Antigen bias in T cell cross-priming

Activated CD8+ T cells detect virally infected cells and tumor cells by recognition of major histocompatibility complex class I-bound peptides derived from degraded, endogenously produced proteins. In contrast, CD8+ T cell activation often occurs through interaction with specialized antigen-presenting cells displaying peptides acquired from an exogenous cellular source, a process termed cross-priming. Here, we observed a marked inefficiency in exogenous presentation of epitopes derived from signal sequences in mouse models. These data indicate that certain virus- and tumor-associated antigens may not be detected by CD8+ T cells because of impaired cross-priming. Such differences in the ability to cross-present antigens should form important considerations in vaccine design.     

Deep human genealogies reveal a selective advantage to be on an expanding wave front

Since their origin, human populations have colonized the whole planet, but the demographic processes governing range expansions are mostly unknown. We analyzed the genealogy of more than one million individuals resulting from a range expansion in Quebec between 1686 and 1960 and reconstructed the spatial dynamics of the expansion. We find that a majority of the present Saguenay Lac-Saint-Jean population can be traced back to ancestors having lived directly on or close to the wave front. Ancestors located on the front contributed significantly more to the current gene pool than those from the range core, likely due to a 20% larger effective fertility of women on the wave front. This fitness component is heritable on the wave front and not in the core, implying that this life-history trait evolves during range expansions.     

Extracellular proteins limit the dispersal of biogenic nanoparticles

High-spatial-resolution secondary ion microprobe spectrometry, synchrotron radiation-based Fourier-transform infrared spectroscopy, and polyacrylamide gel analysis demonstrated the intimate association of proteins with spheroidal aggregates of biogenic zinc sulfide nanocrystals, an example of extracellular biomineralization. Experiments involving synthetic zinc sulfide nanoparticles and representative amino acids indicated a driving role for cysteine in rapid nanoparticle aggregation. These findings suggest that microbially derived extracellular proteins can limit the dispersal of nanoparticulate metal-bearing phases, such as the mineral products of bioremediation, that may otherwise be transported away from their source by subsurface fluid flow.     

Early detection of bovine respiratory disease in young bulls using reticulo-rumen temperature boluses

The use of reticulo-rumen temperature boluses to detect bovine respiratory disease (BRD) was investigated in young bulls following their entry into a fattening unit. Twenty-four bulls received a bolus at entry and were observed for 40 days. As soon as a reticulo-rumen hyperthermia (RH) episode was detected using the bolus, clinical examination was performed by a veterinarian and then repeated every 12-24h until the end of RH episode. Fifty-two RH episodes were detected in 22 animals. High rectal temperatures (40.1±0.6°C) were observed during these episodes. BRD was diagnosed on the basis of clinical examination during 38/52 RH episodes in 21 animals (positive predictive value 73%). The onset of BRD signs always occurred after the onset of RH episodes, with a time-lag from 12 to 136 h, depending on BRD signs. Monitoring reticulo-rumen temperature permits early detection of BRD; however, clinical examination is required to confirm BRD.     

The reproductive potential of the root-knot nematode <Emphasis Type="Italic">Meloidogyne incognita</Emphasis> is affected by selection for virulence against major resistance genes from tomato and pepper

The emergence of virulent root-knot nematode populations, able to overcome the resistance conferred by some of the resistance genes (R-genes) in Solanaceous crops, i.e., Mi(s) in tomato, Me(s) in pepper, may constitute a severe limitation to their use in the field. Research has been conducted to evaluate the durability of these R-genes, by comparing the reproduction of several laboratory-selected and wild virulent Meloidogyne incognita isolates, on both susceptible and resistant tomatoes and peppers. We first show that the Me1 R-gene in pepper behaves as a robust R-gene controlling avirulent and virulent Me3, Me7 or Mi-1 isolates. Although the reproductive potential of the virulent isolates was highly variable on susceptible and resistant plants, we also confirm that virulence is highly specific to a determined R-gene on which selection has occurred. Another significant experimental result is the observation that a reproductive fitness cost is associated with nematode virulence against Mi-1 in tomato and Me3 and Me7 in pepper. The adaptative significance of trade-offs between selected characters and fitness-related traits, suggests that, although the resistance can be broken, it may be preserved in some conditions if the virulent nematodes are counter-selected in susceptible plants. All these results have important consequences for the management of plant resistance in the field.     

