The sclerodermatoid fungi

Those fungi that have been linked to the gasteroid genus Scleroderma by molecular techniques are discussed in relation to secondary metabolites, development, spore morphology, and anatomy. The group contains epigeous and hypogeous components and sequestrate and boletoid members. An intratribal classification is proposed to accommodate these life forms.     

Conventional 3' end formation is not required for NMD substrate recognition in Saccharomyces cerevisiae

The recognition and rapid degradation of mRNAs with premature translation termination codons by the nonsense-mediated pathway of mRNA decay is an important RNA quality control system in eukaryotes. In mammals, the efficient recognition of these mRNAs is dependent upon exon junction complex proteins deposited on the RNA during pre-mRNA splicing. In yeast, splicing does not play a role in recognition of mRNAs that terminate translation prematurely, raising the possibility that proteins deposited during alternative pre-mRNA processing events such as 3' end formation might contribute to the distinction between normal and premature translation termination. We have utilized mRNAs with a 3' poly(A) tail generated by ribozyme cleavage to demonstrate that the normal process of 3' end cleavage and polyadenylation is not required for mRNA stability or the detection of a premature stop codon. Thus, in yeast, the distinction between normal and premature translation termination events is independent of both splicing and conventional 3' end formation.     

Regulation of bacterial virulence by two-component systems

In bacteria, two-component systems (TCS) are widely used signal transduction devices which are engaged in a multitude of gene regulatory systems that respond to changing growth conditions. Many pathogenic bacteria encounter different microenvironments during their infectious cycle and their ability to efficiently adapt to different niches inside and outside of their host organisms is frequently mediated by TCSs, which can, therefore, be considered as an essential prerequisite for their pathogenicity. Although significant progress has been made in the elucidation of basic principles of the signal transduction process itself, in many pathogens the contribution of TCS to bacterial virulence is insufficiently recognized.     

Soybean Aphid Predators in Québec and the Suitability of Aphis glycines as Prey for Three Coccinellidae

Since its invasion of North America in 2000, the soybean aphid, Aphis glycines Matsumura (Homoptera: Aphididae) has notably changed the arthropod community of the soybean agroecosystem. The objectives of this study were to characterize the foliar predatory fauna associated with A. glycines in commercial soybean fields in Québec, Canada, and to evaluate the suitability of A. glycines as prey for three coccinellid species: Harmonia axyridis Pallas, Propylea quatuordecimpunctata L. and Coleomegilla maculata lengi Timberlake (Coleoptera: Coccinellidae). Field surveys showed that several predators responded rapidly to expanding and increasing populations of the soybean aphid. Coccinellidae were the most important aphidophagous predators observed in 2002 (58.6%) and 2003 (44.8%), with mainly four native and naturalized species co-occurring with the soybean aphid throughout the growing season. Measurement of fitness parameters under laboratory conditions (survival, development time, longevity, fecundity) indicated that A. glycines is an excellent prey for the development and reproduction of all three of the coccinellid species studied. The intrinsic rate of natural increase (r_m) was highest for H. axyridis (0.238 d⁻¹), intermediate for P. quatuordecimpunctata (0.215 d⁻¹) and lowest for C. maculata (0.134 d⁻¹).     

The Influence of Previous Mountain Pine Beetle (Dendroctonus ponderosae) Activity on the 1988 Yellowstone Fires

We examined the historical record of mountain pine beetle (Dendroctonus ponderosae Hopkins) activity within Yellowstone National Park, Wyoming, for the 25-years period leading up to the 1988 Yellowstone fires (1963–86) to determine how prior beetle activity and the resulting tree mortality affected the spatial pattern of the 1988 Yellowstone fires. To obtain accurate estimates of our model parameters, we used a Markov chain Monte Carlo method to account for the high degree of spatial autocorrelation inherent to forest fires. Our final model included three statistically significant variables: drought, aspect, and sustained mountain pine beetle activity in the period 1972–75. Of the two major mountain pine beetle outbreaks that preceded the 1988 fires, the earlier outbreak (1972–75) was significantly correlated with the burn pattern, whereas the more recent one (1980–83) was not. Although regional drought and high winds were responsible for the large scale of this event, the analysis indicates that mountain pine beetle activity in the mid-1970s increased the odds of burning in 1988 by 11% over unaffected areas. Although relatively small in magnitude, this effect, combined with the effects of aspect and spatial variation in drought, had a dramatic impact on the spatial pattern of burned and unburned areas in 1988.     

