Location of a new encephalitogenic epitope (residues 43 to 64) in proteolipid protein that induces relapsing experimental autoimmune encephalomyelitis in PL/J and (SJL x PL)F1 mice.

Synthetic peptides of proteolipid protein (PLP) were screened for their ability to induce experimental autoimmune encephalomyelitis (EAE) in SJL/J, PL/J, and (SJL x PL)F1 mice, and T cell lines were selected by stimulation of lymph node cells with PLP peptides. PLP 141-151 was found to be less encephalitogenic in SJL/J mice than PLP 139-151, due to deletion of two amino acids from the amino-terminal end. PLP 139-151 immunization induced relapsing EAE in SJL/J and F1 mice but not PL/J mice. In contrast, PLP 43-64 induced relapsing EAE in PL/J and F1 mice but not SJL/J mice. F1 T cell lines specific for either PLP 43-64 or PLP 139-151 adoptively transferred demyelinating EAE to naive F1 recipients. Haplotypes H-2s and H-2u appear to be immunologically co-dominant in F1 mice in the PLP EAE system, which differs from the H-2u dominance in F1 mice in the myelin basic protein EAE system. The identification of a PLP peptide that is encephalitogenic in PL/J mice, in addition to the previous demonstration of PLP peptides that are encephalitogenic for SWR mice (PLP 103-116) and SJL/J mice (PLP 139-151), lends support to a role for PLP as a target Ag in autoimmune demyelinating diseases.     

Impact of pocket gopher disturbance on plant species diversity in a shortgrass prairie community

Summary We examined the impact of pocket gopher disturbances on the dynamics of a shortgrass prairie community. Through their burrowing activity, pocket gophers (Thomomys bottae) cast up mounds of soil which both kill existing vegetation and create sites for colonization by competitively-inferior plant species. Three major patterns emerge from these disturbances: First, we show that 10 of the most common herbaceous perennial dicots benefit from pocket gopher disturbance; that is, a greater proportion of seedlings are found in the open space created by pocket gopher disturbance than would be expected based on the availability of disturbed habitat. Additionally, these seedlings exhibited higher growth rates than adjacent seedlings of the same species growing in undisturbed habitat. Second, we tested two predictions of the Intermediate Disturbance Hypothesis and found that species diversity was greatest for plots characterized by disturbances of intermediate age. However, we did not detect significant differences in diversity between plots characterized by intermediate and high levels of disturbance, indicating that many species are adapted to or at least tolerant of high levels of disturbance. Third, we noted that the abundance of grasses decreased with increasing disturbance, while the abundance of dicots increased with increasing disturbance.     

The relative influences of host plant genotype and yearly abiotic variability in determining herbivore abundance

Both plant genotype and yearly abiotic variation affect herbivore population sizes, but long-term data have rarely been used to contrast the relative contributions of each. Using a hierarchical Bayesian model, we directly compare effects of these two factors on the population size of a common herbivore, Aceria parapopuli, on Populus angustifolia × fremontii F₁ hybrid trees growing in a common garden across 8 years. Several patterns emerged. First, the Bayesian posterior estimates of tree genotype effects on mite gall number ranged from 0.0043 to 229 on a linear scale. Second, year effect sizes across 8 years of study ranged from 0.133 to 1.895. Third, in comparing the magnitudes of genotypic versus yearly variation, we found that genotypic variation was over 130 times greater than variation among years. Fourth, precipitation in the previous year negatively affected gall abundances, but was minimal compared to tree genotype effects. These findings demonstrate the relative importance of tree genotypic variation in determining herbivore population size. However, given the demonstrated sensitivity of cottonwoods to drought, the loss of individual tree genotypes from an altered climate would have catastrophic impacts on mites that are dependent upon these genotypes for their survival.     

Soil-mediated local adaptation alters seedling survival and performance

Background and aims

Soils can act as agents of natural selection, causing differential fitness among genotypes and/or families of the same plant species, especially when soils have extreme physical or chemical properties. More subtle changes in soils, such as variation in microbial communities, may also act as agents of selection. We hypothesized that variation in soil properties within a single river drainage can be a selective gradient, driving local adaptation in plants.

Methods

Using seeds collected from individual genotypes of Populus angustifolia James and soils collected from underneath the same trees, we use a reciprocal transplant design to test whether seedlings would be locally adapted to their parental soil type.

Results

We found three patterns: 1. Soils from beneath individual genotypes varied in pH, soil texture, nutrient content, microbial biomass and the physiological status of microorganisms. 2. Seedlings grown in local soils experienced 2.5-fold greater survival than seedlings planted in non-local soils. 3. Using a composite of height, number of leaves and leaf area to measure plant growth, seedlings grew ～17.5% larger in their local soil than in non-local soil.

Conclusions

These data support the hypothesis that variation in soils across subtle gradients can act as an important selective agent, causing differential fitness and local adaptation in plants.     

Plant genetic effects on soils under climate change

Background

Many biological questions about N availability and the N cycle require knowledge of the abundance and identity of molecules comprising the pool of organic N. Moreover, basic knowledge of the molecular composition of the soil solution can give rise to new hypotheses via data-driven or inductive reasoning.

