The use of clip cages to restrain insects reduces leaf expansion systemically in Rumex obtusifolius

Abstract. 1. Clip cages have been used widely by experimental ecologists to contain insects on plants.
2. Under controlled conditions, the effect of applying clip cages alone and clip cages and the chrysomelid beetle Gastrophysa viridula on systemic leaf expansion of Rumex obtusifolius was investigated. Treatments were applied to the fully expanded fourth leaf and expansion of leaf 8 was measured over a period of 22 days.
3. The application of clip cages reduced the rate at which leaf area increased and led to reductions in final leaf areas.
4. Clip cages have systemic effects on plant development and these effects are sustained even after the clip cage is removed. Investigators should take this into account in designing experiments.     

Callus,shoot and hairy root formation in vitro as affected by the sensitivity to auxin and ethylene in tomato mutants

We analyzed the impact of ethylene and auxin disturbances on callus, shoots and Agrobacterium rhizogenes-induced hairy root formation in tomato (Solanum lycopersicum L.). The auxin low-sensitivity dgt mutation showed little hairy root initiation, whereas the ethylene low-sensitivity Nr mutation did not differ from the control Micro-Tom cultivar. Micro-Tom and dgt hairy roots containing auxin sensitivity/biosynthesis rol and aux genes formed prominent callus onto media supplemented with cytokinin. Under the same conditions, Nr hairy roots did not form callus. Double mutants combining Rg1, a mutation conferring elevated shoot formation capacity, with either dgt or Nr produced explants that formed shoots with little callus proliferation. The presence of rol + aux genes in Rg1 hairy roots prevented shoot formation. Taken together, the results suggest that although ethylene does not affect hairy root induction, as auxin does, it may be necessary for auxin-induced callus formation in tomato. Moreover, excess auxin prevents shoot formation in Rg1.     

Amelioration of Bacterial Genomes: Rates of Change and Exchange

Although bacterial species display wide variation in their overall GC contents, the genes within a particular species' genome are relatively similar in base composition. As a result, sequences that are novel to a bacterial genome—i.e., DNA introduced through recent horizontal transfer—often bear unusual sequence characteristics and can be distinguished from ancestral DNA. At the time of introgression, horizontally transferred genes reflect the base composition of the donor genome; but, over time, these sequences will ameliorate to reflect the DNA composition of the new genome because the introgressed genes are subject to the same mutational processes affecting all genes in the recipient genome. This process of amelioration is evident in a large group of genes involved in host-cell invasion by enteric bacteria and can be modeled to predict the amount of time required after transfer for foreign DNA to resemble native DNA. Furthermore, models of amelioration can be used to estimate the time of introgression of foreign genes in a chromosome. Applying this approach to a 1.43-megabase continuous sequence, we have calculated that the entire Escherichia coli chromosome contains more than 600 kb of horizontally transferred, protein-coding DNA. Estimates of amelioration times indicate that this DNA has accumulated at a rate of 31 kb per million years, which is on the order of the amount of variant DNA introduced by point mutations. This rate predicts that the E. coli and Salmonella enterica lineages have each gained and lost more than 3 megabases of novel DNA since their divergence. Received: 7 July 1996 / Accepted: 27 September 1996     

A candidate for Lr19, an exotic gene conditioning leaf rust resistance in wheat

Lr19, one of the few widely effective genes conferring resistance to leaf rust in wheat, was transferred from the wild relative Thinopyrum ponticum to durum wheat. Since Lr19 confers a hypersensitive response to the pathogen, it was considered likely that the gene would be a member of the major nucleotide-binding site (NBS)-leucine-rich repeat (LRR) plant R gene family. NBS profiling, based on PCR amplification of conserved NBS motifs, was applied to durum wheat–Th. ponticum recombinant lines involving different segments of the alien 7AgL chromosome arm, carrying or lacking Lr19. Differential PCR products were isolated and sequenced. From one such sequence (AG15), tightly linked to Lr19, a 4,121-bp full-length cDNA was obtained. Its deduced 1,258 amino acid sequence has the characteristic NBS-LRR domains of plant R gene products and includes a coiled-coil (CC) region typical of monocots. The genomic DNA sequence showed the presence of two exons and a short intron upstream of the predicted stop codon. Homology searches revealed considerable identity of AG15 with the cloned wheat resistance gene Pm3a and a lower similarity with wheat Lr1, Lr21, and Lr10. Quantitative PCR on leaf-rust-infected and non-infected Lr19 carriers proved AG15 to be constitutively expressed, as is common for R genes. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Listeria monocytogenes in spontaneous abortions in humans and its detection by multiplex PCR