Genetic stability of three economically important micropropagated banana (Musa spp.) cultivars of lower Indo-Gangetic plains, as assessed by RAPD and ISSR markers

An efficient micropropagation protocol produced large number of plants of the three elite banana (Musa spp.) cultivars Robusta (AAA), Giant Governor (AAA) and Martaman (AAB) from shoot tip meristem. The genetic relationships and fidelity among the cultivars and micropropagated plants as assessed by random amplified polymorphic DNA (RAPD) and inter-simple sequence repeat (ISSR) markers, revealed three somaclonal variants from Robusta and three from Giant Governor. A total of 5330 RAPD and 2741 ISSR fragments were generated with 21 RAPD and 12 ISSR primers in micropropagated plants. The percentage of polymorphic loci by RAPD and ISSR were found to be 1.75, 5.08 in Robusta and 0.83, 5.0 in Giant Governor respectively. Among the two marker systems used, ISSR fingerprinting detected more polymorphism than RAPD in Robusta and Giant Governor with most of the primers showing similar fingerprinting profile, whereas Martaman revealed complete genetic stability.     

Symbiotic bacteria as a determinant of plant community structure and plant productivity in dune grassland

Symbiotic interactions are thought to play a key role in ecosystems. Empirical evidence for the impact of symbiotic bacteria on plant communities is, however, extremely scarce because of experimental constraints. Here, in three complementary experiments, we show that nitrogen-fixing rhizobia bacteria act as a determinant of plant community structure and diversity. Grassland microcosms inoculated with a mixture of rhizobia had a higher above-ground plant productivity (+35%), contained more nitrogen (+85%) and had significant higher community evenness (+34%) than control microcosms without rhizobia. Moreover, three of the four studied legume species required rhizobia to successfully coexist with other plant species. In contrast, the growth and survival of three grass and five forb species were not affected by the presence or absence of rhizobia. Finally, our results also showed that the legume species largely relied on symbiotically fixed nitrogen, both in the field and in the microcosms. This indicates that results in the microcosms are indicative for processes occurring in the field. It is concluded that symbiotic interactions between plants and prokaryotes can contribute to plant productivity, plant community structure and acquisition of limiting resources in legume-rich grassland communities.     

Evidence for transmembrane proton transfer in a dihaem-containing membrane protein complex

Membrane protein complexes can support both the generation and utilisation of a transmembrane electrochemical proton potential ('proton-motive force'), either by transmembrane electron transfer coupled to protolytic reactions on opposite sides of the membrane or by transmembrane proton transfer. Here we provide the first evidence that both of these mechanisms are combined in the case of a specific respiratory membrane protein complex, the dihaem-containing quinol:fumarate reductase (QFR) of Wolinella succinogenes, so as to facilitate transmembrane electron transfer by transmembrane proton transfer. We also demonstrate the non-functionality of this novel transmembrane proton transfer pathway ('E-pathway') in a variant QFR where a key glutamate residue has been replaced. The 'E-pathway', discussed on the basis of the 1.78-Angstrom-resolution crystal structure of QFR, can be concluded to be essential also for the viability of pathogenic varepsilon-proteobacteria such as Helicobacter pylori and is possibly relevant to proton transfer in other dihaem-containing membrane proteins, performing very different physiological functions.     

A nuclear export signal and phosphorylation regulate Dok1 subcellular localization and functions

Dok1 is believed to be a mainly cytoplasmic adaptor protein which down-regulates mitogen-activated protein kinase activation, inhibits cell proliferation and transformation, and promotes cell spreading and cell migration. Here we show that Dok1 shuttles between the nucleus and cytoplasm. Treatment of cells with leptomycin B (LMB), a specific inhibitor of the nuclear export signal (NES)-dependent receptor CRM1, causes nuclear accumulation of Dok1. We have identified a functional NES (348LLKAKLTDPKED359) that plays a major role in the cytoplasmic localization of Dok1. Src-induced tyrosine phosphorylation prevented the LMB-mediated nuclear accumulation of Dok1. Dok1 cytoplasmic localization is also dependent on IKKbeta. Serum starvation or maintaining cells in suspension favor Dok1 nuclear localization, while serum stimulation, exposure to growth factor, or cell adhesion to a substrate induce cytoplasmic localization. Functionally, nuclear NES-mutant Dok1 had impaired ability to inhibit cell proliferation and to promote cell spreading and cell motility. Taken together, our results provide the first evidence that Dok1 transits through the nucleus and is actively exported into the cytoplasm by the CRM1 nuclear export system. Nuclear export modulated by external stimuli and phosphorylation may be a mechanism by which Dok1 is maintained in the cytoplasm and membrane, thus regulating its signaling functions.