Scope

This paper examines the composition of organic N molecules in the soil solution. Our perception of organic N in the soil solution is shaped by analytical approaches, and thus I briefly review approaches for sampling and analysis of the soil solution. I give examples of hypotheses generated by knowledge of the molecular composition of organic N and conclude by suggesting priorities for future research.

Conclusions

Studies of the molecular composition of organic N are very much in their infancy. Amino acids, their oligomers and polymers are consistently large components of the pool of organic N. The soil solution also contains organic N compounds from at least another 12 compound classes, but almost nothing is known about their functional significance. Uncovering the role of these other compounds in the N cycle would enrich our understanding of organic N and the N cycle, and place studies of amino acids and their polymers in a broader context.     

Prediction of the in planta Phakopsora pachyrhizi secretome and potential effector families

Asian soybean rust (ASR), caused by the obligate biotrophic fungus Phakopsora pachyrhizi, can cause losses greater than 80%. Despite its economic importance, there is no soybean cultivar with durable ASR resistance. In addition, the P. pachyrhizi genome is not yet available. However, the availability of other rust genomes, as well as the development of sample enrichment strategies and bioinformatics tools, has improved our knowledge of the ASR secretome and its potential effectors. In this context, we used a combination of laser capture microdissection (LCM), RNAseq and a bioinformatics pipeline to identify a total of 36 350 P. pachyrhizi contigs expressed in planta and a predicted secretome of 851 proteins. Some of the predicted secreted proteins had characteristics of candidate effectors: small size, cysteine rich, do not contain PFAM domains (except those associated with pathogenicity) and strongly expressed in planta. A comparative analysis of the predicted secreted proteins present in Pucciniales species identified new members of soybean rust and new Pucciniales‐ or P. pachyrhizi‐specific families (tribes). Members of some families were strongly up‐regulated during early infection, starting with initial infection through haustorium formation. Effector candidates selected from two of these families were able to suppress immunity in transient assays, and were localized in the plant cytoplasm and nuclei. These experiments support our bioinformatics predictions and show that these families contain members that have functions consistent with P. pachyrhizi effectors.     

Temporal and spatial Bean pod mottle virus‐induced gene silencing in soybean

Virus‐induced gene silencing (VIGS) is a powerful reverse genetics tool in plant science. In this study, we investigated the temporal and spatial silencing patterns achieved by Bean pod mottle virus (BPMV)‐based VIGS in soybean using virus constructs targeting green fluorescence protein (GFP). Silencing GFP enabled an in‐depth analysis of silencing in soybean tissues over time in a transgenic line constitutively expressing GFP. We discovered evidence for variable GFP silencing based on insert orientation and targeted region in the coding sequence. A 3′ sequence in reverse orientation produced the strongest silencing phenotypes. Furthermore, we documented that BPMV VIGS can achieve widespread silencing in a broad range of tissues, including leaves, stems, flowers and roots. Near‐complete silencing was attained in leaves and flowers. Although weaker than in shoots, the observed gene silencing in soybean roots will also allow reverse genetics studies in this tissue. When GFP fluorescence was assayed in cross‐sections of stems and leaf petioles, near‐complete and uniform silencing was observed in all cell types. Silencing was observed from as early as 2 weeks post‐virus inoculation in leaves to 7 weeks post‐virus inoculation in flowers, suggesting that this system can induce and maintain silencing for significant durations.     

Effect of caffeine supplementation on the extracellular heat shock protein 72 response to exercise.

The stimulus for the release of 72-kDa heat shock protein (HSP72) during exercise in humans is currently unclear. Recent evidence in an animal model is suggestive of an involvement of catecholamines. The present study, therefore, investigated the effect of caffeine supplementation, a known stimulator of sympathetic activity, on the extracellular (e)HSP72 response to prolonged exercise. Ten healthy male endurance-trained cyclists were recruited (age: 21 +/- 1 yr, maximum O(2) uptake 61.1 +/- 1.7 ml x kg(-1) x min(-1), mean +/- SE). Each subject was randomly assigned to ingest either 6 mg/kg body mass of caffeine (Caff) or placebo (Pla) 60 min before one of two 90-min bouts of cycling at 74 +/- 1% maximum O(2) uptake. Trials were performed at least 7 days apart in a counterbalanced design. Venous blood samples were collected by venepuncture at pretreatment, preexercise, postexercise, and 1 h postexercise. Serum caffeine and plasma catecholamines were determined using a spectrophotometric assay and high-performance liquid chromatography, respectively. Plasma HSP72 and cortisol were determined by ELISA. Serum caffeine concentrations were significantly increased throughout Caff, while no increases were detected in Pla. Caffeine supplementation and exercise was associated with a greater eHSP72 response than exercise alone (postexercise Caff 8.6 +/- 1.3 ng/ml; Pla 5.9 +/- 0.9 ng/ml). This greater eHSP72 response was associated with a greater epinephrine response to exercise in Caff. There was a significant increase in norepinephrine and cortisol, with no intertrial differences. The present data suggest that, in humans, catecholamines may be an important mediator of the exercise-induced increase in eHSP72 concentration.