Identification of Streptomyces coelicolor M145 genomic region involved in biosynthesis of teichulosonic acid–cell wall glycopolymer

The cell wall of the model actinomycete Streptomyces coelicolor M145 has recently been shown to contain the novel glycopolymer teichulosonic acid. The major building block of this polymer is 2-keto-3-deoxy-D-glycero-D-galacto-nononic acid (Kdn), suggesting initial clues about the genetic control of biosynthesis of this cell wall component. Here, through genome mining and gene knockouts, we demonstrate that the sco4879–sco4882 genomic region of S. coelicolor M145 is necessary for biosynthesis of teichulosonic acid. Specifically, mutants carrying individual knockouts of sco4879, sco4880 and sco4881 genes do not produce Kdn-containing glycopolymer and instead accumulate the minor cell wall component poly(diglycosyl 1-phosphate). Our studies provide evidence that this region is at least partly responsible for biosynthesis of Kdn, whereas flanking genes might control the other steps of teichulosonic acid formation.     

Structure-function relationships in pulmonary surfactant membranes: From biophysics to therapy

Pulmonary surfactant is an essential lipid–protein complex to maintain an operative respiratory surface at the mammalian lungs. It reduces surface tension at the alveolar air–liquid interface to stabilise the lungs against physical forces operating along the compression–expansion breathing cycles. At the same time, surfactant integrates elements establishing a primary barrier against the entry of pathogens. Lack or deficiencies of the surfactant system are associated with respiratory pathologies, which treatment often includes supplementation with exogenous materials. The present review summarises current models on the molecular mechanisms of surfactant function, with particular emphasis in its biophysical properties to stabilise the lungs and the molecular alterations connecting impaired surfactant with diseased organs. It also provides a perspective on the current surfactant-based strategies to treat respiratory pathologies. This article is part of a Special Issue entitled: Membrane Structure and Function: Relevance in the Cell's Physiology, Pathology and Therapy.     

The Interplay of Habitat and Seed Type on Scatterhoarding Behavior in a Fragmented Afromontane Forest Landscape

Scatterhoarding by rodents, whereby seeds are collected and stored for later consumption, can result in seed dispersal. Seeds may be covered in litter on the forest floor (cached) or buried. This is particularly so in the Neotropics for large, nutritious seeds, and where primary dispersers are rare or missing. In African forests, contemporary anthropogenic pressures such as hunting, forest degradation, and fragmentation are contributing toward major declines in large frugivores, yet the potential for scatterhoarding to mitigate this loss is largely unknown. In this study, we used thread‐marked seed to explore the balance between seed predation and dispersal by rodents in Afromontane forest. We studied two tree species in three habitats: (1) continuous forest; (2) continuous forest edge, and (3) small, degraded riparian forest patches. We found that seed removal rates were high and almost the same in all three habitats for both tree species, but that the predation/dispersal balance differed among habitats. In continuous forest, more seeds of each species were scatterhoarded than depredated, and rates of scatterhoarding differed between the two species. In all habitats, burying seeds up to 2 cm belowground was more common than caching. Distances seeds were moved was approximately five times greater in continuous forest than in forest edge or riparian patches. We found strong evidence to suggest that the African pouched rat, Cricetomys sp. nov was responsible for the scatterhoarding.     

Resistance to Bemisia tabaci biotype B of Solanum pimpinellifolium is associated with higher densities of type IV glandular trichomes and acylsugar accumulation

Advances in tomato breeding for pest resistance have been achieved via gene introgression from wild Solanum (section Lycopersicon) species (Solanaceae). Ninety‐nine F₃ families derived from an interspecific cross using as parental lines Solanum lycopersicum L. ‘LAM‐148' (susceptible standard) and Solanum pimpinellifolium L. ‘TO‐937‐15’ (multiple pest resistance accession with type IV glandular trichomes and acylsugar accumulation) were evaluated for their resistance against the whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) biotype B in free‐choice and no‐choice tests for oviposition and adult colonization. The parental lines and eight F₃ families with contrasting levels of resistance against the whitefly were selected and investigated in additional assays, which included the estimation of trichome densities and foliar acylsugar levels. The F₃ families BTR‐302 and BTR‐331 exhibited low amounts of eggs of whitefly and transgressive segregation for type IV glandular trichome density with values greater than that of TO‐937‐15 plants. However, the tested families did not surpass the total foliar acylsugar content found in TO‐937‐15. BTR‐331 exhibited low colonization in the free‐choice test and it was the least preferred F₃ family in the no‐choice test. The higher resistance levels of BTR‐331 were associated with a positive combination of higher type IV trichome density and higher acylsugar levels. Some F₃ families displayed reduced fruit set due to the presence of flowers with style exertion of the antheridial‐cone. Fruit weight at harvest stage of the selected families (from 4.9 to 14.5 g) was lower than that of LAM‐148 (139.5 g) but higher than that of TO‐937‐15 plants (1.3 g). Therefore, although difficult to reach due to the simultaneous segregation of many polygenic traits, the combination of high B. tabaci resistance levels with superior horticultural traits is feasible. These results confirm TO‐937‐15 as a source of biotype B resistance. From the breeding standpoint, the genetic similarity between S. lycopersicum and S. pimpinellifolium would allow a more efficient resistance introgression by facilitating recombination and minimizing the potentially undesirable linkage drag associated with this trait.     