Trapping whiteflies? A comparison of greenhouse whitefly (Trialeurodes vaporariorum) responses to trap crops and yellow sticky traps

BACKGROUND: Greenhouse whiteflies, Trialeurodes vaporariorum (Westwood), are notorious pests that, through the reduction of crop yields and excretion of honeydew, cause significant economic losses for sweet pepper (Capsicum annuum L.) growers. Chemical and biological controls are the two most common forms of whitefly management in greenhouses. Consequently, insecticide resistance and inadequate control have rejuvenated interest in alternative tactics. In the present study, whitefly responses to trap crops (eggplant and squash) and yellow sticky traps were compared in order to identify the most effective traps for dispersing and resident adults. RESULTS: Results indicated that yellow sticky traps were most effective at trapping adult whiteflies. Significantly more dispersing whiteflies were recorded on eggplant than on squash trap crops. None of the traps significantly reduced adult populations on the main crops (peppers) compared with the control. However, yellow sticky traps did significantly reduce oviposition on peppers. CONCLUSIONS: Adult whiteflies were most effectively trapped on yellow sticky traps followed by eggplant trap crops. Further study of whitefly trapping using visual cues may enhance trapping management. Specifically, research combining yellow sticky traps with other control strategies is recommended. Copyright © 2011 Society of Chemical Industry     

Abiotic degradation of lignified cell walls by carbonate and copper salt

This study reports on the destructuration of Wheat straw and Spruce wood cell walls after maceration in potassium carbonate or sodium hydroxide at pH = 10 in the presence of copper acetate. The alkaline treatments had a predominant impact on the wheat straw cell wall components over copper acetate. Either K-carbonate or Na-hydroxide extracted from wheat straw a particular lignin fraction rich in condensed C-C linkages, leading to the unmasking of new ether-linked sub-structures in the cell wall. This unmasking was increased in the presence of copper salt but only in the nonextracted Wheat straw sample incubated in carbonate and not in the corresponding extractive-free sample. This difference was related to the leaching of compounds from the nonextracted cell wall, which could sustain oxidative activity of copper by hindering its precipitation into inactive hydroxide and/or carbonate species. In Spruce wood samples, copper salt was the principal factor impacting on the lignin structure over alkali alone. Its effect was, however, only detected at the level of C-C linked dimers. These results confirmed that unmasking of lignin sub-structures also occurred in Spruce wood, but probably through mechanisms different from that evidenced in Wheat straw.     

Relation between oak tree phenology and the secretion of organic matter degrading enzymes by Lactarius quietus ectomycorrhizas before and during bud break

The ectomycorrhizas (ECM) formed by Lactarius quietus, an ECM fungus specifically associated with Quercus spp., are abundant all the year long. Root and stem growth, beginning before bud break in oak, are strong carbon sinks partially fulfilled with carbohydrate reserves. We hypothesized that L. quietus contributes to providing trees with carbon at bud break through enzymatic activities before photosynthesis begins. Activities of eight secreted enzymes (xylosidase, glucuronidase, cellobiohydrolase, β-glucosidase, N-acetyl-glucosamine, leucine aminopeptidase, acid phosphatase and laccase) relevant to carbon cycling and the release of phophorus and nitrogen from soil organic matter were measured on L. quietus ECMs before, during and after the bud break. Phenological, climatic and pedoclimatic parameters were also measured. Laccase, glucuronidase, cellobiohydrolase and β-glucosidase activities proved to be significantly related to tree reactivation and climate. All these activities can help the formation of new tissues by supplying carbon. L. quietus can behave saprotrophically, using soil organic matter as substrate. This is consistent with the hypothesis that it provides the oak trees with carbon when demand is high and photoassimilates are not yet available.