Early nodulins in root nodule development

The symbiotic interaction between bacteria of the genus Rhizobium and leguminous plants leads to the formation of root nodules, which are specific nitrogen-fixing organs on the roots of plants. Bacteria enter the root by infection threads, and concomitantly cell divisons are induced in the root cortex, which lead to the formation of a meristern. From this meristern the different tissues of the root nodule originate. In the nodule bacteria are released in plant cells and then differentiate into the endosymbiotic bacteroids. These bacteroids are capable of nitrogen fixation.The formation of root nodules involves expression of both bacterial and plant genes. Rhizobium genes involved in nodule formation are the nodulation ( nod ) genes. Nodulespecific plant genes are termed nodulin genes. According to their timing of expression they can be divided into early and late nodulin genes. Early nodulin genes are expressed well before the onset of nitrogen fixation, at the time that the nodule tissue is formed and the roots become infected by bacteria, while expression of late nodulin genes starts shortly before the onset of nitrogen fixation, when the nodule structure has been formed. Therefore only early nodulins can be involved in the infection process and in nodule development. Early nodulin genes expressed during the pea ( Pisum sativum L.) - Rhizobium leguminosarum bv. viciae interaction are the subject of this thesis. Several cDNA clones representing pea early nodulin genes have been isolated and they have been used to study root nodule development and the communication between bacteria and host plant.In chapter 2 we review general aspects of plant development. Recent progresses in understanding the molecular mechanisms underlying animal development are listed, and the possible significance of such mechanisms for plant development is discussed. The features of the root nodule formation system that make it suitable to study particular questions on the molecular basis of plant development are put forward.In chapter 3 the pea early nodulin cDNA clone pPsENOD2 is characterized. The nature of the encoded polypeptide is compared with that of the soybean early nodulin described before. ENOD2 transcripts are localized both in pea and soybean root nodules throughout successive stages of development by in situ hybridization. Data on the primary structure of the ENOD2 protein and localization data are then combined to hypothesise that the function of this early nodulin is to create an oxygen barrier in the root nodule.In chapter 4 the early nodulin ENOD12 is described. The spatial distribution of the corresponding transcript throughout root nodule development is depicted to demonstrate the involvement of ENOD12 in the infection process. We describe the primary structure of the ENOD12 protein and we examine whether ENOD12 gene expression is related to a defense respons. Using a sensitive detection method based on the polymerase chain reaction (PCR) we demonstrate that ENOD12 gene expression is induced by excreted Rhizobium factors and that bacterial nod genes are involved. ENOD12 transcripts found in flower and stem tissue are compared to the ENOD12 mRNAs in nodules using, among other techniques, a novel adaptation of RNase mapping to determine whether the same genes are expressed in these different tissues or not.In chapter 5 it is demonstrated that the accumulation pattern of the transcripts corresponding to the pPsENOD5, pPsENOD3 and pPsENOD14 cDNA clones differs from that of ENOD2 and ENOD12 mRNA. The distribution of the former three transcripts is compared with the distribution of ENOD12 mRNA and the late nodulin leghemoglobin transcript. It is shown that the different transcripts are present at successive stages of development of the infected cell type. The primary structure of the ENOD5, ENOD3 and ENOD14 early nodulins is determined and these data are combined with the localization data of the transcripts to speculate on functions of these proteins, The involvement of different factors to induce expression of different early and late nodulin genes is discussed.In chapter 6 the results described in the previous three chapters are summarized and some additional data on early nodulins are presented. The significance of the availability of early nodulin gene probes to elucidate the mechanisms of communication between rhizobia and legumes, which underly the process of root nodule formation, is discussed. Finally, in chapter 7, the value of the obtained information on early nodulins for studying both specific and general aspects of root nodule development is discussed