AIM: To assess the extent of Listeria monocytogenes in causation of human spontaneous abortions by isolation methods and PCR analysis for the presence of virulence-associated genes. METHODS AND RESULTS: A total of 305 samples comprising blood, urine, placental bits, faecal and vaginal swabs were collected from 61 patients with spontaneous abortions. Listeria spp. were isolated from 10 samples collected from nine (14.8%) patients. Confirmation of these isolates was based on biochemical tests, haemolysis on blood agar, CAMP test, phosphatidylinositol-specific phospholipase C (PI-PLC) assay followed by in vivo pathogenicity tests and multiplex PCR to detect virulence-associated genes (prfA, plcA, hlyA, actA and iap). Three isolates were confirmed as L. monocytogenes. Of these, two isolates turned out to be pathogenic and found to posses all five genes. However, the remaining two haemolytic L. monocytogenes isolates lacking the plcA gene and activity in the PI-PLC assay were found to be nonpathogenic by in vivo tests. CONCLUSIONS: The occurrence of pathogenic L. monocytogenes in cases of spontaneous abortions was 3.3%. It seems that the plcA gene and its expression have an important role as essential virulence determinants in pathogenic Listeria spp. SIGNIFICANCE AND IMPACT OF THE STUDY: The recovery of pathogenic L. monocytogenes isolates from cases of spontaneous abortion indicates the significance of listeric infection in pregnant women.     

Gene mapping of 28S and 5S rDNA sites in the spined loach Cobitis taenia (Pisces, Cobitidae) from a diploid population and a diploid–tetraploid population

We compare the chromosomal 28S and 5S rDNA patterns of the spined loach C. taenia (2n = 48) from an exclusively diploid population and from a diploid–polyploid population using 28S and 5S rDNA probe preparation and labelling, and fluorescence in situ hybridization (FISH). The 5S rDNA was located in two to three chromosome pairs, and separated from the 28S loci for the males and one female (F1) from the diploid population. Loaches from a diploid–polyploid population, and one female (F2) from the diploid population were characterized by at least one chromosome pair with 5S and 28S overlapping signals. The fishes differed mainly in their number of 28S rDNA loci, located on 3–6 chromosomes. All individuals from both populations were characterized by one acrocentric chromosome bearing a 28S rDNA signal on the telomeres of its long arm. The number of major ribosomal DNA in the karyotype of C. taenia by FISH was always higher than the number of Ag-NORs. Our data confirm the extensive polymorphism of NORs in both populations, as already has been observed in closely related Cobitis species, and less polymorphic 5S rDNA pattern. However, this preliminary result highlights the need for a wider scale study.     

Polymorphisms in the promoter region of the porcine antiviral MX1 and MX2 genes

The porcine MX1 and MX2 promoters were characterized in this study. Sequencing of the 332-bp MX1 promoter region identified 15 substitutions and insertions at three positions in 21 pigs from 15 breeds, in which nine genotypes were classified. Among the nine genotypes, no statistically significant differences in the promoter activities were observed after interferon (IFN- α 2b) treatment of transiently transfected cells containing constructs with luciferase reporter plasmids. The 341-bp MX2 promoter region contained regulatory sequences for ISRE, GC box, Sp1 and AP-1, as well as a TATA box. Nucleotide sequences of the MX2 promoter region revealed four substitutions and one deletion, in which six genotypes were classified. Among the six genotypes, a statistically significant difference ( P  < 0.05) in MX2 promoter activities after IFN- α 2b treatment was detected in transiently transfected cells.     

