Arbuscular mycorrhizal fungal communities in plant roots are not random assemblages

We investigated whether arbuscular mycorrhizal fungal (AMF) communities in plant roots are random subsets of the local taxon pool or whether they reflect the action of certain community assembly rules. We studied AMF small subunit rRNA gene sequence groups in the roots of plant individuals belonging to 11 temperate forest understorey species. Empirical data were compared with null models assuming random association. Distinct fungal species pools were present in young and old successional forest. In both forest types, the richness of plant-AMF associations was lower than expected by chance, indicating a degree of partner selectivity. AMF communities were generally not characteristic of individual plant species, but those associated with ecological groups of plant species - habitat generalists and forest specialists - were nonrandom subsets of the available pool of fungal taxa and differed significantly from each other. Moreover, these AMF communities were the least distinctive in spring, but developed later in the season. Comparison with a global database showed that generalist plants tend to associate with generalist AMF. Thus, the habitat range of the host and a possible interaction with season played a role in the assembly of AMF communities in individual plant root systems.     

Arbuscular Mycorrhizal Fungal Networks Vary throughout the Growing Season and between Successional Stages

To date, few analyses of mutualistic networks have investigated successional or seasonal dynamics. Combining interaction data from multiple time points likely creates an inaccurate picture of the structure of networks (because these networks are aggregated across time), which may negatively influence their application in ecosystem assessments and conservation. Using a replicated bipartite mutualistic network of arbuscular mycorrhizal (AM) fungal-plant associations, detected using large sample numbers of plants and AM fungi identified through molecular techniques, we test whether the properties of the network are temporally dynamic either between different successional stages or within the growing season. These questions have never been directly tested in the AM fungal-plant mutualism or the vast majority of other mutualisms. We demonstrate the following results: First, our examination of two different successional stages (young and old forest) demonstrated that succession increases the proportion of specialists within the community and decreases the number of interactions. Second, AM fungal-plant mutualism structure changed throughout the growing season as the number of links between partners increased. Third, we observed shifts in associations between AM fungal and plant species throughout the growing season, potentially reflecting changes in biotic and abiotic conditions. Thus, this analysis opens up two entirely new areas of research: 1) identifying what influences changes in plant-AM fungal associations in these networks, and 2) what aspects of temporal variation and succession are of general importance in structuring bipartite networks and plant-AM fungal communities.     

Sleep apnea modifies the long‐term impact of surgically induced weight loss on cardiac function and inflammation

Objective:

Obesity is frequently associated with obstructive sleep apnea (OSA). Both conditions are proinflammatory and proposed to deteriorate cardiac function. We used a nested cohort study design to evaluate the long‐term impact of bariatric surgery on OSA and how weight loss and OSA relate to inflammation and cardiac performance.

Design and Methods:

At 10‐year follow‐up in the Swedish Obese Subjects (SOS) study, we identified 19 obese subjects (BMI 31.2 ± 5.3 kg m^?2), who following bariatric surgery at SOS‐baseline had displayed sustained weight losses (surgery group), and 20 obese controls (BMI 42.0 ± 6.2 kg m^?2), who during the same time‐period had maintained stable weight (control group). All study participants underwent overnight polysomnography examination, echocardiography and analysis of inflammatory markers.

Results:

The surgery group displayed a lower apnea hypopnea index (AHI) (19.9 ± 21.5 vs. 37.8 ± 27.7 n/h, P = 0.013), lower inflammatory activity (hsCRP 2.3 ± 3.0 vs. 7.2 ± 5.0 mg L^?1, P < 0.001), reduced left ventricular mass (165 ± 22 vs. 207 ± 22 g, P < 0.001) and superior left ventricular diastolic function (E/A ratio 1.24 ± 1.10 vs. 1.05 ± 0.20, P = 0.006) as compared with weight stable obese controls. In multiple regression analyses including all subjects (n = 39) and controlling for BMI, the AHI remained independently associated with hsCRP (β = 0.09, P < 0.001), TNF‐α (β = 0.03, P = 0.031), IL‐6 (β = 0.01, P = 0.007), IL 10 (β = ?0.06; P = 0.018), left ventricular mass (β = 0.64, P < 0.001), left atrial area (β = 0.08, P = 0.002), pulmonary artery pressure (β = 0.08, P = 0.011) and E/E_a ratio (β = 0.04, P = 0.021).

