Exclusion of inefficient Bradyrhizobium japonicum serogroups by soybean genotypes

Soybean [Glycine max (L.) Merr.] forms a symbiosis with serogroups of Bradyrhizobium japonicum that differ in their dinitrogen fixing abilities. The objectives of this study were to identify soybean genotypes that would restrict nodulation by relatively inefficient serogroups indigenous to a large portion of the southeastern USA, and then characterize the nodulation responses of selected genotypes with specific bradyrhizobial strains under controlled conditions. From field screening trials followed by controlled single and competitive inoculations of serogroups USDA 31, 76 and 110, twelve soybean genotypes out of 382 tested were identified with varying levels of exclusion abilities. Soybean nodule occupancies and nodulation characteristics were influenced by plant genotype, environment (i.e. field or greenhouse), bradyrhizobial serogroup, and location of nodules (i.e. tap or lateral root). The cultivar Centennial sustains high seed yields even though it nodulates to a high degree with the inefficient serogroup USDA 31. In contrast, data from the released cultivars Braxton, Centennial and Coker 368 indicate that they may have been selected to exclude the inefficient serogroup USDA 76 from their tap root nodules, possibly contributing to high seed yield.     

Phytoremediation of pyrene in a Cecil soil under field conditions

We evaluated the effects of annual ryegrass (Lolium multiflorum Lam.) and phosphorus (P) availability on the dissipation of pyrene added at a concentration of approximately 600 mg kg-1 dry soil in the top 7.5 cm of a Cecil loamy sand (fine, kaolinitic, thermic Typic Kanhapludults) in a 10-month experiment under field conditions in Clemson, South Carolina. Plastic canopies were installed to prevent flooding of plots and raindrop dispersion of pyrene. Treatment factors were pyrene, vegetation, and available P levels. Each of the eight treatments had four replicates. The soil was adjusted to low and high P concentrations (an average of 41 and 66 kg extractable P ha-1, respectively). After a 175-d lag period for all treatments, the rate of pyrene removal followed first-order kinetics. The first-order rate constant was significantly higher in nonvegetated (0.098 d-1) than vegetated treatments (0.034 d-1). These data suggest that the presence of easily biodegradable organic matter from plant roots slowed the removal rate of pyrene. The levels of available P did not affect the rate of pyrene dissipation. Pyrene decreased below the detection limit of 6.25 mg kg-1 dry soil in all treatments after 301 d.     

Linkage disequilibrium and association of MAPT H1 in Parkinson disease

The MAPT H1 haplotype has been associated with four-repeat (4R) tauopathies, including progressive supranuclear palsy, corticobasal degeneration, and argyrophilic grain disease. More controversial is that the same haplotype has been associated with Parkinson disease (PD). Using H1-specific single-nucleotide polymorphisms, we demonstrate that MAPT H1 is a misnomer and consists of a family of recombining H1 alleles. Population genetics, linkage disequilibrium, and association analyses have shown that specific MAPT H1 subhaplotypes are preferentially associated with Parkinson disease. Using a sliding scale of MAPT H1-specific haplotypes--in age/sex-matched PD cases and controls from central Norway--we have refined the disease association to within an approximately 90-kb interval of the 5' end of the MAPT locus.     

Pre-steady-state kinetic analysis of recombinant Arabidopsis NADH:nitrate reductase: rate-limiting processes in catalysis

Recombinant Arabidopsis NADH:nitrate reductase was expressed in Pichia pastoris using fermentation. Large enzyme quantities were purified for pre-steady-state kinetic analysis, which had not been done before with any eukaryotic nitrate reductase. Basic biochemical properties of recombinant nitrate reductase were similar to natural enzyme forms. Molybdenum content was lower than expected, which was compensated for by activity calculation on molybdenum basis. Stopped-flow rapid-scan spectrophotometry showed that the enzyme FAD and heme were rapidly reduced by NADH with and without nitrate present. NADPH reduced FAD at less than one-tenth of NADH rate. Reaction of NADH-reduced enzyme with nitrate yielded rapid initial oxidation of heme with slower oxidation of flavin. Rapid-reaction freeze-quench EPR spectra revealed molybdenum was maintained in a partially reduced state during turnover. Rapid-reaction chemical quench for quantifying nitrite production showed that the rate of nitrate reduction was initially greater than the steady-state rate, but rapidly decreased to near steady-state turnover rate. However, rates of internal electron transfer and nitrate reduction were similar in magnitude with no one step in the catalytic process appearing to be much slower than the others. This leads to the conclusion that the catalytic rate is determined by a combination of rates with no overall rate-limiting individual process.     

