A DNA-binding bromodomain-containing protein interacts with and reduces Rx1-mediated immune response to Potato Virus X

Plant NLR proteins enable the immune system to recognise and respond to pathogen attack. An early consequence of immune activation is transcriptional reprogramming. Some NLRs have been shown to act in the nucleus and interact with transcription factors. The Rx1 NLR protein of potato binds and distorts double-stranded DNA. However, the components of the chromatin localized Rx1-complex are largely unknown. Here we report a physical and functional interaction between Rx1 and NbDBCP, a bromodomain-containing chromatin-interacting protein. NbDBCP accumulates in the nucleolus, interacts with chromatin and redistributes Rx1 to the nucleolus in a subpopulation of imaged cells. Rx1 over-expression reduces NbDBCP interactions with chromatin. NbDBCP is a negative regulator of Rx1-mediated immune responses to potato virus X (PVX) and this activity requires an intact bromodomain. Previously, Rx1 has been shown to regulate the DNA-binding activity of a Golden2-like transcription factor, NbGlk1. Rx1 and NbDBCP act synergistically to reduce NbGlk1 DNA-binding suggesting a mode of action for NbDBCP’s inhibitory effect on immunity. This study provides new mechanistic insight into how a chromatin localised NLR complex co-ordinates immune signalling following pathogen perception

The Potato Nucleotide-Binding Leucine-Rich Repeat (NLR) Immune Receptor Rx1 is a Pathogen Dependent DNA-Deforming Protein

Plant NLR proteins enable cells to respond to pathogen attack. Several NLRs act in the nucleus, however, conserved nuclear targets that support their role in immunity are unknown. Previously we noted a structural homology between the NB domain of NLRs and DNA replication origin-binding Cdc6/Orc1 proteins. Here we show that the NB-ARC domain of the Rx1 NLR of potato binds nucleic acids. Rx1 induces ATP-dependent bending and melting of DNA in vitro dependent upon a functional P-loop. In situ full-length Rx1 binds nuclear DNA following activation by its cognate pathogen-derived effector protein, the coat protein of potato virus X. In line with its obligatory nucleocytoplasmic distribution, DNA-binding was only observed when Rx1 was allowed to freely translocate between both compartments and was activated in the cytoplasm. Immune activation induced by an unrelated NLR-effector pair did not trigger a Rx1-DNA interaction. DNA-binding is therefore not merely a consequence of immune activation. These data establish a role for DNA distortion in Rx1 immune signalling and defines DNA as a molecular target of an activated NLR

Improved model for secondary neutron production in nucleus-nucleus collision at intermediate energies

In previous work an analytical knockout-ablation coalescence model capable of making quantitative predictions of the neutron spectra from high-energy nucleon-nucleus and nucleus-nucleus collision has been developed. The physics of the knockout-ablation model is similar to that in intranuclear cascade codes using Monte Carlo methods. In the first or knockout stage, the collision between two nuclei results in one or more nucleons being knocked out of the projectile and/or the target nucleus. This results in an excited nucleus (called a prefragment), which is lighter than the original species. This excited prefragment decays to the ground state by emitting one or more nucleons, composites (such as deuterons or alphas) and gammas. This is the ablation (second) stage of the reaction. Significant improvements in model predictions were made previously by incorporating important coalescence effects into the formalism. Coalescence occurs when particles with similar momenta located close together in space recombine to form heavier nuclei, such as deuterons, 3H and 3He. In this work the important effects of alpha particle coalescence are included. The improved theory is described and results for predicted neutron and light ion energy and angular spectra are presented and compared with published measurements of secondary neutron and light ion production for a variety of collision pairs

Coupled neutron transport for HZETRN

Exposure estimates inside space vehicles, surface habitats, and high altitude aircrafts exposed to space radiation are highly influenced by secondary neutron production. The deterministic transport code HZETRN has been identified as a reliable and efficient tool for such studies, but improvements to the underlying transport models and numerical methods are still necessary. In this paper, the forward– backward (FB) and directionally coupled forward–backward (DC) neutron transport models are derived, numerical methods for the FB model are reviewed, and a computationally efficient numerical solution is presented for the DC model. Both models are compared to the Monte Carlo codes HETC-HEDS, FLUKA, and MCNPX, and the DC model is shown to agree closely with the Monte Carlo results. Finally, it is found in the development of either model that the decoupling of low energy neutrons from the light ion transport procedure adversely affects low energy light ion fluence spectra and exposure quantities. A first order correction is presented to resolve the problem, and it is shown to be both accurate and efficient

Overview of secondary neutron production relevant to shielding in space

An overview of experimental secondary neutron measurements relevant to space-related activities is presented. Stopping target yields and cross section measurements conducted at particle accelerators using heavy ions with energies >100 MeV per nucleon are discussed