Factors affecting the structure of Coleoptera assemblages on bracket fungi (Basidiomycota) in a Brazilian forest

Insect–fungal interactions are an important but understudied aspect of tropical forest ecology. Here we present the first large‐scale study of insect communities feeding on the reproductive structures of macrofungi (basidiomes) in the Neotropics. This trophic interaction is not well characterized in most ecosystems; however, beetle consumption of basidiomes is thought to be affected by fungal factors, via mechanisms analogous to those observed in plant–herbivore interactions and in some interactions with fungi as hosts in the Holarctic region. We investigated how the composition of beetle assemblages varies as a function of fungal taxonomic distance, basidiome consistency, and hyphal systems. We collected 367 basidiomes belonging to the orders Polyporales and Hymenochaetales in the subtropical Araucaria angustifolia forest region of southern Brazil, along with any fauna present or without it. Basidiomes were maintained individually in the laboratory in plastic containers for up to three months to allow beetles to develop to adulthood, at which point the beetles were collected. We found that 207 basidiome specimens representing 40 species were associated with beetles. We recorded 447 occurrences of Coleoptera, representing 90 morphospecies from 20 families. We found that assemblages of fungivorous Coleoptera were more similar among more closely related fungi. Furthermore, the beetle assemblages varied as a function of basidiome toughness, which is influenced by sporocarp consistency and hyphal system type. The associations between beetles and basidiomes resemble those reported previously in temperate zones, suggesting continuity in the structure of such associations across a wide latitudinal range.     

Cell death induction and nitric oxide biosynthesis in white poplar (Populus alba) suspension cultures exposed to alfalfa saponins

The present work reports on the biological activity of alfalfa (Medicago sativa) saponins on white poplar (Populus alba, cultivar ‘Villafranca’) cell suspension cultures. The extracts from alfalfa roots, aerial parts and seeds were characterized for their saponin content by means of thin layer chromatography (TLC) and electrospray ionisation coupled to mass spectrometry. The quantitative saponin composition from the different plant extracts was determined considering the aglycone moieties and determined by gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS) analyses. Only soyasapogenin I was detected in the seed extract while several other saponins were found in the root and leaf extracts. Actively proliferating white poplar cell cultures were challenged with the different saponin extracts. Only alfalfa root saponins, at 50 µg ml^?1, induced significant cell death rates (75.00 ± 4.90%). Different cell subpopulations with peculiar cell death morphologies were observed and the programmed cell death (PCD)/necrosis ratio was reduced at increasing saponin concentrations. Enhancement of nitric oxide (NO) production was observed in white poplar cells treated with root saponins (RSs) at 50 µg ml^?1 and release of reactive oxygen species (ROS) in the culture medium was also demonstrated. Saponin‐induced NO production was sensitive to sodium azide and N^G‐monomethyl‐l ‐arginine, two specific inhibitors of distinct pathways for NO biosynthesis in plant cells.     

Mining the plant-herbivore interface with a leafmining Drosophila of Arabidopsis

Experimental infections of Arabidopsis thaliana (Arabidopsis) with genomically characterized plant pathogens such as Pseudomonas syringae have facilitated the dissection of canonical eukaryotic defence pathways and parasite virulence factors. Plants are also attacked by herbivorous insects, and the development of an ecologically relevant genetic model herbivore that feeds on Arabidopsis will enable the parallel dissection of host defence and reciprocal resistance pathways such as those involved in xenobiotic metabolism. An ideal candidate is Scaptomyza flava, a drosophilid fly whose leafmining larvae are true herbivores that can be found in nature feeding on Arabidopsis and other crucifers. Here, we describe the life cycle of S.?flava on Arabidopsis and use multiple approaches to characterize the response of Arabidopsis to S.?flava attack. Oviposition choice tests and growth performance assays on different Arabidopsis ecotypes, defence-related mutants, and hormone and chitin-treated plants revealed significant differences in host preference and variation in larval performance across Arabidopsis accessions. The jasmonate and glucosinolate pathways in Arabidopsis are important in mediating quantitative resistance against S.?flava, and priming with jasmonate or chitin resulted in increased resistance. Expression of xenobiotic detoxification genes was reduced in S.?flava larvae reared on Arabidopsis jasmonate signalling mutants and increased in plants pretreated with chitin. These results and future research directions are discussed in the context of developing a genetic model system to analyse insect-plant interactions.     

EPR characterization of the new Qrc complex from sulfate reducing bacteria and its ability to form a supercomplex with hydrogenase and TpIc3

The Quinone-reductase complex (Qrc) is a respiratory complex with Type I cytochrome c(3):menaquinone reductase activity, recently described in sulfate-reducing bacteria. Qrc is related to the complex iron-sulfur molybdoenzyme family and to the alternative complex III. In this work we report a detailed characterization of the redox properties of the metal cofactors of Qrc using EPR spectroscopy, which allowed the determination of the reduction potentials of five out of six hemes c, one [3Fe-4S](1+/0) center and the three [4Fe-4S](2+/1+) centers. In addition, we show that Qrc forms a supercomplex with [NiFe] hydrogenase and TpIc(3), its physiological electron donors.     

