precluded regeneration of normal plants via direct somatic embryogenesis. Since stem cells of the shoot meristem become established in globular and heart-stage embryos, we deduce that the absence of a shoot in germinating embryos could orginate from deviant differentiation at these early stages of embryogeny.     

Coding tandem repeats generate diversity in Aspergillus fumigatus genes

Genes containing multiple coding mini- and microsatellite repeats are highly dynamic components of genomes. Frequent recombination events within these tandem repeats lead to changes in repeat numbers, which in turn alters the amino acid sequence of the corresponding protein. In bacteria and yeasts, the expansion of such coding repeats in cell wall proteins is associated with alterations in immunogenicity, adhesion, and pathogenesis. We hypothesized that identification of repeat-containing putative cell wall proteins in the human pathogen Aspergillus fumigatus may reveal novel pathogenesis-related elements. Here, we report that the genome of A. fumigatus contains as many as 292 genes with internal repeats. Fourteen of 30 selected genes showed size variation of their repeat-containing regions among 11 clinical A. fumigatus isolates. Four of these genes, Afu3g08990, Afu2g05150 (MP-2), Afu4g09600, and Afu6g14090, encode putative cell wall proteins containing a leader sequence and a glycosylphosphatidylinositol anchor motif. All four genes are expressed and produce variable-size mRNA encoding a discrete number of repeat amino acid units. Their expression was altered during development and in response to cell wall-disrupting agents. Deletion of one of these genes, Afu3g08990, resulted in a phenotype characterized by rapid conidial germination and reduced adherence to extracellular matrix suggestive of an alteration in cell wall characteristics. The Afu3g08990 protein was localized to the cell walls of dormant and germinating conidia. Our findings suggest that a subset of the A. fumigatus cell surface proteins may be hypervariable due to recombination events in their internal tandem repeats. This variation may provide the functional diversity in cell surface antigens which allows rapid adaptation to the environment and/or elusion of the host immune system.     

Iron uptake mechanism in the chrysophyte microalga Dinobryon

The mechanism of iron uptake in the chrysophyte microalga Dinobryon was studied. Previous studies have shown that iron is the dominant limiting elements for growth of Dinobryon in the Eshkol reservoir in northern Israel, which control its burst of bloom. It is demonstrated that Dinobryon has a light-stimulated ferrireductase activity, which is sensitive to the photosynthetic electron transport inhibitor DCMU and to the uncoupler CCCP. Iron uptake is also light-dependent, is inhibited by DCMU and by CCCP and also by the ferrous iron chelator BPDS. These results suggest that ferric iron reduction by ferrireductase is involved in iron uptake in Dinobryon and that photosynthesis provides the major reducing power to energize iron acquisition. Iron deprivation does not enhance but rather inhibits iron uptake contrary to observations in other algae.     

Autosegregation of enzyme loci in agamospermous progenies of triploid plants of sugar beet (<Emphasis Type=Italic>Beta vulgaris</Emphasis> L.)

The ratios of the phenotypic classes of glucosephosphate isomerase (GPI2) and malate dehydrogenase (MDH1 and MDH2) were studied in agamospermous progenies of triploid sugar beet plants. The ratio of the phenotypic classes of these enzymes corresponds to the calculations based on the assumption of polyteny of chromosomes carrying alleles of the enzyme loci accompanied by the loss of extra copies of the alleles in the first division of a cell entering embryogenesis. An increase in the gene dosage due to polyteny leads to the appearance in the progeny with a definite frequency of alleles that were absent in the original parental plant. The notions of “meiotic autosegregation” and “mitotic autosegregation” characteristic of meiotic and mitotic agamospermy are introduced, as well as the term locus polygenotype characterizing not only the allelic composition and the number of chromosomes, but also the number of chromatids carrying alleles of the marker locus in the cell before its entry into embryogenesis.     

Aym1, a mouse meiotic gene identified by virtue of its ability to activate early meiotic genes in the yeast Saccharomyces cerevisiae

Our understanding of the molecular mechanisms that operate during differentiation of mitotically dividing spermatogonia cells into spermatocytes lags way behind what is known about other differentiating systems. Given the evolutionary conservation of the meiotic process, we screened for mouse proteins that could specifically activate early meiotic promoters in Saccharomyces cerevisiae yeast cells, when fused to the Gal4 activation domain (Gal4AD). Our screen yielded the Aym1 gene that encodes a short peptide of 45 amino acids. We show that a Gal4AD-AYM1 fusion protein activates expression of reporter genes through the promoters of the early meiosis-specific genes IME2 and HOP1, and that this activation is dependent on the DNA-binding protein Ume6. Aym1 is transcribed predominantly in mouse primary spermatocytes and in gonads of female embryos undergoing the corresponding meiotic divisions. Aym1 immunolocalized to nuclei of primary spermatocytes and oocytes and to specific type A spermatogonia cells, suggesting it might play a role in the processes leading to meiotic competence. The potential functional relationship between AYM1 and yeast proteins that regulate expression of early meiotic genes is discussed.     

Diversity of β-Globin Mutations in Israeli Ethnic Groups Reflects Recent Historic Events

We characterized nearly 500 β-thalassemia genes from the Israeli population representing a variety of ethnic subgroups. We found 28 different mutations in the β-globin gene, including three mutations (β^S, β^C, and β^O-Arab) causing hemoglobinopathies. Marked genetic heterogeneity was observed in both the Arab (20 mutations) and Jewish (17 mutations) populations. On the other hand, two ethnic isolates—Druze and Samaritans—had a single mutation each. Fifteen of the β-thalassemia alleles are Mediterranean in type, 5 originated in Kurdistan, 2 are of Indian origin, and 2 sporadic alleles came from Europe. Only one mutant allele—nonsense codon 37—appears to be indigenous to Israel. While human habitation in Israel dates back to early prehistory, the present-day spectrum of β-globin mutations can be largely explained by migration events that occurred in the past millennium.     

Hubs of knowledge: using the functional link structure in Biozon to mine for biologically significant entities

Background  

Existing biological databases support a variety of queries such as keyword or definition search. However, they do not provide any measure of relevance for the instances reported, and result sets are usually sorted arbitrarily.