Callose-Regulated Symplastic Communication Coordinates Symbiotic Root Nodule Development

The formation of nitrogen-fixing nodules in legumes involves the initiation of synchronized programs in the root epidermis and cortex to allow rhizobial infection and nodule development. In this study, we provide evidence that symplastic communication, regulated by callose turnover at plasmodesmata (PD), is important for coordinating nodule development and infection in Medicago truncatula. Here, we show that rhizobia promote a reduction in callose levels in inner tissues where nodules initiate. This downregulation coincides with the localized expression of M. truncatula β-1,3-glucanase 2 (MtBG2), encoding a novel PD-associated callose-degrading enzyme. Spatiotemporal analyses revealed that MtBG2 expression expands from dividing nodule initials to rhizobia-colonized cortical and epidermal tissues. As shown by the transport of fluorescent molecules in vivo, symplastic-connected domains are created in rhizobia-colonized tissues and enhanced in roots constitutively expressing MtBG2. MtBG2-overexpressing roots additionally displayed reduced levels of PD-associated callose. Together, these findings suggest an active role for MtBG2 in callose degradation and in the formation of symplastic domains during sequential nodule developmental stages. Interfering with symplastic connectivity led to drastic nodulation phenotypes. Roots ectopically expressing β-1,3-glucanases (including MtBG2) exhibited increased nodule number, and those expressing MtBG2 RNAi constructs or a hyperactive callose synthase (under symbiotic promoters) showed defective nodulation phenotypes. Obstructing symplastic connectivity appears to block a signaling pathway required for the expression of NODULE INCEPTION (NIN) and its target NUCLEAR FACTOR-YA1 (NF-YA1) in the cortex. We conclude that symplastic intercellular communication is proactively enhanced by rhizobia, and this is necessary for appropriate coordination of bacterial infection and nodule development

Nonlinear Time Series Analysis of Nodulation Factor Induced Calcium Oscillations: Evidence for Deterministic Chaos?

Legume plants form beneficial symbiotic interactions with nitrogen fixing bacteria (called rhizobia), with the rhizobia being accommodated in unique structures on the roots of the host plant. The legume/rhizobial symbiosis is responsible for a significant proportion of the global biologically available nitrogen. The initiation of this symbiosis is governed by a characteristic calcium oscillation within the plant root hair cells and this signal is activated by the rhizobia. Recent analyses on calcium time series data have suggested that stochastic effects have a large role to play in defining the nature of the oscillations. The use of multiple nonlinear time series techniques, however, suggests an alternative interpretation, namely deterministic chaos. We provide an extensive, nonlinear time series analysis on the nature of this calcium oscillation response. We build up evidence through a series of techniques that test for determinism, quantify linear and nonlinear components, and measure the local divergence of the system. Chaos is common in nature and it seems plausible that properties of chaotic dynamics might be exploited by biological systems to control processes within the cell. Systems possessing chaotic control mechanisms are more robust in the sense that the enhanced flexibility allows more rapid response to environmental changes with less energetic costs. The desired behaviour could be most efficiently targeted in this manner, supporting some intriguing speculations about nonlinear mechanisms in biological signaling

Policing the legume-Rhizobium symbiosis: a critical test of partner choice

In legume-Rhizobium symbioses, specialised soil bacteria fix atmospheric nitrogen in return for carbon. However, ineffective strains can arise, making discrimination essential. Discrimination can occur via partner choice, where legumes prevent ineffective strains from entering, or via sanctioning, where plants provide fewer resources. Several studies have inferred that legumes exercise partner choice, but the rhizobia compared were not otherwise isogenic. To test when and how plants discriminate ineffective strains we developed sets of fixing and non-fixing strains that differed only in the expression of nifH - essential for nitrogen fixation - and could be visualised using marker genes. We show that the plant is unable to select against the non-fixing strain at the point of entry, but that non-fixing nodules are sanctioned. We also used the technique to characterise mixed nodules (containing both a fixing and a non-fixing strain), whose frequency could be predicted using a simple diffusion model. We discuss that sanctioning is likely to evolve in preference to partner choice in any symbiosis where partner quality cannot be adequately assessed until goods or services are actively exchanged

Understanding implementation of maternal acute illness management education by measuring capability, opportunity and motivation : a mixed methods study in a low-income country