Genetic and developmental analyses of chaetae pattern formation in Drosophila tergites

Summary The role of the achaete-scute complex and extramacrochaetae, Notch, Delta, Enhancer of split and Hairless genes in chaeta patterning in Drosophila tergites was studied in genetic mosaics and in mutant combinations. The mutant phenotypes of different alleles of each gene can be ordered in characteristic topographical seriations. These seriations are related to the pattern of proliferation of histoblasts and the time of singularization of sensory organ mother cells from surrounding epidermal cells. Genetic mosaics of lethal alleles show that these genes are fundamentally involved in this singularization and subsequent differentiation. The study of mutant combinations of alleles of these genes reveals specific relationships of epistasis and synergism between them. The results suggest that spatial and temporal variations in achaete-scute complex functional products in cells, modulated by the activity of other genes involved in signal transduction, define the patterned differentiation of sensory organs in tergites. Offprint requests to: A. García-Bellido     

C1 metabolism inParacoccus denitrificans: Genetics ofParacoccus denitrificans

Paracoccus denitrificans is able to grow on the C₁ compounds methanol and methylamine. These compounds are oxidized to formaldehyde which is subsequently oxidized via formate to carbon dioxide. Biomass is produced by carbon dioxide fixation via the ribulose biphosphate pathway. The first oxidation reaction is catalyzed by the enzymes methanol dehydrogenase and methylamine dehydrogenase, respectively. Both enzymes contain two different subunits in an ₂₂ configuration. The genes encoding the subunits of methanol dehydrogenase (moxF andmoxI) have been isolated and sequenced. They are located in one operon together with two other genes (moxJ andmoxG) in the gene ordermoxFJGI. The function of themoxJ gene product is not yet known.MoxG codes for a cytochromec _551i , which functions as the electron acceptor of methanol dehydrogenase. Both methanol dehydrogenase and methylamine dehydrogenase contain PQQ as a cofactor. These so-called quinoproteins are able to catalyze redox reactions by one-electron steps. The reaction mechanism of this oxidation will be described. Electrons from the oxidation reaction are donated to the electron transport chain at the level of cytochromec. P. denitrificans is able to synthesize at least 10 differentc-type cytochromes. Five could be detected in the periplasm and five have been found in the cytoplasmic membrane. The membrane-bound cytochromec ₁ and cytochromec ₅₅₂ and the periplasmic-located cytochromec ₅₅₀ are present under all tested growth conditions. The cytochromesc _551i andc _553i , present in the periplasm, are only induced in cells grown on methanol, methylamine, or choline. The otherc-type cytochromes are mainly detected either under oxygen limited conditions or under anaerobic conditions with nitrate as electron acceptor or under both conditions. An overview including the induction pattern of allP. denitrificans c-type cytochromes will be given. The genes encoding cytochromec ₁, cytochromec ₅₅₀, cytochromec _551i , and cytochromec _553i have been isolated and sequenced. By using site-directed mutagenesis these genes were mutated in the genome. The mutants thus obtained were used to study electron transport during growth on C₁ compounds. This electron transport has also been studied by determining electron transfer rates inin vitro experiments. The exact pathways, however, are not yet fully understood. Electrons from methanol dehydrogenase are donated to cytochromec _551i . Further electron transport is either via cytochromec ₅₅₀ or cytochromec _553i to cytochromeaa ₃. However, direct electron transport from cytochromec _551i to the terminal oxidase might be possible as well. Electrons from methylamine dehydrogenase are donated to amicyanin and then via cytochromec ₅₅₀ to cytochromeaa ₃, but other routes are used also.P. denitrificans is studied by several groups by using a genetic approach. Several genes have already been cloned and sequenced and a lot of mutants have been isolated. The development of a host/vector system and several techniques for mutation induction that are used inP. denitrificans genetics will be described.