Influence of convex and concave curvatures in a coastal dike line on wave run-up

Due to climatic change and the increased usage of coastal areas, there is an increasing risk of dike failures along the coasts worldwide. Wave run-up plays a key role in the planning and design of a coastal structure. Coastal engineers use empirical equations for the determination of wave run-up. These formulae generally include the influence of various hydraulic, geometrical and structural parameters, but neglect the effect of the curvature of coastal dikes on wave run-up and overtopping. The scope of this research is to find the effects of the dike curvature on wave run-up for regular wave attack by employing numerical model studies for various dike-opening angles and comparing it with physical model test results. A numerical simulation is carried out using DualSPHysics, a mesh-less model and OpenFOAM, a mesh-based model. A new influence factor is introduced to determine the influence of curvature along a dike line. For convexly curved dikes (ad = 210° to 270°) under perpendicular wave attack, a higher wave run-up was observed for larger opening angles at the center of curvature whereas for concavely curved dikes (ad = 90° to 150°) under perpendicular wave attack, wave run-up increases at the center of curvature as the opening angle decreases. This research aims to contribute a more precise analysis and understanding the influence of the curvature in a dike line and thus ensuring a higher level of protection in the future development of coastal structures.Peer ReviewedPostprint (published version

Harm avoidance is related to mismatch negativity (MMN) amplitude in healthy subjects

peer reviewedEvent-related potential (ERP) studies evidenced that some personality dimensions induced different controlled cognitive attitudes towards the processing of information. However, few data are available on the possible relationships between personality and automatic attention or early sensory processing. In the present study the relationships between the mismatch negativity (MMN) and personality described by the Cloninger model of personality were investigated. Subjects were 32 healthy volunteers. The MMN was recorded with frequent stimuli tones of 1470 Hz, 70 dB and 40 ms duration, and target (20%) tones of 1470 Hz, 70 dB, 80 ms duration. The subjects completed a French version of the 226-item self-questionnaire TCI within the day following psychophysiological recording. The results showed that the HA dimension was negatively correlated with the MMN amplitude. The association was more present among women than men. No significant relationship existed between the other dimensions of personality and either the MMN amplitude or latency. These findings suggest that the MMN is related to the behavioral inhibition system (BIS), a fact which is consistent with clinical studies conducted on schizophrenia and anxiety disorders. In conclusion, this study suggests that personality dimensions induce different automatic attitudes towards the processing of information. (C) 2002 Published by Elsevier Science Ltd

The capsule of Porphyromonas gingivalis reduces the immune response of human gingival fibroblasts

BACKGROUND: Periodontitis is a bacterial infection of the periodontal tissues. The Gram-negative anaerobic bacterium Porphyromonas gingivalis is considered a major causative agent. One of the virulence factors of P. gingivalis is capsular polysaccharide (CPS). Non-encapsulated strains have been shown to be less virulent in mouse models than encapsulated strains. RESULTS: To examine the role of the CPS in host-pathogen interactions we constructed an insertional isogenic P. gingivalis knockout in the epimerase-coding gene epsC that is located at the end of the CPS biosynthesis locus. This mutant was subsequently shown to be non-encapsulated. K1 capsule biosynthesis could be restored by in trans expression of an intact epsC gene. We used the epsC mutant, the W83 wild type strain and the complemented mutant to challenge human gingival fibroblasts to examine the immune response by quantification of IL-1β, IL-6 and IL-8 transcription levels. For each of the cytokines significantly higher expression levels were found when fibroblasts were challenged with the epsC mutant compared to those challenged with the W83 wild type, ranging from two times higher for IL-1β to five times higher for IL-8. CONCLUSIONS: These experiments provide the first evidence that P. gingivalis CPS acts as an interface between the pathogen and the host that may reduce the host's pro-inflammatory immune response. The higher virulence of encapsulated strains may be caused by this phenomenon which enables the bacteria to evade the immune system

Irreversible fate commitment in the Arabidopsis stomatal lineage requires a Fama and Retinoblastoma-related module