A major cause of maternal death in low-income countries is a lack of adequate healthcare. The dominant approach to improving care involves continuing professional development but little is known about their impact on practice. Less still is known about the determinants of practice change and barriers to implementation. This study investigated the implementation of an acute illness management course on Ugandan health professionals’ practice and determinants of practice change. Before and after training, 51 nurses, midwives, doctors and clinical officers completed tests of knowledge. Immediately post-course and 1-month later, participants completed questions assessing intention to change practice, practice and determinants of change. Post course, participants took part in focus groups. Post-course, participants reported that they were capable and were motivated to use their knowledge and skills in practice and a lower belief in opportunity to change practice. Behavioural intention was very high and behaviour 1 month later was statistically significantly lower. Three themes emerged: 1) systematic approach changing clinical practice, 2) inter-professional communication, and 3) barriers and facilitators to implementation. Educators should consider behaviour change determinants as important assessments of outcome because they provide crucial implementation of training into practice

A single evolutionary innovation drives the deep evolution of symbiotic N₂-fixation in angiosperms

Symbiotic associations occur in every habitat on earth, but we know very little about their evolutionary histories. Current models of trait evolution cannot adequately reconstruct the deep history of symbiotic innovation, because they assume homogenous evolutionary processes across millions of years. Here we use a recently developed, heterogeneous and quantitative phylogenetic framework to study the origin of the symbiosis between angiosperms and nitrogen-fixing (N2) bacterial symbionts housed in nodules. We compile the largest database of global nodulating plant species and reconstruct the symbiosis’ evolution. We identify a single, cryptic evolutionary innovation driving symbiotic N2-fixation evolution, followed by multiple gains and losses of the symbiosis, and the subsequent emergence of ‘stable fixers’ (clades extremely unlikely to lose the symbiosis). Originating over 100 MYA, this innovation suggests deep homology in symbiotic N2-fixation. Identifying cryptic innovations on the tree of life is key to understanding the evolution of complex traits, including symbiotic partnerships

Jet energy measurement with the ATLAS detector in proton-proton collisions at root s=7 TeV

The jet energy scale and its systematic uncertainty are determined for jets measured with the ATLAS detector at the LHC in proton-proton collision data at a centre-of-mass energy of √s = 7TeV corresponding to an integrated luminosity of 38 pb-1. Jets are reconstructed with the anti-kt algorithm with distance parameters R=0. 4 or R=0. 6. Jet energy and angle corrections are determined from Monte Carlo simulations to calibrate jets with transverse momenta pT≥20 GeV and pseudorapidities {pipe}η{pipe}<4. 5. The jet energy systematic uncertainty is estimated using the single isolated hadron response measured in situ and in test-beams, exploiting the transverse momentum balance between central and forward jets in events with dijet topologies and studying systematic variations in Monte Carlo simulations. The jet energy uncertainty is less than 2. 5 % in the central calorimeter region ({pipe}η{pipe}<0. 8) for jets with 60≤pT<800 GeV, and is maximally 14 % for pT<30 GeV in the most forward region 3. 2≤{pipe}η{pipe}<4. 5. The jet energy is validated for jet transverse momenta up to 1 TeV to the level of a few percent using several in situ techniques by comparing a well-known reference such as the recoiling photon pT, the sum of the transverse momenta of tracks associated to the jet, or a system of low-pT jets recoiling against a high-pT jet. More sophisticated jet calibration schemes are presented based on calorimeter cell energy density weighting or hadronic properties of jets, aiming for an improved jet energy resolution and a reduced flavour dependence of the jet response. The systematic uncertainty of the jet energy determined from a combination of in situ techniques is consistent with the one derived from single hadron response measurements over a wide kinematic range. The nominal corrections and uncertainties are derived for isolated jets in an inclusive sample of high-pT jets. Special cases such as event topologies with close-by jets, or selections of samples with an enhanced content of jets originating from light quarks, heavy quarks or gluons are also discussed and the corresponding uncertainties are determined. © 2013 CERN for the benefit of the ATLAS collaboration

The environmental impact of fertilizer embodied in a wheat-to-bread supply chain

Food production and consumption cause approximately one-third of total greenhouse gas emissions, and therefore delivering food security challenges not only the capacity of our agricultural system, but also its environmental sustainability. Knowing where and at what level environmental impacts occur within particular food supply chains is necessary if farmers, agri-food industries and consumers are to share responsibility to mitigate these impacts. Here we present an analysis of a complete supply chain for a staple of the global diet, a loaf of bread. We obtained primary data for all the processes involved in the farming, production and transport systems that lead to the manufacture of a particular brand of 800 g loaf. The data were analysed using an advanced life cycle assessment (LCA) tool, yielding metrics of environmental impact, including greenhouse gas emissions. We show that more than half of the environmental impact of producing the loaf of bread arises directly from wheat cultivation, with the use of ammonium nitrate fertilizer alone accounting for around 40%. These findings reveal the dependency of bread production on the unsustainable use of fertilizer and illustrate the detail needed if the actors in the supply chain are to assume shared responsibility for achieving sustainable food production