Conclusions:

Patients with sustained weight loss after bariatric surgery display less severe sleep apnea, reduced inflammatory activity, and enhanced cardiac function. Persisting sleep apnea appears to limit the beneficial effect of weight loss on inflammation and cardiac performance.

     

Lolium perenne L. root systems are a collection of Gaussian curve shaped meso diameter class length distributions

Aims

Determine if the root system of Lolium perenne L. (L perenne) is a continuous distribution of diameters, or a collection of discrete diameters classes.

Methods

Plants from tillers of five clones were grown in a local soil amended with lime. Roots were excavated after they were grown in soil for 54 days, washed and imaged with both a commercial scanner (94 px mm^?1) and a high resolution, locally built, imager (204 px mm^?1). Images were converted to diameter class length data with WinRhizo.

Results

Scanned images did not have enough resolution to accurately measure fine roots diameters (<0.09 mm diam.). Therefore the high resolution images were used. The diameter class length distributions (DCLD) of these images demonstrated diameter class clusters (meso diameter classes) which could be modeled with a non-linear Gaussian (normal) curve model. Recreating the whole root system from a compilation of the DCLD, regenerated from the three parameters of each of the Gaussian curves for the root system, produced a distribution visually identical to the original whole root system curve.

Conclusions

L perenne root systems are a collection of meso diameter classes easily described by non-linear Gaussian models. The data set of the parameters from these models is much smaller than a WinRhizo data set, and can reconstruct the original whole system DCLD.     

Global sampling of plant roots expands the described molecular diversity of arbuscular mycorrhizal fungi

We aimed to enhance understanding of the molecular diversity of arbuscular mycorrhizal fungi (AMF) by building a new global dataset targeting previously unstudied geographical areas. In total, we sampled 96 plant species from 25 sites that encompassed all continents except Antarctica. AMF in plant roots were detected by sequencing the nuclear SSU rRNA gene fragment using either cloning followed by Sanger sequencing or 454-sequencing. A total of 204 AMF phylogroups (virtual taxa, VT) were recorded, increasing the described number of Glomeromycota VT from 308 to 341 globally. Novel VT were detected from 21 sites; three novel but nevertheless widespread VT (Glomus spp. MO-G52, MO-G53, MO-G57) were recorded from six continents. The largest increases in regional VT number were recorded in previously little-studied Oceania and in the boreal and polar climatic zones — this study providing the first molecular data from the latter. Ordination revealed differences in AM fungal communities between different continents and climatic zones, suggesting that both biogeographic history and environmental conditions underlie the global variation of those communities. Our results show that a considerable proportion of Glomeromycota diversity has been recorded in many regions, though further large increases in richness can be expected in remaining unstudied areas.     

Strategies to minimize false positives and interpret novel microdeletions based on maternal copy-number variants in 87,000 noninvasive prenatal screens

Background

Noninvasive prenatal screening (NIPS) of common aneuploidies using cell-free DNA from maternal plasma is part of routine prenatal care and is widely used in both high-risk and low-risk patient populations. High specificity is needed for clinically acceptable positive predictive values. Maternal copy-number variants (mCNVs) have been reported as a source of false-positive aneuploidy results that compromises specificity.

Methods

We surveyed the mCNV landscape in 87,255 patients undergoing NIPS. We evaluated both previously reported and novel algorithmic strategies for mitigating the effects of mCNVs on the screen’s specificity. Further, we analyzed the frequency, length, and positional distribution of CNVs in our large dataset to investigate the curation of novel fetal microdeletions, which can be identified by NIPS but are challenging to interpret clinically.

Results

mCNVs are common, with 65% of expecting mothers harboring an autosomal CNV spanning more than 200 kb, underscoring the need for robust NIPS analysis strategies. By analyzing empirical and simulated data, we found that general, outlier-robust strategies reduce the rate of mCNV-caused false positives but not as appreciably as algorithms specifically designed to account for mCNVs. We demonstrate that large-scale tabulation of CNVs identified via routine NIPS could be clinically useful: together with the gene density of a putative microdeletion region, we show that the region’s relative tolerance to duplications versus deletions may aid the interpretation of microdeletion pathogenicity.