The norepinephrine transporter (NET) radioligand (S,S)-[18F]FMeNER-D2 shows significant decreases in NET density in the human brain in Alzheimer's disease: A post-mortem autoradiographic study

Earlier post-mortem histological and autoradiographic studies have indicated a reduction of cell numbers in the locus coeruleus (LC) and a corresponding decrease in norepinephrine transporter (NET) in brains obtained from Alzheimer's disease (AD) patients as compared to age-matched healthy controls. In order to test the hypothesis that the regional decrease of NET is a disease specific biomarker in AD and as such, it can be used in PET imaging studies for diagnostic considerations, regional differences in the density of NET in various anatomical structures were measured in whole hemisphere human brain slices obtained from AD patients and age-matched control subjects in a series of autoradiographic experiments using the novel selective PET radioligand for NET (S,S)-[¹⁸F]FMeNER-D₂. (S,S)-[¹⁸F]FMeNER-D₂ appears to be a useful imaging biomarker for quantifying the density of NET in various brain structures, including the LC and the thalamus wherein the highest densities are found in physiological conditions. In AD significant decreases of NET densities can be demonstrated with the radioligand in both structures as compared to age-matched controls. The decreases in AD correlate with the progress of the disease as indicated by Braak grades. As the size of the LC is below the spatial resolution of the PET scanners, but the size of the thalamus can be detected with appropriate spatial accuracy in advanced scanners, the present findings confirm our earlier observations with PET that the in vivo imaging of NET with (S,S)-[¹⁸F]FMeNER-D₂ in the thalamus is viable. Nevertheless, further studies are warranted to assess the usefulness of such an imaging approach for the early detection of changes in thalamic NET densities as a disease-specific biomarker and the possible use of (S,S)-[¹⁸F]FMeNER-D₂ as a molecular imaging biomarker in AD.     

Phytaspase,a relocalisable cell death promoting plant protease with caspase specificity

Caspases are cysteine‐dependent proteases and are important components of animal apoptosis. They introduce specific breaks after aspartate residues in a number of cellular proteins mediating programmed cell death (PCD). Plants encode only distant homologues of caspases, the metacaspases that are involved in PCD, but do not possess caspase‐specific proteolytic activity. Nevertheless, plants do display caspase‐like activities indicating that enzymes structurally distinct from classical caspases may operate as caspase‐like proteases. Here, we report the identification and characterisation of a novel PCD‐related subtilisin‐like protease from tobacco and rice named phytaspase (plant aspartate‐specific protease) that possesses caspase specificity distinct from that of other known caspase‐like proteases. We provide evidence that phytaspase is synthesised as a proenzyme, which is autocatalytically processed to generate the mature enzyme. Overexpression and silencing of the phytaspase gene showed that phytaspase is essential for PCD‐related responses to tobacco mosaic virus and abiotic stresses. Phytaspase is constitutively secreted into the apoplast before PCD, but unexpectedly is re‐imported into the cell during PCD providing insights into how phytaspase operates.     

A quantitative real-time PCR method for in planta monitoring of Phytophthora infestans growth

Aim: To develop a real‐time PCR‐based strategy for the detection of Paenibacillus larvae vegetative cells and spores to improve the diagnosis and the screening of American foulbrood (AFB), the most harmful pathology of honeybee brood. Methods and Results: A real‐time PCR that allowed selective identification and quantification of P. larvae 16S rRNA sequence was developed. Using standard samples quantified by flow cytometry, detection limits of 37·5 vegetative cells ml^?1 and 10 spores ml^?1 were determined. Compared to spread plate method, this real‐time PCR‐based strategy allowed, in only 2 h, the detection of P. larvae in contaminated honeys. No false‐positive results were obtained. Moreover, its detection limit was 100 times lower than that of the culture method (2 vs 200 spores g^?1 of honey). Conclusion: A rapid, selective, with low detection limit, sensitive and specific method to detect and quantify vegetative cells and spores of P. larvae is now available. Significance and Impact of Study: In addition to honey samples, this real‐time PCR‐based strategy may be also applied to confirm AFB diagnosis in honeybee brood and to screen other apiary supplies and products (bees, pollen, wax), thus broadening the control of AFB spreading.