MediPlEx - a tool to combine in silico & experimental gene expression profiles of the model legume Medicago truncatula

Henckel K, Küster H, Stutz L, Goesmann A. MediPlEx - a tool to combine in silico and experimental gene expression profiles of the model legume Medicago truncatula. BMC Research Notes. 2010;3(1): 262.BACKGROUND:Expressed Sequence Tags (ESTs) are in general used to gain a first insight into gene activities from a species of interest. Subsequently, and typically based on a combination of EST and genome sequences, microarray-based expression analyses are performed for a variety of conditions. In some cases, a multitude of EST and microarray experiments are conducted for one species, covering different tissues, cell states, and cell types. Under these circumstances, the challenge arises to combine results derived from the different expression profiling strategies, with the goal to uncover novel information on the basis of the integrated datasets.FINDINGS:Using our new application, MediPlEx (MEDIcago truncatula multiPLe EXpression analysis), expression data from EST experiments, oligonucleotide microarrays and Affymetrix GeneChips can be combined and analyzed, leading to a novel approach to integrated transcriptome analysis. We have validated our tool via the identification of a set of well-characterized AM-specific and AM-induced marker genes, identified by MediPlEx on the basis of in silico and experimental gene expression profiles from roots colonized with AM fungi.CONCLUSIONS:MediPlEx offers an integrated analysis pipeline for different sets of expression data generated for the model legume Medicago truncatula. As expected, in silico and experimental gene expression data that cover the same biological condition correlate well. The collection of differentially expressed genes identified via MediPlEx provides a starting point for functional studies in plant mutants. MediPlEx can freely be used at http://www.cebitec.uni-bielefeld.de/mediplex

Testing the Waste Based Biorefinery Concept: Pilot Scale Cultivation of Microalgal Species on Spent Anaerobic Digestate Fluids

PurposeA waste based biorefinery approach has been tested.MethodsThis has been investigated by culturing in a 800 L photobioreactor two autotrophic microalgae namely Nannochloropsis oceanica and Scenedesmus quadricauda utilising filtered spent anaerobic digestate fluids of N:P ratio 14.22 as substrate.ResultsSignificant rates of bioremediation simultaneously with biomass and associated end product formation were achieved. Nitrogen and phosphorus of waste based media was decreased up to 90%. The biomass biochemical analysis of the microalgae when grown on the waste based formulated media demonstrated the comparable content of lipids and proteins with the species grown on f/2 media.ConclusionsTheoretical biomethane potential generation, should the algal cultures be placed in an anaerobic digester, was calculated at 0.58 L CH4 g−1 VS for N. oceanica and 0.48 L CH4 g−1 VS for S. quadricauda showing comparable results with other studies of different source of biomass

Mutualism and Adaptive Divergence: Co-Invasion of a Heterogeneous Grassland by an Exotic Legume-Rhizobium Symbiosis

Species interactions play a critical role in biological invasions. For example, exotic plant and microbe mutualists can facilitate each other's spread as they co-invade novel ranges. Environmental context may influence the effect of mutualisms on invasions in heterogeneous environments, however these effects are poorly understood. We examined the mutualism between the legume, Medicago polymorpha, and the rhizobium, Ensifer medicae, which have both invaded California grasslands. Many of these invaded grasslands are composed of a patchwork of harsh serpentine and relatively benign non-serpentine soils. We grew legume genotypes collected from serpentine or non-serpentine soil in both types of soil in combination with rhizobium genotypes from serpentine or non-serpentine soils and in the absence of rhizobia. Legumes invested more strongly in the mutualism in the home soil type and trends in fitness suggested that this ecotypic divergence was adaptive. Serpentine legumes had greater allocation to symbiotic root nodules in serpentine soil than did non-serpentine legumes and non-serpentine legumes had greater allocation to nodules in non-serpentine soil than did serpentine legumes. Therefore, this invasive legume has undergone the rapid evolution of divergence for soil-specific investment in the mutualism. Contrary to theoretical expectations, the mutualism was less beneficial for legumes grown on the stressful serpentine soil than on the non-serpentine soil, possibly due to the inhibitory effects of serpentine on the benefits derived from the interaction. The soil-specific ability to allocate to a robust microbial mutualism may be a critical, and previously overlooked, adaptation for plants adapting to heterogeneous environments during invasion