The presumed totipotency of plant cells leads to questions about how specific stem cell lineages and terminal fates could be established. In the Arabidopsis stomatal lineage, a transient self-renewing phase creates precursors that differentiate into one of two epidermal cell types, guard cells or pavement cells. We found that irreversible differentiation of guard cells involves RETINOBLASTOMA-RELATED (RBR) recruitment to regulatory regions of master regulators of stomatal initiation, facilitated through interaction with a terminal stomatal lineage transcription factor, FAMA. Disrupting physical interactions between FAMA and RBR preferentially reveals the role of RBR in enforcing fate commitment over its role in cell-cycle control in this developmental context. Analysis of the phenotypes linked to the modulation of FAMA and RBR sheds new light on the way iterative divisions and terminal differentiation are coordinately regulated in a plant stem-cell lineage. - See more at: http://elifesciences.org/content/3/e03271#sthash.f3srCCrx.dpu

Quaternary structure of the specific p53-DNA complex reveals the mechanism of p53 mutant dominance

The p53 tumour suppressor is a transcriptional activator that controls cell fate in response to various stresses. p53 can initiate cell cycle arrest, senescence and/or apoptosis via transactivation of p53 target genes, thus preventing cancer onset. Mutations that impair p53 usually occur in the core domain and negate the p53 sequence-specific DNA binding. Moreover, these mutations exhibit a dominant negative effect on the remaining wild-type p53. Here, we report the cryo electron microscopy structure of the full-length p53 tetramer bound to a DNA-encoding transcription factor response element (RE) at a resolution of 21 Å. While two core domains from both dimers of the p53 tetramer interact with DNA within the complex, the other two core domains remain available for binding another DNA site. This finding helps to explain the dominant negative effect of p53 mutants based on the fact that p53 dimers are formed co-translationally before the whole tetramer assembles; therefore, a single mutant dimer would prevent the p53 tetramer from binding DNA. The structure indicates that the Achilles’ heel of p53 is in its dimer-of-dimers organization, thus the tetramer activity can be negated by mutation in only one allele followed by tumourigenesis

Which executive functioning deficits are associated with AD/HD, ODD/CD and comorbid AD/HD+ODD/CD?

Item does not contain fulltextThis study investigated (1) whether attention deficit/hyperactivity disorder (AD/HD) is associated with executive functioning (EF) deficits while controlling for oppositional defiant disorder/conduct disorder (ODD/CD), (2) whether ODD/CD is associated with EF deficits while controlling for AD/HD, and (3)~whether a combination of AD/HD and ODD/CD is associated with EF deficits (and the possibility that there is no association between EF deficits and AD/HD or ODD/CD in isolation). Subjects were 99~children ages 6–12 years. Three putative domains of EF were investigated using well-validated tests: verbal fluency, working memory, and planning. Independent of ODD/CD, AD/HD was associated with deficits in planning and working memory, but not in verbal fluency. Only teacher rated AD/HD, but not parent rated AD/HD, significantly contributed to the prediction of EF task performance. No EF deficits were associated with ODD/CD. The presence of comorbid AD/HD accounts for the EF deficits in children with comorbid AD/HD+ODD/CD. These results suggest that EF deficits are unique to AD/HD and support the model proposed by R. A. Barkley (1997).17 p

Identification of factors required for meristem function in Arabidopsis using a novel next generation sequencing fast forward genetics approach

<p>Abstract</p> <p>Background</p> <p>Phenotype-driven forward genetic experiments are powerful approaches for linking phenotypes to genomic elements but they still involve a laborious positional cloning process. Although sequencing of complete genomes now becomes available, discriminating causal mutations from the enormous amounts of background variation remains a major challenge.</p> <p>Method</p> <p>To improve this, we developed a universal two-step approach, named 'fast forward genetics', which combines traditional bulk segregant techniques with targeted genomic enrichment and next-generation sequencing technology</p> <p>Results</p> <p>As a proof of principle we successfully applied this approach to two Arabidopsis mutants and identified a novel factor required for stem cell activity.</p> <p>Conclusion</p> <p>We demonstrated that the 'fast forward genetics' procedure efficiently identifies a small number of testable candidate mutations. As the approach is independent of genome size, it can be applied to any model system of interest. Furthermore, we show that experiments can be multiplexed and easily scaled for the identification of multiple individual mutants in a single sequencing run.</p