Lactoferrin-derived antimicrobial peptide induces a micellar cubic phase in a model membrane system

The observation of a micellar cubic phase is reported for a mixture of an antimicrobial peptide from the Lactoferrin family, LFampin 265-284, and a model membrane system of dimyristoylphosphatidylcholine/dimyristoylphosphatidylglycerol (3:1), as derived from small-angle x-ray diffraction (SAXD) measurements. The system shows remarkable thermotropic polymorphism: the peptide disrupts the lipid bilayer, forming a cubic phase of the space group Pm3n (t < 28°C), and as the temperature increases it shows a complex phase behavior (not fully clarified by SAXD). The onset, volume fraction of each phase, and phase parameters are seen to vary with peptide/lipid ratio and temperature. The obtained SAXD data represent the first experimental evidence, to our knowledge, of a micellar cubic phase in the context of antimicrobial peptide/membrane interaction. We propose that the micellization of the membrane according to the carpet model, for long proposed as a possible mechanism of action, can go through the formation of a cubic micellar phase.     

Paradoxes of enrichment: effects of increased light versus nutrient supply on pelagic producer-grazer systems

Energy-based plant-herbivore models produce the "paradox of enrichment," a destabilizing influence of enrichment on population dynamics. Because many plants change their carbon : nutrient stoichiometry in response to the light : nutrient supply ratio, enrichment with light can cause a mismatch between the elemental compositions of plants and their herbivores. Herbivore growth rates may then decrease with increased light supply, which is termed the "paradox of energy enrichment." I present a stoichiometric phytoplankton-grazer model that accounts for the dynamical vertical light gradient and explore how algal and grazer densities, mineral nutrient concentration, algal nutrient stoichiometry, and system stability respond to enrichment with light (through changes in irradiance, background turbidity, and water column depth) versus enrichment with nutrients. Parameterized for Daphnia, the model produces several "unusual" phenomena: multiple equilibria (with grazers extinct in spite of high algal biomass at one equilibrium), inconsistent light enrichment effects on stability (light enrichment first destabilizes and then stabilizes), and the paradox of energy enrichment. These phenomena are restricted to the low end of realistic nutrient supplies except in very shallow systems, where high sedimentation rates effectively deplete the water column of nutrients. At higher nutrient supplies, light enrichment produces the classical paradox of enrichment, leading first to an increase in grazers at a stable equilibrium and then to algae-grazer oscillations.     

Can population genetic structure be predicted from life-history traits?

Population genetic structure is a key parameter in evolutionary biology. Earlier comparative studies have shown that genetic structure depends on species ecological attributes and life-history traits, but species phylogenetic relatedness had not been accounted for. Here we reevaluate the relationships between genetic structure and species traits in seed plants. Each species is characterized by a set of life-history and ecological features as well as by its geographic range size, its heterozygote deficit, and its genetic structure at nuclear and organelle markers to distinguish between pollen- and seed-mediated gene flow. We use both a conventional regression approach and a method that controls for phylogenetic relationships. Once phylogenetic conservatism and covariation among traits are taken into account, genetic structure is shown to be related with only a few synthetic traits, such as mating system for nuclear markers and seed dispersal mode or geographic range size for organelle markers. Along with other studies on invasiveness or rarity, our work illustrates the fact that predicting the fate of species across a broad taxonomic assemblage on the basis of simple traits is rarely possible, a testimony of the highly contingent nature of evolution.     

Phomopsidone, a novel depsidone from an endophyte of the medicinal plant Eupatorium arnottianum

The medicinal plant Eupatorium arnottianum can be found in the Northeast and center of Argentina and the South of Bolivia. From plant material collected in Argentina an endophytic Phomopsis was isolated. The fungus was identified by microscopic features and analysis of its ITS sequence. Cultures yielded, besides mellein and nectriapyrone, a novel depsidone derivative for which we propose the name phomopsidone (1). The structure of 1 was determined from its spectroscopic data.     

Labeling, detection and identification of newly synthesized proteomes with bioorthogonal non-canonical amino-acid tagging

A major aim of proteomics is the identification of proteins in a given proteome at a given metabolic state. This protocol describes the step-by-step labeling, purification and detection of newly synthesized proteins in mammalian cells using the non-canonical amino acid azidohomoalanine (AHA). In this method, metabolic labeling of newly synthesized proteins with AHA endows them with the unique chemical functionality of the azide group. In the subsequent click chemistry tagging reaction, azide-labeled proteins are covalently coupled to an alkyne-bearing affinity tag. After avidin-based affinity purification and on-resin trypsinization, the resulting peptide mixture is subjected to tandem mass spectrometry for identification. In combination with deuterated leucine-based metabolic colabeling, candidate proteins can be immediately validated. Bioorthogonal non-canonical amino-acid tagging can be combined with any subcellular fractionation, immunopurification or other proteomic method to identify specific subproteomes, thereby reducing sample complexity and enabling the identification of subtle changes in a proteome. This protocol can be completed in 5 days.