Conclusions

Our study thoroughly investigates a common source of NIPS false positives and demonstrates how to bypass its corrupting effects. Our findings offer insight into the interpretation of NIPS results and inform the design of NIPS algorithms suitable for use in screening in the general obstetric population.

     

Cell type‐specific regulation of ciliary transition zone assembly in vertebrates

Ciliopathies are life‐threatening human diseases caused by defective cilia. They can often be traced back to mutations of genes encoding transition zone (TZ) proteins demonstrating that the understanding of TZ organisation is of paramount importance. The TZ consists of multimeric protein modules that are subject to a stringent assembly hierarchy. Previous reports place Rpgrip1l at the top of the TZ assembly hierarchy in Caenorhabditis elegans. By performing quantitative immunofluorescence studies in RPGRIP1L^?/? mouse embryos and human embryonic cells, we recognise a different situation in vertebrates in which Rpgrip1l deficiency affects TZ assembly in a cell type‐specific manner. In cell types in which the loss of Rpgrip1l alone does not affect all modules, additional truncation or removal of vertebrate‐specific Rpgrip1 results in an impairment of all modules. Consequently, Rpgrip1l and Rpgrip1 synergistically ensure the TZ composition in several vertebrate cell types, revealing a higher complexity of TZ assembly in vertebrates than in invertebrates.     

Direct activation of trpl cation channels by G alpha11 subunits.

G proteins of the Gq/11 subfamily functionally couple cell surface receptors to phospholipase C beta (PLC beta) isoforms. Stimulation of PLC beta induces Ca2+ elevation by inositol 1,4,5-trisphosphate (InsP3)-mediated Ca2+ release and store-dependent 'capacitative' Ca2+ entry through Ca(2+)-permeable channels. The Drosophila trp gene, as well as some human trp homologs, code for such store-operated channels. The related trp-like (trpl) gene product also forms a Ca(2+)-permeable cation channel, but is not activated by store depletion. Co-expression of the constitutively active Gq subfamily member G alpha 11 (G alpha 11) with trpl enhanced trpl currents 33-fold in comparison with co-expression of trpl with other G alpha isoforms or G beta gamma complexes. This activation could not be attributed to signals downstream of PLC beta. In particular, InsP3 infusion, modulation of protein kinase C activity or elevation of intracellular calcium concentration failed to induce trpl currents. In contrast, purified G alpha 11 (but not other G protein subunits) activated trpl channels in inside-out patches. We conclude that trpl is regulated by G11 proteins in a membrane-confined manner not involving cytosolic factors. Thus, G proteins of the Gq subfamily may induce Ca2+ entry not only indirectly via store-operated mechanisms but also by directly stimulating cation channels.     

Secondary succession and summer herbivory in a subarctic grassland: community structure and diversity

A field experiment was established in a subarctic grassland in the Finnish Lapland to study the role of summer herbivory in plant community succession Perennial vegetation and moss cover were removed in an area of 324 m² The site was divided into four blocks, of which two were fenced to prevent herbivory by large mammals (reindeer, hare)
Early successional changes in the vegetation were assessed Mean species richness per 3 × 3 m plot was consistently higher in the fenced area, indicating that herbivory can suppress small-scale diversity Herbivory affected the height of several plant species However, there was no correlation between frequency and height of individual species There was a weak indication that taller species were more successful m early succession when grazed Light competition is apparently not a key process determining successional change Thus, in early stage of succession, summer herbivory has little effect on diversity by limiting light competition, and most species are equally successful in grazed and ungrazed plots There was some indirect evidence about competitive interactions in the developing community However, unlike temperate grasslands, large mammal herbivory and competition for light seem not to be important determinants of community change in this subarctic grassland (at least what concernes early successional stages) This may be explained by the harshness of local climate, and abundance of light due to the polar day     

Disruption of XIAP-RIP2 Association Blocks NOD2-Mediated Inflammatory Signaling

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