A new broccoli × broccoli immortal mapping population and framework genetic map: tools for breeders and complex trait analysis

A unique broccoli × broccoli doubled haploid (DH) population has been created from the F₁ of a cross between two DH broccoli lines derived from cultivars Green Duke and Marathon. We genotyped 154 individuals from this population with simple sequence repeat and amplified fragment length polymorphism markers to create a B. oleracea L. var. italica ‘intra-crop’ specific framework linkage map. The map is composed of nine linkage groups with a total length of 946.7 cM. Previous published B. oleracea maps have been constructed using diverse crosses between morphotypes of B. oleracea; this map therefore represents a useful breeding resource for the dissection of broccoli specific traits. Phenotype data have been collected from the population over five growing seasons; the framework linkage map has been used to locate quantitative trait loci for agronomically important broccoli traits including head weight (saleable yield), head diameter, stalk diameter, weight loss and relative weight loss during storage, as well as traits for broccoli leaf architecture. This population and associated linkage map will aid breeders to directly map agronomically important traits for the improvement of elite broccoli cultivars.     

Abstract coding of audiovisual speech: beyond sensory representation

Is there a neural representation of speech that transcends its sensory properties? Using fMRI, we investigated whether there are brain areas where neural activity during observation of sublexical audiovisual input corresponds to a listener's speech percept (what is "heard") independent of the sensory properties of the input. A target audiovisual stimulus was preceded by stimuli that (1) shared the target's auditory features (auditory overlap), (2) shared the target's visual features (visual overlap), or (3) shared neither the target's auditory or visual features but were perceived as the target (perceptual overlap). In two left-hemisphere regions (pars opercularis, planum polare), the target invoked less activity when it was preceded by the perceptually overlapping stimulus than when preceded by stimuli that shared one of its sensory components. This pattern of neural facilitation indicates that these regions code sublexical speech at an abstract level corresponding to that of the speech percept.     

DisCoTune: versatile auxiliary plasmids for the production of disulphide-containing proteins and peptides in the E. coli T7 system

Secreted proteins and peptides hold large potential both as therapeutics and as enzyme catalysts in biotechnology. The high stability of many secreted proteins helps maintain functional integrity in changing chemical environments and is a contributing factor to their commercial potential. Disulphide bonds constitute an important post-translational modification that stabilizes many of these proteins and thus preserves the active state under chemically stressful conditions. Despite their importance, the discovery and applications within this group of proteins and peptides are limited by the availability of synthetic biology tools and heterologous production systems that allow for efficient formation of disulphide bonds. Here, we refine the design of two DisCoTune (Disulphide bond formation in E. coli with tunable expression) plasmids that enable the formation of disulphides in the highly popular Escherichia coli T7 protein production system. We show that this new system promotes significantly higher yield and activity of an industrial protease and a conotoxin, which belongs to a group of disulphide-rich venom peptides from cone snails with strong potential as research tools and pharmacological agents.     

Echoes of the spoken past: how auditory cortex hears context during speech perception

What do we hear when someone speaks and what does auditory cortex (AC) do with that sound? Given how meaningful speech is, it might be hypothesized that AC is most active when other people talk so that their productions get decoded. Here, neuroimaging meta-analyses show the opposite: AC is least active and sometimes deactivated when participants listened to meaningful speech compared to less meaningful sounds. Results are explained by an active hypothesis-and-test mechanism where speech production (SP) regions are neurally re-used to predict auditory objects associated with available context. By this model, more AC activity for less meaningful sounds occurs because predictions are less successful from context, requiring further hypotheses be tested. This also explains the large overlap of AC co-activity for less meaningful sounds with meta-analyses of SP. An experiment showed a similar pattern of results for non-verbal context. Specifically, words produced less activity in AC and SP regions when preceded by co-speech gestures that visually described those words compared to those words without gestures. Results collectively suggest that what we ‘hear’ during real-world speech perception may come more from the brain than our ears and that the function of AC is to confirm or deny internal predictions about the identity of sounds.